Three Years of Cathodic Protection Surveys on the Fuel Gas Line of a Single-Unit Power Station, El Paso (2023-2026)

The buried gas line at a single-unit power station in El Paso shows what a short to ground does to a cathodic protection system, and what happens when it is finally cleared. We surveyed it in November 2023, May 2025 and May 2026.

The system

The carbon steel line starts at two supplier meter stations outside the main gate, runs north to a supply selection skid inside the fence, and comes aboveground at a riser beside the generating unit. Two pole-mounted rectifiers, each rated 35 V and 25 A, protect it, and there are five test points: the two rectifiers, the skid, a test station about halfway, and the unit riser.

2023 and 2025: a line that would not polarize

In November 2023 the instant-off readings were between -350 and -650 mV, far short of -850 mV. We found two reasons. The flange kits at one supplier skid tested good, but instrumentation tubing ran across them and connected the plant piping to the supplier piping. And the riser at the unit had no insulating kit at all, so the buried line was tied to plant grounding and structural steel. We turned the rectifiers up as far as we could without risking nuisance trips and recommended a flange kit at the riser at the next shutdown and a call to the gas operator about the tubing. A bigger CP system was not the answer, because it could push stray current onto the suppliers lines.

In May 2025 the plant was in a maintenance shutdown, and the rectifiers had been off for an unknown time. Turned back on, they were delivering about 14 A each, and four of the five test points still fell short, with the riser at the unit reading only -340 mV off. The same two problems were still there.

2026: isolation restored

By May 2026 the isolation had been restored. We found the rectifiers delivering about 3 A each and the line more negative than it needed to be. With the pipe no longer feeding the plant ground, its current demand had dropped, so we turned both rectifiers down to their lowest taps, about 2.6 V and 18 to 20 mA, to avoid overprotection and stretch the life of the anodes. The interrupted survey that followed read between -1,150 and -1,390 mV off at all five test points.

Related work

Earlier surveys at other stations in the same city are in the baseline power station CP surveys. The test method is explained under interrupted potential surveys.