Shallow Buried Fuel Gas Line: Stability Maintenance in the Arctic

Alyeska Pipeline Service Company (APSC), operator of the Trans-Alaska Pipeline System (TAPS), maintains a supporting fuel gas line (FGL) extending 148.4 mi south of Prudhoe Bay. This line, which is 10 in. nominal diameter for the first 33.9 mi and 8 in. diameter beyond that, has supplied natural gas since 1977 to three pump stations south of Pump station 1. The FGL was originally buried a minimum of 36 in. below ground surface (within the active layer of an ice-rich permafrost regime); it runs primarily along the Dalton Highway as buried piping, with two above-ground highway crossings and one elevated bridge crossing. Its route includes both thaw-stable and thaw-unstable segments, some of which have proven vulnerable to thermokarst formation. In addition, the FGL is subject to water infiltration and erosion from seasonal surface water overflow, which also can contribute to or cause loss of cover materials. Because of these dynamics, Alyeska has developed a set of monitoring methods for the FGL. These include use of in-line curvature and corrosion inspection tools, field surveys, periodic “linewalk” surveillance, and LIDAR interpretation. This paper describes these tools, as well as the maintenance approaches that Alyeska has developed over the last 46 years to maintain line stability and protection.