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

Abstract

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.

Analyzing Welding Performance of Metal Using Artificial Neural Network

“…e shear strength is the opposite, decreasing first and then decreasing again [15][16][17][18][19][20].…”

Vessel relocation strategy for multiple steel catenary riser fatigue damage mitigation

“…However, for non-symmetrical relocation programs, the patterns will be skewed about the nominal station. In previous work for symmetric relocation optimisation for single SCR [31], it was found that the optimum relocation program (𝛼, 𝑅, 𝑝) was (30deg, 5%, 19). A further investigation of this relocation program showed that although 19 stations gave the least effective fatigue damage, the number of stations beyond 𝑝 = 9 along 𝛼 = 30deg, for 𝑅 =5% contributed very little reduction to the effective damage of the SCR TDZ as shown in Table 4 and Figure 8.…”

“…The application of alternative materials for SCR pipes can provide increased strength and resistance to corrosion. An example of such material is titanium [2,[17][18][19][20], which can significantly improve the SCR ability to accommodate considerable stress and fatigue damage considering its high flexural rigidity. Many advancements have been made in riser soil interaction modelling, such as developing non-linear riser soil interaction models [21][22][23].…”

“…Decoupling the SCR from the vessel motion reduces the dynamic top tension, TDZ stress, and fatigue damage. The use of upset pipe end (thicker pipe sections at welded joints) and titanium welding connection for deepwater SCR are now being explored to improve the fatigue life of the riser at critical joints [19,26]. Vessel relocation involves the movement of the riser host platform from one location or station to another to enhance the fatigue damage spreading over a longer section of the SCR TDZ [27][28][29][30].…”

Vessel relocation solution for steel catenary riser touch down fatigue management

“…However, at the touchdown zone, a longer section of the SCR interacts in a complex way with the nonlinear seabed, resulting in high and intricate fatigue response patterns that pose great challenges to manage. Several efforts have been committed by research institutions and the offshore industries to increase the application of SCRs for deepwater hydrocarbon extraction [11][12][13]. These solutions include the SCR configuration change such as steel lazy wave and shaped riser solutions [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32], the alternative material application for SCR design such as high strength material including titanium for the riser pipe joint [2,11,[33][34][35], the advancement in riser soil interaction modelling such as the development of non-linear riser soil interaction models [36][37][38], the decoupling of SCR from vessel motion such as the uncoupled steel catenary riser systems [39][40][41][42], the vessel relocation to effect fatigue damage spreading along the SCR TDZ [12,[43][44][45], the use of upset pipe end and titanium welding connection to improve the life of the riser at welded joints [11,35...…”