Stainless discoloration problem

[Brew]

Does anyone have any ideas on reducing the discoloration of the burn thru when welding SS pipe? We are currently purging with 99.999% pure Argon, but we're still experiencing some blueing, especially in the HAZ. Any suggestions or experiences would be greatly appreciated!

[Mike Sherman]

Talk to your welding supplier about "pickling and passivating" your finished product. He can supply you with the necessary chemicals. You can also get information from your steel manufacturer on specifics or pick up a copy of ASM Metals Handbook published by ASM International Materials Park Newbury, Ohio 44065.

[Brew]

Thanks for the tips on the literature! I'll check into it.
We already pickle and passivate with a nitric (sometimes citric)bath, but I dont know all the details. Unfortunately, it doesnt always remove all the discoloration.
Sometimes, my weldor and myself can get a weld with no color, but cant seem to re-create it scientifically.

[tigman]

Hi,I'm new to the group and find it quite interesting.
I work in a sheetmetal shop and when we weld S.S. We use a little electric cleaner that is about the size of a battery charger to remove all discoloration.The machine has a wand that is wraped with a cotton strip and dipped a a chemical cleaner and a ground that is attached to the piece to be cleaned.This unit will remove dicoloration on a 3" weld in about 5 seconds on 10ga. I don't know who makes it but if you would like to know I can look at it on Monday.The only name I can remember off hand is its called the boss.
Hope this helps Scott.

[HackAsaw]

I'm going to go out on a limb here and suggest the technique isn't consistent for whatever reason if your metals are.....

an irregular draft? inconsistent heat or speed? loose connection anywhere in your torch lines? items not postively grounded but perhaps laying on something that is?

it's a tight rope act to keep the bead brightly colored without getting any of the blue which means it's too hot due to current flow or moving too slow......and heck no it doesn't go away easy but you can sand or scotch brite it away

dull gray is just right after the most intense blue coloring.... and that means crap

I'm a mostly self taught greenhorn rookie so understand this limb is somewhat of a precarious perch

[Thomas Harris]

I had a stainless pan I fabricated for maple syrup finishing. It was 20 guage 304 stainless stock. When I used the thing it developed a raninbow color where the flame contacted the bottom. (showed up on the inside) It was always full of water while boiling commenced. I checked on the internet and such to find if this was destroying the corrosion qualities of my pan. The best explanation described the color as variations in the thickness of the passivated later. Supposedly light is reflected/refracted differently and hence the prism effect. The article also mentioned no lack of corrosion protection from this type of coloration. May be different than what you speak of, but it was quite pecular looking just the same.

[Jerry]

I'm not extremely knowledgeable in back gas techniques
( do's and don'ts) . But I have done this a few times and have always had a clear colr inside where I was purging.

I believe the gas is heavier therefor the need to make sure inner pipe has had sufficiant time to fill the weld area. I also poke a couple holes in duct tape that I cover on end to allow air to be pushed out of and have the gas pressure regulated to around 15 I believe.

Good Luck hope it helps. I do believe that a while back there was a thread started on back gasing or purging of weld area.

[aircraft]

I'm guessing this is on the outside?
Are you using heat sinks?
If you can't get it off with a wire brush, more than likely your loosing gas coverage. Or if your using a heat sink that could also cause it.
We use a very large 1" cup or trailing gas or if it's small enough in the gas chamber it goes.

[Brew]

Good feedback all!
There is evidence to suggest that discoloration DOES adversely affect corrosion resistance, and many of our pharmacuetical customers are now requiring colorless welds on all of their SS piping, instead of just the orbitally welded sanitary tubing.
As of now, we are removing color mechanically, but I'd really like to find a way to acheive this kind of weld quality without spending valuable time blasting,grinding, or polishing every joint.
I think we may just have to keep trying different techniques until we come up with what works for us. But the frustrating part is that we cant seem to ALWAYS get colorless punch, but we can usually get some colorless using any of the myriad of techniques we've already tried.
Thanks again for the responses.

[HackAsaw]

well, I build a lot of stainless pieces for my bikes and I know which beads were devoid of any blue,the dark burgandies, or gray colors before and after polishing...... these bikes have also been ridden on the beaches and such

the gray stuff has been cooked useless and the other less desireable colors are subject to corrosion..... just not as quickly

the bright or lightly colored bead seems to be as good as the parent metals and are easy to bring to a high polish



to enlarge click this

these won't rust and I do find regular shaped items much easier to obtain consistent coloring of beads....

my experience tells me that finding the magic combo of current flow, shortest arc length, and speed of travel is what you are seeking....... it is a very fine line and it's nice when you can walk the cup instead of having to weld behind your head with six mirrors with your arm detached from your shoulder

one other thing you may consider is using a higher grade fill rod

[Brew]

Actually guys, I'm referring to the inside weld, the punch thru, autogenous welding. What I was really hoping to find was a magic gas mixture, or maybe a purge pressure that would help keep the color down.
The outside of the pipe gets bead blasted as a matter of course, so the color on the outside isn't really relevant, but thanks anyway.

[chip hayden]

have you tried solar flux? i don't know if it would eliminate the heat tint. www.solarflux.com

[Guest]

Brew, are you speaking of automatic machine orbitall welding tubing and pipe?? I have done quite a bit of that. If I understand you correctly....your customer wants clean welds on the inside of the pipe. Here some things that may be affecting your weld...not waiting long enough to purge before starting to weld....possible air leaking in...being blown in from the topside, in other words, pressure inside the pipe is not equal to the pressure from the topside, causing a small amount of air to contaminate the inside weld. {assuming this a butt weld} The pressure is critical in orbital welding...if there is too much on the inside, it will cause the weld to be concave inside due to the excess pressure. I used to use 22 CFH inside and out. Hope this helps.

[Brew]

Yeah Rocky, that's pretty much what I'm talking about, but we're trying to duplicate the "look" of orbital with manual welding. I've already upped the purge pressure and time, with minimal success. Any other suggestions???

[HackAsaw]

it may be helpful if you disclose how you are attempting this duplication but I would think thatsome type of spinning chuck would be very helpful for straight tubing and a rest for the torch would as well


I am but a caveman and I lay a three jaw on my table

put tube in

spin with hand

walk cup

textboook results just about everytime