INSPECTION & TESTING OF MATERIALS

COMPILED BY: SYED HAIDER ALI

(COURSE MATERIAL FOR DEPARTMENTAL PROMOTION EXAMINATION (DPE))

Chapter # 1: METALLOGRAPHIC EXAMINATION:

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Chapter # 1: METALLOGRAPHIC EXAMINATION: ................................................................... 6 1.1 INTRODUCTION: ......................................................................... 6 1.2 METALLURGICAL MICROSCOPE: .................................................... 6 1.3 SPECIMEN PREPARATION: ............................................................ 8 1.5 MICRO AND MACRO EXAMINATION:............................................. 13 1.6 STUDY OF MICROSTRUCTURES: .................................................. 14 Chapter # 2: Tensile Testing .............................................................................................................. 19 2.1 INTRODUCTION: ....................................................................... 19 2.2 PROCEDURE OF TENSILE TESTING: ............................................. 19 2.3 TENSILE PROPERTIES: ............................................................... 21 2.4 EXPERIMENTAL RESULTS OF TENSILE TESTING: ........................... 26 Chapter # 3: Bend Test ....................................................................................................................... 28 3.1 INTRODUCTION: ....................................................................... 28 3.2 TYPES OF BEND TEST: ............................................................... 28 3.3 EXPERIMENTAL RESULTS OF BEND TEST: ..................................... 31 Chapter # 4: Compression Testing .................................................................................................... 33 4.1INTRODUCTION: ........................................................................ 33 4.2 COMPRESSION FRACTURE: ......................................................... 34 4.3 WHY PERFORM A COMPRESSION TEST? ....................................... 34 4.4 TYPICAL MATERIALS: ................................................................. 36 Chapter # 5: Impact Test ................................................................................................................... 37 5.1 INTRODUCTION: ....................................................................... 37 5.2 CHARPY IMPACT TEST ................................................................ 38 5.3 EXPERIMENTAL PROCEDURE FOR CHARPY IMPACT TEST ................ 38 5.4 NATURE OF IMPACT TEST: .......................................................... 39 5.5 RESULTS OF THE IMPACT TEST: .................................................. 39 Chapter # 6: Hardness Testing .......................................................................................................... 41 6.1 INTRODUCTION: ....................................................................... 41 6.2.1 Machinery and Tools: .............................................................. 41

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6.3 VICKERS HARDNESS TESTING: ................................................... 43 6.4 COMPARISON OF TYPICAL HARDNESS TESTS: .............................. 44 6.5 ACCURACY OF ANY INDENTATION HARDNESS TEST: ..................... 45 6.6 ADVANTAGES & DISADVANTAGES OF DIFFERENT TYPES OF TESTS: 46 6.7 EXPERIMENTAL RESULTS OF HARDNESS TEST: ............................. 47 Chapter # 7: An Overview of Non-Destructive Testing ................................................................... 49 7.1 INTRODUCTION TO NDT: ........................................................... 49 Defects generated during service life ................................................. 50 7.2 BENEFITS OF NON-DESTRUCTIVE TESTING: ................................. 52 7.3 APPLICATION OF NDT: ............................................................... 53 Chapter # 8: Liquid Penetrant Inspection ........................................................................................ 56 8.1 INTRODUCTION: ....................................................................... 56 8.3 PROPERTIES OF PENETRANTS: .................................................... 62 8.4 PHYSICAL PROPERTIES OF PENETRANTS: ..................................... 62 8.5 PROPERTIES OF DEVELOPERS: .................................................... 63 8.6 ADVANTAGES OF LIQUID PENETRANT INSPECTION ....................... 64 8.7 LIMITATIONS OF LIQUID PENETRANT INSPECTION ........................ 64 8.8 APPLICATION OF LIQUID PENETRANT INSPECTION ........................ 64 Chapter # 9: Magnetic Particle Inspection ....................................................................................... 66 9.1 INTRODUCTION: ....................................................................... 66 9.2 BASIC PRINCIPLES OF MAGNETIC PARTICLE TESTING: .................. 66 9.3 MAGNETIZING CURRENTS: ......................................................... 68 Table 2.1: Magnetizing Currents Used in Magnetic Particle Testing ........ 68 9.4 MAGNETIZATION:...................................................................... 69 9.5 METHODS OF INDUCING MAGNETIC FIELDS: ................................ 72 9.6 APPLICATIONS OF MAGNETIC PARTICLE INSPECTION: ................... 73 9.7 ADVANTAGES & LIMITATIONS OF MAGNETIC PARTICLE INSPECTION: ............................................................................................................. 74 Chapter # 10: Ultrasonic Flaw Detection .......................................................................................... 75

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10.1 INTRODUCTION:...................................................................... 75 10.2 TO MEASURE THE SOUND VELOCITY OF A MATERIAL: .................. 75 10.3 THE ULTRASOUND VIBRATIONS: ............................................... 76 10.4 PIEZO ELECTRIC EFFECT: ......................................................... 77 10.5 BEHAVIOUR OF ULTRASOUND WAVES ........................................ 77 10.7 TRANSDUCERS: ....................................................................... 81 10.7.3 Polarized Ceramics: ............................................................... 82 10.8 TRANSVERSE PROBES: ............................................................. 83 10.9 APPLICATIONS OF ULTRASONIC TESTING: ................................. 85 Chapter # 11: Radiography................................................................................................................ 86 11.1 INTRODUCTION:...................................................................... 86 11.2 PRINCIPLES OF RADIOGRAPHY:................................................. 86 11.3 PRODUCTION OF X-RAYS: ........................................................ 87 11.4 EXPOSURE FACTORS:............................................................... 88 11.5 GAMMA – RAY RADIOGRAPHY: .................................................. 89 11.6 COMPARE/ CONTRAST PROPERTIES OF X – RAYS AND - RAYS: ... 90

11.7 RADIOGRAPHIC FILMS: ............................................................ 91 11.8 FUNDAMENTALS OF RADIOGRAPHY: .......................................... 93 11.9 THE RADIATION HAZARDS: ...................................................... 96 11.10 PROTECTION AGAINST RADIATION: ......................................... 96 11.11 MEASUREMENT OF RADIATION RECEIVED BY PERSONNEL: ......... 97 Chapter # 12: Chemical Analysis ...................................................................................................... 98 12.1 ANALYSIS OF FERROUS MATERIALS (IRON / STEEL): ................... 98 12.2 ANALYSIS OF NON-FERROUS MATERIALS: .................................. 98 12.3 WATER AND ALLIED MATERIALS:............................................... 98 12.4 ANALYTICAL TECHNIQUES USED: .............................................. 99 Chapter # 13: Spectroscope.............................................................................................................. 101 13.1 INTRODUCTION:.................................................................... 101

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13.2 OPTICAL EMISSION SPECTROSCOPY, THEORY OF OPERATION: ... 101 13.3 PHOTOMULTIPLIER TUBE: ....................................................... 102 13.4 ELECTRONIC PROCESSING: .................................................... 103 Chapter # 14: Metalloscope.............................................................................................................. 105 14.1 THE METALLOSCOPE ANALYTICAL METHOD: ............................. 105 14.2 APPLICATIONS: ..................................................................... 106 14.3 SPECIAL FEATURES: .............................................................. 107 Chapter # 15: X-Ray Fluorescence Spectrometer .......................................................................... 110 15.1 INTRODUCTION:.................................................................... 110 15.2 FEATURES: ........................................................................... 110 15.3 PRINCIPLE: ........................................................................... 111 Chapter # 16: Paint Section ............................................................................................................. 118 16.1 INTRODUCTION:.................................................................... 118 16.2 HISTORICAL: ........................................................................ 118 16.3 PIGMENTS: ........................................................................... 119 16.4 BINDERS (OR FILM-FORMER): ................................................. 120 16.5 SOLVENTS (OR THINNERS):.................................................... 121 16.6 SURFACE PREPARATION AND PAINT APPLICATION: ................... 122 16.7 METHODS OF TEST FOR PAINTS: ............................................. 127 MULTIPLE CHOICE QUESTIONS .............................................................................................. 129 REFERENCES .................................................................................................................................. 132 SUGGESTED READING MATERIAL FOR FURTHER READING ........................................ 134

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CHAPTER # 1: METALLOGRAPHIC EXAMINATION:
1.1 INTRODUCTION:
Metallography consists of the microscopic study of the structural characteristics of a metal or an alloy. Metallography is the general study of metals and their behavior, with particular references to their microstructure and macrostructure. Microstructure is the characteristic appearance and physical arrangement of a metal as observed with a microscope. Macrostructure is the appearance and physical arrangement as observed with the naked eye or with a low power magnification. Microstructure and macrostructure of a metal or an alloy are closely interrelated with each other and knowledge of both is essential for full understanding of any metal. Metallography has wide scope and for the reason, a number of precise techniques (e.g. electron microscopy, field ion microscopy, etc.) have been developed for the purpose.

1.2 METALLURGICAL MICROSCOPE:
Metallurgical microscope is by far the most important tool of the metallurgist form both the scientific and technical standpoint. A metallurgical microscope helps determining: 1. Grain size and shape. 2. Size, shape and distribution of various phases and inclusion. 3. Mechanical and thermal treatments of the alloys. A large range of metallurgical microscope is available, for the above-mentioned purposes, all using the principal of examination by light reflected from the specimen surface (since metal specimens are opaque).

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FIG: METALLURGICAL MICROSCOPE (OPTICAL).

1.2.1 C ONSTRUCTION:
A drawtube-carrying eyepiece at its top end slides within the body tube of the microscope, with the help of a rack and pinion device by rotating coarse and fine adjustment knobs. Sliding of drawtube within the body-tube varies the distance between the eyepiece and the objective and thus helps focusing the object. Fine adjustment facilitates final focusing of the object. The objective, fitted at the down end of the body tube, resolves the structure of the metal (specimen) whereas the eyepiece enlarges the image formed by the objective. Eyepieces are made in a variety of powers, such as X5, X8, X10, etc, marked on the top of the eyepiece. The source of light is inside the microscope tube itself. Light is diffused with the help of a diffusing disc. The width of the light beam is controlled by the iris diaphragm. The incident light strikes the plane glass reflector kept at 450 and is partially reflected down onto the specimen. The rays of light get returned by reflection from the (polished) specimen, pass through the objective and glass reflector to form the final image which can be seen through the eyepiece.

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A photographic camera may be mounted above the eyepiece in order to record permanently the metallographic structure of the alloy. The maximum magnification obtained with the optical microscope is about 2000X.

1.3 SPECIMEN PREPARATION:
1.3.1 INTRODUCTION:
Specimen preparation or polishing is necessary to study its microstructure, because the metallurgical microscope makes use of the principle of reflection of light (from the specimen) to obtain the final image of the metal structure. Satisfactory metallographic results can be obtained only, when the specimen has been carefully prepared. Even the most costly microscope will not reveal the metal structure if the specimen has been poorly prepared. A properly prepared metal specimen is flat, does not contain scratches, is nicely polished, and is suitably etched.

1.3.2 PROCEDURE :
The procedures for preparing the specimen for both macro and micro examination is the same, except that in the latter case the final surface finish is more important than in the former.

1.3.2.1 SELECTION

OF

SPECIMEN:

The choice of a specimen for microscopic study may be very important. If a failure is to be investigated, the specimen should be chosen as close as possible to the area of failure and should be compared with one taken from the normal section

1.3.2.2 CUTTING

OF THE

SPECIMEN:

If the material is soft, such as nonferrous metals or alloys and non-heat treated steels, the section may be obtained by manual hacksawing. If the material is hard, the section may be obtained by use of an abrasive cut-off wheel.

1.3.2.3 MOUNTING

THE

SPECIMEN:

Specimens that are small or awkwardly shaped, wires, small rods, sheet metal specimens, thin sections, etc, must be appropriately mounted in a suitable material to facilitate intermediate and final polishing.

Bakelite is the most common thermosetting resin for mounting. The specimen and the correct amount of Bakelite powder, or Bakelite preform, are placed in

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the cylinder of the mounting press. The temperature is gradually raised to 1250C and a molding pressure of about 20 K Newton is applied simultaneously. Time is setted for mounting is 15 min and for cooling is 8 min. The mounted specimen is ejected from the molding die after cooling.

FIG: MOUNTED SPECIMEN READY FOR GRINDING.

1.3.2.4 OBTAINING FLAT SPECIMEN SURFACE :
It is first necessary to obtain a reasonably flat surface on the specimen. This is achieved by using a fairly coarse file or machining or grinding, by using a motor driven emery belt. During the grinding operation the specimen kept cool by frequent dropping in water. The rough grinding is continued until the surface is flat and free of nicks burrs, etc, and all scratches due to the hacksaw or cutoff wheel are no longer visible.

1.3.2.5 INTERMEDIATE

AND

FINE GRINDING:

Intermediate and fine grinding is carried out using emery papers of progressively finer grade. The emery papers should be of very good quality in respect of uniformity of particle size. Four grades of abrasives used are: 220 grit, 320 grit, 400 grit and 600 grit (from coarse to fine); the 320 grit has particle sizes (of the silicon carbide) as about 33 microns and 600 grit that of 17 microns (1 micron = 10-4 cm). The specimen is first ground on 220 grit paper, so that scratches are produced roughly at right angle to those initially existing on the specimen and produced through preliminary grinding or coarse filing operation.

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Having removed the primary grinding marks, the specimen is washed free of No. 220 grit. Grinding is then continued on the No. 320 paper, again turning the specimen through 900 and polishing until the previous scratches marks are removed. The process is repeated with the No.400 and No. 600 papers. Grinding with the No. 200, No.320, etc. papers could be done in the following ways. The specimen may be hand-rubbed against the abrasive paper, which is laid over a flat surface such as a piece of glass plate. The abrasive paper may be mounted on the surface of a flat, horizontally rotating wheel and the specimen held, in the hand, against it. In either case, the surface of the abrasive paper (with a water proof bases) shall be lubricated with water so as to provide a flushing action to carry away the particles cut from the surface.

1.3.2.6 POLISHING :
The polishing compound used in Al2O3 (alumina) powder (with a particle size of 0.05 microns) placed on a cloth covered rotating wheel. Distilled water is used as a lubricating. Polishing removes fine scratches and very thin distorted layer remaining from the intermediate and fine grinding.

1.3.2.7 ETCHING:
1.3.2.7.1 Necessity: Even after polishing, the granular structure in a specimen usually cannot be seen under the microscope; because grain boundaries in a metal have a thickness of the order of a few atom diameters at best, ad the resolving power of a microscope is much too low to reveal their presence. In order to make the grain boundaries visible, after fine polishing the metal specimens are usually etched. Etching imparts unlike appearances to the metal constituents and thus makes metal structure apparent under the microstructure. 1.3.2.7.2 Method: Before etching, the polished specimen is thoroughly washed in running water.

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Then, the etching is done either by (i) immersing the polished surface (of the specimen) in the etching reagent or by (ii) rubbing the polished surface gently with a cotton swab wetted with the etching reagent. After etching, the specimen is again washed thoroughly and dried. Now, the specimen can be studied under the microscope.
TABLE: ETCHING REAGENTS FOR MICROSCOPIC EXAMINATION:

ETCHING REAGENT Nitric (natal)

COMPOSITION

USES

REMARKS

acid White nitric acid In carbon steels. (1) 1-5ml to darken pearlite and give contrast between Ethyl or methyl pearlite colonies, (2) to reveal ferrite alcohol (95% or boundaries, (3) to absolute) differentiate ferrite 100 ml from martensite. (also alcohol) amyl

Etching rate is increased, selectively percentages of HNO3. Reagent 2 (picric acid) usually superior. Etching time a few seconds to 1 min.

Picric (picral)

acid Picric 4g

acid For all grades of carbon steels: annealed, normalized, Ethyl or methyl quenched, and tempered, alcohol (95% or spheroidized, absolute) austempered. For all 100 ml low-alloy steels attacked by this reagent.

More dilute solutions occasionally useful. Does not reveal ferrite grain boundaries as readily as natal. Etching time a few seconds to 1 min or more.

Ferric chloride Ferric chloride 5g Structure of austenite and Hydrochloric acid nickel and stainless hydrochloric 50ml steels. acid Water 100ml

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Ammonium Ammonium hydroxide and hydroxide hydrogen 5 parts peroxide Water 5 parts Hydrogen peroxide 2-5 parts Ammonium persulfate Ammonium persulfate 10 g Water 90 ml Palmerton reagent Chromic 200g Sodium 15 g Water 1,000 ml Ammonium molybdate Molybodic acid (85%) 100g Ammonium hydroxide (sp gr 140 ml Water 240 ml Filter and add to nitric acid (sp gr 1.32 ) 60ml 0.9)

Generally used for Peroxide content copper and many of varies directly with its alloys. copper content of alloy to be etched immersion or swabbing for about 1 min. Fresh peroxide for good results.

Copper, brass, bronze, Use either cold or nickel, silver, boiling, immersion. aluminum bronze.

oxide General reagent for Immersion with zinc and its alloys. gentle agitation. sulfate

Rapid etch for lead Alternately swab and its alloys; very specimen and wash suitable for removing in running water. thick layer of worked metal.

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Hydrofluoride acid

Hydrofluoric acid (conc) 0.5 ml H2O 99.5 ml

General microscope Swab with soft for aluminum and its cotton for 15 s. alloys.

1.5 MICRO AND MACRO EXAMINATION:
Micro-examination Micro-examination or micrography involves the study of the structures of metals and their alloys under a microscope at magnifications form X20 to X2000. The observed structure is called the microstructure. Micro-examination involves much smaller areas and brings out information which can never be revealed by low magnification (macro examination). The aim of micro-examination is Macro-examination Macro-examination involves the study of the structure of metals and their alloys by the naked eye or by low power magnification up to X15. The observed structure is called the macrostructure – macro-section of upset forging. Macro-examination gives a broad picture of the interior of a metal by studying relatively large sectioned areas. The aim of macro-examination is

To determine the size and shape of To reveal the size, form and of crystallites the crystallites which constitute an arrangement (dendrites) in cast metals. alloy. To reveal structures characteristic of To reveal fibres in deformed metals. certain types of mechanical working To reveal shrinkage porosity and gas operations. cavities. To discover micro defects (non- To reveal cracks appearing during metallic inclusions, micro cracks, certain fabrication processes. etc.) To show chemical non-homogeneity To determine the chemical content in the distribution of certain of alloys (e.g., annealed carbon constituents appearing in alloys upon steels) their solidification from the liquid To indicate quality of heat state. treatment, mechanical properties, To indicate non-metallic inclusions etc. such as slag, sulphides and oxides. Micro examination requires proper

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surface preparation of the specimen To indicate method of manufacture, before studying it under the e.g., forging, casting, welding and microscope. brazing. Micro examination requires that the To find the cause of failure of a polished specimen surface should component part. be etched with a suitable reagent. Surface preparation for macro examination follows similar lines to those for micro-examination but need not be taken to such a high degrees of surface finish and so the final stages of polishing can be omitted. Macro-examination is also carried out on an etched surface.

1.6 STUDY OF MICROSTRUCTURES:
Metallography is the science of evaluating metal structures and is an important field of metallurgy. The metallographer must prepare the specimen to obtain a true image of the structure and then exactingly evaluate the structure. Examination and study of microstructure of the specimen is required to determine the metallurgical effects of heat-treatment, manufacturing processes (such as welding) etc. Trained metallographers are able to evaluate the microscopical appearance of metals and to indicate the past history of the metals so that the advisability of particular metallurgical methods can be predicted. All metallurgical processes have definite effects on the structure of the metals used and the metallurgical nature of processes can be studied in terms of these metallographic effects. Following the microstructures of some important constituents.

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FIG: GRAIN STRUCTURE OF SOLUTION-ANNEALED ALLOY 625 BAR (191 HV); ACETIC GLYCEREGIA ETCH; MAGNIFICATION BAR IS 100 UM LONG

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FIG (A): AS-HOT ROLLED GRAIN STRUCTURE OF CUSTOM AGE 625 PLUS, FINISH ROLLED AT 1007 C; ACETIC GLYCEREGIA ETCH; MAGNIFICATION BAR IS 100 UM LONG; FIG (B) MATERIAL IN FIG (A) AFTER SOLUTION ANNEALING AT 968 0C; ACETIC GLYCEREGIA ETCH; MAGNIFICATION BAR IS 100 UM LONG.

FIG : PARTIALLY RECRYSTALLIZED WASPALOY GRAIN STRUCTURE; 1010 C SOLUTION ANNEAL AND DOUBLE AGED; MODIFIED BERAHA'S TINT ETCH; MAG. BAR IS 100 UM LONG.

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FIG 3 MATERIAL IN FIG. 1 AFTER SOLUTION ANNEALING AT 1010 C; ACETIC GLYCEREGIA ETCH; MAGNIFICATION BAR IS 100 UM LONG; FIG 4 NECKLACE-TYPE DUPLEX GRAIN STRUCTURE IN ASFORGED EXPERIMENTAL 625-TYPE ALLOY; ACETIC GLYCEREGIA ETCH; MAGNIFICATION BAR IS 100 UM LONG

FIG (A) GRAIN BOUNDARY CARBIDE NETWORK IN THE CENTER OF A 305-MM DIAMETER ASFORGED BILLET OF ALLOY 600; GLYCEREGIA ETCH; MAGNIFICATION BAR IS 50 UM LONG; FIG

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(B) FINE MC-TYPE CARBIDES IN A 140-MM DIAMETER BAR OF SOLUTION-ANNEALED ALLOY 625; UNETCHED; MAGNIFICATION BAR IS 100 UM LONG

FIG: PRECIPITATION OF INTERGRANULAR ETA PHASE IN PYROMET 31 AFTER 1,500 HOURS AT 816 C (A); GLYCEREGIA; MAGNIFICATION BAR IS 25 UM LONG (NOTE THE GRAIN BOUNDARY CARBIDES); ETA PHASE IN A PYROMET 31 SPECIMEN SOLUTION ANNEALED AT 954 C (B); GLYCEREGIA ETCH; MAGNIFICATION BAR IS 10 UM LONG

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CHAPTER # 2: TENSILE TESTING
2.1 INTRODUCTION:
2.1.1 TENSILE STRENGTH :
“The ratio of maximum load to original cross-sectional area is called Tensile Strength or Ultimate Tensile Strength. The unit of tensile strength is Kg / cm2”. “A tensile test measures the resistance of a material to a slowly applied force”.

2.2 PROCEDURE OF TENSILE TESTING:
The essential features of a round (cylindrical) test specimen are the diameter D0, parallel length PL, gauge length L0 and end fillet radius r. Tensile test is carried out by gripping the ends E, E of the specimen in a tensile testing machine (Bench Hound Tensometer), and applying an increasing pull on to the specimen till it fractures.

Fig: Tensile test specimen

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During the test, the tensile load as well as the elongation of a previously marked gauge length in the specimen is measured with the help of load dial of the machine and extensometer respectively. These readings help plotting stressstrain curve.

FIG: STRESS-STRAIN CURVE FOR DUCTILE STEEL.

After fracture, the two pieces of the broken specimen are placed as it fixed together and the distance Lf between two gauge marks and the diameter Df at the place of fracture are measured.

FIG: SHOWS THE BENCH TENSOMETER.

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FIG: SHOWS THE SPECIMEN, CLAMP, PIN AND COLLAR FOR TENSILE TESTING.

2.3 TENSILE PROPERTIES:
A tensile test helps determining tensile properties such as tensile strength, yield point or yield strength, percentage elongation, percentage reduction in area and modulus of elasticity. The properties that may be determined by a tension test follow:

2.3.1 PROPORTIONAL LIMIT:
It is found for many structural materials that the early pert of the stress-strain graph may be approximated by a straight line OP in fig. In this range, the stress and strain are proportional to each other, so that any increase in stress will result in a proportionate increase in strain. The stress at the limit of proportionality point P is known as the proportional limit.

2.3.2 ELASTIC LIMIT:
If a small load on the test piece is removed, the extensometer needle will return to zero, indicating that the strain, caused by the load, is elastic. If the load is continually increased, then released after each increment and the extensometer checked, a point will be reached at which the extensometer needle will not return to zero. This indicates that the material now has a permanent deformation. The elastic limit may therefore be defined as the minimum stress at which permanent deformation first occurs. For most structural materials the elastic limit has nearly the same numerical value as the proportional limit.

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FIG: STRESS – STRAIN DIAGRAM FOR DUCTILE STEEL.

FIG: STRESS – STRAIN DIAGRAM FOR A BRITTLE MATERIAL.

2.3.3 YIELD POINT:
As the load in the test piece is increased beyond the elastic limit, a stress is reached at which the material continues to deform without an increase in load. The stress at point Y in fig is known as the yield point. This phenomenon occurs only in certain ductile materials. The stress may actually decrease momentarily,

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resulting in an upper and lower yield point. Since the yield point is relatively easy to determine and the permanent deformation is small up to yield point, it is a very important value in the design of many machine members whose usefulness will be impaired by considerable permanent deformation. This is true only for materials that exhibit a well-defined yield point.

2.3.4 YIELD STRENGTH :
Most nonferrous materials and the high-strength steels do not possess a welldefined yield point. For these materials, the maximum useful strength is the yield strength. The yield strength is the stress at which a material exhibits a specified limiting deviation from the proportionality of stress to strain. This value is usually determined by the offset method. In fig, the specified offset OX is laid off along the strain axis. Then XW is drawn parallel to OP, and thus Y, the intersection of XW with the stress-strain diagram, is located. The value of the stress at point Y gives the yield strength. The value of the offset is generally between 0.10 and 0.20 percent of the gauge length. Yield Strength = Load at Yield point A0 = ( /4 D02)

2.3.5 ULTIMATE STRENGTH :
As the load on the test piece is increased still further the stress and strain increase, as indicted by the portion of the curve YM for a ductile material, until the maximum stress is reached at point M. The ultimate strength or the tensile strength is therefore the maximum stress developed by the material based on the original cross-sectional area. A brittle material breaks when stressed to the ultimate strength (point B in fig), whereas a ductile material will continue to stretch. Ultimate tensile strength = Ultimate load A0

2.3.6 BREAKING STRENGTH :
For a ductile material, up to the ultimate strength, the deformation is uniform along the length of the bar. At the maximum stress, localized deformation or necking occurs in the specimen, and the load falls lff as the area decreases. This necking elongation is a non-uniform deformation and occurs rapidly to the point of failure (fig). The breaking strength (point B, fig), which is determined by dividing the breaking load by the original cross-sectional area, is always less

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than the ultimate strength. For a brittle material, the ultimate strength and breaking strength coincide.

2.3.7 DUCTILITY :
The ductility of a material is indicated by the amount of deformation that is possible until fracture. This is determined in a tension test by two measurements.

2.3.8 ELONGATION :
This is determined by fitting together, after fracture, the parts of the specimen and measuring the distance between the original gauge marks. Elongation (percent) = Lf – L0 L0 Where Lf = final gauge length L0 = original gauge length, usually 2 in.. In reporting percent elongation, the original gauge length must be specified since the percent elongation will vary with gauge length. 100

2.3.9 REDUCTION

IN

AREA:

This is also determined from the broken halves of the tensile specimen by measuring, the minimum cross-sectional area and using the following formula: reduction in area (percent) = A0 – Af A0 Where A0 = original cross-sectional area Af = final cross-sectional area 100

2.3.10 MODULUS

OF

ELASTICITY

OR

YOUNG‟S MODULUS:

Consider the straight-line portion of the stress-strain curve. The equation of a straight line is y = mx + b, where y is the vertical axis, in this case stress, and x is the horizontal axis, in this case strain. The intercept of the line on the y-axis is b, and in this case it is zero since the line goes through the origin. The slope of the line is m. when the equation is solved for m, the slope is equal to y/x. Therefore, the slope of the line may be determined by drawing any right triangle and finding the tangent of the angle , which is equal to y/x or stress / strain. The slope is really the constant of proportionality between stress and strain

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below the proportional limit and is known as the modulus of elasticity or Young‟s modulus. The modulus of elasticity, which is an indication of the stiffness of a material, is measured in pounds pr square inch. For example, the modulus of elasticity of steel is approximately 30 million psi, while that of aluminum is 10 million psi. Therefore, steel is approximately three times as stiff as aluminum. The modulus of elasticity is a very useful engineering property and will appear in formulas dealing with design of beams and columns where stiffness is important. Young‟s Modulus of Elasticity (E) = Stress at any point within the elastic limit Strain at that point = PL0 A0 L Where P = Load at any point up to the elastic limit. L0 = Gauge length A0 = Original area L = Elongation of change in L0 at any load P, while the specimen is within the elastic zone.

2.3.11 TRUE STRESS – TRUE STRAIN:
The decrease in engineering stress beyond the tensile point occurs because of our definition of engineering stress. We used the original area A0 in our calculations, which is not precise because the area continually changes. We define true stress and true strain by the following equations. True stress = t = F A True strain = t = dl = ln (l / lo) lo = ln (Ao / A) Where A is the actual area at which the force F is applied. The expression ln ( A0 / A) must be used after necking begins. The true stress-strain curve is compared to the engineering stress-strain in fig. The true stress continuous to increases after necking because, although the load required decreased, the area decreases even more.

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FIG: TRUE STRESS-STRAIN AND CONVENTIONAL STRESS-STRAIN DIAGRAMS FOR MILD STEEL.

2.4 EXPERIMENTAL RESULTS OF TENSILE TESTING:
Aluminum Alloy Sheet: Tensile Strength (N / mm2) Elongation % (Gauge length 50 mm) 115.12 21.66

Mild Steel Plate: Condition Tensile Strength (N / mm2) Yield Strength (N / mm2) Elongation % Mild Steel Pipe: Condition Tensile Strength (N / mm2) Normalized 515.1 Rolled 548 421 19

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Yield Strength (N / mm2) Elongation %

262.4 29.5

Alloy Steel: Tensile Strength (lb / inch2) Yield Strength (lb / inch2) Elongation % (Gauge length 5.65 A 83791 54367 16.5

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CHAPTER # 3: BEND TEST
3.1 INTRODUCTION:
A bend test is preferred for brittle materials such as Cast Iron, in which case it may serve also as a simpler substitute for the tension test. A bend test may well be used as a good shop test for acceptance purposes, but not for research purpose. A bend test is also carried out on other materials such as cast steel and welded joints in order to ascertain the degree of ductility or to test the bond between materials. A bend test is required when a component is required to be used under a static load. Cracks are likely to be developed on the opposite surface of the loading and the structure is likely to fail under exceeding the safe limit of safety factor. Usually weldments are tested for bend test to 1800. The surface of U bend is observed for any cracks visually or by dye penetrant method.

3.2 TYPES OF BEND TEST:
3.2.1 GUIDED BEND TEST :
The quality of the weld metal at the face and root of the welded joint, as well as the degree of penetration and fusion to the base metal, are determined by means of guided bend tests. These tests are made in a jig (fig. 3-1). These test specimens are machined from welded plates, the thickness of which must be within the capacity of the bending jig. The test specimen is placed across the supports of the die that is the lower portion of the jig. The plunger, operated from above by a hydraulic jack or other device, causes the specimen to be forced into and to assure the shape of the die. To fulfill the requirements of this test, the specimens must bend 180 degrees and, to be accepted as passable, no cracks greater than 1/8 in. (3.2 mm) in any dimension should appear on the surface. The face bend tests are made in the jig with the face of the weld in tension (i.e., on the outside of the bend) (A, fig. 3–2). The root bend tests are made with the root of the weld in tension (i. e., on outside of the bend) (B, fig. 3-2). Guided bend test specimens are also shown the in figure 3-3.

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FIG 3.1: GUIDED BEND TEST JIG.

FIG 3.2: GUIDED BEND TEST SPECIMENS.

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FIG 3.3: GUIDED BEND AND TENSILE STRENGTH TEST SPECIMENS.

3.2.2 FREE BEND TEST:
1. The free bend test has been devised to measure the ductility of the weld metal deposited in a weld joint. A test specimen is machined from the welded plate with the weld located as shown at A, figure 3-4. Each corner lengthwise of the specimen shall be rounded in a radius not exceeding one-tenth of the thickness of the specimen. Tool marks, if any, shall be lengthwise of the specimen. Two scribed lines are placed on the face 1/16 in. (1.6 mm) in from the edge of the weld. The distance between these lines is measured in inches and recorded as the initial distance X (B, fig. 34). The ends of the test specimen are then bent through angles of about 30 degrees, these bends being approximately one-third of the length in from each end. The weld is thus located centrally to ensure that all of the bending occurs in the weld. The specimen bent initially is then placed in a machine capable of exerting a large compressive force (C, fig. 3-4) and bent until a crack greater than 1/16 in. (1.6 mm) in any dimension appears on the face of the weld. If no cracks appear, bending is continued until the specimens 1/4 in. (6.4 mm) thick or under can be tested in vise. Heavier plate is usually tested in a press or bending jig. Whether a vise or other type of compression device is used when making the free bend test, it is advisable to machine the upper and lower contact plates of the bending equipment to present surfaces parallel to the ends of the specimen (E, fig. 3-4). This will prevent the specimen from slipping and snapping out of the testing machine as it is bent.

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FIG3.4: FREE BEND TEST OF WELDED METAL.

2. After bending the specimen to the point where the test bend is concluded, the distance between the scribed lines on the specimen is again measured and recorded as the distance Y. To find the percentage of elongation, subtract the initial from the final distance, divide by the initial distance, and multiply by 100 (fig. 3-4). The usual requirements for passing this test are that the minimum elongation be 15 percent and that no cracks greater than 1/16 in. (1.6 mm) in any dimension exist on the face of the weld. 3. The free bend test is being largely replaced by the guided bend test where the required testing equipment is available. The percentage elongation is obtained as follows: Percentage elongation = Z – B B Where B is the original distance between gauge lines Z is the distance between gauge lines after the bend 100

3.2.3 BACK BEND TEST :
The back bend test is used to determine the quality of the weld metal and the degree of penetration into the root of the Y of the welded butt joint. The specimens used are similar to those required for the free bend test except they are bent with the root of the weld on the tension side, or outside. The specimens tested are required to bend 90 degrees without breaking apart. This test is being largely replaced by the guided bend test.

3.3 EXPERIMENTAL RESULTS OF BEND TEST:

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Mild Steel Plate: Folding test (1800 bend) Zn Coated Steel Specimen: Folding Test (900 bend) of Welded Mild Steel: Folding test (1800 bend) No crack is appeared (Satisfactory) Not Satisfactory (Cracks and detachment Zn coat at bend observed). 1 ½ Thickness (Satisfactory)

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CHAPTER # 4: COMPRESSION TESTING
4.1INTRODUCTION:
A compression test determines behavior of materials under crushing loads. The specimen is compressed and deformation at various loads is recorded. Compressive stress and strain are calculated and plotted as a stress-strain diagram which is used to determine elastic limit, proportional limit, yield point, yield strength and, for some materials, compressive strength.

FIG: SHOWS THE COMPRESSIVE STRESS – STRAIN CURVE.

Like tensile test, compression test is also conducted on a universal testing machine. In compression test, the piece of material is subjected to end loading which produces crushing action. Whereas in a tension test, the piece elongates in a direction parallel to the applied load; in a compression test, it shortens. Compression specimens or test pieces are limited to such a length that bending due to column action does not take place. For uniform stressing of the compression specimen, a circular section is to be preferred over other shapes. The square or rectangular is also often used. In order to avoid bending of the specimen, a height-diameter ratio of 10 is suggested as a practical upper limit. The ends of specimen to which load is applied should be flat and perpendicular to the axis of the specimen.

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Refer figure compression testing; great care must be exercised to obtain accurate centering and alignment of specimen and bearing blocks in the testing machine. The compression test specimen say of 25mm diameter and 25mm long cylindrical is loaded between the fixed and movable cross-heads, compressive load is read from the scale at breakage/crushing of the specimen to determine the crushing strength. Depending upon the size of the specimen, extensometer may be fitted upon it as in tensile testing. Though the compression test ranks low on the list of routine acceptance tests for metals, it can be used to obtain useful data in such fields as plastics and ceramics. The compression test is not used for most metals because it is not as reliable an indicator of ductility as is the tensile test and the reduction of area test.

4.2 COMPRESSION FRACTURE:
A major deficiency of the compression test standard is that compressive strength is uniquely defined only for catastrophic failure by crushing or fracture. However, cylindrical specimens of all but the most ductile materials will develop cracks when they are compressed. The cracks generally initiate on the outer surface of the compressed specimen. As the specimen is further deformed, the already initiated cracks propagate, and new cracks initiate.

4.3 WHY PERFORM A COMPRESSION TEST?
“Axial compression testing is a useful procedure for measuring the plastic flow behavior and ductile fracture limits of a material. Measuring the plastic flow behavior requires frictionless (homogenous compression) test conditions, while measuring ductile fracture limits takes advantage of the barrel formation and controlled stress and strain conditions at the equator of the barreled surface when compression is carried out with friction.

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Axial compression testing is also useful for measurement of elastic and compressive fracture properties of brittle materials or low-ductility materials. In any case, the use of specimens having large L/D ratios should be avoided to prevent buckling and shearing modes of deformation.” The image at right shows variation of the strains during a compression test without friction (homogenous compression) and with progressively higher levels of friction and decreasing aspect ratio L/D (shown as h/d) 1.

MODES OF DEFORMATION IN COMPRESSION TESTING

The figure to the right illustrates the modes of deformation in compression testing. (a) Buckling, when L/D > 5. (b) Shearing, when L/D > 2.5. (c) Double barreling, when L/D > 2.0 and friction is present at the contact surfaces. (d)

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Barreling, when L/D < 2.0 and friction is present at the contact surfaces. (e) Homogenous compression, when L/D < 2.0 and no friction is present at the contact surfaces. (f) Compressive instability due to work-softening material1.

4.4 TYPICAL MATERIALS:
The following materials are typically subjected to a compression test. 1. Concrete 2. Metals 3. Plastics 4. Ceramics 5. Composites 6. Corrugated Cardboard

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CHAPTER # 5: IMPACT TEST
5.1 INTRODUCTION:
Although the area under the stress – strain diagram, may obtain the toughness of a material the impact test will give an indication of the relative toughness. Generally, notch – type specimens are used for impact tests. Two general types of notches are used in bending impact tests, the keyhole notch and the V notch. Two types of specimens are used, the Charpy and the Izod, shown in Fig.

FIG: NOTCHED BAR IMPACT TEST SPECIMENS.

The Charpy specimen is placed in the vise so that it is a simple beam supported at the ends. The Izod specimen is placed in the vise so that one end is free and is therefore a cantilever beam. The ordinary impact machine has a swinging pendulum of fixed weight that is raised to a standard height depending upon the type of specimen tested. At that height, with reference to the vise, the pendulum has a definite amount of potential energy. When the pendulum is released, this energy is converted to kinetic energy until it strikes the specimen. The Charpy specimen will be hit behind the V notch, while the Izod specimen, placed with the V notch facing the pendulum, will be hit above the V notch. In either case, some of the energy of the pendulum will be used to rupture the specimen so that the pendulum will rise to a height lower than the initial height on the opposite side of the machine. The weight of the pendulum times the difference in heights will indicate the

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energy, usually in foot – pounds, absorbed by the specimen, or the notched impact strength. From the description of the test, it is apparent that the notched-bar impact test does not yield the true toughness of a material but rather its behavior with a particular notch. The results are useful, however, for comparative purposes. The notched-bar test is used by the aircraft and automotive industries, which have found by experience that high impact strength by test generally will give satisfactory service where shock loads are encountered.

5.2 CHARPY IMPACT TEST
The Charpy Impact test is type of fracture toughness test. This measures the amount of energy that is required to fracta ure a material that is experiencing impact loading. This impact energy can be measured by finding the difference in height of the hammer at the start and the end of its swing. This measurement is done on a dial indicator that is connected to the pendulum arm. This can be seen in the impact tester that is shown below:

5.3 EXPERIMENTAL PROCEDURE FOR CHARPY IMPACT TEST
The Charpy Impact Test will be done on several chosen metals. Each metal will be tested under two conditions: room temperature (about 25°C), and liquid Nitrogen temperature (about -196°C). We will examine the effect of temperature on toughness.

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5.4 NATURE OF IMPACT TEST:
In order to select a material to withstand a sudden intense blow, we must measure a material‟s resistance to failure in an impact test. Many test procedures have been devised, including the Charpy test. The test specimen may either be notched or unnotched; the V-notched specimens better measure the resistance of the material to crack propagation. In the test, a heavy pendulum which starts at an elevation h0 swings through its arc, strikes and breaks the specimen, and reaches a lower final elevation hf. By knowing the initial and final elevations of the pendulum, the difference in potential energy can be calculated. This difference is the impact energy absorbed by the specimen during failure. The energy is usually expressed in foot-pounds (ft-lb) or joules (J), where 1 ft-lb = 1.356J. The ability of a material to withstand an impact blow is often referred to as the toughness of the material.

5.5 RESULTS OF THE IMPACT TEST:
The results of a series of impact tests performed at various temperatures are shown in fig. At high temperatures, a large absorbed energy is required to cause the specimen to fail, whereas at low temperature the material fails with little absorbed energy. At high temperatures the materials behaves in a ductile manner, with extensive deformation and stretching of the specimen prior to failure. At low temperatures, the material is brittle and little deformation at the point of fracture is observed. The transition temperature is the temperature at which the material changes from ductile to brittle failure. A material that may be subjected to an impact blow during service must have a transition temperature below the temperature of the material‟s surroundings. For example, the transition temperature of steel used for a carpenter‟s hammer should be below room temperature to prevent chipping of the steel. Not all materials have a distinct transition temperature (fig). BCC metals have transition temperatures but most FCC metals do not. FCC metals have high absorbed energies, with the energy decreasing gradually and slowly as the temperature decreases.

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FIG: TYPICAL RESULTS FROM A SERIES OF IMPACT TESTS.

The impact energy corresponds to the area contained within the true stress-true strain diagram. Materials that have both high strength and high ductility have a good toughness because they display virtually no ductility.

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CHAPTER # 6: HARDNESS TESTING
6.1 INTRODUCTION:
The property of hardness largely determines the resistance to scratching, wear, penetration, machinability and the ability to cut. Hardness testing is widely used for inspection and control. Heat treatment or working usually results in a change in hardness. When the hardness resulting from treating a given material by a given process is established, it affords a rapid and simple means of inspection and control for the particular material and process. The various hardness tests are described below: 6.2 ROCKWELL HARDNESS TEST: In the Rockwell Hardness Test either a small steel ball or a diamond cone is used as the indenter. The diamond is used for harder materials. It differs from the BHT in that the indenter and the loads are smaller and the RHN is read directly from the machine dial. It is applicable to the testing of materials having hardness beyond the range of the BT.

6.2.1 MACHINERY AND TOOLS:
There are two Rockwell machines, the normal tester for relatively thick sections, and the superficial tester for thin sections. The minor load is 10 Kg on the normal tester and 3 Kg on the superficial tester. Indenters include hard steel balls 1/16, 1/8, 1/4 and 1/2 in. in diameter and a 1200 conical diamond (brale) point. 1. Screw 2. Hand wheel 3. Machine platform 4. Dial

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FIG: ROCKWELL HARDNESS TESTER

6.2.2 PROCEDURE

OF

HARDNESS TESTING :

Test piece is placed upon the machine. The machine dial is showing any reading. Hand wheel is turned, thereby raising the test piece up against the steel ball indenter till the needle on the dial reads zero. This applies minor load. Major load is applied by pressing the crank provided on the right hand side of the machine. Crank is turned in the reverse direction thereby with drawing major load but leaving minor load applied. Hand wheel is rotated and the test piece is lowered. At this stage, the hardness of the test piece material can be directly read from the dial scale. There are two scales on a Rockwell Testing Machine, i.e. „B‟ scale and „C‟ scale. „B‟ scale uses a steel ball indenter whereas a diamond cone penetrater is employed for measuring hardness on C scale.

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In Rockwell Hardness Testing, the minor load for all cases is 10 Kg whereas major loads for scales C and B are 150 and 100 Kg respectively (including minor load).

6.3 VICKERS HARDNESS TESTING:
In this test, the instrument uses a square based diamond pyramide indenter with an included angle of 1360 between opposite faces. The load range is usually between 1 and 120 Kg. The Vickers Hardness Tester operates on the same basic principle as the Brinell Tester, the numbers being expressed in terms of load and area of the impression. As a result of the indenters shape, the impression on the surface of the specimen will be square.

Fig: Vicker Tester The length of the diagonal of the square is measured through a microscope fitted with an ocular micrometer that contains knife-edges (movable). The distance between knife-edges is indicated on a counter calibrated in thousandths of a millimeter. The formula may be used for measuring Vickers Pyramid Hardness Number (HV). HV = 1.854 L d2

Where L = applied load, Kg

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d = diagonal length of square impression, (mm).

The Vickers Tester is applicable to measuring the hardness of very thin sheets as well as heavy sections because of a result of the latitude in applied loads.

6.3.1 PROCEDURE :
To carry out the Vickers test the specimen is placed on the anvil and raised by a screw mechanism until it is closed in to the point of indenter. The load is slowly applied to the indenter and then released; operation of the foot lever reset the machine. After the anvil is lowered, a microscope is swung over the specimen and the diagonal of the square indentation measured by adjusting movable knife-edge. The readings thus obtained can be directly converted in to DPN by consulting the tables providing the machines. The following important precautions should be observed. 1. The foot paddle must be pressed gently and fully. 2. Zero of the microscope counter must be checked every time a reading is taken.

Fig: Vicker diamond pyramide indenter and indention.

6.4 COMPARISON OF TYPICAL HARDNESS TESTS:
Table: Comparison of typical hardness tests.

Test Brinell

Indenter 10-mm ball

Load 3000 Kg

Application Cast iron and steel

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Brinell Rockwell A Rockwell B

10-mm ball Brale 1/16 in. ball

500 Kg 60 Kg 100 Kg

Nonferrous alloys Very hard materials Brass, steel low-strength

Rockwell C Rockwell D Rockwell E Rockwell F

Brale Brale 1/8 in. ball 1/16 in. ball

150 Kg 100 Kg 100 Kg 60 Kg

High-strength steel High-strength steel Very soft materials Aluminum, materials Hard materials soft

Vickers

Diamond pyramid Diamond pyramid

10 Kg

Knoop

500 g

All materials

6.5 ACCURACY OF ANY INDENTATION HARDNESS TEST:
Some of the factors that influence the accuracy of any indentation hardness test are:

6.5.1 C ONDITION

OF THE INDENTER :

Flattening of a steel-ball indenter will result in errors in the hardness number. The ball should be checked frequently for permanent deformation and discarded when such deformation occurs. Any sign of chipping should check diamond indenters.

6.5.2 IMPACT LOADING :
Besides causing inaccurate hardness readings, impact loading may damage diamond indenters. The use of a controlled oil dashpot will ensure smooth, steady operation of the loading mechanism.

6.5.3 SURFACE C ONDITION

OF THE

SPECIMEN :

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The surface of the specimen on which the hardness reading is to be taken should be flat and representative of sound material. Any pits, scale, or grease should be removed by grinding or polishing.

6.5.4 THICKNESS OF THE SPECIMEN:
The specimen should be thick enough so that no bulge appears on the surface opposite that of the impression. The recommended thickness of the specimen is at least ten times the depth of the impression.

6.5.5 SHAPE

OF THE

SPECIMEN:

The greatest accuracy is obtained when the test surface is flat and normal to the vertical axis of the indenter. A long specimen should be supported so that it does not tip. A flat surface should be prepared, if possible, on a cylindrical-shaped specimen, and a V-notch anvil should be used to support the specimen unless parallel flats are ground, in which case a flat anvil may be used. If a Rockwell hardness test is made on a round specimen less than 1 in. in diameter without grinding a flat, the observed reading must be adjusted by an appropriate correction factor.

6.5.6 LOCATION

OF IMPRESSIONS :

Impressions should be at least 2 ½ diameters from the edge of the specimen and should be at least 5 diameters apart for ball tests.

6.5.7 UNIFORMITY

OF

MATERIAL:

If there are structural and chemical variations in the material, the larger the impression area the more accurate the average hardness reading. It is necessary to take many readings if the impression area is small to obtain a true average hardness for the material.

6.6 ADVANTAGES & DISADVANTAGES OF DIFFERENT TYPES OF TESTS:
The selection of a hardness test is usually determined by ease of performance and degree of accuracy desired. Since the Brinell test leaves a relatively large impression, it is limited to heavy sections.

This is an advantage, however, when the tested is not homogeneous. The surface of the test piece when running a Brinell test does not have to be so

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smooth as that for smaller impressions; however, using a microscope to measure the diameter of the impression is not so convenient as reading a dial gauge. Because of deformation of the steel ball, the Brinell test is generally inaccurate above 500 HB. The range may be extended to about 650 HB with a tungsten carbide ball. The Rockwell test is rapid and simple in operation. Since the loads and indenters are smaller than those used in the Brinell test, the Rockwell test may be used on thinner specimens, and the hardness as well as the softest materials can be tested. The Vickers tester is the most sensitive of the production hardness testers. It has a single continuous scale for all materials, and the hardness number is virtually independent of load. Because of the possibility of using light loads, it can test thinner sections than any other production test, and the square indentation is the easiest to measure accurately. The microhardness test is basically a laboratory test. The use of very light loads permits testing of very small parts and very thin sections. It can be used to determine the hardness of individual constituents of the microstructure. Since the smaller the indentation, the better the surface finish must be, a great deal more care is required to prepare the surface for microhardness testing. The surface is usually prepared by the technique of metallographic polishing. The principal advantages of the Sceleroscope are the small impressions that remain the rapidity of testing, and portability of the instrument. However, results tend to be inaccurate unless proper precautions are taken. The tube must be perpendicular to the test piece, thin pieces must be properly supported and clamped, the surface to be tested must be smoother than for most other testing methods, and the diamond tip should not be chipped or cracked.

6.7 EXPERIMENTAL RESULTS OF HARDNESS TEST:
Medium Carbon Steel: Hardness in VPN at 30 Kg Condition 336 Hardened and Tempered

Mild Steel Pipe: Hardness in VPN at 30 Kg Condition 139 Normalized

Austenitic Stainless Steel:

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Hardness in VPN at 30 Kg Condition

114 Austenitic and Rolled

Copper Alloy: Hardness in VPN at 10Kg Condition 103 Cast

Tempered Martensite Steel: Hardness in VPN at 30 Kg Condition 216 Tempered Martensite

Copper Base Studs: Hardness in VPN at 10 Kg 184

Martensitic Stainless Steel (410): Hardness in HRB Hardness in HRC 70 45

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CHAPTER # 7: AN OVERVIEW OF NON-DESTRUCTIVE TESTING
7.1 INTRODUCTION TO NDT:
A non-destructive test is an examination of a component in any manner, which will not impair its future use. Although non-destructive tests do not provide direct measurement of mechanical properties, yet they are extremely useful in revealing defects in components that could impair their performance when put in service. Defects of many types and sizes may be introduced to a material or a component during manufacture and the exact nature and size of any defects will influence the subsequent performance of the component. It is therefore necessary to have reliable means for detecting and monitoring the rate of growth of defects during the service life of a component or assembly. The origin of defects in materials and components are shown in figure.

Defects, which may be introduced during the manufacture of raw materials or the production of castings

Stress Segregation Cracking

Shrinkage Porosity

Gas Porosity

Slag

Inclusions

Defects, which may be introduced during the manufacture of components

Machining Residual Faults

Heat Treatment Defects

Welding Defects Stress Cracks

Defects, which may be introduced during component assembly

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Missing Parts Additional Assembled Parts

Incorrectly Welding Defects

Additional Stress Cracking

DEFECTS GENERATED DURING SERVICE LIFE

Fatigue Thermal Instability

Corrosion

Stress Corrosion

Wear

Creep

FIGURE: ORIGINS OF SOME DEFECTS FOUND IN MATERIALS AND COMPONENTS.

Often the first stage in the examination of a component is visual inspection. Examination by the naked eye will not reveal much other than relatively large defects, which break through the surface. The effectiveness of visual inspection can be increased through the use of a microscope. The most suitable type of microscope for visual examination of a surface is a stereomicroscope. A high degree of magnification is not necessary and the majority of microscopes available for this type of inspection have magnifications in the range from 5 to 75. Visual inspection need not be confined to external surfaces. Optical inspection probes, both rigid and flexible, have been developed for the inspection of internal surfaces and these probes may be inserted into cavities, pipes and ducts. Using well-established physical principles, a number of non-visual inspection systems have been developed which will provide information on the quality of a material or component and which do not alter or damage the components or assemblies, which are tested. The basic principles and major features of the main non-destructive testing (NDT) systems are given in table.

TABLE:

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System

Feature

Applicability

Liquid penetrant

Detection of defects, break the surface.

which Can be used for any metal, many plastics, and glassy and glazed ceramics.

Magnetic particle

Detection of defects, which break the surface and subsurface defects close to the surface.

Can only be used for ferro-magnetic materials (most steels and irons)

Electrical Detection of surface defects and Can be used for any methods (Eddy some sub-surface defects. Can metal. currents) also be used to measure the thickness of a non-conductive coating, such as paint on a metal.

Ultrasonic testing

Detection of internal defects but Can be used for most can also defects surface flaws. materials.

Radiography

Detection of internal defects Can be used for many surface defects and the materials but there are correctness of part assemblies. limitations on the maximum material thickness.

All these NDT systems co-exist and, depending on the application, may either be used singly or in conjunction with one another. There is some overlap between

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the various test methods but they are complementary to one another. The fact that, for example, ultrasonic testing can reveal both internal and surface flaws does not necessarily mean that it will be the best method for all inspection applications. Much will depend upon the type of flaw present and the shape and size of the components to be examined. Non-destructive tests (NDT) are inspection methods that are usually used to search for the presence of defects in components, without causing any effects on the properties of the components. The types of defects detectable are cracks, porosity, voids, inclusions, etc. Modern NDT is used by manufacturers to: ensure product integrity and reliability; prevent failure, accidents and saving lives; make profit for users; ensure customer satisfaction; aid in better product design; control manufacturing process; lower manufacturing costs; maintain uniform quality level; ensure operational readiness. The table below shows the types of NDT methods used today. Commonly Used Methods Ultrasonic Radiography Dye Penetrant Magnetic Particle Inspection Eddy Current Other Methods Visual Methods Acoustic Emission Thermography Holography Potential - drop

7.2 BENEFITS OF NON-DESTRUCTIVE TESTING:
One obvious and clear benefit that can be derived form destructive testing is the identification of defects undetected, could result in a catastrophic failure that money and possibly in lives. But the use of these benefits in many ways. the judicious use of nonthat, if they remained would be very costly in test methods can bring

The introduction of any inspection system incurs cost but very often the effective use of suitable inspection techniques will give rise to very considerable financial savings. Non-only the type of inspection but also the stages at which inspection is employed is important. It could be very wasteful to reserve the use of a nondestructive test technique for the inspection of small castings or forgings until

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after all the machining operations have been carried out on the parts. In this case it would be preferable to examine the product before costly machining is commenced and those components with unacceptable flaws rejected. It should be emphasized that not all flaws, which may be located at this stage, warrant rejection. Some surface discontinuities might be of such a size that they would be removed at the machining stage. While effective quality control inspection can result in financial savings and help to prevent catastrophic failures in service, it is also true to say that the imposition of too many or too sensitive inspection systems can be very wasteful in terms of both time and money. Excessive inspection may not result in an increase in product performance or reliability. Absolute perfection in a product is impossible to achieve and attempting to get very close the ideal can prove to be very expensive.

7.3 APPLICATION OF NDT:
Application Bearing Industries Problem Definition for Rollers Raceway Cracks Possible Solution Eddy Current (Complex normally Resonant Inspection handling required)

Cracks on ends

Magnetic Particle Inspection (not 100% reliable) Resonant Inspection) Ultrasound Resonant Inspection Resonant Eddy Current Inspection

Inclusions

Hardness Problems

Problem Definition for Balls Cracks

Possible Solution Eddy Current (Complex normally required) Ultrasound Resonant Eddy Current Inspection handling

Inclusions (rarely encountered) Hardness Problems

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Problem Definition for Bearings and Possible Solution Rings Raceway Cracks Magnetic Particle Inspection (not 100% reliable) Ultrasound (limited application) Magnetic Particle Inspection (not 100% reliable) Ultrasound (limited application) Resonant Inspection (limited application) Ultrasound Resonant application) Eddy Resonant application) Resonant application)

Cracks on other surfaces

Inclusions

Inspection

(limited

Hardness Problems

Inspection

Current (limited

Forging problems

Inspection

(limited

Application Steel Industry Problem Definition for Billets Cracks Inclusions and Central Pipe Material structure Problem Definition for Bar Cracks Possible Solution Magnetic Particle Inspection Ultrasound Eddy Current Possible Solution Eddy Current (Complex normally Magnetic Particle Inspection Ultrasound Eddy Current handling required)

Inclusions Material Mix

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Problem Definition for Rings Cracks Inclusions Material Mix

Possible Solution Magnetic Particle Inspection Ultrasound Eddy Current

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CHAPTER # 8: LIQUID PENETRANT INSPECTION
8.1 INTRODUCTION:
“Liquid penetrant inspection” is a method of detecting and indicating surface discontinuities in relatively non-porous materials. Penetrant remaining in the discontinuity after the penetrant on the surface has been removed provides an indication by contrast with the unbroken background. The objective of the liquid penetrant method of inspection is the detection of surface discontinuities (cracks, porosity, laps, seams, or evidence of other surface imperfections) rapidly and economically with a high degree of accuracy. Common liquid penetrant inspection methods include both direct visual observation and fluorescent systems where the indication is its own light source. Radioactive liquid penetrant may be applicable in special situations and in this case radiation-counting equipment is used to detect concentrations of the penetrant. 8.2 PROCEDURE:

8.2.1 PRE-C LEANING

OR

SURFACE PREPARATION :

Good cleaning is essential in order to obtain reliable penetrant indications. Great care must be taken to assure that the arts are clean and dry. The cleaning technique being used will be determined by the type of foreign material present and may require either mechanical, solvent, etch, ultrasonic, or special surface preparation to assure adequate cleaning. Descriptions of some of these processes follow.

8.2.1.1 MECHANICAL CLEANING :
Grit or vapor blasting, wire brushing, or grinding may be required to remove dirt, paint, rust, scale or other surface materials.

8.2.1.2 DETERGENT

AND

SOLVENT CLEANING :

Solvents or detergents may be used to remove oil, grease, and loose dirt, etc. from the surface of the part.

8.2.1.3 ETCH CLEANING:
Etchants may be used to remove smeared metal and clean surface of rust. The type etchant used will depend upon the material being inspected.

8.2.2 SURFACE PREPARATION:

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Special techniques have been devised to open discontinuities so that the penetrant is assured of penetrating. One such technique involves stressing the parts near the yield point of the material. A second technique involves the application of ultrasonic vibrations to clean foreign material from tight discontinuities.

8.2.3 DRYING:
Following the cleaning operation it is imperative that parts that have been cleaned be thoroughly dried. If moisture or liquids remain in the discontinuity the penetrant cannot flow into it. Warm air directed onto the part or oven drying is very desirable to assure evaporation of any water, solvent or cleaning solution from the discontinuity.

8.2.4 APPLYING PENETRANT:
Apply penetrant to the surface of a clean, dried part or section to be inspected by any method that will thoroughly wet the surface, i.e., dipping, spraying, or brushing. All surfaces should be thoroughly covered to allow capillary action to suck the penetrant into the discontinuity. The time required to obtain optimum penetration should be determined experimentally, i.e., by successively processing parts at longer dwell times until no further increase in indications is found. The normal dwell time for a penetrant is 10 to 30 minutes.

FIG: PENETRANT ON SURFACE SEEPS INTO CRACK.

Long penetration times will not affect the inspection sensitivity unless the penetrant is allowed to dry on the surface of the parts. If the surface penetrant becomes dry it must be reactivated by re-application of the penetrant, otherwise the part will be difficult to wash and exhibit high background. Some gain in sensitivity may be obtained by heating the part before applying the penetrant. The advantages gained may be offset by certain disadvantages such as volatilization of penetrant, difficulty in washing, and higher background thus heating to increase sensitivity is not normally recommended. In fact, if a very

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hot part is sprayed with fluorescent type penetrant, the heat may destroy the effectiveness of the penetrant by reducing its fluorescence; this may also happen if a very hot part is immersed in penetrant.

8.2.5 REMOVING EXCESS PENETRANT :
Penetrant removal is the most important step in the processing of parts for inspection; tight control of the various parameters must be maintained to assure a good, reproducible result. Over-washing of parts will remove the penetrant from the discontinuities while under-washing will leave too much penetrant on the part surface and cause excessive background and hide indications.

FIG: WATER SPRAY REMOVES EMULSIFIED PENETRANT.

The adequacy of the rinse is normally judged through visual observation during the rinse operation. With fluorescent penetrant, rinsing is performed under or near a black light. When background fluorescence has been removed, rinsing is discontinued. With visible penetrants, absence of visible color indicates that rinsing is complete. Abnormally high rinse pressures or overly long rinse times should be avoided to minimize the possibility of removing penetrant from flaws. Removal of penetrant is dependent upon the type of penetrant system used. 8.2.5.1 Water Washable System: Excess penetrant is generally removed from the surface in a water washable system by dipping the part into an air or mechanically agitated tank of water or by spraying the part with low-pressure water (approximately 40psi). If dip washing is used, usually two tanks are required; this removes the bulk of the excess penetrant in the first while the final wash removes the residual carried over from the first tank. The older type penetrants required warm to hot water, around 1500F; the newer water washable penetrants generally need only room temperature water.

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8.2.5.2 Post Emulsification System: Excess post-emulsification penetrant is generally removed by dipping the part into emulsifier for a predetermined time period followed by washing the part either by dipping in water tanks or by water spraying. The emulsifiers, required to render the penetrant oil water soluble, fall into two general classifications, (1) lipophilic or an oil base material and (2) hydrophilic or a water base material. The lipophilic type emulsifier is the most commonly used although the hydrophilic system is starting to make gains. 8.2.5.3 Solvent System: Excess penetrant is removed from the surface of the part by wiping with a dry absorbent towel followed by rewiping the surface using a clean towed dampened with a solvent remover recommended by the penetrant manufacturer, normally a universal solvent such as a trichlorethylene type material. Again care must be taken to just dampen not saturate the cloth with the solvent. Excess solvent will displace and remove penetrant from discontinuities.

8.2.6 DRYING:
Parts must be thoroughly dry before developer is applied. One method is to place them in a drying oven at a temperature of 1800F for a sufficient time to ensure drying but not so long that excessive degradation of the penetrant occurs. Under no circumstances should the drying temperature exceed 2500F. Parts should be removed from the drier as soon as they are dry; if allowed to remain in the drier too long, the test sensitivity will be reduced because of dye degradation. Even at 2500F dye degradation occurs rapidly, within five minutes noticeable effects are evident. The 1800F temperature is recommended to provide a reasonable margin of safety during drying. Higher temperatures may be desirable to reduce processing time, but when they are used, extreme care should be exercised to avoid over-exposure. A second method, which is also satisfactory, is by drying with a blast of high velocity air. Clean air should be used so that parts are not splattered with oil or water, which would recontaminate the surfaces.

8.2.7 APPLYING DEVELOPER:
The function of the developer is to absorb or draw the penetrant that is entrapped in the discontinuities to the surface thereby increasing the visibility of flaw indications. The developer action appears to be a combination of solvency effect, adsorption, and absorption. The developer powder exerts a combination adsorptive-absorptive effect on penetrant residues drawing residual penetrant to

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the surface. As the penetrant disperses through the developer powder, the inspector readily observes it. In the case of the non-aqueous wet and film type developers, solvent action has been shown to play a part promoting the withdrawal action and enhancing the indications.

FIG: DEVELOPER ACTS LIKE A BLOTTER TO DRAW PENETRANT OUT OF CRACKS.

There are four types of developers in common use, namely the dry, wet, nonaqueous wet, and film types. 8.2.7.1 Dry Developer: The dry developer is readily distinguishable from the “wet” type by its very fluffy nature and its high bulk density. In normal use, the dry developer is blown onto the surface from which penetrant has been removed and dried. Blowing off with air or shaking removes excess.

8.2.7.2 Aqueous Wet Developer: There are three types of wet developer in common use: developer powder is suspended in water, developer powder actually soluble in water, and a liquid developer dilutable with water. 8.2.7.3 Non – Aqueous Wet Developer: Non-aqueous wet developer is similar to the wet developer except that the developer solids come already suspended in a volatile solvent. The volatile solvent tends to pull penetrant from indications by solvent action, and accelerates drying so that a supplementary drying operation is not required. A thin film of the non-aqueous wet developer is desirable to give the ultimate in sensitivity. Spray application, using a fine atomizing spray such as a paint spray gun, will provide this fine film coverage. 8.2.7.4 Film Developer: The film type developer, as the name implies, forms a plastic film over the penetrated area as it dries. It is normally spray applied, as with the non-aqueous wet type, the solvent carrier acting to draw penetrant into the film. As the film

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dries, the exposed penetrant indications set in a pattern indicative of the discontinuities in the surface being inspected. This film provides a permanent record of the discontinuity pattern and can be peeled from the surface and retained for reference.

8.2.8 INSPECTION:
After the proper developing time has transpired the part is ready for inspection and evaluation. The process used determines the lighting used to inspect the part; white light of sufficient intensity is used for the visible dye method while black light is used for the fluorescent dye method. The black light as used in penetrant inspection has been standardized as peaking at 3,650-angstrom units; this is the peak transmission wavelength for common black light filters. Recommended intensity level for black light is a 200-foot candle at 12 inches.

FIG: BLACK LIGHT CAUSES PENETRANT TO GLOW IN DARK VISIBLE PENETRANT INSPECTED UNDER WHITE LIGHT.

The contrast of the penetrant to the background will indicate the location and the size of the indication. It is necessary to verify that the indication is valid and not a false indication due to background or spurious precipitates. This is done by lightly brushing the questioned area or wiping the area with a solvent dampened brush, re-dusting and re-inspecting. Determine the type, location and size of the discontinuity and interpret to applicable acceptance standard. It if is reject able by the standard then the part is suspect and should be repaired or rejected. The quality of inspection is no better than the ability of the inspector to find and then to evaluate present. Following the inspection operation the developer generally should be removed from the part before it is returned to service. Rinsing with a pressure water spray, dipping into a water tank, or wiping the developer from the surface can accomplish this. Critical parts, usually those subjected to high temperature may require that residual penetrant be removed form the part prior to further processing to assure that there will be no possible reaction with the material.

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This may be accomplished by dipping part into a solvent material, either liquid or vapor.

8.3 PROPERTIES OF PENETRANTS:
The penetrants are specially formulated liquids which flow over the surface of the test piece to give a reasonably uniform coating which then migrate in to the cracks open to the surface they show the following properties:

8.3.1 CAPILLARY ACTION:
The ability of the penetrant to enter the cavity is dependent on the capillary action; inverting the fine tube upright in a reservoir of liquid can see this. The liquid will rise in to the tube until equilibrium is reached between the upward capillary pressure and the downward air pressure. The capillary pressure is given by P = 2 S Cos / D Where, S is surface tension D is diameter of the tube is the contact angle P is the capillary pressure The formula shows that as increase in the surface tension or decrease in the contact angle or tube diameter will increase the capillary pressure and therefore capillary rise in the tube.

8.3.2 AIR DIFFUSION:
Penetration of the penetrants in to the cavity is further enhanced by diffusion of the entrapped air through the penetrant. By this process it is possible for the penetrant to fill the cavity completely.

8.4 PHYSICAL PROPERTIES OF PENETRANTS:
8.4.1 VISCOSITY – MODERATE VISCOSITY:
If too thick, penetration and development will take longer time. If too thin, the penetrant will drain away quickly during washing.

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8.4.2 SURFACE TENSION – HIGH :
High surface tension will increase the capillary pressure.

8.4.3 WETTING ABILITY – HIGH :
Wetting ability increases as the contact decreases.

8.4.4 DENSITY

OF

SPECIFIC GRAVITY – LESS

THAN

W ATER:

Most penetrants are hydrocarbons and have a specific gravity of less than unity. Contaminants will sink to the bottom of the penetrant bath.

8.4.5 INFLAMMABILITY – NON FLAMMABLE:
Halogenated hydrocarbons are non-flammable.

8.4.6 RESISTANCE

TO

CONTAMINANTS – HIGH:

The penetrant should be capable of dissolving a path into contaminated defects, through a wide range of contaminants.

8.4.7 TOXICITY – LOW
Preferably the penetrants used should be non-toxic.

8.4.8 C HEMICAL INERTNESS:
Chemical inertness should be low as possible.

8.5 PROPERTIES OF DEVELOPERS:
A developer requires following characteristics.

8.5.1 HIGH ABSORPTION:
By reverse capillary action the developer draws penetrant out of the cavity.

8.5.2 FINE GRAIN:
To disperse easily and to form a thin uniform coating over the surface.

8.5.3
It must be capable to providing a contrasting background for indications, especially when colored penetrants are used.

8.5.4

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Non - fluorescent, so as to form a black background to fluorescent dyes in black light.

8.5.5
Easily removable after completion of the inspection.

8.5.6
Not harmful for the parts being inspected or to the operator.

8.6 ADVANTAGES OF LIQUID PENETRANT INSPECTION
1. Extremely sensitive to surface indications. 2. Material and equipment relatively inexpensive. 3. Relatively simple, trouble-free process. 4. Part geometry not particularly a problem.

8.7 LIMITATIONS OF LIQUID PENETRANT INSPECTION
1. Discontinuities must be open to the surface. 2. Inspection fairly messy. 3. Cost of inspection relatively high due to processing time. 4. No easy method to produce permanent record.

8.8 APPLICATION OF LIQUID PENETRANT INSPECTION
The application of liquid penetrant testing is extremely wide and varied. The system is used in the aerospace industries by both producers for the quality control of production and by users during regular maintenance and safety checks. Typical components that are check by this system is tube i.e. rotor disc and blades, aircraft wheels, castings, forged components and welded assemblies. Many automotive parts, particularly aluminum castings and forgings, including pistons and cylinder heads, are subjected to this form of quality control inspection before assembly. Penetrant testing is also used for the regular in service examination of the bogie frames of railway locomotive and rolling stock in the search for fatigue cracking. 1. Grinding cracks 2. Heat affect zone cracks 3. Poor weld penetration

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4. Heat treatment cracks 5. Fatigue cracks 6. Hydrogen cracks 7. Inclusions 8. Laminations 9. Micro shrinkage 10.Gas porosity 11.Hot tears 12.Cold shuts 13.Stress corrosion cracks 14.Intergranular corrosion

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CHAPTER # 9: MAGNETIC PARTICLE INSPECTION
9.1 INTRODUCTION:
Magnetic particle inspection is one of the several non-destructive tests by industry to control the quality of the many products on the market. This is a method of detecting the presence of cracks, laps, tears, seams, inclusions and similar discontinuities in ferromagnetic materials such as iron and steel. The method will detect surface discontinuities too fine to be seen by naked eye and will also detect discontinuities that lie slightly below the surface. It is not applicable to non-magnetic materials.

FIG: FERROMAGNETIC MATERIAL HAVING SURFACE AND SUB-SURFACE DISCONTINUITIES.

Magnetic particle inspection may be carried out in several ways. The piece to be inspected may be magnetized and then convert with fine magnetic particles (iron powder), this is known as the residual method. Or the magnetization and application of the particles may occur simultaneously, this is known as the continuous method. The method depends for its operation on the fact that when the part under test is magnetized, magnetic discontinuities that lie in a direction generally transverse to the direction of the magnetic field will cause leakage field. The presence of leakage field and therefore presence of discontinuity is detected by the use of finely divided ferromagnetic particles applied over the surface, some of the particles being gathered and collected by the leakage field. This collection of magnetic particles forms an outline of discontinuity and indicates its location, size, shape and extent.

9.2 BASIC PRINCIPLES OF MAGNETIC PARTICLE TESTING:
When a magnetic medium (dry particle or liquid suspension) is applied to the part and a distortion in the lines of force occurs, there are leakage fields and the medium is drawn to these areas in a form of buildup. Leakage fields are lines of force that leap through the air from one side of a break in the material to the

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other side. It is the abrupt change in permeability that causes this particle buildup. Several other phenomena can cause this condition and they will be discussed later.

Fig: Principle of magnetic particle test.

Two phenomenon of magnetic particle testing occur: Abrupt changes in permeability distorting the lines of force result in leakage fields at the poles. Any fine ferromagnetic testing material will be drawn to these areas and will out line the leakage field (fig).

FIG: ACCUMULATION OF MAGNETIC POWDER IN LEAKAGE FIELD. IRON PARTICLES ARE HELD BY THE LOCAL LEAKAGE FIELD OF A SHARP DISCONTINUITY IN A BAR MAGNET.

(a) No discontinuities

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(b) Internal Discontinuity parallel to Field

(c) Surface Discontinuity

(d) Deep Sharp Discontinuity (900 to Field)

(e) Round Discontinuity

(f) Shallow Sharp Discontinuity (900 to Field)
FIG: EFFECT OF VARIOUS TYPES OF DISCONTINUITIES ON MAGNETIC FORCE LINES.

9.3 MAGNETIZING CURRENTS:
Magnetizing currents are the various types of electrical currents used to produce the magnetic fields. Table summarizes the various currents used, their uses, advantages and disadvantages in magnetic particle inspection. Both ac and dc have their place in the testing spectrum. Direct current is the most acceptable for sub-surface disclosures in new material or parts acceptance. Alternating current methods favor the surface and are; therefore, most revealing for fatigue cracks nucleating in ferrous structural members.

TABLE 2.1: MAGNETIZING CURRENTS USED IN MAGNETIC PARTICLE TESTING

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Current DIRECT (dc)

Use Detection of both surface and subsurface discontinuities. Primary used for subsurface.

Advantages Full penetration of flux into object permitting indication of sub-surface discontinuities.

Disadvantages Difficult to demagnetize. Battery maintenance. Fixed voltage.

ALTERNATING (ac)

Detection surface discontinuities.

of Relatively easy to demagnetize provides maximum flux density on surface for best sensitivity in detecting surface discontinuities. Particle mobility.

Shallow penetration of flux making ac ineffective for subsurface discontinuities.

HWAC*

Detection of both surface and subsurface discontinuities. Most sensitive for sub-surface discontinuities.

Higher flux densities Relatively for the same difficult to average current. demagnetize. Full penetration of flux into object permitting indication of subsurface discontinuities. Can be obtained from some test equipment as ac by addition of rectifies and switch. Particle mobility.

9.4 MAGNETIZATION:
Magnetic fields may be induced either directly or indirectly. In direct magnetization, the current is passed directly through the part. Placing the part in a magnetic field that is generated by an adjacent current conductor induces indirect magnetization. Parts are usually magnetized by inducing both a circular field and a longitudinal field, but at separate intervals.

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Magnetization of certain metals is possible to reveal surface or sub-surface cracks or discontinuities using a medium (finely divided iron powder) having magnetic attraction. The medium is applied on to the surface under examination. A useful rule for determining the direction of current and magnetic field is called right hand rule.

Different methods employed for magnetization may be classed as follows:

9.4.1 CIRCULAR MAGNETIZATION:
When the magnetic field surrounds a conductor carrying an electric current, this is known as circular magnetization. In this case the testing object may be magnetized by passing current through the article by means of contacts or prods or direct induction.

This makes the circular field between the contact points. Circular magnetization will detect discontinuities that are between 450 and 900 to the lines of force.

Fig: Indirect Circular Field Magnetization

Fig: Direct Circular Field Magnetization by Prod Method

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9.4.2 LONGITUDINAL MAGNETIZATION:
In this case the magnetic field is induced in to the specimen. This magnetization used for inspection of large surface areas to surface discontinuities and can locate discontinuities in any direction. The longitudinal magnetization is induced into specimen by coil or yoke (just like a prod). Central Conductor Magnetization: This is done by placing current carrying conductor in to the specimen. This type of magnetic field has some of the characteristics of both circular and radial field. This is referred to as parallel field magnetization and this is done a magnetic field results whose magnitude and direction are determined by the two imposed field.

Fig: Longitudinal Magnetization in Field of a Coil.

9.4.3 YOKE MAGNETIZATION:
In Yoke Magnetization, the magnetic lines formed from the pole to pole and the optimum flaw indication when oriented perpendicular to pole direction (transverse defects).

Fig: Longitudinal Field Induced by a Yoke. Note different field directions existing in weld area.

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9.4.4 MAGNETIZATION

WITH

ELECTRIC CONDUCTOR :

A.C Magnetization is preferred for maximum surface sensitivity and offers special operating advantages, including straight forward demagnetization after testing, whereas D.C. appears to permit the detection of defects lying more deeply in the material.

Fig: Induced Current Magnetization

9.5 METHODS OF INDUCING MAGNETIC FIELDS:
Method Direct Magnetization Head Shot-Solid Circular Simultaneous Not effective for Magnetic Conductor magnetization magnetization of circumferential (Specimen) of solid steel entire length. defects. objects up to 12‟ in length. Head Shot-Hollow Hollow steel Simultaneous Not effective for Magnetic Conductor objects up to magnetization of any defects on (Specimen) 12‟ in length; entire length. internal surface external nor for surfaces only. circumferential defects on outer surface. Prods Partial Good sensitivity Arc burns Application Advantages Limitations

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magnetization of large weldments, castings, etc.

over small area. possible. Magnetic field can be rotated by relocation of prods. Equipment is portable.

Indirect Magnetization Central Conductor Hollow steel objects when internal surface must be inspected. Provides greatest Not effective for flux density on circumferential inner surface defects. simultaneous magnetization of entire length. Can be used for I.D. and O.D. Insp. Longitudinal Field

Indirect Magnetization Coil Shot Solenoids Longitudinal and Coils magnetization of solid or hollow steel objects.

Good sensitivity for circumferential defects.

For objects over about 18‟‟ long coil must be relocated for successive tests. Not effective for longitudinal defects.

Yokes

Special cases of Peculiar to longitudinal special magnetization application. over a small area.

the Distorted, troublesome field concentration. Fixed field strength.

9.6 APPLICATIONS OF MAGNETIC PARTICLE INSPECTION:
The principal industrial uses of magnetic particle inspection are in-process inspection, final inspection, receiving inspection and in maintenance and overhaul.

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Although in-process inspection is used to highlight defects, as soon as possible in the processing route, a final inspection gives the customer a better guarantee of defect-free components. During receiving inspection, both semi-finished purchased parts and raw materials are inspected to detect initial defects, incoming rod and bar stock, forging blanks and rough castings are inspected in this way. The transportation industries (road, rail, aircraft and shipping) maintain planned overhaul schedules at which critical parts are inspected for cracks. Crankshafts, frames, flywheels, crane hooks, shafts, stream turbine blades and fasteners are examples of components vulnerable to failure, in particular fatigue failure. Hence, there is a need for regular inspection.

9.7 ADVANTAGES & LIMITATIONS OF MAGNETIC PARTICLE INSPECTION:
Magnetic particle inspection is a sensitive means of detecting very fine surface flaws. It is also possible to obtain indications from some discontinuities. If is often unnecessary to have an elaborate pre-cleaning routine and it is sometimes possible to obtain good indications even if a flaw contains contaminating material. While magnetic particle inspection is not a quantitative test, a skilled and experienced operator may be able to give an estimate of the breadth and depth of cracks. The equipment necessary is comparatively cheap. The major limitations of the technique are that it is only suitable for ferromagnetic materials. When large components are to be inspected, extremely large currents are required and care will be needed to avoid localized heating and surface burning at the points of electrical contact. The sensitivity of magnetic particle inspection is generally very good but this will be-reduced if the surface of the component is covered by a film of paint or other non-magnetic layer.

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CHAPTER # 10: ULTRASONIC FLAW DETECTION
10.1 INTRODUCTION:
Ultrasonic techniques are very widely used for the detection of internal defects in materials, but they can also be used for the detection of small surface cracks. Ultrasonic is used for the quality control inspection of part processed material, such as rolled slabs, as well as for the inspection of finished components. The techniques are also in regular use for the in-service testing of parts and assemblies. Sound is propagated through solid media in several ways and the nature of sound will be considered first.

Velocity of sound in common materials m/sec: Materials Al Brass Cu Steel Perspex H2O Air Longitudinal 6320 4280 4660 5900 2730 1430 330 Shear 3130 2030 2260 3245 1400 -

10.2 TO MEASURE THE SOUND VELOCITY OF A MATERIAL:
By comparison, the comparison is made with a material of known velocity such as steel at 5900 m/sec.

Velocity of sound in steel unknown Velocity of sound in unknown Velocity of Sound of Unknown Vernier

=

CRT reading of

Unknown specimen thickness by vernier = Velocity of Steel Unknown thickness by

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CRT reading of unknown as calibrated of Steel

10.3 THE ULTRASOUND VIBRATIONS:
The ultrasound vibrations are those which operate 20,000 cycles/sec or more. These vibrations are elastic in nature and depend on modulus of elasticity (E) and density of the material under examination.

V=

Eg / l

Where, E = modulus of elasticity g = acceleration due to gravity (384 inch / sec2) l = density of material.

Examples of ultrasound velocity of some materials are:

Materials

Velocity in/sec 105 2.46 1.82 0.77 2.27 2.37 2.10 1.43 2.26 0.77 2.26 0.59

E (psi

106)

(gm / cm3)

Al Cu Pb Mg Ni 60 /40 Ni-Cu Ag Stainless Steel P.E. Quartz H2O

10.4 16.0 2.4 6.6 30.0 26.0 10.9 28.5 11.6 10.0 -

2.70 8.96 11.34 1.74 8.90 8.90 10.49 7.30 0.90 2.65 1.00

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Crystals that produce ultrasound vibrations are Quartz (SiO2) Tourmaline Barium Titanate

10.4 PIEZO ELECTRIC EFFECT:
“Piezo Electric Effect” involves the production of ultrasound waves (20,000 cycles and above) if a particular crystal is connected to an electric main and if an electric energy is capable of producing 20,000 cycles and above as the mechanical energy or the mechanical vibration then it is said to posses the “PIEZO ELECTRIC EFFECT”.

10.5 BEHAVIOUR OF ULTRASOUND WAVES
Reflection: In accordance with the same laws of light waves the angle of incident equal to the angle of reflection when beamed on a specular reflector with no loss of intensity. Refraction: The beam can be bend as in light waves seeing angularly on object in water will have this effect. Diffraction: Diffraction at the extremes of the very narrow reflector, directional charge termed scatter occurs where the above rules do not apply. Interface Behavior: At an interface of two medias with differing sound velocities ultrasonic waves will be partly reflected and partly transmitted. This resistance to the flow of energy is known as “Acoustic Impedance”. Between Perspex and steel 87% of transmitted energy is lost crossing the interface and a further 87% is lost on its returns journey crossing the interface and only 1.69% is available for display on “cathode ray tube”.

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Attenuation: This is the lose of ultrasonic energy by traveling through a medium due to scattering and absorption.

Mode Conversion: The transformation of ultrasonic energy usually due to reflection, causing a change of waveform and velocity. At the interface of the Perspex probe shoe mode conversion takes place. In certain cases mode conversion may cause a major portion of the energy to be reflected away from the transducer. 10.6 BASIC PRINCIPLES OF ULTRASONIC TESTING Mechanical vibrations can be propagated in solids, liquids and gases. The actual particles of matter vibrate, and if the mechanical movements of the particles have a regular motion, the vibration can be assigned a frequency in cycles per second, measured in hertz (Hz), where 1 Hz = 1 cycle per second. If this frequency is within the approximate range 10 to 20,000 Hz, the sound is audible; above about 20 kHz, "the sound" waves are referred to as ultrasound or ultrasonic. The ultrasonic principle is based on the fact that solid materials are good conductors of sound waves. The waves are not only reflected at the interfaces but also by internal flaws (material separations, inclusions, etc.). As an example of a practical application, if a disc of piezoelectric materials is attached to a block of steel (Figure 1a), either by cement or by a film of oil, and a high- voltage electrical pulse is applied to the piezoelectric disc, a pulse of ultrasonic energy is generated in the disc and is propagated into the steel. This pulse of waves travels through the metal with some spreading and some attenuation and will be reflected or scattered at any surface or internal discontinuity such as an internal flaw in the specimen. This reflected or scattered energy can be detected by a suitably placed second piezoelectric disc on the metal surface and will generate a pulse of electrical energy in that disc. The time- interval between the transmitted and reflected pulse is a measure of the distance of the discontinuity from the surface, and the size of the return pulse can be a measure of the size of the flaw. This is the simple principle of the ultrasonic flaw detector and the ultrasonic thickness gauge. The piezoelectric discs are the "probes" or "transducers"; sometimes it is convenient to use one transducer as both transmitter and receiver. In a typical ultrasonic flaw detector the transmitted and received pulses are displayed in a scan on a time base on an oscilloscope as shown in Figure 1b.

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FIGURE: BASIC PRINCIPLE OF ULTRASONIC TESTING WITH A COMPRESSIONAL PROBE

(a) Set-up (b) Standard A-scan display Three methods of Ultrasonic Flaw Detection are used to detect the flaw in a material.

10.6.1 PULSE ECHO

OR

REFLECTION METHOD :

The “Pulse Echo Method” uses only one transducer that serves as both transmitter and receiver.

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Fig: The pulse echo or reflection method. The time required for a pulse to travel through the metal, reflect off a discontinuity on the opposite side and return to the transducer is measured with an oscilloscope. When the ultrasonic waves strike and interface, a portion is reflected and returns to the transducer both the initial and the reflected pulse can be displayed on the oscilloscope. From the oscilloscope display we measure the time required for the pulse to travel from the transducer to the reflecting interface back to the transducer. If we know the velocity at which the pulse travel in the material we can determine how far the elastic wave travel and can calculate the distance below the surface at which the reflecting interface is located. If there is no flaws in the metal, a beam reflects from the opposite side of the metal and our measured distance correspond to twice the wall thickness. If a discontinuity is present and properly oriented beneath the transducer at least the portion of pulse reflects from the discontinuity and resistors at the transducer in a shorter period of time. Our calculation shows that the discontinuity lies within the material and even tells us the depth of discontinuity below the surface.

10.6.2 THROUGH TRANSMISSION METHOD :
In “Through Transmission Method” an ultra sound pulse is generated and detected at the opposite surface by the 2nd transducer. The initial and transmitted pulses are displayed on the screen at the oscilloscope. The loss of energy from the initial to the transmitted pulse depends on whether or not a discontinuity is present in the metal.

The presence of discontinuity reflects a portion of the transmitted beam, thus reducing the intensity of the pulse at the receiving transducer.

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Fig: Through transmission method, contains a receiving and a transmitting transducers.

10.6.3 RESONANCE METHOD :
In both the reflection and transmission methods, the elastic wave is treated as energy particles. In the Resonance Method we utilized the wave like nature of the phonon. A series of pulses generated and travels through the material as an elastic wave. By selecting a wavelength or frequency, so that the thickness of the metal is a whole number of half wavelengths, a stationery elastic wave is produced and reinforced in the metal. A discontinuity in the metal prevents resonance from occurring.

10.7 TRANSDUCERS:
The main transducers are grouped as under: 1. Quartz 2. Lithium Sulphate 3. Polarized Ceramics 4. Barium Titanate 5. Lead Zirconate 6. Lead Metaniobate 7. Lead Zirconate Titanate.

10.7.1 QUARTZ :
Properties: 1. High resistance to wear.

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2. Insoluble in water. 3. Resists ageing. 4. Uniform characteristics, electrical and mechanical stability.

Limitations: 1. Least efficient generator of acoustic energy. 2. Requires high voltage to drive at low frequency.

10.7.2 LITHIUM SULPHATE :
Properties: 1. Most efficient receiver of ultrasound. 2. Low electrical impedance. 3. Operators well on low voltage. 4. No ageing. 5. Good resolution, easily damped. Limitations: 1. Low mechanical strength. 2. Soluble in water. 3. Crystal decomposes at 1600C.

10.7.3 POLARIZED CERAMICS:
1. Efficient generator of sound. 2. Operators at low voltage. 3. Used up to 3000C.

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The simple form of probe, transmitter or receiver consist of an x-cut crystal coming directly into contact with a specimen and launching sound waves perpendicular to the face of the crystal. Electrical energy is applied through the central core of the co-axial cable to the metallised side of the crystal and earth returns from the electronic equipments is from the work phase of the crystal by way of the outer metal sheath of the cable.

10.8 TRANSVERSE PROBES:
10.8.1 PROBE CONSTRUCTION:
There are several types of transmitter probe in use but each type consists of a crystal that is placed in contact, either directly or through a protective cover, with the material under test. There are several materials that may be used as transducer crystals and these include natural quartz, barium titanate, lead niobate and lithium sulphate. A step voltage of short duration is applied to the crystal and this cause the crystal to vibrate at its natural frequency. After the step voltage has been removed the crystal oscillation is required to die as soon as possible, and the crystal is usually backed by a damping material to assist this process. Probes may be of the normal type, or be angled. 10.8.1.1 Normal Probes: A normal probe is designed to transmit a compression wave into the test material at right angles to the material surface. In some cases the crystal surface is uncovered so that it may be placed directly, via an oil or water film, in contact with the test material. Alternatively, the crystal may be protected by a layer of metal, ceramic or Perspex. In the last case the Perspex block may be shaped to allow for normal transmission into material with a curved surface.

(i) (iii)

(ii)

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(a) 10.8.1.2 Angle Probes: Angle probes are designed to transmit shear waves or Rayleigh waves into the test material. The general construction of an angle probe is similar to that of a normal probe with the crystal embedded in a shaped Perspex block. There is a reflected compression wave produced at the Perspex / metal interface. This reflected wave could possibly return to the crystal and give confusing signals. To obviate this an absorbent medium, such as rubber, is built into the probe an alternative method is the shape the Perspex block in such a way that the reflected wave is „bounced‟ around several times until its energy is dissipated. This is possible since Perspex has a high absorption coefficient.

FIGURE: CONSTRUCTION OF ANGLE PROBE. PROPERTIES OF COMMON “CRYSTAL” MATERIALS

Material

Quartz

Lithium Surface 75 (disintegrate)

Barium Titanate 120

PZT5 Ceramic

Curie Temperature 0 C Transmitting Constant Receiving Constant Density

575

340

2

16

140

320

50

175

15

24

2.65

2.055

5.4

7.5

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103 Kg/m3 Acoustic Impedance (Z) Dielectric Constant (E) Coupling Coefficient (%) 15.2 11.2 24 28.4

4.5

10

1050

1500

11

38

45

68

10.9 APPLICATIONS OF ULTRASONIC TESTING:
Ultrasonic methods are suitable for the detection, identification and size assessment of a wide variety of both surface and sub-surface defects in metallic materials. The method particularly attractive for the routine inspection of aircraft and road and rail vehicles in the search for incipient fatigue cracks. The equipment is extremely portable relatively inexpensive and extremely versatile, and this has helped ultrasonic testing to become an indispensable tool for those concerned with all aspects of quality control and quality assurance.

The use of an angle probe for the checking of circumferential welds in a large diameter pipeline.

The accurate thickness measurements can be made using an ultrasonic pulseecho technique.

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CHAPTER # 11: RADIOGRAPHY
11.1 INTRODUCTION:
Very short-wave length electromagnetic radiation, namely X-rays or -rays, will penetrate through solid media but will be partially absorbed by the medium. The amount of absorption that will occur will depend upon the density and thickness of the material the radiation is passing through, and also the characteristics of the radiation. The radiation that passes through, and also the characteristics of the radiation. The radiation that passes through the material can be detected and recorded on either film or sensitized paper, viewed on a fluorescent screen, or detected and monitored by electronic sensing equipment. Strictly speaking, the term radiography implies a process in which an image is produced on film. When a permanent image is produced on radiation-sensitive paper, the process is known as paper radiography. The system in which a latent image is created on an electrostatically charged plate and this latent image used to produce a permanent image on paper is known as xeroradiography. The process in which a transient image is produced on a fluorescent screen is termed fluoroscopy, and when the intensity of the radiation passing through a material is mentioned by electronic equipment the process is termed radiation gauging. It is possible to utilize a beam of neutrons rather than X-rays or inspection purposes, this being termed neutron radiography. -rays for

After an exposed radiographic film has been developed, an image of varying density will be observed with those portions of the film that have received the largest amounts of radiation being the darkest. As mentioned earlier, the amount of radiation absorbed by the material will be a function of its density and thickness. The amount of absorption will also be affected by the presence of certain defects such as voids or porosity within the material. Thus radiography can be used for the inspection of materials and components to detect certain types of defect. The use of radiography and related processes must be strictly controlled because exposure of humans to radiation could lead to body tissue damage.

11.2 PRINCIPLES OF RADIOGRAPHY:
The basic principle of radiographic inspection is that the object to e examined is placed in the path of a beam of radiation from an X-ray or -ray source. A recording medium, usually film, is placed close to the object being examined but on the opposite side from the beam source (as shown in fig) X or gamma radiation cannot be focused as visible light can be focused and, in many

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instances the radiation will come from the source as a conical beam. The object will absorb some of the radiation but some will travel through the object and impinge on the film, producing a latent image. If the object contains a flaw that has different absorptive power from that of the object material, the amount of radiation emerging from the object directly beneath the flaw will differ from that emerging from adjacent flaw-free regions. When the film has been developed there will be an area of different image density that corresponds to the flaw in the material. Thus the flaw will be seen as a shadow within the developed radiograph. This shadow may be of lesser or greater density than the surrounding image, depending on the nature of the defect and its relative absorptive characteristics. The developed radiograph is a two-dimensional representation of a threedimensional object and the image may be distorted both in size and shape compared with the test piece. The position of a flaw within a test piece cannot be determined exactly with a single radiograph but by taking several radiographs with the beam directed at the object from a different angle for each exposure, it should be possible to determine the exact position of the flaw in relation to the thickness of the object.

11.3 PRODUCTION OF X-RAYS:
The X-rays are generated in a highly evacuated glass envelope having anode and cathode both made from tungsten metal. The design of the cathode should be such that the e- emitted from the cathode are converged on a single point of anode which when hit the anode are reflected to the out ward direction. The X-rays are produced as a result of emission and hitting on to anode. About 99% of the energy of e- is converted into heat and only 1% X-rays are produced. These X-rays possess high penetrating power for the materials, because they are of short wave length, longer wavelength X-rays are also emitted which spoils the contrast of the film. Therefore longer X-rays have to be filtered through a thin sheet of Cu filter. The design of the cathode should be cup-shape so that the e- hit a single point at anode and the emitted X-rays make a spectrum on to the specimen and the film behind. In order to avoid perforation at a single point of anode, it is desirable to rotate the anode at slow speed so that the excess amount of heat is dissipated and anode life prolonged. In X-ray tube the electrons are accelerated while a difference of potential between a source of electrons called the cathode and the target. The difference of potential is referred to as a tube voltage (CRT). Since electrons in motion

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comprised sand electric current the number of moving electrons determine the magnitude of the electric current. The flow of electrons in the X-ray tube is called the “tube current”.

11.4 EXPOSURE FACTORS:
There are very many factors that govern the formation of a satisfactory image on radiographic film. When it is desired to radiograph some object or component, the composition, density and dimensions of the object will largely determine the quality of the radiation that will be used. The source must produce radiation which will be sufficiently penetrating for the type and thickness of material to be inspected, and so X-ray tube voltage or type of -radiation source will be selected accordingly. The selection of a particular grade of radiographic film will be made on the basis of its sensitivity to the variations of radiation intensity that are expected after transmission through the object. However, the amount of radiation expected to reach the film will be affected by several other factors, including the intensity of the incident radiation (governed by the X-ray tube current or the strength of a -source in curies), the source to film distance and the exposure time. The correct exposure for a particular application may be determined by a process of trial and error or by using an aid such as an exposure chart that relates to a specific grade of film. It will be noticed that one axis of the chart is marked in milliamp-seconds. The intensity of radiation emitted from an X-ray tube at any particular tube voltage is proportional to the

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tube current and so, if a radiograph were made with an exposure time of 8 seconds at a tube current of 20 mA, an equivalent radiograph could be obtained, assuming tube voltage to be constant, with a 16 second exposure at 10 mA or a 10 second exposure at 16 mA.

11.5 GAMMA – RAY RADIOGRAPHY:
Gamma radiations, a product of radioactive decay, are extensively used in the testing of castings and welded objects. Radium and its salts decompose at a constant rate, giving out gamma rays that are of much shouter wavelength and more penetrating (than ordinary X-rays). Radium and radon were originally employed as gamma-ray sources but more convenient sources are available at present in the form of isotopes, for example cobalt 60. It is an isotope produced by neutron irradiation and can be used in place of radium; it is much cheaper as well. The apparatus necessary for gamma-ray radiography is very simple. Most cobalt-60 sources are cylindrical, with dimensions of 3 by 3 to 6 mm and sealed in an appropriate container or capsule. Unlike X-rays, gamma-rays from its source are emitted in all directions; therefore a number of separate castings having cassette film, fastened to the back of each casting, are disposed in a circle around the source placed in a central position (see fig.).

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This way, many castings can be radiographed simultaneously and overnight exposures may be taken without continuous supervision.

11.6 COMPARE/ CONTRAST PROPERTIES OF X – RAYS AND - RAYS:
11.6.1 X-RAYS :
1. These are electromagnetic radiations. 2. The equipment is costly and bulky. 3. Electric supply is needed. 4. Source to film distance is kept large 36‟‟, 18‟‟.

5. X-rays penetration in to the material is limited say 2‟‟ thick or 3‟‟ thickness of steel but higher thickness (4‟‟–5‟‟) very expensive equipment. 6. When desired can be used. 7. Higher the KV, greater the depth of penetration. 8. No problem of storage the equipment. 9. X-rays are unidirectional.

11.6.2

- RAYS:

1. These are also electromagnetic radiations. 2. The equipment is relatively cheaper and handlable. 3. No electric supply is required. 4. Focus to film distance is kept low; 12‟‟, 6‟‟ very or close to film. 5. Sources like iridium 192 are used up to 2‟‟ thick steel, but cobalt 60 can be used up to 6‟‟ steel thickness. 6. The source of -ray decays and eventually discarded decay depends on its half-life. 7. Higher the source strength, greater the penetration. 8. The equipment has to be stored in special underground pits. 9. -Rays can be used circumferentially.

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11.7 RADIOGRAPHIC FILMS:
11.7.1 CONSTRUCTION :
X-ray films are basically similar to the films used in ordinary photography. Both consist essentially of a radiation-sensitive layer known as the emulsion, coated on a flexible transparent support, called the base. However, unlike most other photographic films, X-ray films have an emulsion coating on each side of the base. This increases the speed of the film and improves the contrast of the final image. In addition to the emulsion coatings, X-ray films have two other coatings on each side of the base. These are subbing layers that ensure that the emulsion adheres to the base, and super coats to protect the emulsion from pressure damage during normal handling. The manufacture of X-ray film is a complicated process, most of which has to be carried out under safelight conditions or in total darkness. High standard of cleanliness and precise control of materials and techniques are essential to ensure a reliable and consistent product. Super coat Emulsion Subbing Layer Base Subbing Layer Emulsion Super coat
FIGURE: CONSTRUCTION OF RADIOGRAPHIC FILM.

11.7.2 PROCESSING :
One of the most important aspects of the entire radiographic procedure is the processing of x-ray and gamma ray films. It must always be remembered that even the best possible techniques and exposure of x-ray and gamma ray films result in radiographs which are only as good as the processing they have received. Therefore, the fundamentals must be carefully learned and rigorously

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followed or the resulting radiographs will be inconsistent in quality, varying form poor to mediocre. The purpose of processing x-ray and gamma ray films is primarily to convert the invisible latent image (produced in the film emulsions by exposure to x-ray, gamma ray, or light) to a visible permanent image. Processing as well as the handling of x-ray and gamma ray film is carried out in a processing room (dark room) under subdued lighting (safelight) of a color to which the film is relatively insensitive.

11.7.3 STEPS
1. Development:

ARE I NVOLVED IN

FILM PROCESSING :

Developers are usually available preformulated and ready for use by simply dissolving in water (if in powder form) or by dilution with water according to the mixing instructions that accompany them. When exposed film is immersed in properly prepared developer, the solution penetrates the emulsion and begins to affect the exposed silver bromide crystals and transforms them to metallic silver. The longer the development, the more silver is formed and density of the image is increased. 2. Arresting Development: After the developing process, the film is dripping wet with developer and the developing action must be stopped or at least greatly reduced before the film enters the fixer solution. There are two methods of dealing with this problem in manual processing. They are the use of a water rinse to reduce the developing action or the use of an acid stop bath to stop it. 3. Fixing: The purpose of fixing the film is to remove all the undeveloped silver salts of the emulsion leaving the black silver in the gelatin of the emulsion as a permanent image. Another important function of the fixer is to harden the gelatin to allow warm air during and subsequent storage without damage to the emulsion. When the film immersed in the fixing solution the milky appearance (which were produced during developing) disappears after some time. 4. Washing: The purpose of washing the films after the fixing process is to remove all of the fixer from the emulsion. Residual thiosulfate, an ingredient of fixer chemicals, caused finished radiographs to turn brown after a period of years if not removed during processing. The washing of films is an important step in the processing cycle. Films should be washed from 10 to 30 minutes in running water at

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temperatures ranging from 600F to 700F depending on the type of fixer used, the type of film and the water flow rate in the wash tank. 5. Prevention of Water Spots:

Immersing When films are removed after washing, small water spots cling to the surface of the film and if the films are fried rapidly, the water spot areas are still wet while the rest of the emulsion is dry. Uneven drying such as this causes distortion of the gelatin, changing the density of the silver image. This results in spots that are not only visible but also troublesome in the finished radiographs. the washed films for 1 to 2 minutes in a wetting agent and allowing them to drain for 1 or 2 minutes before placing them in the dryer can largely prevent such “water spots”. 6. Drying the Film: To prepare the finished radiographs for reading and storage, they obviously must be dried. If the number of radiographs to be dried is small and time is not a factor, they can be “air dried”. Hangers can be placed on convenient racks over a drain and the films dried slowly in the atmosphere, frequently overnight. In this method, care must be exercised that the films are not touching each other or they will stick together and damage the emulsion. Dust and dirt in the air will cling to the surface of the films, so clean drying conditions must be selected.

11.8 FUNDAMENTALS OF RADIOGRAPHY:
The -ray sources emit -rays (+ , + particles in small quantity) all the time from zero time to the level of their complete depletion. They decay and posses half-life. The half-life is the time of decay of dps equal to half of its original dps. There are various sources used in industrial radiography and these posses ½ life as follows: Sources Iridium Ir192 Cobalt Co60 Cesium Cs137 Uranium Ur234 Half Life 74 days 5.3 years 33 years 1600 years

11.8.1 CURIE:

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Source strength is reported in curie. Curie is the unit of radioactivity which is equal to 3.7 1010 dps. milli curie micro curie milli micro curie 3.7 107 3.7 104 37

A reasonable and economical source strength for Ir192 is = 30 curie.

11.8.2 RADIOACTIVE DECAY:
The amount of a radioactive decay remaining after a period of time t can be calculated if the amount initially present is known, using the expression. N = N0 exp (- t) = N0 exp (-0.693 t / T) where N = no. of atoms of material remaining. N0 = no. of atoms of material initially present. = Decay constant = 0.693 / T t = time elapsed T = half – life of material Co60 has a half-life of 5.3 years. The activity of a 10-c source of Co60 at the end of 2 years is N = N0 exp (-0.693 / 5.3) (2) = N0 exp (-0.26) = 0.771 N0.

11.8.3 ROENTGEN :
The roentgen is defined as “that quantity of X or radiation such that the associated corpuscular emission per 0.001293 g of dry air (equal 1 cm3 at 00C and 760 mm Hg) produces, in air, ions carrying 1 esu of quantity of electricity of either sign”.

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11.8.4 PENETRAMETERS (IMAGE QUALITY INDICATORS ):
The detection of any flaws as a result of radiographic examination by X-rays depend of the quality of the radiograph obtained, this quality being dependent on the radiographic technique used. An image quality indicator, often called penetrameter, is used to assure that the proper radiographic technique has been used. The penetrameter is used only to show that the technique was satisfactory and is not intended for use in judging the size of discontinuities nor for the establishment of acceptance limits of material. Several types of penetrameter have been proposed and used including wire, step, and flat type. In any case, the penetrameter must be made of material radiographically similar to the object being radiographed. There should always be at least one penetrameter used for each film exposed. Wire-types penetrameters are widely used in Europe. A typical wire-types penetrameters are the standard of Deutsche Industrial – Norm (DIN), which consists of a series of seven parallel wires of diameters varying in arithmetic or geometrical progression, as shown in figure. The wires are mounted in low X-ray absorbent flexible rubber envelope.

Fig: Image Quality Indicator (IQI).

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11.9 THE RADIATION HAZARDS:
X-ray and -radiation can cause damage to body tissue and blood, but any damage caused is not immediately apparent. The effects of any small doses of radiation received over a period of time are cumulative, and so all workers who may be exposed to even small quantities of radiation should have a periodic blood count and medical examination. Strict regulations cover the use of X-rays and -rays, and the quantity of radiation that workers may be exposed to. The unit of quantity of X-ray or radiation is the roentgen that is based on the amount of ionization caused in a gas by the radiation. The roentgen expresses a radiation quantity in terms of air rather than in terms of radiation. The roentgen expresses a radiation quantity in terms of air rather than in terms of radiation absorbed by the human body. The unit that has been adopted for radiation absorbed by the body is the sievert (Suva) that is defined as energy absorption of 1 joule per kilogram. Formerly the unit used was the rad (radiation absorbed dose) – 1 Sv = 100 rads. Medical authorities consider that there is a maximum permissible radiation dose which can be tolerated by the human body, and this dose is started as being that amount of radiation which, in the light of current knowledge, will not cause appreciable harm to the body over a number of years. The currently accepted dose for classified workers, namely those who are engaged in radiography, is 1 mSv (0.1 rad) for a normal five-day working week. The maximum dosage rate for a year is 50 mSv (5 rads) and the total cumulative dose received by a classified worker should not exceed (180+50 N) Sv, where N is the number of years by which the worker‟s age exceeds 18. No person aged less than eighteen should be engaged in radiography. It is also considered that persons, other than classified workers, who might work in the general vicinity of radiography activity should not receive more than 15 mSv (1.5 rads) per year and this means that adequate shielding and protection should be provided around X-ray and -ray installations.

11.10 PROTECTION AGAINST RADIATION:
The intensity of radiation falls off as the square of the distance from the source, and so distance from the source can be an effective and relatively cheap form of protection. However, a fixed X-ray unit is usually housed in a laboratory and the walls of the laboratory are constructed in such a manner as to afford the necessary shielding. The United Kingdom regulations state that radiation on the outer side of the shielding should not exceed 7.5 Sv (0.75 millirads) per hour or, if only classified radiography workers have access to the area, should not

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exceed 25 Sv (2.5 millirads) per hour. The walls of an X-ray unit, therefore, are usually lined with a thickness of lead or made to have a high absorption factor using barium concrete. Any glazing will be of thick lead-silicate glass. The X-ray unit controls should be placed outside the shielded room. There are many cases where the material to be radiographed is too large to be taken into an X-ray laboratory and radiography must be carried out on site, for example, in a workshop or aircraft hanger. In these cases it is distance that will give the necessary protection and a sufficiently large area must be raped of and warning signs posted to keep all personnel outside the danger area. It may be possible for the control panel to be placed sufficiently far away from the X-ray or -ray source as to be outside the roped-off area. If this is not possible and the control unit has to be close to the source, then the operator must be protected by means of portable lead screening while exposures are made. The criterion is always that a classified worker must not be exposed to radiation at a level in excess of 25 Sv (2.5 millirads) per hour and that the maximum radiation level for any other person must not exceed 7.5 Sv (0.75 millirads) per hour.

11.11 MEASUREMENT OF RADIATION RECEIVED BY PERSONNEL:
The extent of radiation that may be received by classified workers in the field of radiography must be monitored and this is best achieved by recording the dosage received on a radiation monitoring film (film badge) or by using a pocket ionization chamber. The film badge type of radiation dosemeter is based on the principle that the density recorded on the film, is directly related to the amount of radiation to which the film has been exposed. This type of dosemeter consists of a small piece of film packed in a light-tight paper envelope and held within a small plastic container that is pinned or clipped to the operator‟s outer clothing. The film badge is carried by the operator for some pre-determined time and is then processed under standardized conditions. The density of the processed film is compared with pieces of film of the same type and batch that have been exposed to known levels of radiation and processed under the same conditions. Pocket-type ionization dosemeters are usually of similar size to a pen and are carried in the operator‟s pocket. They posses a scale and pointer that will indicate the dose received in milli-roentgens. It is a statutory requirement in the United Kingdom that full records be kept of the radiation doses received by classified radiographic workers.

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CHAPTER # 12: CHEMICAL ANALYSIS
12.1 ANALYSIS OF FERROUS MATERIALS (IRON / STEEL):
1. Low carbon steel 2. Carbon and alloy steel of medium carbon contents 3. Carbon and alloy steel of high carbon contents 4. Case hardening steel 5. Cast irons 6. Tool materials 7. Wrought stainless steels 8. Wrought heat resisting alloys 9. Nickel – base and cobalt – base heat resisting casting alloys 10.Magnetic materials 11.Electrical contacts materials

12.2 ANALYSIS OF NON-FERROUS MATERIALS:
1. Copper and copper alloys (Brass and Bronze) 2. Aluminum and its alloys 3. Tin and its alloys (with metal bearings) 4. Magnesium and its alloys (magnesium anode) 5. Zinc anode 6. Lead and its alloys (solders) 7. Nickel alloys 8. Titanium and its alloys

12.3 WATER AND ALLIED MATERIALS:
1. Distilled water

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2. Chemicals 3. Soaps and detergents 4. Pigments 5. Additives and grease bases 6. Boiler compound and scale 7. Rust removing compound 8. Refractory materials 9. Electrolytes

12.4 ANALYTICAL TECHNIQUES USED:
12.4.1 VOLUMETRIC :
Chemical analysis in which the quantity of each element determined by reacting the sample solution with a known volume of suitable solutions of known (i.e. standardized) concentration.

12.4.2 GRAVIMETRIC:
Gravimetric is a method of chemical analysis in which the quantity of each element determined by the comparison of gravity of the sample solution with a known volume of suitable solutions of known (i.e. standardized) concentration.

12.4.3 COLORIMETRIC :
Colorimetric is a method of chemical analysis in which the quantity of each element determined by the color comparison of metal solution and standard solution.

12.4.4 ELECTROLYSIS:
Electrolysis is a method of chemical analysis in which the quantity of each element determined. Chemical changes induced in an electrolyte by the passage

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of a current. In a solution of a metal it results in deposition of the metal on the cathode. Quantity of each element determined by taking the differences of the weight of cathode before and after deposition of the metal.

12.4.5 SPECTROPHOTOMETRY :
The Spectrophotometry has been is the method for the analysis of elements present in metals and alloys. The Spectrophotometry employs the principles of optical emission spectroscopy (OES). Spectroscope, XRF, Metalloscope etc are used in Spectrophotometry.

\

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CHAPTER # 13: SPECTROSCOPE
13.1 INTRODUCTION:
The Spectroscope has been specifically designed for the analysis of elements present in metals and alloys. It is a compact, easy-to-operate, accurate and repeatable, high-speed laboratory elemental analysis spectrometer. The Spectroscope is an analytical tool which detects and quantifies the presence of elements that exist in the metals / alloys. Although state-of-the-art technology has allowed this optical emission spectrometer to be made faster, more accurate and easier to operate, the basic theory of its operation has not changed in over half a century. The Spectroscope employs the principles of optical emission spectroscopy (OES).

13.2 OPTICAL EMISSION SPECTROSCOPY, THEORY OF OPERATION:
Optical emission spectroscopy (OES) is a technique for detecting and quantifying the presence of elements in a material. OES utilizes the fact that each element has unique atomic structure. When subjected to the addition of energy, each element emits light of specific wavelengths, or colors. Since no two elements have the same pattern of spectral lines, the elements can be differentiated. The intensity of the emitted light is proportional to the quantity of the element present in the sample allowing the concentration of that element to be determined. Figure provides a simplified view of the events that take place in the OES process. Figure shows a sketch of an atom in its ground state. Under normal conditions, prior to excitation, the electrons in the atomic structure of each element revolve in their lower energy or “ground state”. To keep things simple, only one electron is shown in figure, which would be the case for a sodium atom. During excitation, the energy of the source is imparted to the oil or fuel sample, causing it to vaporize. Atomic electrons absorb energy and are temporarily forced away from the nucleus of the atom into a higher, unstable orbit, as illustrated by figure. After reaching this unstable state, the electrons release this absorbed energy as they return to the ground or stable state. The energy released has a specific value corresponding to the particular electron transition that has occurred in the excited atom. The energy is given off in the form of light, as illustrated in figure. The light has a specific frequency or wavelength (frequency is inversely proportional to wavelength) determined by the energy of the electronic transition. Since many transitions of different energy are possible for complicated atoms that have many electrons, light of many different wavelengths is emitted. These spectral lines of light are unique to the atomic structure of only one element. The intensity of the spectral lines is proportional to the concentration of the element present in the sample. If more than one element is present in the sample, spectral lines of distinctively different

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wavelengths will appear for each element. These lines must be separated in order to identify and quantify the elements present in the sample. Usually only one spectral line among many possible choices is chosen to determine the concentration of a certain element. This line will be chosen for its intensity and freedom from interference from spectral lines of other elements. To accomplish this an optical system is required.

All optical emission spectrometers consist of three main components to become a system. These components are 1) an excitation source, 2) an optical system, and 3) a readout system. 1. The excitation source introduces energy to the sample. 2. The optical system separates and resolves the resulting emission from that excitation into its component wavelengths. 3. The readout system detects and measures the light that has been separated into its component wavelengths by the optical system and presents this information to the operator in a usable fashion.

Figure: The Excitation Process in an Atom.

13.3 PHOTOMULTIPLIER TUBE:
Figure shows a typical PM tube with a window where the light enters. Figure is a cross section illustration of the tube.

As photons of light enter through the window of the PMT, they strike the first target, or dynode. The dynode surface is specially coated so that each photon striking it knocks off several electrons that are then directed to the second dynode. The second dynode attracts the electrons because it is at a higher

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electric potential (voltage) than the first dynode. For every electron hitting the second dynode several new electrons are released. These electrons are attracted to the third dynode and so on for several more dynodes, each one being at a higher voltage with regard to the previous dynode. The end result is that the photons that entered the tube are converted into a proportional electrical current, greatly amplified, and stored by a capacitor for subsequent measurement.

FIGURE: PHOTOMULTIPLIER TUBE (PMT)

13.4 ELECTRONIC PROCESSING:
At the end of the excitation or “burn” cycle, each PMT integration circuit capacitor has been charged in proporti0n to the amount of light received to the PMT during the burn cycle. The remainder of the analysis is performed by the electronic processing section of the system. First, digit values are determined for the charge on the capacitor. (In actual fact, the charge on the capacitors is checked and converted 100 times per second. Each value is then converted by the electronics, which refers to a calibration curve kept in memory, to concentration readout of the amount of the element present in the sample. Concentration is usually expressed in parts per million (ppm) although the Spectroscope may be programmed to read out in percent. This information is displayed on a video screen, or can be printed out on a printer. Once the

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analysis is completed and the results recorded, the system is ready for the next analysis. The analysis results remain in memory and may be recalled until the start button is depressed for the next analysis.

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CHAPTER # 14: METALLOSCOPE
It has been developed for use in every day spectroscopic analysis work.

14.1 THE METALLOSCOPE ANALYTICAL METHOD:
14.1.1 QUALITATIVE ANALYTICAL METHOD :
After fixing the sample in place, when the source unit is brought into operation, an A.C. arc light is produced between the sample and the graphite electrode. This is observed through the eyepiece. The eyepiece on this instrument is fixed in such a position that the spectrum lines come to about the center of the field of vision. We shall now take as an example the analysis of Mn in iron and steel. Firstly the eyepiece is fixed at the Mn position. The field of vision is then compared with the type of card. On this card half the length of the lines is shown but these are Mn lines. Actually, these Mn lines do not appear half-length, but to make the lines easily noticeable half-lengths have been shown. When this looked for Mn line appears the presence of Mn is confirmed and, further, by the degree of intensity of the line the amount present may be measured. Nine spectrum cards of this type for iron and steel use and four for light alloys are supplied as accessories. These cards have been prepared form results of observations of the emission spectra of standard samples and cover the complete range of analyzed elements. Once the user has become accustomed to spectrum analysis it will be no longer necessary to use these cards, but they are very useful for training the beginner.

14.1.2 QUANTITATIVE ANALYSIS :
One of the important features of the METALLOSCOPE is the ease with which quantitative analysis may be done. As an example of this we take the analysis of Mo in iron and steel. When a quantitative analysis is required, a card is used. The card shows the seven wavelengths lines for iron (steel) and also the amount of Mo contained. For example it shows that, when the intensity of Mo line (5,533.0A0) as appeared in the field of vision is equal to the intensity of the iron line (5569A0), the amount of Mo contained is proved to be 0.5%. These seven spectrum lines are determined by carefully observing he spectra obtained from the emission of a standard sample containing a known quantity of Mo and then

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choosing out other lines of intensity comparable with that of the Mo. A sample containing an unknown quantity of Mo is now caused to emit and the resultant spectra observed. The Mo line is brought to the center of the field of vision and observed and their intensity compared with that of the seven lines for iron.

14.2 APPLICATIONS:
1. Inspection of Materials on Delivery: This instrument is most suitable for the spectroscopic examination, either in quantity or extract, of large quantities of material on delivery. When quantity (bulk) examinations are carried out the percentage of rejected material is clearly shown and it is thus possible to clearly distinguish between the supplier with the high percentage of satisfactory material and that with a high percentage of rejected material. Should the supplier protest, a spectrum photograph can be prepared as proof of the test result. Quality Control of Molten Metal: Prior to pouring, remove a small sample from the crucible and, after cooling, carry out a spectroscopic analysis with the METALLOSCOPE. If the composition is other than that prescribed, the necessary ingredients may be added and a further analytical test made. Even when quantitative analyses are carried out, only about a minute is required. 3. IN the Sorting |of Scrap: Because of its speed and ease of operation, the efficiency of the METALLOSCOPE is fully displayed in the sorting of scarp. Since there is a source unit built into the instrument, if a long electric power cord and earth are used it may be set up anywhere out of doors ready for instant use. So that the pilot lamp may be readily seen outside as well as inside buildings, a 6 V lamp is used in order to ensure this degree of brightness. It is not necessary to take the trouble to shape, grind, or polish each sample of scrap, but the analysis may be carried out on the scrap in its original form. The time taken for each analysis is only a matter of seconds. 4. Determination of the Composition of Alloys of all Kinds: In qualitative analysis of all types of alloys the speed of the METALLOSCOPE is absolutely unrivalled. It is possible to carry out the qualitative analysis of iron, steel aluminum, copper, and other alloys in a matter of from a few seconds to one minute at the outside. Again, from the point of view of ease of operation,

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efficiency can be further increased by operating several METALLOSCOPE together. In carrying out a quantitative analysis of the elements in steel, the speed of this instrument is once more exhibited. The time taken for the analysis of each sample is about one minute. The quantitative analysis of a aluminum alloys cells for the comparison with a standard sample. This means that the analysis is more difficult than of, say, steel, but once the operator has gained some experience in the work, it is possible to analysis each sample in a few minutes.

5. Determination of the Composition of Samples of all Kinds: When analyzing samples in powder or liquid form, a depression made in a graphite bar and then filled with the sample material. This is used as the lower electrode. It will be seen that, in this way, solid samples but also powders, liquids, paper, cloth etc., can easily be subjected to composition analysis.

6. For Teaching in Schools: Because the METALLOSCOPE is easy to operate, simply constructed, is troublefree and inexpensive, anybody can use it anywhere to carry out the analysis of any material. It can therefore be said that it is highly suited to spectroscopic analysis experiments conducted in schools.

14.3 SPECIAL FEATURES:
1. Most Suited to on-the-Spot Jobs: Since the spectroscope and the source unit are incorporated in a single unit the instrument is exceedingly handy for use on work sites. 2. Simple to Operate: Simply constructed, the source unit being designed for convenient and easy operation, by pressing only the main switch and starter button it is possible to obtain a steady alternating current arc light.

3. Speedy Analysis is Possible:

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The complex and troublesome photographic process is avoided and visually, over the whole visible region of wavelength range, rapid determination of sample compositions can be carried out. 4. Quantitative Analysis is Possible: Not only qualitative, but also quantitative analysis can be carried out quickly and easily. 5. Dispersion is High: The dispersion is high because two spectroscope prisms are employed. At 4,861 A0 it is 1.6 A0 /mm. 6. Resolving Power is high: At 4,861 A0 is / 0.155 A0) = 31,401 (wavelength difference where analysis is possible,

7. Aperture is Large and Bright: F = 1: 10. 8. Changeover of Samples done Efficiently: The electrode holder mounting renders unnecessary the adjustment of the gap between the electrodes each time samples are changed over. A graphite electrode is installed in the lower side.

9. Photographing is also Possible: If the camera (supplied at extra cost) is attached, a spectrum photograph can be quite easily taken.

TABLE: METALLOSCOPE DISPERSION AND RESOLVING POWER.

Dispersion (A0/mm)

Resolving Power

Wavelength On focusing ( ) A0 surface

Through Through Resolving 10 X 20 X Power Eyepiece Eyepiece ( / )

Wavelength Difference Analyzed ( ) A0 0.035

4,000

9

0.9

0.4

113,660

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4,395 4,861 5,876 8,000

18 33 70 284

1.8 3.3 7.0 28.4

0.9 1.6 3.5 14.2

58,285 31,401 14,793 3,661

0.075 0.155 0.397 2.185

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CHAPTER # 15: X-RAY FLUORESCENCE SPECTROMETER
15.1 INTRODUCTION:
An energy dispersive X-ray fluorescence spectrometer (EDXRF), which allows the nondestructive simultaneous quantitative and qualitative analysis of specimens of any shape and any size, is an element analyzer. Its element detection range has been widened to C to U from the conventionally available range of Na to U, and it guarantees a high resolution, 149 eV.

15.2 FEATURES:
The conventionally available detectable element range from Na (sodium) has been widened to C (carbon) to U (uranium) with. Provided with a high-performance X-ray detector that needs to be supplied with liquid nitrogen only before measurement, which reduces the maintenance cost. Besides, a detector that requires no liquid nitrogen is optionally available. A large-sized specimen chamber that allows even a large irregular-shaped specimen to be measured and an automated specimen exchange mechanism that allows continuous measurement of up to 16 specimens, are provided as standard. A built-in automatic filter exchange mechanism permits the setting of the optimum measurement conditions suited for a specimen. A high-output X-ray generator allows efficient analysis of low-concentration specimens, microvolume specimens, and thin film specimens. The software operates in a windows environment, allowing editing to be performed with other types of commercially available software, thus simplifying report generation. Employment of the FP method (fundamental parameter method) allows specimens to be analyzed even without a standard specimen. The specimen chamber is constructed so as to be cleaned with extreme ease. Double or triple safety designs are employed to prevent S-ray hazards.

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15.3 PRINCIPLE:
15.3.1 GENERAL:
When X-rays (primary X-rays) are illuminated from the X-ray tube to the specimen, fluorescence X-rays having wavelengths (energies) peculiar to the constituent elements of the specimen are generated from the elements. Qualitative analysis can be made by investigating the wavelengths of the fluorescence X-rays and quantitative analysis by investigating the X-ray dose.

The energies are investigated by two methods. One is to optically separate them and the other is to use the energy separation characteristic of the X-ray detector. The former is called the wavelength dispersive method and the latter the energy dispersive method. The element analyzer employs the latter method.

As seen from the figure above, since the energy dispersive X-ray spectrometer has no moving parts and employ a simple optical system, its structure is simple and compact. And since the detector can be installed near the specimen, the Xray solid angle of collection can be made large, thus offering many features such as high sensitivity, low X-ray tube power, and the detection of basically all elements.

The Element Analyzer, as compared with the conventional EDXRF, has been improved in performance such as sensitivity for light elements, energy resolution, quantitative accuracy, and also in the ease of maintenance.

15.3.2 GENERATION

OF

PRIMARY X-RAYS:

The primary X-rays that are illuminated onto a specimen is obtained from the Xray tube. The X-ray tube, a type of a vacuum tube, consists of an anode and a cathode sealed in a vacuum.

Thermions generated from a filament, which is a cathode, are accelerated by a high voltage (high electric field) and collide with the target.

Upon collision with the target, there arises an interaction between the electrons and the target substance and the energy is converted into the following manner:

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Conversion into heat Generation of characteristic X-rays Generation of continuous X-rays

15.3.3 GENERATION

OF

FLUORESCENCE X-RAYS :

Fluorescence X-rays are characteristic X-rays generated by the interaction between X-rays and a substance. They have the same physical properties as the characteristic X-rays included among primary X-rays. They differ only in the cause of generation (excitation source).

When primary X-rays are made incident on a substance (specimen), all their energy is sometimes given to inner shell electrons of atoms that constitute the substance, as a result of one type of interaction. The electrons that are given the energy are ejected out of the atoms, which are ionized. This ionized state is unstable and only lasts until an electron in a higher orbit fills the vacancy created by the ejected electron (transition). Here energy equivalent to the energy difference between the two orbits is emitted as X-rays. They are called fluorescence X-rays.

The energy level possessed by each electron orbit varies with the type of element. Therefore, the wavelength (energy) of fluorescence X-rays varies also with the type of element, which makes it possible to carry out elemental analysis by examining wavelengths.

15.3.4 X-RAY OPTICAL SYSTEM:
15.3.4.1 Atmosphere: X-rays attenuated in intensity during their interaction with a substance. As their energy lowers, the intensity lowers, so it is best that there is nothing in the Xray path (vacuum). An evacuation system is thus needed, but as light element spectra are not influenced by a pressure about 10 Pa, a rotary pump is used for evacuation purpose.

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Liquid specimens have a high vaporization pressure and as this pressure exerts an adverse influence on the evacuation unit and detector window, measurement cannot be done during evacuation. Liquid specimens are measured in the atmosphere. Light elements, which present the problem of being absorbed by the atmosphere, are analyzed in a He atmosphere (options), which absorbs Xrays little.

15.3.4.2 X-Ray Shutter: X-rays, which are harmful to the human body, must be prevented from leaking in any case. When opening the cover for specimen exchange, the X-ray shutter is closed in synchronism with the operation of the cover open/close lever. If the shutter cannot be closed, the power for the X-ray tube is switched off. 15.3.4.3 Filters:

Among the scattering X-rays, which were mentioned in the previous paragraph, characteristic X-rays of primary X-rays may clearly show up as peaks, depending on the specimen. Normally, such peaks are ignored at the time of data processing, but considerable hinder the analysis of elements having peaks in their vicinity. Especially when they are contained in very small quantities, they are hard to separate. In a case like this, small peaks of the specimen can be made visible by elimination the above-mentioned characteristic X-rays from the primary X-rays used for excitation. For this purpose, the XRF is equipped with a mechanism for automatic exchange of three types of filters, as standard. 15.3.4.4 Primary Collimator:

This is an aperture for limiting the specimen surface region that is irradiated with X-rays. The XRF is provided four types of collimators ranging from 1 mm to 7mm in a aperture size. 15.3.4.5 Specimen Tray:

Primary X-rays are applied to the specimen from its underside. This system, alloying specimens of various shapes to be set easily, is advantageous for measuring liquid specimens (because the generation of a gaseous body can be prevented easily).

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There is provided a 24-mm-diam. hole on the underside of the specimen tray. 15.3.4.6 Secondary Collimator: This is provided for eliminating X-rays scattering from objects other than the specimen. It is usable also for adjusting the X-ray intensity.

15.3.5 DETECTION

OF

X-RAYS :

15.3.5.1 Principle of X-Ray Detection: The fluorescence X-rays incident on detector, as in the generation principle of Xrays, utilizes the phenomenon that incident X-rays emit all their energy due to interaction with Si (a constituent element of the detector) and thereby eject orbital electrons (photoelectron effect). The photoelectrons thus caused run in the Si crystal and generated Auger electrons and Si fluorescence X-rays, and lose their kinetic energy while ionizing the Si atoms. The Si fluorescence X-rays are reabsorbed by the detector or lost by ejecting out of the crystal. Within the crystal, Si fluorescence rays and Auger electrons ionize Si atoms and lose the given kinetic energy. Since the energy needed for ionization is constant for individual crystal, the energy of the X-rays is found by measuring the charge quantity of ion pairs thus caused. When the X-rays caused by interaction are not absorbed in the detector, but ejected outside, the number of ion pairs is reduced by the amount of the energy not absorbed. The peaks thus caused are called escape peaks. The number of ion pairs produced here has a statistical fluctuation. Furthermore, spectra obtained from detection of X-rays of a single wavelength have a spread. The degree of this spread is called the energy resolution. With the energy dispersive fluorescence X-ray spectrometer, this value directly becomes the (energy) resolution of the instrument. 15.3.5.2 Semiconductor Detector: The Si semiconductor detector, consisting of a p-i-n type diode fitted with electrodes, is sealed in a vacuum with the P portion as an X-ray incidence plane. X-rays are made incident from an X-ray incidence window, but as X-rays are not a little absorbed, the sensitivity especially for light elements is largely influenced by the window material. So far, Be film has been used as a window material, but its detection limit was up to Na at most. With the Jsx-3201, detection can be started at C by the use of a newly developed atmospheric-pressure ultra thin window (UTW).

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By the way, the amount of electric charge to be measured is very small. Therefore, any factor that causes noi8se must be reduced as much as possible. Since temperature is a typical factor in this sense, cooling is essentially required. For this reason, liquid nitrogen is used for semiconductors. Sealing them in vacuum is effective in insulating both heat and high bias voltage (several hundreds of voltages). 15.3.5.3 Conversion into Electric Signals: The electric charge caused by X-rays is converted into a voltage signal by means of a preamplifier. The preamplifier is located as close to the detector as possible, to avoid the influence of stray capacitance and external noise as much as possible. Field-effect transistors, which used for the initial stage of the preamplifier, are cooled in vacuum during use together with the semiconductor, to ultimately reduce noise. A charge-voltage conversion circuit, which is an integrating circuit, is used partly because the rise time of a signal in the detector varies with the depth in the detector where the signal charge takes place, and partly in order to avoid the influence of stray capacitance.

FIG: BLOCK DIAGRAM OF THE DETECTOR AND PREAMPLIFIER

15.3.6 X-Ray Counting System: This system is used to separate and accumulate the intensity information of signals from the detector for each unit energy of X-rays (10 eV), and send the information into a computer. As shown by the figure below, the system is composed of a pulse processor, an AD converter, and a data memory.

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15.3.7 Analysis:

15.3.7.1 Qualitative Analysis: From the principle of fluorescence X-ray generation, it is known in advance what element peaks appear and where in a spectrum and how high their intensities are. The results are included in a database. In either automated or manual qualitative analysis, the desired peaks can be found from among the spectrum data obtained, and compared with the database.

15.3.7.2 Quantitative Analysis: 15.3.7.2.1 FP Method Quantitative Analysis: The FP method (Fundamental Parameter Method) is a method of theoretically calculating the fluorescence X-ray intensity on the basis of the instrument‟s various parameters and physical fundamental parameters. The FP method means the method of calculating the fluorescence X-ray intensity. Following are the some quantitative analysis methods that use the FP method. 1. Reference method 2. Quantitative analysis as stochiometry oxides or compounds 3. Quantitative analysis with remaining components 4. Designating fixed elements 5. Dilution method

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15.3.7.2.2 Calibration Curve Method:

The calibration curve method is to obtain the relationship between the fluorescence X-ray intensity and the element concentration by measuring a known specimen, and thereby obtain the element concentration of an unknown specimen from its intensity. This method has been conventionally in wide use, as a high-accuracy fluorescence X-ray analysis method. Below are the names of various calibration curves method. 1. Linear calibration curve 2. Quadratic equation calibration curve 3. Matrix-corrected calibration curve

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CHAPTER # 16: PAINT SECTION
16.1 INTRODUCTION:
The major ingredients of paint are pigments (including extenders), binder (which may be organic or inorganic), and solvent or thinner. A dispersion of the pigment in the binder constitutes the paint film, the properties of which are determined to a large extent by the nature of the binder. The solvent or thinner is used to render the pigment / binder mixture sufficiently fluid for application as a thin film, after which it is lost by evaporation. Small quantities of other materials are incorporated, depending on the type of paint and the purpose for which it is intended. Conventional air-drying paints contain “driers” which are organic salts of the metals lead, cobalt, zirconium and manganese. Generally two, or sometimes three of these are used to obtain the optimum drying and hardening of a paint film. Organic salts of calcium and zinc are used for special purposes. In addition, anti-skinning agents, anti-settling agents, thixotropic agents, or fungicides may be incorporated.

16.2 HISTORICAL:
Paints have been used for decorative purposes for many centuries.

In classical Greece extensive use was made of paint in sculpture (for the hair, lips and eyes of status), architecture, and in painting ships. It was also used in interior decoration and by artists. The evolution and use of paints in Europe was mainly by artists, although a limited amount was consumed in ship painting. The Industrial Revolution, however, created a demand for paint to protect machinery and this was the start of the modern paint industry. The paints were based mainly on drying oils, and this type remained in common use to about the end of the first quarter of the present century when oleoresinous varnishes and, later, alkyd resins gradually replaced the oils. Nevertheless, British Standard specifications for oil-type paints are still current. Since World War II, rapid developments have taken place in the field of high polymers, leading to new types, of resin suitable for use in paints. These have enabled the paint technologists to satisfy the demand for high-performance coatings with rapid drying or curing times to meet modern production schedules.

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Such resins include epoxies, polyurethane, alkyd/amino, vinyl, acrylics, silicones, and chlorinated rubber.

16.3 PIGMENTS:
These are finely divided solids, the average particle size of which can vary from 0.2 to 20 m (micrometers). They may be inorganic or organic in constitution. The general classification of pigments can be illustrated by the following scheme: -Pigments

Inorganic

Organic (Manufactured)

Natural

Manufactured

True Pigments

Extenders

True pigments

Extenders have been included with the inorganic pigments since they are all inorganic solids. They differ from „true‟ pigments in their behavior when dispersed in organic media. True pigments exhibit opacity or hiding power in varying degree, whereas extenders are practically transparent. Extenders are sued in certain types of paints (notable undercoats, primers and some low-gloss finishes) to modify or control physical properties. They make no contribution to color (unless they are very impure) or to opacity. True pigments are used to provide color and opacity or hiding power. In finishes they contribute to durability. A pigments film is more weather-resistant than an un-pigmented film of the same binder. In primers for metals, specific pigments are used to check or inhibit corrosion of the metal. The majority of natural pigments are oxides or hydroxides of iron but may contain appreciable quantities of clay or siliceous matter. The colors are less bright than the corresponding manufactured oxides and hydroxides.

The manufactured inorganic pigments contain the whites and a wide range of colors, including yellows, reds, oranges, greens and blues. Carbon black,

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consisting essentially of elementary carbon, is usually included in the inorganic pigments. The organic pigments cover the entire spectrum range, but the brilliance and opacity vary considerably. There are no white organic pigments and organic blacks find only limited use; carbon black satisfies most paint requirements. In general, organic pigments are brighter than the inorganic counterparts but show much greater variation in opacity and in light-fastness, the latter particularly when mixed with white. Organic pigments derived form plant and animal sources are no longer employed in paint manufacture. Although some possess bright self-colors, they lack permanence.

16.4 BINDERS (OR FILM-FORMER):
This is the continuous phase in a paint film, and is largely responsible for the protective and general mechanical properties of the film. Film properties depend also on the nature of the pigment, the degree to which the pigment is dispersed in the binder, and the volume of film occupied by the pigment (the “pigment volume concentration”). The majority of binders are organic materials – oleoresinous varnishes, resins containing fatty acids from natural oils alkyds, epoxy esters, urethane oils), treated natural products (cellulose nitrate, chlorinated rubber), and completely synthetic polymers. A few inorganic binders are used, notably pre-hydrolyzed ethyl silicate, quaternary ammonium silicate and alkali silicates (sodium and lithium) that are pigmented with zinc dust to give primers for steel work. The two latter silicates are also used I fire-resisting paints for stage scenery. Organic binders can be divided into two general classes – convertible and nonconvertible.

16.4.1 CONVERTIBLE BINDERS :
These undergo a chemical reaction in the film. In the conventional oxidizing binders, oxygen is absorbed and the film slowly sets and then dries to a product that is no longer soluble in the solvents used in the liquid paints. The drying and hardening of the film, is catalyzed by “driers” and since oxygen absorption is involved, there is a limit to the thickness of film that will dry through. The two-pack materials, notable epoxies and polyurethanes, cure by chemical reaction between two components I the film. Absorption of oxygen is not involved and thicker coatings can be applied. By the use of low molecular weight

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resins and hardeners, “solventless” epoxy systems can be produced and very thick films can be applied and cured.

16.4.2 THERMOSETTING BINDERS :
These are also known as “thermo-hardening” and as “stoving” types. As in other convertible coatings, film hardening is the result of three-dimensional linking of the polymer molecules, but in this case it is brought about by the action of heat. The film is cured much more rapidly and attains the full resistance to reagents and solvents in a fraction of the time required by the air-drying types. Stoving of the films is carried out in either got-air convection ovens or in infrared ovens heated by either electricity or gas. Certain types of coating, especially those that cure by a free radical mechanism, can be cured in seconds only, by either an electron beam or ultraviolet radiation. Since no heat is involved this process is suited to wood finishes and is used for polyesters and acrylics.

16.4.3 NON-C ONVERTIBLE BINDERS :
These do not depend on chemical reaction of any sort for film formation, the process consisting solely or evaporation of solvents. The film remains soluble in the parent solvent blend and is therefore classed as “non-convertible”. Such materials are often designate “lacquers” and are usually applied by spray (especially a second coat) since the solvents present tend to dissolve the previously applied coat. This would be disturbed or “lifted” if brushing were employed. Typical examples of non-convertible binders are chlorinated rubber and cellulose nitrate. A very large number of polymers are now available, and by the choice of suitable combinations it is possible to produce industrial finishes capable of withstanding almost all types of conditions and service.

16.5 SOLVENTS (OR THINNERS):
These are usually volatile organic liquids in which the binder or film former is soluble. When the paint film is deposited on a surface the solvent should evaporate completely. It plays no part in film formation and is used solely as a means of conveying the pigment / binder mixture to the surface as a thin uniform film.

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Classes of materials used as solvents include aliphatic and aromatic hydrocarbons (with the exception of benzene), esters, ketones, esters and ether-esters of ethylene glycol, and alcohols. The fact that these materials are volatile, flammable and possess a degree of toxicity has raised a number of serious problems. Atmospheric pollution by solvents can be appreciable in areas containing a number of paint consuming industries.

16.6 SURFACE PREPARATION AND PAINT APPLICATION:
CONSTRUCTIONAL and industrial steel work is coated by a number of techniques, selection of which is dependant on whether coating application is to be performed on-site r in the factory. For site work the traditional brush or spray application is preferred, whilst in the more controllable conditions afforded by factory application, sophisticated automated spray, dip, roller and electrophoretic coating techniques are amongst those widely used. Prior to applying surface coatings, it is essential that the metal surface is in a suitable condition. For this reason it is convenient, prior to discussing application techniques, to review the methods used to prepare ferrous articles for painting.

16.6.1 SURFACE PREPARATION:
It is important when coating iron and steel work that any surface mill scale or corrosion products are removed prior to application. It is not uncommon for firmly adherent scale and rust to be painted over, and in practice, it is usually over these areas that coating failure subsequently occurs. Mill scale is a complex oxide film formed on the surface of ferrous metals during the post-fabrication cooling period. The composition of the oxide layer is determined by the oxidation conditions experienced by the metal. At temperatures below 5700C, a two-layer scale consisting of magnetite (Fe3O4) and hematite (Fe2O3) is formed on the metal with the hematite layer being outermost.

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Above 5700C, a third iron oxide known as wustite (FeO) is formed, and the position and thickness ratio of these oxide layers relative to the ferrous substrate is shown in fig.

HEMATITE (Fe2O3)

Thickness ratio:

1 MAGNETITE (Fe3O4) 5-10

WUSTITE (FeO)

100

IRON SUBSTRATE

FIG: SCHEMATIC DIAGRAM OF SCALE FORMED ON IRON AND STEEL AT HIGH TEMPERATURES.

The composition of the oxide layer is further modified by the rate at which the metal is allowed to reach ambient temperatures. Fast cooling will produce a metastable FeO layer, whilst a slower cooling rate will result in dissociation of the FeO layer to produce Fe3O4 and Fe. The oxidizing atmosphere also influences the nature of the scale such that a low partial pressure of oxygen will increase the wustite content of the scale whilst depressing hematite formation. Atmospheric exposure of iron or steel work with a layer of mill scale will ultimately lead to a delamination of the scale from the metal surface. This delamination process is attributable to differences in the thermal expansion coefficients of the scale and metal and occurs regardless of the presence of surface coatings.

16.6.2 SCALE

AND

RUST REMOVAL :

A wide variety of techniques are currently utilized for the surface preparation of iron and steel and these include mechanical and manual processes, chemical processes and flame cleaning. Selection, however, will depend on a number of operational factors, for example the size of the article, its situation and cost considerations.

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Weathering of steel work by exposure to the atmosphere in racks or stocks is a traditional method of descaling. This technique does not produce a uniform surface and, additionally, results in the formation of atmospheric corrosion products that also must be removed before any final finishing operations. Consequently the application of this technique is limited. Hand or power driven hammers, chisels, wire brushes, scrapers and grinding machines fall into the category of manual cleaning methods. They are suitable for either factory or site use, but their application to the descaling of large areas tends to be labor intensive and therefore costly. In general, manual cleaning methods do not produce a high degree of surface cleanliness and care must be exercised to avoid damage to the metal surface. Mechanical cleaning methods are now preferred for most applications. Shot or grit blasting is the most efficient method of surface preparation. The adherent scale or rust is removed by the impact of high velocity particular abrasive. The grit or shot is propelled in a jet or narrow stream against the metal by compressed air and the degree of surface finish obtained is dependent upon the type and coarseness of the abrasive used the air pressure and the “dwell-time” of the abrasive jet on any one area of the surface. Several types of abrasive compound can be used including carborundum, alumina, cast iron shot and slag. The process may be performed inside a cabinet by an operative stationed outside, or in the open if the operator is properly protected and a suitable suction device for recovery of the abrasive is available. Priming should follow blast cleaning as soon as possible and certainly within four hours; zinc-rich primers are the preferred type for structural steelwork. Chemical removal of adherent surface oxide layers is carried out by immersing the article in dilute aqueous solution of a mineral acid. The process is only satisfactorily operated in a factory or specialized finishing works and is limited by the size of the section that can be dipped. The acids used are sulphuric and hydrochloric, although phosphoric acid is used to a limited extent. Inhibitors are added to the acids to reduce attack upon the bare metal surface. Sulphuric and phosphoric acid dip vats are normally maintained at a temperature of 600 – 800C, whilst hydrochloric acid baths are used at ambient temperatures. The immersion time of the article in the bath is dependent on the temperature and the concentration of acid used. The nature of the surface oxide layer is also a contributory factor. When a mill scale formed by slow cooling is present on the surface, attack of the acid will occur preferentially at the Fe3O4 / Fe metal-scale interfacial layer causing delamination of the oxide.

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Cleaning is more difficult when the article has been fast cooled since a thick stable innermost FeO layer is present. Acid attack is not concentrated at the interfacial oxide layer and removal of the scale is by a progressive solution process involving all of the oxide layers. Longer immersion times are necessary in this situation and there is a greater hazard of acid attack on the base metal. Most baths contain cathodic inhibitors. For example ethylene thiourea, in order to minimize metal loss.

After removal of rust and scale all traces of residual acid are removed from the surface of the article by washing in water. It is preferable that drying and paint operations should follows as quickly as possible to prevent atmospheric rusting of the metal surface.

Ferrous metals can be descaled by means of a flame cleaning process employing an oxy-acetylene flame, which, by virtue of the difference between the coefficients of expansion of the oxide and the substrate metal, effectively loosens and facilitates removal of the oxide layers. The advantage of this process is that the metal surface is left in a completely dry state after cleaning. Furthermore grease and oil on the surface are removed by the flame treatment but this can deposit carbonaceous films on the metal surface. Painting operations should be performed whilst the surface is still warm, since it is possible for condensation of moisture to occur on the metal surface when it is cooled.

Flame cleaning is also useful for removing old paint but respirators should be worn by operatives if lead-containing paints are present, or are suspected of being present, on the metal. The method is less satisfactory for thin sheet or sections less than 6mm thick due to the risk or bucking, and flame cleaning should not be used in confined spaces or near inflammable materials.

16.6.3 PRETREATMENT PROCESSES :
After removal of bulk scale and rust from iron and steel it is normally necessary to remove all grease and oil from the surface and to passivate residual oxide films prior to application of coatings.

These pretreatments vary in complexity depending upon the nature of the surface contaminants and the severity if the environment to which the article is

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to be exposed during service. However, regardless of service conditions, pretreatment processes should be considered essential in that they improve adhesion of subsequently applied coatings.

In general pretreatment processes involving solvent or emulsion cleaning procedures (that is degreasing operations) precede chemical scale or rust removal processes to which the article is to be subjected but follow mechanical treatment operations. However it is not necessary to degrease the surface after shot blasting or flame cleaning as the surfaces have no residual contaminants and require painting immediately.

Solvent cleaning will effectively remove oils and greases from metal surfaces; however, it will not remove corrosion products, finger marks or inorganic flux residues. The process is only conveniently operated in the factory, with the articles either being immersed in a bath of a suitable organic solvent, for example petroleum spirit, or suspended in condensing trichlorethylene or similar solvent vapor. With very large articles, or for on-site operations, it is usually possible to wipe over the surface with petroleum spirit using a succession of clean swabs taking care to avoid merely spreading the contamination over the surface.

Treatment of ferrous articles with aqueous alkaline cleaners will remove all types of contamination with the exception of corrosion products. The treatment is normally by bath immersion although high-pressure spraying techniques are used.

A variety of cleaning agents are used including sodium hydroxide, sodium carbonate, sodium phosphate and sodium metasilicate. The normal working strength of the solution for bath immersion is 5% and it is used at a temperature of 90 – 1000C. Solutions of greater dilution can be used for the spray process since the pressure of the spray on the surface of the metal exerts a mechanical “scrubbing” action that assists removal of contamination. Greater cleaning efficiency can be achieved by electrolytic treatment of the metal in an alkaline bath. The article to be cleaned is made the cathode of a cell and the resultant hydrogen evolution at the metal surface produces an intense surface “scrubbing” action. Any electrolytically deposited contamination is removed by reversing the current flow that is making the article anodic, during the final stages of the process.

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After cleaning by alkaline process articles should be efficiently rinsed in hot water and dried ready for painting as rapidly as possible. Failure to remove alkaline residues can result in attack on subsequently applied coatings.

Oil-in-water emulsions using petroleum solvent as the dispersed phase, and either water or dilute alkaline solution as the continuous phase are used as cleaning agents. With emulsions, cleaning may be effected by spray or dipping, the articles finally being washed thoroughly with hot water and dried rapidly.

16.7 METHODS OF TEST FOR PAINTS:
The purposes of test for paints are:

1. To check the reliability of paints. 2. To check the corrosion resistance of paints. 3. To check the protection of metals by paints. 4. To check the life of paints.

16.7.1 DETERMINATION SHEAR:

OF THE

VISCOSITY

OF

PAINT

AT A

HIGH RATE

OF

The viscosity of paint and other liquids that are non-Newtonian in behavior may vary considerably with the applied rate of shear. Because of this it is desirable to have an instrument of simple principle for the measurement of viscosity at rates of shear obtaining during the application of paints. Features of the instrument are the ease of use and the control of the temperature of the sample whilst under test. This latter point is very important because paint viscosity may change by up to 6% /0C. The instrument is normally set to measure the viscosity at 200C. It is designed to measure viscosity over the range 0 to 0.5 NS/m2 (i.e. 0 to 5 poise) since this covers the useful application viscosity of most paints.

16.7.2 DETERMINATION

OF

FLASH POINT (CLOSED CUP METHOD):

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For determining the flash point of paint, varnish or related product when tested in the manner, the method is suitable for use over the temperature range 50C – 650C.

16.7.3 FLASH POINT:
The lowest temperature in 0C (at an air pressure of 101.3 KPa) at which solvent vapor from the product under test confined I a closed cup gives rise under the conditions of test to an air / vapor mixture which can be ignited by an external source of ignition.

16.7.4 PRESSURE TEST :
A test for determining under standard conditions whether a single coat film or a multicoat system of paints or related materials after a specified drying period is sufficiently dries to resist damage when two painted surfaces are placed in contact under pressure.

16.7.5 VISUAL COMPARISON

OF THE

COLOR

OF

PAINT:

For standardized color comparison, it is necessary to have an observer with normal color vision, and reproducible illumination and viewing conditions. Most paints are required to match a standard in daylight, but the spectral composition of daylight varies considerably. Although it is difficult to control precisely the spectral distribution of artificial daylight sources, individual sources are more stable over a limited period than daylight and therefore enable more reproducible color comparisons to be made.

16.7.6 DETERMINATION OF RESISTANCE CONDENSATION CONDITIONS:

TO

HUMIDITY

UNDER

This is a method for determining the resistance to humidity under condensation conditions of a single coat film or multicoat system of paint, varnish or related product.

16.7.7 BEND TEST :

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Bend test is used to find out the bending property of the paint. After preparation and coating of test panel it is inserted in bend test apparatus so that it may subsequently be bent with the paint film outside. Finally assess the film for cracking or loss of adhesion, ignoring any failure occurring less than ¼ in (6mm) from the edge of the panel.

16.7.8 SCRATCH RESISTANCE TEST:
Scratch test is used for determining the scratch resistance of single films or systems of films of paints or allied materials. After preparation and coating of test panel, clamp it and start the motor of the apparatus (which contains a needle) to scratch the film. Finally the panel is removed and examine.

16.7.9 IMPACT (FALLING WEIGHT) RESISTANCE:
This is used to determining the resistance to impact of a single coat film or a multicoat system of paints, varnishes or related materials. After sampling and coating the test shall be carried out at a temperature of 23 20C and a relative humidity of 50 5% unless otherwise specified. Coated panel is placed and tool holder is allowed to drop freely and strike the panel. Remove the panel and examine the coating visually for cracking and loss of adhesion.

MULTIPLE CHOICE QUESTIONS
1. Compression test is used for ……. materials. (a) ductile (c) brittle (b) hard (d) none of these

2. The metal specimen for tensile test is, (a) of standard dimension (b) either round or flat (c) both (a) & (b) (d) neither (a) nor (b)

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3. Hardness of material determines the resistance of (a) scratching (c) machinability

materials to,

(b) wear and indentation (d) all (a), (b) & (c)

4. The time of loading in BHN test is, (a) 1 second (b) 15 second (c) 5 minutes (d) not specified, it can be anything between 31 to 45 minutes Vicker‟s diamond pyramid method of hardness determination does not gives accurate result in case employed for, (a) polished and hardened steel surfaces (b) rough forging on heterogeneous materials like grey cast iron (c) soft materials (d) hard materials Rockwell hardness test is useful for, only soft materials only hard materials rapid routine tests on finished products none of these The ability of a material to withstand suddenly applied loads is called its, (a) hardness (c) creep strength (b) impact resistance (d) none of these

Liquid penetrant inspection is, applied to non-ferrous metals. used for detection of surface cracks. both (a) & (b)

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neither (a) nor (b)

Magnetic particle inspection is, a non-destructive method. based on distortion of magnetic field by cracks and flaws. suitable for detection of cracks caused by quenching, fatigue, blowholes in casting, defects in welding and seams in rolled and forged products. all (a), (b) & (c)

10. Which of the following is not a non-destructive method? (a) Ultrasonic testing (b) Magnetic particle inspection (c) Radiography (d) Wohler fatigue test

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REFERENCES
1. Material Science and Metallurgy, by “Dr. O.P. Khanna”

2. Metallurgy for Engineers “Rollason”

3. Introduction to Physical Metallurgy, by “Sidney H Avner”

4. Mechanical Testing of Metals and Metallic Joints, by “Christoph Wiesner”

5. Metals Hand Book, Vol. 8, Mechanical Testing, ASM, Metals Park Ohio, 1985.

6. Non-Destructive Testing by “WARREN J. McGONNAGLE

7. Non-Destructive Testing by “BARRY HULL” and “VERNON JOHN”

8. Non-Destructive Testing, by “ASNT”.

9. Non-Destructive Testing by “DR. FASIH-UL-HAQ USMANI”

10.Own observations and experimental work”.

11.BS 3889, Methods for Non-Destructive Testing of Pipes and Tubes

12.ASM Metals Handbook, Vol.11, Non-Destructive Inspection and Quality Control, American Society of Metals.

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13.Out Lines of Paint Technology, by Gretchen Cagle.

14.Handbook of Radiographic Apparatus and Techniques, International Institute of Welding.

15.Industrial Radiography, AGFA-GAVAERT Ltd.

16.M.G. SILK, Ultrasonic Transducers for Non-Destructive Testing, Adam Hilger Ltd.

17.J.L.TAYLOR, Basic Metallurgy for Non-Destructive Testing, British Institute of Non-Destructive Testing.

18.Metallography of Super Alloys, by G.P. Vander Voort, Buchler.

19.Metals Hand Book, Vol. 8, Mechanical Testing, ASM, Metals Park Ohio, 1985.

20.Metallurgy Fundamentals, by Daniel A. Brandt

21.Materials Science and Engineering An Introduction, by William D. Callister

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SUGGESTED READING MATERIAL FOR FURTHER READING
“TESTING OF MATERIALS” (Fazal Karim)

OR

Chapters 4,6,7,8,10 & 12 of (Warren J. McGonnagle)

“ NONDESTRUCTIVE TESTING”