Galvanized steel pipe should never be used for any hot water service due to the reason that heat destroys the zinc protective finish.  Although the higher temperatures found at domestic hot water systems are mostly involved, higher deterioration can even be measured at galvanized steel run-out waste pipe serving kitchens and bathrooms.

For most older buildings were galvanized steel pipe was installed for domestic cold water service, brass was installed for the hot water side due to this known vulnerability.  Certain cities and geographical areas such as Chicago and elsewhere specified galvanized steel pipe for hot water service, which has now resulted in widespread hot water system failures.  A very common finding from any ultrasonic testing investigation of galvanized steel hot water pipe is to show significant corrosion, in itself defining that the galvanized finish has been lost.  Once this occurs, the underlying bare carbon steel pipe corrodes at an accelerated rate; producing significant rust deposits then restricting flow and reducing line pressure.

Since such piping systems are typically threaded, a substantial threat exists at each connection point due to the loss of approximately 50% of the pipe wall during the threading process.  As pipe diameter decreases, so does its wall thickness, which results in lesser service.  An even greater threat exists at all swing type expansion joints given that in addition to its inherent physical weakness, expansion and contraction adds additional stress.  In the worst cases, a complete pipe separation at the threads will produce catastrophic damage.

No options exist other than to replace the pipe with copper, as new galvanized steel pipe will fail even sooner.  Once the problem is discovered, substantial wall loss will have occurred – thereby preventing any form of relining or pipe coating.

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