Comparative analysis of failure consequences using qualitative and quantitative methodologies

As a management tool, risk-based inspection (RBI) addresses an area of risk management not completely addressed in other organizational risk management Efforts, such as process hazard analysis (PHA) or reliability-centered maintenance (RCM). The RBI approach is a defined process for establishing and managing an inspection program based on understanding the failure probability and consequences of each equipment item. The RBI approach can focus the inspection program of the facility on the higher-risk equipment items, reducing the overall plant risk of a catastrophic failure while simultaneously providing a significant reduction to the cost of the ongoing inspection program. Moreover, it ensures all damage mechanisms identified in the corrosion study are being addressed. This paper outlines the different types of RBI models, i.e., qualitative, semi-quantitative, and quantitative models. Moreover, it provides insights into the basis of the most widely used quantitative RBI models in the oil and gas industry, i.e., API risk models, and then implemented them through a case study at an offshore gas production platform to evaluate and critically discuss the difference in the calculated consequences of failure resulting from the two methodologies of estimating the impact areas. The case study presented in this paper demonstrated the inconsistency in the calculated risk resulting from the two risk models, whereas the difference was several orders of magnitude for some equipment items. The resulting inspection and maintenance plans are likely to be significantly different if the same risk matrix and risk tolerance are used for both risk models.