0e81 spe 10402.1: new techniques of pipeline inspection

8/12/2019 0E81 SPE 10402.1: NEW TECHNIQUES OF PIPELINE INSPECTION

1/11

.

;,

0E81 SPE 10402.1

NEW TECHNIQUES OF PIPELINE INSPECTION

.

J.L. HerveM.T.S. Ling

Offshore EngineersTotal Oil Marine Ltd.

J. Und.-iPipeIine EngineerNorek Hydro A/S

Cavrlght 19S1Society of Petroleum Engineers of AIME

INTRODUCTIONThe Frigg Field Transportation System wae commissioned in 1977. Sincesterthg production, Total Oil Marine hae initiated and maintained an Inservice inspection programme designed to identify any condition of the linewhich may lead to failure of the line either in the short or long term.Until 1980, the main problems on the pipeline were identified as shortterm stability problem% We believe that our current inspection programmeis adequate to identify rapidly any area of concern. In 1981 our maineffort is to determine the beet methods for identifying longer termproblems such ae internal and external corrosion. Our current programmetherefore now hee three main aspects. The external inspection, performedroutinely over the pact four years, cathodic protection inspection tested in1980, and an internal pigging programme which was initiated in 1978.The full inspection programme will be the subject of this paper.


2/11

,

0E131 SPE M144XL2NEW TECHNIQUES OF PiPELINE INSPECTION1. External Inspection /Total Oil Marine uses a number of external inspection methods which arewell known in the North Sea area, and are readUy avdlable fromestablished contractors. The particular method chosen depends upon thetype of inspection required and the location of the work.1.1 LandfaU SurveyThe sactim from PK (Kilometre Post) O to approximately PK 2 ia thebeach area and due to the local conditima presents specific problems.More usual inspection techniques, as uaad for the offshore aaction of thepipelinaa cannot be used due to the constraints of the area. In past yenraour policy has been to perform a routine visual and pipb bUrifd survey withdivers. During 1%31 we have adopted a more flexible approach, makinguse of side scan sonar end detailed bathymetry to delineate areaa of scour.Divers are then used in a mare seiective manner to inspect any areas ofinterest.1.2 Offshore SurveyFor the offshore aectlon of the pipelines our aim has been to monitor thegeneral status of the lines whilst performing detailed inspection work onareas of concern. We have found that side scan sonar followed by detailedvisual survey by means of unmanned submersible satisfactorily fulfils ourraquiremanta.1.2A External Inspection, Line Statue MonitoringOur norm8i procedure m ~ . :%rm early in the weather window side scansonar rms on each nide of each pipeline. A high frequency (100 KHz)sonar flown 20-30 melraa offset from the pipeline is sufficient to provide iequate Informatim m the status of the lines, and to define buriai,trench and scour c0nditiOn8. We find that two runs, ona on each side ofthe line are ss nti lto accumtely define condition, position andrequirement for detaiIed inspection.1.26 Detailed Visual InspectionTha detailed inspection programme is normaUy performed by unmannedsubmersible (Figure 1). In the past we have made use of mannedsubmeraiblee but the general improvement of the unmanned craft and theadvantages of cost have resulted in the use of the latter system.The foUowing specific featurea are included in the submersible spread:-Sonar for location of the pipeGood observational capabilitiesColour video systemColour still photographic systemTransverse trench profiler systamNavigatitm and positioning system


3/11

;

OE81 SPE 10402.3NEW TECHNIQUES OF PIPELINE INSPECTION1.3 Cancluaba8We have found that in all case8 careful attention to the performance ofthe work is essential to the successful acquisition of the correct surveyie8U1tS. To this end our policy is to jointly compile with the contractor afield specifications document. This document details the scope of work,i.e. the inspection work required (location, standard, video, ph~tographic),and the method of work. Close offshore supervision of th > work byexperienced pipeline inspection engineers 18 essential to maintain the8tandSrd of work throughout the survey period.2. CORROSION INSPECTIONOur pipeline hea now been in position for more than seven years andhaving satisfactorily solved our external inspection problems 80 that we canperfOrm essential stabilisation work in the same season we have focusedour attention on corrosion inspection. Our aim has been to approach theinspection in the same way as our external inspection programme . inother W0rd8, monitoring the general status of the lines whilst performingdetailed inspectim work on the areas where the condition i8 interpreted asmore doubtful.2.1 Cathodic Protection, Line Status MonitoringFor the first part of our nspection we have made use of a trailing wiresystem (Figure 2) whereby, whiIe measuring the potential of the linerelative to a siiver/silver chloride reference cell, a permanent connect it:.is maintained with the pipeline at the landfall or at the platform riser.The system provides a general potential status of the Iine which may beused to delineate areas where abnormal potentials occur. It is expectedthat the survey will have to be repeatad regularly before an accurateconclusion of the status 1s acquired. The system is obviously limited bythe requirement to fly the fish, carrying the remote reference cell, asclose as possible to the pipelines. We are attempting to solve thisrequirement by attention to accurate navigation end the use of a transitsonar, or a distance from pipe device.During 1981 we have succesafuIly performed over 1100 kms of survey. Wehave found, however, that in the North Sea area geomagnetic anomaliescan cause a significant effect on the recorded pipe potential. Ourpmgramme has included recording these anomalies which have shown goodcorrelation with the anomalies in the survey records. Detailed analysismethods have been used to filter out the anomalies from the recordedpotentials and to calculate the pipe potential.2.2 DetaiIed Cathodic Protection InspectionThe detailed cathodic protection inspection also preaenta specific problems.Two systems are now available in the North Sea. During our 1980inspection progremme, we teeted one of these systems which waa asubmersible mounted cathodic protection survey probe. The equipmentconsi8te of a submersible mounted probe, with two , aference cells and aremote reference cell positioned at some distance up the submersible%umbilical.


4/11

.

:

.8CIE81SW 10402.4

NEW TECHNIQUES OF PIPELINE INSPECTIONRecordere m the support vessel provide en instantaneous read-out givingthe company% dfahore representative an immediate indication of thectmro8ion problem. Though the etated accuracy (~ 10nN/) of the sy8tem 18very good, some difficulties ari8e. These include, with the particularsystem we have used, the requirement to keep the probe at a ccn8tantheight above the pipeline and a requirement of repeated calibration.An alternative 8y8tem 18 available which makes u8e 6f the current den8ityaround the pipeline to calculate the pOtt3fNid 8tatu8 of the line. Again,tlw etated accuracy of the system i8 very good, but aa the techniquerequires detailed ceiculetiona before determination of the true potential8tatus of the pipelines, there are some obvious limiteticms.2.3 ConclusionsCathodic protection 8urvey technique8 for underwater pipelinea are still aten edy etage of development. Accuracy is still limited and interpretationdifficulu @r experience 8ugge8t8 that the method 8elected and theconfidence in the methnd re8ta entirely with the engineer who ha8iEJ8p0n8ibilityfor the 8urvey. Our 81RIi8 to uee exi8ting techniques to thebest of their ability in order to try to localise and remedy at the earliestmoment any deficiency in the pipeline cethcdic protection system. We. 8heU a180 continue to investigate available sy8tem8 by means of fieldtrials, which are the sole criteria ffJr 8elacticn of an effective 8urveytechnique.3. INTERNAL INSPECTION BY CORROSION INSPECTION PIGThe natu~ of the North Sea long distance pipeline tran8portaticn 8y8tem8haa motivated t~ development of advanced internaJ corrosicn inspectionpig% Using field-proven practical idea8 and principles, it ha8 been poesibleto create a design speciflcaticm to build an advaoced self contained 321tool to inspect AP1 5LX grade X-6 3/4~ wall thickness pipe joints and torecord true ga8 temperature. Before the new tool waa accepted enexten8ive capablIity test was arranged by Total Oil Marine and had to bepaeeed in Aberdeen,3.1 Oesign CriteriaTctal Oil M@ne8 knowledge about intelligent pigs is mairdy derived fmmthe comprehensive teete performed with the Vetcolog (in 197 ) and Linelog(in 1979 and 1981) in our te8tline8 (Figures 3,4) located in Aberdeen.Ba8Bd on thi8 unique experience we were able to specify the de8ign whichwouid give us optimum ra8ults in th~ Frigg Transportation Sy8tem.In addition to specifying the acceptance levels of detecticn and grad ng forth tool perfcrmence, much effort waa spant to specify pioeline I.D.re8trictiona that mu8t be negotiated by the inspection tool i.e. valvemisalignment, flowtee barring etc.


5/11

,

..

. ,.OE81 SPE 104OL5

NEW TECHNIQUES OF PIPELINE INSPECTION3.2 System ComponentsThe inetrumanted pig cmists basically of the standard three elements i.e.the drive section in the front, the combined magnetizing/transducer sectionin the centra, and the electronic amplifiers and recording system in therem of the pig (see Figure 5). In addition the 32 tool irmorpora.ea twoother special devices which are an acoustic pinger and a gas temperatureprobe. The pinger is of dual cylinder construction mounted onto the pigsdrive Secticn, however the pinger transducer la mounted OntO the toolstranducer section to obtain a metal to metal contact with th pipe for thetransmitted acoustic eignaia During the fimt survey run a diver with apinger receiver located on the seabed adjacent to the pipe wea able todetect the pig 1 mile ewayo The temperature device consiata of apiatinum m8i8t& ~ element housed in a prasaura te8t8d dUMiniUm houaihgwhich la isolated by nylon mountings from the ateei body of the tool%instrument section. The gas temparatura i8 read digitally off a spareclmnnel on the magnetic tape.The dummy tool eke consists basically of the standard three elemanta a8the instrumented pig and also includaa the same acou8tic pinger. Agauging ring 18 located at the cantra of the dummy magnetiser and hae adiameter equal to the shoe collapse d ameter of the live magnetiser.3.3 Acceptance Tent ResultsThe tool detectad about 95% of ail the defects introduced in our pullteatiine and approximately 80% of defects detected were graded correctly.Several tool limitution8 can be summarised aa follow- -No defectscan be detected near to circumferential or longitudinal weldsThe tool indicate8 some unidentified defectsThe grading 18not very accurateDefects of leas that 15% wait penetration are not detectedDefects with a width of less than 0.5 are not confidently detected.Both the 32 live tooi and the dummy tool can succeasfuily negotiate our2.RD 90 riser bend8, and ail the properly constructed barrad flowteaa etc.A differential pressure of naar to 5 bam 18 needed to move these pigsthrough the riser bend8.It can be concluded that both pigs succesafuiiy met our agreed acceptancecriteria. (Figure 6)3.4 Pigging ProgrammeWe propose to follow a conservative approach in that safety andoperational pipeline requiramenta are of prime importance. During the1981 survey before launching the live 32 tool, we used a pra.piggingprogramme as foIlows:-


6/11

;e

-

... .,. : .t.,., ,..

NEW TECHNIQUES OF PIPELINE INSPECTION

Four batching (LBCC-2) and cleaning pigs (VantageTwo caliper pig trainsDummy tool

OE81 SPE N14U2.6

iv)

This pre~pigging programme waa intended to minimise the risk -of gettingany pig stuck in the pipeline. However, we have on standby a set ofUnicaet pigs and intend to have an EPRS (Emergency Pipeline RepairService) to tackie such an event in the future.F~ pig location Wrp~e8 (in additi~ to tb acoustic pingere) a special?mmputer pmgramme has been used succeeafully to predict pig runningtitnea and eetlmatad timae of arrival.3.5 ConclusionsAfter having performed a mrioue prcgramme in testing axisting Intelligentpigs, Total Oil Marine LtcL was in a position to specify the design criteriaf6r a prototype 32n intelligent pig. Deepita the tools severe limitations(failure to detect defacte near to welds, grading Inaccuracy etc.) webelieve that this pig is the best operational tool available in the markettoday to suit our raquiraments.Our confidence was supported by the eucceeeful completion of the plannedpigging programme performed in a pipeline aacticn during June, 1981.More and more mntractora are actively involved in development of nawimproved tools baaed on ultraamica and radioactive isotcpea and we expectsome new tools to ba avaiiable within 3-5 yamw.4. NON DESTRUCTIVE ;ESTING FOR UNDERWATER PIPELINEAND RISER inspectionNon D(38tNCtiVa Testing (NDT) haa now become a major p@ of 8Ub-8~Inepacticn pmgrammea for platforms, but. has not been extensively ueed on8Ub-8eS pipt3iifW8. The techniques include ultraecnica, magnetic particlelnapection, x-rI y gammagraphy, and electric potential measurements. TotalOil Marine8 present tdm ia therefora to fully evaluate all the availabletechniques, and to define procedures, interpretation, coete, andqUalifiC8tiM of the h18pSCtOMfOr thdi applicathn to 8ub-8ea pipalinainspection.During 1981, we shall ba performing a trial on ttm pipeline to. demonstratethe applicatia of NDT techniques.The vertical risere at MCPO1 are in a permanently dry anvimnment andcan therefore be inspected easily and regularly using conventionalhspaetim methode. Our pmcadure is to ~rform every thrae monthe,visual and ultrasonic inspections on the bendb, at convenient Iocationa. onthe straight sections,crossovers,Ziafle joints and pig trapa. The approachseems reliable and any ohange in wall thickness immediately obviowStrain gauges are attached to the riser anchor blocks at the bottom of theshaft which allows us to check if any risar movemant is taking place. Inaddition the cathodic protection status of the riaere in continuouslymonitored using a permanent Morgan BerkeIey System.


7/11

. ..------- ----- ...

NEW TECt-lNIQLIES OF PIPELINE INSPECTION5. COSTS OF THE INSPECTION PROGRAMMEThe COS* of the annual inspection programme are a

0E81 SPE 10402.7

significant feature ofthe annual operating costa. In 19B0, the total costa w6110in the order of0.25 - 0.3% of the total pipeline investment.The typical unit coats per kilometre of the survey methods described area8 foilow@-Lendfall Survey, Total/km g20,tJO0External Survey, Line Status Monitoring ToteI/km S150External Survey, Detailed Inspection Total/km S3,000Cathodic protection, Line Statue Monitoring Total/km 2150Cathodic Protection, Detailed Inspection Total/km S3,500Internal Inspection, Linaiog TotaI/km S2,000It can be men from the above figures that the c)~sts of pipeline inspectioncan be very significant. There era clear coat ~Jrantages in the delineation. . of problem area8 by means of monitoring techniques such as side scansonar or cathodic protection monitoring.6. CONCLUSIONSPipeline inspection is a combination of different methods. The methodsfor external visual inspection are now well established. In 1961 our maineffort and investment is to investigate and use techniques for inspectingthe cathodic protection status &Td internal condition of the pipelines. Ourinspectim techniques are therefme turning in emphasis from the shorterterm problems, which are now Satisfactorily resolvad by means of wellestablished maintenance techn qiies, to the longer term problems which willexist over the life of the pipelines.7. REFERENCESA. BARES, J.L. HERVE, M.T.S. LINGInspection and Maintenance of Frigg Pipeline Transportation SystemPaper Reference EUR 158, Proceeding of the 19S0 European OffshorePetroleum Conference and Exhibition.8. ACKNOWLEDGEMENTSWe would like to acknowledge theTotal Oil Marine, for allowing theSub Sea Surveys Ltd., for diagramHarco Corporation, for diagram of

helpful assistance of the folIowinWpresentation of the paper.of Consub 2.the I-larco C.P.L. technique.


8/11

.

.1

;

.

OEB1 SPE MIMINEW TECHNIQUES OF PIPELINE INSPECTION

Copyright 1981American Institute of Mining,

Metallurgical end Petroleum Engineers Inc.This paper was prepared for the Off8hara Europe f31 Conference inconjunction with the Aberdeen Petroleum Saetlon of the Society ofPetroleum Engineers of AIME, held in Aberdeen, Scotland 15-16 September19S1. Permiaaion to copy is raatricted to en ebatract of not more than300 words. Illustrathme may not be copied. The abstract should contehconapitwous acknowledgement of where and by whom the paper iapraaented. Publioatim eleawhere after publication in the Journal ofPetroleum Technology or the Society of Petroleum Engineers Journal isuauelly granted upm request to th Editor of the appropriate journalprovided agreemmt to give proper credit is made.


9/11

b

,.

.

.

,.

.

:

>

>

i

.. .. ..-. -. . . . .

A.B;::Q.H..::K.k.N.o.P.o.R.s.T.u.

UnMla l CabhSY7tdcf antwymqFaanAthxhmMswIsTrknFmnI&w LaT~-**dnlt WtStltao LQllPVdbl TIDuxhrSW CummBawmmw.Lard lwmtwSm. La umd Ttnm?u*WsWs4uImsubmtwmf?ofkCP Prdmsd4d Pllmks(*wlAdumdf$S4mw CnnM19d).

Fig. 1.

F19.2


10/11

fig. 3 INTELLIGENT PIG

Ouudl LertuWI4T0eet ( lzsrnatfa) ~

J LtV Ifw HW LW LW LW LW LW LW id9Jdltscf321nchfqx

LW - LJght-wunHW - I+aNy-dl

Flg.4 PULL TESTLINE


11/11

.

. . ..._ .

k---j

17?. Hscwy-vmll

ms~ft. wavy-wall Ist.L t-w] @m EndF19.5 32 BEND TEST - UNE

32 N7ELumw7 PIGnPfcAL PmRmwcE CURVES

t

0e81 spe 10402.1: new techniques of pipeline inspection

Documents