Enbridge Pipelines (NW) Inc. (formerly Interprovincial Pipe Line (NW) Ltd.) owns and operates a buried 323mm diameter crude oil pipeline from Norman Wells, NWT to Zama, AB. The pipeline is approximately 869 km in length, with the route following a portion of the Mackenzie River Valley in the Northwest Territories. The pipeline routing is through discontinuous permafrost that has the potential to interact with the pipeline through frost heave, slope movement and thaw settlement that can produce extreme structural stresses in the pipe wall. Given the proper conditions, these stresses may localize and the pipeline will deform plastically, causing pipe wall wrinkling.
This paper reviews the general structural design and discusses the inspection and monitoring of the structural integrity of the pipeline, as well as the intervention criteria used to determine when structural mitigation is required. This case study will discuss the discovery of a wrinkle from internal inspection pig data, field dig verification, installation and monitoring of field instrumentation and the pipeline repair technique that was utilized.