Determine Appropriate NDT Method

7/24/2019 Determine Appropriate NDT Method

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Note: The source of the technical material in this volume is the Professional

Engineering Development Program (PEDP) of Engineering Services.

Warning: The material contained in this document was developed for Saudi

Aramco and is intended for the exclusive use of Saudi Aramcos

employees. Any material contained in this document which is notalready in the public domain may not be copied, reproduced, sold, given,

or disclosed to third parties, or otherwise used in whole, or in part,

without the written permission of the Vice President, Engineering

Services, Saudi Aramco.

Chapter : Inspection For additional information on this subject, contact

File Reference: COE10902 J.L. Mckissack on 874-2514

Engineering EncyclopediaSaudi Aramco DeskTop Standards

Determining The Appropriate

Application Of Nondestructive Testing Methods


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Engineering Encyclopedia Inspection


Application of Nondestructive Tests Methods

Saudi Aramco DeskTop Standards

CONTENTS PAGES

EVALUATING THE CAPABILITIES AND LIMITATIONS OF

VISUAL WELD EXAMINATIONS .......................................................................... 1

Purpose ............................................................................................................ 1

Advantages ...................................................................................................... 1

Examination Requirements.............................................................................. 1

Examination Aids ............................................................................................ 2

Common Applications..................................................................................... 3

Limitations....................................................................................................... 3

Common Discontinuities ................................................................................. 3


LIQUID PENETRANT TESTING ............................................................................. 4

Purpose ............................................................................................................ 4

Advantages ...................................................................................................... 4

Principles of Liquid Penetrant Testing (PT).................................................... 4

Types of Penetrants ......................................................................................... 5

Types of Developers........................................................................................ 6

Common Applications..................................................................................... 6

Limitations....................................................................................................... 6

Common Discontinuities ................................................................................. 6

Nonrelevant Indications................................................................................... 6


MAGNETIC PARTICLE TESTING .......................................................................... 7

Purpose ............................................................................................................ 7

Advantages ...................................................................................................... 7

Principles of Magnetic Particle Testing (MT) ................................................. 7

Test Equipment................................................................................................ 9

Types of Magnetic Particles and Methods of Application ............................ 11

Common Applications................................................................................... 11


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Limitations..................................................................................................... 12

Common Discontinuities ............................................................................... 12

Nonrelevant Indications................................................................................. 12


ULTRASONIC TESTING ........................................................................................ 13

Purpose .......................................................................................................... 13

Advantages .................................................................................................... 13

Principles of Ultrasonic Testing (UT) ........................................................... 13

Test Equipment.............................................................................................. 15


Limitations..................................................................................................... 18




RADIOGRAPHIC TESTING ................................................................................... 19

Purpose .......................................................................................................... 19

Advantages .................................................................................................... 19

Principles of Radiographic Testing (RT)....................................................... 19

Sources of Radiation ..................................................................................... 22

Dangers of Radiation ..................................................................................... 23

Radiation Monitoring .................................................................................... 24

Radiation Safety ............................................................................................ 24

Variables of Exposure ................................................................................... 24

Film Quality .................................................................................................. 25


Limitations..................................................................................................... 27Common Discontinuities ............................................................................... 27



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ELECTROMAGNETIC TESTING........................................................................... 28

Purpose .......................................................................................................... 28

Advantages .................................................................................................... 28

Principles of Electromagnetic Testing (ET) .................................................. 28

Test Equipment.............................................................................................. 29


Limitations..................................................................................................... 30


SPECIALIZED TESTING METHODS .................................................................... 31

Infrared Inspection ........................................................................................ 31

Holiday Detector ........................................................................................... 31

Instrumented Scraper..................................................................................... 32

Acoustic Emission ......................................................................................... 32

WORK AID 1: CAPABILITIES AND LIMITATIONS OF VISUAL

WELD EXAMINATION .......................................................................................... 33

WORK AID 2: CAPABILITIES AND LIMITATIONS OF LIQUID

PENETRANT TESTING .......................................................................................... 34

WORK AID 3: CAPABILITIES AND LIMITATIONS OF MAGNETIC

PARTICLE TESTING .............................................................................................. 35

WORK AID 4: CAPABILITIES AND LIMITATIONS OF

ULTRASONIC TESTING ........................................................................................ 36


RADIOGRAPHIC TESTING ................................................................................... 37


ELECTROMAGNETIC TESTING........................................................................... 38

GLOSSARY ............................................................................................................. 39

ADDENDUM ........................................................................................................... 41


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Saudi Aramco DeskTop Standards 1

EVALUATING THE CAPABILITIES AND LIMITATIONS OF VISUAL WELD

EXAMINATIONS

Purpose

The purpose of a visual weld examination (VT) is to detect visible surface discontinuities on a

weldment. VT is the most frequently used method of examination, and welders and welding

inspectors continuously use VT during welding operations to make better quality welds. VT

often will identify problems during welding that can be repaired in process to prevent the

discovery of a discontinuity by a subsequent nondestructive test.

Advantages

VT is the quickest and most cost-effective method of NDT for use in the identification of a

surface discontinuity on a weld. Because the VT method of NDT requires the fewest

technical and interpretive skills, VT also is the simplest NDT method to learn. The use of VTthroughout the welding process significantly improves the success of subsequent NDT and

reduces the cost of repairs.

Examination Requirements

The tool that is used to perform VT is the human eye. The following are the requirements for

the performance of VT:

Visual Acuity - Personnel who perform VT must pass an annual eye

examination in accordance with industry standards. The eye examination

checks for conditions such as visual acuity, color blindness, and depthperception.

Distance - The examiners eye should be located within 24 inches and at an

angle of not less than 30 degrees to the surface of the weld that is being

examined to conduct a direct visual examination. Mirrors can be used to

improve the angle of vision.

Access - If the area to be examined is not directly accessible, an examination

aid can be used. Examination aids are covered later in this Module.

Lighting- A flashlight or other additional lighting should be used to sufficientlyilluminate the area that is to be examined. A minimum of 35 foot candles of

light should be available for normal visual weld examinations. When

performing VT for small indications, a minimum of 50 foot candles of light

should be available. If required by procedure, a light meter can be used to

determine the exact amount of illumination that is available.


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Examination Aids

Examination aids sometimes are used to facilitate visual examinations. The following are

examples of commonly used visual examination aids:

Mirrors

Portable Lighting

Flashlights

Light Meters

Straight Edges and Rulers

Magnifying Lenses

Boroscopes

Microscopes

Video Cameras

Weld Gages

When the use of examination aids (such as boroscopes) is necessary to perform remote

examinations, the image resolution must be at least equal to the image resolution that is

attainable by direct visual examination.

Several types of weld inspection gages are available to simplify the measurements of complex

weld configurations when conducting VTs. The following are the capabilities of the weld

inspection gages that are used at Saudi Aramco:

Cambridge Gage- This gage can measure undercut, weld reinforcement, bevel

angle, root opening, fillet weld size, and joint mismatch.

GAL Hi-Lo Gage- This gage can measure joint mismatch, root opening, and

weld reinforcement.

AWS Type Gage - This gage also can measure various sizes of standard fillet

welds.


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Common Applications

As was stated earlier, visual weld examination is the most frequently used method of NDT at

Saudi Aramco. The following are common applications for visual weld examinations:

To determine the size and length of fillet welds on structural members.

To inspect the weld joint fit-up including bevel angle, root opening, land, and

cleanliness of piping welds.

To inspect the proper fit-up of socket weld fittings on small diameter pipe.

To inspect in-process welds and completed welds prior to additional NDT.

Limitations

Because VT cannot detect subsurface discontinuities, the obvious limitation of VT is that the

discontinuity must be located on an exposed surface of the component or weld. Additionally,

VT only will identify discontinuities that are visible to the human eye; therefore, minute

discontinuities may not be detected.

Common Discontinuities

The following are the common discontinuities that can be detected during a visual

examination:

Cracks

Slag

Porosity

Undercut

Cold Lap

Arc Strikes

Refer to COE 109.01 for a description of the common discontinuities.


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EVALUATING THE CAPABILITIES AND LIMITATIONS OF LIQUID

PENETRANT TESTING

Purpose

The purpose of liquid penetrant testing (PT) is to detect discontinuities on the surface of non-

porous materials.

Advantages

Read the Introduction to Lesson 2 in the ASNT Manual. The introduction describes the

following major advantages of PT:

Good sensitivity

Inexpensive

Simple

Wide range of uses

Principles of Liquid Penetrant Testing (PT)

PT uses the principle of capillary action to detect discontinuities. When a liquid penetrant is

applied to the surface of a material, capillary action will cause the penetrant to enter any small

openings that exist on the surface of the material. After the excess penetrant is removed, a

developer is applied to the surface of the material to draw the absorbed penetrant back out of

the openings. If the application of the developer causes the penetrant to be drawn back out of

an opening, discontinuities are present on the surface of the material. Refer to the Penetrant

Inspection Principles section on page 2-2 of the ASNT Manual for a more detailed description

of the principles of PT. Figure 1 shows that PT can be broken down into the following basic

steps:

Clean the surface.

Apply the penetrant to the surface that is to be inspected.

Remove the excess penetrant.

Apply a developer.

Page 2-3 of the ASNT Manual explains that these basic steps can be expanded to include the

preparation of the inspection surface and the determination of the type of penetrant and

developer that is to be used. Preparation of the surface to be inspected is important because

dirt or contamination could mask surface discontinuities.


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The actual steps that Saudi Aramco personnel should follow to perform PT are located in

SAIP-04-P, Liquid Penetrant Examination of Welds and Components. Refer to the copy of

SAIP-04-P that is located in the Addendum for the actual steps.

Use Word 6.0c or later to

view Macintosh picture.

Figure 1. Principles of PT

Also, refer to the section of the ASNT Manual titled Liquid Penetrant Processing Cycle that

begins on page 2-9. This section provides additional information on the principles of PT.

Types of Penetrants

Penetrants are classified as color contrast (visible dye) or fluorescent. The color contrast(visible dye) penetrant can be seen with the unaided human eye; the fluorescent penetrants

require the use of a black light to make the fluorescent penetrant visible.

Refer to the Liquid Penetrant Materials section on page 2-5 of the ASNT Manual for a more

detailed description of the types of penetrants. This section also describes the classification of

penetrants in reference to the method of removal that is used. The following are the methods

of penetrant removal:

Water washable

Post-emulsifiable

Solvent removable

Saudi Aramco normally only uses the color contrast (visible dye) solvent removable

penetrants.


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Types of Developers

Saudi Aramco only uses dry aerosal developers. The type of developer that is used depends

on the type of penetrant that is used. Typically, the same family of penetrant material is used

throughout the inspection process. The use of penetrant materials from different families

requires special permission from the Saudi Aramco Inspection Department. If this permission

is not obtained, the PT may not be acceptable. Table 1-1 on page 9 of SAIP-04-P, which is

located in the Addendum, lists the families of penetrant materials that are used at Saudi

Aramco.

Common Applications

At Saudi Aramco, the most common use of PT is to check welds such as socket welds and

root passes on pressure vessels, storage tanks, and piping systems. PT also is the best method

for use in the identification of surface discontinuities on non-magnetic materials, such as

aluminum and stainless steel. PT also can be used on magnetic steels when magnetic particletesting cannot be performed. The Applications section that begins on page 2-17 of the ASNT

Manual provides additional information on the applications of PT.

Limitations

The major limitation of PT is that it cannot detect subsurface discontinuities. Because of this

limitation, PT is not a sufficient NDT for many critical weldments in which the volume of the

weld must be examined. PT also is not conducive to high temperature applications and

special penetrants and developers are required for even moderate temperature use. SAIP-04-P

only applies to penetrant tests that are performed on materials that have a maximum

temperature of 125oF. Because surface coatings block discontinuity openings, anotherlimitation of PT is that it cannot be performed on surfaces that are covered with paint or with

other coating materials. The lengthy PT dwell time, sometimes up to 45 minutes, can limit its

application. Refer to the Limitations section of the ASNT manual that begins on page 2-13

for more information on the limitation of PT.


Surface cracks, porosity, undercut, and cold laps are the most common discontinuities that are

detected by PT. Although these discontinuities are open to the surface, the size of the

discontinuity can be too small to allow detection by VT; therefore, PT is used. PT is more

sensitive than VT on small, tight imperfections.

Nonrelevant Indications

The paragraph on Liquid Penetrant, Nonrelevant Indications, on page 14-3 of the ASNT

Manual provides examples of common nonrelevant indications. The majority of nonrelevant

indications that are related to PT are the result of improper cleaning prior to the application of

the developer.


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EVALUATING THE CAPABILITIES AND LIMITATIONS OF MAGNETIC

PARTICLE TESTING

Purpose

The purpose of magnetic particle testing (MT) is to detect discontinuities that are open to the

surface or near the surface of ferromagnetic materials.

Ferromagnetic materials (e.g., iron, steel, and associated alloys) are those materials that can

be strongly magnetized. Paramagnetic materials (e.g., sodium metal) can be slightly

magnetized and diamagnetic materials (e.g., copper) cannot be magnetized.

Advantages

A major advantage of MT is that, for most applications at Saudi Aramco, MT uses portable

test equipment that is relatively simple to use. When compared to PT, MT also has thefollowing advantages:

MT is less labor intensive.

After the initial investment, MT is less expensive to perform.

MT can detect some subsurface defects.

MT has less post test clean-up.

Other advantages exist for the use of one MT method over another MT method for particular

applications. Table 3-2 that is on page 3-9 of the ASNT Manual summarizes the advantages

of the different methods that are used to perform MT.

Principles of Magnetic Particle Testing (MT)

Magnetic particle testing is based on the principle of magnetism. Magnetism is the ability of

one ferromagnetic material to attract other ferromagnetic materials. Magnetic fields exist

within and around a permanent magnet or around a conductor that carries an electric current.

These magnetic fields are made up of magnetic lines of force that are perpendicular to the

direction of the electric current flow. When a discontinuity exists in a ferromagnetic material,

the discontinuity results in a distortion in the magnetic lines of force and creates a leakage

field in which the magnetic testing particles are gathered. The visual gathering of magnetic

particles indicates that a discontinuity may exist in the material that is being tested.


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Figure 2 illustrates the following principles of MT:

An electric current is passed through a test object to create a magnetic field in

the test object (i.e., the test object is magnetized).

Magnetic particles are applied to the surface of the magnetized test object.

The test object is evaluated for gathered magnetic particles.



Figure 2. Principles of MT

For a more detailed explanation of the principles of MT, refer to pages 3-1 through 3-11 ofthe ASNT Manual.

The actual steps that Saudi Aramco personnel should follow to perform MT are located in

SAIP-05-P, Magnetic Particle Examination of Welds and Components. Refer to the copy of

SAIP-05-P that is located in the Addendum for the actual steps.


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Test Equipment

Various kinds of test equipment are used to establish the magnetic field in the test object.

Figure 3 illustrates the portable yokes and prods that are most commonly used during

fabrication and construction of petroleum extraction and refining facilities. Large stationary

equipment is mostly used in manufacturing and production facilities because these facilities

require continuous MT.

The following methods are used at Saudi Aramco to establish the magnetic field:

Indirect Method- This method uses an electromagnetic yoke to pass a magnetic

field through the test object. The test object completes a magnetic circuit with

the yoke that results in the establishment of a magnetic field in the test object.

Yokes can use AC, Half Wave (HW) DC, or DC current to establish magnetic

fields.

Direct Method - This method uses prods to pass electrical current through the

test object. The current that passes through the test object establishes the

magnetic field. Prods also can use AC, HWDC, or DC current to establish

magnetic fields.


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Figure 3. Yoke and Prod Methods


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The use of AC current results in a magnetic field that is fairly shallow in the test material; the

use of DC current provides a deeper magnetic field. However, DC current also has more of a

tendency to permanently magnetize the test objects.

For additional information on test equipment, such as large stationary and demagnetizing

equipment, refer to the Equipment for Magnetic Particle Testing section that is on pages 3-13

through 3-18 of the ASNT Manual. Also, refer to pages 4-1 through 4-16 of Lesson 4 of the

ASNT Manual.

Types of Magnetic Particles and Methods of Application

Magnetic particles can be suspended in liquid or they can be in the form of a dry powder.

The method of application depends on the test situation. The following methods can be used:

The wet method uses magnetic particles that are suspended in a liquid such as

oil or water. The magnetic particles may be fluorescent or non-fluorescent.The mixture is applied by allowing it to flow over the test object.

The dry method uses magnetic particles in the form of a dry powder. The

magnetic particles are non-fluorescent, but the particles are available in

different colors. The particles are applied by allowing them to lightly settle on

the surface of the test object. The particles must be applied lightly and evenly

to the surface.

Stress corrosion cracking in pressure vessels consists of micro cracks that are not visible to

the human eye and which are usually undetectable using dry magnetic particle testing.

However, through use of wet fluorescent MT, the stress corrosion cracking can be reliablydetected.

The wet method of magnetic particle testing generally provides a more sensitive inspection

because the wet method is able to detect minute discontinuities. For additional information on

the types of magnetic particles, refer to the Methods, Materials, and Sensitivities section that

is on pages 3-11 through 3-13 of the ASNT Manual.

Common Applications

Magnetic particle testing is used to inspect carbon steel weldments, socket welds on piping,

weld bevel preps, structural fillet welds, valve bodies, shafts of rotating equipment, pumpimpellers, machined parts, vessels, and storage tanks. The use of MT is particularly important

for vessels and tanks that are susceptible to sulfide stress and hydrogen induced cracking.

For additional information on the common applications of MT, refer to the Typical Uses in

Industry section of the ASNT Manual that begins on page 4-16.


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Limitations

The major limitations of MT are that it can only be used to find defects that are near the

surface of ferromagnetic materials, and that MT can magnetize the component that is under

test. MT will not find deep-seated discontinuities; however, this limitation is primarily based

on whether AC or DC current is used and the type of magnetic particle that is used.


The most common discontinuities that are found by MT are surface or near-surface cracks,

porosity, undercut, and cold lap.


For information on the common nonrelevant indications, refer to the Interpretation of Results

section that is on pages 4-18 through 4-20 of the ASNT Manual and to the paragraphs onMagnetic Particle, Nonrelevant Indications that are on pages 14-2 and 14-3 of the ASNT

Manual.


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EVALUATING THE CAPABILITIES AND LIMITATIONS OF ULTRASONIC

TESTING

Purpose

The following are the primary purposes of ultrasonic testing (UT):

To detect surface and subsurface discontinuities in metallic materials

To measure the thickness of metallic materials.

UT, unlike the previously discussed methods of NDT, can be used to inspect the entire

volume of the test object.

Advantages

The following advantages of UT make it a widely used method of testing for defects in a

variety of situations:

UT is extremely sensitive.

UT displays the size and location of discontinuities.

UT can be used on almost any type of metallic material.

UT can be used on all but the very complex weldments.

UT only requires access to one side of the test object.

UT can be performed through use of portable equipment.

UT is safe to perform.

For a more detailed discussion of the advantages of UT, refer to the Introduction on pages 5-1

and 5-2 of the ASNT Manual.

Principles of Ultrasonic Testing (UT)

Figure 4 illustrates the basic principles of UT. UT is a more complex method of NDT than isVT, PT, or MT. UT uses a pulse generator to generate an electrical signal that is supplied to a

transducer. The transducer uses this electrical signal to generate and emit ultrasonic energy.

The ultrasonic energy causes mechanical vibrations (wave propagation) that are in the form of

a sound wave that travels through a test object. After the wave travels through the test object,

the transducer receives the return signal and sends it through a process circuit. The output of

the process circuit is sent to a cathode ray tube. If the wave encounters a discontinuity in the

test object, the return signal will reflect the disruption of the wave.


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The ability of the ultrasonic system to detect small defects (e.g., the sensitivity) is a function

of the wavelength of the emitted ultrasonic energy.

When ultrasonic energy (sound wave) is transferred into a material, the distance that the wave

travels can be determined through use of an oscilloscope. If the wave does not encounter a

discontinuity, only the initial and return signals appear on the oscilloscope screen. However,

if the wave encounters a discontinuity, part of this energy is reflected back and three

indications (initial signal, return signal, and reflected signal) will appear on the oscilloscope

screen. A qualified inspector can determine the approximate size and the location of the

discontinuity from these indications.



Figure 4. Principles of UT


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For a more detailed explanation of the principles of UT, refer to the following sections of

Lesson 5 of the ASNT Manual:

Principles of Wave Propagation (pages 5-2 through 5-4)

Properties of Waves (pages 5-4 through 5-9)

Attenuation (pages 5-9 through 5-12)

Generation and Reception of Ultrasound (pages 5-12 through 5-19)

Test Equipment

The following are the basic test equipment components that are used to perform UT:

Transducer - This device is used to convert energy from one form to anotherform. As illustrated in Figure 5, UT typically uses piezoelectric devices that

deliver straight or angle ultrasonic beams to detect discontinuities in test

objects. These devices (transducers) are used both to transmit and receive

ultrasonic signals. For additional information on transducers, refer to the

Transducers section on pages 6-1 through 6-12 of the ASNT Manual.

Couplant- A couplant is a medium that is used to facilitate the transmission of

ultrasonic energy between the transducer and the test object. For additional

information on couplants, refer to the Couplants section on page 6-12 of the

ASNT Manual.

Pulse Generator and Oscilloscope- The pulse generator is used to generate the

input electrical signal to the transducer and the oscilloscope is used to display

the return signal on a cathode ray tube (CRT). For additional information on

pulse generators and oscilloscopes, refer to the Generator/Indicator Equipment

section on pages 6-12 through 6-18 of the ASNT Manual.


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Figure 5. Straight and Angle Beam Transducers


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Other important pieces of test equipment are calibration blocks and reference blocks.

Calibration and reference blocks are used to help ensure that the test equipment is properly

operating. Because the operation of the test equipment can directly affect the inspectors

interpretation of the test results, proper operation of the test equipment is extremely important.

For a more detailed discussion of calibration and reference blocks, refer to the Calibration and

Standard Reference Blocks section that is on pages 6-18 through 6-21 of the ASNT Manual.

Also refer to the Calibration and Standards section that is on page 7-20 of the ASNT Manual.

Proper operation of the equipment is very important because it directly affects an inspectors

interpretation of test results.

The specific test equipment that is needed to perform UT is dependent on the UT test method.

The two test methods are contact and immersion. The test method that is used is dependent

on the test situation and the material characteristics of the test object. For additional

information on the test methods, refer to the General Considerations in the Selection of

Method section that is on pages 7-1 through 7-5 of the ASNT Manual.

Contact Testing is the test method that is widely used at Saudi Aramco. Contact testing can

provide different types of CRT display patterns that are known as scans. The type of CRT

display pattern that is used is dependent on the application. The following types of CRT

display patterns can be used:

A Scan - An A scan is the usual type of CRT display that is used in

ultrasonic material testing. A scans indicate the depth of a discontinuity.

B Scan - B scans provide a view of an object in a plane that is

perpendicular to the direction of movement of the transducer signal and the

surface of the test piece. The B scan also can indicate the depth of a

discontinuity. The B scans are typically used in medical applications. A

photograph of the CRT display screen is often taken for record purposes.

C Scan- C scans provide a plan view of an object. A plan view is a view

through the object from the inspection surface. The CRT display of a C scan

also can be photographed.

Additionally, hand held ultrasonic thickness gages also use the contact testing method to

provide spot thickness determination. Ultrasonic thickness gages provide a digital display of

the material thickness and are capable of storing large quantities of thickness data.

Immersion testing requires the use of special scanning equipment, and this method is not

currently used at Saudi Aramco. Immersion testing is primarily used by manufacturers to

examine production parts. Immersion testing also is used by NDT organizations to examine

and map test parts and specimens.


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Common Applications

A major application of UT at Saudi Aramco is thickness gaging for corrosion detection. UT

also is used to inspect the integrity of weld bevel prep areas, full penetration butt welds, and

plate material. For more information on the applications of UT, refer to the Specific

Applications section that is on pages 7-11 through 7-20 of the ASNT Manual.

Limitations

Because of the many variations of testing methods, UT is the least limited method of NDT.

However, the following limitations do exist:

UT can only be performed by highly skilled technicians.

UT cannot be used on very rough surfaces without surface preparation.

UT cannot always be used on course grain materials (castings).

UT cannot detect discontinuities that are parallel to the ultrasonic beam.

UT cannot be used to check some weld joint configurations (i.e., socket welds).

For additional information on the limitations of UT, refer to the General Considerations in

Selection of Method section that is on pages 7-1 through 7-5 of the ASNT Manual.


UT can be used to detect both surface and subsurface discontinuities. All of the base metaland weld discontinuities that were presented in Module COE 109.01 are commonly detected

through use of UT. These discontinuities include cracks, porosity, undercut, incomplete

penetration, lack of fusion, slag, and root concavity or convexity. Another common

discontinuity that is identified through use of UT is an unacceptable decrease in wall

thickness that is due to erosion or corrosion.


The paragraph on Ultrasonic, Nonrelevant Indications on page 14-3 of the ASNT manual

provides examples of common nonrelevant indications. The majority of nonrelevant

indications that are discovered through use of UT are related to component or weldconfigurations that are actually different than those indications that are expected by the UT

technician.


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EVALUATING THE CAPABILITIES AND LIMITATIONS OF RADIOGRAPHIC

TESTING

Purpose

The purpose of radiographic testing (RT) is to detect surface and subsurface discontinuities in

various materials. SAGI 448.010, Radiographic Examination, contains the actual steps that

Saudi Aramco personnel should follow to perform radiographic examinations. Refer to the

copy of SAGI 448.010 that is located in the Addendum for the actual steps.

Advantages

The following are the advantages of RT, and these advantages are similar to the advantages of

UT:

RT is extremely sensitive.

RT can identify both surface and subsurface discontinuities.

RT can be used on a wide variety of materials.

RT provides a permanent record that shows the size and location of

discontinuities.

RT can be used through use of portable equipment.

Principles of Radiographic Testing (RT)

Figure 6 illustrates the basic principles of RT. RT uses radioactive sources (x-ray, gamma

ray, or neutron beams) to emit photons that penetrate the test object. The energy and

wavelength characteristics of these photons allow them to be used to penetrate any material.

The physical characteristics of the test object determines the amount of the energy beam that

passes through the material. Any changes in material thickness or density will affect the

amount of energy that passes through the test object. The portion of the photons that pass

through the test object are used to expose a special type of film. The image that is produced

on the film will show any changes in the density of the areas that are exposed to the

penetrating radiation. For more detailed information on the principles of RT, refer to the

Principles of Radiography section that is on pages 8-2 and 8-3 of the ASNT Manual.


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Figure 6. Principles of RT

Figure 6 shows an example of the double wall radiographic technique that is used to

examine piping or small pressure vessel welds. Figure 7 also shows examples of panoramic

and elliptical radiographic techniques that also are used on piping welds. Figure 7 points

out the relative location of the radiographic source for each technique. Note that the

panoramic technique requires that the radiation source be placed inside the pipe or vessel.


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Figure 7. Radiographic Techniques


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Sources of Radiation

Radiation is the energy that is given off due to a nuclear reaction at the atomic level. This

energy may be in the form of an electromagnetic wave or a particulate. Photons, which are

small packets of energy that are caused by radioactive decay, display both wave and particle

characteristics. Figure 8 shows the following sources of radiation for RT that is performed at

Saudi Aramco:

X-Ray Machine

Cobalt - 60

Iridium - 192

Figure 8. Sources of Radiation for RT


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The following are the types of electromagnetic radiation that are used to perform radiography

at Saudi Aramco:

X-rays

Gamma rays

X-rays are generated in electronic X-ray tubes of the linear accelerator type. The tubes may

be portable to allow performance of radiographic examinations in the field. For more detailed

information on the production and characteristics of X-rays, refer to pages 8-4 through 8-10

of the ASNT Manual.

The sources of gamma rays are the disintegrating nuclei of radioactive isotopes. The

following are the radioactive isotopes that Saudi Aramco uses to produce gamma rays:

Iridium-192 (Ir-192)

Cobalt-60 (Co-60)

For more detailed information on gamma rays, refer to pages 8-10 through 8-12 of the ASNT

Manual.

Neutron radiography uses particulate radiation. Because neutron radiography has few current

uses, it will not be discussed in detail. For more information on neutron sources, refer to

pages 8-12 and 8-13 of the ASNT Manual.

Dangers of Radiation

The penetrating nature of radiographic rays presents a danger to people. These rays pass

through the body in the same way in which they pass through the test object and, if the

exposure is excessive, the rays can cause permanent damage to the human body. A

significant danger exists when sources of radiation are not properly handled. This danger is

magnified by the fact that there are no immediate signs that tell people that they are being

exposed to harmful amounts of radiation. Overexposure to radiation may cause radiation

sickness, permanent damage to vital body organs or, in severe cases, death.

Because of these dangers, special precautions and safety procedures must be strictly followed

by personnel who handle radiation sources. SAGI 9.100, Ionizing Radiation Protection, sets

the general guidelines that all Saudi Aramco personnel must follow to protect themselves

against ionizing radiation. This instruction is used by personnel who are involved in all

aspects of storage, handling, and use of radioactive sources.

SAIP-08, theIndustrial Radiation Safety Manual, provides more specific guidelines for Saudi

Aramco personnel who use radioactive sources to perform RT.


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Radiation Monitoring

Because the senses of the human body cannot detect the presence of radiation, special

monitoring equipment must be used. Section 4.09 of SAIP-08, Personnel Monitoring

Equipment, identifies devices that are used to measure the actual exposure of personnel during

the performance of RT. These devices include film badges, dosimeters, and radiation survey

meters. Section 5.0 of SAIP-08, Radiation Monitoring Equipment, identifies the devices that

are used to perform radiation surveys. A radiation survey meter is used to check radiation

levels in a given area. This information is needed to determine personnel stay times and

shielding requirements.

Radiation Safety

The following are the basic radiation safety techniques that are used to reduce personnel

exposure to ionizing radiation:

Time- As the amount of time that is spent near a radiation source decreases, the

exposure to the radiation decreases.

Distance - As the distance from a radiation source increases, the exposure to

the radiation decreases.

Shielding- As the amount of shielding that is between the radiation source and

personnel increases, the amount of exposure decreases.

For more detailed information on radiation safety, refer to the Radiation Safety section that is

on pages 9-7 through 9-21 of the ASNT Manual.

Variables of Exposure

In this section, the term exposure refers to exposing the test object to the radiation source.

Many variables must be considered to ensure that the exposure produces a usable image. The

radiograph is not acceptable as proof that the test object is free of defects unless it is of good

quality. Every effort must be made to achieve the highest quality image so that all of the

discontinuities can be identified. The following are the most important factors that must be

considered in the achievement of the highest quality image:

The type, position, and intensity of the radiation source.

The thickness, density, and configuration of the test object.

The type and position of the film.

Film process time and chemical temperatures.


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Basically, the image that is produced is a shadow that is created as the radiation passes

through the test object. The Geometry Exposure section that is on pages 8-13 and 8-14 of the

ASNT Manual describes how shadow formation applies to RT. The Essential Variables of

Exposure section that is on pages 8-15 through 8-20 of the ASNT Manual describes how

variations in the source, test object, and the film affect exposure. Refer to these sections of

the ASNT Manual for more detailed information on the variables of exposure.

Film Quality

A penetrameter is used to check the quality of the image that is produced on the radiographic

film. A penetrameter is typically a wire or block that is made from the same material as the

test object. The dimensions of the penetrameter are critical because the dimensions represent

the thickness of the object that is being examined. The penetrameter is used to confirm the

sensitivity of the radiograph. The penetrameter is not used to determine the size of

discontinuities. The penetrameter image is a permanent record that proves that the technique

that is used to perform the RT produced a good quality radiograph. ASTM wire type

penetrameters and hole type penetrameters are commonly used at Saudi Aramco. Typical

placement of a hole type penetrameter is shown in Figure 9. This figure shows a

penetrameter that is 0.060" thick that is positioned along the side of a butt weld with the 1T

(0.060" diameter), 2T (0.120" diameter), and the 4T (0.240" diameter) holes identified. For

more detailed information on penetrameters, refer to the Elements of Radiographic

Interpretation section that is on pages 9-21 through 9-23 of the ASNT Manual.

The quality of the radiographic technique is evaluated through examination of the

radiographic contrast and definition of the image that is produced on the film. Radiographic

contrast is defined as the density differences from one area on the film to another area on the

film. Contrast is necessary to make the details that are within the image area visible.

Radiographic definition refers to the sharpness of the outline of the image that is on the film.

Two methods can be used to improve radiographic contrast and definition. The first method

is the use of radiographic screens that intensify the radiation that exposes the film. The

second method is the chemical amplification of the film during the development process that

can improve the sensitivity of underexposed film.

For more detailed information on the use of radiographic screens, refer to the Screens Used in

Radiography section that is on pages 8-20 through 8-28 of the ASNT Manual.


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Figure 9. Typical Penetrameter Placement

For more detailed information on the types and characteristics of the various films that are

used to perform RT, refer to the Recording of Exposure section that is on pages 8-36 through

8-42 of the ASNT Manual.

For more detailed information on film development, refer to the Film Processing

Fundamentals section that is on pages 8-42 through 8-47 on the ASNT Manual.

For a summary of all the variables of exposure, refer to the Choice of Factors in Practical

Radiography section that is on pages 9-1 through 9-7 of the ASNT Manual.


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Common Applications

The major application of RT at Saudi Aramco is to examine critical full penetration welds in

piping and pressure vessels for discontinuities. Critical welds require a high degree of

confidence because of the potential hazards that are associated with their failure. RT is an

effective way to achieve this confidence. The governing codes and standards provide specific

requirements for the performance of RT.

In general, RT and UT are used for similar applications. At Saudi Aramco, RT also is used to

evaluate the effects of erosion and corrosion on component and piping wall thickness.

Limitations

The following are the major limitations for the use of RT:

RT only can be performed by highly skilled technicians.

RT cannot detect discontinuities that are perpendicular to the rays.

RT exposes personnel who are in the area to radiation.

The following conditions may limit the use of RT:

Weld joint geometry.

Accessibility and geometry of radiographic technique.

Because RT that is performed on piping or vessels that contain fluid does not produceacceptable results, another limitation is that piping systems and vessels must be drained prior

to the performance of RT. Also access is needed to both sides of object being radiographed

(source on one side, film on the other).


RT is used to find both surface and subsurface discontinuities. All of the base metal and weld

discontinuities that were presented in Module COE 109.01 are commonly detected through

use of RT. These discontinuities include cracks, porosity, undercut, incomplete penetration,

lack of fusion, slag, tungsten inclusions, and root concavity and convexity. For more

information on discontinuities, refer to pages 9-24 through 9-36 of the ASNT Manual.


The paragraph on Radiography, Nonrelevant Indications that is on page 14-3 of the ASNT

Manual provides an explanation of common nonrelevant indications. The typical nonrelevant

indications are film scratches and water marks.


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ELECTROMAGNETIC TESTING

Purpose

The purpose of electromagnetic testing (ET) is to detect surface and limited subsurface

discontinuities in various materials or to measure material properties (such as coating

thickness) by checking for changes in eddy currents or magnetic fields that are generated in

the test object.

Advantages

The major advantage of ET is that the testing methods can be specialized to cover a wide

range of applications. For example, magnetic flux leakage techniques are extensively used on

ferromagnetic materials; eddy current testing can be used on any material that conducts

electricity. Other advantages are as follows:

ET can produce indications that are proportional to the size of the discontinuity.

ET can be automated to perform inspections at high speeds and low cost (this

advantage applies to production lines and is not applicable at Saudi Aramco).

Principles of Electromagnetic Testing (ET)

The basic principles of MT provide a good background for learning the principles of ET.

However, those principles will be expanded because of the methods that are used to evaluate

the indications that are obtained through ET.

Electromagnetic induction is the basis for the operation of electric generators, motors,

transformers, and electromagnetic testing. Electromagnetic induction is the ability to induce a

current into an adjacent object. Figure 10 shows how ET uses alternating current that is

passed through a test coil to induce current into a test object. These induced currents are

closed loop currents and they are known as eddy currents. Eddy currents are perpendicular

to the magnetic fields. ET measures the changes in the impedance of the test coil that results

from the changes in the flow of eddy currents. The changes in the flow of eddy currents are

caused by discontinuities in the test object. Eddy currents cannot be generated with an input

of direct current.

A significant factor in the ability to perform ET is the magnetic permeability of the test object.

Magnetic permeability is a measure of the magnetic tendency (ferromagnetic, paramagnetic,

or diamagnetic) of a material and, because eddy currents are induced by a magnetic field, the

magnetic permeability of the test material will have a strong influence on the eddy current

response.


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Figure 10. Principles of ET

The Fundamentals of Electromagnetic Theory section that is on pages 10-2 through 10-9 of

the ASNT Manual further describes the principles of ET. For additional information, refer to

the Test Coils section that is on pages 10-9 and 10-10 of the ASNT Manual and to the

Instrumentation section that is on pages 10-10 through 10-15 of the ASNT Manual.

Test Equipment

The specific test equipment that is needed to perform ET depends on the specific test method;

however, all ET requires some type of oscillator (to generate ac current), a coil, an impedance

detector, and a display unit. ET equipment comes in a variety of shapes, sizes, and

arrangements that depend on the requirements of the specific test. Figures 10:13 and 10:14

that are on page 10-12 of the ASNT Manual show several examples of the coils and

instruments that are used to perform ET.


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Common Applications

ET is a very specialized method of NDT and is commonly used at Saudi Aramco for the

following reasons:

To inspect heat exchanger tubes.

To perform magnetic flux leakage testing of ferromagnetic materials.

To check dry film coating thickness of lined pipes.

To check material thicknesses.

For more detailed information on the common applications, refer to Lesson 11 of the ASNT

Manual.

Limitations

The major limitation of ET is that it will only find discontinuities that are within

approximately one half inch of the surface. The equipment that is required to perform ET is

very sophisticated and, as with UT and RT, ET also requires highly skilled technicians to

analyze the results. Other limitations are described in Lesson 11 of the ASNT Manual.


ET can be used to find discontinuities in welds and base metals; therefore, the discontinuities

are the same as those discontinuities that are identified by the other methods of NDT. These

discontinuities include cracks, incomplete penetration (on thin materials), and lack of fusion.

For more detailed information on common discontinuities, refer to the Discontinuities section

that is on pages 11-1 through 11-11 of the ASNT Manual.


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SPECIALIZED TESTING METHODS

Infrared Inspection

Infrared inspection uses a special camera (scanning radiometer) that captures real time heatvariation data from an electron beam to produce a heat sensed picture (thermogram) that

shows the amount of heat that is being radiated from a component.

Infrared inspections are used to monitor for heat loss in the following components at Saudi

Aramco:

Boilers

Furnaces

Stacks

Bearings

Electrical switchgear and connectors

Transformers

Electric motors

Cryogenic storage tanks

For more detailed information on infrared inspections, refer to the Infrared/Thermal Testingsection that is on pages 12-10 through 12-22 of the ASNT Manual.

Holiday Detector

Protective coatings are used to prevent corrosion in many piping systems and components.

Damage to these protective coatings can result in a corrosion problem. Small cracks or

pinholes that are in a protective coating are called holidays. At Saudi Aramco, a special

device that is called a holiday detector is commonly used to check the integrity of protective

coatings. The holiday detector works through application of an electric charge to the pipe

wall. After the charge is applied, the pipe is checked for grounds. The existence of grounds

or arcs indicates the presence of a defect in the protective coating. The test equipment that isused for detection depends on the specific application.


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Detectors are broken down into high and low voltage applications. High voltage systems can

use from 10,000 to 40,000 volts and are used on large sections of pipe to check for internal as

well as external coating defects. Low voltage systems use less than 100 volts. The voltage is

applied through use of a sponge and electrolytic solution and is only used to locate defects in

external coatings.

Instrumented Scraper

The instrumented scraper is a device that is used to inspect pipeline internals. Magnetic flux

or ultrasonic detection instruments are attached to the scraper and the scanner can then travel

inside of the pipeline. The major advantage of the instrumented scraper is that the inspection

can be performed while the pipeline is in service. At Saudi Aramco, a common application of

the instrumented scraper is to check for internal and external corrosion or to detect dents or

obstructions in pipelines. The instrumented scraper does not require that the external surface

of the pipe be accessible, which provides 100% inspection capability of pipelines that are

buried (underground) or submerged (underwater).

Acoustic Emission

Acoustic Emission (AE) uses techniques that are similar to UT. Sound waves are passed

through a test object that is subjected to stress to check for discontinuities. As discontinuities

develop, they emit mechanical vibrations that can be identified by the AE transducer. At

Saudi Aramco, AE is used to check for defects in composite materials, such as fiberglass or

plastic. The common defects that are found by AE include cracks, voids, and laminations.

The typical applications at Saudi Aramco include inspections of lift truck booms and tanks

that are made of composite materials. For more detailed information on acoustic emission,

refer to the Acoustic Emission section that is on pages 12-23 through 12-30 of the ASNT

Manual.


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WORK AID 1: CAPABILITIES AND LIMITATIONS OF VISUAL WELD

EXAMINATION

The capabilities and limitations for visual examination that are listed below are to be used as

a guide to perform Exercise 1.

Capabilities:

Detects surface discontinuities that are visible to the human eye.

Can perform dimensional inspections with the aid of weld gages.

Limitations:

Cannot detect subsurface discontinuities.

Cannot examine welds that are more than 24" away from the examiners eye

without examination aids.

Cannot examine welds when the examiners eye is at an angle of less than 30o

from the surface that is being examined.

Cannot examine welds in less than 35 foot candles of illumination.


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WORK AID 2: CAPABILITIES AND LIMITATIONS OF LIQUID PENETRANT

TESTING

The capabilities and limitations for liquid penetrant testing that are listed below are to be

used as a guide to perform Exercise 2.

Capabilities:

Detects surface discontinuities on non-porous materials that may not be

detected during a visual examination.

Limitations:

Cannot detect subsurface discontinuities.

Cannot be used when the material temperature is above 125o

F.

Cannot be used on surfaces that are covered with paint or other coatings.

Cannot be performed in less than approximately 45 minutes.


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WORK AID 3: CAPABILITIES AND LIMITATIONS OF MAGNETIC PARTICLE

TESTING

The capabilities and limitations for magnetic particle testing that are listed below are to be


Capabilities:

Detects surface and near-surface discontinuities in ferromagnetic materials.

Limitations:

Cannot detect discontinuities throughout the entire volume of a weldment.

Cannot be used on nonmagnetic materials.

Can magnetize the object being examined.


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WORK AID 4: CAPABILITIES AND LIMITATIONS OF ULTRASONIC TESTING

The capabilities and limitations for ultrasonic testing that are listed below are to be used as a

guide to perform Exercise 4.

Capabilities:

Detects surface and subsurface discontinuities.

Measures material thicknesses.

Limitations:

Requires highly skilled technicians.

Cannot be used on rough surfaces.

Cannot detect discontinuities that are parallel to the beam.

Cannot be used on some coarse grain materials (castings).

Cannot be used on all weld joint configurations (ie. socket welds).


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WORK AID 5: CAPABILITIES AND LIMITATIONS OF RADIOGRAPHIC

TESTING

The capabilities and limitations for radiographic testing that are listed below are to be used

as a guide to perform Exercise 5.

Capabilities:

Detects surface and subsurface discontinuities in various materials.

Limitations:


Cannot detect discontinuities that are perpendicular to the rays.

Cannot be used when personnel in the area would be exposed to radiation.

Cannot be used on all weld joint configurations.

Cannot be used when physical clearances do not allow for proper radiographic

geometry.

Cannot be used when large amounts of fluid will be in contact with a

weldment.

Requires access to both sides.


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WORK AID 6: CAPABILITIES AND LIMITATIONS OF ELECTROMAGNETIC

TESTING

The capabilities and limitations for electromagnetic testing that are listed below are to be


Capabilities:

Detects surface and subsurface discontinuities.

Measures coating thicknesses.

Detects magnetic flux leakage in ferromagnetic materials.

Limitations:


Cannot reliably detect discontinuities that are more than 1/2" below the surface

in nonmagnetic materials.


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GLOSSARY

capillary action Tendency of a liquid to enter small cracks in the test object

because of the difference in cohesive forces between the liquid

(penetrant) and the surfaces of the crack.

composite A material that combines different substances to produce structural

properties not present in the individual substances.

electromagnetic Accelerated electric charges called photons whose energy is a

function of the frequency or wavelength of the radiation.

foot candles Unit of measure for the amount of light present in a given area.

One foot candle equals 1 lumen per square foot.

image resolution The sharpness or clarity of the picture produced by theexamination aid.

integrity Condition of being free of defects.

non-porous A property of a material that prevents a liquid or gas from being

easily absorbed into the surface of the material.

oscilloscope An instrument that is used to trace the electronic signal generated

by UT. The signal is displayed on the screen of a cathode-ray tube

(CRT) to provide an instantaneous indication.

particulate Subatomic particles that are generated by radioactive decay.

penetrameter Also called an image quality indicator (IQI), it is a device that is

placed in the area being radiographed and is used to determine the

quality and sensitivity of the radiograph.

piezoelectric Property of certain crystals to produce an electric current when a

mechanical stress is applied.

prods Hand-held electrodes that are used in the direct method of

magnetization. The prods are used to pass electric current through

the test object. The current establishes the circular magnetic fieldin the test object.

radioactive isotope Unstable elements whose decay produces gamma radiation.

shielding Material (typically lead or concrete) that is used to stop or reduce

the radiation generated by a gamma or x-ray source.


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stay time The length of time that a person can stay in an area before he

receives an allowable does of radiation.

test object A component or weldment that is being subjected to a

nondestructive test.

yoke U-shaped device that is used in the indirect method of

magnetization. The yoke contains a permanent magnet or an

electromagnet that generates a magnetic flux field. The test object

is then placed inside the yoke to complete a magnetic circuit.


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ADDENDUM

SAUDI ARAMCO PROCEDURES AND INSTRUCTIONS

SAIP-04-P - Liquid Penetrant Examination of Welds and Components

SAIP-05-P - Magnetic Particle Examination of Welds and Components

SAGI 448.010 - Radiographic Examination

Determine Appropriate NDT Method

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