A Risk based Maintenance (RBM) Interval Decision Making Model to Support Life Extension of Subsea Oil and Gas Facilities

A substantial number of production facilities in the subsea oil and gas industry are approaching

their anticipated service life and thus, require to undergo a life extension program. In effect, the volume of maintenance activities to be undertaken on facilities in the subsea fields is growing rapidly. The current inspection and maintenance decision-making approaches to support life extension of subsea oil and gas facilities are mainly based on subjective experience and judgement of inspectors and engineers which may be inconsistent, inaccurate and unreliable. Therefore, it is of great interest for asset managers to propose sound approaches for maintenance of subsea facilities operating beyond their original design life. In this study, a quantitative risk-based maintenance (RBM) interval decision-making model is presented to minimize cost as well as the overall risk associated with life extension. The model provides an effective tool for maintenance planning of subsea equipment during the extended phase of operation by considering the probability of failure and the consequences associated with failures of the equipment. The likelihood of failure is modelled using Weibull distribution due to its inherent flexibility, and the failure parameters are determined using physical equipment data by means of maximum likelihood estimation (MLE) method. On the other hand, the economic consequences of failure is calculated by considering asset loss, production loss, human health loss and maintenance cost. The proposed framework is applied to a case study involving a subsea flowline and the results are discussed and evaluated.