Application of Reliability Based Design and Assessment to Maintenance and Protection Decisions for Natural Gas Pipelines

This paper describes a detailed assessment that was carried out to investigate the practical implications of using the Reliability Based Design and Assessment (RBDA) methodology, as described in Annex O of CSA Z662, as a basis for evaluating existing pipelines and making decisions on maintenance planning and damage prevention strategies. Two key pipeline failure threats are addressed, namely corrosion and equipment impact. The assessment was based on a number of test cases covering a wide range of diameters, grades, pressures, location classes and corrosion severities. The reliability levels associated with these cases were calculated as a function of time and compared to the reliability targets. Cases that did not meet the targets were re-analyzed with increasingly enhanced maintenance measures until the targets were met. Maintenance actions considered included higher maintenance frequencies and more stringent repair criteria for corrosion, and enhancements to such parameters as right-of-way patrol frequency and condition, public awareness programs and dig notification response for equipment impact. The results demonstrate that the reliability targets can be met through the implementation of reasonable and practical maintenance measures for the cases considered. The impact of using RBDA on the expected failure rates is discussed. In addition, the diameter and class ranges of pipelines requiring enhanced maintenance over the current norm are identified.