Avoiding Faults: AC Current Mitigation on a Large Diameter Steel Pipeline—Case Study

In 2015, the Willamette Water Supply Program (WWSP) in Beaverton, Oregon, was completing alignment selection for its new 1.67 m (66-in.) diameter, welded-steel water transmission pipeline. A “pinch point” in the alignment required the pipeline to pass within a reduced public right-of-way, “squeezed” between two electrical substations, and perpendicular to underground control, substation ground fault conduits, communication cables, and overhead transmission lines connecting the two substations. The existing electrical infrastructure and public utilities presented unique design and constructability challenges that included underground and overhead vertical clearances, potential impact of ground faults, and maintaining existing controls. Several methods of addressing the ground fault concerns were evaluated, including encasement, large diameter isolation flanges or joints, increased pipeline depth to attain a minimum separation distance, and modifications to the electrical facilities themselves. This paper presents the reasons for selecting this challenging pipeline alignment, the initial and intermediate mitigations considered, and the selected solutions.