An AC interference study and mitigation design was performed for a pipe replacement project. The project was broken up into multiple phases due to a construction schedule that spans multiple years. This paper is a case study examining the process of performing a piece-wise vs a holistic mitigation design for the pipeline. Designs are based on field data and software modeling. Designs for each approach are compared and their differences and benefits are explored.
AC interference analyses are an important part of designing an adequate cathodic protection system on a pipeline when collocations with high voltage powerline(s) occur. Modeling software has been developed to create accurate simulations of what is occurring in the real world to create the best mitigation designs for operators. Many of these studies are proposed due to pipeline replacements that update pipelines from coatings with coal tar to fusion bonded epoxy (FBE). FBE has a much higher coating resistance than coal tar. This results in less AC current being grounded to the soil and fewer and smaller holidays in the coating which can contribute to higher AC voltages and AC current densities along the pipeline.[1] When performing AC interference studies, the goal is to mitigate AC voltages below 15 VAC to limit the shock hazard to personnel and current density below 30 A/m2 to ensure AC corrosion is low risk. [2,3]
When pipeline replacement projects are proposed, much of the information shared by a client is only from the replacement pipe area. However, it is important to look at the entire pipeline route, including areas that are not being replaced to provide the most accurate mitigation design, as current can attenuate farther than the replacement sections on the pipeline if it is not isolated from the replacement section.
