Don Field Decommissioning Programme (pdf, 7.8MB) null - BP

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DON-BP-001Don Field Decommissioning ProgrammeInspections on both the 8in pipelines were performed on an annual basis during theperiod 1990 to 2002. The technique used was either sidescan sonar or visual RemotelyOperated Vehicle (ROV), or a combination of the two. Sidescan was performed morefrequently, with visual ROV often used to supplement sidescan inspection shortfalls atthe extreme ends of the pipeline and to examine specific anomalies. A full General VisualInspection (GVI) was last carried out in 2009.Figure 10.20 Typical Cross-section of 8in Pipelines5.3.2 Operational HistoryBurialThe 8in production pipeline (PL598) has had a consistent burial profile. Exposure levelshave remained extremely low, and are generally associated with features such as tie-inspools and approaches to the Don manifold and crossings which were designed to beuntrenched. Post-installation, 643m of the line was exposed (4.8%). However, this slightexposure has decreased during the lifetime of the pipe as a result of remedial work andnatural backfilling. Remedial rock dump and mattress placement was performed in 1991,1992 and 1994 to restrain buckles, which also removed associated exposure. Theseremedial features have since become partly buried by seabed sediment. The 2009 GVIsurvey has confirmed our understanding that the stability of the pipeline remains stablein an out of use condition.The 8in water injection pipeline (PL599) has had a consistent burial profile. Levels ofexposure have remained extremely low and generally associated with design featuressuch as tie-in spools and approaches to the Don manifold, crossing and tee.Post-installation, 355m of the line was exposed (2.04%). However, this slight exposurehas decreased during the lifetime of the pipe as a result of remedial work and naturalbackfilling. The 2009 GVI survey has confirmed our understanding that the stability of thepipeline remains stable in an out of use condition.SpanThe 8in production pipeline has had very few spans. The few spans reported have beenassociated with upheaval buckling rather than seabed movement. By 1994, all spanswere successfully rock dumped.Pipelines10-20 May 2011
Don Field Decommissioning ProgrammeDON-BP-001Where spans were reported in more than 1 year, only moderate change in length andheight was observed. Since buckling is an anomaly caused by pressure and temperatureeffects during operations, no further buckles or associated spans will occur.The 8in water injection pipeline has had very few spans. Spanning is not a concern onthis pipeline and there has been no requirement for remedial measures (eg rockdumping or mattressing) due to spans.None of the spans on the 8in pipelines has exceeded the FishSafe criteria of10m x 0.8m.5.3.3 Overall Burial TrendThe historical burial trend is detailed in Table 10.3. Results of these surveys indicatedthat there have been minor changes in the total length of exposed pipeline year to year,but after the remedial works, exposed areas have been extremely limited, with no trendof change or development.YearTotal Exposed LengthMetres (1) Proportion of Line (%) (2)PL598 PL599 PL598 PL5992009 267 296 1.53 (0.18) 1.7 (0.43)2002 266 253 1.49 (0.46) 1.36 (0.47)2001 245 287 1.40 (0.86) 1.65 (0.72)2000 264 – 1.52 (0.95) –1999 168 – 0.96 (0.96) –1998 248 353 1.43 (0.66) 2.03 (1.55)1997 147 143 0.84 (0.12) 0.83 (0.42)1996 242 207 1.39 (0.20) 1.20 (0.70)1995 143 207 0.82 (0.15) 1.21 (0.76)1994 196 270 1.30 (0.02) 1.57 (0.64)1993 158 225 1.00 (0.25) 1.30 (0.89)1992 183 116 1.20 (0.37) 0.68 (0.68)1991 (3) 833 355 4.80 (3.69) 2.04 (1.17)Notes: (1) Figures show length including spoolpieces.(2) Figures in brackets show the percentage of pipeline exposed excluding spoolpieces(ie after completion of remediation activities).(3) 1991 survey was performed prior to rock dump remedial work.Table 10.3 Exposure History of 8in PipelinesPipelinesMay 2011 10-21
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Executive SummaryMay 2011 2-5Table
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Descriptions of Items to be Decommi
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