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Under-Slab Hot Water Piping Corrosion and Leaks

Random leakage failures of under-slab piping were observed to have occurred in a large subdivision. The subdivision was built by a single contractor and the plumbing had been installed by the same plumbing contractor. The homes were a post-tensioned slab-on-grade design with under-slab copper piping. The subdivision was located in a previous area that was a ranch. Our review indicated that the leakage was due to corrosion that initiated on the exterior surfaces of the hot water piping. The cold water piping was unaffected. Chemical analysis of the soil-sand backfill adjacent to the piping revealed the presence of ammonia. A review of aerial photographs indicated that the affected homes were located in the livestock feeding area of the prior ranch. Since ammonium hydroxide is a strong copper corrosive agent, it was believed to be the source of the pipe leakage. The leaking under-slab plumbing was isolated and replaced with above-slab piping.

Satish Almaula		Plant failure and root cause analysis; process and design engineering analysis; process technology development and testing; plant engineering, operations, maintenance and safety management; plant and process control system management.

Philip Lindsay, P.E.		Corrosion failure analysis, metallurgy, piping systems, corrosion mitigation, materials selection.

Geoffrey Egan, Ph.D.		Engineering mechanics, welding engineering, stress and fatigue analysis, risk analysis, nondestructive examination, project management.

Eric Sullivan, P.E.		Metallurgy, welding, failure analysis, fire and explosion investigations, equipment, piping.