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Pipeline Technology Journal 2-2015

Latest developments and news from the pipeline industry

RESEARCH / DEVELOPMENT / TECHNOLOGY The pipelines installation occurred during Saipem’s 2014 lay season in the North Sea, utilising Saipem’s S-lay vessel Cas- toro Sei. The vessel is seen in S-lay pipelay mode in Figure 2. Automated Ultrasonic Testing (AUT) was proposed as the principal Non-Destructive Testing (NDT) method during S-lay welding for the Hejre project pipelines welding. An Engineering Critical Assessment (ECA) was carried out to assist with the derivation of flaw acceptance criteria for welding during pipeline construction. The assessment was preferred to good workmanship criteria, in line with associat- ed Industry codes DNV OSF101 [1] and BS7910 [2]. The AUT flaw acceptance criteria were established by adjusting the ECA results as necessary, to include an AUT safety margin against under-sizing. The various steps of the ECA are presented in the following sections, considering the different aspects of the design life individually for each export pipeline. These included the short term installation phase, the as-laid condition phase and the pre and post trenching term prior to operation and the long term of 30-year operating condition. The design aspects for the operating condition and in particular, the fatigue loads to the pipelines are discussed, as it is found that they directly affect the ECA. The operating schedule advised by DONG E&P was utilised in the assessments. It was thought to be on the high end of conservative side if compared with what has been seen in the Industry by Saipem in the past. An alternative operating schedule is also presented, analysed and discussed in this paper for comparative purposes and better under- standing of the performance and integrity of these thin wall pipelines (i.e. in the vicinity of 10mm wall thickness mark) when put to service. The emphasis on its impact primarily to the ECA is presented. In Ta- ble 1 below, fundamental design details for the Hejre pipelines are presented. These include dimensions and material properties. FRACTURE AND FATIGUE DATA INPUT Peak loadings for fracture assessments were obtained from pipelay and design engineering. The data were derived from static and dy- namic lay along with Bottom Roughness Analysis, Crossings Analy- sis and Upheaval Buckling Analysis for the project. During S-lay pipelay, fatigue damage on the pipelines may occur, due to variable loading on the vessel’s “stinger” and as related to adverse weather conditions. The limiting sea state for pipelay was established to be 3m significant wave height. Installation analysis predicted that the following spectra are representative for the limiting weather condition, as shown in Table 2. Figure 2: Saipem’s Castoro Sei S-Lay Pipelay Vessel Property Units Pipieline 12” Oil Export 12” Gas Export Steel Grade - HFW 450 SD SMLS 450 SFD Manufacturing Method - HFW Seamless Outside Diameter mm 323.9 Wall Thickness mm 11.1 Anti-corrosion Coating 3LPE - 3mm x 954kg/m3 Internal Flow Coating Epoxy - (Gas Export Pipeline only) < 0.180 mm x 1340kg/m3 Table 1: Hejre Pipelines – Design Details Oil Export Pipeline Gas Export Pipeline Fatigue Loading Spectrum Installation Occurrences (Cycles) Stress Range (MPa) Occurrences (Cycles) Stress Range (MPa) 242 24 240 14 649 52 642 36 862 82 853 62 859 102 850 90 702 109 695 118 487 112 482 121 292 114 289 127 152 116 151 125 70 117 69 123 28 118 28 125 10 119 10 126 Table 2: Hejre Pipelines –Fatigue Loading in Installation Condition 38 PIPELINE TECHNOLOGY JOURNAL 2422424014 6495264236 8628285362 85910285090 702109695118 487112482121 292114289127 152116151125 7011769123 2811828125 1011910126

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