2006-Aberdeen-9-Palmer-Jones.pdf

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UNDERSTANDING THE RESULTS OF AN INTELLIGENT PIG INSPECTION

By Roland Palmer-Jones, Penspen Integrity, Newcastle-upon-Tyne, UK

Introduction

Intelligent pigs are used extensively or inspecting pipelines! T"eir use "as #een increasingrapidly due to t"eir proven #eneits, expanding capa#ilities, and legislative re$uirements!

T"e result o an intelligent pig inspection is an inspection report wit" a list o deects! To gaint"e ull #eneit rom an inspection t"e pipeline operator must understand t"e inspectionprocess, and w"at t"e list o deects means or t"e immediate and t"e uture integrity o t"epipeline!

T"e Inspection Process

Running an intelligent pig in a pipeline is a signiicant pro%ect wit" potential saety andoperational implications! &ny pigging operation s"ould #e careully planned to ensure t"at t"ecorrect tool is used, t"at appropriate pipeline cleaning is carried out, t"e pig will not get stuc',contingency measures are in place to locate and remove a stuc' pig, and t"at saeprocedures or pig launc", receive, and "andling are ollowed! (uidance on managing anintelligent pig inspection is availa#le)*!

&ssessing +eects

T"ere are a num#er o recognised deect-acceptance or itness-or-purpose./ met"odsavaila#le or assessing t"ese deects or example &012 B34(, and &PI 567/, #ut t"esemet"ods are simply calculation met"odologies8 t"ere are many issues related to t"e inputdata and t"e engineering assessment t"at also need to #e resolved in order to "ave a ullunderstanding o t"e pipeline condition! T"ese include tolerances on pig data, t"e age o t"epipeline, t"e product transported, t"e operation o t"e pipeline cyclic pressures/, t"ermalexpansion loads, ground movement loads, and t"e type and cause o t"e deect!

9onse$uently, it is good practice to approac" deect assessments "olistically! T"is meanst"at all aspects o t"e pipeline:s integrity are ta'en into account, and it is not viewed simplyas an exercise o inputting smart pig data into an e$uation and simply o#taining a predictedailure pressure or t"e deect!

T"is paper provides a process or reviewing any set o inspection data, and gives somesimple guidance on understanding t"e results o an intelligent pig inspection, #ased onexamples or calliper, magnetic lux lea'age 1;


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Level 2 Integrity

Assessment

To fully understand the

problem and consider

whether pipeline is

safe to operate in

damaged condition.

Preliminary Assessment

Evaluation of inspectiondata and pipeline condition.

Consider implications for

future integrity.

Inspection

Level 1 Integrity

Assessment

Confirm

condition of line

is satisfactory and

set future

inspection

schedule

Immediate !pert

Assessment

"efine re#uirements for shut

down$ or pressure reduction.

External inspection to

confirm condition.

%urther Assessment and

repairs&rehabilitation orreplacement as re#uired

Confirm defect

identification, and sizing

with inspection vendor.

'e#uire

'e(inspection

Severe defectsnsatisfactory performance

Some or no defects

Evidence of a

po ten tia l p ro!lem

Everything loo"s #$

%endor

#perator and

vendor

Level 2 Integrity

Assessment

To fully understand the

problem and consider

whether pipeline is

safe to operate in

damaged condition.

Preliminary Assessment

Evaluation of inspectiondata and pipeline condition.

Consider implications for

future integrity.

Inspection

Level 1 Integrity

Assessment

Confirm

condition of line

is satisfactory and

set future

inspection

schedule

Immediate !pert

Assessment

"efine re#uirements for shut

down$ or pressure reduction.

External inspection to

confirm condition.

%urther Assessment and

repairs&rehabilitation orreplacement as re#uired

Confirm defect

identification, and sizing

with inspection vendor.

'e#uire

'e(inspection

Severe defectsnsatisfactory performance

Some or no defects

Evidence of a

po ten tia l p ro!lem

Everything loo"s #$

%endor

#perator and

vendor

;igure 4 &ssessing Intelligent Pig +ata

Inspection

T"ere are now pu#lis"ed standards t"at "elp operators t"roug" t"e intelligent pig inspectionprocess N&92 RP ?4?@-@??@)*8 &PI 44A3)*8 and &0NT I


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standards re$uired #y t"e contract! I t"is it t"e case, a re-inspection may #ere$uired!

c/ To conirm t"at t"ere is no am#iguity over t"e deects reported, or example dueto terminology suc" as crac' li'e. used to reer to deects!

d/ To conirm t"at t"e deects reported are credi#le! T"at is, t"ey are expected ort"ere is a reasona#le explanation or t"eir presence! ;or example, numerous roc'dents. are common in large diameter t"in wall ons"ore pipelines8 "owever, smalldiameter t"ic' wall os"ore pipelines s"ould not contain a large num#er o dents!

e/ (ive a $ualitative assessment o t"e condition o t"e pipelineD &re t"ere manydeects or %ust a ewE

T"is initial review does not re$uire a "ig" level o expertise in pipeline deect assessment ora detailed understanding o t"e inspection tec"nology! It does re$uire an appreciation opipeline deects, w"at causes t"em and t"eir signiicance! It also re$uires an appreciation ot"e capa#ilities and limitations o t"e inspection tec"nology! T"is review s"ould not #e carriedout #y someone wit" limited experience o pipeline integrity management!

I severe deects are reported, t"en immediate action will #e re$uired! T"is may #e animmediate s"utdown or pressure reduction, or rapid expert evaluation to consider t"e needor s"utdown or pressure reduction! T"e signiicance o deects will depend on t"e pipelinedesign, materials and operation!

0evere deects includeD

9orrosion or any metal loss/ more t"an C?F t"roug" t"e pipe wall!

+ents or #ore reductions/ greater t"an AF o t"e pipe diameter!

+ents wit" associated gouging metal loss/, or crac'ing!

+ents on seam or girt" welds o poor $uality!

9rac's!

Buc'les!

T"e results o t"is review will dictate t"e need or urt"er assessment! = course wit" somepipelines t"ere are 'nown pro#lems and t"e re$uirement or expert assessment o t"edeects will #e o#vious #eore t"e inspection is carried out!

I t"e inspection "as not #een satisactory t"en a re-inspection may #e re$uired!

2xpert &ssessment

;ollowing t"e preliminary assessment, some urt"er assessment will #e re$uired! T"is may#eD

i/ & #asic assessment limited to conirming t"at t"ere are no signiicant pro#lems,and setting t"e proposed date o t"e next inspection #ased on t"e predictedoperating conditions!

ii/ &n integrity evaluation t"at provides an assessment o t"e overall condition o t"epipeline, give recommendations or uture repairs, estimates t"e potential growt"or degradation rate o t"e deects and provided recommendations or utureinspection to ensure deects can #e repaired #eore t"ey #ecome critical!

iii/ & detailed urgent deect assessment to evaluate t"e need or continued s"utdownor pressure reduction and identiy appropriate repair met"ods!

Page 3of 18 Copyright 2006, Pigging Products and Services Association.


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;itness or Purpose 1&ssessment

& itness-or-purpose. assessment #etter descri#ed as an engineering critical assessment. ),*/, calculates t"e ailure condition o a structural deect and compares it wit" t"e operatingcondition o t"e structure!

T"e itness or purpose o a pipeline containing a deect may #e estimated #y a variety omet"ods ranging rom previous relevant experience, to model testing, or analytically! T"eselatter assessments can #e #yD

(eneric met"ods ),*,

Traditional pipeline industry met"ods )-*,

Recognised pipeline codes developed using t"e traditional met"ods ),*,

Pu#lications rom pipeline researc" groups )-*,

Best practice. pu#lications emerging rom Joint Industry Pro%ects )-*!

Key 9onsiderations

&ny operator conducting a itness or purpose calculation s"ould consider t"e ollowing),,*D

Understand t"e deect G w"at caused it, "ow it may #e"ave!

T"e engineer doing t"e assessment - experience, training, independence, overview,support!

&ssessment met"ods G use #est practice!

T"e conse$uences o t"e deect ailing!

;urt"er details o t"ese considerations are given in Reerence !

Input +ata

T"e type and level o detail o inormation t"at is re$uired in any assessment depends on t"edept" and scope o t"e assessment! T"e issues t"at typically s"ould #e considered include)*D

4! T"e pipeline G geometry, materials, operation, environment, "istory, etc!!@! 0tresses G all loads acting, uture c"anges, cyclic loads, construction, residual, etc!!3! Inspection met"od G capa#ility, relia#ility and accuracy!H! +eect G cause, dimensions, type, location, growt", etc!!5! 9onse$uences G lea', ignition, pollution, etc!!

;urt"er details are given in Reerence !

9onsiderations w"en Using Intelligent Pig +ata!

T"e ollowing points s"ould #e considered w"en using intelligent pig data to aid a itness-or-purpose assessment)*D

&'e use (fitness for purpose) in the pipeline integrity !usiness as (a failure condition will not !e reached during

the operation life of the pipeline). *ote that fitness for purpose also has a +different legal meaning, particularly

in the construction !usiness, with differing lia!ility.



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Pigs cannot detect all deects, all o t"e time!

Pigs measurements "ave associated errors!

Pigs cannot discriminate #etween all deects!

Treat simple deect assessments #y pigging companies e!g! t"e 2R;./ wit" care Gt"ey may not #e appropriate or all deects and all pipelines!

Use all availa#le inspection data G e!g! past inspection reports!


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T"ere are two #asic types o calliper pig, single c"annel and multi c"annel! 0ingle c"annelpigs will report t"e c"ange in #ore and t"e location on t"e pipeline! >"at t"ey will not identiyis t"e orientation o t"e dent!

=vality

=vality is generally not a pro#lem or pipeline integrity, unless t"ere are signiicantover#urden loads! =n a new pipeline8 "owever, ovality in excess o code limits may #e anindication o poor construction, and s"ould #e rectiied #y t"e construction contractor! Notet"at excess ovality may #e ound at ield #ends and can result in "ig" stress concentrations,possi#ly leading to t"e development o atigue crac's, i t"e pipeline is su#%ect to signiicantpressure or temperature cycles!

+ents

+ents are potentially signiicant deects and re$uire careul evaluation! 2ven a smoot" dentwit" no associated metal loss/ may "ave a s"ort atigue lie, and dents wit" gouges in or t"ataect a weld may "ave low #urst pressures and s"ort atigue lives! +ents may #e co-incidentwit" ovality, #ot" t"e ovality and dent s"ould #e considered in any assessment, as t"ecom#ination will lead to a "ig"er stress concentration! T"e critical parameters re$uired toassess t"e signiicance o a dent areD

+ept" percentage o external diameter/

9urvature G 'in'ed dents, or s"arp dents, "ave "ig" strains, "ig" stressconcentrations, and are more li'ely to "ave crac's associated wit" t"em t"an smoot"dents!

=rientation G dents at t"e top o t"e pipe, in ons"ore pipelines, are unli'ely to #econstrained see #elow/, and are more li'ely to #e due to external intererence, andmore li'ely to "ave associated metal loss t"an dents at t"e #ottom o t"e pipeline!

+ents at t"e #ottom o t"e pipeline are generally constrained t"e weig"t o t"e pipeand cover restrict movement due to c"anges in internal pressure/ and are "ence lessli'ely to develop atigue crac's!


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@! I t"e dent "as a dept" o more t"an @F o diameter it is li'ely to #e eit"er aconstrained roc' dent not serious/ or in service damage possi#ly serious/!9onstruction dents due to "andling, etc!, will usually #e pus"ed out. #y t"e "ydrotest!+ents less t"an @F o diameter are generally accepta#le, provided t"ere is nogouging or weld associated!

3! I t"e dent a dept" o more t"an AF o diameter, it may exceed code limits! 9odeslimit dent dept" to AF o diameter, #ut note t"at t"is is due primarily to t"e potentialrestriction o pig passage!

H! Is t"e dent at a location w"ere t"ird party damage is credi#le e!g! near a roadcrossing/E

5! &re t"ere any records o recent excavation wor' in t"e vicinity o t"e dentEA! Is t"ere an explanation t"at could #e used to s"ow t"at mec"anical damage is

unli'ely G e!g! t"e dent may #e on a ield #end and "ave #een caused #y t"e #endingmac"ineE

6! Is t"ere any evidence o coating damage in t"e area o t"e dent rom a recent coatingsurvey! ;or in service mec"anical damage to result in a gouge, t"e coating would"ave to #e damaged!

It s"ould #e noted t"at or ons"ore pipelines w"ic" tend to "ave a relatively t"in wall, dentsdue to roc's in t"e trenc" or "andling damage during construction are common, #ut aregenerally not a signiicant pro#lem or pipeline integrity!

(eometry Pigging - =s"ore

=s"ore pipelines tend to "ave t"ic'er walls t"an ons"ore lines, and oten "ave a concretecoating to provide sta#ility! 9onse$uently, dents are muc" less common t"an or ons"orepipelines!

& dent reported in an os"ore pipeline may #e residual construction damageD sometimesduring pipelay in #ad weat"er t"e pipe will impact t"e rollers on t"e lay #arge stinger, or may#e #ent over t"e end o t"e stinger! T"is type o damage s"ould #e identiied #y a precommissioning survey! It s"ould #e noted t"at t"e damage may not #e at t"e #ottom o t"epipe, as some twisting o t"e pipe as it goes rom t"e #arge to t"e sea #ed is possi#le! I t"edamage was caused during construction t"en it will "ave #een su#%ect to a "ydrotest, andconse$uently may #e accepta#le even i it exceeds standard code limits!

&lternatively t"e dent may #e due to impact #y a s"ip anc"or, trawl gear, a dropped o#%ecte!g! a sta#ilisation #loc'/, or, in s"allow water, #y a s"ip!

>"at to loo' or in a geometry pig report o a dent in an os"ore pipelineD

4! +ept" G t"e dent dept" provides a primary indication o t"e potential severity!-. 0"ape - t"e s"ape o t"e dent may provide an indication o t"e cause o t"e damage,

or example i t"e dent is due to an anc"or snag t"ere may #e denting to #ot" sides ot"e pipe see ;igure @/! T"e s"ape o t"e dent may also give some indication o t"e

possi#ility o associated metal loss!3!


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H! 0ea#ed scars G sonar survey data can provide clear evidence o scars on t"e sea#edcaused #y o#%ects #eing dragged across it!

5! 0"ipping incidents G I a s"ip drags an anc"or, etc!, t"e details s"ould #e reported!T"ese reports can provide an indication o t"e cause o t"e incident, t"e sie andmass o t"e anc"or, etc!!

;igure @ 1odel o +enting 9aused #y &n &nc"or 0nagging & Pipeline

&s stated previously, dents on os"ore pipelines are unusual and i one is reported t"enexternal inspection is prudent! T"is s"ould conirm t"e presence or ot"erwise o any weig"tcoat damage, anti corrosion coating damage, gouging, or t"e presence o welds!

1apping Pig

1apping pigs are designed to plot t"e route o t"e pipeline! T"ey tend to #e used i t"e aslaid inormation is poor, i t"ere is concern over possi#le ground movement, i up"eaval orlateral #uc'ling is suspected, or i it "as proved diicult to locate deects reported #y ot"erinspections!

I t"e intention is to loo' into pro#lems associated wit" movement, t"e data can #e used toestimate t"e #ending strains in t"e pipe! It is a common misconception t"at multipleinspection sets are needed to asses t"e condition o t"e pipeline! 1ultiple data sets areneeded to monitor movement8 "owever, t"e #ending strains can #e estimated using t"e pipe

curvature given #y one set o data! T"e strains can t"en #e compared wit" allowa#le limits!T"e #ending strain associated wit" eatures suc" as ield #ends and t"e curves due to laying



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pipe on an uneven sea #ed s"ould #e wit"in t"e strain limits o t"e material or designstandard!

>"en assessing t"e total strain in t"e pipe it is necessary to consider not only t"e #ending#ut also any strains due to8 pipe lay8 extension or example w"ere a pipe "as #een dragged#y an anc"or/8 internal pressure8 and t"ermal expansion!

1;< Inspection

Intelligent pigs t"at use t"e principle o 1agnetic ;lux


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9orrosion

1;< inspections generally report corrosion as metal loss.! T"ere may #e a comment t"at it ispossi#ly corrosion., or t"at it is not manuacturing-related.! To ma'e an assessment, anunderstanding o t"e cause o t"e corrosion is critical! 2xternal corrosion may "ave #eencaused #eore t"e pipe was coated, particularly or pipelines t"at were coated over t"editc".! Internal corrosion may "ave occurred w"ile t"e pipe was in transit to t"e constructionsite, or w"ile it was in storage at site see ;igure 3/!

;igure 3 Pipe in 0torage >it" 0urace Internal 9orrosion

arious evidence rom t"e inspection, com#ined wit" #asic inormation on t"e pipelineconstruction and operation, can #e used to identiy t"e pro#a#le cause o t"e corrosion!

Internal 9orrosion

&ctive internal corrosion is li'ely to #e extensive, t"at is, it occurs in more t"an one location!

It also tends to occur at t"e #ottom o t"e pipe w"ere water and de#ris can collect! 2rosioncorrosion can result in metal loss at t"e outside o #ends, and top-o-line corrosion results indeects at t"e top o t"e pipe, w"ere water condenses due to t"e cooling eect o wateroutside t"e pipe, alt"oug" it s"ould #e noted t"at condensing conditions also cause corrosionin t"e lower $uadrant o t"e pipe as well!

+ierent patterns o internal corrosion t"at may #e seen in intelligent pig data are considered#elowD

Isolated internal corrosion at random orientation! T"is may #e manuacturing or pre-construction damage!

0"allow lines o internal corrosion t"at do not run across girt" welds see ;igure H/,and w"ic" c"ange orientation rom one pipe to t"e next! T"is may #e corrosioncaused during transport or storage!



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0"allow general internal corrosion at low points on t"e route, and at t"e #ottom o t"epipe! T"is may #e operational. corrosion! It could also #e corrosion caused #yallowing untreated water to enter t"e pipeline during construction! T"e possi#ility t"att"is is active corrosion s"ould #e considered, or example, i t"e pipeline transportswaxy crude oil and cleaning pigs are run wee'ly t"en it is unli'ely to #e activecorrosion!

Numerous deep internal corrosion pits at t"e #ottom o t"e pipeline at low points on acrude oil pipeline t"at is not used continuously and is only rarely cleaned! T"is isli'ely to #e active micro#ially assisted internal corrosion!

Numerous deep internal corrosion pits at t"e #ottom o t"e pipe and close to girt"welds! T"ere are li'ely to #e active preerential weld corrosion! T"ere may #e moresevere deects actually in t"e weld t"at it is diicult to detect or sie rom t"e pig data!

;igure H


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Isolated pits at any orientation on a pipeline wit" a good $uality coating e!g! usion#onded epoxy/! T"ese may #e active corrosion sites and could #e related to eectssuc" as &9 intererence! T"e corrosion growt" rate may #e relatively "ig"!

0"allow general corrosion at ar#itrary orientations! I t"e pipe was coated over t"editc" t"is may #e corrosion caused w"ile t"e pipe was in transit or storage!

(eneral corrosion towards t"e #ottom o t"e pipe see ;igure 5/, at low points on t"epipeline route! T"is is t"e typical pattern o external corrosion w"ere t"e coating "as#ecome degraded! T"e corrosion tends to t"e #ottom o t"e pipe due to dierentialaeration and to low points on t"e route as t"ese tend to #e wetter t"an "ig" ground!

(eneral corrosion close to t"e girt" weld! T"ese may #e active corrosion deects andare li'ely to #e a result o pro#lems wit" t"e application o t"e ield %oint coating, w"ic"as a ield-applied coating may not #e as good as a actory-applied coating actory!T"e growt" rate may #e low unless t"e pipeline is operated at elevated temperaturee!g! M3?deg 9/

9orrosion along t"e seam weld! T"ese may #e active and could #e related to tenting.o a tape wrap type o coating see ;igure A/

1ultiple deep corrosion pits see ;igure 6/! T"ese are may #e active and may #e

related to micro#ially assisted corrosion! T"e growt" rate is li'ely to #e "ig"!


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;igure A :Tenting: = & Tape >rap 9oating

;igure 6 1ultiple +eep Pits



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;igure C Ruc'ing o a Tape 9oating

(ouges

+amage suc" as a gouge may #e reported as a metal loss. anomaly! I t"e damage istowards t"e top o t"e pipe, in an ons"ore pipeline, andor appears long and narrow t"en itmay #e a gouge see ;igure 7/! T"ere may #e some evidence o denting w"ic" can #eidentiied in t"e inspection data, or t"e metal loss may #e at a location w"ere excavations are'nown to "ave ta'en place!



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;igure 7 (ouges

Ultrasonic 1etal


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times t"is particular tool "as #een used to detect t"is particular type o crac' and "ow manyconirmatory inspections were carried out i!e! "ow #ig is t"e data#ase o deects t"at t"eanalyst is usingE

0ummary

Intelligent pigging is a costly and disruptive activity! Lowever, it provides a "uge $uantity overy useul inormation on t"e pipeline! & 'nowledge o pipeline integrity issues, pipelineoperation and inspection tec"nology can #e com#ined to optimise t"e assessment o t"edata!

& preliminary assessment o t"e results o an intelligent pig inspection is a critical step inensuring t"at t"e correct action is ta'en regarding pressure reductions, repair, and urt"erassessment! T"is preliminary assessment must #e carried out #y someone w"oD

Knows t"e pipeline design, construction and operation!

Understands t"e inspection tec"nology Is aware o t"e signiicance o dierent types o pipeline deect!

T"e ollowing 'ey points s"ould always #e considered w"en reviewing an inspection report!

4! 9an t"e cause o any deects reported #e identiied and are t"ey credi#leE@! Is it possi#le t"at t"e deects may #e growing, and w"at mec"anisms are t"ere or

t"isE3! >"at is t"e growt" rateEH! +oes t"e data suggest an unexpected type o deect and i so was t"e tool suita#le

or measuring t"is deect or does a dierent tool need to #e runE5! T"e assessment s"ould use as #uilt and operational records and previous inspection

and monitoring data to esta#lis" as clear a picture as possi#le!A! 2ven i no deects re$uire repair w"ic" deects re$uire conirmatory inspectionE



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Reerences

&. &non, In-


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&4. Knau (, Lop'ins P, T"e 2PR( (uidelines on t"e &ssessment o +eects inTransmission Pipeline (irt" >elds., 3R International, 35, Ja"rgang, Let, 4?-44477A, pp!A@?-A@H!

-5. Bood R, (alli 1, 1arews'i U, Roovers P, 0teiner 1, area 1, 2PR( 1et"ods or&ssessing t"e Tolerance and Resistance o Pipelines to 2xternal +amage Part @/., 3R

International, 4@4777, pp! C?A-C44!-&. Re (, Pistone , ogt (, +emoonti (, Jones + (, 2PR( Recommendation or 9rac'&rrest Toug"ness or Lig" 0trengt"

2006-Aberdeen-9-Palmer-Jones.pdf

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