CSCC of stainless steel in HCl

[bob330]

Greetings,

Are austenitic stainless steels subject to CSCC in Hydrochloric acid that is not contaminated with chlorides coming from alternate sources than the acid itself (like NaCl)? My thoughts were that the acid in water should disassociate into hydronium ions and chloride ions the latter of which could lead to SCC issues. However, since CSCC only happens within a given range of electrochemical potential, I figured it may be possible that severe general corrosion may be the only result of placing austentic SS in HCl.

Thanks,
Bob

 

[EdStainless]

Boiling HCl (18%) is one of the few environments that will cause general corrosion on common stainless grades.
You do not get CSCC in HCl service, but tiny amounts of residual acid can cause significant problems later.
Remember, not only is the HCl disassociating, but water also. The chemistry is rather complicated.

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[bob330]

Thanks EdStainless,

Thanks a ton for your help. What happens to the stainless if you are at a temperature below the boiling point at 18% concentration such as 175F? Do you get severe pitting or just general corrosion? Also, what happens at stronger concentrations like 35% just below the boiling point. All my references simply state to never use common grade austenitic stainless steels in HCL but they never mention what actually happens by dicussing pitting versus general corrosion versus SCC.

Thanks,
bob

 

[EdStainless]

With 304, at any concentration and temperature you get general corrosion. At 18% and boiling the rate is roughly 0.030" - 0.090" per hour.
As you move to higher alloy grades the attack is still general, but the surface get rougher. It is almost like continuous pitting.
On high alloy grades like superaustenitic or superferritic you don't get much general attack, but you can get severe pitting.
I know that the books warn of CSCC, but I have only seen it in hot HCl vapor applications.

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Rust never sleeps
Neither should your protection

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