Abstract

An AC study and mitigation design was performed and installed to address corrosion risks. After a few years of operation, the site was revisited due to changing conditions and increasing AC current densities. For the second evaluation, new modeling software was used to evaluate the risk. This paper is a case study comparing the two modeling software techniques, and evaluation on the impact of the field data quality, and a lesson learned on addressing AC corrosion risk.

Introduction

AC interference studies have become increasingly popular in an industry where shared right of ways have increased and there has been a better understanding of how AC interacts between pipelines and powerlines that are collocated with each other. While modeling software for AC interference studies have been developed since the 1990s, advancement in AC interference processes have occurred as more has been learned over the years. When performing an AC interference study there are three steps that need to be completed: field data collection, modeling, and mitigation design. Within this paper, we can compare a project from ten years ago to a project from today to understand the developments that have been made over the course of time to improve the way we develop our mitigation designs. Over the past ten years we have learned how to improve the quality of field data we collect, shown advancements in what is offered by modeling software's, and developed mitigation designs that more efficiently meet our clients needs.

In 2011 and 2013, EN was commissioned by a client to perform an AC interference study along a 16" natural gas pipeline with a wall thickness of 0.25" and Fusion Bonded Epoxy (FBE) coating that runs for about 8.5 miles. The pipeline had an existing cathodic protection system. The cathodic protection is a sacrificial anode system with an anode placed every 1000 feet. There is one rectifier located on the line at the north substation and two bonds. One bond is located on the southern end of the line and connects to an 8" pipeline that runs from the southern substation. The second bond is connected to a 16" pipeline that runs west from the center of the pipeline. The pipeline is collocated with three Powerlines. Two powerlines are 138kV lines that parallel the entire pipeline. The third powerline is a 345kV lines that parallels half of the pipeline. An image of the area being studied can be seen in Figure 1.

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