[TheForge] stainless rust

[ries]

Most rust on stainless, especially on 304 or 316, is actually surface  
contamination by mild steel.
Grinding particles, steel wire brush residue, or just scraping a steel  
tool against stainless can all leave enough microscopic carbon steel  
bits embedded in the stainless to rust.
The stainless itself doesnt rust- just the gunk you got on it.

So the first step is always to mechanically remove the contamination-  
with a brand new sanding disc, or a stainless steel wire brush that  
hasnt been used on mild steel, or with that new fangled non metallic  
steel wool- its some kind of plastic with abrasive attached, kinda  
like a 3m abrasive pad. Or a 3M abrasive pad, that often works pretty  
well.

My little electropolisher is a dc power supply, like a battery  
charger- and it does help clean up stainless- I mostly use it to clean  
the discoloration from tig welds. It wont remove little bits of carbon  
steel, though. The big tanks, with heated acid and 1000 amp power  
supplies, at the commercial electropolisher will clean up most steel  
inclusions, but not my little one.

I use citric acid, like Jim recommended. I think Nitric an Muriatic  
are way overkill for stainless, and on a boat where there is all kinds  
of adjacent stuff you dont really want to acid wash, I would be  
careful. In the commercial electropolishing shops, they use phosphoric  
acid, which is much milder than either nitric or muriatic, and even  
then they water it down. They do use it heated, however, and they use  
electricity with it.

So my advice is, first, mechanically clean, sand, or polish.
In most cases, acid is overkill for a little rust.

I tend to send heavily forged stuff out for electropolishing, which is  
black from the forging.

ries


On May 12, 2009, at 10:25 AM, Andy Gladish wrote:

Ries has a gee-whiz little electric box that looks like a battery  
charger
that he uses with a solution of some kind to clean up welds on  
stainless-
maybe that would work on this too. Gotcher ears up, Ries?

On Mon, 11 May 2009 19:14:52 -0700, Steve howell <ballardforge at msn.com>
wrote:

> Guys,
>
> Is there an 'easiest' way to remove rust stains from stainless welds?
> Boat owner client of mine has polished stainless rails on his ~1980's
> boat and the welds have stained badly. Naval Jelly? Tank passivation  
> is
> out of the question.
>
> Thx,
> Steve
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Ries Niemi
Industrial Artist
http://www.riesniemi.com/