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Understanding and Managing Risk

By Greg Alvarado, Chief Editor at Inspectioneering Journal. June 3, 2013

This is the third of four blogs in a series about Risk Based Inspection (RBI). You can read the previous blogs on a history and reasons for RBI and on starting to define risk. This post deals with the second half of the equation used to define risk:

Consequence of Failure (COF) x Probability of Failure (POF) = RISK

The POF side of the risk equation would include but not be limited to:
  • Corrosion/materials/metallurgical engineer familiar experienced in the particular process
  • Inspector or inspection engineer familiar with the unit
  • Operations person familiar with the operating practices and history of the unit (this is where operating NOT according to design and other operations related anomalies are identified) and future likely operating practices
  • Process engineer familiar with the process and planned future operating practices
  • RBI expert that is intimately familiar with the technology algorithms and sensitivity weightings of inputs and outputs

Experience has shown me that, in the absence of an experienced operations person, or experienced process engineer, a very good, experienced corrosion/materials/metallurgical engineer with experience in that particular process is a tremendous asset and essential to a credible RBI program. They understand the deterioration dynamics, including subtle, yet important nuances and can extract this information from operations, inspection, etc.

As I often point out to students in the API RP 580/581 course, RBI is largely about how much confidence one needs to have in what one believes to be the true damage state of the equipment. This “needs to have” is dictated by the risk number or risk value versus the risk target.

Often times, but not always, one can live with a higher corrosion rate, for example, early in the life of a relatively thick-walled vessel. As the wall is consumed and damage accumulation increases, it becomes increasingly important to pay more attention to managing this equipment. Ideally, one would use the RBI process to determine time required for getting more accurate and perhaps precise data (especially where assumptions are driving the risk), retirement, or if justified, a Fitness for Service (FFS) analysis. One could also use the process to determine the necessity of a design modification, e.g. installing a liner, a process change, etc., or in other words, something to mitigate the POF and risk.

In the next post, I’ll discuss uncertainty in RBI risk thresholds. You can always post questions or feedback to our LinkedIn Discussion Group. You can also sign up for our email newsletter, Inspectioneering Turnaround, for a weekly dose of AIM intelligence.


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