Failure pressure ratios and implied reliability levels for corrosion anomalies on gas transmission pipelines

This study investigates the relationship between the failure pressure ratio (FPR) and implied reliability level for corrosion anomalies on natural gas transmission pipelines governed by the Canadian oil and gas pipeline standard CSA Z662-15 The model recommended in Annex O of CSA Z662-15 is adopted to evaluate the burst pressure capacity of a given corrosion anomaly on a pipeline, and the first-order reliability method (FORM) is used to evaluate the reliability index of the anomaly by considering uncertainties associated with the pipe geometric and material properties, ILI-reported anomaly sizes, operating pressure and accuracies of the burst pressure capacity models. The analysis results suggest that the FPR-reliability index relationship for pipelines with utilization factors greater than or equal to 0.72 is independent of the pipe attributes and geometry of the corrosion anomaly, if the measurement error associated with the ILI-reported anomaly depth is relatively small. Sensitivity analyses are carried out to examine the sensitivity of the FPR-reliability index relationship to the measurement error associated with the ILI-reported anomaly depth.