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Pipeline Technology Journal 2-2015

Latest developments and news from the pipeline industry

RESEARCH / DEVELOPMENT / TECHNOLOGY As-laid fatigue data were also calculated as part of the pipelines design and considered in the ECA. They were derived from crossing design fa- tigue analysis. Such data are presented in Table 3. Details of the oper- ation schedule provided by DONG E&P of the pipelines is presented in Table 4. As indicated from the operational data in the Tables, the following have been allowed in the operational schedule for both pipelines for the du- ration of their design life of 30 years: • One “long” shutdown per fortnight (26 occurrences annually) • Two “short” shutdowns per week (104 occurrences annually). Stress ranges data were derived during design engineering for both un-corroded and corroded conditions. The ECA performed by Saipem Ltd for the purposes of developing AUT flaw acceptance criteria which was utilised during the offshore campaign was strictly adhered to mentioned data supplied by Compa- ny, thought to be on the high end of conservative side, compared with Saipem’s past experience. An alternative operating schedule is also presented, analysed and dis- cussed in this paper for comparative purposes and better understand- ing of the performance and integrity of these thin wall pipelines when put to service. For the purposes of establishing a “true” fit-for-purpose ECA based flaw acceptance criteria, a “scaled down” schedule was also assessed. The purpose was to evaluate the impact on the ECA and subsequently the flaw acceptance criteria. The following alternative schedule was considered for sensitivity pur- poses, as based on past Saipem experience: • One “long” shutdown annually • Four “short” shutdowns annually WELDING CRITERIA FOR OFFSHORE CONSTRUCTION The girth welds were produced by Saipem’s Gas Metal Arc Welding (GMAW) process during pipelay on the Hejre Development Project. They were inspected by AUT and procedures established and validated by Saipem and approved by Company. The Ultrasonic equipment used to inspect all welds was the Pipe WIZ- ARD V4 system. The system provided adequate number of examination channels to ensure the complete volumetric examination of the weld through thickness in one circumferential scan. Depth and height of indications were evaluated and sentenced using both the Pulse Echo (PE) and Time-Of-Flight Diffraction (TOFD), in ac- cordance with the AUT Acceptance Criteria. Sizing was performed by PE and TOFD, with PE as the primary method. When a distinguishable TOFD diffracted signal information was ob- tained, it was used to improve the sizing and characterization by the existence of a top and bottom diffracted signal. For off-bevel flaw, in case of distinguishable TOFD top and bottom diffracted signals, TOFD was used to determine the indication height; otherwise PE channels were used. The repaired welds were inspected by performing the following steps: AUT inspection of repaired weld (PE + TOFD + Mapping Channels) to verify that the previous defects have been removed and for detection of any new indications that might appear during the repair welding pro- cess. And: Manual Ultrasonic Testing (MUT) in accordance with the MUT Procedure. The repair area was assessed by MUT, us- ing MUT specific acceptance criteria, as per DNV-OS-F101 [1], in compliance with Offshore Pipeline Welding Specification for the project. Oil Export Pipeline Gas Export Pipeline Fatigue Loading Spectrum As-Laid Fatigue Loading Spectrum As-Laid Occurrences (Cycles) Stress Range (MPa) Occurrences (Cycles) Stress Range (MPa) In-Line VIV In-Line VIV 951 120 114 66 Cross-Flow VIV Cross-Flow VIV 150 173 14535 53 Reference Reference Crossing at KP85.8 Crossings at KP22.0 and KP 22.4 Table 3: Hejre Pipelines – Fatigue Loading in As-Laid Condition Oil Export Pipeline Occurrences Annualy Temperature (C) Pressure (barg) Max Frequency Min Max Min Max Shutdown (long) days 26 4 75 0 100 Shutdown (short) hours 104 Constant 0 100 Gas Export Pipeline Occurrences Annually Temperature (C) Pressure (barg) Max Frequency Min Max Min Max Depressuration of Pipeline 1 -12 50 0 150 Shutdown (long) days 26 -12 50 70 150 Shutdown (short) hours 104 4 50 Constant Table 4: Hejre Pipelines – Variable Loads in Operation Condition PIPELINE TECHNOLOGY JOURNAL 39 95112011466 1501731453553 Shutdown (long) days 264750100 104 Constant 0100 1 -12500150 Shutdown (long) days 26 -125070150 104450 Constant

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