Risk-Based Inspection: Utilizing Metrics, Maximizing the Value

This is part 2 in a multi-part series. Part 1 set the stage in explaining the basics of RBI, including

• How confidence and uncertainty are managed effectively
• The importance of a good materials/ corrosion/damage mechanisms review
• Factoring NDE into the RBI equation – credits and debits
• The importance of good, realistic, credible RBI calculation models based on sound and industry accepted technological basis
• Explanation of RBI as a relative risk ranking tool
• Importance of consistency to ensure relativities and therefore risk rankings are valid
• Risk is dynamic
• The pitfalls and liabilities in using “black box” technologies

As I am most familiar with API Base Resource Document 581, I will continue to use this technical basis for this article. Other important reasons for using this document:

• The document is available in the public domain for reference
• It is most often referenced by developers and users of most, if not all, RBI software tools
• It is very comprehensive and fully develops the risk, i.e. consequence and likelihood of failure scenarios to establish a full understanding
• Once one is able to grasp the technical basis of API’s quantitative approach (more qualitative approaches are included in this document, also) it is easier to back off or “zoom out”, validate and understand the more qualitative approaches

Risk Refresher

For the sake of the RBI discussion, Risk is the combined consideration of consequence/s of failure (CoF) and probability of failure (PoF). It should include considerations for safety, environmental impact, business interruption, equipment repair and replacement costs, etc. Output measures should be provided for both sides of the risk equation and combined.