Photo Gallery F6: Galvanized Steel / Domestic Cold Water Service
Galvanized steel pipe has been widely installed for domestic cold water systems and has generally provided excellent service for over 125 years. It was also commonly installed for sanitary waste, vent, and rain leader systems. Our ultrasonic investigation relating to galvanized steel pipe installed in 1896 at one downtown New York City building property for domestic water service, only replaced a few years ago, remains our oldest example. Since then many changes have occurred – mostly related to its deteriorating quality and greater corrosion susceptibility. Whereas earlier examples of galvanized steel pipe had a layer of zinc protection so thick it could be carved with a knife, the zinc coating for today’s products are so thin they will often not even survive the groove rolling process. Foreign pipe manufacturers appear to produce to lowest quality product, and with almost all pipe today ERW rather than seamless, zinc protection at the longitudinal seam adds another vulnerability.
For older buildings constructed before about 1965, galvanized wrought iron pipe was often installed since the wrought iron provided a stronger bond to the zinc protective finish – substantially extending service life. Our recent UT investigation at an older downtown NYC property constructed in 1960 identified not only galvanized wrought iron sanitary waste and vent pipe, but extra heavy pipe still exceeding ASTM specifications of 0.500 in. after 64 years of service!
This has produced an interesting dichotomy. The higher quality older pipe provides far longer life but has been in service a much longer period of time. New galvanized steel pipe should be at the beginning of a long service interval, yet offers far less service due to its lower quality. The net result has been to document failures to newer and much older galvanized steel piping systems at a similar rate.
Most buildings having galvanized steel pipe installed for any system are now experiencing problems, with a 65 year service life common for most parts of the country. For domestic water service, the first concern is obvious for leaks and failure; followed by taste and odor complaints or pressure and flow related problems caused by constricting rust deposits. Today, the replacement of old galvanized steel pipe which originally provided 65 to 75 years of service with new galvanized steel pipe offers questionable benefit; that new pipe likely providing 20 or less years of service. Our investigation of one large property where side wall pinholes appeared at 12 in. schedule 40 galvanized steel pipe after only 5.5 years provides a clear warning to its use.
