Advantages of Using Reliability Analysis Techniques to Improve RBI Risk Accuracy

Introduction

Mechanical integrity and inspection professionals often rely on risk-based inspection (RBI) to determine equipment risk levels, prioritize inspections, and develop subsequent mitigation actions. In some equipment, if a leak occurs, there may not be a significant loss in production or an effect on the environment. In those cases, risk is rated as low despite the probability of failure being high. RBI risk can be plotted in a continuous log chart and calculated quantitatively. Figure 1 shows the concept based on which the RBI recommendations are generated when a fully quantitative RBI study is done. The figure reads that inspection should be done on the same date, or before, when the risk reaches the predetermined risk level (risk target). Accordingly, remedy actions are not required for those assets where the total risk associated with them does not reach the risk target.

RBI methodology assesses risk based on the likelihood and consequences of an event, typically with each asset evaluated individually. Reliability-based approaches can incorporate the potential risks associated with multiple simultaneous events of separate assets. Furthermore, they consider the consequences of non-release events. In the following case study, the risk of an individual exchanger tube leak may be assessed as “low” when RBI methodology is applied. But, if two or more exchanger tube leaks occur simultaneously, the consequences could be significantly higher. Statistical reliability-based methodologies can be applied to better assess the risks associated with potential simultaneous events involving separate assets.