Development and Qualification of Alternative Solutions for Improved Fatigue Performance of Deepwater Steel Catenary Risers

Several initiatives have been undertaken by the operators, engineering companies, product manufacturers, and regulatory bodies to enable increased use of steel catenary riser (SCR) design in development of deepwater and ultra-deepwater fields. Some of these efforts focus on improvement in understanding of soil-structure interaction at SCR touch down zone (TDZ) and its impact on fatigue damage estimates through analytical studies, laboratory testing, or in-field monitoring of SCR behavior. Through recent studies and laboratory testing work for floating platforms with SCR, the need for significant enhancement of SCR design at TDZ through implementation of alternate solutions has been identified. This paper presents a summary of the work undertaken in a Joint Industry Project (JIP) during 2004 to 2007 [1, 2] to develop solutions and undertake qualification tasks for four alternatives with potential to improve fatigue performance at TDZ by factor of up to 10 or more. The solutions considered at SCR TDZ include: thick light-weight coating over steel riser sections; steel riser sections with upset ends; high strength steel riser sections with integral connectors; and a titanium segment. The major qualification tasks undertaken for each solution will be identified and discussed. The qualification program undertaken for each solution varied and in some cases, it also included manufacturing of samples, laboratory and full-scale fatigue testing, and post-failure evaluation. Through significant qualification activities undertaken in this JIP, progress has been made to bring these solutions to project ready state for their consideration at the frond end engineering design (FEED) stage. Such design enhancements would enable increase in selection of SCR design for production and export riser applications under severe operating conditions, harsh environment, and floating systems with high motions.