AC Mitigation is making material selections to add forms of grounding to the pipeline system. Without a decoupler installed between the grounding and the pipeline, these systems would reduce the effectiveness of the cathodic protection system due to the additional bare surface area being added to the protected structure. There are four (4) primary reasons why a pipeline operating company would need AC Mitigation:
They operate a pipeline that is co-located in a high voltage transmission right of way
- …..and experiencing high induced AC voltage on their system causing 15 volts AC or greater. This has a potential to shock any personnel that come into contact with the structure
- …..and need to lower AC current density in order to reduce corrosion threat.
- Prevent voltage spikes during fault conditions of the AC transmission system
- AC mitigation strategies can be found in NACE SPO177-2014
- The United States Department of Transportation (DOT) published 49 CFR Part 195 to establish rules for controlling corrosion of hazardous liquid transmission pipelines. Subsection 195.575 addresses safeguards and states:
“… (e) If a pipeline is in close proximity to electrical transmission tower footing, ground cables, or counterpoise, or in other areas where it is reasonable to foresee fault currents or an unusual risk of lightning, you must protect the pipeline against damage from fault currents or lightning and take protective measures at insulating devices.”