Quantitative Pipeline Risk Assessment and Maintenance Optimization

The quantitative risk assessment tool was used to calculate the failure rates, failure consequences and risk levels along the pipeline. Safety risk was characterized by the individual risk ratio, which was defined as the maximum individual risk associated with a given segment divided by the tolerable individual risk. Tolerable individual risk values were defined as a function of population density following the approach developed by MIACC and the UK HSE. Financial risk was expressed in dollars per km-year and included a dollar equivalent for public perception. The recommended maintenance plan was defined as the minimum cost option that achieved a tolerable safety risk. The first step in developing the plan was to identify all segments that do not meet tolerable risk criteria (i.e., segments with an individual risk ratio greater than 1). For each of these segments a number of potential maintenance scenarios that address the dominant failure threats were selected. A cost optimization analysis was then carried out in which the total expected cost associated with each maintenance option was calculated as the sum of implementing the option plus the corresponding financial risk component, amortized over the inspection interval. This analysis was used to identify the minimum cost alternative that meets the individual risk constraint. Outcomes of the analysis included the best maintenance option (e.g., inline inspection, hydrostatic test) and the optimal time interval for segment re-evaluation.