304 weld passivation?
304 weld passivation?
(OP)
I have a new laserwelded assembly of 304sst tubing. It is for a medical application and oxidation is therefore not a good thing.
The supplier is currently passivating the raw tubes after cutting but before welding.
Is it generally necessary to passivate the final assembly to stabilize the surfaces near the welds? There is no filler material added in welding.
The supplier is currently passivating the raw tubes after cutting but before welding.
Is it generally necessary to passivate the final assembly to stabilize the surfaces near the welds? There is no filler material added in welding.





RE: 304 weld passivation?
Also, if this device requires sterilization with usage, I would further recommend electropolishing.
A medical device manufacturer should have SOPs established for following applicable ASTM & FDA specs.
RE: 304 weld passivation?
The supplier has had some difficulties removing the solutions from the finished assy due to the long small tube ID and space between tubes [at non-welded transitions]. Will a swab wipe of nitric acid based passivation solution have any effect on the oxide film stability or does the thermally formed layer need to be stripped off before re-establishing a more stable layer? Any other ideas for 'spot passivation' techniques to address just the welded areas? [This assy is 8" long with a .009 ID, and has various other tubes welded to step it up to .08".]
RE: 304 weld passivation?
For more info on electropolishing, see Thread330-50008.
The weld scale on SS cannot be removed by nitric acid alone; it is necessary to add either HF (hydrofluoric acid) or ammonium bifluoride. It can also be removed by electropolishing or abrasively removed. See some cleaning procedures in ASTM A380 or http://www.assda.asn.au/Teastain.pdf
The more difficult it is for the supplier to remove solutions from the assembly, the more difficult it will be to remove any contamination in use, and hence the more important it has to have a smooth finish.