Nondestructive Testing Methods Training Workbook

© 2010. Hobart Institute of Welding Technology EW512-6 Nondestructive Testing Methods

NondestructiveTesting Methods

Training WorkbookEW-512-6

Written bythe Staff of Hobart Institute

of Welding Technology

Additional copies can be obtained from:Hobart Institute of Welding Technology

400 Trade Square EastTroy, Ohio 45373

www.welding.org(937) 332-5433

© 2009. Hobart Institute of Welding Technology, 400 Trade Square East, Troy, Ohio, U.S.A.All rights reserved.

Printed in the United States of America.ISBN: 978-1-936058-23-5

iii

iv

TABLE OF CONTENTS

TOPIC PAGE

Glossary of Welding Terms v

Introduction to Nondestructive Testing Methods 1

Principles of Visual Testing 7

Principles of Penetrant Testing 13

Principles of Magnetic Particle Testing 19

Principles of Ultrasonic Testing 25

Principles of Radiographic Testing 30


TOPIC 1

INTRODUCTION TO NONDESTRUCTIVE TESTINGOBJECTIVE

To be able to define and identify the purpose for nondestructive testing and the symbols used to indicate

INTRODUCTION

This section includes an overview of nondestruc-tive testing, its purpose, the basic principles in-volved with the most common types, giving a de-scription of the symbols used to indicate methods of inspection.

Nondestructive testing is an evaluation process in which no damage occurs to completed welds or to the surrounding structure provided the proper procedures are followed. It is used to qualify pro-cedures, welders, and to monitor the quality of production welding.

Nondestructive testing, whether in the shop or field, can be used for detecting small discontinui-ties and defects quickly and effectively. The most common methods for nondestructive testing are: Visual

Penetrant

Magnetic particle

Ultrasonic

Radiographic

Penetrant Testing

Visual Testing

Magnetic Particle Testing

1


When choosing an inspection method, take into consideration the advantages and limitations of the method.

The sensitivity of each method reflects its ability to respond to a discontinuity’s size, shape and loca-tion. Visual inspection is limited to discontinuities exposed to the surface. Radiographic inspection could be used to detect discontinuities on or below the surface. The method to employ is based largely on the degree of quality required for the weldment.

For example, to verify quality, visual or magnetic particle inspection may be all that is required for low pressure piping, whereas high pressure piping may require radiographic testing.

Cooperation between design, welding, and quality engineers is required to determine which testing methods to use in order to meet the testing require-ments of the weldment.

Once the decision is made, it becomes the quality assurance engineer’s responsibility to provide the qualified inspector with the details of the inspection requirements, so the weld can be inspected cor-rectly.

Radiographic Testing

Ultrasonic Testing

Magnetic Particle Testing

2


Methods of indicating inspection type will be nec-essary when nondestructive testing is required. This is generally done on engineering drawings by the use of nondestructive testing symbols and writ-ten procedures.

II. NONDESTRUCTIVE TESTSYMBOLS

Nondestructive testing symbols are standardized much like the symbols used for welding. A refer-ence line is used in the same manner as welding symbols, and is as long as necessary for adding information.

An arrow is used to direct the information to the de-sired location. It can be placed at either end of the reference line, pointing up or down, on either side where welds are to be placed.

The side of the joint the arrow points to is referred to as the “arrow side”. The opposite side is called the “other side”. It is important because it specifies which side of the welded joint is to be inspected.

3©2009, Hobart Institute of Welding Technology EW 512-6 Nondestructive Testing Methods

Methods of indicating inspection type will be .deriuqer si gnitset evitcurtsednon nehw yrassecen

This is generally done on engineering drawings by the use of nondestructive testing symbols and written procedures.

I I . N O N D E S T R U C T I V E T E S T

SYMBOLS

Nondestructive testing symbols are standardized much like the symbols used for welding. A reference line is used in the same manner as welding symbols, and is as long as necessary for adding information.

An arrow is used to direct the information to the desired location. It can be placed at either end of the reference line, pointing up or down, on either side where welds are to be placed.

The side of the joint the arrow points to is referred to as the “arrow side”. The opposite side is called the “other side”. It is important because it specifies which side of the welded joint is to be inspected.

Other side Arrow side

Other sideArrow side

MT 6

RT 25%

3

1411

1411

PTPT

PN-17

GTAW

45

45

1414

© 2010. Hobart Institute of Welding Technology EW512-6 Nondestructive Testing Methods 4

The symbols use initials to indicate the test method to be used. They are:

VT = visual testingPT = penetrant testingMT = magnetic particle testingUT = ultrasonic testingRT = radiographic testing

When the test symbol is located below the reference line, it signifies that inspection is to be performed on the arrow side of the joint. When placed above the line, it indicates the inspection is to be performed on the other side.

The test symbol can be placed on both sides of the reference line to indicate that each side of the weld is to be inspected.

The symbol is centered between a break in the reference line when it doesn’t matter on which side the inspection is to be performed. In all cases, the inspection is for 100% of the weld unless otherwise noted.

Details, such as testing procedures, specification, processes, or other pertinent information are sometimes placed at the end of the reference line inside a “tail bracket”.

When less that 100% of the length is to be inspected, it can be specified by a section length or percentage located to the right of the symbol. The required sections or areas are usually specified in the written procedures. When no percentages are noted, 100% of the weld is to be checked.

©2009, Hobart Institute of Welding Technology EW 512-6 Nondestructive Testing Methods

The symbols use initials to indicate the test method to be used. They are:

VT = visual testingPT = penetrant testingMT = magnetic particle testingUT = ultrasonic testingRT = radiographic testing

When the test symbol is located below the reference line, it signifies that inspection is to be performed on the arrow side of the joint. When placed above the line, it indicates the inspection is to be performed on the other side.

The test symbol can be placed on both sides of the reference line to indicate that each side of the weld is to be inspected.

The symbol is centered between a break in the reference line when it doesn’t matter on which side the inspection is to be performed. In all cases, the inspection is for 100% of the weld unless otherwise noted.

Details, such as testing procedures, specification, processes, or other pertinent information are sometimes placed at the end of the reference line inside a “tail bracket”.

When less that 100% of the length is to be inspected, it can be specified by a section length or percentage located to the right of the symbol. The required sections or areas are usually specified in the written procedures. When no percentages are noted, 100% of the weld is to be checked.

VTPT

Other side Arrow side


Other side

side


Arrow


Arrow sideOtherside

RT + PTRT

UT

RTA-12

MT 6

RT 25%

4


The all around test symbol is used when the in-spection is to be performed completely around a welded joint.

The number of tests to be performed is indicted in parenthesis. The symbol shown here specifies four applications of magnetic particle inspection.

Multiple reference lines are nondestructive test symbols combined with other nondestructive or welding symbols. The order in which operations and tests are performed is indicted by the order of the lines. The first operation is the closest to the arrow.

This multiple reference line shows a single Vgroove weld with melt through to be inspected on the arrow side with a combination of visual and radiographic testing methods. Visual inspection is performed on the other side. Inspection details are located in procedure T-28.

The engineering staff can provide information for welding and inspection using symbols and notes on the engineering drawings.

Knowledge of the testing methods, procedures, and the symbol elements, can enable you to bet-ter understand this common language and help to maintain higher quality at lower cost.


The all around test symbol is used when the inspection is to be performed completely around a welded joint.



This multiple reference line shows a single V- groove weld with melt through to be inspected on the arrow side with a combination of visual and radiographic testing methods. Visual inspection is performed on the other side. Inspection details are located in procedure T-28.


Knowledge of the testing methods, procedures, and the symbol elements, can enable you to better understand this common language and help to maintain higher quality at lower cost.

MT(4)

RT + PTRT

1

2

3

T

( (

( (Oth

erAr

row

Oth

er

side

sBo

th

side

Basic testing symbolArrow

Test-all-aroundsymbol

Test in field

Length of sectionto be tested

(N)

Number of tests

Reference line

Tail

Specificationor other reference

L

5

VT + RTVT

T28


The all around test symbol is used when the inspection is to be performed completely around a welded joint.



This multiple reference line shows a single V- groove weld with melt through to be inspected on the arrow side with a combination of visual and radiographic testing methods. Visual inspection is performed on the other side. Inspection details are located in procedure T-28.


Knowledge of the testing methods, procedures, and the symbol elements, can enable you to better understand this common language and help to maintain higher quality at lower cost.

MT(4)

RT + PTRT

1

2

3

T

( (

( (Oth

erAr

row

Oth

er

side

sBo

th

side

Basic testing symbolArrow

Test-all-aroundsymbol

Test in field

Length of sectionto be tested

(N)

Number of tests

Reference line

Tail

Specificationor other reference

L

5

VT + RTVT

T28


TOPIC 1

REVIEW QUESTIONS

1. Define the purpose of nondestructive testing:

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

2. Where are nondestructive symbols placed?

_______________________________________________________________________________________

_______________________________________________________________________________________

3. List the common methods of nondestructive testing:

_______________________________________________________________________________________

_______________________________________________________________________________________

4. How long should the reference line of a nondestructive test symbol be?

_______________________________________________________________________________________

_______________________________________________________________________________________

5. An arrow is used to direct the information to:

_______________________________________________________________________________________

_______________________________________________________________________________________

6. The side of the joint the arrow points to is called the:

_______________________________________________________________________________________

_______________________________________________________________________________________


TOPIC 2

PRINCIPLES OF VISUAL TESTINGOBJECTIVE

To be able to identify the basic principles and applications of visual testing.

INTRODUCTION

Visual testing is the most popular and widely used nondestructive testing method. It consists of examining weld and overall weldments and comparing the evaluation to a set of standards.

When correctly applied, it is an effective method of quality control insuring conformance to a procedure and allowing errors to be corrected. This leads to production of a higher quality weldment at reduced costs.

Visual inspection practice requires the inspector to be familiar with all duties which apply to inspection, such as: • Learning to read blueprints • Having a knowledge of welding • Processes specification • Procedures and workmanship standards

The inspector must be capable of making: • Responsible judgments • Accurately recording data • Writing concise reports

Even though visual testing is the simplest methodof performing inspections, detailed written proceduresare needed to ensure proper application of the inspection.

7


PREWELD INSPECTION

To perform preweld inspection, an inspector be-comes familiar with all aspects of the job, such as:

• Material specification• Bill of materials• Welding procedures

When completely familiar with all the written de-tails, the inspector compares the dimensions of all the parts, checking dimensions to engineering drawings, and verifying tolerances of parts to en-sure proper final fit-up of the weldment.

The inspector examines the joint preparation and surface conditions of the materials for proper cleaning and lack of flaws. Poor fit-up, contaminat-ed base metal surfaces, improper equipment, and incorrect settings can lead to weld discontinuities or defects.

If backing is specified, it should be in accordance with the job specifications and be correctly and securely fastened. The tack welds become part of the finished weld and should meet the same soundness requirements.

Preweld inspection should include examining the equipment to insure it is in proper operating condition.

8


IN-PROCESS VISUAL INSPECTION

In-process welding begins with: • Verifying specified procedure • Observing welds during production • Deleting problems before completion of

welds • Observing welder skill • Verifying proper interpass temperatures • Assuring interpass cleaning requirements

are met • Comparing each pass or layer to a sample

workmanship standard

VISUAL TESTING OF FINISHEDWELDS

The inspector should compare the finished welds or weldments to the engineering drawings or specifications. This assures: • Proper part dimensions • Weld size • Weld location • The correct amount of welds on the weldment

Accuracy of the measurement is more importantthan the method of measuring. A good-lookingweld could be rejected if it is not the correct size.

Tools, such as high-low gage, fllet weld gage, or a scale can be used to measure correct dimensions.

Another part of post-weld inspection is the exami-nation of the weld surface. Common discontinui-ties visible to the surface area are: • Cracks • Porosity • Overlap • Arc strikes • Undercut • Spatter


Each of these problems has allowable limits described in the applicable code or inspection procedure.

After welding, the weldment may also reveal base metal defects such as delamination, cracking, or excessive distortion, which should be clearly marked for repair.

Documentation of visual testing begins once all aspects of before, during, and after welding inspection has taken place. This consists of the inspector evaluating the results to decide whether the welds or weldments meet the prescribed specification.

The inspector must make reports of every detail and keep complete records. Generally, any items which do not meet the requirements are noted and described. Any repairs made during production should be reported.

Good record keeping is essential. Whenever such detailed records are required, they are normally signed or certified by the fabricator, and copies are sent to all persons entitled to receive them.

10


Visual inspection is an invaluable quality control technique. Caution must be taken before drawing conclusions.

Welds with good surfaces are often good quality, but surface appearances will not prove careful workmanship took place.

To be reasonably sure of weld quality, all phases of visual inspection must be accomplished.


TOPIC 2

REVIEW QUESTIONS

1. The visual inspector must be capable of: (list three)

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

2. To perform “preweld inspection” the inspector must be familiar with: (list three)

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

3. List four things an inspector must check for when performing “in-process” visual inspection.

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

4. List four things the inspector should check on the finished welds or weldments.

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

5. Any items not meeting the test requirements are:

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________


TOPIC 3

PRINCIPLES OF PENETRANT TESTINGOBJECTIVE

To identify the basic principles and applications of penetrant testing.

INTRODUCTION

Penetrant testing is a highly sensitive method used for detecting discontinuities which are less likely to be detected by visual inspection. A flaw such as a fine crack open to the surface could go undetected during visual examination, but would be exposed with the proper application of the penetrant test.

A unique characteristic of penetrant testing is its capillary action. It is the ability of a liquid to redistribute itself into or between closely fitted surfaces. This allows a flaw or discontinuity to be detected.

Liquid penetrant has certain limitations. Generally, it cannot be used on materials with very porous or highly absorbent surfaces. These materials could likely give false indications.

The two basic types of liquid penetrant testing are: • Fluorescent • Visible dye

Both types have several variations, but share the same basic procedures. They are the application of a liquid penetrant, the removal of the excessive penetrant, and the application of a developer to draw penetrant from any openings in the surface.


The main concept of both types of penetrant is to read the contrasting colors. For example, when fluorescent penetrant is applied to a surface containing a defect or discontinuity, the solid surface will appear as a deep violet. The flaw will show up as a yellow-green glow under an ultraviolet light. This is the most sensitive method.

Visible dye penetrant appears as a bright indication on a white background. It is easy to apply and is performed under normal lighting conditions.

The surface should be cleaned before application of the penetrant. There are several methods of cleaning. Precaution should be practiced when performing these cleaning operations because they involve chemicals. They may be highly flammable or toxic if inhaled.

Some cleaning methods such as grinding, chipping, machining, or shot blasting can prevent parts from being accurately inspected because discontinuities can be hidden by these procedures.


The penetrant is applied after the proper cleaning procedures have been completed. It can be applied by dipping, brushing, or spraying the area to be tested. The most portable method is by pressurized spray cans.

WATER WASHABLE PENETRANT is a dye placed in a water-based solution. For nonporous materials, it provides the lowest sensitivity because of the ease of penetrant washout of shallow openings.

POST EMULSIFIABLE PENETRANT is a dye placed in an oil-based solution. The post emulsifiable variation needs an application of an emulsifier to chemically break down the oil base of the excessive penetrant to render it water washable. For shallow surface openings, it allows for greater sensitivity because the penetrant remains in the openings as the emulsifier is washed away.

SOLVENT REMOVABLE PENETRANT remains the most popular. It is usually applied by a spray can to the inspection surface. Then, after a specified time, known as the dwell time, it is removed from the surface with a solvent on a cleaning cloth, leaving the penetrant trapped below the surface intact. When performed correctly, it can reveal ultra-fine openings only a few micro-inches in size.


APPLY VISIBLE DYE PENETRANT

Step 1

Penetrant is applied to a properly cleaned surface by brushing, dipping, or spraying. The method of application is based on the amount and size of the part being inspected

Step 2

Allow sufficient dwell time so the penetrant can enter any openings. Dwell time is based on the type of material and the degree of accuracy required. Longer time allows penetrant into smaller openings. Refer to the testing procedure or manufacturer’s recommendation for dwell time (usually 5 minutes to several hours).

Step 3

Remove the excess penetrant by the appropriate means. When using water washable penetrant, rinse excess with a spray of water. Water temperature and angle of spray should be specified in a written test procedure. This avoids washing out of penetrant.

When using the post emulsifiable penetrant, emulsifier dwell time should be monitored so only excess penetrant is removed.

Step 4

After the surface is properly cleaned and dried, the developer is applied. The blotter action of the developer draws out the penetrant left in any openings in the test area.

Wet developers are powders suspended in liquid. They can be applied by dipping, brushing or spraying.

Dry developer is in powder form and is dusted on the test surface.

The pressurized spray can is the most portable method of applying penetrant, cleaner, and developer.


It is important to apply a smooth and even coating over the surface. Avoid heavy layers of developer. Thick coverings might obscure small indications.

Allow for correct dwell time. The developer generally takes about one-half the penetrant dwell time or whatever is recommended by the procedure.

Step 5

Examine and record test data drawn from the results of the penetrant test.

FLUORESCENT DYE PENETRANTINSPECTIONThis type of penetrant testing is done in the same way as visible dye penetrant, except a fluorescent light source is needed to read the results after the dwell time on the developer has elapsed.

GENERAL INFORMATION ONPENETRANT INSPECTION

When penetrant inspection is performed on multipass welds, the penetrant must be thoroughly cleaned between every pass. Welding over test solutions could create discontinuities.

Penetrant testing is an invaluable quality control technique. Like visual testing, care must be taken in drawing conclusions. The depth of a flaw cannot reasonably be measured. The inspector can only see penetrant indications that appear on the surface.

The larger the flaw and the longer the time allowed for penetrant bleed out, the larger the indication will appear.

In conclusion, remember that the proper application of this test is based on the steps discussed and by following the details of the written test procedures.


TOPIC 3

REVIEW QUESTIONS

1. List two surfaces liquid penetrant cannot be used on:

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

2. Dye placed in a water-based solution is called:

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

3. List three methods of cleaning to avoid when using penetrant testing:

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

4. What precautions must be followed when performing penetrant testing on multi-pass welds?

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________


INTRODUCTION

Magnetic particle testing is a highly sensitive method used for locating: • Cracks • Porosity • Slag inclusions • Other discontinuities in materials and

welds which can be magnetized

A simple bar magnet can simulate this testing method. When a small amount of magnetic particles are placed on a bar magnet, the particles are attracted only to the ends, which are referred to as the north and south poles.

If the magnet is notched, the magnetic lines of force pass through the air, creating new north and south poles on each side of the notch. Magnetic particles will be attracted to the new poles.

When a part being tested is magnetized, the part will act like a magnet. The magnetizing is done either by passing a current through it or by placing it in a strong magnetic field.

TOPIC 4

PRINCIPLES OF MAGNETIC PARTICLE TESTINGOBJECTIVE

To identify the basic principles and applications of magnetic particle testing.


A surface flaw or one slightly under the surface will attract and hold the magnetic particles in a pattern similar to the outline of the flaw. Magnetic particles can be applied by a dusting bag, atomizer, spray gun, or brush depending on whether a wet solution or dry powder is used. The particles in dry powder form must be applied evenly and excessive particles should be removed.

The wet solution provides a greater sensitivity for fine surface cracks because it consists of a much smaller particle size.

The dry powder remains more sensitive for flaws located below the surface.

This testing method is highly sensitive to discontinuities open to the surface and becomes less sensitive as the flaw depth increases. This method is sensitive to discontinuities down to one quarter inch below the surface.

WET SOLUTION FORSURFACE DISCONTINUITIES

DRY POWDER FORSUBSURFACE DISCONTINUITIES


The two types of magnetic fields used are circular magnetization and longitudinal magnetization. The size and shape of the weldment to be tested determines the type to be used.

Circular magnetization either passes a current through the piece to create a field, or creates a field in which a cylindrical part may be placed.

Longitudinal magnetization passes a current around the piece to create a field through the piece.

Circular magnetization is provided by using a set of prods. Walking the prods along the weld provides full coverage. Extreme caution should be practiced to insure that no arcing takes place between the test surface and the prods.

Longitudinal magnetization can be applied by a coil, a wrapped coil, or a yoke.

The yoke method is the most practical and widely used method. It is also the safest because no current comes in contact with the test surface eliminating arcing on the surface.


Magnetic particle testing uses the different characteristics of alternating current (AC) and direct current (DC). Equipment availability and degree of sensitivity required determine the type of current to be selected.

Alternating current provides the least sensitivity and magnetizes only the surface of the specimen, instead of the entire thickness of the part. Therefore, it should be limited to locating surface discontinuities.

Direct current penetrates throughout the thickness of the test specimen. It is the more sensitive of the two currents, and is recommended for use on welds when looking for subsurface discontinuities.

Visual evaluation is performed on all indications represented by accumulated particles on the surface.

The inspector evaluates the shape, sharpness, width and height of the particle pattern to determine the type of discontinuity or defect.


EVALUATION OF TEST RESULTS

Many factors should be taken into consideration in order to make precise judgments. Careful evaluation by a trained inspector is important. Decisions should be based on requirements specified through applicable specifications, procedures, or codes.

Further nondestructive testing, such as ultrasonic or radiographic may be required on a questionable indication.

REPORTS AND RECORDS

A concise record of the test results should be developed once all inspection has been completed. The clear transparent tape method uses clear tape placed over the indication. This allows the particle indication to be transferred to a test report form. The tape with the particles stuck to the back is placed over a simple sketch of the weldment.

A photograph of the tested surface may also be taken and attached to the final report.

CLEAN-UP OF TEST SURFACE

Demagnetizing a part may be necessary after all reports are finished and visual inspection has been performed. Some components may retain enough magnetization to attract metal shavings, causing excessive wear during service operations. It may also make it difficult to have quality welds.

CONCLUSION

Remember that proper application of this test is based on having qualified personnel to perform the testing procedures and carefully following the steps previously discussed.


TOPIC 4

REVIEW QUESTIONS

1. Name three discontinuities located by magnetic particle testing:

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

2. The ends of a bar magnet are called:

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

3. Which of the two types of electrical current (AC and DC) is the most sensitive?

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

4. Once the inspection has been completed, what should be done?

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________


TOPIC 5

PRINCIPLES OF ULTRASONIC TESTINGOBJECTIVE

To identify the basic principles and applications of ultrasonic testing.

INTRODUCTION

Ultrasonic testing is a highly sensitive method used for critical applications where quality is very important. This method is used for detecting:

• Cracks• Inclusions• Laminations• Other discontinuities in welds and various

other materials.

The inspection method is similar in principle to the sonar that military ships use to detect submarines. The ship’s sonar device transmits inaudible sound waves which reflect off the submarine and are received as signals on a screen.

Ultrasonic testing is performed in a similar manner. A device called a transducer is coupled with the part. It provides mechanical sound waves that are transmitted into the weld or base metal to detect flaws.

Transducers are made in a limitless variety of sizes and shapes. There are two common wave types, the straight beam and the angle beam. The test surface determines which transducer to use. The angle beam is used where the reinforcement would interfere. The angle beam can be placed to one side of the weld. It produces no back reflection. It is important in detecting discontinuities and flaws in pipe and tubing welds.


Couplants eliminate the air gap between the transducer and the specimen. A variety of liquids or pastes are used to insure proper transmission of the sound waves.

Sound waves travel into the specimen and, if interrupted or reflected, the transducer will receive an echo. The signal is sent to the ultrasonic unit where it is amplified and displayed on a screen.

While the display screens of early ultrasonic units used a cathode ray tube or CRT, more modern display screens are liquid crystal display or LCD. The display consists of a straight base line. When sound waves are interrupted, a break will appear on this base line. These breaks are referred to as vertical pips. An inspector interprets these pips to determine flaw depth and location.

The large pip appearing on the left is called the initial pulse. It represents the top surface of the specimen. Sound waves travel through and are reflected back to the transducer. The pip to the right is called the back reflection. It represents the bottom surface of the specimen.


The flaw depth and location can be displayed by any pip signals that appear between the initial pulse and back reflection. When a transducer is moved across a block with a pre-drilled hole at three inches in depth, all pips will appear at the three-inch mark on the scale.

The amplitude or height of the pip will give some indication of the size of the flaw. The higher the pip, the larger the reflected area of the flaw.

ADVANTAGES AND LIMITATIONS OFULTRASONIC TESTING

When compared with other nondestructive testing methods, some of its most outstanding features are accurately determining flaws, depths and location; it can be used on practically all nonporous metals or materials; and battery operated equipment makes it ideal for field applications.

The ultrasonic method of inspection requires a highly trained and skilled operator and it is difficult to contact test complex configurations and rough surfaces.


Equipment must be carefully calibrated prior to use. Calibration is normally done by using a standard reference block.

VARIATIONS

Immersion testing is another variation similar to the contact method. It is used quite often in testing of larger components. This test is conducted with both the transducer and component submerged in water. The water acts as a couplant allowing the signals to be transmitted into the part.

The aircraft industry uses this method for testing irregular or complex-shaped components.

CONCLUSION

Ultrasonic testing can be a very valuable tool for inspection of weldments provided the proper equipment is used, personnel are well-trained, and properly written tests are used.


1. List three discontinuities that can be detected by ultrasonic testing:

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

2. What are the two types of transducers?

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

3. When compared to other nondestructive testing methods, ultrasonic testing’s most outstanding feature is:

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

4. What are two disadvantages of ultrasonic testing?

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________


INTRODUCTION

Radiography is a sensitive method used for detecting flaws found in castings, welds, and various metal structures.

It is the most reliable form of nondestructive inspection, used extensively in the welding industry for critical situations, such as pipe welding and pressure vessels. This inspection method is similar to s-rays used by hospitals to detect a broken bone.

The x-ray machine sends invisible radiation through the body to a sheet of photographic film similar to photographic film used in cameras. Since bones absorb more x-rays than the surrounding flesh, they appear lighter on the developed film. Breaks show up darker because x-rays pass through them more easily.

TOPIC 6

PRINCIPLES OF RADIOGRAPHIC TESTINGOBJECTIVE

To identify the basic principles and applications of radiographic testing.


RADIOGRAPHIC TESTING

Radiographic inspection of welds is done with a similar x-ray generating machine or with a radioactive material called isotopes. These generate higher energy gamma rays.

It provides data for a more exacting evaluation and a permanent record in the form of a photographic image called a radiograph.

When radiation is passed through the item being tested, flaws appear lighter or darker than the surrounding metal.

A radiograph of a piece of metal with varying thicknesses will show up on the processed film as different shades of darkness. The thinner materials show up darker because it allows more energy to reach the film.

The amount of radiographic energy absorbed is based upon the material’s mass or density. For example, when steel and aluminum blocks of the same size are exposed to the same intensity of radiographic radiation, the aluminum will cause a darker image because it isn’t as dense as the steel and absorbs less energy.


An internal flaw, such as scale, trapped slag, or porosity will show up as a darker area on the film. When evaluating these indications, care must be exercised. False images can be caused by dirt, static electricity, or poor film processing, leading to the wrong conclusion.

Because of many variables such as exposure, intensity of radiation and film-processing techniques, a device called an image quality indicator (IQI), or penetrameter, is often used. It is placed on the object being radiographed, usually off to one side of the desired weld section.

There are two basic types if IQIs: hole type and wire type. Hole type penetrameters are usually rectangular pieces of material with the same radiograpic absorption as the material being tested. They vary in thickness and have a series of holes with different diameters. Wire type penetrameters use wires of varying diameters. With both types of IQIs, the sensitivity of a radiographic image is determined by which of the holes or wire diameters is visible.

A densitometer measures the film density. This indicates if the correct lightness or darkness of the film has been achieved in order to better detect flaws during interpretation.


The success of radiographic inspection depends greatly upon the training and experience of the operator.

SAFETY

Radiographic inspection must be performed by a qualified operator because of the potential dangers from radiation which can cause death or serious injury if safe practices are not followed.

Do not enter areas where x-ray or gamma ray sources are used without permission or supervision of an experienced radiographer.

For gamma ray methods, the radioactive isotopes are always on or emitting radiation. The must be stored and transported in special containers referred to as pigs. Isotopes should be used only by a qualified radiographer. Radiation detecting devices must be worn in order to detect radiation. Examples of such devices are survey meters and special film badges.

CONCLUSION

All aspects of radiography must be handled only by an experienced operator who knows the importance of safety and has the skill to interpret results and maintain proper records.


TOPIC 6

REVIEW QUESTIONS

1. Name two critical situations where radiographic testing is used:

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2. The amount of radiographic energy absorbed is based on:

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3. Name three things that can cause “false” images on a radiograph:

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4. The device used to obtain the proper exposure on a radiograph is called a:

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GLOSSARY OF WELDING TERMS

Acceptable weld - A weld that meets the applicable requirements.

Arc strike - A discontinuity resulting from an arc, consisting of any localized remelted metal, heat affected metal, or change in the surface profile of any metal object.

Backing - A material or device placed against the back side of the joint adjacent to the joint root, or at both sides of a joint in electroslag and electrogas welding, to support and shield molten weld metal. The material may be partially fused or remain unfused during welding and may be either metal or nonmetal.

Backing strip - Backing in the form of a strip.

Codes - A system of principles or rules.

Complete fusion - Fusion over the entire fusion faces and between all adjoining weld beads.99

Contaminants - Implies intrusion of or con-tact with dirt or foulness from an outside source, making the piece unfit or unclean.

Crack - A fracture type discontinuity char-acterized by a sharp tip and high ratio of length and width to opening displacement.

Crater - A depression in the weld face at the termination of a weld bead.

Defect - A discontinuity or discontinuities that, by nature or accumulated effect, ren-der a part or product unable to meet mini-mum applicable acceptance standards or specifications. The term designates reject-ability.

Discontinuity - An interruption of the typical structure of a material, such as a lack of ho-mogeneity in its mechanical, metallurgical, or physical characteristics. A discontinuity is not necessarily a defect.

Fillet weld - A weld of approximately trian-gular cross section joining two surfaces ap-proximately at right angles to each other in a lap joint, T-joint, or corner joint.

Interpass temperature - In a multipass weld, the temperature of the weld area be-tween weld passes.

Joint design - The shape, dimensions, and configuration of the joint.

Overlap - The protrusion of weld metal be-yond the weld toe or weld root.

Porosity - Cavity-type discontinuities formed by gas entrapment during solidification.

Procedure - The detailed elements of a pro-cess or method used to produce a specific result.

Slag inclusion - A discontinuity consisting of slag entrapped in weld metal or at the weld interface.

Welding procedure qualification record - A record of welding variables used to pro-duce an acceptable test weldment and the results of tests conducted on the weldment to qualify a welding procedure specification.

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Documents

Nondestructive Testing Methods Training Workbook