Synergetic Implementation of LOPA and RBI Methodologies for Pressure Relief Device Inspection Interval Optimization

This paper presents an optimization analysis methodology for the preventive maintenance interval of a Pressure Relief Device (PRD) that could not be executed at its original planned interval due to the failure of its isolation valve. Initially, deferral analysis for the maintenance of this PRD was performed using Layers of Protection Analysis (LOPA), but the method for updating the initial Risk Reduction Factors for the PRD was not standardized and was qualitatively adjusted by the analysis team. As a result, the risk of deferring the maintenance was initially considered intolerable, and the unit was planning to shut down to execute the preventive maintenance. To address this issue, a second analysis was developed, which consisted of a synergy between risk-based inspection methodologies and LOPA. This resulted in an optimized maintenance interval for this PRD, which allowed the unit to operate safely until the next shutdown window while satisfying operational risk thresholds and financial goals that were initially jeopardized. To ensure reliable adoption of the results of this analysis, it was necessary to thoroughly review both methods to confirm the level of convergence between the results obtained when they were conducted separately. This paper also describes the steps taken to standardize the updating of initial Risk Reduction Factors for PRDs and identifies the equivalent parameter in LOPA and RBI methods that enable the synergy in optimizing maintenance and inspection intervals at the refinery.

Keywords: LOPA, RBI, Pressure relief devices, Safety valves, Inspection interval, Refinery.

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