TIG welding a root

Date 03-13-2003 18:38

First, maybe try opening up the bevel angle to about 35-37.5 deg. Root opening approx 1/16" - 3/32" . this will allow better access to the root. I would use a 3/32" Dia. 2% Thoria tungsten sharpended to a fine point, remember to sharpen the tungsten transverse to the axis of the Tungsten. I would use Argon instead of helium, it gives a cooler arc. Flow rates of 20 - 30 cfm .Filler material should be ER70S-6 3/32" Dia.
Position should be either flat or Horizontal (for plate). If you want use run on and run off tabs to get a feel before you start in to the joint, that's ok.

Strike the arc and stabilize before any forward movement, ensure that you have a decent puddle before you start adding filler material to the leading edge of the puddle. Depending on your root opening and heat setting your travel speed will vary. Remember, you are carrying alot smaller of a puddle and will have to pause briefly to ensure fusion along the bevel edges. Watch the puddle, when it starts to fludder its time to move.

When adding filler material dab it in to the leading edge of the puddle and carry it up along the edges.

I haven't welded in a long time, so some of this info may be a little off, i hope that someone on the forum, could confirm or add to my comments.

Hope this helps,

colin

By cccasey (**)

Date 03-13-2003 21:25

Just adding to what colins wrote, you may want to try the "on the wire" technique for your root pass. Basically you bevel your plate to a knife edge with no root face then using a 1/16" root opening, position a 3/32" E70S-2 tig rod along the axis of the joint. (almost laying the rod in the groove, while still holding it in your non-torch hand). This is similar to using a consumable insert ring on pipe welds, use the same parameters as Colins recommended and you should see good penetration with little to no root reinforcment depending on your plate position. The key is your amperage and speed combination. Practice and you'll get it!
Curt

By overthehill (*)

Date 03-14-2003 17:28

I used to do quite a bit of tig pipe in refineries and petrochemical plants. There are many different techniques to run root, but try using a 1/8 tungsten and 1/8 wire. Like colins mentioned, open the bevel up (37.5 deg.), with feathered edges. Tack up with a 1/8 spacer for the first tack. Remove it, even up the gap and run the second tack. The gap should draw together slightly so a 1/8 rod will just not fit through. Use a small cup on the torch and rest it right on the sides of the bevel. Angle the torch away from the weld (push) and adjust the tungsten for the arc gap. Lay the wire right in the gap, light the arc, and with a very slight flicker of the wrist (kind of like a case of the shakes), scoot the cup up the bevel, running right over the rod. I only ever used Miller 8 banks or Lincoln SA200's, so I don't know the amperage, but you want to run relatively hot and fast to produce a smooth, slightly over flush, bead on the backside. If the backside is concave, the gap may be too tight or your moving too slow and sucking the root back up. Run the second pass the same way, but use a slightly larger cup. It should rest on the sides of the bevel without hitting the weld build up. Scoot it up the bevel, running right over the rod. Don't move too slow, you can still suck the root back out, especially when your welding on SS. This technique requires perfect bevel preparation and joint fit up. If the gap is too wide, hold the rod so the tip of the rod is just on the backside of the gap. On pipe, we would rest the rod on a tack, so the rod was actually going through the inside of the pipe. Same torch technique, small cup rested in the bevel. Depending on the width of the gap, you may need to feed wire, but try keeping the tip of the rod in the puddle, reducing the risk of internal undercut. For narrow gaps, I alway ground them open. Some welders like to open a keyhole and dip the rod on narrow gaps, but that can get awkward in field situations. It also increases the chance of internal undercut, which is difficult to repair. Like any other type of root, metal preparation and fit up is very important. Uniformity makes the whole thing a lot easier.

By welder_guy2001 (***)

Date 03-15-2003 02:31

thanks to you all for the tips. I'll practice what you said on some 2" dia. 1/8" wall SS tubing I'm making into handrails. don't worry...the butt welds don't have to be full penetration...only partial. but I'll try out a full pen. weld anyway

By overthehill (*)

Date 03-15-2003 05:28

2" dia 1/8 wall SS is going to be slightly more difficult than 3/8" CS. If you get the chance, throw together some 4" or 6" CS coupons to practice on. You'll have a little more time to work it out.

By welder_guy2001 (***)

Date 03-15-2003 07:14

i know it'll be significantly harder just because of the SS factor. but, this is what I have to work with for now, and the welding is going to have to be done anyway. if i get it, great...if not, I'll just practice w/ some carbon steel later. thanks!

By dasimonds (**)

Date 03-15-2003 11:58

you can achieve a full pen weld with the stainless tubing with a square cut on the end of the tubing, no bevel. No gap. No filler. Use argon to purge the tubing. Hard to say on the amperage. You'll have to play around with it. Start at say 50 amps. I'm geussing. But with a little practice, you'll have it down in no time. Keep a tight arc and your tungsten out of the puddle. When your done, a little flapping, and you'll never know the tubing used to be 2 pieces.
The key to fusing is clean and no gap.

Hope this helps.
Dale Simonds

By wfriii27007 (*)

Date 03-19-2003 22:48

Hey, 3/32 tungston 2% or red, and filler rod get your key hole started and go from there adjust heat as you see fit.