Engineering expert Frank Baumann, PE, is a registered corrosion engineer, certified water treatment operator and certified water quality analyst. Here he writes on the internal corrosion of plumbing.
Among a homeowner’s more traumatic experiences, especially if the home is fairly new, ranks the telltale wet spot on the living room carpet (if the plumbing is in the slab), or the soggy bits of not-so-dry-wall (if the plumbing runs overhead.) An inspection is likely to reveal more than just a single trouble spot, and the usual verdict is an expensive replumbing job. The homeowner is upset and wants to be made whole, so he sues the most likely culprit – the water company. After all, it was the water that caused the problem. Or was it not?
The corrosion engineer, in trying to determine the most probable cause of a plumbing system failure, must look for, not just one, but two factors: 1) What initiated the problem, and 2) what propagated it.
There are some aggressive (corrosive) waters which will dissolve metals with which they come into contact, just as there are some saturated ones that deposit heavy scale in water heaters and hot water systems. An aggressive water will usually cause general corrosion. That is, it will dissolve metal at a uniform rate throughout the internal pipe surfaces. The loss of metal at any one point is thus very minor, and the system generally attains its design life. If the same loss of metal were to be confined to just a few small points in the system, however, the loss of metal at those ‘pits’ may result in perforation of the pipe and catastrophic failure of the system due to ‘pitting corrosion’. While there are some waters with a greater propensity to cause pitting, the great majority of pitting corrosion is initiated by factors other than the water.
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