Passivating stainless steel

[Shield Arc]

When I worked in a fab shop in the 1970s. We did a lot of stainless steel work for the Trojan, Satsop, and Hanford nuclear plants. We had a clean room, with stainless steel tables. Had stainless steel pads over the jaws of the vices. Stainless steel caps that went over the hammers. They really tired to eliminate the amount of carbon steel tools we used in the clean room.

 

[BukitCase]

Before I read RNG's excellent post I saw your comment about the etched glass - my immediate reaction was "crap, that stuff has HF in it (not Harbor Fright) - In the last 25 years of my working life, we used HF and Nitric in pickling tanks - that combo would remove several thousands of an inch from a "non-corrodable" Zirconium slab in about 4 minutes - and a hand print sized exposure left untreated can stop your heart.

Not something you wanna "wing it" with... Steve

 

[Sodo]

HF,,,,, Well, Amazon has SurfOx Treatment which is phosphoric based ,,,,

RNG you know some stuff - thanks for joining the discussion. Forgot about flapper discs, I suppose I can grind off the weld bead with my old wheel then polish it with a virgin flapper disk.

This video https://www.youtube.com/watch?v=DSdBpCuj_5U uses cream of tartar and lemon juice. Which the host says the lemon juice is for the clean fresh smell :laughing: but I suppose citric acid plays a part. Cream of tartar is potassium acid salt of tartaric acid (a carboxylic acid). Then there's BarKeeper's friend, which uses Oxalic acid. I might try these because I have them here, now. Every method uses an acid, it almost seems like any acid that attacks iron may be worth a try (but I want it to end up bright).

Hence my question to the forum chemists: My project has no cooking scum or fingerprints to rub off. It's just a coloration thats a little darker than the surrounding area. If the acids concoction actually 'brightens' the stainless steel in the area where I worked it, did it "passivate"? And will it remain bright like the rest of the item?

I would like to find a source for just one tube of Walter 54A061 Surfox-G PH Neutral Weld Cleaning Electrolyte, 100ml tube.

 

[Kyle_in_Tex]

yes, if you clean it with a carbon wire wheel or a grinding disk embedded with carbon steel, it will promote rust in the stainless part.

 

[Sodo]

So,,,,, back to the main question,,,,, if I grind it and polish it - with uncontaminated tools - will the wound rust in an outdoors environment?

 

[Shield Arc]

It looks like a Mig weld. What type of stainless steel filler metal did you use? Did you use a tri mix gas?

 

[Gary Fowler]

I have never seen stainless steel that did not remain shiny after fabrication as long as you kept carbon contamination from it. I have been involved with miles of pipe fabrication and if you grind with a new abrasive wheel or flapper wheel, you wont have any color change and you wont need passivation on the piece.

When we did get some carbon steel contamination, we would flapper the area then use phosphoric acid to remove the carbon.
Please stay away from anything with Hydro-fluoric acid in it. That is very dangerous stuff that even in small amounts will absorb thru the skin and attack your bones. VERY BAD STUFF. Phosphoric will do the same thing albeit a bit slower.

 

[Kyle_in_Tex]

So,,,,, back to the main question,,,,, if I grind it and polish it - with uncontaminated tools - will the wound rust in an outdoors environment?

They use it in salt water marine environments all the time. So yes, passivate it, no contamination and it will work great.

 

[Sodo]

Shield here is a pic of the welder. It's a MIG of sorts, no idea what gas used, and I couldn't see the plug so I can't answer everybody's next question



During a period following fabrication, it seems to me that Stainless can discolor as the recently exposed surface iron molecules rust. Then once these surface molecules are gone (deplete) and the rust staining rubs off its bright again. I'm pretty sure "passivation" mostly just accelerates this process, ",,,,,better living thru acids! " In Marine applications - saltwater, I bet the surface iron depletes quickly.

I want to grind off this high weld in such a way that it goes entirely unnoticed. I think we're onto it, finishing with an uncontaminated flapper. But if any rust coloration appears on the surface after a few weeks it may upset some customers, who will think their part has a globule of iron that's gonna rust right thru. Some will be OK if told "sorry it will be a few months, you just have to wait for the iron to deplete." Others will want a replacement. I have only one Sunday remaining to research this - gotta do something Monday AM.

 

[Shield Arc]

I figured it out years, and years, and years ago, it is cheaper, and less frustrating to play by the rules.

I got a feeling you used carbon steel filler metal, and C-25 gas.

Stainless Steel MIG Welding with Compact Welders