Weld Discontinuities

Note: The source of the technical material in this volume is the ProfessionalEngineering Development Program (PEDP) of Engineering Services.

Warning: The material contained in this document was developed for SaudiAramco and is intended for the exclusive use of Saudi Aramco’s employees.Any material contained in this document which is not already in the publicdomain may not be copied, reproduced, sold, given, or disclosed to thirdparties, or otherwise used in whole, or in part, without the written permissionof the Vice President, Engineering Services, Saudi Aramco.

Chapter : Welding For additional information on this subject, contactFile Reference: COE11404 A.A. Omar on 874-6127

Engineering EncyclopediaSaudi Aramco DeskTop Standards

Identifying Weld Discontinuities

Engineering Encyclopedia Welding


Saudi Aramco DeskTop Standards

Contents Pages

INTRODUCTION................................................................................................................ 1

DETERMINE THE DIFFERENCE BETWEEN WELD DISCONTINUITIES ANDDEFECTS ............................................................................................................................ 2

Weld Quality ............................................................................................................. 2

Acceptance Criteria ................................................................................................... 2

Type of Weld Discontinuities..................................................................................... 3

Dimensional................................................................................................... 3

Structural....................................................................................................... 3

Property Related............................................................................................ 3

Causes of Weld Discontinuities.................................................................................. 8

Fabrication Induced Discontinuities................................................................ 8

Construction Induced Discontinuities ............................................................. 9

Nonrelevant Indications ................................................................................10

MODES OF IN-SERVICE FAILURE OF DEFECTIVE WELD JOINTS ...........................11

Overload Failures .....................................................................................................11

Fatigue Failures ........................................................................................................12

Delayed Hydrogen Cracking.....................................................................................12

Corrosion Failure .....................................................................................................13

Incorrect Repairs......................................................................................................13

IDENTIFY NONDESTRUCTIVE TESTING METHODS USED TO DETECT WELDDISCONTINUITIES...........................................................................................................15

Visual Inspection......................................................................................................15

Visual Acuity ................................................................................................16

Distance........................................................................................................16

Access ..........................................................................................................16

Lighting ........................................................................................................16

Common Applications...................................................................................16

Liquid Penetrant .......................................................................................................17

Magnetic Particle......................................................................................................18




Indirect Method ............................................................................................19

Direct Method ..............................................................................................19

Ultrasonic.................................................................................................................20

Transducer....................................................................................................22

Couplant.......................................................................................................22

Pulse Generator ............................................................................................22

CRT Display.................................................................................................22

"A" Scan.......................................................................................................22

"B" Scan.......................................................................................................23

"C" Scan.......................................................................................................23

Radiographic ............................................................................................................24

Time.............................................................................................................25

Distance........................................................................................................25

Shielding.......................................................................................................25

GLOSSARY........................................................................................................................29

WORK AIDS ......................................................................................................................31

WORK AID 1. HOW TO DETERMINE THE DIFFERENCE BETWEEN WELDDISCONTINUITIES AND DEFECTS................................................................................31

Work Aid 1A. Weld Acceptance Criteria ..................................................................31

Work Aid 1B. Type of Weld Discontinuities.............................................................33

Work Aid 1C. Causes of Weld Discontinuities..........................................................35

WORK AID 2. HOW TO DETERMINE MODES OF IN-SERVICE FAILURE OFDEFECTIVE WELD JOINTS .............................................................................................37

WORK AID 3. HOW TO DETERMINE THE APPROPRIATE NONDESTRUCTIVETESTING METHODS USED TO DETECT WELD DISCONTINUITIES .........................38

Work Aid 3A. How to Determine the Appropriate Application of Visual WeldExaminations (VT) ...................................................................................................38

Work Aid 3B. How to Determine the Appropriate Application of LiquidPenetrant Tests.........................................................................................................39

Work Aid 3C. How to Determine the Appropriate Application of MagneticParticle Testing ........................................................................................................39




Work Aid 3D. How to Determine the Appropriate Application of UltrasonicTesting .....................................................................................................................40

Work Aid 3E. How to Determine the Appropriate Application of RadiographicTesting .....................................................................................................................41

Table of Figures Pages

Figure 1.Examples of Dimensional Discontinuities ..................................................... 4

Figure 2. Cracks in Welds......................................................................................... 5

Figure 3. Slag Inclusions........................................................................................... 5

Figure 4. Lack of Fusion........................................................................................... 6

Figure 5. Incomplete Root Penetration ..................................................................... 6

Figure 6. Weld Undercut .......................................................................................... 6

Figure 7. Cold Lap ................................................................................................... 7

Figure 8. Root Concavity ......................................................................................... 7

Figure 9. Arc Strike.................................................................................................. 7

Figure 10. Weld Porosity.......................................................................................... 8

Figure 11. Principles of PT ......................................................................................17

Figure 12. Principles of MT.....................................................................................19

Figure 13. Principles of UT......................................................................................21

Figure 14. Principles of RT......................................................................................24

Figure 15. Radiographic Techniques........................................................................27

Table 1. Allowable Weld Reinforcement ...................................................................31

Table 2. Types of Weld Discontinuities and Their Indications ..................................33

Table 3. Causes of Weld Discontinuities and Their Indications..................................35

Table 4. Modes of In-service Failure and their Common Occurrences/Indications .....37



Saudi Aramco DeskTop Standards 1

INTRODUCTION

This Module contains information on the discontinuities and defects that are commonly found inwelds. It also covers the primary causes of weld discontinuities and their affect upon weld joint in-service reliability. It also covers the modes of failure in addition to the nondestructive testingmethods that can be used to detect weld discontinuities. The emphasis of the content is placed onthe location of discontinuities that are within a weld and the nondestructive testing method is bestsuited to detect a given discontinuity.

The material is presented in the following sections:

• Determining the Difference Between Weld Discontinuities and Defects

• Determining the Cause of Discontinuities and Their Mode of In-Service Failure

• Identifying Nondestructive Testing Methods Used to Detect Weld Discontinuities

In order to communicate clearly, the following definitions used in welding inspection are given forthis module:

• A weld defect is an unacceptable discontinuity in weld joint properties, such as,physical, mechanical, or metallurgical properties.

• A discontinuity is an interruption in the continuity of any of the weld properties.

• A weld discontinuity is considered a defect when its size and/or quantity exceedacceptance limits imposed by the applicable standard, code, or project specification.

• A weld discontinuity is not necessarily a defect.




DETERMINE THE DIFFERENCE BETWEEN WELD DISCONTINUITIES ANDDEFECTS

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

• Type of Weld Discontinuities

• Causes of Weld Discontinuities

Weld Quality

Weld quality is defined as the level of perfection that a weld exhibits. Weld quality pertains to theentire volume of weld metal that is in a weldment as well as to the surface appearance of aweldment. Because most welding operations are manually performed by welders, weldmentimperfections are not uncommon; however, because engineers can evaluate the service of aweldment and relate the intended service to a specific level of weld quality, weldmentimperfections are not necessarily a problem.

Certain products, components, systems, and facilities require a higher level of weld quality thando others. The reason for this increased level of weld quality is the inherent danger of theproducts, 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 notproperly constructed. The level of weld quality that is required for nuclear power plants andhigh pressure storage vessels is higher than the level of weld quality that is required foratmospheric storage tanks that present fewer safety risks. Construction standards that identify theminimum level of weld quality for the components and systems that are fabricated at SaudiAramco were discussed in COE 114.02.

Acceptance Criteria

In order to be acceptable, weld imperfections/discontinuities must meet the criteria that are listedin the applicable construction standards, such as API 1104 and AWS D1. The term "acceptancecriteria" 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 maximumallowable 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 theweld imperfections is the acceptance criteria, the allowable quantity is usually specified per unitlength of weld.




Type of Weld Discontinuities

The types of welding discontinuities are as follows:• Dimensional

• Structural

• Property related (chemical, mechanical, or metallurgical)

Dimensional

Dimensional discontinuities refer to interruptions in continuity of the weld size, shape, andfinished dimensions. Incorrect weld size and profile, along with weld distortion are the mostpronounced dimensional discontinuities that if left uncorrected can lead to in-service failure byfatigue or overload (see Figure 1).

Structural

Structural discontinuities are discontinuities that develop within the weld during welding. Theyinclude slag inclusion, porosity, cracks, incomplete fusion, inadequate joint preparation andundercuts (see Figure 2 through 10).Depending upon their type and extent, a single or combination of these discontinuities can lead toan in-service pipeline leak or rupture, causing an environmental and personal disaster.

Property Related

The most pronounced of these discontinuities are those related to welding consumables and basemetal properties. Use of incorrect chemistry and/or mechanical properties of filler metals andfluxes often leads to premature in-service failure of pipeline welds. Such failures are due to weldmetal cracking, high hardness, and using metals susceptible to corrosion.

Not all weld discontinuities are caused by improper welding conditions or welding consumables.Base metal properties that do not meet the prescribed requirements of chemical composition,metallurgical structure, mechanical properties and surface conditions, can also result inunacceptable weld discontinuities that lead failure either during fabrication or in-service. ColorPlates 1 and 2 are examples of the following, respectively:

a. A defective 904L stainless steel weld neck flange forging that resulted in hot tears9cracks) in the heat-affected -zone (HAZ) during welding

b. A severely laminated carbon steel plate material that resulted in in-service failure of alongitudinal filled weld of a pipeline repair sleeve and lamellar tearing of the sleeve shell.

Note: For color plate pictures refer to the separate Color Plate Booklet.




Figure 1.Examples of Dimensional Discontinuities

Figure 2 shows cracks in welds. Cracks in welds are unacceptable discontinuities. They areeither 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 dueto stresses that are developed during the welding process.




Figure 2. Cracks in Welds

Figure 3 shows slag inclusions. Slag inclusions are located within a weld and occur whenimpurities or flux contaminate a weld. Slag inclusions are the result of improper interpasscleaning.

Figure 3. Slag Inclusions

Figure 4 shows lack of fusion. Lack of fusion is generally located at the weld metal and basemetal interface, and it occurs when the molten weld metal does not fuse completely with anadjacent weld bead or with the base material. Lack of fusion is generally the result of inadequateheat or excessive travel speed.




Figure 4. Lack of Fusion

Figure 5 shows incomplete root penetration. Incomplete root penetration occurs when the weldmetal 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 5. Incomplete Root Penetration

Figure 6 shows weld undercut. A weld undercut is a groove that is melted into the toe or root ofa weld and that is left unfilled by the weld metal. Undercut results in a depression on the surfaceof the base metal at the point at which the weld metal contacts the base metal. Undercut isgenerally the result of excessive heat and travel speed.

Figure 6. Weld Undercut

Figure 7 shows cold lap. Cold lap occurs when the weld metal freezes too quickly and does notfuse with the surface of the base metal. Cold lap typically is found on the cover pass at the toe ofthe weld. Cold lap is generally the result of inadequate heat and excessive travel speed.




Figure 7. Cold Lap

Figure 8 shows root concavity. Root concavity occurs in weld joints that are welded from oneside only, an example of which would be pipe. Root concavity results from excessive heat, toowide of a root opening, or insufficient deposited weld metal.

Figure 8. Root Concavity

Figure 9 shows an arc strike. Arc strikes are caused by dragging the electrode over the surface ofthe base metal in an effort to initiate an arc for welding.

Figure 9. Arc Strike

Figure 10 shows weld porosity. Weld porosity is caused by inadequate flux or shielding gascoverage, 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. Moistureor other contaminants (e.g., oil, penetrant, temperature-indicating crayon residue) on the basemetal can also vaporize during welding and result in gas bubbles that are trapped in the weldmetal.




Figure 10. Weld Porosity

Causes of Weld Discontinuities

There are two causes of weld discontinuities as follows:• Fabrication induced

• Construction induced

Fabrication Induced Discontinuities

Fabrication as used in this module refers to steel mill fabricated welds such as pipe seam welds. Italso refers to shop and field fabricated welds such as girth and seam welds of pipe, pipeline,pressure vessels, tanks, etc.

The primary factors that result in weld discontinuities during fabrication are poor workmanshipand the use of incorrect welding parameters and procedures

Poor Workmanship. A high percentage of weld defects can be attributed to poor workmanshipduring both shop fabrication and field construction. This includes poor joint fit-up, inadequatejoint support, misalignment, arc strikes, and lack of joint cleaning.

Color Plate 3 is an example of misaligned internal seam weld of a steel mill fabricated SAWAPI5L grade X52 pipe of a forty year old crude oil pipeline. This discontinuity resulted inrepeated failures both in-service and during revalidation pressure testing.

Color Plate 4 is an example of incorrectly fitted and welded branch connection of API 5L gradeX60 pipeline that failed in -service. The branch pipe sticker was fitted and welded after thereinforcing pad was installed and welded to the header pipe. This practice is incorrect. Thesticker must be welded to the header pipe and pressure tested prior to installing and welding thereinforcing pad.




Use of Incorrect Welding Parameters or Procedures. All fabrication and construction codesand standards require welding to be performed by qualified welders utilizing qualified weldingprocedures. As was discussed in COE 114.02, a welding procedure is a document that specifiesthe parameters that will be used for the fabrication of weld joints of a specified material ordifferent material grades. These include material type and grade, joint design, welding processes,welding consumables, preheat and method of application, interpass temperature, welding currentand arc voltage ranges, welding position, direction of the weld progression, welding speed andpost weld heat treatment (PWHT). Incorrect changes or non-compliance of any one of theseparameters can result in defective welds that may fail in-service prematurely.

In addition to poor workmanship, weld defects that often lead to in-service failure can beattributed to the following parameters:

• High chemistry base metal such as pipe fittings

• Inadequate or no preheat

Color Plate 5 through 7 are typical examples of in-service failures of pipeline weld joints causedby use of the above described parameters.

Construction Induced Discontinuities

The term construction in this module refers to field work involving linings, fit-up, clamping andsupport of the weld joints. It also includes lifting the line while the pipeline is being built. Themost pronounced types of construction induced discontinuities are as follows:

• Root bead crack

• Lack of fusion

• Incomplete penetration

• Displacement of the internally deposited root bead

These types of discontinuities are frequently found in pipeline girth welds that are welded byautomatic welding systems because of the following reasons:

• Quick retrieval of the internal line up clamp and welding head while the hot and fillpasses are being deposited by the outside welding head.

• Lifting the free end of the pipe for lining and fitting-up the next joint while theprevious joint is being welded.

• Misalignment of the welding wire with the joint

• Poor joint design

• Poor end preparation

For manual welding, the most critical type of construction induced pipeline weld defect iscracking of the root bead. This is often caused by one of the following:




• Inadequate joint support

• High restraint causing stress

• Removing the joint support immediately after completion of the root pass. This isespecially true with the fitting-to pipe weld joints that are supported by slings held byeither fork lifts or side booms.

Color Plate 8 shows typical examples of these defects; a combination of weld discontinuities of(a) displaced internal root bead, (b) lack of side wall fusion (LSF), and © incomplete penetrationindicate by the arrows

Nonrelevant Indications

Nonrelevant indications are indications that are revealed by nondestructive testing but that arenot caused by actual weld discontinuities. The majority of nonrelevant indications are directlyrelated either to the improper use of a nondestructive testing method or to the examiner's abilityto properly perform the nondestructive testing method. Examples of typical nonrelevantindications include the following:

• Scratches or water spots on radiographic film.

• Sharp lines on radiographic film due to severe changes in the section thickness of thematerial that was radiographed.

• Liquid penetrant indications that result from the inability to adequately remove all ofthe surface penetrant.

• Flow lines and magnetic writing indications that are revealed by magnetic particleexamination.

• UT reflections that are due to the interface of mating parts rather than due to adiscontinuity.

Based on the method of NDT, the configuration of the component that is being examined, and theappearance of the indication, such indications can be determined by the NDT technician to benonrelevant.




MODES OF IN-SERVICE FAILURE OF DEFECTIVE WELD JOINTS

In-service failures of defective welds can occur in one or more of the following modes:

• Overload failure

• Fatigue failure

• Delayed Hydrogen cracking

• Corrosion failure

• Incorrect repair

These modes are briefly discussed and illustrated in the following case histories.

Overload Failures

Failures of defective pipeline welds can occur in joints containing cracks, incomplete penetration,and poor fit-up, if these joints are exposed to high pressure.

Case History #1

An overload failure occurred in a 10” by ½” w.t. API 5L grade X60 crude oil flowline. Therewas a catastrophic failure when the pressure increased to well shut-in pressure following a suddenshut-down of the gas and oil separation plant (GOSP). The failure occurred in one of the pipejoints that contained several “Hook” type cracks in the ERW seam weld (see Color Plate 9). Asa result, the four kilometer long flowline fractured into seven pieces that were scattered over aone square kilometer area (see Color Plate 10).

Case History #2

This incident concerns an overload failure of SCECO’s 115KV transmission line monopoles in1982. A severe wind storm, reportedly in excess of 70 mph, struck the Eastern Province of SaudiArabia during the night of October 28, 1982. As a result, several of SCECO’s 115 KVtransmission line monopoles collapsed and broke into many pieces. Many others were badlydamaged as the top portions snapped off of the main pole. This incident happened west ofJu’aymah and Ras Tanura.

Metallographic examination revealed that the monopoles failed by overload. The failure wasinitiated along defective seam welds. Incomplete weld penetration and high-low conditions of theabutting edges of the formed monopole resulted in reduced wall thickness and severe notch alongthe seam welds. The resulting wall thickness could not sustain the force and bending momentsthat occurred during the wind storm. Wall thickness along the seam welds was 30% less than thenominal plate thickness. Color Plate 11 (a & b) show a typical failure of the monopoles and theimproper fit-up resulting in sharp notches.




Fatigue Failures

Fatigue failures of pipeline welds are common in joints containing stress risers and that areexposed to cyclic loading and reverse bending. Such conditions often lead to the initiation ofgrowth of fatigue cracks that result in a leak or a rupture of the weld joint.

Case History #3

In this case, a 36”by ¾” w.t. API 5L grade X60 offshore crude oil pipeline lost some of its weightcoating due to mechanical damage. The line was located in relatively shallow waters on softsandy bed with strong tidal waves where vortex shedding is a problem. Loss of the concreteweight coating allowed the affected section of the line to float. This section was exposed torepeated flexing (reverse bending) and failed by fatigue at two of its girth weld joints. The girthwelds were seven pipe joints apart. Both welds contained severe stress risers caused by acombination of poor joint fit-up (high-low), incomplete weld penetration, and lack of side wallfusion of the root bead. Color Plate 12 shows (a) fractured girth weld, (b) fractured surface, and( c ) metallographic weld cross-section.

Case History #4

Another example of in-service fatigue failure that is encountered quite frequently is that of socketwelds and branch connections that are exposed to vibration such as compressor or pump piping.

Failures often occur at the toe of the socket weld on the pipe side. The welds did not blendsmoothly with the surface of the pipe which resulted in a sharp notch as shown in ColorPlate 13 a & b. the joint experienced cyclic bending. These failures can be prevented byfabricating weld that blends smoothly with the surface of the pipe with concave and a longer legsize on the pipe-side. In addition, the joint should be stiffened by two plane gusseting which isshown in Figure c

Delayed Hydrogen Cracking

Delayed hydrogen cracking is one of the primary modes of pipeline weld joint failures. For thisfailure to occur, the following three conditions must be present:

• Susceptible hard microstructure

• Hydrogen

• Stress




Hard microstructure occurs in high chemistry (high carbon equivalent (CE)) carbon steel materialsthat are welded with or without inadequate preheat. The resulting hard microstructure issusceptible to cracking y atomic hydrogen. Atomic hydrogen is generated from different sourcesduring welding. These sources include welding coonsumables such as electrode coatings, weldingfluxes and gases, and moisture and hydrocarbon contaminants on the steel surface. Both weldmetal and the HAZ of the weld joint can be embrittled by atomic hydrogen which diffuses into themolten metal and the HAZ during welding. (Refer to Color Plate 5 and 7 which showedexamples of delayed hydrogen cracking

Corrosion Failure

Although not very common, defective pipeline seam and girth welds can fail in the environment byinternal or external corrosion. Crevice pitting and galvanic corrosion are frequently encounteredin welds due to incomplete penetration, porosity, slag inclusion, incorrect chemical compositionof the weld metal and susceptible weld metal and HAZ microstructure. Such failures are oftenexperienced by welds in corrosive raw or sea water service or environments.

Case History #5

Several case histories of internal and external corrosion of pipelines seam and girth welds wereexperienced by many oil and gas companies, including Saudi Aramco. The most susceptible seamwelds are those of the non-normalized ERW pipe. Color Plate 14 (a) is an example of in-servicefailure of girt weld metal corrosion of high alloy austenitic stainless steel piping (Avesta 254SMOpiping) in sea water service. A combination of incorrect weld metal composition and crevicecorrosion was determined to be the cause of this failure.

Case History #6

Color Plate 14 (b) is another example of girth weld and HAZ corrosion failure of an API 5Lgrade X60 pipeline in water injection service. The failure was caused by poor FBE internalcoating of the girth weld which contained significant amounts of porosity and slag inclusions.

Incorrect Repairs

In-situ weld repairs are generally more difficult to perform and control than those performed inthe shop. This is especially true when the repairs are made on pipelines where joint access islimited and where dissimilar metals are involved.




Case History #7

A case history involving such a failure is shown in Color Plate 15. A 904L austenitic stainlesssteel weld-o-let of a 1” drain line on a 16” API 5L grade X60 trunkline was ground out andrewelded using nickel-based (Inco 182) electrode. The weld-o-let to pipe weld joint was groundout on the assumption that it was originally welded with carbon steel electrode. The line is in highpressure wet sour gas service. The rewelded joint failed after two months in-service by hydrogensulfide stress cracking. Metallographic examination of the failed joint revealed a very hardstructure (30_40HRC at the weld interface with the trunkline O.D. surface. The examination alsorevealed that the joint was initially welded with E-309 austenitic stainless steel electrode at theground area was rebuilt with E-7018 electrode prior to rewelding it with the Inco 182 electrode.The mixing of the carbon steel with the stainless steel weld metal resulted in formation of hardweld metal structure that is very susceptible to sulfide stress cracking. The correct repair shouldhave been made by either of the following two methods:

1. Cutting the pipe section containing the subject joint and installing a new insert pipepup piece with a shop fabricated drain joint, or

2. Grinding at least 1/8” deep zone in the header pipe to remove all traces of theaustenitic stainless steel prior to rebuilding the affected area with E-7018 weld metal.




IDENTIFY NONDESTRUCTIVE TESTING METHODS USED TO DETECT WELDDISCONTINUITIES

This section contains a description of the nondestructive testing (NDT) methods that are used todetect weld discontinuities at Saudi Aramco. The information provides an overview of thenondestructive testing methods, and it includes a description of the basic principles and commonapplications 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 visibleto the human eye. A visual inspection is the quickest and most cost-effective method of NDT thatcan be used to identify a surface discontinuity on a weld. Due to the complexity of theinformation that is involved, mastery of visual inspection methods and the ability to accuratelyinterpret results requires extensive training.

The visual inspection is the most frequently used method of examination, and welders and weldinginspectors continuously use visual inspections during welding operations to improve the quality ofwelds. Visual inspections often will identify problems during welding that can be repaired "inprocess" 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 ofcommonly used visual inspection aids:

• Mirrors

• Portable lighting

• Flashlights

• Light meters

• Straight edges and rulers

• Magnifying lenses

• Borescopes

• Microscopes

• Video cameras




• Weld gages

The tool that is used to perform visual inspections is the human eye. The following are therequirements to perform a visual inspection:

• Visual acuity

• Distance

• Access

• Lighting

Visual Acuity

Personnel who perform visual inspections must pass an annual eye examination in accordancewith industry standards. The eye examination checks for conditions such as visual acuity, colorblindness, and depth perception.

Distance

To conduct a visual inspection, the examiner's eye should be located within 24 inches and at anangle of not less than 30 degrees to the surface of the weld that is being examined. Mirrors canbe 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 tobe inspected. A minimum of 35 foot candles of light should be available for normal visualinspections. When visual inspections for small indications are being performed, a minimum of 50foot candles of light should be available. If required by a procedure, a light meter can be used todetermine the exact amount of illumination that is available.

Common Applications

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.




Liquid Penetrant

The purpose of liquid penetrant testing (PT) is to detect discontinuities that are open to thesurface of non-porous materials. Figure 11 shows that PT can be broken down into the followingbasic 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 isapplied to the surface of a material, capillary action will cause the penetrant to enter any smallopenings that exist on the surface of the material. After the excess penetrant is removed, adeveloper is applied to the surface of the material to draw the absorbed penetrant back out of theopenings. If the application of the developer causes the penetrant to be drawn back out of anopening, discontinuities are present on the surface of the material. Because dirt or contaminationcould mask surface discontinuities, proper preparation of the surface to be inspected is important.

Figure 11. Principles of PT

Saudi Aramco only uses color contrast, visible dye, solvent removable penetrants and the dry airspray developers. The type of developer that is used depends on the type of penetrant that isused. 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 SaudiAramco 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 developersare required for even moderate temperature use. SAIP-04-P only applies to PTs thatare performed 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 theliquid 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 andstainless steel.

• To check for surface discontinuities on magnetic welds when magnetic particle testingcannot be performed.

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

Magnetic Particle

The purpose of magnetic particle testing (MT) is to detect discontinuities that are either on thesurface 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 oneferromagnetic material to attract other ferromagnetic materials. Magnetic fields exist within andaround a permanent magnet or around a conductor that carries an electric current. Thesemagnetic fields are made up of magnetic lines of force that are perpendicular to the direction ofthe electric current flow. When a discontinuity exists in a ferromagnetic material, thediscontinuity results in a distortion in the magnetic lines of force, and it creates a leakage field inwhich the magnetic testing particles are gathered. The visual gathering of magnetic particlesindicates that a discontinuity may exist in the material that is being tested.

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 testobject (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

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

• Indirect Method

• Direct Method

Indirect Method

This method uses an electromagnetic yoke to pass a magnetic field through the test object. Thetest object completes a magnetic circuit with the yoke, which results in the establishment of amagnetic field in the test object. Yokes can use ac, half wave (HW) dc, or dc current to establishmagnetic fields.

Direct Method

This method uses prods to pass electrical current through the test object. The current that passesthrough the test object establishes the magnetic field. Prods also can use ac, HWdc, or dc currentto establish magnetic fields.




The use of ac current results in a magnetic field that is fairly shallow in the test material; the use ofdc current provides a deeper magnetic field; however, dc current also has more of a tendency tomagnetize 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. Thewet method of magnetic particle testing generally provides a more sensitive inspection because thewet method is able to detect minute discontinuities. The method of application depends on thetest situation. The following methods can be used:

• The wet method uses magnetic particles that are suspended in a liquid such as oil orwater. The magnetic particles may be fluorescent or non-fluorescent. The mixture isapplied by allowing it to flow over the test object.

• The dry method uses magnetic particles in the form of a dry powder. The magneticparticles are non-fluorescent, but the particles are available in different colors. Theparticles 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.

The major limitation of MT is that it can only be used to find defects that are at or near thesurface 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, valvebodies, shafts of rotating equipment, vessels, and storage tanks (wet or dry particlemethod)

• To check vessels and tanks that are susceptible to sulfide stress and hydrogen inducedcracking (wet particle method)

Ultrasonic

The primary purposes of ultrasonic testing (UT) are to detect volumetric discontinuities inmaterials and to measure the thickness of materials. UT, unlike the previously discussed methodsof 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 iseither VT, PT, or MT. UT uses a pulse generator to generate an electrical signal that is suppliedto a transducer. The transducer uses this electrical signal to generate and emit ultrasonic energy.The ultrasonic energy causes mechanical vibrations (wave propagation) in the form of a wave totravel through a test object. After the wave travels through the test object, the transducerreceives the return signal and sends it through a process circuit. The output of the process circuitis sent to a cathode ray tube. If the wave encounters a discontinuity in the test object, the returnsignal will reflect the disruption of the wave. The ability of the ultrasonic system to detect smalldefects (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 travelscan 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 waveencounters a discontinuity, part of this energy is reflected back, and three indications (initialsignal, return signal, and reflected signal) will appear on the CRT display screen. A qualifiedinspector can determine the approximate size and the location of the discontinuity from theseindications.

Figure 13. Principles of UT




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

• Transducer

• Couplant

• Pulse Generator

• CRT Display

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 thetransducer and the test object.

Pulse Generator

The pulse generator is used to generate the input electrical signal to the transducer.

CRT Display

The CRT display is used to display the return signal.

Other important pieces of test equipment are calibration blocks and reference blocks. Calibrationand reference blocks are used to help ensure that the test equipment is properly operating.Because the operation of the test equipment affects the examiner's interpretation of the testresults, proper operation of the test equipment is extremely important.

Contact testing is the test method that is widely used at Saudi Aramco. Contact testing canprovide different types of CRT display patterns that are known as scans. The type of CRT displaypattern that is used is dependent on the application. The following types of CRT display patternscan be used.

• "A" Scan

• "B" Scan

• "C" Scan

"A" Scan

An "A" scan is the usual type of CRT display that is used in ultrasonic material testing. "A" scansindicate the depth of a discontinuity.




"B" Scan

"B" scans provide a view of an object in a plane that is perpendicular to the direction ofmovement of the transducer signal and the surface of the test piece. The "B" scan also canindicate the depth of a discontinuity. "B" scans are typically used in medical applications. Aphotograph 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 theinspection 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 varietyof 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).

The following are the common applications for ultrasonic examinations:

• Thickness gauging for corrosion detection.

• Inspection of plate material for laminations.

• Inspection of full penetration groove welds in structural members, piping, and pressurevessels.




Radiographic

The purpose of radiographic testing (RT) is to detect internal weld discontinuities and not onlysurface and subsurface discontinuities. Figure 14 illustrates the basic principles of RT. RT usesradioactive sources (x-ray, gamma ray, or neutron beams) to emit radiographic rays that penetratethe test object. The energy and wavelength characteristics of these rays allow them to be used topenetrate any material. The physical characteristics of the test object determine the amount of theenergy beam that passes through the material. Any changes in material thickness or density willaffect the amount of energy that passes through the test object. The portion of the rays that passthrough the test object are used to expose a special type of film. The image that is produced onthe film will show any changes in the density of the areas that are exposed to the penetratingradiation.

Figure 14. Principles of RT

Radiation is the energy that is given off due to a nuclear reaction at the atomic level. This energymay be in the form of an electromagnetic wave or a particulate. Photons, which are small packetsof 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 Aramcoare X-rays and gamma rays. X-rays are generated in electronic X-ray tubes of the linearaccelerator type. The tubes may be portable to allow performance of radiographic examinationsin the field. The sources of gamma rays are the disintegrating nuclei of radioactive isotopes. Thefollowing 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 thebody 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 whensources of radiation are not properly handled. This danger is magnified because there are noimmediate 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 bypersonnel who handle radiation sources. SAGI 9.100 (Ionizing Radiation Protection) sets thegeneral guidelines that all Saudi Aramco personnel must follow to protect themselves againstionizing radiation. This instruction is used by personnel who are involved in all aspects ofstorage, handling, and use of radioactive sources.

Because the senses of the human body cannot detect the presence of radiation, special monitoringequipment must be used. Section 4.09 (Personnel Monitoring Equipment) of SAIP-08 identifiesthe devices that are used to measure the actual exposure of personnel during the performance ofRT. 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 performradiation surveys. A radiation survey meter is used to check radiation levels in a given area. Thisinformation is needed to determine personnel stay times and shielding requirements.

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

• Time• Distance• Shielding

Time

As the amount of time that is spent near a radiation source decreases, the exposure to theradiation 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, theamount of exposure decreases.




The term "exposure" refers to exposing the test object to the radiation source. Many variablesmust be considered to ensure that the exposure produces a usable image. The radiograph is notacceptable as proof that the test object is free of defects unless it is of good quality. Every effortmust be made to achieve the highest quality image so that all of the discontinuities can beidentified.

The following are the most important factors that must be considered in the achievement of thehighest 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 radiographicfilm. A penetrameter is typically a wire or block that is made of the same material as the testobject. The dimensions of the penetrameter are critical because the dimensions represent thethickness of the object that is being examined. The penetrameter is used to confirm the sensitivityof the radiograph. The penetrameter is not used to determine the size of discontinuities. Thepenetrameter image is a permanent record that proves that the technique that is used to performthe RT produced a good quality radiograph. ASTM wire-type penetrameters and hole-typepenetrameters are commonly used at Saudi Aramco.

Figure 14 showed an example of the "double wall" radiographic technique that is used to examinepiping 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 relativelocation of the radiographic source for each technique. Note that the "panoramic" techniquerequires that the radiation source be placed inside of the pipe or vessel.




Figure 15. Radiographic Techniques




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

• 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 ultrasonicexaminations, 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 wallthickness

• To check for linear and nonlinear weld indications such as cracks, slag inclusions, lackof fusion, and porosity.




GLOSSARY

capillary action Tendency of a liquid to enter small cracks in the test object becauseof 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, alack of homogeneity in the mechanical, metallurgical, or physicalcharacteristics.

electromagnetIc wave Accelerated electric charges called photons whose energy is relatedto the frequency of the wavelength.

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

foot candles Unit of measure for the amount of light that is present in a givenarea. One foot candle equals 1 lumen per square foot.

inspection The interpretation of the results that were obtained from anondestructive examination.

non-porous Materials that are free of pores or porosity and that are non-permeable to liquids.

nonrelevant indication An indication that is obtained during a nondestructive test and that isa result of a normal or known condition in a material and that is notthe result of a discontinuity or defect.

penetrameter Also called an image quality indicator (IQI), the penetrameter is adevice that is placed in the area that is being radiographed, and it isused to determine the quality and sensitivity of the radiograph.

piezoelectric Property of certain crystals to produce an electric current when amechanical stress is applied.

radioactive isotope Unstable elements whose decay produces radiation.

shielding Material (typically lead or concrete) that is used to stop or to reducethe amount of radiation that is generated by a gamma or an x-raysource.




stay time The length of time that a person can stay in an area before hereceives too much radiation.

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




WORK AIDS

WORK AID 1. HOW TO DETERMINE THE DIFFERENCE BETWEEN WELDDISCONTINUITIES AND DEFECTS

This Work Aid is designed to help the Participant perform Exercise 1.

Work Aid 1A. Weld Acceptance Criteria

Selected weld acceptance criteria from ASME B31.1, Power Piping, are listed below and are tobe 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

• Table 1.

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

Table 1. Allowable Weld Reinforcement

Maximum Thickness of ReinforcementThickness of Base Metal, in. Design Temperature

>750°F 350°F to 750°F <350°FUp to 1/8, inclusive 1/16 3/32 3/16Over 1/8 to 3/16, inclusive 1/16 1/8 3/16Over 3/16 to ½, inclusive 1/16 5/32 3/16Over ½ to 1, inclusive 3/32 3/16 3/16Over 1 to 2, inclusive 1/8 1/4 1/4Over 2 5/32 The greater of ¼ in. or; 1/8 times the

width of the weld (in Inches).

Magnetic Particle Examination Acceptance Standards


• 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 lessfrom edge to edge.

• Ten or more rounded indications in any 6 sq. in. of surface where the major dimension of thisarea does not exceed 6" and where the area that is chosen is in the most unfavorable locationrelative to the indications being evaluated.

Liquid Penetrant Examination Acceptance Standards


• 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 lessfrom edge to edge.

• Ten or more rounded indications in any 6 sq. in. of surface where the major dimension of thisarea does not exceed 6" and where the area that is chosen is in the most unfavorable locationrelative to the indications being evaluated.

Radiography Examination Acceptance Standards

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

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

• Any other elongated indication that has a length greater than:

• 1/4" for t up to 3/4" inclusive

• 1/3 t for t from 3/4" to 2-1/4" inclusive

• 3/4" for t over 2-1/4" where t is the thickness of the thinner portion of the weld

NOTE: “t” is the thickness of the weld being examined. If a weld joins two members withdifferent thicknesses at the weld, t is the thinner of these two thicknesses.

• Any group of indications in line that have an aggregate length that is greater than t in a lengthof 12t, except where the distance between the successive indications exceeds 6L, where L isthe longest indication in the group.




Work Aid 1B. Type of Weld Discontinuities

Refer to Table 2 to determine the type of discontinuities and their indications.

Table 2. Types of Weld Discontinuities and Their Indications

TYPE OF WELDDISCONTINUITY

INDICATIONS

Dimensional Interruptions in continuity of the weld size, shape, and finisheddimensions. Incorrect weld size and profile, and weld distortion areworst.

Can lead to in-service failure by fatigue or overload

Structural Develop within the weld during welding. A single or combination of thesediscontinuities can lead to an in-service pipeline leak or rupture

Cracks in welds Longitudinal or transverse. Surface cracks or subsurface. Occur in aweld due to stresses developed during the welding process

Slag inclusions Located within a weld. Occur when impurities or flux contaminate aweld. The result of improper interpass cleaning.

Lack of fusion Generally located at the weld metal and base metal interface. Molten weldmetal does not fuse completely with an adjacent weld bead or with thebase material. Generally the result of inadequate heat or excessive travelspeed.

Incomplete rootpenetration

Weld metal does not completely penetrate into the root area and consumeboth of the base materials. Generally the result of inadequate heat orexcessive travel speed.

Weld undercut Is a groove that is melted into the toe or root of a weld and is left unfilledby the weld metal. Results in a depression on the surface of the basemetal where the weld metal contacts the base metal. Generally the resultof excessive heat and travel speed.

Cold lap Occurs when the weld metal freezes too quickly and does not fuse withthe surface of the base metal. Typically found on the cover pass at the toeof the weld. Generally the result of inadequate heat and excessive travelspeed




Root concavity Occurs in weld joints welded from one side only. Results from excessiveheat, too wide of a root opening, or insufficient deposited weld metal

Arc strikes Caused by dragging the electrode over the surface of the base metal in aneffort to initiate an arc for welding.

Weld porosity Caused by inadequate flux or shielding gas coverage, oxygencontaminates the molten weld metal prior to solidification. Typicallylocated within the weld. Moisture or other contaminants on the basemetal can result in gas bubbles trapped in the weld metal.

Property Related Main ones are related to welding consumables and base metal properties.Failures are due to weld metal cracking, high hardness, and using metalssusceptible to corrosion.




Work Aid 1C. Causes of Weld Discontinuities

Refer to Table 3 to determine the type of discontinuities and their indications.

Table 3. Causes of Weld Discontinuities and Their Indications

CAUSED OF DISCONTINUITIES INDICATIONS

Fabrication Induced Caused by poor workmanship and the use ofincorrect welding parameters and procedures.

Poor workmanship Poor joint fit-up, inadequate joint support,misalignment, arc strikes, and lack of jointcleaning.

Use of Incorrect Welding Parameters orProcedures

Incorrect changes or non-complianceparameters can result in defective welds thatmay fail in-service prematurely.

• High chemistry base metal such as pipefittings

• Inadequate or no preheat

• Incorrect filler metal, electrode coating, orwelding flux

Construction Induced The most pronounced types:• Root bead crack

• Lack of fusion

• Incomplete penetration

• Displacement of the internally depositedroot bead




Automatic welding Frequently found in pipeline girth welds weldedby automatic welding systems:• Quick retrieval of the internal line up clamp

and welding head while the hot and fillpasses are being deposited by the outsidewelding head.

• Lifting the free end of the pipe for lining andfitting-up the next joint while the previousjoint is being welded.

• Misalignment of the welding wire with thejoint

• Poor joint design

• Poor end preparation

Manual Welding Most critical type is cracking of the root bead.Often caused by one of the following:• Inadequate joint support

• High restraint causing stress

• Removing the joint support (slings held byeither fork lifts or side booms) immediatelyafter completion of the root pass.




WORK AID 2. HOW TO DETERMINE MODES OF IN-SERVICE FAILURE OFDEFECTIVE WELD JOINTS

Use Table 4 to assist in completing Exercise 2. This table lists the modes of in-service failuresand their indications

Table 4. Modes of In-service Failure and their Common Occurrences/Indications

Mode of Failure Common Occurrence/Indications

Overload failure Occurs in joints containing cracks, incomplete penetration, andpoor fit-up, if exposed to high pressure.

(Refer to Case History #1 and 2).

Fatigue failure Occurs in joints containing stress risers and that are exposed tocyclic loading and reverse bending. Often lead to growth offatigue cracks that result in a leak or a rupture of the weld joint.

(Refer to Case History #3 and 4).

Delayed Hydrogen cracking One of the primary modes of pipeline weld joint failures. Thefollowing three conditions must be present:• Susceptible hard microstructure; occurs in high CE

carbon steel materials

• Hydrogen

• Stress

Corrosion failure Not very common; crevice pitting and galvanic corrosion due toincomplete penetration, porosity, slag inclusion, incorrectchemical composition of the weld metal, and susceptible weldmetal and HAZ microstructure.

Often happens in corrosive raw or sea water service orenvironments. (Refer to Case History #5 and 6.

Incorrect repair More difficult to perform and control than those performed inthe shop, especially when the repairs are made on pipelineswhere joint access is limited and where dissimilar metals areinvolved. (Refer to Case History #7.




WORK AID 3. HOW TO DETERMINE THE APPROPRIATENONDESTRUCTIVE TESTING METHODS USED TO DETECTWELD DISCONTINUITIES

Work Aid 3A. How to Determine the Appropriate Application of Visual WeldExaminations (VT)

The basic Information for visual examination listed below are to be used as a guide to performNDT.

Advantages:

• Quickest and most cost effective method.

• Simplest to learn

• Detects surface discontinuities that are visible to the human eye.

• Can perform dimensional inspections with the aid of weld gages.

• Improves success of subsequent NDT

• Reduces costs of repairs.

Common Applications:

• 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 ofpiping 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:

• Cannot detect subsurface discontinuities.

• Cannot examine welds that are more than 24" away from the examiner’s eye withoutexamination aids.

• Cannot examine welds when the examiner’s eye is at an angle of less than 30o from thesurface that is being examined.

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

Common Discontinuities:

• Cracks

• Slag




• Porosity

• Undercut

• Cold Lap

• Arc Strikes

Work Aid 3B. How to Determine the Appropriate Application of Liquid PenetrantTests

Capabilities:

• Detects surface discontinuities on non-porous materials that may not be detected during avisual examination.

Advantages:

• Good sensitivity

• Inexpensive

• Simple

• Wide range of uses

Common Applications:

• Most common use of PT is to check welds such as socket welds and root passes on pressurevessels, storage tanks, and piping systems.

• Best method for use in the identification of surface discontinuities on non-magnetic materials,such as aluminum and stainless steel.

• Can be used on magnetic steels when magnetic particle testing cannot be performed.

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.

Common Discontinuities Detected:

• Surface cracks, porosity, undercut, and cold laps.

Work Aid 3C. How to Determine the Appropriate Application of Magnetic ParticleTesting

Capabilities:

• Detects surface and near-surface discontinuities in ferromagnetic materials.




Applications:

• Used to inspect carbon steel weldments, socket welds on piping, weld bevel preps, structuralfillet welds, valve bodies, shafts of rotating equipment, pump impellers, machined parts,vessels, and storage tanks

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.

Limitations:

• Cannot detect discontinuities throughout the entire volume of a weldment

• Cannot find deep-seated discontinuities

• Cannot be used on nonmagnetic materials

• Can magnetize the object being examined

Common Discontinuities Detected:

• Surface or near-surface cracks, porosity, undercut, and cold lap

Work Aid 3D. How to Determine the Appropriate Application of Ultrasonic TestingCapabilities:

• Detects surface and subsurface discontinuities

• Measures material thickness

Applications:

• Thickness gaging for corrosion detection

• Inspecting the integrity of weld bevel prep areas, full penetration butt welds, and platematerial

Advantages:

• 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.




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 (i.e. socket welds).

Work Aid 3E. How to Determine the Appropriate Application of RadiographicTesting

Capabilities:

• Detects all surface and subsurface base metal and weld discontinuities in various materials.

Limitations:

• Requires highly skilled technicians.

• 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.

Documents

Weld Discontinuities