"Pitting corrosion of duplex UNS S31803 by HCl at pH 2"

Question:

"A problem with a dryer of starch solution. The starch solution enters at pH 2 due to 0.17%HCl The enveloppe of the dryer (in duplex UNS S31803) is externally heated by thermical fluid at 280°C After four months there are already some pitting corrosion: few on first half (entering of starch solution),and more on second half (exit of dry starch.) Is this pitting corrosion logical? What material do you think would be better than duplex UNS S31803 ?"

Answer:

Yes, the pitting sounds reasonable based on your description of the environment. We cannot make absolute materials recommendations in this venue; however you might consider one of the "super" austenitic stainless steels, i.e., AL6XN, Sandvik 254SMO, etc. with high molybdenum and nitrogen for pitting resistance to hot, dilute HCL. Other, more expensive alloys would include nickel alloy C-22.

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