Reliability Study on the Life Extension of Subsea Umbilical Systems

Abstract

Subsea umbilicals are a critical element on most subsea oil & gas production systems. They can include hydraulic conduits and electrical and/or optical cables that serve as a critical lifeline, connecting topside facilities and equipment to subsea architecture, distributing multiple elements including power, chemicals, and communication functions throughout the deepest and harshest of environments. Globally, thousands of subsea umbilical systems are approaching or have reached the end of their design lives after 15-25 years of operation. In many cases, operators would have a need to continue using such umbilical systems for longer, but they are unsure whether that can be done or if they need to invest in new replacement umbilicals. To make the right decision, operators need a well-defined process for evaluating the risks of continuing to produce using the existing umbilical systems. This paper presents a simple methodology for assessing risks related to extending the life of subsea umbilical systems. This method helps operators identify the most critical areas of the system and their associated risks, and helps estimate the reliability of the system in its current and future states. Upon review of available literature and current practices, it was determined that there were no industry standards for extending the life of umbilicals. The method described here is in line with the guidelines and recommendations of API RP 17N [Ref. 1]. The approach includes a review of the available information related to the life of the asset along with risk identification, risk assessment and recommendations for risk mitigation. Reliability models using field data and available literature are used to quantify the system reliability under different conditions, including life-extension scenarios. The proposed method is demonstrated using an actual business case from the North Sea, where risks associated with the life extension of a given umbilical system were identified and reviewed, and where the work has supported the operator's decision-making process.