Cathodic Protection in El Paso

Where the current goes in a power plant

Buried gas piping inside a power plant shares the ground with copper grounding grids and structural steel. At one station the piping was not isolated from that metal, so most of the protective current went to the grounding grid and the structural steel instead of the pipe, the old sacrificial anodes were being used up faster than expected, and the piping was not adequately protected. At another, a fuel gas line needed about ten times the current its coating should have needed, a sign of shorts to other plant metal, failed coating or both.

On that line, isolation was the fix: after isolation repairs in 2024 it read -1.00 to -1.15 V instant off at all three test points. At another station, instrumentation tubing run across an insulating flange and a riser with no insulating kit had kept a gas line from polarizing.

Dry ground

During a grounding survey at one station, the soil was so dry and resistive that Wenner four-pin measurements could not produce usable data. The two deep anode wells of one system we installed, each 250 feet deep with ten mixed metal oxide anodes in coke breeze, are drying out too: one rectifier circuit went from 2.9 ohms in 2023 to 19.2 ohms in 2026. The annual reports recommend soaking each well through its vent pipe every month until the piping is fully isolated.

Grounding matters here as well. At one generating unit, static charge from a new turbine oil had been relieved with grounding triads that formed two isolated grounding systems, not tied to the station ground, and we recommended bonding them together underground.

A gas line that cannot be pigged

One fuel gas line is not configured for in-line inspection, so we judged its coating from the surface with an ACVG survey. The original magnesium anodes were left connected as a check, since each one shows up as a large coating defect. Of 19 indications, 8 were anodes and 11 appeared to be coating anomalies. We recommended exposing the five at highest risk, and validation digs followed in 2020.