Mitigation of Arcing Risks to Pipelines Due to Phase-to-Ground Faults at Adjacent Transmission Powerline Structures Wolfgang Fieltsch, P. Eng. wfieltsch@corrosionservice.com Corrosion Service Company Limited 2-498 Markland St. Markham, ON L6C 1Z6 Canada Bryon Winget, P. Eng. Pacific Gas and Electric Company 375 North Wiget Lane Walnut Creek, CA 94598 USA ABSTRACT Although the probability of a phase to ground fault occurring at a specific transmission powerline tower and resulting in an arc to an adjacent pipeline may be quite small, the risk cannot be ignored due to the severity of the potential consequences. A sustained arc to a pipeline could result in melting of the pipe wall and catastrophic failure of the pipeline. Additionally, the powerline fault current would be trans- ferred directly to the pipeline via the arc, resulting in safety risks, the potential for additional arcing risks at crossings with foreign structures, and a risk of damage to isolating flanges and to cathodic protection equipment upstream and downstream of the fault location. In order to ensure there is no risk of arcing, a critical or “safe” separation distance between the pipeline and any part of the powerline tower foundation or grounding system must be maintained. This paper discusses how to determine the critical separation distance that is required to avoid an arc based on research, literature and standards, and explores mitigation options in circumstances where this distance cannot be feasibly maintained. Calculations and mitigation measures from a case study and a pilot site will be presented. Keywords: AC Mitigation, AC Interference Pipelines, Arcing, Powerline Fault, Transmission Powerlines, High Voltage AC (HVAC), Phase-to-ground Fault INTRODUCTION This paper discusses how to determine the critical separation that is required to avoid an arc based on research, literature and standards, and explores mitigation options in circumstances where this critical distance cannot be feasibly maintained. An arcing investigation program implemented by a California gas and electric utility is presented as a case study, with specific risk assessment and mitigation details provided for a pilot location. 1 Paper No. 4389 ©2014 by NACE International. Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to NACE International, Publications Division, 1440 South Creek Drive, Houston, Texas 77084. The material presented and the views expressed in this paper are solely those of the author(s) and are not necessarily endorsed by the Association.