Geometry Monitoring of the Trans-Alaska Pipeline

An important aspect of the ongoing operation of the buried sections of the Trans-Alaska Pipeline System (TAPS) is the curvature imposed on the pipeline by differential settlement of the surrounding soil as a result of thawing of ice-rich subsurface soils. High pipe curvature is a source of concern since it can potentially lead to wrinkling of the pipe wall and/or tensile fracture of the pipe at girth welds. Alyeska Pipeline Service Company has monitored pipeline settlement using different techniques since start up of the line in 1977. This paper provides a brief historical overview of how the techniques used to monitor pipe settlement have evolved over the life of TAPS. The paper also provides a discussion of the how the pipe geometry is currently monitored using the BJ Pipeline Inspection Services (BJ) Geopig® smart pig. The discussion includes a brief description of the Geopig measurements which are numerically processed to obtain the three-dimensional pipeline displacement and curvature (bending strain) profiles. Several illustrations of this technology are presented. The paper concludes with a summary of how Alyeska's state-of-the art pipeline geometry monitoring program is used to help make decisions related to maintaining the structural integrity of TAPS.