Asset Integrity Control: Prioritization of Offshore Topside Flange Openings During Preventive Maintenance Shutdowns

Abstract

Top side flange inspection on offshore production and process facilities (P&PFs) has been a challenging task, due to complex geometries, produced crude oil and gas quality changes over the production well’s maturity, as well as the stringent regulatory requirements that need to be followed to assure the anticipated integrity of the operating assets. The complex geometries hinder the use of non-destructive testing (NDT) testing approaches and necessitate shutting down the system or subsystem in order to disassemble the flange to perform close visual inspection (CVI). Using risk-based asset integrity (AI) assessment and control (RBAIA&C) approaches, it is possible to classify the flanges into different classes, according to probability of failure (PoF). The PoF is estimated by considering the last inspection date, past inspection data, findings from similar locations/systems in the same offshore facility, etc. Together with consequence of potential failures (CoF), it is possible to estimate the risk of a potential failure due to the loss of integrity of a selected flange. Although several flanges are qualified to be disassembled, based on RBAIA&C activities, it is not possible to take all of them off during a certain preventive maintenance (PM) shutdown. Currently, ad hoc approaches have been used to further prioritize the flanges that have been recommended for inspection during a PM shutdown, based on RBAIA&C activities. The aforementioned jeopardizes the integrity of flanges and subsequently the overall system, possibly leading to catastrophic accidents. This manuscript demonstrates a methodology for the systematic further prioritization of flanges that need routine CVI. The flange inspection related system analytics have been incorporated with the analytic hierarchy process (AHP) to make logical further prioritization with sufficient transparency. The approach has been demonstrated with an illustrative case study that has been chosen from an offshore P&PF. A sensitivity analysis has also been performed and is presented to demonstrate how to carry out trade-off evaluations between different factors in the flange prioritization in a PM shutdown.