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topic 5701

Pickling Duplex Stainless Steels


(2000)

I am looking for advice on the advisability of pickling a welded plate type heat exchanger which we are having fabricated for refinery service from duplex stainless, type SAF2205. The fabricator wants to pickle and I am worried about this. Because it will not be possible to inspect the condition of the exchanger internally during pickling and passivating, I'm concerned that pickling my introduce risk of local corrosion at crevices, especially since it will be difficult to ensure complete flushing and draining. Does anyone pickle SAF2205 materials? If so, why?

Colin Stevenson
- Western Australia


(2000)

A very short section in ASM's Metals Handbook, Volume 5: Surface Engineering , Surface Cleaning, Finishing, and Coating, (American Society for Metals, Metals Park, Ohio, USA 44073) says, (may I summarize?):

1. the metal surface must be clean before etching
2. suitable solutions are determined by experimentation
3. a by-product of the etch is ferric chloride, a very potent pitting agent
4. the etching solutions are very strong acids

So I would say that your all of the concerns you voiced must be addressed by the person recommending the etch, and that each answer should be documented by published or private research. Regards, Tom

pooky
tom pullizi signature
Tom Pullizzi
Falls Township, Pennsylvania



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