Risk-based inspection (RBI) approach to plant life management

Many items of power generation, refining and petrochemical process plant degrade with time in service and regular condition inspection is generally implemented to provide on-going assurance of integrity. The inspection strategies adopted are usually formulated in recognition of general and plant specific failure experience, with safety regulators, insurers and statutory requirements superimposed. Although probability and consequence of failure are implicit factors, these strategies are not generally founded on a risk basis. However, as the business climate becomes increasingly competitive, downward pressure on operating costs is driving operators to examine the effectiveness of their inspection programmes within a cost-benefit framework. This paper presents a structured, risk-based approach to defining plant inspection programmes and demonstrates how risk assessment can be used to optimise maintenance and operating costs. The approach is applied in a progressive manner such that low risk equipment is identified and addressed by qualitative assessment and only items of concern are analysed quantitatively. For these items, both the probability of failure and the cast consequences are determined and used to calculate the risk exposure as a function of service time. This potential cost is compared with the costs of inspection and plant refurbishment to optimise the maintenance strategy. Operating costs can also be reduced by examining the effects of alternative operating regimes on production and risk exposure. The approach is illustrated in this paper by specific examples of the application of risk-based inspection (RBI) and plant assessment.