Inspectioneering Journal

Likelihood of Failure + Consequence = Risk

The World of Risk-Based Inspection - Significant Activity in the Hydrocarbon Process Industries

By John Reynolds, Principal Consultant at Intertek. This article appears in the March/April 1995 issue of Inspectioneering Journal.

Many promising advances are being made in inspection technologies, today. Some are going to provide opportunities for companies to maintain and increase equipment mechanical integrity, quite possibly at lower costs.

Risk-Based Inspection (RBI) planning is one of those inspection technologies that I'm excited about. Sixteen refining and petrochemical companies have joined together in a joint-sponsored program administered by the API to develop RBI technology for the hydrocarbon process industry. Though Quantified Risk Assessment and RBI are not new, much effort was necessary to develop and adapt the technology for the hydrocarbon process industry. That work is going on now. When completed it will lead to a new RBI Recommended Practice (RP) for the hydrocarbon process industry. Optimistically, I hope to see the API RP on RBI published in about three years. Our goal is to produce a document that can be utilized by plant inspection/engineering personnel to prioritize process equipment based on risk.

In a nutshell, the methodology involves a quantitative assessment of the likelihood of failure and the consequence of failure associated with each piece of pressure equipment, piping included, in a particular process unit. The bottom line results will be a prioritized list, based on calculated risk, of each piece of pressure equipment in a process unit. Piping is best evaluated in manageable segments. Hence, the inspector and engineer will know where to focus their limited resources to reduce the chances of failure for their highest risk equipment. Would you agree, the approach makes sense?

Of course one might say, "I already know what your highest risk equipment is, and we're inspecting it every six months."

However, often in our qualitative assessment (gut feel) approach, we end up putting more of our inspection resources into equipment with a higher probability of failure, sometimes giving little or no weight to the potential consequences of failure. Without a more structured approach, it is entirely possible to give inadequate attention to a fairly non-corrosive section of piping carrying light hydrocarbons, that we seldom or never inspect, which might be susceptible to cracking or brittle fracture. Whereas, a piece of piping in a fairly corrosive acidic process, carrying condensate (high probability of failure, but relatively low consequence), might be receiving more inspection attention than the piping that could go "boom in the night". Believe me, it happens!

An RBI assessment, in a process unit with 300 vessels and piping circuits, might just reveal that a portion of high-risk equipment in your plant is deficient in receiving an adequate share of your inspection resources. With your new-found insight from an RBI assessment, you may choose to shift some of your resources from lower priority equipment to higher priority candidates.

Clearly, in such a short note, I can only "whet your appetite" for what RBI is all about. For those companies that would like to get in on the "front end" of this developing technology, you can contact the API about joining this group-sponsored effort. Additionally, the National Petroleum Refiners Association (NPRA) is planning a workshop on RBI at their next maintenance conference in San Antonio in May of 1995.

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