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Does soft water corrode stainless steel

Will using soft water in a stainless steel cooling tower destroy the stainless steel?

Phil Olson
Plant shop employee - Mojave, California, U.S.A.
August 25, 2011

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Soft water will not, in general, attack or corrode stainless steel unless the pH is low and the chloride or fluoride concentration is high.

Lyle Kirman
consultant - Cleveland Heights, Ohio
August 29, 2011

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It depends on how the water has been softened. If it is natural soft water it should not, but if it has been artificially softened using a cheap water softener, it may contain high levels of chloride that will certainly attack most stainless steels. In general, any water that contains high halide levels will exhibit corrosive activity against steels. If you are using artificial softened water, try improving your water treatment by using de-ionised water, but make sure your plant is working correctly, and the conductivity remains very low (i.e., less than 5uS), because the DI system uses a chloride ion exchange that, if out of balance, can cause high chloride levels to be produced.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
September 28, 2011

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A brine regenerated softener that is operating correctly should not increase the chloride concentration in the softened water. Unfortunately, many softeners fail to thoroughly rinse all of the brine out of the IX resin, and this can lead to a spike in the sodium chloride concentrations right after a regeneration.

Lyle Kirman
consultant - Cleveland Heights, Ohio
September 29, 2011

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Lyle, I agree totally that a correctly operated water softener should not increase the chloride concentration, but the caveat is "correctly working". There can also be issues with the cheap domestic water softeners, that just rely in the addition of salt (sodium chloride) to reduce the water hardness.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
October 6, 2011