MACAW´S PIPELINE DEFECTS

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MANUFACTURING CONSTRUCTION OPERATION COATING AND CP DEFECT INTERACTION

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M

ACAW

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S

PIPELINE DEFECT

S

ACKNOWLEDGEMENTS

We are grateful to allthe colleaguesand friends in the pipeline industry that have contributed materialandconstructive commentsduring the preparation of this book. In particular we wish to thank the following organisationsandindividuals:

MACAWEngineering Ltd GE PIIPipeline Solutions KD Efird

J O'Shea

Lithgow Associates

David Norman Corrosion Control TWI -TheWelding Institute

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~DITiJHlr.. UABO Editor:

Dr Colin Argent Technical Ed ito rs:

Dr Kevin Prosser (Metallurgy & Welding) David Norman (Coatings)

Associate Editors: Peter Morgan Roger Weatherhead

"'00LI5JlER - Macaw's Pipeline Defects ISBN 0-9544295-0-8 Publi shed by:

Yellow PencilMarketing Co. Ltd. IPHouse,London Road, Basingstoke, Hampshire RG24 7J L UK

[email protected]

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----Neither the publishersor the authors, editorsand contributorsand their employingorganisations, nor any persons actingon behalf of them a) makesany warranty,express or implied,with respect to the useof anyinformation,apparatus, method or processdescribed inthis publicationorthat suchuse may not infringe privately owned rights or b) assume anyliabilities with respect tothe use of,or for damagesresulting from the use of any information,apparatus, method orprocess disclosed inthis publication,and the useof anysuch materials,processesor methods is solely at theriskof the user. Data containedwithinthispublicationis protected by copyright.All rightsreserved. No partof thispublication may be reproduced,stored in a retrieval system,or transmitted in any form or byany means electronic, mechanical,photocopying, recording orotherwise with the prior permission of the publisher.

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MA

CAW

'S

PIPELINE

DEFECTS

INTRODUCTION

Theaimofthis book is to illustratethe rangeofdefectsthat maybe encountered in high pressure steel pipelines and pipeline coatings.It givesadviceon the probable cause and significance of the defects and commentson appropriate remedialactions.Thisbookisnot intended as a complete"Do It Yourself Manual"for thediagnosis and analysis of defects and useofthismanualwillnot maketheuser an"Instant Expert': Many ofthedefects require analysisand diagnosis bya qualified expert using specialist analytical techniques.

The defects included in this book encompass allaspects of high pressure steel pipeline manufacture,construction and operation.

The section on manufacture includes defectsin steel plate, seamless pipeand seam weldsproduced by electrical resistancewelding (ERW) and submerged arcwelding (SAW). Girth weldsaredealt

with in the section on construction along with poor construction practicessuch as lackof cover, electricalshorts, poor pipe support etc.

The section dealing with operational defectsencompassesinternal corrosion, externalcorrosion,erosion,fatigue,third party damage,denting and buckling. Faults intheexternal corrosion control system aredealtwith in separate sections. Coating defectsare shown forthecommon typesofmillapplied pipecoating and field appliedgirth weld coatings.Common problemswith cathodic protection schemesare also illustrated. Thefinal sect ion of the book shows examplesof the inter-action between fault conditionsto create anew integrity riskto the pipeline;for exampleshieldingof the cathodic protectionby adisbonded coating to createthe conditionsforstress corrosion cracking.

Each section in thisbook has been compiled and edited by experienced engineers with many yearspractical experiencein pipelineengineering, metallurgy, welding, coatings and corrosion.Webelievethisvolume will provide a useful pictorial reference for engineersworking inthepipelineindustry. We would welcome constructive comment,suggestions or contributions that wouldenhancethepracticalvalueof future editions.

All photographs and information contained in this document are intended for guidance only.No comment or suggestionshould be adoptedasan authoritative action without seeking additional guidance from the relevant codes,procedures or specialistadvisors. No responsibility canbetakenfor any problems whichmay ariseas aresultof the use of any information contained within this document.

,~; MACAW'S PIPELINE DEFECTS

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MANU

FACTURI NG

DEFEGS

Tne first section dealswithdefectsthat occur during steelrnakinq, rolling of the platefor pipe manufacture and the manufacturing process itself. In principle, all critical defectsof this kind should be eliminated in the proof test carried out in the pipe mill.

Thesecond section considers defects that maybe introduced into the pipeline during the construction process. Critical defectsof thiskind should be detected in the post construction hydrostatic pressure test.

OP

ERATtONAl.

DEFEOS

The third section of the book deals with defects that initiate andgrowafterthe pipeline has been commissioned. These defects may initiate from a pre-existinq fault within the pipe or they may initiate from anareaof thepipe surfacethat is freeof any manufacturing or

const ructionfaults.

Operational faults represent the largest problem for the pipeline operator who must assesswhichdefects are likelyto develop,the rate at which they will develop and the consequences for pipeline safety.

Allof these issuesaredealt withinthe operational riskassessmentforthe pipeline and the findings of this risk assessment will decide the frequency and type of periodic proof tests or inspections designed to prevent operational failures.

MA

CAW 'S

PfP EU NE DEF ECTS

COATING AND

CP DEFE

CTS

The fourthsection dealswith defects in the external pipe coating and the cathodic protection system. These faults create theconditionsin whichexternal corrosion can develop.

DEFECT INTERACTION

The final section provides examplesof how defects interact to generate new or modified risks to pipeline integrity.

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MANUFACTURING DEFECTS

INTRODUCTION

This sectiondealswith defectsgenerated intheplate, thepipeorthe seam weldsup to the timewhen the pipe passesthe final milltestand isdeclared 'fit for purpose' and isshipped to theclient.

Major manufacturing faults will be detected bythe NDT inspection inthe pipe mill,during the cold expansion ofthe pipe(thisis applied to most U-and-D formed,straight seam, submerged arc welded (SAW) pipe and some spirally welded pipe) orbyhydrostatictesting of the individual pipes.

Ifthe pipe wasnot subject to a high-level milltest thenthecriticaldefectsshould be detected in the post construction proof test.

Wherethereisnorecord ofeithertype of testasignificanceofdefect assessment may be required for mill defects identified from intelligent pit inspections or non destructive testing examination.

Boththe milltests andthe post

construction pressuretestaredesigned to locate defects with a significant'through wall'cornponent.Thesetests are not optimised to locate defects running paralleltothepipewall,such as centre line segregations or laps.Defectsrunning parallel to the pipe wall may assume greater significancefor structural integrity in specificoperating conditions, for examplewherethe pipelineis subject to bending loads induced from ground movement or where sour service corrosion mechanisms areactive.

Minor surface irregularities, such as small lapsor rolled inscale,pose no immediate threat to pipelineintegrity but can initiate pitting corrosion.Much pipeis shipped by sea,asdeck cargo,orcoatedat coastal coating plants.Ineither case these small irregularities canaccumulatesalt and moisture below thepipesurface.Special cleaning isrequiredto remove alltracesof

salt and moisture, including pre-heating, waterwashing and chemicaltreatment. Surface defects such as laps,sliversand blisters alsocreate 'holidays:or defectsin thin film coatings.

Manufacturing defects are not normally considered to posea major risk to pipeline integrity if they have been subject to a mill test andapost construction hydrostatic pressure test. Reassessment of

manufacturing defectsmay be required wherethere is evidencefor growth in service,for example by corrosion or fatigue. Manufacturing defects are dealt within four sections.

r, MACAW'S PIPELINE DEFEers 2

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MANUFACTURING DEFECTS

INTRODUCTION

Section One describesdefects in rolled plate including structural featuresthat become apparent during standard tests. Platedefectsmay be carried forward into straight seam,ERW and spirally welded pipe.

SectionTwodeal swith seamlesspipe that is formedfrom a steelbillet.Thebillet ispiercedand then progressivelyformed into apipe.Seamless pipeshowsvariable

wallthickness along itslength due tothis pipeforming process.Many ofthe defects found in seamless pipe originate as defectsin theingotfrom which the pipe wasformed.

Section Three deals with ERW,Electric Resistance Welded,pipe.Early ERWseam weldswerecreated by passingan electric currentthrough thearea of theweld fromcontactson eitherside ofthefusion line.Controlof weld quality wasa particular problem with this type of

welding.Modern ERW pipe is produced

using the HFI, High Frequency Induction, technique and thisgenerally produces seam weldsof consistent quality.Most of thefeaturesshowninthissection relate to weld quality but featureslisted under plate defectsmay alsobepresent.

Section Four dealswith straightseam DSAW (double submerged arc welded) pipe and concentrateson seam weld defects.Thesedefectsmay alsobe found inspirallywelded DSAW pipe.In both these typesof pipe the edgesof the plate

arecrimped before the plate isformed

into the pipeshape.Thiscrimping action gives more precise'fit-up'for the sea m welding process. The crimp geometry will be removed in cold expanded pipe but

this area may be subject to higher strain during hydrostatic pressure testing.

Features listed under platedefectsmay alsobe presentin both straight seam and spirally welded pipe.

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MANUFACTURING:

PLATE DEFECTS

BLISTERS

A void, close to the pipesurface,enclosed

by athin filamentof steel.

Entrapment ofgasreleased duringthe solidification ofthe steel.

Not structurally significant

Maycause problems with holidaysin thin

filmcoatings.Superficia lblisters may be

removed by grinding before applicat ion

of the coating.

Possibleinitiation sitefor pitting corrosion if theblister is contaminated

with soluble saltsduring storageor

transport.

(10)

MANUFACTU RIN G: PLATE DEFECTS

CENTRE LINE SEGREGATIONS

Concentrationsof non-metallic matenal in the mid-wall position Including carbon and manganese rich bands.

During solidification non-metallic material maybecome concentrated at the centreof theingot which isthelast area to solidify.

Centreline segregationsare generally not structurally significantfor pressure retention.

Theymay provide aninitiation point for cracking insourservice and may contribute to weld defects.

(11)

MANUFACTURING: PLATE DEFECTS

CENTRE LINE SPLITS

Cracking aong tbe cenueline ofthe plate in test pieces.

Line of weaknessin thematerial caused by aligned inclusions or segregations.

These features area symptom ofthetest and are not usually structurally

significant.

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INDENTATIONS

Adepression inthepipe surface.When viewedin sectionthegrain structurein the steel follows theoutline of the depression.

Pieces of scrap or foreign bodies that have beenrolled intotheplatesurface.

Commonly thesefeatures are relatively shallow and are too small to be

st ructurally signincant.

Indentations should be checked with

respect to the pipe specification.

~ ' MACAW'S PIPELI NEDEFECTS

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MANUFAUURING:

PLATE DEFEUS

LAMINATIONS

A discontinuity lying parallel to the pipe

surface,usuallymarked by a

concentration of non-metallics,

Rolling-out of inclusions, blow holes 0 1

pipes in the parent material.

Large laminations may be structurally significant.Some older pipelinescontain

pipes with large laminations that have

not created asafetyhazardinmany years service.

Surface breaking laminations may contribute to coating faultsand may serve asan initiationpoint for pitting corrosion.

Superficial laminations may be removed

by grinding before application of the

coating.

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MANUFACTURIN

G:

PLATE DEFECTS

LAPS

A Rap of metal lying flat on the pipe surface,usuallywith atrapped residue of

oxide or scale beneath it.

A metalprotrusion that is folded and rolledintothehot metalsurface during

rollingofthe platefrom whichthe pipeis made.

Generally small laps have littleor no

structural significance. Laps do create

holidays, or defects,in thinfilm coatings.

Soluble saltstrapped inthe scaleor oxidesbeneath the lap mayinitiate corrosion pitting.

Superflcial lapsmay be removed by grinding beforeapplication ofthe coating.

(15)

SEPARATIONS, CHARPY

Cracks, or crack like featuresthat appear inthefractureface of mechanicaltest

pieces.

Separationsappearin ( harpy, CrackTip Opening Displa cementand Drop Weight

TearTest pieces.Theiroccurrencemaybe

influenced by steel chemistry and plate

rolling conditions, particularly heavy deformationat low rolling temperatures.

Thecrack like featuresare related tothe steel structure,for examplefine bandsof martensite.

." MACAW'SPIPELINEDEFEGS

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MANUFACTURING: PLATE DEFECTS

SEPARATIONS, CTOD

Cracks,or cracklikefeatures that appear in the fracture face of mechanicaltest pieces.

Separationsappearin Charpy. CrackTip Opening Displacement and Drop Weight

TearTest pieces.Their occurrencemay be

influenced by steel chemistry and plate rolling conditions, particularly heavy

deformation at low rolling temperatures.

The cracklike featuresare related to the

steel structure,forexampiefinebandsof

martensite.

(17)

MANUFACTURING:

PLA

TE

DEFECTS

SEPARATIONS, DWTT

Cracks,or cracklikefeatures that appear in thefracture faceof mechanicaltest pieces.

Separationsappearin Charpy, CrackTip Opening Displacement and Drop Weight Tear Test pieces.Theiroccurrencemay be influenced by steel chemistry and plate rolling conditions, particularly heavy deformation at low rolling temperatures. The crack likefeaturesare related tothe

steel structure,forexamplefine bandsof martensite.

(18)

MANUFACTURING: PLATE DEFECTS

SLIVER

•

A thin.Elongatedflap ofmetal rolled into thepipesurface,oftenwith oxide or scale trapped beneath it.

Rolling out of surfaceasperities, protrusions or solidified splashesof

molten metal.

(OMMENF ~ - --- ~- -.- ~

Small sliversare not structurally

significant.Soluble salts contained wit hin

scale or oxidesbeneath the slivermay initiate pitting corrosion.Sliversalso createholidaysin thin film coat ings. Superficialsliversmay be removed by grinding before application of the coating.

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-MANUFACTU RI NG: SEAMLESS PIPE DEFECTS

COPPER PENETRATION

Crack like features normally at right anglesto the pipe or plate surface.

Copper contamination occurs during the Pilger Mill process, For example following external contamination from defective equipment.Copper on thepipe surface penetrates into grain boundaries and forms a lineof weakness that may open up,into crack like features,under st ress.

In extreme cases the cracks can extend through thepipewall.

Copper cracking should be detected by the Quality Control and pipe inspection proceduresinthe pipe mill.

(20)

MAN

UFACTURING :

SEAMLESS PIPE DE

FECTS

DOUBLE SHELL

A discontinuity inthe pipe wallthat In

extreme cases, splits the pipewall into two segments.

Commonly associated with an

interrupted pour at the ingot stage which

allowssurface oxidation to occurwithin

the partiallyformedingotTheline of oxide remainsasa zone of weakness in

the finished ingot and separation occurs

along the zone during forging.

Separationsthat run at an angletothe

pipe wall may be structurally significant

and should be detected by the inspection proceduresin the pipe mill.

Separationsthat run paralleltothepipe surfacemay not bedetected,but may not be structurallysignificant.

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MANUFACTURING: SEAMLESS PIPE DEFECTS

INGOT DEFECTS

Irregular shaped crack-like defects running intothe pipewallatahighangle to the pipe surface.

Defectsin the surfaceof the original ingot that have not been removed during scarfing in the pipeforming process.

Smallsurfacedefectsarenot structurally significa ntbut maycreate defectsin thin film coatings.

Superficial defects may be removed by grinding before application of the coating.

(22)

MANUFACTURING: SEAMLESS PIPE DEFECTS

LAMINATIONS

A discontinuity lying parallel to the pipe surface, usuallymarked by a

concentration of non-metallics.

Rolling-out of inclusions,blow holes, pipesor ingot cracks in the parent material.

Largelaminations may be structurally significant. Some older pipelinescontain pipes with large laminationsthat have not created a safetyhazard in many years service.However,such defects could pose aproblem if through-thickness stresses are generated in thepipe wall,for exampleduring top tap or repairwelding operations.

Surface brea king laminations may contributeto coatingfaultsand may serveasan initiation pointfor pitting corrosion.

e: MACAW'S PIPELINE DEFECTS 18

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M

ANUFACTURING :

SEAMLESS PIPE DEFECTS '

LONGITUDINAL SURFACE LAPS

Afiapof metallying fiatonthe pipe surface, usuallywithatrappedresidue of oxide or scalebeneath it

A metalprotrusionthatis folded and deformedinto thehot metal surface during the pipe-forming process.

Generally small laps have little or no structural significance.Laps do create holidays, ordefects,inthin film coatings. Soluble salts trappedin the scale or oxidesbeneath the lap mayact asa corrosion 'hot spot' andinitiate pitting. Superficial surface laps may be removed bygrinding beforeapplicatio,n ofthe coating.

(24)

MANUFAUURING: SEAMLESS PIPE DEFECTS

MANUFACTURING DEFECTS

Irregularshapeddefects in thepipewall

Solidification defects in the ingot that are carried through into the pipeor piecesof lapped materialthat havefallenout.

Significant manufacruring defects should

be identifiedby pressure testing in the pipe mill orduring the pre

commissioning pressure test.

(25)

SLAG INCLUSIONS

Non-metallic inclusions In the pipe wall.

Caused whenaningot iscontaminated with slag.ln wellcontrolled pipe production most slag inclusions are removed during the piercing process and when theendsof the ingot are trimmed during the pipe forming process.The shapeoftheslaginclusionwill be governed by the forging process.

Slaginclusionsare usually too smallto be structurally significant.However, surface brea king slag may initiate a corrosion'hot spot'or a defect in athinfilm pipe coating.Superficial slag inclusions may

be removed by grinding before " , 

application of the coating.

,

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MANUFACTURING: SEAMLESS PIPE DEF ECTS

SURFACE DEFECTS

Shallowdefects thatappear atthepipe surface.

Variouscauses including ingot defects,

longitudinal surface laps, slag inclusions, slivers,transversetearsand surFace

roughness.

Most defects are not structurally significant but may create defectsinthin filmcoatingsand act as an initiation

point for pini ng corrosion.

'f, MACAW'S PIPELINEDEFEGS

(27)

TRANSVERSE TEARS

Crack like features atthe pipe su rface

running in the hoop direction.

Cracks intheingot,for example transverse shrinkage cracks, maybe

carriedthrough to the pipe if insufficient

material is removedfrom the ingot

surfaceduring thescarfing process.

Transverse tears may create defects in thin film coatings. Superficial transverse tears may be removed by grindingbefore application of thecoating.

(28)

8

MANUFACfURING: SEAMLESS PIPE DEFECTS

UNEVEN WALL THICKNESS

Seamless Pipe

Variation in wallthickness along apipe,

commonly in a spiral pattern.

:

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Variationinwallthicknessmay occur

E _du_rin_{g th}_{e Pi}_lger_process_._The_p_ip_e_i_s

E I 5 rn rn Q) ₄ t: .>c: u 3

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2

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0 - rotated as it progressesthrough the

Pilgermill andthisresultsinthe spire] pattern of wallthicknessvariation.The variation may be -5 - 10% of wall

-

I

thickness,but in extreme cases the variation mayexceed 1O%.

j

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0 60 12 0 18 0 240 30 0 360

Location - Degrees

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MANUFACTURING:

ERW PIPE DEFECTS

BURN MARKS

Local area of transformed,hardened, microstructure.It occurs oneitherside of

the seam weld on the outersurfaceof thepipe.Burn marks may beassociated with lack of fusion intheseam weld.

Poor or intermittent electrical contact between the rollers used to introduce the electrical current to the pipe.The rollers are locatedeithersideofthejoint lineon

the outersurfaceof the pipe.Burn marks arenot found on HighFrequency Induction welded pipe.

Good maintenance and operation of the pipemaking equipment in the mill.Repair is not usually required unless the burn marks are extensive when local dressing of the pipewall,within acceptable

g ri nd~ g limits, and subsequent NDT

inspection to confirmfreedomfrom cracking should be carried out.

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MANUFACTUR

ING:

ERW PIPE DEFECTS

DIVERTED INCLUSIONS

•

Aligned,non-metallicinclusionsin the

parent strip are diverted through 90

degrees at the weld seam causing a plane of weakness.

Poor quality,dirty,parent strip.The inclusions become realigned as a

consequenceofthewelding process.

Use good quality, clean, strip.

Repair isnot usually required unlessthe

planeof weaknesshas resulted in a fracturethrough thepipewall.When repair is required, replace the pipe or

installa repairclamp.

LINEOFWELD

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MANUFACTURING: ERW PIPE DEFECTS

HOOK CRACKS

Internalor externalcracks within theweld, usually curved in shape.The cracks are axial andat right anglestothe pipe surface.

Poor quality, dirty strip.

Use

goo

d

quality,cleanstrip.Replace pipe or install repair clamps or repair shellsas appropriate.

(32)

MANUFACTURING:

ERW PIPE

DEFECTS

LACK OF FUSION

Axial,crack like, planarfaultsat the mid point of the weld.

Incorrect welding parameters,for example low welding current input which leads to insufficient resista nce heating atthejoint line.

Lack of fusion may be associated with burnmarks onthe outersurface of the pipe.

Ensure good maintenanceand operation of the pipemakingequipment inthe mill. Replace pipe or install repair clamps or shellsasappropriate.

i', MACAW'S PIPELlNE.DEFECTS

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MANUFACTURING: ERW PIPE DEFECTS

MISSED NORMALISING

Lackof grain refinedstructure atthe weld line,leading to poor weldlinetoughness. Visibleon the macro-section asthe well defined heat affected zone on either side

of the line of the weld.

Misalignment of pipe mill induction heat treatmentcoilsothat on-line post weld treatment misses theweld zone

Ensure correct set up of the weld line tracking equipment in the pipe mill. Missed normalising can lead to failure along the weld line by brittle fracture when the pipelineis subject tosevere service conditions. Thisproblem is only detected bypipeline failure so. replacement is necessary.

~ MACAW'SPIPE LINE DEF[-erS

LINE OF WELD

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MANUFACTURING

:

ERW PIPE DEFECTS

SEAM MISPLACED TRIM

LINEOF WELD

.Axial groove or depression aligned to onesideofthe seam weld.

Misalignment of the weldtrim grinding toolwiththeresultthat grinding is offset from the centre line of the weld.

Ensure correct set-up,maintenance and operationoftheequipment in the pipe mill.

Misplaced trim isunlikely to contribute to pipefailure,except inthe most extreme operating conditions, so repair is not normally required.

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MA

NUFACTURING:

ERW PIPE DEFECTS

SEAM OVERTRIM

Axialgroove or depression onthe lineof the seam weld.

Excessgrindingof the weld flash.

Ensure correctmaintenance, set-up and operation of the pipe making equipment in the mill.

Overtrlrn is unlikely to contribute to pipe failure exceptin the most extreme operatingconditions.Repair is not

normally necessary. LINEOF WELD

(36)

MANUFACTURING: ERW PIPE DEFECTS

SEAM UNDERTRIM

Linearfeaturestanding proud of the pipe

surface ontheline of the seam weld.

"

Insufficient grinding of the weld flash

Ensure correct set-up, maintenance and

operation ofthe equipment inthe pipe

mill.

Undertrim is unlikely to contribute to

pipefailure,except in the most extreme operating conditions,sorepairis not normally required.

UNE OF WELD

(37)

MANUFACTURING:

S

AW

/

SPIRAL P

IPE

DEFECTS

'

CONCAVE CAP

Concave profile in the weld cap.

Insufficientweldmetalcaused byatravel

speedthatistoo fastor bytoo fewweld

runs.Concave cap ismost common at

the3 o'clockand9 o'clockpositionson the pipe.

Use aslow travel speed.Add astripper' run to the 3 o'clock and 9 o'clock

positions before cappinginorderto build up the thickness locally.

Not a significant defect if the total weld thickness isgreaterthan the pipe wall

thickness.

(38)

MANUFACTURING: SAW/SPIRAL PIPE DEFECTS

COPPER CRACKING

Cracking in the weld metal,normally close to theweld centre line. Cracks followtheweld solidification structure.

Accidental introduction ofcopper into the weld pool eitherfrom build up of copperdustfrom fillerwire coatingor from melting of electrode contact tube.

Ensurecorrect maintenance and operation ofthe seam weld equipment in the pipe mill.

Cut out affected pipe and replace.

(39)

MANUFAGURING: SAW/SPIRAL PIPE DEFECTS

END CRACK

Axial cracklocatedat the endof thepipe.

End cracksareusually small,<10 mm long.Theyarecaused by the stress inducedin thepipe whenthe end plugs areforcedinto thepipe during the mill hydrostatic test.

End cracks may not be identified in the hydrostatictest carriedout inthepipe millbecause theleakrate istoo smallto be detected.Thecracks arevisibleonthe radiographsof girthwelds and canbe detected at thisstage of construction. Leakratesmay betoolowtodetect in the pre-commissioning hydrostatic pressure test.

Cracks found during construction must be cut outand thepipere-welded.

©MACAW'S PIPELINE DEFEc rs

(40)

HARD SPOTS

Hardness Survey 4'0 0 m m 2 00 m m Local areaof hardmicrostructurein a

pipewhichmaybe susceptibleto in

service cracking.

Accidental rapid cooling of a smallareaof

the plateduring hot rolling,for example

by water contamination.

Ensure correct maintenance and

operation of the rolling equipment in the

plate mill.Hard spots may be susceptible

to hydrogen cracking ifthe service

conditions areconduciveto this.Cracking

would not be expected in hard spots

covered by an effective,adherent coating.

Shallow hard spots maybeground

followed by Non DestructiveTesting to checkfor cracking.Replace the pipe when the hard spot and associated cracking is too big to grind.

(41)

MANUFACTURING: SAW/SPIRAL PIPE DEFECTS

HOT CRACK

Solidification crackin the centreline of

theweld bead.Tendstooccur towards the end of a pipe in the last metal to solidify.

Low meltingpointimpuritiesintheweld

metal, possibly diluted from dirty parent

plate.Poor solidification profile in the

weld,forexampleahigh bead depthto width ratio.Stresson theweld during

solidiricanon.

Ensure correct welding procedures and welding conditions in the pipe mill.Cut

out the pipe section and replace.

(42)

MANUFACTURING: SAW/SPIRAL

P

IPE

DEFECT

S

HOT TEAR AT LAMINATION

Solidificationcrackin the weld bead that

has initiated from a band of segregation

in the parentplate.

Plane of weakness and highchemistry materialat segregated band inthe plate initiatesa crack in the adjacent weld bead during weld pool solidification.

Use clean plate.

Mayonlybediscovered ifthe pipe sees severe service.

Cut out and replace the affected pipe.

Alternative repair procedures may be acceptablesubject to afulldefect assessment.

(43)

MANUFACTURING: SAW/SPIRAL PIPE DEFECTS

HYDROGEN CRACKING

Transverse cracks in weld bead often lying on alternate 45° planes.Also referred to as'chevron'cracking.

Damp flux, high strength consumables.

Only found in thickwall (>25 mrn) and high strength (> API5LX60) pipe. Prevented by correct consumable storage and handling.

Mayonly cause problemsinsevere service conditions.

Cutoutand replacetheaffected pipe. Alternativerepairprocedures may be acceptablesubject toa fulldefect assessment.

(44)

MANUFACTURING: SAW/ SPIRAL PIPE DEFECTS

LACK OF FUSION, SIDEWALL

DE5CRIPlIQN

Lineardefect at weld sidewall,or in top

edgeof the weld.

Incorrect positioning of welding head or

incorrect welding parameters resulting in lack of fusion.

Ensure weldline trackingequipment is

functioning correctly.

Ensurecorrect welding proceduresare used.

May cause failure during cold expansion

inthe pipemill otherwise itmayonlybe discoveredifthepipe sees severe service

conditions

Cut out and replace the affected pipe.

Alternativerepair procedures may be

acceptable subject to a full defect

assessment.

(45)

LACK OF INTER PENETRATION

Linear deject between the inside and outsideweld beads.The cracklikedefect isaligned through the wall thickness.

Rootface too largeor weldingconditions incorrect.

Ensure accurate machining of the root face and correct choice of welding conditions.

I

~ _Lo_ok_f_o_r_s_ufficien_t_in_terpenet_ration_o_f_t_he external and internal weld beads on macro-sections taken during the Manufacturers Procedure Qualification Test.Checkalso during routineQuality Cont rol testing.

May only be discovered if the pipe sees severe service.

(46)

MANUFACTURING:

SAW/SPIRAL PIPE DEFECTS

MISALIGNMENT

Lackof fusion in the seam weld.

Misalignment ofthe weld bead resulting

in lack offusion at somepoint in theweld profile.

Misalignment can producelargedefects

in the seam weld whichshould be

detected in the milltest orpre

commissioning hydrostatic test.Testing ZONE OF LACKOF FUSION IN below 105% ofthe specified minimum

D

S

A

W SEA

M

W

E

L

D

yield strength (SMYS) maynotrevealall

defects.

(47)

ROOF TOPPING

•

Peaking at the SAWseam weld.

Pipe milldefect caused byfailure to crimp the plate edges sufficiently before the 'Uand 0' pipeforming process.

Improve mill practice

May beacceptable withinspecified limits

if pipedoes notseesevere service.

Otherwise reject the pipe

(48)

MANUFACTURING: SAW/SPIRAL PIPE DEFECTS

SLAG INCLUSIONS

.

Non-rnerallic inclusions in the pipe wall.

Caused whenthe source steelhasahigh sulphur content and manganeseor

calcium sulphide Inclusionsareformed.

Theirshape dependson the type of inclusion and the plate rolling process.

Slag inclusionsareusually too smallto be structurally significant. However, surface

breaking Inclusions may initiate corrosion

orcreate a defect inathin filmpipe coating.

•

(49)

SURFACE LAP AT WELD

'

.

Crackingin close proximity to theseam weld and running parallel to it.

Longitudinalingot cracks that are carried

throughinto therolledplate.Suchcracks may occurat any point inthe pipeplate. Cracksclose tothe edge ofthe platemay open up during the welding process.

Assessthe structural Significanceof the cracksand repair or reject the pipe as

appropriate.

(50)

TOE CRACKS

Cracksat tne junction betweenthe submerged arc bead and the pipe

surface.

Causes of toe cracksinclude:platesurface

contamination,poor platesurface quality,

roiled in scale, inclusions that lead to

crackingat theweldtoe. Delaminationof inclusions may occurduring weld cooling with subsequent cracking during

cold expansion in the pipe mill or during a hydrostatic pressure test.

Useclean, high quality plate.

May only be discovered if the pipe sees severe service conditions.

(51)

MANUFACTURING: SAW/SPIRAL PIPE DEFECTS

TOP HAT CRACKING

Solidillcation crack in the weld bead initiated from a change in profile at the weld fusion boundary.

Poor weld bead profile leading to concentration of SHain during weld bead solidification.

Ensurecorrect choiceofwelding parameters,weld bead geometryand high purity pipe and welding consumables.

May onlycause problemsin severe service

(52)

MANUFACTURING: SAW/SPIRAL PIPE DEFECTS

UNDERCUT

.. ~.

Alin ardefectattheedgeofthe internal

or external weld bead.

Metalisremoved fromthe edge ofthe weld bead by the force of the welding arc when the welding current 15 toohighor when theangleof the welding electrode

incorrect

Undercut isusually aroundeddefect and, providedit isnot too deep,limited lengths ofundercut areallowedinmost

specifications.Undercut can be repaired,

if necessary, bygrindingoutthedefect and carrying out a local weld repair.

(53)

(54)

CONSTRUCTION DEFECTS

INTRODUCTION

Construction defects include girth weld faults, poor construction standards, mechanical damage,corrosion and ground loading.

Section One deals with girth weld defects.

These include lackof fusion, lack of penetration, cracking,porosity and slag intrusions. Girth welding proced ures and consumables should be carefully selected and shouldbe subjectedto a weld qualification procedure to verify that the proposed practices produceweldsof the required quality. Non-destructive testing of all welds should also identify major weld defects.

SectionTwo deals with poor construction standards. Poor construction standards produce features in the pipelinethat do not posean immediate threat to integrity but may contributeto thedevelopment of operationaldefects, for exampledueto stress concentration.

Mechanical damage,in the form of dents, kinks and gougingdoesoccurduring construction but significant faults should be detected in thepost construction, hydrostatic pressuretest. Some mechanica l damage will survivethistestand may be detected,many years later,duringan intelligent pig inspection.As a general rule all mechanical damage detected in this wayshould bereassessed asthoughit had occurred after construction. Mechanical damagedefectsareincluded under Operatlonal Defects.

Both internal and external pitting corrosion can occur in pipe if it isstored incorrectly during construction.After construction this corrosion will be dormant,in most circumstances:However, all corrosion

identified by an intelligent pig inspection should be considered'active' unless it can beclearlydemonstrated that it occurred during construction.Corrosion isincluded under Operational Defects.

(55)

CONSTRUCTION DEFECTS

66

Tungst en Inclu sion

67

68 69 70 71 72 73 74 75

76

77

78

79

80

81

82

83 84

Butt Welded Patch Cold Bend Kink Contacts

Eccentric Touching Case

Incorrect Pipe Support Lack of Cover

Lamellar Tearing Mit re Bend

No Field Joint Coating Unprotected Risk 85

86

87

88 89 90 91 92 93 94

(56)

CONSTRUCTION: GIRTH WELD DEFECTS

ARC STRIKES

A localised heat affected zone on the surface of the pipe.Anarc strikemay produce hardening,andin high strength hardenablesteels cracking may occur.

Anarcstrikefrom amisplaced electrode during the welding process.

Arc strikes are an indication ofpoor workmanship and acceptance levels are normallydefined in thewelding specification.Pre-qualification of welders may also help to reduce arcstrikes.

During construction shallow featuresmay not require repair. largefeatures should be dressed or removed according to the weld acceptancespecification. Arcstrikes are generally notacause to

excavate a pipeline.Arc strikeslocated during other work may be dressed.

{, MACAW S PIPEliNEDEFEGS 54

(57)

CONSTRUQION: GIRTH WElD DEFECTS

BURN THROUGH

Localarea wherethe root bead ISmissing. Often covered by the next pass.

Alsoknown as'window:

Welding current too high.

Poor electrode manipulation.

Root face too small.

Use correct welding parameters and

weld geometry.

(58)

CONSTRUCTION: GIRTH WELD DEFECTS

CAP UNDERCUT

A smooth groove between the capping run of the weld and the parent plate.

Current too high.

Incorrect electrode manipulation.

Adjust current to the electrode diameter.

(59)

CO

NSTRUCTION:

GIRTH WELD DEFECTS

CONCAVE ROOT

Concave profile of the root run.

Current too high.Incorrect joint preparation,for example the root gap is too large.Concave root occurs most commonly at the 6 o'clockposition on the pipe.

Adjustthe current to suit thejoint Width. Not significant if the contour of the root is smoothand the totalweld thickness is greaterthanthe wall thickness of the pipe.

(60)

COPPER CRACKING

Finecracking inthe weld metal,often with associated copper inclusions, and concentrated at the grain boundaries.

Arc strikingonto thecopperbacking bar. Welding torch contact tip touching the side of the weld bead.

Contamination fromthermit orpin

brazing compounds.

Ensure clamp backing bars arein good conditionand thatweld fit upis good. Alternativelyuse cera mic backing strips.

Avoid contact tip touching the bevel. Usually only significant if the cracking is extensive. Smallareas maybe dressed by grinding followed by MPI inspection. Somestandards specifyacceptablelevels

of penetration for brazing of cathodic protection connections.

(61)

CONSTRUCTION: GIRTH WELD OEFEas

EXCESS CAP HEIGHT

.

-Excessweld reinforcement on the cap. usuallygreaterthan3mm.lt ismore commonat the6 o'clock position.

Incorrect electrode manipulation and too many weld runs.

Select current to match thejoint width. Adjust finalfiller passheight.for example

bygrinding, beforeapplying cover pass weld reinforcement.

Grind to a smooth profileorremove

completely by grinding and re-weld.

Excesscap height usually only has

I.

structuralSignificanceinafatigue situation due to increased stress

concentrationat the weld cap-to-pipe intersection.

(J MACAW'S PIPELINEDEfECTS

(62)

CONSTRUCTION:

GIRTH WELD DEFECTS

EXCESS PENETRATION

Excess weld metalin theroot of the weld,

usually morethan 3 mm.

Toolargearoot gap orincorrect

electrode manipulat ion. Excess penetration is most common atthe12

o'clock position.

Use the correct root gap and I,',oelding

technique.

Grind to asmooth profile.

@ MACAW'SPIPELINE DEFECTS 60

(63)

Weld metalhydrogenfissures, or 'fish eyes' arecircular orelliptical features on

weld fracturesurfaces,usually tensile

specimens, with a shiny grey appearance and adark'eye'at. the centre.

Dissolvedhydrogen 'Inthe weldmetal

which triggersa low duculny fracture

when the rnarerlal is strained.Found

especially in test speornens from welds madewrth cellulosic electrodes which arestrained ashort timeafterwelding.

Reqarded as an artefact caused by the test.ing process and of no significa nce For

rhe real weld They can be avoided by

using a low hydrogen welding process, by Increasing the delay time between welding andtesting,orbygl\ling the

weld a low temperature hydrogen .

removal trea tment.Repairis not

necessary.

CONSTRUCTION: GIRTH WELD DEfECTS

FISH EYES

(64)

H CRACKI NG CAP HAZ

Cracking Originating at the edge of the weld cap and following the heat affected

lone.

Hydrogen from the welding process. Low interpasstemperature and rapid

cooling after welding.

Excess stresson the completed weld

Use a low hydrogen welding process.

Maintain adequate interpass

temperature,Wrap the complete weld to slow the cooling rate Avoid high stress on

new ly completed weld s.

(65)

CONSTRUCTiON: G!RTH WELD DEFECTS

H CRACKING, ROOT HAZ

Cracksinitiating inthe heat affected zone

of the root bead and propagati ng up the heat affectedzone or into the weldmetal. Alsoknown as 'cold cracks'or 'underbead

cracks'

Insufficient pre-hea t or insufficient

mrerpass temperature

Poor weldabilityof the pipeorfittings

Delay betweenthe root and hot pass welding

Lift height too greatdurtnq frontend

skidding

Damp consumables

(66)

CONSTHUCTION: GIRTH WELD DEFECTS

H CRACKING, WELD METAL

Cracking in the weld metal. Often

transversetotheweld aXIs and lying at an

angle of 45° to the weld surface.

May have a 'staircase' appearance at high

magnification

Insufficient pre-heat or rnterpass

temperature. Damp consumables High strenqth consumables

Heavy wall pipe,narrow weld

preparations

Cut out weld and remake

(67)

- - - -

-

-CONSTRUCTi ON:GIRTH WELD DEFECTS

LACK OF FUSION, INTER RUN

Lack of fusion between adjacent weld beads Alsoknown as'cold laps'

InsuffiClef1 l melting of groove faces dunng welding.

Insufficient current.

Contamination oroxidanonof the groove faces.

Adjust (he current to SUit the electrode

diameter and welding position.Clean _\

groovefaces properly before welding.

(68)

CONSTRUCTiON: GIRTH WELD DEFECTS

LACK OF FUSION, ROOT

Lack of fusionbetweentheedgeof a fully penetrated root beadandthe root face

on onesideof the jomt,Also knownas

'missed edge'.

Incorrect electrode angle

Inadequate clea ning of the root face

Maybe acceptableif within specified length limits,typically 25mm in300mm of weld lengthoOtherwise grind out and repair by re-welomq

(69)

CONSTRUCTION: GIRTH WElD DEFECTS

LACK OF FUSION, SIDEWALL

Occurs as planardiscontinuitiesbetween successive weld passesor between the weld bead and the pipe.Lack of side wall fusion is especiallycommon in

mechanised gas metal arc welds.

Lack ofcompletemelting between weld beads or between the weld bead and the pipe caused bywrongelectrodeangle, Insufficient melting current or poor cleaning of thejoint faces.

Use correct welding parameters and clean the Joint faces.

Limited lengthsof lack of fusionare allowed In most standards, For example 50 mm In 300mm of weld.

• I _

f

,

(70)

CONSTRUCTION: GIRT H W ELD DEFECTS

LACK OF INTER PENETRATION

Failureof inside weld bead and outside weld bead to penetrate,especiallyIn mechanised gas metal arc"velds.

Root Face too large Bevel angle too narrow Welding current too low

May be accepta bleif thedimensionsare withinacceptable limits ,typically50mm

in 300 mm weld length.Otherwisegrind out and repair

(71)

LACK OF PEN ETRATION

Ineom plete penetration of the weld through the full thickness of the JOi nt to leave an unFused crevice, typicallyin the root run,

Root gap too small Rootface too large Welding current too low Electrodeangle mcorrecr

May be acceptable

i

f

within specified

length limits,typically 25 mm in 300 mm of weld length.Otherwisegrind out and repalr,

(72)

MISALIGNMENT

Misa lignment of thepipe ends acrossthe weld bead to produce an asymmetric weld Alsoknown as'Hi-La'

Poor Fit up, possibly caused by pipe ovahryroof topping at the pipe seam weld or handling damage to the pipe,

Improvefit up by the use of stronger clamps and JOinting bars,

Rotate pipes For betterFit up, Replace pipes or match endsof Individual pipes,

Repair not normally required jf the weld and cap Forma smooth rransmonwith the parent plate,

<;,MACAW'S PIPELlN[ DEFECTS 70

(73)

CON STRUCTION; GIRTH WELD DEF ECTS

POROSITY, CLUSTER

A group of poreswithin the weld metal

Lack of shielding gas or damp shielding gasfor gas metal arcweldsand gas tungsten arc welds.

liVlnd disruption of shield gas Arc length too long

Weld preparation damp or greasy

May be acceptable if evenly distributed within specified limits, usually based on disrnbunon diagrams Otherwise grind out and repair

(74)

CONSTRUCTION: GIRTH WELD DEFECTS

PARALLEL SLAG LINES

Linearvoids or slagInclusions most commonly Foundbetweenthefirstand second pass weldsIn manual'stovepipe' welds, and often appear on radiographs astw o parallellines Alsoknown as 'waggon track:

Slag resulting from insufficient grinding of the root bead external surface before making the second pass, or insufficient cu.rrent used for the hot pass.

Ensuregrindingof theroot beadto remove convexity and to clean out slag at thesidewalls.Increasehot passwelding current.

May be acceptable Within specified limits. Otherwisegrind out and repair.

(75)

MISPLACED CAP

Weld capping run IS misplaced to one

sideso that it does not fully cover the underlying filler pass, especially In gas metal arc welds,

Poor control of eiectrode position

Place electrode correctly Grind, if necessary, and re-weld

LINE OF W W

(76)

CO

NSTR

U

CT

IO

N

:

G

IRTH

WELD

D

EFECTS

POROSITY, ROOT

A continuous pore inthe centre orthe

root bead Also known as'ho llow bead:

Incorrect electrode angle

Root gap too narrow

lm punues or excessalloying In the parent plate

May be acceptable wit hin speofieo lengt h limits, typically 50 mm in 300 mm weld length,Otherw lse grind out and repair,

~' M,;ctSt'i PIPELlN[ DEFECTS

(77)

CONSTRUCTiON: GIRTH WELD DEFECTS

POROSITY, ISOLATED

Isolated gaspores in theweld metal

Minor disturbances In The g3s shielding or disruption of the weld pool dunnq solidIf/cation.

Gasshieldflow ratestoo high.

Weld preparation damp or greasy.

May be acceptable within specified limits, usually based on distribution diagrams.

Otherwisegrind out and repair.

(78)

COf\jSTRUCTION: GiRTHWELD DEFECTS

POROSITY

,

PIPING

reproduced wnh [heperrmsSIOn of ,WI Lid

Elong3tedporosity in theweldbead.

Also known aswormholesor herring

bone porosity.

Dissolved gasleaving theweld poolas it

solidifies.

Removethe sourceof dissolved gas, For

examplebettershielding,clean weld

preparation etc.

May be acceptablewithin specified limits, usually based on distribution diagrams Otherwise grind out and repair.

(, ~ MACAW'S PIPELINE DEFFCTS

(79)

CONSTRUCTION: GIRTH WELD DEF ECTS

POROSITY, SCATTERED

Scatteredgaspores In theweld metal.

Weld pool solidifying too rapidly whilst supersaturated with dissolved gas.

Remove source of dissolved gas. Increase welding heat input

May be acceptablewithin specified limits, usually based on distribution diagrams. Other wise grind out and repair.

• - - - - - - - - - > - - - - -

• <

(80)

CONSTRUCTION:GIRTH WELD DEFECTS

REPAIR, WELD CRACK

Hydrogen cracksassociated with repair

welds.

Poor repai r welding practice such as, lack

of pre-heat or use of si ngle back weld run instead of two.

Cut out the weld and remake it.

(81)

COf\JSTRUCTJON: GIRTH WELD DEFECTS

ROOT BEAD SLAG INTRUSION

Trapped slag at theinside edge of the

root weld bead,often asscdated with a cracklikelack of Fusion defect,

A Feature of stovepipeweldingwith

cellulosic electrodes which is not properlyunderstood but is thought to be associated with poor weld pool flUidity.

Pay particular attention to weld preparation dirnenstonsand jomrfit up. Change the type of cellulosic electrode.

Change 1:0low hydrogenelectrodeor other root bead process.

Maybe acceptable IFnot extensive.TlusIS

not covered by the normal pipe welding

standards,and ISoften interpretedas lack

of root fusion,and those defectlimits are applied. " -~ !vlACAW'5 9iPEUNE Dt ~~CTS

.

'

-' _"_~_I' r ' ;j' 79

(82)

CONSTRUCTION: GIRTH WELD DEFECTS

ROOT UNDERCUT

A grO::lVe or channel melted into the pipe

metal adjacent to theroot or caprun which has not been filled with weld metal.

Too high a welding current Incorrect electrode angle

May be acceptable within specified length limits, typically25mrn In a 300 rnrn weld length Otherwi se grind out

and repair.

-.. ~ MAC,~W'S PI PEUNE DEF ECT) 80

(83)

CONSTRU CTION:GIRTH WELD DEFECTS

SOLIDIFICATION CRACKS

Crack Inthe centreofthe weld bead,

especiallywithin hot pass.Also known as

'hot tear'

Poor weld bead solidification pattern, for

example a large depth to width ratio.

Excessive restraint I stress on the weld during solidification.

Impurities in the weld pool

Correct deficiencies. Change weld

consumables. Grind out and repair

reproduced with the "ermilllOn of 7W1 Lrd

'"o f MACAW'S PIPELINE OEFEGS

(84)

CONSTRUCTION: GIRTH Wa D DEFECTS

STOP START DEFECT

Alack of fusion, alackoffillora lackof penetrationatthestop/ startposition, often in the root bead.Alsoknown as 'poor pick up.

Failureto overlapthe stop / startposition when changing electrodes.

Failure to grind the crater,failureto fillthe crateror Failureto establishweld pool properly when re-stnkinq,

Visually acceptable within specified limits,

depending on the type of defect.

P MACl\W'S PiPEUNE DEr=r-.:crs

(85)

- - --- -- - - - -- - - --

-CONSTRUCTION: GIRTH WELD DEFECTS

TRAPPED SLAG

-_.

.-Slag trapped between individual weaves of the weld run.Also known as'slag holes:

Current too low

Weaving technique too rapid

Maybe acceprablewithinspecified limits.

Otherwise cut out and repair.

(86)

CONSTRUCTION: GHH H WELD DEFECTS

TUNGSTEN INCLUSION

lsolatedinc!usions of undissolved tungstenin the weld bead.Appears as a white spot on the weld radiograph

Contact betweenthe tungsten electrode andthe weldpool when gas tungstenarc vveldmg ISused,especialiy manual GTAW. Occursespeciallywuhm stop

I

starts

Avoid contact between the tungsten electrodeand the weld pool.

Use highfrequencystartingor soft start equipment insteadof theconventional touch starting.

May be acceptable within speofied limits, typicallyspecified as a maximum number per weld Otherwisegnnd out and repair

,.,' ~;A Ci\W ' S PIPELINE OtFi'CTS

(87)

CONSTRUCTION: CONSTRUCTION DEFECTS

BUTT WELDED PATCH

Butt welded patch in a pipeline

During construction a manhole hasbeen cut Into a pipe to gain access to the

Inside of the pipe for weld repairs.The 'cut out' is thenwelded backinto thepipeline

with a butt weld.

This is unacceptable construction practice.The area of the patch should be cut OUl and replacedor repairedwith a full encirclement sleeve.

(88)

CONSTRUCTION: CONSTRUCTION DEFECTS

COLD BEND KINK

Circumferential kink or rip ple in pipe that

has been subject tocoldbendingInthe field

Caused by poor control of the field

bending process

Discard the pipe or cut out affected area.

.'.;MACAW'SPIPEUNf DHEGS 86

(89)

CONSTRUCTION: CONSTRUCTION DEF ECTS

CONTACTS

The pipeline is In electrical contact with

'foreign' structures such as pipe supports or reinForcing bars In concrete

Poor construction practice

Electrical contacts createa drainonthe

applied cathodic protection current and may prevent effective protection.

Galvanic or interference current corrosion

may resultand lead to rapid pittlllg and throughwall penetration in theaffected area.

(90)

CONSTRUCTION: CONSTRUCTION DEF ECTS

ECCENTRIC TOUCHING CASING

The casing IS not alignedparallelwith the carrier pipe and,in extreme cases IS In

contact with the carrier pipe

Poor construction practice or ground

movement after construction

Electrical contact betweenthe casing

and the carrierpipe may create alocal drain on the applied cathodic protection and create a localised corrosion cell.

(91)

CONSTRUCTION: CONSTRUCTION DEFECTS

INCORRECT PIPE SUPPORT

Aboveground pipe issupportedon objectsotherthan manufactu redor shaped pipe supports.

Poor construction practice.

inco rrect pipe supp orts may create problems that Include stress

concent ration,damage to the protective coating or electrical contactsthat interferewith theefficientoperation of the applied cathodic protection.

(92)

CONSTRUCTiON: CONSTRUCTION DEFECTS

LACK OF COVER

Shallow depth of burial.

Poor construction practice.

The pipe is particularly vulnerable to third

party mechanical damageand

vandalism.

(93)

CONSTRUCTION: ONSTRUCTIOl\j DEFECTS

LAMELLAR TEARING

A crack like Feature within the plane of

the plate

La mellar teannq is associated With Al let welds Through thickness stress, associated With the ,Neldlng process, causes opening In non-metallic Inclusions.

Can occur dunnq construcuon under attachment welds but lamellar tearing is more likely to occur when welding Fittings to old pipelines for repair or for hot tapping purposes.

Lamellar rearing is most marked in dirty plate.Small tears may not require attention but large tears should be assessed.

(94)

CONSTRUCTION: CONSTRUCTION DEFECTS

MITRE BEND

Mitre bends, also known as'lobster back bends'are made by welding together short piecesof pipe with mitred ends.

Mitre bends are not SUi tablefor high pressurepipelines. Possible problems include difficulty in ensuring satisfactory weld quality and poor fatigue

performance of the resulting bend. Mitrebendsshouldbe replaced with forged bends In high pressure pipelines

(95)

CONSTRUCTION:

CON

STRUCTION

DEFECTS

NO FIELD JOINT COATING

Coatingofthe fieldjoint areais incom plete

Poor construction practice

The exposed bare metal creates a drain on the applied cathodic protection will

induce coating undercutand subsequent disbonding if stored In this condition for

prolonged period s.

(96)

CONSTRUCTION: CONSTRUCTlON DEFECTS

UNPROTECTED PIPE

The pipeline IS exposed above ground

without security FenCing or other protective measu res.

Exposed pipe may be susceptible to vandalism,sabotage or accidental damage.

,' MACAWSPIPH Ir<f DEf ECTS 94

(97)

(98)

OPERATIONALDEFECTS

INTRODUCTION

Operationa l defects include the range of feat uresthat initiate and grow whenthe pipeline is in service.The defect grol'vt h mechanisms include:

• External corrosion

• Internal corrosion

• Erosio n

• Fatigu e

• Mech an ical damage

• Ground movem ent Failure mod e

Corrosion, erosion and fatigue are time depende nt processes for which the time frame betwee n initiation and Failure may run to many years.Intlus case theoperator can manage the problem within the accepted safety envelope for the pipeline, with an integrated prog ramme of monitor ing, remedial treatme nt,

rehabilitation or renew al.

96

Mech anicaldamage and ground movem ent can develop almost instantaneously.The pipeline operato r must therefore focuson prevention.

A corrosion risk assessme nt is norm ally carried out at the desrq n stage of a new pipeline.Thisallow s the designer,and operator,to identi fythemajorrisksto pipeline integrity and to Include measures for their prevent ion or cont rol.

The risksto pipeline inte grity may change with time.For example,urban

development may encroach on a buried pipeline and increase the risk of third

party damage.The product carried in gathering line system may beco me prog ressively sour as the hydrog en sulph ide content in the product increases due to contamination of the reservoir. Repeat riskassessments are therefore advisab le.

(99)

Section One deals with external

corrosion. Externalcorrosion is controlled by the combined use ofaprotective

coating and cathodic protection.Afault, or anomaly, IS required in both the

coating and the applied cathodic protection for corrosion to occur. On high pressu re pipelines a form of stress modified

c

orros

.

on

stress corrosion

cracking, may be a risk.

"

-

..,

, I _/

/

"""'

~~,

~

- -- ' - - I - -' : l.l

Section Two deals with internal corrosion

that,in mostcases,requires the presence of free water for corrosion to be active. Mechan isms include sweet corrosion. in

the presence of water and carbon dioxrde.andsour corrosioncracking Sour

service requires thepresence of

hydrogen sulphide in the transported

product.Graphsinthis section usethe

clockfaceas ameansof pipe orientation

(see diagram bottom left).

SectionThree dealsWith erosion. Erosion occurswhere particles, dropletsor bubbles in the flow impinge on the metal surface and remove small particles of the pipe wall.

Section Four deals with fatigue and fatigue cracking under an operating

regime in which the internal pressureof the pipeline is subject to fluctuations.

OPERAfIONALDEFECTS

INTRODUCTION

Section Five deals with mechanical damage from earth rnovinq and excavation equipment, piling and other

agricultural or construction practices.

Section SIX deals with ground movement.Ground movement may be

slow and progressive, as in the caseof soil

creep on ahillside.Itmay alsobe

instantaneousas inthe caseof

earthquakes, landslips,and collapseInto subterranean VOids.Ground movement

becomes a problem when il generates

significant strain in the pipeline.

Section Sevendealswith pipelinefailure

modes, and in particularrupture.

(100)

OPERATIONA L DEFECTS

•

(101)

OPERATIO NAL: EXTERNAL CORROSION

ARCING

Sev

e

re.

localised meta!losswhichmay show signs ofmolten material, such as solidified globules.

Direct shorting from power lines

In thisfault condition through wall

penetration may occurin a veryshort

time.

MACAW´S PIPELINE DEFECTS

W' S P

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PIPELINE DEFECT

S

ACKNOWLEDGEMENTS

•

.

•

MA

CAW

'S

PIPELINE

DEFECTS

INTRODUCTION

MANU

FACTURI NG

OP

ERATtONAl.

MA

CAW 'S

PfP EU NE DEF ECTS

CONTENTS

COATING AND

CP DEFE

CTS

MANUFACTURING DEFECTS

INTRODUCTION

INTRODUCTION

PLATE DEFECTS

BLISTERS

CENTRE LINE SEGREGATIONS

CENTRE LINE SPLITS

INDENTATIONS

PLATE DEFEUS

LAMINATIONS