PR-015-113601-R02 Validation of Internal Corrosion Threat Models for Dry Natural Gas Pipelines

Abstract

This report documents the verification and validation (of the probabilistic models developed previously to predict internal corrosion (IC) threats in nominally dry natural gas pipelines. Model uncertainty quantification showed that "low temperature, high pressure" posed the greatest IC threat. To validate the model, actual measurements were compared to model-predicted wall loss. The comparison included information from an IC failure, investigated by the National Transportation Safety Board (NTSB), with in-line inspection (ILI) data sets from five pipeline operators. Two of the pipeline operator data sets showed wall loss measurements either evenly distributed at all locations around the circumfer-ence of the pipe or predominantly at the top of the pipe. These measurements agreed with negligible wall loss predicted by the model. Two other operator data sets measured significant wall loss occurring at the bottom of the pipe. These measurements agreed with non-negligible risk of IC also predicted by the mod-el. The 5th operator data set confirmed the analysis of ILI data uncertainty and corroborated the validation results. For the NTSB investigated failure, the model prediction is in good agreement with the post-failure examination because the model predicted a very high IC risk for this pipeline that failed. This validation provides increased confidence that the previously developed models can differentiate between negligible and non-negligible wall loss occurring in a dry natural gas pipeline.