New Century and Integrity Plus Blog

Planning for Interactive Threats: Part 2 of 2

Posted by Sarah on Apr 24, 2019 9:33:26 AM

Pipeline Oil Spill

In Part I of this series, we covered what constitutes an interactive threat. Now that you have a handle on what an interactive threat is, how can you use this information to help you plan for them in your Integrity Management Plan (IMP)?

When identifying threats and their interactions, start by:

  • Reviewing the industry failure database
  • Reviewing industry papers and past experiences
  • Consulting Subject Matter Experts (SME)
  • Developing and implementing a risk assessment process to ensure evaluation of threat interaction

In a PHMSA-sponsored study, Eduardo Munoz and Michael J. Rosenfeld proposed a normalizing approach to quantifying the increased likelihood of failure due to threat interactions. The likelihood of failure from each threat includes a portion that involves that threat alone and a portion that involves interaction with other threats. To evaluate the likelihood of failure from multiple threats, your risk model should appropriately account for both portions.

According to Munoz and Rosenfeld, the likelihood of failure (probability) from the two threats can be expressed as:

𝑃𝑇 = 𝑃1 + 𝑃2 + 𝑃𝑖


P1 = failure probability from threat 1 individual factors

P2 = failure probability from threat 2 individual factors

Pi = increased failure probability from threat 1 and threat 2 interactions

(See Appendix K of U.S. DOT PHMSA DTPH56-14-H00004)

“Pi in this expression is evaluated by considering the increased conditional probability of failure from threat 2, given the interactive factors from threat 1. In this example, the increased likelihood of failure from external corrosion due to ineffective CP combined with the existing coating damage from previous pipe damage will be higher than the likelihood of failure from external corrosion if no coating damage is present. Accordingly, that will increase the probability Pi in the above expression used to evaluate the probability of failure from either threat.”

This is just one method to plan for interactive threats in your IMP. We know there is a lot to consider, so let our Risk & Integrity experts help you determine what is right for you and your specific IMP!

Topics: Integrity Management, Integrity, Risk Management, Inspection Data, pipeline risk, Risk uncertainty, interactive threats, integrity management plans

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