A probabilistic method for prioritizing repairs following an ILI crack tool run

摘要

Following an ILI crack tool run, the operator must make decisions on digs and repairs. The traditional approach entails ranking flaws by means of deterministic burst pressure calculations. Some operators have begun to incorporate probabilistic methods into their decision process, but burst pressure is still the primary criterion. Aside from the fact that traditional pipeline fracture models contain severe modeling errors, ranking by burst pressure is not optimal when the line is subject to significant pressure cycling. The indications that pose the biggest threat may not be the largest flaws. Moderately-sized flaws near a pumping station discharge may fail sooner than larger flaws further downstream. The probabilistic framework presented herein provides a rational basis for prioritizing repairs following an ILI tool run. The model accounts for uncertainty in flaw dimensions and material properties. It also considers the pressure cycling at each flaw location, as well as time-dependent damage due to the initiation of fatigue cracks at seam weld flaws.