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unknown stainless steel

General welding questions that dont fit in TIG, MIG, Stick, or Certification etc.

Re: unknown stainless steel

Postby GreinTime » Wed Mar 15, 2017 2:00 am

Olivero wrote:Hahaha.

now that we settled that :lol:

Do you know if you have to repassivate stainless after any welding regardless? From what i know you can loose the corrosion resistance if its cooked too much but I believe that if you don't overcook you can get away with just cleaning it up?

Got any info on that one? Always wanted to know if I should feel bad for leaving a stainless weld un-passivated.

If you cook it, it's beyond passivation as you've boiled the chromium out. The color you see is contamination from atmosphere, and passivation, whether with paste or with a machine, removes the contamination. @rick_h will have a better answer as to why you passivate in the food service industry.

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Re: unknown stainless steel

Postby LtBadd » Wed Mar 15, 2017 5:17 am

Olivero wrote:Do you know if you have to repassivate stainless after any welding regardless? From what i know you can loose the corrosion resistance if its cooked too much but I believe that if you don't overcook you can get away with just cleaning it up?
Got any info on that one? Always wanted to know if I should feel bad for leaving a stainless weld un-passivated.

As you know the 300 series stainless is used in many applications, most of which aren't passivated. If good welding procedures are used the haz can be controlled and passivation isn't required. In sanitary applications it can be required as well as piping for the water and chemical industry. It really depends on the use (the environment) the part will operate in.

At my last job we welded 316L, duplex and other stainless piping which all had to be passivated (electropolished) per the customers requirements.
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Re: unknown stainless steel

Postby exnailpounder » Wed Mar 15, 2017 6:57 am

Olivero...here is a great article on passivation. http://www.thefabricator.com/article/tu ... -stainless
I have quenched stainless with wet rags to draw out heat when welding thick to thin to hold down warpage and my well water has tons of iron in it and it will turn a stainless weld black. That's not good. You need a process to remove that iron and let the metal reform an oxide layer. Oxalic acid is one way but is more of a pickle.
Last edited by exnailpounder on Wed Mar 15, 2017 7:21 am, edited 1 time in total.
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Re: unknown stainless steel

Postby cj737 » Wed Mar 15, 2017 7:15 am

exnailpounder wrote: I have quenched stainless with wet rags to draw out heat when welding thick to thin to hold down warpage and my well water has tons of iron in it and it will turn a stainless weld black. That's not good.

You might consider investing in 5 gallons of Distilled Water from the store and keeping it handy as a quench bucket in lieu of using your well water. Cheaper than acid and saves you from contamination of all your welded metals. ;)
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Re: unknown stainless steel

Postby exnailpounder » Wed Mar 15, 2017 7:30 am

cj737 wrote:
exnailpounder wrote: I have quenched stainless with wet rags to draw out heat when welding thick to thin to hold down warpage and my well water has tons of iron in it and it will turn a stainless weld black. That's not good.

You might consider investing in 5 gallons of Distilled Water from the store and keeping it handy as a quench bucket in lieu of using your well water. Cheaper than acid and saves you from contamination of all your welded metals. ;)

I do alot of welding for homebrewers on their kegs. Sometimes they bring over brand new kegs and when I weld on them I will try to keep warpage and distortion down as much as possible by drawing out heat with a damp rag. On an old beater keg, not so much. I actually have used distilled water but I don't even do it that way anymore. In reality, all stainless should be repassivated all the time, every time, but who can afford to do that? My way is more of a pickle and wouldn't be acceptable in true food service but it's better than nothing for a brewer. I learned of Oxalic acid from a friend of mine that welds for brewers too.
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Re: unknown stainless steel

Postby Keith_J » Fri Mar 17, 2017 3:08 pm

Phosphoric acid will passivate since it only dissolves the iron, leaving chromium. On magnet test, 300 series stainless becomes slightly magnetic with cold work. Test mid sheet and folded corners with a powerful neo magnet. I have some stainless spoons that are only magnetic on the spoon, handles are non magnetic.
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