Evaluation of Crack Growth and Material Toughness Effects on Probability of Pipeline Failure

Abstract

Probabilistic fracture mechanics (PFM) analysis can provide insights into the relative benefits of various pipeline integrity management options in reducing the probability of a pipeline failure. For example, a prior analysis (1) showed that In-Line Inspection (ILI) technology can achieve a greater level of safety, at longer reassessment intervals, than other integrity management techniques such as Hydrostatic Pressure Testing in a line subject to an aggressive Stress Corrosion Cracking (SCC) environment in relatively high toughness pipe base material. This paper extends that study to evaluate the effects of different crack growth mechanisms, such as fatigue crack growth (FCG) in gas and liquid pipelines as well as materials with differing fracture toughness levels (i.e. Seam Welds vs. Base Metal). PFM analysis can address these growth mechanisms and toughness distributions and serve as a valuable tool for weighing the effects of different assessment techniques, repair criteria and reassessment intervals on pipeline integrity. The analysis can also be used to study the effects of probability of detection (POD) of the ILI techniques as well as enhanced repair (dig) criteria. This paper presents a series of case studies to illustrate the utility of the PFM approach for comparing integrity management options for pipelines subject to different crack growth mechanisms and fracture toughness properties.