We are using the following procedure:
Tig on stainless steel, 3/32" tungsten, 3/32" rod, 1/8" thick plate, 3/32" open root butt joint with about a 30 degree bevel on each plate, Flat Horizontal and Vertical positions. Progression on vertical is up. We are using Argon shielding gas and backing gas. We are laying the rod in the groove and just fusing the root in and then we are using the dipping and moving technique with stringer beads for the cover passes. Flat works out pretty good, but with the horizontal and vertical we are having some trouble sugaring through our root pass, and even the 1/8" plate around the root sometimes. The vertical seems to be especially problematic. We are using the foot pedal to control the amperage, but we are trying not to use any more amperage than it takes to wet the puddle in.
Is dipping the rod and moving hotter or deeper penetrating than just fusing in the rod?
Do you have any suggestions that might make this a little easier?
Hello Louis, I'm sure that others will chime in on this, but here goes: I do feel you are making a mistake as you said in using the dip technique with your additional passes. Almost all of the pipe that I have been around that has been tig welded will be done as you described in your root pass method. The rod will be laid in on the center of the joint and the cup will be walked back and forth to spread the weld metal out to the edges of the groove evenly. This method will limit the heat input to the parent metal and concentrate the majority of the welding arc energy on the rod. Even in a plate situation the same type of rules can certainly apply. One other slight change you might consider would have to do with the filler metal, most that I have been around will use 1/8" rod, the larger diameter helps to avoid having a ball form on the end of the rod as the walking of the cup is done. Also if you aren't already doing this you will want to keep the purge on for at least the root pass and the hot pass after that(hot pass might not even be the correct term here, as it isn't designed to burn out slag entrapment as might be done on E6010 roots), personally, I would keep the purge on for the entire course of the weld. Look at the grind angle on your tungsten, it should have a long taper, and the extention of the tungsten should also be out there quite a ways, the low angle that this creates will help to limit the heat input and thus help with the sugaring problem. The weaving motion that I have desribed means that the puddle is actually kept rather small and by weaving, you are able to spread the weld metal over a larger area with a thinner deposition than you would have if you tried to use a large puddle to cover this same width and used a dipping method. Hope this has helped out a bit. Regards, aevald
By Lawrence 
Date 01-31-2007 16:06
Edited 01-31-2007 16:11
Louis,
Good question. I'm a bit confused about one point. If you are using argon backing gas, how is it that you are experiencing "sugaring"?
Sugaring is usually described as melt thru on stainless when no backing gas is present. It is rough and black/grey.
So tell us a bit more about the back side of your root passes.
Here are a few things to think about along the way.
1. If your bevel goes to a knife edge or even anything less than 0.060 I don't think you need an open root at all.
If you have a thicker land I would still suggest trials with a smaller open root. This will make it easier to have more consistant melt thru.
2. With stainless. The dip or lay wire technique are pretty much a matter of operator preference. Although the angle of torch and wire can be critical with the lay wire and improper angles for either can cause balling of the filler wire causing an inconsistant deposit.
3. You might want to explore a 1/16 dia. filler for your root and the larger filler for you cover passes. Again a matter of preference and ease of control.
Allen's on the money pipe welding techniques "cup walking etc." can be applied to your plates as well in most cases. If you were working with plates "sheet metal" any thinner than you mentioned I might advise against cup walking a butt joint for Heat input/distortion reasons.
It sounds like you might be losing purge through the weld gap, since the flat is OK. Lawrence is right, close up the gap a bit (3/32 is alot for 1/8" material), feather edge it and it should help. Plus, with 1/8" thickness you should only need one additional pass after the root.
Yes I'm sorry about the sugaring part. We are getting melt through. It sugars every now and then because of the way we have it set up, but I know what causes that. We have the SS plates laying flat against a 3/8" thick CS plate and two 1/8" spacers, one on each side of the root. This traps the gas in the void and shields the back also. It works well with a 90 degree torch angle, but if you tilt the torch in the direction of travel too far you lose your shielding on the backside. Not a perfect setup I know, but it works good enough for this job. It's really the melt through that causes the biggest problem.
It takes at least two cover passes because the face opening is ΒΌ" wide after being beveled and tacked together.
We are feathering the edge.
If we close up the root (how close should we go?) would we have to up the amps to get the melt throughwe want?
I've been taught to let part of the rod's diameter set through the root opening and then just fuse it in with as little heat as possible so as to not get suck back on the root.
Also wouldn't larger rods used on the face result in you having to use more heat and therefore melt through even worse?
Thanks
Hello again Louis, when you described your process for "purging" the back side of this weld, in most instances this wouldn't be considered as a real purge. In another part of your post you spoke of having melt through I believe you called it. Are you actually trying to come up with a full-penetration weld on these joints or just trying to get close? The other gentlemen who replied to your post had some really great suggestions for trying different techniques for attaining full penetration welds on these joints, I believe they also questioned how you were providing backing gas for this application. A true backing gas situation here would probably entail the use of some special fixturing and require a secondary source of shielding gas. Another possibility here would include the use of a backing paste such as solar flux or some other similar product. After looking at your original post and what I replied with, I would probably agree with js55 and Lawrence's post with regards to the fact that this would only require two passes to properly fill this joint configuration. I also agree that answers to your real questions require additional information on your part. Trying to provide backside protection for your current set-up would probably not be possible due to torch angle changes that are required relative to weld position and a few other variables. As has also been stated here in the various posts, torch angle, filler rod deposition or position angle, tungsten grind angle, filler rod diameter, and joint design and set-up, backing application, will have a distinct influence on finish welds. Hope this has helped some. Regards, aevald
By Louis 
Date 01-31-2007 21:20
Edited 01-31-2007 21:23
No this would not be considered back purging by AWS standards or any other code, but it does work if you keep the proper torch angle throughout the root pass you will not sugar the back.
We could not get the gas to the back side if we completely close the root gap. The procedure we are using for the root pass is working. We can get the root appearance to be acceptable even to the standards of the AWS D1.6 welding code for structural stainless steel, but we are having trouble with the melt through either of the root pass itself or the adjacent basemetal. When it does this there was no shielding gas back there because we were welding over the now welded root and it allows the melt through on the back to sugar.
We were going to try a 1/16" rod on the face in an effort to cut down on the heat it takes, however I think what some of you have said about the dipping technique could be the problem. If we don't dip often enough and we move up we might not be carrying enough metal with us and that lets it heat up too much and melt through.
We have a 1/4" gap on the face when tacked up. Using a 3/32" rod if we use the fusing technique should we weave the rod with the torch from side to side or just keep it in the middle?
Thank you.
I think we need to talk about best practices and what is "good enough"
The argon backing technique you are currently using will not lend itself to cup walking period. The torch angles required will not get sufficient argon to the back of the joint.
Next. If you lay wire in the root gap, this in itself will also stop argon gas from reaching the back of the weld at the melt zone.
But don't dispair. There are alternatives.
I know several code shops that use no bevel, an open root and backing tape to protect the root. After the root pass they back gouge or back grind the root to sound metal and weld the back side. This process can be done in two passes. You could even use GMAW spray transfer or GMAW-P with this technique and increase productivity 10X
Making argon backing tooling is not as complex as you might think.... Most stainless welders have a few in there tool boxes.. Maybe we should digitize some photos and post them for you.
The amount of prep and attention to back side protection is directly related to your part's operating requirements. If we are talking about a stainless cattle feed box than what you are currently doing is prolly just fine. However, if you are looking for something that is more like code quality than the posters here will be able to offer many types of advice..
There really are alot of alternatives.
Yes you would think that laying the rod in the joint would prevent the gas from getting to the back side, but it doesn't. The root won't sugar if you keep a 90 degree work and travel angle. Maby we just don't have it laying in there that tight. I'm not any good at walking the cup, but I agree with what you said, because of the way we are doing it I don't believe it would work.
This is just a little test for some maintenance men in a chicken processing plant. This is not to any code, but if they pass they can weld on the floor of the plant. I was not wanting to go to a whole lot of expense and trouble to do it the right way. I know that sounds bad, but when I was tacking these plates I do it face down against a flat 3/8" thick plate and I realized the tacks were not sugaring because the gas was being trapped down in the groove. That's when I came up with the idea of using the spacer. That part I think works pretty well, but the melt through after is the problem.
Thanks for all your help.
