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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 : Welding For additional information on this subject, contact

    File Reference: COE11405 A.A. Omar on 873-3705

    Engineering EncyclopediaSaudi Aramco DeskTop Standards

    Identifying Weld Discontinuities

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    CONTENTS PAGES

    DETERMINING THE DIFFERENCE BETWEEN WELD DISCONTINUITIES AND

    DEFECTS.............................................................................................................................................1

    Weld Quality...........................................................................................................................1

    Acceptance Criteria.................................................................................................................1

    Weld Discontinuities.................................................................................................2

    Nonrelevant Indications ............. .............. ............ .............. ............ .............. ............. 8

    Weld Defects .............................................................................................................9

    IDENTIFYING NONDESTRUCTIVE TESTING METHODS USED TO DETECT

    WELD DISCONTINUITIES..............................................................................................................10

    Visual Inspection ..................................................................................................................10

    Liquid Penetrant....................................................................................................................12

    Magnetic Particle ..................................................................................................................14

    Ultrasonic..............................................................................................................................17

    Radiographic.........................................................................................................................20

    WORK AID 1: GUIDES FOR DETERMINING THE DIFFERENCE BETWEEN

    WELD DISCONTINUITIES AND DEFECTS ....................................................25

    Visual Inspection Acceptance Standards ..............................................................................25

    Magnetic Particle Examination Acceptance Standards .........................................................26

    Liquid Penetrant Examination Acceptance Standards...........................................................26

    Radiography Examination Acceptance Standards.................................................................27

    GLOSSARY.......................................................................................................................................28

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    DETERMINING THE DIFFERENCE BETWEEN WELD DISCONTINUITIES AND

    DEFECTS

    This section of the Module provides background information on weld discontinuities and defects. This section

    includes the following topics that are pertinent to the discussion: Weld Quality

    Acceptance Criteria

    Weld Quality

    Weld quality is defined as the level of perfection that a weld exhibits. Weld quality pertains to the entire

    volume of weld metal that is in a weldment as well as to the surface appearance of a weldment. Because most

    welding operations are manually performed by welders, weldment imperfections are not uncommon; however,

    because engineers can evaluate the service of a weldment and relate the intended service to a specific level of

    weld quality, weldment imperfections are not necessarily a problem.

    Certain products, components, systems, and facilities require a higher level of weld quality than do others. Thereason for this increased level of weld quality is the inherent danger of the products, components, systems, or

    facilities that are manufactured or constructed by welding. Historical data and experience have taught design

    engineers that certain facilities and components, such as nuclear power plants and high pressure storage vessels,

    can be extremely dangerous if not properly constructed. The level of weld quality that is required for nuclear

    power plants and high pressure storage vessels is higher than the level of weld quality that is required for

    atmospheric storage tanks that present fewer safety risks. Construction standards that identify the minimum

    level of weld quality for the components and systems that are fabricated at Saudi Aramco were discussed in

    COE 114.02.

    Acceptance Criteria

    Construction standards express the required level of weld quality in terms of the maximum weld imperfections

    that are allowed in a weldment. In order to be acceptable, weld imperfections must meet the criteria that are

    listed in the applicable construction standards such as API 1104 and AWS D1.1 that were identified in ModuleCOE 114.02. The term acceptance criteria is used by construction standards to define the required level of

    weld quality. Typically, the weld acceptance criteria that are presented in construction standards are a list of the

    maximum allowable weld imperfections. These imperfections can refer to the size (length, width, diameter) of

    the weld imperfection or to the quantity of the weld imperfections. When the quantity of the weld

    imperfections is the acceptance criteria, the allowable quantity is usually dependent on the thickness of the base

    metals that are welded. Thicker materials can generally have a larger quantity of weld imperfections than can

    thinner materials.

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    In addition to weld quality, the weld acceptance criteria that are contained in the construction standards also can

    pertain to the physical attributes of a weldment. The following criteria are examples of acceptance criteria that

    apply to the physical attributes of a weldment:

    Minimum fillet weld size.

    Maximum weld reinforcement (root and face).

    Maximum concavity and convexity of a fillet weld.

    Maximum mismatch in groove welds.

    Minimum weld transition requirements between members of unequal thickness.

    Weld Discontinuities

    A weld discontinuity is defined as an interruption of the typical structure of a weldment such as a lack of

    homogeneity in the mechanical, metallurgical, or physical characteristics of the weldment. Not all weld

    discontinuities are considered to be weld defects. Only those weld discontinuities that do not meet theapplicable acceptance criteria are considered to be weld defects; therefore, weld discontinuities that meet the

    applicable acceptance criteria are not considered detrimental to the strength of a weldment.

    Typical weld metal discontinuities that are encountered in welds at Saudi Aramco are presented in Figures 1

    through 10.

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    Figure 1 shows cracks in welds. Cracks in welds are unacceptable discontinuities. They are either longitudinal

    (aligned with the weld bead) or transverse (perpendicular to the weld bead). Cracks can be either surface cracks

    or subsurface cracks, and they generally occur in a weld due to stresses that are developed during the welding

    process.

    Figure 1. Cracks in Welds

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    Figure 2 shows slag inclusions. Slag inclusions are located within a weld and occur when impurities or flux

    contaminate a weld. Slag inclusions are the result of improper interpass cleaning.

    Figure 2. Slag Inclusions

    Figure 3 shows lack of fusion. Lack of fusion is generally located at the weld metal and base metal interface,and it occurs when the molten weld metal does not fuse completely with an adjacent weld bead or with the base

    material. Lack of fusion is generally the result of inadequate heat or excessive travel speed.

    Figure 3. Lack of Fusion

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    Figure 4 shows incomplete root penetration. Incomplete root penetration occurs when the weld metal does not

    completely penetrate into the root area and consume both of the base materials. Incomplete root penetration is

    generally the result of inadequate heat or excessive travel speed.

    Figure 4. Incomplete Root Penetration

    Figure 5 shows weld undercut. A weld undercut is a groove that is melted into the toe or root of a weld and that

    is left unfilled by the weld metal. Undercut results in a depression on the surface of the base metal at the point

    at which the weld metal contacts the base metal. Undercut is generally the result of excessive heat and travel

    speed.

    Figure 5. Weld Undercut

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    Figure 6 shows cold lap. Cold lap occurs when the weld metal freezes too quickly and does not fuse with the

    surface of the base metal. Cold lap typically is found on the cover pass at the toe of the weld. Cold lap is

    generally the result of inadequate heat and excessive travel speed.

    Figure 6. Cold Lap

    Figure 7 shows root concavity. Root concavity occurs in weld joints that are welded from one side only, an

    example of which would be pipe. Root concavity results from excessive heat, too wide of a root opening, or

    insufficient deposited weld metal.

    Figure 7. Root Concavity

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    Figure 8 shows a crater pit. Crater pits are located on the weld bead surface, and they are generally associated

    with Gas Tungsten Arc Welding (GTAW). Crater pits result from the rapid breaking of the electric arc so that

    the weld puddle freezes too quickly and shrinks, which leaves a small void.

    Figure 8. Crater Pit

    Figure 9 shows an arc strike. Arc strikes are caused by dragging the electrode over the surface of the base metal

    in an effort to initiate an arc for welding.

    Figure 9. Arc Strike

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    Figure 10 shows weld porosity. Weld porosity is caused by inadequate flux or shielding gas coverage, which

    allows oxygen to contaminate the molten weld metal prior to solidification. Porosity can be located on the weld

    surface, but it is typically located within the weld. Moisture or other contaminants (e.g., oil, penetrant,

    temperature-indicating crayon residue) on the base metal can also vaporize during welding and result in gas

    bubbles that are trapped in the weld metal.

    Figure 10. Weld Porosity

    Nonrelevant Indications

    Nonrelevant indications are indications that are revealed by nondestructive testing but that are not caused by

    actual weld discontinuities. The majority of nonrelevant indications are directly related either to the improper

    use of a nondestructive testing method or to the examiners ability to properly perform the nondestructive

    testing method. Examples of typical nonrelevant indications include the following:

    Scratches or water spots on radiographic film.

    Sharp lines on radiographic film due to severe changes in the section thickness of the material

    that was radiographed.

    Liquid penetrant indications that result from the inability to adequately remove all of the

    surface penetrant.

    Flow lines and magnetic writing indications that are revealed by magnetic particle

    examination.

    UT reflections that are due to the interface of mating parts rather than due to a discontinuity.

    Based on the method of NDT, the configuration of the component that is being examined, and the appearance

    of the indication, such indications can be determined by the NDT technician to be nonrelevant.

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    Weld Defects

    A weld defect is a discontinuity that does not meet the acceptance criteria of the applicable construction

    standard. A weld defect, as determined by the construction standards, would probably result in the premature

    failure of the weld. Welds that have defects must be repaired so that the defect is either completely removed

    from the weld or is sufficiently reduced in size so that the defect meets the acceptance criteria. The welddiscontinuities that were shown in Figures 1 through 10 would or would not be classified as defects depending

    on acceptance criteria.

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    IDENTIFYING NONDESTRUCTIVE TESTING METHODS USED TO DETECT

    WELD DISCONTINUITIES

    This section contains a description of the nondestructive testing (NDT) methods that are used to detect weld

    discontinuities at Saudi Aramco. The information provides an overview of the nondestructive testing methods,

    and it includes a description of the basic principles and common applications of each of the following methods:

    Visual Inspection

    Liquid Penetrant

    Magnetic Particle

    Ultrasonic

    Radiographic

    Visual Inspection

    The purpose of visual inspection is to detect surface discontinuities on weldments that are visible to the human

    eye. A visual inspection is the quickest and most cost-effective method of NDT that can be used to identify a

    surface discontinuity on a weld. Due to the complexity of the information that is involved, mastery of visual

    inspection methods and the ability to accurately interpret results requires extensive training.

    The visual inspection is the most frequently used method of examination, and welders and welding inspectors

    continuously use visual inspections during welding operations to improve the quality of welds. Visual

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

    discovery of a discontinuity by a subsequent nondestructive test.

    Inspection aids sometimes are used to facilitate visual inspections. The following are examples of commonly

    used visual inspection aids:

    Mirrors

    Portable Lighting

    Flashlights

    Light Meters

    Straight Edges and Rulers

    Magnifying Lenses

    Boroscopes

    Microscopes

    Video Cameras

    Weld Gages

    The tool that is used to perform visual inspections is the human eye. The following are the requirements to

    perform a visual inspection:

    Visual Acuity - Personnel who perform visual inspections must pass an annual eye

    examination in accordance with industry standards. The eye examination checks for

    conditions such as visual acuity, color blindness, and depth perception.

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    Distance - To conduct a visual inspection, 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. 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.

    Lighting- A flashlight or other additional lighting should be used to sufficiently illuminate the

    area that is to be inspected. A minimum of 35 foot candles of light should be available for

    normal visual inspections. When visual inspections for small indications are being performed,

    a minimum of 50 foot candles of light should be available. If required by a procedure, a light

    meter can be used to determine the exact amount of illumination that is available.

    Common applications for visual inspection include the following:

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

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

    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.

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    Liquid Penetrant

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

    porous materials. Figure 11 shows that PT can be broken down into the following basic steps:

    Cleaning the surface.

    Application of the penetrant to the surface that is to be inspected.

    Removal of the excess penetrant.

    Application of a developer.

    Visual inspection for indications.

    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.

    Because dirt or contamination could mask surface discontinuities, proper preparation of the surface to be

    inspected is important.

    Figure 11. Principles of PT

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    Saudi Aramco only uses color contrast, visible dye, solvent removable penetrants and the dry air spray

    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.

    The following are the major advantages of PT:

    Good sensitivity

    Inexpensive

    Simple

    Wide range of uses

    The following are the major limitations of PT:

    Inability to detect subsurface discontinuities.

    Not conducive to high temperature applications. Special penetrants and developers are

    required for even moderate temperature use. SAIP-04-P only applies to PTs that areperformed on materials that have a maximum temperature of 125oF.

    Extensive surface preparation required.

    Surfaces that are covered with paint or other coatings cannot be examined with the liquid

    penetrant method. The coating prevents the occurrence of capillary action.

    The lengthy dwell time (sometimes up to 45 minutes) of liquid penetrant examinations.

    The following are common applications for liquid penetrant examinations:

    To check for surface discontinuities on non-magnetic welds such as aluminum and stainless

    steel.

    To check for surface discontinuities on magnetic welds when magnetic particle testing cannot

    be performed.

    To check socket welds and root passes on pressure vessels, storage tanks, and piping welds.

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    Magnetic Particle

    The purpose of magnetic particle testing (MT) is to detect discontinuities that are either on the surface of or near

    the surface of ferromagnetic materials. Ferromagnetic materials (e.g., iron, steel, and associated alloys) are

    those materials that can be strongly magnetized.

    Magnetic particle testing is based on the principle of magnetism. Magnetism is the ability of one ferromagneticmaterial 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 it 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 12 illustrates the following basic 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 12. Principles of MT

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    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, which 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.

    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 magnetize the test objects.

    Depending on the circumstances of the part that is tested, demagnetization may be necessary.

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

    magnetic particle testing generally provides a more sensitive inspection because the wet method is able to

    detect minute discontinuities. 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.

    The following are the major advantages of MT, in comparison to PT:

    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 cleanup.

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    The major limitation of MT is that it can only be used to find defects that are at or near the surface of

    ferromagnetic materials.

    The following are the common applications for magnetic particle examinations:

    To check carbon steel weldments (wet or dry particle method).

    To check socket welds on piping, weld bevel preps, structural fillet welds, valve bodies, shafts

    of rotating equipment, vessels, and storage tanks (wet or dry particle method).

    To check vessels and tanks that are susceptible to sulfide stress and hydrogen induced

    cracking (wet particle method).

    Ultrasonic

    The primary purposes of ultrasonic testing (UT) are to detect volumetric discontinuities in materials and to

    measure the thickness of materials. UT, unlike the previously discussed methods of NDT, can be used to

    inspect the entire volume of a weld.

    Figure 13 illustrates the basic principles of UT. UT is a more complex method of NDT than is either VT, PT, or

    MT. UT uses a pulse generator to generate an electrical signal that is supplied to a transducer. The transduceruses this electrical signal to generate and emit ultrasonic energy. The ultrasonic energy causes mechanical

    vibrations (wave propagation) in the form of a wave to travel 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. 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 (wave) is transferred into a material, the distance that the wave travels can be

    determined through use of CRT display. If the wave does not encounter a discontinuity, only the initial and

    return signals appear on the CRT display 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 CRT display screen. A qualified inspector can determine the approximate size and the location of the

    discontinuity from these indications.

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    Figure 13. Principles of UT

    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 another form. These

    piezoelectric devices (transducers) are used to both transmit and receive ultrasonic signals.

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

    energy between the transducer and the test object.

    Pulse - The pulse generator is used to generate the input electrical signal to the transducer and

    the CRT display is used to display the return signal.

    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 affects the examiners interpretation of the test results, proper operation of the test equipment is

    extremely important.

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    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. 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 the view through the

    object from the inspection surface. The CRT display of a C scan also can be photographed.

    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 a variety of materials including most metals.

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

    UT only requires access to one side of a weld structure or component.

    UT can be performed through use of portable equipment.

    UT is safe to perform.

    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 is difficult to use on course grain materials (castings).

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

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

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    The following are the common applications for ultrasonic examinations:

    Thickness gaging for corrosion detection.

    Inspection of plate material for laminations.

    Inspection of full penetration groove welds in structural members, piping, and pressure

    vessels.

    Radiographic

    The purpose of radiographic testing (RT) is to detect internal weld discontinuities and not only surface and

    subsurface discontinuities. Figure 14 illustrates the basic principles of RT. RT uses radioactive sources (x-ray,

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

    wavelength characteristics of these rays allow them to be used to penetrate any material. The physical

    characteristics of the test object determine 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 rays 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 penetratingradiation.

    Figure 14. Principles of RT

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    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. The two types of electromagnetic radiation

    that are used to perform radiography at Saudi Aramco are X-rays and 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. 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:

    Cobalt-60 (Co-60)

    Iridium-192 (Ir-192)

    The penetrating nature of radiation 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 because there are no immediate signs to 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 whohandle 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.

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

    must be used. Section 4.09 (Personnel Monitoring Equipment) of SAIP-08 identifies the 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 (Radiation Monitoring Equipment) of SAIP-08 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.

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    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.

    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 positioning of the film.

    Film processing time and chemical temperatures.

    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 of 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 penetrametersand hole-type penetrameters are commonly used at Saudi Aramco.

    Figure 14 showed an example of the double wall radiographic technique that is used to examine piping or

    small pressure vessel welds. Figure 15 shows examples of panoramic and elliptical radiographic

    techniques that also are used on piping welds. Figure 15 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 of the pipe or vessel.

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    Figure 15. Radiographic Techniques

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    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 performed through use of portable equipment.

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

    RT can only be performed by highly skilled technicians.

    RT cannot detect discontinuities that are located perpendicular to the rays.

    The following conditions may limit the use of RT:

    Weld joint geometry.

    RT exposes personnel who are in the area to radiation.

    Accessibility and geometry of the radiographic technique.

    Common applications for radiographic examinations are similar to the application for ultrasonic examinations,

    and they include the following:

    Examination of critical full penetration welds in piping and pressure vessels.

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

    To check for linear and nonlinear weld indications such as cracks, slag inclusions, lack of

    fusion, and porosity.

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    WORK AID 1: GUIDES FOR DETERMINING THE DIFFERENCE BETWEEN

    WELD DISCONTINUITIES AND DEFECTS

    This Work Aid is designed to help the Participant perform Exercise 1. Selected weld acceptance criteria from

    ASME B31.1, Power Piping, are listed below and are to be used as guides to perform Exercise 1.

    Visual Inspection Acceptance Standards

    The following discontinuities are unacceptable:

    Cracks on external surfaces.

    Undercut on surface that is greater than 1/32" deep.

    Weld reinforcement greater than the weld reinforcement that is specified in Figure 16.

    Incomplete penetration (applies only when the inside surface is readily accessible.

    Maximum Thickness of Reinforcement forDesign Temperature

    Thickness of Base Metal, in. > 750oF 350oF - 750oF < 350oFUp to 1/8, incl. 1/16 3/31 3/16

    Over 1/8 to 3/16, incl. 1/16 1/8 3/16Over 3/16 to 1/2, incl. 1/16 5/32 3/16

    Over 1/2 to 1, incl. 3/32 3/16 3/16Over 1 to 2, incl. 1/8 1/4 1/4

    Over 1 5/32 The greater of 1/4 in. or 1/8 timesthe width of the weld in inches

    Figure 16. Allowable Weld Reinforcement

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    Magnetic Particle Examination Acceptance Standards

    The following discontinuities are unacceptable:

    Any cracks or linear indications.

    Rounded indications with dimensions that exceed 3/16".

    Four or more rounded indications that are in a line and that are separated by 1/16" or less from

    edge to edge.

    Ten or more rounded indications in any 6 sq. in. of surface where the major dimension of this

    area does not exceed 6" and where the area that is chosen is in the most unfavorable location

    relative to the indications being evaluated.

    Liquid Penetrant Examination Acceptance Standards

    The following discontinuities are unacceptable:

    Any cracks or linear indications.

    Rounded indications with dimensions that exceed 3/16".

    Four or more rounded indications that are in a line and that are separated by 1/16" or less from

    edge to edge.

    Ten or more rounded indications in any 6 sq. in. of surface where the major dimension of this

    area does not exceed 6" and where the area that is chosen is in the most unfavorable location

    relative to the indications being evaluated.

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    Radiography Examination Acceptance Standards

    Welds that are shown by radiography to have any of the following types of discontinuities are unacceptable:

    Any type of crack or zone of incomplete fusion or penetration.

    Any other elongated indication that has a length greater than:

    1/4" fortup to 3/4" inclusive

    1/3 tfortfrom 3/4" to 2-1/4" inclusive

    3/4" fortover 2-1/4" where tis the thickness of the thinner portion of the weld

    NOTE: tis the thickness of the weld being examined. If a weld joins two members with different

    thicknesses at the weld, tis the thinner of these two thicknesses.

    Any group of indications in line that have an aggregate length that is greater than tin a length

    of 12t, except where the distance between the successive indications exceeds 6L, where L is

    the longest indication in the group.

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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.

    defect An unacceptable discontinuity as defined by the code.discontinuity An interruption of the typical structure of a material; for example, a lack of

    homogeneity in the mechanical, metallurgical, or physical characteristics.

    electromagnetic Accelerated electric charges called photons whose energy is related to the

    frequency of the wavelength.

    examination The procedure or method that is used to conduct a destructive or a

    nondestructive test.

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

    foot candle equals 1 lumen per square foot.

    inspection The interpretation of the results that were obtained from a nondestructive

    examination.

    nonporous Materials that are free of pores or porosity and that are nonpermeable to

    liquids.

    nonrelevant An indication that is obtained during a nondestructive test and that is a result

    of a normal or known condition in a material and that is not the result of a

    discontinuity or defect.

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

    UT. The signal is displayed on the screen of a cathode-ray tube (CRT) to

    provide an instantaneous indication.

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

    is placed in the area that is being radiographed, and it 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.

    radioactive isotope Unstable elements whose decay produces radiation.

    shielding Material (typically lead or concrete) that is used to stop or to reduce theamount of radiation that is generated by a gamma or an x-ray source.

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

    much radiation.

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

    nondestructive test.