Pickling and passivation treatment
Pickling and passivation treatment
(OP)
dear friends,
is it possible to eliminate the pickling and passivation treatment in reactors? why?
thanks and regards,
is it possible to eliminate the pickling and passivation treatment in reactors? why?
thanks and regards,





RE: Pickling and passivation treatment
RE: Pickling and passivation treatment
RE: Pickling and passivation treatment
RE: Pickling and passivation treatment
Regards,
Mike
RE: Pickling and passivation treatment
RE: Pickling and passivation treatment
I have seen SS uniformly pit because of containmined iron picked up in the fabrication process and we had to go back and passivate it.
RE: Pickling and passivation treatment
Mark Hutton
RE: Pickling and passivation treatment
I've performed a light nitric acid wash (passivation) before in place on a vessel because of what we thought was contaiminated free iron on the inside surface. We had a lot of dark spots forming about 1/8 to 1/4 inch apart... our vessel had the measles.
You can't see free iron initally but you can sure see scale if you buy a head hot formed and don't ask for it to be blasted.
RE: Pickling and passivation treatment
Pickling is the chemical removal of surface oxides (e.g., heat treat & welding scale) and the chromium-depleted layer of metal immediately beneath heat-treated stainless. Often used are reducing acids (sulfuric, hydrochloric & hydrofluoric) which can cause hydrogen embritttlement. Definitely not a 'deep oxidation.'
Nitric acid, an oxidizing acid, is used to protect stainless steel from excessive attack by the hydrofluoric acid used to attack oxides. Typical pickling solutions are given in 'TABLE A1.1 Acid Descaling (Pickling) of Stainless Steel' of ASTM A380.
Pickling should only be done once or sometimes not at all in the fabrication of a stainless steel vessel (except for any subsequent welds).
Passivation per ASTM A967 uses nitric or citric acid solutions to selectively leach iron and nickel (and remove contaminants, e.g., zinc from contact with galvanized material) whilst creating a more protective, Cr2O3-rich oxide film. Cf. pickling, which removes all metals including Cr.
There are additional passivation processes used in maintainance procedures, most notably, an ammoniated citric acid solution (aka ammonium citrate).
Passivation can be repeated as necessary, with little harm to the substrate.
Hope this helps,
Ken
RE: Pickling and passivation treatment