Improving Fitness-for-Purpose Methodology and Safety Target Definitions on Geohazard Related Pipe Deformation

Abstract

Previous practices at Enbridge Pipelines Inc. regarding allowable deformation and/or strain in pipelines were closely mirrored to current North American standards and did not effectively manage the time dependent aspect of active slope movement and other similar progressive external force phenomena applied to a pipeline. In addition, variability in soil spring values and/or soil displacements utilized in FEA assessments can lead to significant variability between predicted pipeline strain demand and actual conditions. Furthermore, the risk tolerance of a potential and significant deformation that could impact the serviceability of one pipeline in a Right of Way (ROW) including multiple pipelines was not well defined. Shutting down several pipelines in a ROW until it could be proven that they are fit-for-service is time consuming. In addition, it requires a good amount of engineering work to address the significant uncertainty in confirming if a pipeline has not deformed beyond a safe limit when the latest deformation in-line inspection predates significant soil movement. A better tool was required to allow a more precise assessment. A better fitness-for-purpose approach has been developed and used to both predict when a timely repair would be required and conservatively set the In-line Inspection (ILI) re-inspection interval to monitor the condition of the pipe. This approach allowed to step away from the greater uncertainty associated with understanding the impact of soil movement on the pipe integrity. This paper presents the methodology used by Enbridge to redefine its fitness-for-purpose methodology using proven strain-deformation correlation models and strain rates estimated through multiple arrays of strain gauges. The discussion will include how the safety targets were re-engineered to account for multiple pipelines in a ROW.