stainless tig welding

[johnson697]

Did some stainless welding on some .040 i think 308 and was wondering if anyone knew of a way to keep from sugaring on the back side, without using another tank to purge on the backside,got the right heat on the weld side ,nice gold and blue colors but got the sugaring effect on the inside?

[earla]

How about something like this? http://www.superiorflux.com/stainles...ckup_flux.html
I have not used this, but it's supposed to work.

[earla]

Here is another brand. http://www.solarflux.com/Pages/Productinfo.html

[Paul Moir]

You need to prevent the back side from seeing oxygen. Coating with one of the fluxes is one option (one I've never exercised, being allergic to the extra work of cleaning it). Protecting the back side with argon (back purging) is your second option. A third is to use a close fitting aluminium backer, which also makes welding thinner stainless much easier. I sometimes will fit the aluminum backer with an argon supply via a nipple to eliminate the slight oxidation you get. On more elaborate things where you can't really get a close fit, sometimes I'll machine a gas delivery groove in the backer.

Gold/blue is just a function of gas coverage during cooling, and is in no way "right". No oxidation (no colour) is more "right". Or you could just pickle it which is even more "right".

[johnson697]

how do you pickle the weld?

[johnson697]

also i understand why the sugaring on the back side happens...just wondered what all the different ways to keep from getting it.Can you weld it and not get any discoloring,have a friend of mine that can a little bit but not the whole lenth of the weld?

[Paul Moir]

If you just want to get rid of most, then the backer is often the easiest. It'll get rid of almost all of the sugaring.

The only trick to getting no colouring is to have argon shielding present until the work drops below ~300C or so. Big cup, lots of gas, taking lots of breaks. Not really efficient.

To pickle a weld, first go to your LWS and ask for some pickle juice. If you get a funny look, say, "ya know, for pickling stainless." If they continue to give you a funny look, you can now be sure they know as little as you suspected and it's time to move onto the next LWS. When you find a good one, you can get a jug. It's basically some powerful acids in a paste form so you can apply overhead and on verticals, often mixed with an indicator so you can know if you've neutralized it. I use Avesta Blue One, but any will do.

You take a jug of this stuff back to the shop, then you read the instructions and the MSDS (I'm not "that guy", but for this stuff you really need to do it. Most use hydroflouric acid which can do really evil stuff to tissue, never mind the regular old blindness, etc, from the various other acids in the mix.) Normally you slop the stuff onto your (cooled) weld, wait 30 min - 2h, rinse it off and give the weld a quick scrub with a scotchbrite or a stainless wire brush. Your welds will then look beautiful, with no visible heat marks, and will never rust if you haven't formed a crevice. Where you apply the juice will go a bit dull & light, so for cosmetic applications with no further finishing, you should mask off areas you do not wish to treat.

Bad news is that some LWS will charge between $50-$100 for a jug. Good news is it'll last a long, long time. Better news is, if you're doing it for money they'll be beating a path to your door with their stainless work.

dythor here said you can use citric acid to pickle as a safer alternative. I haven't tried it. My suspicion is it'll passivate but not pickle, but like I said I haven't tried it.

[Rambozo]

how do you pickle the weld?

Dunk it in pickling solution.

also i understand why the sugaring on the back side happens...just wondered what all the different ways to keep from getting it.Can you weld it and not get any discoloring,have a friend of mine that can a little bit but not the whole lenth of the weld?

IT is all about controlling the heat and the atmosphere. For a long weld you will often need a trailing shield. The trailing shields cover the area behind the torch with purge gas while it's still hot. Another option is to use an electronic cleaner. This is a lot easier than pickling, as you don't need a lot of solution. These are great for food service, where weld appearance is a huge issue. Here is an example of a machine that does this. There are many makers of these and some do all kinds of other stuff, like this.

[Paul Moir]

Been looking at those. Can't use the Avesta in production areas obviously.

Another:
http://www.youtube.com/watch?v=NoKa4TBxmRE

Did try a quick experiment with a 24vdc power supply, some silicone rubber foam (perforated for conduction) and an acid, but while it produced lots of fumes, it was super slow. Might have to just go commercial on this.

[Ray C]

This is a very good thread. I hope the original poster is OK if I ask some questions related to this topic...

Is the color of a SS bead or, the area in the HAZ an indication of the integrity/strength of the weld or, is this mainly an issue of aesthetics?

Similarly, if a SS weld bead comes-out dark with a sooty appearance (but cleans-up with some brusing), is it an indication the weld was too hot or not enough gas used and that the integrity of the whole piece is now damaged?...

I hope the questions make sense...

PS: Can you tell I just did my first practice TIG welds on SS this weekend? Here's are some pictures. The semi-circular piece was the very first attempt. Figure-8 on the inside seam and standard pause/push bead on the backside. The other plate was experimenting by cutting the plate into many pieces and welding it all back together using different heats, filler size, etc. After that, I cut it up to inspect penetration and did some bending to test. All welds had full penetration and the piece only bent when clamped in a vise and manhandled with a 24" crescent wrench. BTW: the SS is unknown type and I used 308L filler. The pieces are 4" diameter between 3/8 and 1/8" thick.

Anyhow, back related to this thread, after welding those pieces, it doesn't seem they will ever return to the bright shiny chrome appearance they first had.

[Rambozo]

Is the color of a SS bead or, the area in the HAZ an indication of the integrity/strength of the weld or, is this mainly an issue of aesthetics?

There is a small effect on strength, but a large effect on corrosion resistance.

Similarly, if a SS weld bead comes-out dark with a sooty appearance (but cleans-up with some brusing), is it an indication the weld was too hot or not enough gas used and that the integrity of the whole piece is now damaged?...

Yes, too hot and or oxygen present while it was still above critical temperature. This is usually confined to the HAZ and again is more of a corrosion issue than strength, although there can be some loss of integrity. It all depends on the condition of the weld and how the damage was done.

[Paul Moir]

Ray C:

Anyhow, back related to this thread, after welding those pieces, it doesn't seem they will ever return to the bright shiny chrome appearance they first had.

They will if you pickle them. They may require polishing if you need a reflective surface but it'll put it back to matt.

Here's a few stainless pics showing some typical defects. These were from a pretty good environment for stainless (washdown, occasional passivation), if it was brine or marine they'd be a lot worse.

Typical pickled weld @ 10 years service. A bit of black oxide remains (pickling won't work well on that) and there's a spot down at the bottom where the colour was never scrubbed off. Also you'll see a slightly gray haze at the edge of the HAZ, which is typical:


Typical unpickled weld (colour brushed off only). Same conditions:


Sugaring causing crevices. This is one big problem with sugaring; it creates a pit that can't be ground out without going deep into the weld. This weld was ground and pickled.


Incomplete penetration causing a crevice (butt weld, ground and pickled, #18 gauge, back side):


Contamination. Weld was originally wire wheeled with a steel wire wheel. The weld was then immediately pickled, but the area above the weld wasn't. This defect has been passivated many times, but continues to rust. (I think it's the rust pits from the original defect.) I don't have a picture of grinding contamination caused by grinding steel in the vicinity of stainless, but it's similar. **Do not grind steel near stainless or you will contaminate your stainless with embedded steel**