Wales, S., Lee, T., Carra, C., and Potts, A.E., Paper Number SPE-176170, SPE Asia Pacific Oil and Gas Conference and Exhibition, Jakarta, Indonesia, 20-22 October, 2015.

Abstract

Mooring Integrity Management has gained much interest in recent years as the failure rate for FPS mooring systems has been found to be significantly higher than expected. Existing mooring integrity management practices have not provided adequate protection against such failures. This paper provides an overview of recent advancements in the understanding of fundamental degradation mechanisms applicable to mooring systems and improvements to mooring system integrity.

Advancements in the understanding of mooring system degradation mechanisms will be explored through reviews of recent Joint Industry Projects (JIPs) that have looked at corrosion mechanisms for chain and wire rope, as well as remaining life assessment for corroded chain links. Recent advances in understanding of wire rope birdcage formation and degredation will also be presented.

Improvements to the approaches to management of mooring integrity will be provided by an overview of the DeepStar® supported industry study that has developed Model Guidelines for Mooring Integrity Management (MIM) for permanent mooring systems (AMOG, 2013). These Model Guidelines serve as the foundation for future implementation of risk-based inspection planning for mooring systems. The framework for a risk-based inspection program can be used by the operator to meet the risk profile of the individual facility as well as corporate and regulatory guidelines. The guidelines identify the required practices at each stage of the mooring system life cycle in order to minimize the risk of degradation mechanisms arising from design, construction, installation and operations practices.

Fundamental to the reliability of this methodology are the means to estimate the long-term degradation processes, such as corrosion, wear, fatigue and constructional disturbance, and the commensurate reduction in residual strength capacity and degraded fatigue endurance. The former of these aspects has been the subject of two JIPs, which have advanced the understanding of corrosion and wear processes (SCORCH JIP) and the commensurate reduction in strength and fatigue endurance (Chain FEARS JIP). The latter, constructional disturbance, is the subject of a proposed JIP, leveraging observations of degredation with numerical techniques.

This paper summarizes significant contributions to the understanding of the key causes of mooring component degradation and improved techniques for the effective management of mooring system integrity.