Radiography Latest

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NDT COURSE MATERIAL PREPARED BY TEAMOF M/S. INSPECTION NETWORK

LEVEL-II RADIOGRAPHY TESTING


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LEVEL-II

RADIOGRAPHY TESTING


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INDUSTRIAL RADIOGRAPHY

1.0 INTRODUCTION :

Radiography is non-destructive testing method to find out the internal discontinuities present in a component

or assembly. It is based on differential absorption of penetrating radiation by the part being

inspected. Radiographic inspection is used extensively on castings and weldments for steam power

equipments (boiler and turbine components and assemblies) like Superheaters, Water Walls,

Downcomer Pipes, Connecting tubes and Headers and other high pressure systems and valves.

2.0 PRINCIPLE :

2.1 Studying the homogeneity of an opaque material using penetrating radiation is called radiography. The

shadowgraph obtained in radiography is a radiograph. When penetrating radiation such as X-

rays or Gamma-rays pass through a material, it gets absorbed or attenuated. The degree of


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absorption depends upon the thickness as well as physical

density variation in the object. Higher the thickness, higher the absorption and

lesser the amount of radiation passing through the part to record in the film. In the component ,

if any discontinuity of lesser density exists, more amounts of radiation will be

emerging out. These penetrated radiation is let to fall on the photographic film.

2.2 Photographic films are very sensitive to X-rays and Gamma-rays. When the films are

exposed, photo chemical reaction takes place which can be converted to black and

white image of internal structural variation of the part, by a process known as film

processing.

2.3 The following discontinuities can easily be detected by radiography:


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3.0 RADIATION SOURCES :

3.1 X-rays :

3.1.1 Conventional X-ray machines ranging from 100 KV to 420 KV and high and high energy X-

ray machines such as Linear Accelerators and Betatrons energy ranging from 2 MeV to 25 MeV are

used for industrial radiography purposes. Portable equipment upto 300 KV are available

for field radiography.

A.WELD DISCONTINUITIES: B.CASTINGDISCONTINUITIES

1. Gas holes and porosities 1. Sand inclusions

2. Slag inclusions 2. Gas inclusions

3. Tungsten inclusion 3. Shrinkage

4. Lack of fusion 4. Hot tear

5. Lack of penetration 5. Crack

6. Crack 6. Cold shut

7. Undercuts 7. Unfused chaplets

8. Burnthrough 8. Chills


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3.1.2 When fast moving electrons are suddenly stopped by a target X-rays are generated.

To make the electron free from cathode and move towards the anode (target) current of the

order of several kilo-voltage and to heat the filament and control the electron quantity, current of the

order of milli-amperage is required. In other words, the quality of the X-rays produced are controlled by

kilo-voltage and quantity by milli-amperage. Associated with X-rays huge amount of heat is

produced and it is very much essential to dissipate the heat to cool down the equipment to increase

the life of the tubes. The X-rays bulb is immersed in oil bath and the oil bath in turn is cooled down by

water circulation.


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K.V Penetration range mm of steel

X-rays Tubes

150 15mm

250 40mm

400 65mm

K.V Penetration range mm of steel

High Energy Sources

2 MeV 6mm to 250mm

4 MeV 25mm to 300mm

3.2.0 Gamma-Ray Sources :

3.2.1 Certain naturally available elements with high atomic number like radium dis-integrates

to another element by shedding out positively or negatively charged particles.

This disintegration is always associated with production of gamma rays and these

self-decaying process is known

TABLEI

PENETRATING POWER CF X-RAYS OF VAPIOUS

KILO-VOLTAGE


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As radio-activity is induced artificially by bombarding the element with Neutrons. Such

elements with the same atomic number but with different mass number are called

'ISOTOPES'. These radioactive isotopes are gamma-rays generators.

3.2.2 Commonly used gamma-ray sources and their properties are given in Table-II.

TABLE - II

Sl.No.

Name of theIsotope

SymbolMain energy

MeVHalf LifePeriod

Application

01 Cobalt-60 Co60 1.33; 1.17 5.3 Yrs35mm to

200mm steel

02 Iridium-192 Ir. 192 0.61 to 0.29 71 days10mm to

60mm of steel

03 Cesium-137 Cs137

0.66 33 Yrs

10 mm to

75mm of steel

04 Thulium-170 Tm 170 0.084 to 0.96 127 days

2mm to 10mmof steel or

upto 25mm ofAluminium


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For thermal power station applications, Ir. 192 is commonly used for filed

radiography. Since Co.60 got greater hazard comparing to Ir. 192 its application is usually

restricted to closed enclosures. However for the examination of higher thickness

components, Co.60 is also being used at times in field radiography.

Due to self decay process, the strength of the source reduces to half at the end of each

one half life period. This process is continuous and it becomes necessary to replenish

the source at some time.

3.3 Properties of X-rays and Gamma-Rays :

3.3.1 Both are electromagnetic radiation traveling In Straight line with the velocity of

light. Their presence cannot be felt by any of our organ. They Ionize the medium to which they

pass through. Their photo chemical properties are


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advantageously used to expose films and fluorescent properties for fluoroscopy. But destruction

of living cells poses radiation hazard.

3.3.2 X-ray can be generated as and when required and its energy an be controlled. Where as the

emission of gamma- rays are spontaneous and its energy level cannot be changed. Depending upon the

thickness and type of material, the correct isotope is to be selected. The size of the gamma-ray

equipment is small comparing to X-ray machine and is free from external power and no cooling

system is required. Hence isotopes are widely used in erection site and the facility to keep the

source inside the pipe is and added advantage of isotopes over X-ray machine. But gamma-ray source

is a self decaying one so a recurring expenditure on changing the source is unavoidable.


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4.0 RECORDING MEDIA :

4.1.0 X-ray films are the recording media in radiography. Unlike photographic films, X-

ray films are coated on both sides of a transparent flexible base of either cellulose

triacetate or polyester, using proper adhesive.

4.2 Films are classified as slow speed, medium speed and fast speed depending upon the

grain size of the emulsion.

Table-III below gives the type of Industrial Radiographic films as per ASTM E 94/74.

TABLE - III

Film TypeDescription

Speed Contrast Graininess01. Low Very High Very Low

02. Medium High Low

03. High Medium High


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For the radiography of high pressure components either type-I or type-II films are used. The followin

are the brands of different films commonly used for radiography.

Type-I

01. Afar Geared

D2,D4,D5

02. Indus NDT 55

03. Kodak M.

Type-II Films

01. Agfa Gevaert D7

02. Indu NDT 65; 70

03. Kodak A, AA.

5.0 INTENSIFYING SCREENS :

5.1 All the radiation reaching the film will not inter-act with the emulsion to have photo-chemical reactio

99% of the radiation falling on the film will just pass through it. To increase the photo-chemic

reaction


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and thus to cut short the exposure time and to increase the radiographic contrast radiographic

screens known as intensifying screens are pressed into intimate contact with the film during

exposure. Screens are of two types, viz., metallic screens (usually lead screens) and fluorescent

intensifying screens.

5.2 Lead Screens :

It is the combination of filtration and intensification that makes lead screens the most widely

used in industrial radiography. Low energy radiation is more readily absorbed by a lead screen

than high energy radiation. Because scattered radiation from a test piece is always of a lower

energy than the incident beam passing through a test piece, a lead screen will absorb a relatively

high percentage of unwanted scattered radiation than the image forming radiation. Scattered

radiation arise mainly from the test piece (internal scattering) and from the table


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or floor on which the film with its holder is placed during exposure (back scatter). Because

of the need to filter out both internal scatter and back-scatter, two screens are normally used. The screen

that faces the subject and source of radiation is refereed to as the front screen and the screen behind the

film towards the table or floor is referred to as the back screen; both screens absorb scattered

radiation.

In practice the front screen is the thinner of the two because the image forming radiation always

must pass through the screen. The usual thickness of the front lead screen is 0.1mm and back screen is

0.15mm for Ir.192.


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5.3 FLUORESCENT SCREENS :

Fluorescent intensifying screens fluoresce or produce light when excited by X-rays or Gamma

rays. Certain compounds such as calcium tungstate or barium lead sulphate have the property o

emitting light immediately upon excitation by short-wave length radiation. These screens are widel

used in medical radiography and its use in pressure part's radiography is not permitted.

6.0 FILM PROCESSING :

6.1 By a chemical process the latent image formed during exposure is made visible and permanent. Th

film are to be handled in a dark room fitted with safe light. The safelight will give the required illuminatio

and at the same time the particular colored light will not affect the film. Generally lights with olive green o

red orange filter is used as safelight. The film emulsion will get affected by high temperature. So the dar

room should be air- conditioned.


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6.2 The film processing includes 5 steps.

6.2.1 Developing :

In developer the exposed silver bromide is reduced to silver developer is an alkaline solution

of various compounds and the reducing action is slow at temperature below 180C. At temperature

above 300C, the film emulsion will get damaged. Hence the developer temperature is to be

maintained at 200C by refrigeration system and the recommended developing time is 5

minutes at 200

C. Prolonged development will fog the image. Development in higher temperature will

result in poor contrast.

6.2.2 Rinsing :

Once the developing is over, the film turn to black colour and the same time is not

transparent due to the existence of undeveloped emulsion on the film. The unexposed

emulsion will again react with light when it is taken out in ordinary light and turn black.


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Hence, it is essential to remove the unexposed emulsion before going for the removal or

fixing. The developer on the film is to be removed or neutralized by rinsing. So,

after developing, film is immersed in another tank containing ordinary water or

water with glacial acetic acid for few minutes to stop the developing action.

6.2.3 Fixing :

In fixer, the in exposed silver bromide is dissolved away any only the converted silver

which is black in color will remain on the film which will represent the internal structural

variation of the part. The fixer solution is acidic in nature.

6.2.4 Washing :

The film coming out of fixer will have chemicals carried over, which the to be thoroughly

washed, otherwise the film will get discoloured after some time, when in storage.


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To remove the chemicals, films are thoroughly washed in running water.

6.2.5 Drying :

After washing the films in running water for about 20 to 25 minutes, films are dried. Dust free

hot air of temperature 1000F to 1200F is used for drying the film. Drying Cabinet or rooms are

used for drying the film. Once the film is dried, the radiograph is ready for evaluation.

7.0 IMAGE QUALITY INDICATORS ( PENETRAMETERS):

7.1 Penetrameters are used to determine the ability of the radiographic process to record images

of small flaws or the sensitifity. Penetrameters are of known size and shape and have the same

attenuation characteristics as the material in the test piece. Penetrameters preferably are located in

regions of maximum test piece thickness and greatest test


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Piece to film distance, and near the outer edge of the central beam of radiation. The image

of the Penetrameters that appears on the finished radiograph evaluated during Interpretation to assure

that the desired sensitivity, definition and contrast have been achieved in the developed image.

Penetrameters of different designs have been developed by various standards-making

organizations. Applicable codes, specifications or purchase agreements usually

determine the type of Penetrameters to be used.

7.2 The three basic types of Penetrameters in used are:

1. Plaque type

2. Wire type and

3. Step wedge type

7.2.1 Plaque type penetrameter consists of strips of material of uniform thickness with holes drilled

through them. ASTM, ASME and AWS specifies for such type Penetrameters.


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Designation

The holes are 1T, 2T and 4T in diameter, where T is the thickness of the plaque. Various

degrees of image quality can be measured by using plaque type Penetrameters of different thickness.

Sensitivity is usually expressed in terms of Penetrameters thickness (as a percentage of test piece

thickness) and resolution is determined by the smallest hole size visible in the radiograph. For instance,

an image quality level of 2 - 2T indicates that the thickness of the Penetrameter equals 2% of

section thickness and the 2T hole is visible. If image quality of 1-1T were required, a radiograph would

be acceptable if the outline of a 1% penetrameter and the 1T hole in that penetrameter were

distinguishable.

7 2 2 Wire type penetrameter :


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7.2.2 Wire type penetrameter :

A typical wire penetrameter is the standard of DIN 54109, which consists of sixteen of wires of each

of three metals-steel, aluminium and copper. The wire diameters decreases in geometric progression from

3.2mm (wire No. 1) to 0.1mm wire number 16.

TABLEIV

NUMBER

(MM)

1 3.2

2 2.5

3 2.0

4 1.6

5 1.25

6 1.07 0.8

8 0.63

9 0.5

10 0.4

11 0.32

12 0.25

13 0.2014 0.16

15 0.12

16 0.10


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The Standard for a given materials is contained in the plastic envelopes, suitably

marked for identification. Each envelops contains seven wires Viz.

DIN 62 FE 1 ISO 7

DIN 62 FE 6 ISO 12

DIN 62 FE 10 ISO 16

In contrast to the ASTM System, the DIN System does not provide constant

sensitivity, the sensitivity varies with test piece thickness within each thickness range.

% Sensitivity = of smallest wire seen of the Radiograph

Thickness under the penetrameter x 100

Lesser the value, higher the Sensitivity.


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7.2.3 Step Wedge Penetrameter :

Usually have either an arithmetic or geometric progression of stop thickness. A

plain step wedge penetrameter is useful only for determining the ability of a radiograph to

resolve variations in test piece thickness it cannot be used to evaluate the effect of geometric

unsharpness. However, if a plain step wedge is modified by drilling holes in each

step, it becomes sensitive to geometric unsharpness. This type of design is used by the

British Welding Research Association (BWRA) and French Navy (AFNOR).

8.0 DIFFERENT TECHNIQUS OF RADIOGRAPHY :

8.1 In a simple radiographic techniques, source is kept at one side and film is kept at opposite

sides of the object as shown in Figures -1. This is a single wall single image

techniques. Welds similar to plate weld or in big cylinder can be radiographed with this

techniques. When the length of the weld is more, the weld is divided into small Segments to

suit the film length available and processing


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Capability. Sufficient overlap is to be given at the we should see that density of the weld will go

untested. is within the range of -15% and + 30%.

8.2 The inspection of complex shapes most often required multiple exposures, usually with different

viewing directions. The selection of views for each exposure depends primarily on the shapes of the

section of the test piece to be inspected with that exposure and the probable orientation of suspected

flaws. There are other three major inspection techniques for tubular section or pipes Viz., the double wall

double image techniques, double wall single image techniques and panoramic.

8.2.1 Double Wall Double Image Techniques :

This techniques is applicable mainly to sections of no more than 3 " O.D. This techniques produces

a radiograph in which the images of both walls of a tubular section are


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Super imposed on one another. The beam of radiation is directed towards one side of

the section and the recording surface is placed on the opposite side, usually tangent to the

section.

Fig : Set up for a Double Wall Double Image Techniques

Two exposures, 90 apart are required to provide complete converge when the ratio of OD

to ID is 1.4 or less. When the ratio of OD to ID is greater than 1.4, the number of exposure

required to provide complete coverage can be determined by multiplying that ration by 1.7

and rounding off to the next higher integer. The circumferential displacement between shot is

found by dividing 180 by the number of shots if the number is even. When an odd number of

exposures are required for complete coverage, the angular spacing between shots as an can

be determined by dividing 360 by the number of shots as an alternative to dividing 180 by the

number. This alternative cannot be used when the number of shots is even because


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of half of the resulting radiographs would be mirror images of the remaining

radiographs and sections of the outside circumference would not receive adequate coverage.

Variation of the double wall, double image techniques, sometime called the

'Corona' or 'off set' techniques is often used the inspection of circumferential butt welds in small

diameter tubing and pipe (Fig. above.) In the corona techniques, the central beam is

directed at activate angle to the run of the tube 'see fig. above) so than a straight band. The

offset angle of the radiation beam must be large enough that the image of the upper section of

the weld zone does not overlap the image of the lower portion, but not so large as to introduce an

unnecessary degree of distortion. Also the larger the offset angle, the greater the probability that

the techniques will fail to detect incomplete fusion at the root of a plain butt weld. The correct

number of


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The area of coverage is limited by geometric unsharpness and distortion at the

extremities of the resolved image for the hollow cylinders that are less than about 15 in. In

outside diameter. For larger cylinder, film size is the usual limiting factor. There must be

enough overlap between adjacent exposures to ensure that all the outside circumference is

clearly recorded.

8.2.3 Panoramic Exposures :

This techniques can be used to radiograph the entire circumference of a pipe in single

exposure or several small components arranged in a semi-circle by keeping the source at

the centre. By providing a hole near the weld in a thick walled pipe (Gamma hole), the gamma-

ray source can be inserted inside the pipe to the centre and the entire weld can be

radiographed in one exposure. By this method

exposure, and the circumferential location of corresponding view can be


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exposure, and the circumferential location of corresponding view can be

determined for the corona techniques in the same manner as for the basic double wall,

double image technique.

8.2.2 Double Wall, Single Image Technique :

Double Wall, Single image technique is applicable mainly to hollow cylinders and tubular

sections exceeding 3" in outer diameter. This techniques producers a radiographic

image of only the section of the wall that is closest to the recording plane, although the

radiation penetrates both walls, the source is positioned relatively close to the section, so

that the blurring caused by geometric unsharpness in the image of the cylinder wall close set

to the source makes that image completely in distinguishable. Only the image of the wall

section closest to the film is sharply defined. Exposures are calculated on the basis of

double the wall thickness of the hollow section as they are for the double wall, double image

techniques.


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the disadvantage of giving longer exposure due to the double wall penetrating and

several exposures to cover full circumference can be avoided.

9.0 GEOMETERIC UNSHARPNESS :

9.1 Radiographic definition varies according to the geometric relationships among size, source

to object distance and object to image distance. When radiation from a finite size

produces a shadow that portion of the image that is in shadow for radiation emanating

from all points on the surface of the source is a region of complete shadow, known as the umbra.

Portions of the image that are in show for radiation from some portion, are regions of

partial shadow, known as penumbra. The degree of geometrical unsharpness in equal

to the width of the penumbra.


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Geometrical Unsharpness (Penumbra)

Effect of shadow formation by different parameter.

Mathematically, the geometric unsharpness is determined from the laws of similar triangle as

illustrated can be expressed as

0g = s x t

f

Where 'S' is the size of the source or focal spot, it is the object to image distance and 'F' is

the source to object distance. The amount of geometric unsharpness can be reduced by

lengthening the source to object distance, reducing the size of the source or focal spot or reducing

object to image distance.

In applications, where the maximum unsharpness must be kept below a specific known value

(Specified by the

governing code) so as to resolve certain types and sizes of flaws, the radiographer can

d t i th i i t bj t di t f i t f th ti i b


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determine the minimum source to object distance for a given part from the equation given above.

10.0 Density :

Another factor controlling the quality of the radiograph is density. The quantitative measure of

blackening of a photographic emulsion called density .

Density D = log10 Io

It

Where D = Density

Io = Intensity of light incident on the film.

It = Intensity of light transmitted through the film.

Density Capacity Io / It

0 1

0.3 2

0.6 41.0 10

2.0 100

3.0 1000

4.0 10000

Density can be measured using a densitometer or can be compared with a precalibrated density


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Density can be measured using a densitometer or can be compared with a pre calibrated density

strip. The minimum density recommended for radiographs with X rays is 1.8 and with gama

rays is 2.0 Maximum can be 3.5 to 4.0 Higher intensity illuminator is required for viewing up the

radiographs above density. 2.0

11.0 INTER PRETATION OF RAIOGRPAHS :

11.1 A Qualified interpreter must :

a. define the quality of the radiographs image which includes a critical analysis of the radiographic

producers and the image developing producers.

b. Analyses the image to determine the nature and extent of any abnormal condition in the test

piece.

c. Evaluate the test piece by comparing interpreted information with standards or

specification and .

d. Report inspection results accurately, Clearly and within proper admistrative channels.


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11.2 Viewing or Radiographs :

Viewing of radiographs should be done in an area with subdued lighting to minimize distracting

reflections from the viewing surface. The viewing apparatus should have on opal glass o

plastic screen large enough to accommodate the largest film to be interpreted. The screen should be

illuminated from behind with light of sufficient intensity to reveal variations in photographic density

upto a nominal film density of at least 3.0. There may be a need for a smaller, more intensely

illuminated viewer for evaluating small areas of film having densities upto 4.5 or more. Viewing

screens of high intensity illuminator should be cooled by blowers or other suitable apparatus

to prevent excessive heat form damaging films and to extend lamp life.

12.0 RADIOGRAPHIC APPEARANCE OF SPECIFIC TYPE OF FLAWS :

(G )


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12.1 Porosity (Gas Holes)

The porosity may be spherical, elongated or worm hole shapes and in pattern that are

random, clustered or linear on a radiograph, the spherical voids have the appearance

of rounded dark area, while the non-spherical voids have an elongated dark area with

smooth outline.

12.2 Tungsten Inclusion :

Tungsten inclusions are lighter than the surrounding areas and may be rounded or irregular.

12.3 In complete Penetration :

Appears as a dark straight line though the centre of the weld. The width of the indication

is determine by the root gap and amount of weld penetration.

12 4 Slag Inclusion :


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12.4 Slag Inclusion :

Appears darker than the surrounding area and may be irregular in shape or elongated

in the direction of the deposited weld bead.

12.5 Lack of Fusion :

Appears as a dark indication usually elongated and varying in width.

12.6 Crack :

Appears as a dark jagged or straight line.

12.7 Icicles (Tear Drops) :

Appears as individual, rounded lighter indications with an occasional small dark spot in the

centre of drop.

12.8 Burn Through :

Appears as an individual darkened area of elongated or rounded contour which may be

surrounded by a

lighter ring.


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12.9 Under Cut :

Appears as a relatively straight and narrow dark line and can be located on either or both

sides of the root opening locations.

13.0 EVALUATION :

13.1 A flaw detected by radiography is meaningless unless compared to a known condition.

Evaluation consists of comparing the interpreted image with the least acceptable conditions in

terms of the type, size quantity and severity level of any flaws that are found. The result

of this comparison is a judgments to accept or reject the part.

ULTRASONIC INSPECTION


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ULTRASONIC INSPECTION

1.0 INTRODUCATION :

1.1 UL transonic inspection is a non destructive destine method to find out surface and sub-

surface discontinuity in a components vibrational waves which have a frequency above the

hearing range of the normal ear are called 'UL transonic' waves i.e., frequency above 20,000

Cps. UL transonic waves used in the industrial applications are in the range of 200K cps. to

20M Cps. (25 MHz). The sound waves travel through the materials with some attendant loss

of energy (attenuation) and are reflected at interfaces. The reflected beam is detected and

analyzed to define the presence and location of flaws.

2.0 PRINCIPLES :

When UL transonic waves from a generating crystal are made to propagate in a material

through proper coupling, it will be partially reflected or refracted when there is change

i di i t f th f di ti it th it f


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in medium or an interface say the presence of a discontinuity or the opposite surface

of the sound entry. The energy of the reflected UL transonic waves depends upon the

severity of the defect, the area of the orientation with respect to the direction of the sound entry. the

reflected wave or the transmitted wave is picked by a receiver and amplified for evaluation.

3.0 BASIC EQUIPMENTS :

3.1 Most UL transonic inspection system include the following basic equipment.

3.1.1 An electronic signal generator that produces bursts of alternating stage when electrically

triggered.

3.1.2 A sending transducer (probe or search unit) that emits a beam of UL transonic waves when

bursts of alternating voltage are applied to it.

3.1.3 A couplet to transfer UL transonic waves to the test piece.

3.1.4 A receiving transducer to accept and correct the output of UL transonic waves from the test

piece. One single transducer can be used both as a transmitter and receiver.

3.1.5 An electronic device to amplify and if necessary modify the signals from the receiving


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transducer.

3.1.6 A display or indicating device to characterize or record the output from the test piece. The display

device may be an Oscilloscope, a chart or strip recorder, a marker, indicator or alarm device, a

computer print out.

3.1.7 An electronic clock or timer.

4.0 TRANSDUCERS :

4.1 Transducers are the ear in UL transonic testing Generation and detections of UL

transonic waves for inspection is accomplished by means of a transducer element acting

through a couplet. The active element in a search unit is a piece electronic crystal.

Piezo electricity is ' pressure electricity'. As the name implies, an electric charge is developed by the

crystal when pressure is applied to it.

Conversely, when an electrical field is applied, the crystal mechanically deforms (Changes

shape). The most


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Common types of Piezo electric materials used for UL transonic search units are quartz,

lithium sulphate, and polarized ceramics such as barium titanate and lead metaniobate.

5.0 GENERAL CHARACTERSTICS OF ULTRANSONIC WAVES :

5.1 UL transonic waves are mechanical waves that consist of vibrations of the atomic or

molecular particulars of a substances about the equilibrium positions of these particles. They can

propagate in an elastic medium, which can be soiled, liquid or gaseous but not in vacuum. Like

Light beams, ultrasonic beams are reflected from surfaces, refracted when they

cross a boundary between two substances that have different characteristic sound velocities

and diffracted at edges or around Obstacles. Scattering by rough surfaces or particulars

reduces the energy of an ultrasonic beam, comparably to the manner in which

scattering reduces the intensity of a light beam.

5.2 Velocity is the product of frequency and wave length.


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y p q y g

V = f

Where V = Velocity in metres per second.

f = frequency in hertz (Cycles per second)

= wave length in meters per cycles.

on the basis of the mode of particles displacement, Ultrasonic waves are classified a

longitudinal waves, transverse, waves, surface waves and lamb waves, Ultrasonic waves also follo

Snell's law.

5.3 LONGITUDINAL WAVES :

Longitudinal waves : Sometimes called compress ional waves are the type of Ultrasonic waves mos

widely used in the inspection of metals. They travel through metal as a series of alternates compression

and refaractions in which the particles transmitting the wave vibrate back and forth in the directions o

travel of the waves. Longitudinal ultrasonic waves are readily propagated in liquids and gases a

well as in elastic solids. The velocity

of longitudinal Ultrasonic waves is about 6000 m/ seconds in steel 1500 m per second in water


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of longitudinal Ultrasonic waves is about 6000 m/ seconds in steel, 1500 m. per second in water

and 330 M per sec. in air.

5.4 TRANSVERSE WAVES :

Transverse waves or shear waves are also extensively used in the Ultrasonic inspection of

metals. It travels with a velocity of 50% of the longitudinal wave velocity of the same

materials. Air and water will not support transverse materials.

5.5 Surface Waves :

Surface waves are another type of Ultrasonic waves used in the inspection of metals. These

waves travel along the flat or curved surface of relatively thick solid parts. Surface

waves are subject to less attenuation in a given materials than are longitudinal or transverse

waves. They have a velocity approximately 90% of the transverse wave velocity in the same

materials.

6 0 MAJOR VARIABLES IN ULTRASONIC INSPECTION :


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6.0 MAJOR VARIABLES IN ULTRASONIC INSPECTION :

6.1 Frequency :

6.1.1 Frequency of the Ultrasonic waves used affects inspections capability in several ways.

Sensitivity or the ability of an Ultrasonic inspect on system to detect a very small discontinuity, is

generally increased by using relatively high frequencies system to give simultaneous,

separate ` indications from discontinuities that are close together both in

depth below the frequency band with and in closely related to pulse length, but is not affected by

frequency. Penetration or maximum depth in a materials from which useful indications can be

detected is reduced by the use of high frequencies.

6.1.2 Table :

Recommended frequencies for different applications

200 KHz to 1 MHz - Examination of castiron and steel

castings are relatively coarse grained materials such as copper.

400 KHz to 5 MHz - Castings steel, Equilibrium brass


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and other materials with refined grain size.

1 MHz to 5MHz - Rolled products, metallic sheets, plate,

bars and millets.

2.25 MHz to 10 MHz - Drawn and extrude products bars

tubes and sheets.

1 MHz to 100 MHz - Forgings

1 MHz to 2.25 MHz - Welding.

6.2 Angle of Incidence :

Only when an Ultrasonic wave is incident at right angles on an interface between two materials

(angle of incidence = 0') transmission and reflection occur at the interface without any change in beam

direction. at any other angle of incidence refraction and mode conversion (Splitting the wave and a

change in the nature of wave motion) take place. Longitudinal waves splits into longitudinal wave and

steer wave when the beam strike the surface at an angle.

The angle of incidence can be adjusted in such a way that the longitudinal waves grade the surface and


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only shear wave exists in the part. Hence confusion arising out of both the waves picking up the

discontinuity can be avoided.

6.3 COUPLANT :

The couplant as the name implies couples the transducer to the surface of the test specimen

to ensure efficient sound transmission from transducers to test surface. This is done by something out the

irregularities of the test surface and by excluding all air between the transducers and the test specimen.

Commonly used couplants are water, glycerin. machine oil, grease, paraffin etc. For a smooth surface

water, glycerin or machine oil can be used. Grease is used for the rough surface and also when test is to

be conducted in a vertical alone of over- head position. The couplant materials must be homogenous and

free from solid particles or air bubbles.

7.0 TYPES OF TESTING :

7.1 Descending upon the probe is positioned with the part the testing method is classified as

Contac testing and immersion


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testing. Also the examination is further classified as' scan 'B' scan and 'C' scan by the way how

the indications are displayed for interpretation.

7.2 The most widely used techniques is contact testing, 'A' Scan display due to its simplicity

in operation and minimum in number and size of equilibrium to be handled. In 'A' scan the

indication is displayed on cathode ray tube (CFT) as vertical pipes or echoes. The height of the

echo respecting the severity of the discontinuity and its location denotes the location of the

discontinuity with respect to the entry surface Ultrasonic beams are send as pulled beams and the

techniques is known as pulse echo techniques.

By suitably calibration the time base, the depth of the discontinuity can be directly read out from the

CRT.

7.3 Sound beam can be directed to the test piece at an angle also. Such of testing are


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known as and beam testing.

FIG : CONTACT TESTING ANGLE BEAM SCANNIG

In angle beam testing shear waves are used for testing. The angle is selected in such a way that

the longitudinal waves grazes the surface and shall not interfere with the result. Depending upon

the thickness, the angle of refraction is chosen.

Thickness mm Upto 15mm 15 30 30 to 60 Over 60

Angle 800 700 600 450

The distance read out from the CRT is not the actual depth or the defect is not exactly under the

probe as in the case of normal beam scanning. The depth of the discontinuity and the location of it

have to be Calculated based upon the refracting angle.

8 0 CALIBRATION AND STANDARDISATION


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8.0 CALIBRATION AND STANDARDISATION :

8.1 Specially designed calibration blocks are used in contact testing to check the operation

of ultrasonic instruments and transducers and to make certain adjustments to the instruments and

transducers to best suit the testing conditions. Al though Various types of reference blocks are

available, the commonly used is the one designed by the international Institute of welding. With this

block, the test range, Institute of welding. With this block, the test range, sensitivity, reflection, angle

of the probe etc. Can be checked, Reference blocks establish a standards of comparison, so that

echo amplitudes can be evaluated in terms of flaw size.

8.2 The size of the discontinuity cannot be estimated directly without making any prior

standardization. Reference blocks with known size of flaws are used for standardization. The height

of the echo from a known

size of the discontinuity is adjusted to a certain level before conducting actual tests Also the same


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size of the discontinuity is adjusted to a certain level before conducting actual tests, Also, the same

size of discontinuity will not produce equal height echo when its location varies from the surface.

height echo when its location varies from the surface When distance increases, the sound beam

gets attenuated and hence there will be a reduction in amplitude. Hence a distance amplitude

correction curve is to be plotted before starting any test. The echoes obtained from the part is

compared to this curve and to be decided whether the discontinuity is acceptable one of to be

repaired with respect to the applicable code. The size of the reference hole will vary with respect

to the thickness of the part being tested. Flat bottom holes of square notches or 'V' notches for

angular beam testing. Calibration blocks and reference blocks are used to obtain reasonable

consistent test results when tests are conducted by various times and conditions.

9.0 ADVANTAGES AND LIMITATIONS :

9.1 Advantages:

9.1.1 Most sensitive to planar defects such as cracks.


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9.1.2 Test results are known immediately.

9.1.3 Testing can be automatic and the results recorded.

9.1.4 Equipment is portable.

9.1.5 Penetration capable is high

9.1.6 One side acceptability is enough for testing

9.2 Limitations :

9.2.1 Couplant is required.

9.2.2 Small, thin and complex parts may be difficult to test.

9.2.3 Reference standard is required for evaluation of indications.

9.2.4 Operator skill is much counted for the efficiency of the test.

10.0 APPLICATION OF ULTRASONIC TESTING :

10.1 UL transonic inspection has been successfully used to defect flaws in cast and wrought

metal parts and in welded, brazed and bonded joints during productions and service.

Contact inspection is more widely used because it involves portable equipment and because of it


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versatile and applicable to wide range of situations.

10.2 Inspection of Welded Joints :

10.2.1 Welded joints may be Ultrasonically inspected using either the straight beam

or the angle beam technique is most often used because of one reason being that the surface of

the weld does not have to be ground flush, as is necessary for straight beam inspection. Another

reason being that all the flaws shall not be oriented in such a way that it can be picked up in

straight beam scanning. The orientation of defects like lack of fusion and cracks are usually

longitudinal to the weld axis and are very well favorable for angle beam scanning where the sound

beam strike the joint at right angle whereas there are chances of getting these defects missed in

normal beam scanning. The type of the flaws usually encountered in the weld of porosity, slag,

incomplete penetration, lack of fusion and cracks. Spherical porosity will produces a small

amplitude echo, even when the sound beam strikes at an angle to the joint. Slag

produce stepped indication which are maximum at right angles to the joints.


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10.2.2 It is mandatory for elector slab welding to examine by ultrasonic method also after

normalizing. Induction Pressure welds (IPW) are suitable only for ultrasonic testing as lack of

bonding is the major defect encounter in the process. Welding of Vanadium steels are

ultrasonically examined after stress relating.

10.3 In addition to flaw detections, Ultrasonic are used for thickness measurements also.

pocket size meters (also known as D- meters) are available for fields application with which we can

measure thickness upto 300mm with an allowance of -0.1mm. The results can be read out on an

oscilloscope screen, on a meter or can be printed out. When measuring the thickness care must

be taken to see that both the sides are parallel and initial calibration of the equipment is done with a

known thickness of same composition of the part being tested with approximately same thickness

of the job.

MAGNETIC PARTICLE TESTING

1 0 Introduction :


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1.0 Introduction :

The magnetic particles method of non-destructive testing is one of the most common method

for finding dis continuities in materials. This method is used for detecting surface and sub-

surface discontinuities in Ferro- magnetic materials. Magnetic particles testing is a relatively

easy and simple test method that can be applied to finished components billets hot rolled bars

forgings and castings. It can also be used to check processing operations such as machining,

grinding and heat treatment.

The objective of magnetic particles testing is to ensure product reliability by providing means of

a) Obtaining a visual of an indication related to a discontinuity in or on the surface of the

materials.

b) Disclosing the nature of discontinuities without impairing the materials.

c) Separating acceptable and unacceptable materials in accordance with ore-determined

standards.

2.0 PRINCIPLE OF MAGNETIC PARTICLES TESTING :


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2.0 PRINCIPLE OF MAGNETIC PARTICLES TESTING :

The basic principle in magnetic particle testing is that when a component is magnetized,

magnetic lines of force or magnetic flux will be created. Any discontinuity in the materials will cause

set up magnetic poles as well as leakage of magnetic flux.

If some media which are Ferro magnetic in nature such as iron powder is dusted over

the surface of the components, the powder accumulates at the region of the leakage flux and the

appearance of the powder build up will resemble the nature of the discontinuity.

2.1 STEPS IN TESTING :

The method involves three essential steps.

a) Magnetizing the materials or a part under test.

b) Applying the Ferro- magnetic particles over the surface.

c) Examining the surface for powder patterns or

indications.

3.0 METHODS OF MAGNETISATION :


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Magnetization of the materials can be carried out principally in two ways viz., Circular

magnetization and longitudinal magnetization.

3.1 CIRCULAR MAGNETISATION :

A circular magnetic field is induced into the component in two ways either by directed

passing the current through the component or indirectly through a central conductor surrounded

by a hollow article.

4.0 MAGNETISING CURRENTS :

Straight direct current (D.C) alternative current (A.C) and halfwave rectified direct

current (HWNC) are all used. The following are their relative merits and demerits.

4.1 DIRECT CURRENT (D.C)

Straight DC is suitable for yokes and solenoids. The penetration power of DC is more

than that of AC. However DC cannot be stepped up or down easily.

4.2 ALTERNATIVE CURRENT (A.C) :

The current alternates at specified frequency. This type of current created a maximum


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p q y yp

flux at the surface of the magnetized article and has relatively les penetrating ability. The

advantage of using AC is that the voltage can be stepped up to down. Also the reversal of the

magnetizing current cause magnetic particles more mobile facilitating their collection at leakage

fields. AC is the best suited for locating surface discontinuities.

4.3 H.W.D.C

Half wave Direct Current is produced by rectifying an alternative current during the

positive cycles. The use of rectified current has got the following advantages.

1. AC at any commercial frequency can be used.

2. Penetration is directly comparable to that of DC.

3. The pulsating effect of the rectified wave is helpful in adding mobility to the

magnetic particles.

4. There is a definite advantage in locating deep seated discontinuities.

5.0 CUPPENT REQUIREMENTS :

The required amount of magnetizing current is effected by the permeability of the metal, the


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shape and thickness of article and the type of discontinuities sought. However, the following can be use

as 'Rule' of Thumb method :-

1. Circular magnetization with head shot method. 800 -1000 amps. Per inch dia. or cross

section with

HWDC 500 -600 amps. per inch of dia. cross

section with A.C.

2. For circular magnetization with prods. 90-110 amps.

per inch of prod-spacing for thickness upto ."

100 -125 amps. per inch of prod- spacing for

thickness more than ".

Prod spacing can be kept between 4" and 8" for

effective testing.

3. Longitudinal magnetization using coils.

Amps = 45.000 x 1

L/D T

Where L is the length and D is the dia. of the article and T is the number of turns in the coil.


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(Limitations). L not more than 18" and L/D between 2& 15.

6.0 TESTING MEDIUM: (MAGNETIC PARTICLES) :

The particles used are in all the cases finely divided Ferro magnetic materials. The

properties of these materials very over a wide range for different applications including magnetic

properties, size shape, density, mobility and visibility and contract. The medium any be dry powder

with various colours for better contract or liquid paste either black, red or fluorescent for use with

black light.

DRY METHOD : In dry method, the powder is sprinkled over by dusting by hand bulbs or

mechanical blowers. The medium any be dry powder with various colours for better contract or

liquid paste either black, red or fluorescent for use with black light.

2. WET METHOD : In the wet method, the particles are suspended in a carrier liquid

such as kerosene and applied

by spraying, brushing, or sub merging the article in the bath. The concentration of the particles


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in the bath should be such that the indication of dis-continuity is clear without too much overall

surface coverage. The recommended concentration for 100 cc of bath for non-fluorescent

particles passing the current in continuous method.

In general, the following are the requirements of the particles used for magnetic particles testing.

i Non-toxic

ii Fine divided

iii Ferro magnetic

iv Free from contaminates

v High permeability

iv. Low retentively

vii High colour contrast

viii Correct size range.

7.0 SURFACE PREPARATION :


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Usually as welded, as cast, as forged or as formed surfaces are suitable for magnetic

particles testing However excess scales, ripples, slag, etc., may interfere with the interpretation of

the powder patterns. Also, flakes, heavy built up of paints, rust, grease etc, are to be cleaned,

sand blasting wire brushing, filling, grinding etc., are used for removing interfering substances.

8.0 LOCATION OF DISCONTINUITIES :

It is possible with suitable technique to locate discontinuities on the surface as well as

below surface upto 5mm deep. Discontinuities located on the surface appear as sharp and distinct

lines whereas sub-surface discontinuities appear as irregular, rough ands fuzzy indication varies

with the depth of its location below the surface. Correct interpretation of the pattern revealed by

sub- surface discontinuities require a certain skill on the part of the operator.

9.0 DEMAGNETISATION :

Since all Ferro magnetic materials possess retentively there will be certain amount of


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residual magnetism left on the materials tested. the amount of residual magnetism depends on the

magnetizing current, its strength and nature (AC or DC) and the permeability of the materials. De

magnetization is essential for components to be used in spacecrafts, aero planes, bearings etc., where

pick up of iron particles cause damage to the part. De- magnetization is done by passing the

Component through an AC field of gradually reducing current or by periodically reversing and reducing

the DC Current.

10.0 FINAL CLEANING :

When the magnetic particle testing is completed, the components are cleaned of the

magnetic particles . This is accomplished by the use of air, solvent washes and wiping etc.

11.0 TEST EQUIPMENT :

The equipment used for magnetic particles testing ranges from heavy complex automated

handling system

To small light weight portable units. The following particulars as considered in the selection ofan equipment.

i) Wet or Dry method


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) y

ii) AC or DC Degree of automation

iv) De- magnetization

v) Amperage required

vi) Tank capacity

vii) Air supply

viii) Line voltage requirements

ix) Accessories needed.

12.0 CLASSIFICATION OF DISCONTINUITIES :

The magnetic particle indication observed can be classified into three categories.

(a) Dis- continuities (b) Non- relevant indications and (c)

False indications.

Dis

Continuities can be classified as surface discontinuities and sub

surface discontinuities. Inmagnetic particle testing, surface discontinuities magnetic particle testing, surface dis continuities

produce sharp, distinct, clear cut and tightly held patterns. Typical examples of this type of defects Are not

cracks in welds, heat treatment cracks, grinding cracks, forging laps, hot tears in castings,

other magnetic materials in the surrounding formation of contractions in the objects such as keys


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and spleens in the shafts.

False indications are those wherein the magnetic particles are held for reasons other than the flux

leakage such as the magnetic particles getting stored in the rough surface.

13.0 APPLICATION :

Magnetic particle Inspections is widely used in process control and in the maintenance.

The root welding of a header butt joint or dumb circumferential seam or similar type joints are

magnetic practically tested after gack gouging before going for full welding. Magnetic particle

Inspections is a widely used method for examining fillet welds. For detaching any surface cracks

after stress relieving magnetic particles inspections is the best method. All such inspections can

be carried- out using Prod- techniques. Prod method is one way of circularly magnetizing the

components by directly passing the current. Large area can be tested part by part and the

direction

of the field can be changed very easily by relocating the prods. Care must be taken to see that the

prod tips are cleaned properly and current is switched only after establishing proper contrast;


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p p p p y y g p p

otherwise excessive arising will take place and can methods can be put into service quite

extensively damage the surfaces. Fillet welds in columns and beams are another area where

magnetic particle inspection the shut down used. During maintenance operation thermal power

plant again these method can be put in to service quite extensively.

LIQUID PENETRANT INSPECTION

1.0 INTRODUCTION :

1.1 Liquid penetrate Inspection is a non destructive

testing method for finding discontinuities that are open to the

surface of solid and essentially nonporous materials.

Indications of flaws can be found regardless of the size,

configuration, internal

structure or chemical of flaw orientation. Liquid Penetrant can seep surface into (and drawn into) various

types of minute well suited for the detection of all types of surface cracks, laps, porosity, shrinkage areas,


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yp yp p p y g

laminations and similar discontinuities. It is used extensively for the inspection of wrought and cast

products of both ferrous and non ferrous metals, power metallurgy parts, ceramics, plastics and glass

objects and both in fabrication and in maintenance.

1.2 Limitations :

The major limitation of liquid penetrat inspection is that it can detect only imperfections that are open to the

surface. Extremely rough or porous surfaces are likely to produce false indications.

2.0 Principle :

2.1 The method employs a penetrating liquid which is applied over the surface and enters the

discontinuity or crack, subsequently after the excess penetrant which exudes or is drawn back out of the

crack is observed indicating the presence and location of the discontinuity. When the penetrant is applied

on the surface, the penetrant enters the discontinuity which is open to the surface by capillary action. The

capillary action wick. In a narrow crack, the capillary presence P is given by the formula.

P = 2S Cos0W

Where = S = Surface tension of the liquid


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0 = Equilibrium contact angle of the liquidand surface of the crack.

W = Width of the crack.

It can be seen that the capillary action is free from gravitational force and hence thepenetrant test can be conducted at any positions.

3.0 TEST METHOD :

Regardless of the type of penetrant used and regardless of other variation in the basicprocess, liquid penetrant inspection requires

the following 5 steps :

1. Surface preparation

2. Application of penetrant

3. Excess penetrant removal

4. Application of developer

5. Inspection

3.1 Surface Preparation :

The material surface to be tested will be having convering such as paints and metallic platics

and contaminants such as dirt, grease, rust, scales, acids, chromates

These coverings will prevent the entry of liquid penetrate into the flaw. Unless it is removed,


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and made the surface clean, dye will not enter the void and there are changes of accepting the defective

ness. So the first step in the penetrant examination is 'Surface preparation'.There are many possible

ways to clean the surface. Any method that will into harm the surface coatings. Shot and sand blasting

are not generally recommended. But there are time when they must be used. When they are, the risk is

run that a discontinuity, otherwise open to the surface might be closed. When shot or sand blasting must

be used, the discontinuities can be reopen with a very slight amount of material from the surface. 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 such as vapour

degreasing, to assure adequate cleaning and make the discontinuity free of contaminants and open to

the surface. A cleaning solvent is used as a final cleaner.

The cleaner used must be capable of dissolving and flushing away the typical oil and


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grease often found on metal components. The two contaminants, oil and grease are penetrant

themselves and would certainly block the entrance of the penetrant. Also the cleaner must be

volatile so that it easily evaporate out of tight discontinuities and does not remain to ilute or

prevent the entrance of the penetrant. Typical suitable cleaners used are Acetone, percholore-

ethylene, Isopropyl alcohol and Methylene chloride, all of which evaporate readily at normal

temperature.

Application of Penetrant :


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Apply penetrant to the surface of a clean dried part or section to be inspected by any

method that will thoroughly wet the surface. Either dipping, spraying, pouring or brushing can be

adopted. All the surface should be thoroughly covered to allow capillary action to such the

penetrant into discontinuity. Penetrant must cover at least one half inch. either side of a

weldments and for all other surfaces at least one inch. around the area to be tested.

With Dye Penetrant properly applied, sufficient time should be allowed for the penetrant to enter

all the discontinuities, for capillary action to do the job. This time is called the penetration time or

dwell time. The two variables for dwell time are the type of material being examined and type of

discontinuity for which the test is conducted.

While there is no maximum penetration time is recommended, the penetrant should be wet prior

to starting the next step. Because of this, once the minimum dwell time is reached, it is best to

start the next step of

best to start the next step of excess penetrant removal while the penetrant is still wet. In common, a


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dwell time of 5 minutes to 10 minutes is given. The Temperature of the part should not be less

160C and more than 520C.

3.3 Step-3 Excess Penetrant Removal :

3.3.1 The presence of any discontinuity is indicated only by the entrapped or penetrated due

and not be the one on the surface. So before pulling back the dye from the discontinuity the

excess penetrant on the surface is to be removed. If the removal is delayed for any reason and

the penetrant has dried, reapply the penetrant to the surface prior to starting the step of excess

penetrant removal. When removing excess penetrant, care must be taken not to do anything

that may remove the penetrant from the discontinuity. This is one reason for having the

penetrant wet prior to starting the removal of excess penetrant.

The Method of removing the excess penetrant depends upon the type of penetrant used. There are

three types of penetrant, viz.

1. Water washable

2 P t l ifi bl


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2. Post emulsifiable

3. Solvent removable

Type (1) is directly washable by water, whereas type (2) is to be made water washable by

emulsification after the dwell time is elapsed. Solvent removable type dye is generally used in site

applications because of its simplicity in use and minimum in size of equipments.

3.3.2 An organic solvent, recommended by the manufacture of the penetrant may be used for

excess penetrant removal of solvent removable type penetrant. Flsuhing the surface by cleaner is

not permitted. First the surface is cleaned with a dry lint free cloth and then by moistening the cloth

and then by moistening the cloth with the recommended cleaner. Full removal of the excess

penetrant is judged by the absence of color on the cloth if we have used ordinary visible dye and

the absence of fluorescence in the case of fluorescent dye, when the part is viewed under black

light.

3.4 Step-3 Developer Application :


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3.4.1 Developer is a highly absorbent power and is applied to the item being inspected after the

excess penetrant is removed. The developer absorbs the dye penetrant from the discontinuities with

a blotting action, spreading the dye to form visible indications. The image of the discontinuity is

formed in the developer itself as the dye carrying penetrant spreads out around the edges of the

discontinuity it has left. Thus, even slight traces of penetrant are drawn form discontinuity and as

they diffuse in the developer their film thickness is increased and the penetrant is fixed in the

developer.

3.4.2 Developer can be either dry or wet. The wet may be aqueous or non-aqueous

suspendable type. Non-aqueous suspendable type developers are commonly used for general

application. Before applying non aqueous developer, the surface should be dry. The non aqueous

developer is applied by spraying using a hand pump or an aerosol can.

3.4.3 Development time :

The time form the application of the developer to the time the article is inspected is th

development time. Rule of Thumb tell to use a time that is approximately one half the penetration time (dwe


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time) used. The development time however includes the time in the drier oven also. Development is

minimum time. It must be long enough to assure that the developer has had time to draw the penetrant from

the discontinuity. If the article is inspected too soon, The Spreading of the dye will be more and the indicatio

may not have reached their maximum, indentcity and therefore be overlooked and if more time is cover th

spread will be enlarged.

If fluorescent dye is used, the inspection should be done under black having wave length 3650A.

3.4.4 Post Cleaning :

After the completion of Inspection all the left over chemical are to be cleaned form the surface.

3.5 INSPECTION :

3.5.1 Discontinuities at the surface will be indicated by the bleeding out of the penetrant. Howeve

localized surface

irregularities such as from machining marks or other surface condition like press fittings may produce

non-relevant in dictations.


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3.5.2 Relevant indications or true indications are those which result from mechanical

discontinuities. Only these indications are to be studied for giving the results. Liner indications are those

indications in which the length is more than three times the width. Rounded indications are those which

are circular of elliptical with the length less than three times the width.

3.5.3 False indications are due to improper removal of excess penetrant such as penetrant on the

hands of the operator or penetrant rubbing of an indication on one specimen to technique an retesting, it

is possible to determine either the indication is false or not.

3.5.4 While interpreting the indications, the following are to be assessed:

i. Type of Indications : Whether continuous line, intermittent line round or small dots. This

ensures to determine

the nature of discontinuities present. Continuous line indications are caused by cracks, cold shuts,

forging laps, scratches and die marks. Interminations are caused by gas holes or pin holes etc. small

dots represents find porosity or micro shrinkage


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dots represents find porosity or micro shrinkage.

ii) Extent of discontinuities as evidence by the extension of indications. This has to be viewed form two

angles. One how deep the discontinuity goes inside the surface. This can be seen from the

brightness of the indications. Deeper the discontinuity, brighter the indications. Another method is the

removal of developer surface after nothing the size of the indications on the surface. Once the depth

of the discontinuity is approximately known, the nature of discontinuity and its other dimensions

such as length, how far they are separated etc. are to be noted.

iii. What effect the indicated discontinuity have on the service life of the specimen. or other wards,

Whether th discontinuities can be accepted or not. This requires the knowledge on the part of the

interpreter to the following.

(a) Whether there is a governing code or standard to which the specimen

has to satisfy.

(b) Whether there is many further processing in which

the discontinuity may disappear.


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c) Previous knowledge of similar parts and processes,

4.0 APPLICATION OF PENETRANT INSPECTION :

Penetrant Inspection is widely used both in fabrication and maintenance. Fillet welds like

drum dished ends, attachment stubs, header hand hole plates. R.G. hole plug welding etc. are

inspected by penetrate test. Any modification work during periodical over haul of their boiler as in

scalloped bar welding, attachment welding in super heater are tested by penetrate inspection method.

As it can be applied on any kind of materials unlinking to magnetic particles inspections and

as is free from and external energy like electricity for operation, and as it can be operated by minimum

technical knowledge, it is a very versatile test method. But before putting the chemicals into use. it is to

be a Ascertained the halogen and Sulphur content should not be harmful to the materials being tested.

The testing area should be properly Ventilated, so that the chemicals will not be hazardous to the

operator. Exhaust of an should be provided when test is conducted inside a closed vessel.

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