AC Interference Testing and Mitigation in Colorado

What AC interference does to a pipeline

When a buried pipeline runs alongside high-voltage transmission lines or electrified rail, the AC field induces voltage on the pipe. That causes two problems. Anyone who touches a test station, valve or other exposed appurtenance can get a shock from the touch voltage. And at small coating holidays, AC corrosion can attack the pipe even while the cathodic protection potentials look acceptable. Neither shows up until someone measures the AC.

A fault on the power line makes it worse for a short time: the induced voltage rises sharply, and a tower close to the pipe can push fault current into the soil around it, which can damage the coating and the pipe.

How a pipeline beside a transmission line picks up AC, and what to measure before it becomes a safety or corrosion problem.

Why Colorado corridors see it

As the Front Range grows, pipelines, transmission lines and rail get squeezed into the same narrow corridors, and new transmission projects keep adding sources. In the DJ Basin, gathering lines cross power line corridors again and again. Rocky, high-resistivity ground also makes mitigation grounding harder to get low, so designs have to be based on soil readings from the actual right-of-way. Our article on high-resistivity Rocky Mountain soils explains why.

What we do about it

• Measure. We measure induced AC voltage and current on your structures in the field, along with your CP readings, as part of our interference testing practice.
• Model. We work out which crossings and parallels drive the readings, and what happens under fault conditions on the power line.
• Mitigate. Where the readings call for it, we design the mitigation: gradient control at test stations and valves, grounding along the line, and decoupling devices that pass AC to ground without draining the CP current. Designs are PE-stamped where required.
• Confirm. A follow-up survey checks that the mitigation works, and the results go in your integrity file.

Our engineers are licensed Professional Engineers with active and past licensure in multiple states, and we work in Colorado from our Westcliffe office. Stepan V. Eero, M.S., P.E. is a NACE CP Specialist (CP4). The Colorado engineering services page lists our other work in the state, and our article on what causes cathodic protection interference covers DC interference.

Talking to us about your pipeline

• Call (866) 621-6920 or write to us through the contact form, and mention any power lines or rail sharing the corridor. We typically respond within one business day.
• You get a scoped proposal and a free quote up front. Our rate schedule is available on request.
• Our licensed PEs supervise the surveys and the reports, which are PE-stamped where required.
• We also have an office in Coldspring, Texas, and work in other states.