Summary for stripping nickel and gold from 303 stainless Discussion
Stripping nickel/gold from Type 303 stainless with nitric acid unexpectedly left the base heavily etched, even though the shop normally uses nitric on other stainless steels without problems. In the thread, Craig Ingalls asks whether SS303 behaves differently from other stainless during stripping. Art Cambell says 303 should be inert enough in nitric and suspects an accidental galvanic cell in the strip tank: if some parts stripped sooner while hanging on the same metal bar, the stainless could have become anodic relative to the more noble gold/nickel, causing attack. He notes that his shop wraps nitric strip bus bars with plater’s vinyl tape to prevent this. Russell Richter adds a caution to verify whether the material was 303L and to make sure there is no chloride in the nitric acid, since contamination could change the result.
Q. We recently stripped a nickel/gold finish from an SS303 base using a nitric acid solution. The result was a heavily etched SS303. We routinely use nitric to strip various SS bases without etching, but this 303 behaved differently. Is there something unique about SS303, as compared to other SS, with respect to stripping?
Craig Ingalls
plating shop employee – Anoka, Minnesota, USA
September 20, 2012
A. 303 has enough chrome in it I would expect it to be inert in nitric strip.
I suspect you may have had an accidental galvanic cell in your strip tank. If there were parts that stripped sooner than others hanging on the same metal bar in electrical contact, then the stainless areas may have became anodic relative to the more noble gold/nickel parts.
We wrap our nitric strip bus bars with plater’s vinyl tape to prevent that from happening to us again.
Art Cambell
– OKC, Oklahoma
October 11, 2012
A. Was it 303L? are you sure there is NO chloride in the nitric acid.
Russell Richter
– Danbury, Connecticut, USA
October 25, 2012