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ABSTRACT The Nord Stream Pipelines offshore the Baltic Sea have been designed for a life of 50 years. Special focus was put in the selection of the mainline actuated valves: The design of the pipelines isolation system was driven by the achievement of high levels of safety, reliability and availability. 48-in, Top-Entry metal-seated Ball Valves and Double-Expanding Gate Valves were selected. The supply of these valves involved very challenging developments for the design, manufacturing and testing of valves and actuators, also considering the demanding environmental conditions on the Russian side. This paper summarizes the most relevant issues related to the design and testing of valves and actuators. INTRODUCTION The twin Nord Stream Pipelines, 48-in dia., 1,200+ km long, connecting Vyborg (Russia) to Greifswald (Germany) offshore the Baltic Sea, have been designed with the segmented pipeline concept (with Design Pressures of 221 barg to 177.5 barg), for a life of 50 years. Special focus was put at the early design stage in the selection of the mainline actuated valves, which have the functions of pipeline Pressure Protection (PPS), Emergency Shut-Down (ESD) and Isolation. The development of the isolation system of the pipelines was driven by the achievement of high levels of safety, reliability and availability over the system design life. 48-in, Top-Entry metal-seated Ball Valves (PPS & ESD) and Double- Expanding Gate Valves (Launch & Receive Traps isolation) were selected as the most appropriate valve types for their operational function. The main issues related to valve design were:—Achievement of very good metal-to-metal seal performance recovering the inherent massive deflections consequence of the valve size, combined with a high operating pressure. —Guarantee of long term operation, avoiding any need of maintenance shut-down.
- Energy > Oil & Gas > Upstream (1.00)
- Materials > Metals & Mining (0.70)
Nord Stream Project - Baltic Sea Environment: Hydrogen Damage Assessment For Line Pipe Steel And Anode Material Selection
Gentile, Manuela (Saipem S.p.a.) | Cattalini, Marco (Saipem S.p.a.) | Fehervari, Mauro (Saipem S.p.a.) | Tomaselli, Luca (Saipem S.p.a.) | Ragazzoni, Stefano (Saipem S.p.a.) | Gjedrem, Trond (Nord Stream AG)
ABSTRACT Baltic Sea is characterised by anoxic conditions with the proliferation of Sulphate Reducing Bacteria (SRB), which generate significant amounts of H2S in the sediment, and presents drastic seasonal changes in salinity due to ice melting fresh water contribution. H2S in the seabed environment may promote the diffusion of hydrogen into the pipeline steel which needs to be resistant to hydrogen induced damage phenomena (HIC, SSCC). Resistance to HIC was ensured by the selection of an adequate chemical composition for the linepipe steel. During the engineering phase a methodology to quantify the risk of external SSCC was proposed. In order to assess the most reliable design value of H2S concentration and pH for pipeline design, their representative distribution functions in seabed mud were found, and using Montecarlo statistical method the environmental conditions were characterized. Baltic environment, classified following the ISO15156 Ed. 2003 approach, is "mild sour" and therefore it is necessary to qualify the steel material for Region 1. A conservative target test conditions can be assumed: i.e. an H2S concentration and pH, safely representative of 99.99% percentile of the Baltic environment. If steel material is tested and proven resistant to such environment, the residual probability of SSCC susceptibility is equal to the joined probability for a pipeline of a bare metal surface exposed to a seabed mud with a "sour condition" worse than the test condition. In this case, the calculated probability is only 10 - 10 that is acceptable for DNV rules. Beside SSCC phenomena, the presence of elevated concentrations of H2S in sea water and sea sediments has been reported to be detrimental for cathodic protection aluminium sacrificial anodes performance. In order to verify the possibility to adopt aluminium sacrificial anodes for the cathodic protection of a pipeline in H2S environments, a bibliographic study supported by results of a dedicated test campaign has been performed considering different sea water and sediment environments with elevated H2S concentrations.
- Materials > Metals & Mining (1.00)
- Energy > Oil & Gas > Upstream (1.00)