AC-Induced Corrosion on Pipelines in the Eagle Ford Shale
by Cal Chapman
New pipeline construction is going “fast and furious” in the Eagle Ford Shale region, in the West Texas “Wolfcamp”, “Bone Spring” and related shales, and all across mid-America with the Bakken, Niobrara and other successful unconventional oil and gas plays. Companies who build and operate pipelines must attract customers with product to move, secure the land over which pipeline right-of-ways will be cobbled together, and then construct the pipelines.
What happens when a pipeline runs near a high-voltage AC power line?
When soil resistivity is lower, and the voltage driving current along the AC power lines is high enough, the pipeline acts like the “secondary winding” of a transformer. It receives AC power from the high-voltage lines by what is called “electrical induction.” Once that power builds on the pipeline, AC electric current flow is going to happen. When that AC current finds a place to “jump off” the pipeline to go back to the AC power grid, corrosion holes are created in the pipeline metal. This is AC-induced corrosion, and it is a severe threat to pipeline integrity.
This induced AC power may even pose safety risks to the welders, laborers, operators and other people building the pipeline! AC power can actually build up on the pipe as it sits above grade on cribbing. Any time a pipeline is located in “near parallel” to parallel arrangement with high-voltage AC power lines, even for just a mile or two, a qualified corrosion engineering consultant should be brought in to check the situation.
Risks of AC-induced Corrosion and Voltage Buildups
These risks for AC-induced corrosion and unsafe voltage buildups are significant. A recent story about a Barnett Shale area worker, directed to do some repair to a chemical injection system for a pipeline’s internal corrosion control system, tells the tale. The gentleman walked up to a chemical injection point and reached up to close a small ball valve, before changing out some injection equipment. The AC voltage buildup on this pipeline was so great that, when he touched the valve handle, he was hurled backwards by the jolt of “grounding out” the induced AC power! From what was passed on, he did not suffer lasting injuries. But this was way more than 15 volts of induced AC (the maximum “safety” voltage threshold), and a significant current passed through part of his body for the instant he was in contact with both the pipe and the earth.
AC Mitigation Systems Might Be Needed
If the opportunity for AC power buildup on the pipeline is pronounced, then “AC mitigation” systems must be designed and installed. Similar to electrical grounding and lightning protection approaches, these mitigation systems are specialized in design, construction and monitoring. Recognizing the need for them is paramount, especially when soil resistivities are low and chemical ions such as chlorides are present in higher concentrations in soils. A lot of the soils in the Eagle Ford Shale play have this “not good” combination of resistivity and soil chemistry factors. The same can be said, too, for a lot of West Texas and southeastern New Mexico.
Cal Chapman is co-founder of Chapman Engineering, which began business in fall 1988. He is a licensed “Cathodic Protection Specialist” through the National Association of Corrosion Engineers (NACE, now called NACE International), and is a licensed professional engineer in Texas and New Mexico. Chapman Engineering provides cathodic protection, AC mitigation, coatings and corrosion protection specifications, and other engineering services. The company performs environmental compliance, assessment and remedy services in oilfield, petroleum wholesale, and industrial settings. In-house staff includes engineers, geologists, corrosion technicians and environmental scientists. Please contact Chapman Engineering at 800-375-7747.