CP Surveys of Buried Chilled, Hot and Cooling Water Piping, Houston and Austin (2021-2026)

Since 2021 we have surveyed the cathodic protection on buried water piping at an office complex in Houston, Texas, and in 2022 at a manufacturing plant in Austin. Client details are confidential.

Water piping between buildings

The Houston complex runs hot and chilled water from a central plant to several high-rise buildings. Most of the piping runs on racks inside the parking garages, but several segments are buried. Those segments are dielectrically coated carbon steel, meant to be protected by six impressed current systems. The buried piping is not isolated from the aboveground piping or at the building tie-ins, so it is coupled to structural steel, copper grounding and other buried metal.

The first survey

An earlier survey by others had judged protection by on potentials of -850 mV with the CP current flowing, without saying how voltage drop was considered. When we inspected the rectifiers in April 2021, three newer units were wired for 240 V input on a 120 V supply, so they could deliver only about half their rated output. One unit had no AC power, one had a blown secondary fuse, one older unit did not sound healthy, and one had been demolished. Some test stations could not be found and one was damaged. The high-rise buildings also blocked the satellite signal our GPS-synchronized interrupters need, so off potentials were taken by switching the nearest rectifier by hand.

Repairs and adjustments

After others restored power and replaced the fuse, we rewired three rectifiers for the correct 120 V input and raised their outputs, one of them to 17.6 A. Continuity testing at two valve pits confirmed that the four parallel lines are bonded together, although how that is done is not known. At the retest in May 2021, one rectifier was working normally but delivering no current, which pointed to its anode bed: either a poor connection to the anodes or anodes at the end of their life.

Five surveys on

The complex has been surveyed again in 2022, 2024, 2025 and 2026. Repair work in 2022 found that at least some of the original buried pipe is bare steel under thick thermal insulation, not coated pipe as believed. Moisture trapped between insulation and steel corrodes the pipe, and the insulation shields it from CP current. In 2026 the piping near one building still received no current, through a broken anode lead or depleted anodes, and a fault upstream was tripping the breaker that feeds that rectifier. We recommended an exploratory excavation by hydro-vac, supplemental anodes, troubleshooting the breaker and surge arrestor, and insulating flanges at the underground to aboveground transitions.

A plant that was never protected

The Austin plant has about 800 feet of buried, dielectrically coated cooling water piping up to 42 inches in diameter, built before 1990. Its records called for magnesium anodes, but no anode leads were found in either test station, and pipe-to-soil potentials of about -200 to -380 mV matched unprotected aged steel. No insulating flange kits were installed on any riser, many risers showed coating wrap failure, and we found no evidence that the anodes were ever installed. We recommended isolating the buried piping first, which would let a low-maintenance galvanic system work, and an extent-of-condition assessment.

CP surveys for facilities

How protection is measured is explained on our page for cathodic protection potential surveys.