Next Generation Hit Rate Fault Tree for Third-Party Activities
Daniel Fujinaga, Howard Yue, Riski H. Adianto, Mark Stephens · 2024
Abstract Fault tree models have been developed and used over the past two decades to estimate the frequency with which buried onshore pipelines are damaged during third-party ground disturbance activities. The estimated hit rate values can be combined with an estimated probability of failure given hit to assess the likelihood of pipeline failure due to third-party mechanical damage in a comprehensive quantitative risk assessment of a pipeline. Public domain and proprietary fault tree models that the authors are aware of have all been developed from pre-2010 research efforts, which highlights the need for an updated model that better reflects the most recent third-party damage statistics and modern damage prevention measures currently being employed or considered by pipeline operators. In response to this need, a next generation model for estimating the hit rate from third-party activities on a pipeline alignment has been developed for buried onshore pipelines as part of a joint industry project (JIP) that commenced in 2020. The new hit rate model can be considered hierarchical, consisting of an upper aggregation subtree and lower-level fault trees. The upper-level subtree delineates external interference activities based on the types of equipment involved and the season (i.e. summer versus winter) in which they occur. While previously developed models usually only address general excavation involving excavators or backhoes as the sole interference activity type, the new model also considers vertical and horizontal drilling and agricultural tilling. The lower-level fault trees address the effectiveness of the various available damage prevention measures, with due consideration of the various equipment types and season of occurrence combinations defined in the upper-level aggregation subtree. In developing this new hit rate model, the seasonally dependent frequency of ground disturbance activity on the pipeline alignment by equipment type and the effectiveness of candidate damage prevention measures at reducing the hit frequency were calibrated using the latest available information in the public domain and from JIP participants. In addition, the outputs obtained from the new hit rate fault tree were validated using the most recent historical hit rate data found in the public domain. To illustrate the predictive capabilities of this new third-party damage fault tree model, the relative effectiveness of selected damage prevention measures is examined through a set of comparative scenario analyses.