While offshore arctic pipelines have been under consideration for more than 25 years, few have been built. Renewed interest in offshore arctic oil and gas has necessitated the design of pipelines capable of both overcoming the technical challenges of the arctic offshore environment and minimizing the risk to it. This paper describes a quantitative risk assessment completed by BMT Fleet Technology Limited on the risk of an oil spill for several design alternatives of the proposed Liberty Pipeline that would be used to transport oil onshore from a production site in the Alaskan Beaufort Sea. For the purposes of the study, risk was defined as the volume of oil expected to be released over the planned pipeline 20-year life. The investigation considered the risks associated with ice gouging, strudel scour, permafrost thaw subsidence, operational failures, corrosion, third party activities and thermal loads leading to upheaval buckling. Event probabilities for these hazards were established through the development of event trees used to combine historic operational failure statistics and those estimated through engineering analysis. A pipeline leakage consequence model was developed to quantify the oil volume released during pipeline failure events associated with rupture, through-wall cracking and pinhole leaks. The model considered secondary containment and the expected performance of leak detection and monitoring systems. The time to leak detection, shut down, and line evacuation were used in estimating the total spill volumes. The paper provides an overview of primary elements of the risk assessment including the hazard identification, reliability analysis and consequence modeling, and describes the challenges involved in this comparative risk analysis completed for this unique environment.

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