AC Interference Data Logging on Pipelines Near Wink and Sarita, Texas (2019)

In 2019 we logged AC pipe-to-soil potentials on pipelines that share corridors with overhead power lines, at eight locations near Wink in West Texas and three near Sarita in South Texas. Client details are confidential.

Why AC on a pipeline matters

A buried pipeline that runs alongside or crosses a high-voltage AC line can pick up an induced voltage. That voltage changes with the load on the power line through the day, so a single reading can miss the worst hour. A high induced voltage can be a shock hazard at test stations and risers, and it can drive AC corrosion at small coating holidays. Before deciding whether mitigation is needed, an operator needs to know how high the voltage gets and for how long.

West Texas: eight locations, 48 hours

In May 2019 we set data logging multimeters at eight predetermined locations on a crude oil and gathering system in the Permian Basin near Wink. The lines ranged from 4 to 12 inches, and several paralleled or crossed high-voltage transmission and distribution lines. Each logger was connected through a nearby test station or riser, with a portable copper-copper sulfate reference electrode, and recorded the AC potential every 20 seconds for 48 hours. Average AC potentials at the logged locations ranged from about 0.5 to 4.5 volts, with short spikes. The highest levels were on a 12-inch crude oil line, where one logger averaged 4.5 volts, mostly between 2 and 7 volts, with spikes up to 12.5 volts.

South Texas: a failed flange skews the test

In July 2019 we logged three locations on a 10-inch pipeline near Sarita, where a 345 kV transmission line crosses the pipe at about 30 degrees roughly 500 feet from one test station. The average AC potential there was only 0.26 volts. In the field we found the reason: an insulating flange recently installed at a valve station had failed, shorting the section under test to a gathering line and its well casing and in effect grounding it. Recorded AC potentials were likely lower than they would be once the flange was repaired, so the data had to be read with that in mind.

What the data is for

Logged data shows the operator where AC levels are highest, how they vary over a day, and whether mitigation design should follow. How AC and DC interference are assessed is explained on our page for interference testing.