Vessel relocation strategy for multiple steel catenary riser fatigue damage mitigation

Abstract

In previous work, the vessel relocation methodology for a single steel catenary riser (SCR) was developed to extend the fatigue life of the SCR touchdown zone (TDZ). The method was developed considering symmetrical vessel relocation programs, where the vessel offsets about the nominal station in all directions is equal. However, in actual field applications, the production platform hosts multiple SCRs of different azimuth, cross-section geometry and global configurations. Also, the symmetrical relocation consideration eliminates the potentials of exploring non-symmetrical relocation patterns that may be suitable candidate solutions. These considerations add complexity to the problem since, for example, each of the SCR may have unique optimum relocation programs (ideal solutions), but one global optimum solution is required. In this work, we extend the symmetrical relocation method and apply the index matching technique to solve the multi-objective optimisation problem. The non-symmetrical relocation of this methodology for multiple SCRs is demonstrated by comparing the global optimum solutions with those of the no-relocation case. The developed approach can be applied to new and existing SCRs for life extension purposes.