As part of Pacific Gas and Electric Company’s (PG&E) on-going commitment to public safety, the company has begun a comprehensive engineering validation of its gas transmission facilities that will ultimately support the reconfirmation of maximum allowable operating pressure (MAOP) for these assets.
In addition to 6,750 miles of line pipe, PG&E’s gas transmission system contains over 500 station facilities. Since this set of facilities is not only large but diverse, and the validation effort for these facilities is expected to be an extensive, multi-year process, a methodology for the prioritization of the facilities needed to be developed to facilitate planning of the process for the efficient mitigation of risk. As a result, DNV GL was retained to develop and implement a risk-based prioritization methodology to prioritize PG&E’s gas transmission facilities for the engineering validation and MAOP reconfirmation effort. Ultimately, a weighted multiple criteria decision analysis (MCDA) approach was selected and implemented to generate the prioritization.
This MCDA approach consisted of the selection of relevant criteria (threats) and the weighting of these criteria according to their relative significance to PG&E’s facilities. Relevant criteria selected for inclusion in the analysis include factors that are important in order to assess both the short- and long-term integrity of the facility as a whole as well as the integrity of features for which design records cannot be located. The criteria selected encompass stable threats, time-dependent threats, as well as environmental impact. Enormous amounts of data related to design, operations, maintenance history and meteorological and seismic activity in addition to other environmental data were evaluated with this newly developed methodology to assess the relative risks of the facilities. Pilot field visits were performed to validate the selection of the various criteria and to confirm the outcome of the analysis.
The novelty of this approach lies in the prioritization of facilities in a coherent risk-based manner. The described approach can be used by operators of oil and gas facilities, either upstream, midstream or downstream.