Integrity inspection planning updated with cost of risk

Abstract

The industry expenditure savings motive requires a cost/benefit analysis to optimise Integrity Management budgets. The challenge of estimating precise risk costs requires that numeric Probabilities of Failure (PoF) be known at the highest possible level of confidence, as equipment items specific PoFs govern the actual probability of financial losses and safety implications.

The first-hand information on the equipment actual integrity condition is contained in numeric results of integrity inspections. In practice, these results are seldom analysed statistically, being collapsed into single ‘worst case’ values. This simplification prevents assessing of equipment specific actual PoFs and from quantifying failure risks when using traditional methods.

We developed a new-generation inspection planning and assessment strategy applied to oil and gas pressure equipment. Evaluating equipment PoFs enables assessing risk costs and optimising the budgets, as well as setting justified internal inspection coverage and frequency objectives. This is achieved by a statistical analysis of numeric inspection data. Existing inspection data (such as ultrasonic testing spot-checks) can be used for a first-pass analysis. Statistical plotting of such data automatically visualises the data quality, and the relevant recommendations for improving inspection coverage or tools are drawn where necessary.

We found that two criteria drive integrity decision making: failure total costs and annual fatality expectancies. These criteria are mutually complementary. Both need to be considered for a safe and profitable plant operation. Equipment individual risk control strategy is then developed from safety compliance and budget savings maximising standpoints, thereby also enabling confident design and procurement decisions.

This is a new-generation strategy suitable for bringing together all branches of plant management and for improving confidence of the parties. We see it as an evolutionary update to Risk Based Inspection and Maintenance practice, which is now in high demand due to cost pressures.