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Results
Nord Stream Project - Assisting Pipelaying On Soft Seabed: Gravel Berm Stability And Intervention Work Refinement
Bartolini, Lorenzo M. (Saipem S.p.a.) | Zenobi, Daniela (Saipem S.p.a.) | Canu, Marcello (Saipem S.p.a.) | Mele, Fiorenzo (Saipem S.p.a.) | Modesto, Luisa A. (Saipem S.p.a.) | Watkins, John (Nord Stream AG)
ABSTRACT The Nord Stream Project (NSP) twin pipeline system running from Vyborg, Russia, to Lubmin, Germany, cross several areas affected by severe seabed unevenness which are located mostly in the Russian and Finnish sectors of the pipelines route in the Gulf of Finland. As a consequence the pipeline vertical configuration typically presents several consecutive free spans separated by different lengths of pipeline sections where on seabed. The discontinuities in support points induce bending stress on the pipeline which may be unacceptable when both static and fatigue strengths are considered. The remedial works, consisting of seabed preparation and free span reduction by means of gravel dumping, were designed at the detailed design stage based on the predicted as-laid pipeline configuration and seabed properties. However several major uncertainties existed at the design stage that could threaten pipeline integrity in the temporary condition and also through the design life. The presence of very softy clays could threaten the geotechnical stability of the rock intervention works. The unpredictability of the soft clay strength and the presence or not of thin sediments layers over rock outcrops could change the final pipeline configuration. Also several large unavoidable boulder fields were crossed where the final pipe profile could not be reasonably predicted. Therefore, detailed engineering analysis was extended and integrated into the project execution phase and the design continuously updated and optimized on the basis of the actual pipeline configuration measured during the survey campaigns performed just after pipeline installation. The scope of the detailed design review using the as-found pipeline configuration (both as-laid and post-hydrotest) was to check the pipeline integrity during its whole lifetime and, at the same time, to target the most cost efficient solution. Actually, it is typical for the execution of large offshore projects the necessity to minimize demob/stand-by time for big vessels and equipments in order to optimize the overall construction schedule and reduce cost consequences.
Nord Stream Project - Route Selection And Optimised Intervention Work Design To Meet Design Criteria
Guidi, Filippo (Saipem S.p.a.) | Pettinelli, Daniele (Saipem S.p.a.) | Tosi, Francesco (Saipem S.p.a.) | Iannucci, Ester (Saipem S.p.a.) | Albanese, Simona (Saipem S.p.a.) | Watkins, John (Nord Stream AG)
ABSTRACT Design of the two 48-inch Nord Stream Pipelines involved the crossing, along the Gulf of Finland and the Baltic Sea, of severe and very long uneven seabed areas in combination with very low seabed soil strength. Since the routing phase, attention has been paid in avoiding the sharpest outcrops and selecting the smoothest passages in the transversal rocky ridges. Gravel supports, designed for free-span mitigation against static and fatigue stress, have been optimized in order to avoid very large gravel volumes, which in many cases would have been not feasible, and in the meantime reduce the expected high settlements due to low strength of the foundation soil together with the severe load conditions (support height and pipeline loads). The design optimization involved in particular the post-lay gravel dumping which was scheduled through three different campaigns to be performed, namely 1) immediately after laying, 2) before the planned flooding and 3) after pipeline de-watering. The 1 post-lay dumping campaign was introduced in Nord Stream Project to optimise the gravel works required to mitigate the pipe fatigue stress in temporary condition and/or the static stress in the occurrence of an accidental flooding condition, avoiding a bigger prelay support for the same purpose. A new approach to assess the effect of a storm on short term free-span fatigue has been adopted. The 2 post-lay dumping campaign was foreseen in order to guarantee the pipe structural integrity against pressure test. The 3 post-lay dumping campaign was instead included to dump all gravel supports needed for operating condition only, which will not face the high load from pressure test with consequent gravel saving (approach already successfully adopted during Langeled Project in the North Sea). The very low soil bearing capacity pushed towards an unconventional solution also for the cable crossings.
- Europe > Norway > North Sea > Northern North Sea > North Viking Graben > PL 054 > Block 31/6 > Troll Field > Sognefjord Formation (0.99)
- Europe > Norway > North Sea > Northern North Sea > North Viking Graben > PL 054 > Block 31/6 > Troll Field > Heather Formation (0.99)
- Europe > Norway > North Sea > Northern North Sea > North Viking Graben > PL 054 > Block 31/6 > Troll Field > Fensfjord Formation (0.99)
- (18 more...)