Natural gas transmission pipeline systems can extend thousands of kilometers and traverse both populated and less populated areas. Traditionally, risk assessment of natural gas pipelines performed by TC Energy mostly focuses on evaluating the impact of pipeline failures to occupants of nearby structures. However, it is recognized that natural gas pipelines at road crossings or otherwise running in proximity to roads may also pose risks to motorists or other roadway users. Incidents of pipeline failures damaging road infrastructure, resulting in casualties, have been seen in the past.

This paper reports work undertaken to investigate the risk assessment of natural gas transmission pipelines considering the consequence of pipeline failures to roadway users in addition to occupants of nearby structures. Differences between how pipeline failure consequences should be evaluated for motorists travelling at a high speed in vehicles versus occupants of non-moving structures were investigated. Relevant factors that are unique to consequence assessment for roads, such as vehicle speed and relative position between roads and pipelines, were identified, and the way in which these unique factors can be incorporated in risk assessment was studied.

Based on the results from the study, TC Energy updated its System Wide Risk Assessment program to include consequence of pipeline failures associated with roads and roadway users. Data from a total of over 180,000 km of roadway segments across North America that are located in proximity to TC Energy’s over 90,000 km of natural gas transmission pipelines were analyzed. The societal risk with and without roads were evaluated and compared. The impact of considering roadway traffic in the risk assessment in different areas was assessed and the importance of proper consideration of roadway users in quantitative pipeline risk assessment was demonstrated. The methodology developed in the study is useful in advancing the overall accuracy of risk assessment for the pipeline industry, and particularly for pipeline operators in the US, provides a quantitative assessment tool to evaluate the risks associated with roadway driven Moderate Consequence Areas (MCA) and prioritize the integrity work accordingly.

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