Is Insulation Corrosion Proof?

If you are among those engineers who think that insulation, apart from energy conservation, also gives protection against external atmospheric corrosion, then you are wrong. Poorly specified and wrongly installed insulation can corrode even stainless steel. Corrosion under insulation is a major cause for concern in contributing to unexpected failures. Corrosion takes place unnoticed under the seemingly perfect insulation and eventually leads to a sudden failure.

Austenitic stainless steels are susceptible to chloride induced stress corrosion cracking (SCC) at temperatures above 65 0C. Since chlorides can ingress along with water through insulation, insulated austenitic stainless steel surfaces are vulnerable to SCC. Insulated austenitic stainless steel surfaces operating at temperatures above 65 0C should have protective coating. Further, chloride free (< 10 ppm) insulating materials are recommended for this application. Duplex stainless steels have a high resistance to SCC and do not require external coating.

Materials most vulnerable to corrosion under insulation are ferritic steels operating in the range of -10 0C to 120 0C. Special attention is required for equipment and piping that operate below the atmospheric dew point.

Corrosion under insulation can be prevented through good insulation practices. Installation of good weatherproofing absolutely must. Further these should be properly and periodically maintained. Yet small quantities of moisture will sneak in through the insulation and to guard against this corrosion, a protective paint is recommended under the insulation.