Do austenitic stainless steels have good resistance to carbonic acid attack?

Q: We have a fin-tube style heat exchanger in which we mix natural gas and liquid water, and use an exhaust gas stream to vaporize the water and preheat the fuel mixture. We have a new water recovery process in which we condense the water out of a carbon dioxide rich exhaust stream and feed this into the heat exchanger. It has been observed that the recovered water is slightly acidic at a pH 4.5, and it has been attribute to the presence of dissolved carbonic acid in the water. The tubes of the heat exchanger are 304H Stainless Steel. Is corrosion something we should be concerned about for the long term operation of this unit?

A: Austenitic stainless steels like 304H generally have good resistance to carbonic acid attack. Whether you see any long term corrosion problems in this unit will likely depend on the specifics of your application including what impurities are present. For example, under acidic conditions chlorides (even at low levels) are notorious for causing various forms of localized corrosion.

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