Regulations for pipeline operators within the Oil and Gas Pipeline Industry are becoming increasingly rigorous especially in the fields of pipeline integrity and emergency response and as such the need for equally rigorous approaches to analyzing, understanding, managing, and reporting of the effects of a pipeline release has increased. Trans-Northern Pipelines (TNPI) undertook a detailed fate and transport modeling project for its Ontario and Quebec based pipeline systems. These pipeline systems are relatively complex products delivery systems that handle multiple fluids and, for some pipeline segments, allow for flow in either direction. The goals of the project included understanding and improving risk management of the systems through consequence reduction and to identify and quantify potential impact to surrounding areas and risk receptors within the vicinity of the pipeline systems. The receptors are the focal points that receive the negative impact if there is a leak (i.e. pin-hole, small and large scenarios) or rupture of the pipeline. These can include health/safety, environmental, property damage, reputation and public disruption, and financial impacts. The outcomes from the project included a continuum of potential release volumes along the pipeline systems for each product and operational scenario from which a spatial representation of the potential impact areas (due to overland flow) along the pipeline system were derived and locations were identified where potential release volumes (i.e. initial and drain down volumes) could affect streams and could possibly be transported along the stream. Potential impact areas and representations of the stream transport were used to identify possible risk receptors. A unique aspect to this modeling project was that it was undertaken utilizing a four dimensional (4D) model thus allowing for the results to be visualized within a GIS and as animations; both of which facilitated visualization of potential release impact over time (e.g. a 48 hour period). Utilizing the time domain provided unique insights that were used to augment TNPI’s emergency response plan. Based on a review of the preliminary results Trans-Northern undertook additional effort to investigate what-if scenarios for valve placement. The purpose of these what-if scenarios was to quantify the improvement of additional valves on lowering the overall potential impact and thus allowing for a quantitative basis for valve placement.
Current federal regulations in the U.S. require excavation of plain dents identified through in line inspection surveys based primarily on depth. Industry experience, and previous research, has shown that the depth of the dent, alone, is not sufficient to assess dent severity and that releases could occur at dents below the excavation threshold (Dawson, 2006). Canada’s National Energy Board released a safety advisory on June 18, 2010, to all companies under their jurisdiction regarding two incidents involving shallow dents. The safety advisory stated that all integrity management programs should be reviewed and updated where appropriate to address the threat posed by shallow dents. Similar incidents have raised awareness in the United States and elsewhere around the world. This paper focuses on an extensive multi-year effort to analyze the fitness for service of unconstrained shallow dents on multiple pipeline systems. Fatigue and strain analyses were performed to determine the serviceability and estimate the remaining service life. The dents in this study included both topside dents and bottomside dents that were previously evaluated through excavation to be unconstrained. Results of the fatigue and strain assessments are presented, along with field results of dents that were chosen for excavation. Comparison of the fitness for service results and subsequent excavation findings were performed to improve an ongoing campaign to prioritize several hundred in-service unconstrained dents. Maximum strain levels of the dents were calculated based on the geometry of the dent as determined by radial sensor measurements from in line inspection surveys. The results of the in-line inspection and field measurement comparisons were analyzed to determine the accuracy and possible adjustments of strain assessments for the ongoing fitness-for-service program.
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