Questions about the Tig 6g pipe test

Date 07-06-2005 17:40

A local welding place test for a tig position. A lil about myself. I have done Tig welding at a welding school in all postions steel thin materials, and did stringers on pipe and saw demonstrations on how to weld two beveled pies together. In my past ive done alot of oxy aceytelene welding also. My questions are when you take the test what schedule and how many amps to use on wall thickness. I know the second pass you turn machine up hot pass. I am a right handed welder so i would approach the test with my right knee on groundleft knee up two work pedal. Do they make you use the pedal? I would think bump start or button on torch. Can you make it around the pipe not knealing? Is there a height guidline where u place the pipe you have to follow on taking the pipe 6g test? I have done walking the cup method and thats what they require also. I probably ask them do they want anything written too? Any extra advice would be helpful Thanks

By medicinehawk (**)

Date 07-07-2005 08:19

Most places who want TIG - pipe welders do not use a foot pedal. Alot of places I have tested at will let you set the height of the coupon (if kneeling is a problem) but many places have a fixture which clamps the coupon after you tack it on the bench.
Usually if a shop wants a tig/pipe welder they will test you on stainless steel pipe as that would require(usually) to tig the coupon out ALL the way whereas carbon steel pipe would use a tig root & hot pass with 7018 for the fill & cap.
You need to be specific (what alloy you are welding ) as the amperage is quite different for each, but here is a ball park setting: for stainless steel-304L or 316L you would use 55 to 70 amps DCEN. For carbon steel you might use 100 to 125 amps DCEN.
If they test you on stainless pipe, you would have to set up a purge for the inside of the pipe and if you have never done it before......there is no way to explain it to have you pass it (the test) in other words, you're screwed.
If they didn't specify pipe in the job description, then they may have you weld some plate together just to see what kind of bead you can put down (pray for this to be the case). It really depends on what type of shop this is and what they manufacture.
Good luck & be well.

By jay72chevy (*)

Date 07-07-2005 23:36

Thanks for the reply. I have welded Smaw Stainless steel. That seems similar to 70 18. Is the tig stainless steel welding similar to welding steel pipe also?

By medicinehawk (**)

Date 07-08-2005 08:30

It is similar as you'd "walk the cup" but as I said, you have to purge the ID of the pipe with Argon. It is tricky if you have never done it, but anything new just takes practice to get used to.
Usually, they will give you 2"-sched-40, 304L or 316L coupons. You should have a seperate flow meter to set the purge flow rate. Tape a hose to one end of the coupon(before tacking) and set the purge at 35-40 cfh and seal the other open end of the pipe. Set the gap at 1/8". There are several ways to tack it up but as I said it is tricky because you somehow have to ground the pipe while taking care to make sure the tape is tight so the argon stays inside the coupon. The easiest way to do it is to tack the pipe to the bench with the pipe vertical(4G) and then tape the hose to the bottom end of the coupon. Crank up the purge, use a gap wire and carefully put a tack (1/4" long) where there is no mismatch. Remove the gap wire and eyeball the gap opposite the first tack and place another tack. Move the coupon so the gap is even and place the final two tacks. Usually whoever is watching you do this will let you tack it up however you see fit. Examine your tacks carefully to make sure that there is no "sugaring" going on. This would indicate a leaking purge(lack of gas to the heat affected zone). To avoid this (they will bust you out for it) you have to make sure the seal is good with the tape. Assuming the tacks are "clean" you are ready to put the coupon in the 6G. Place the longest tack at the 6 o'clock position.
Now you are ready to weld the coupon and whoever is testing you will let you go for it.
I assume this part is in your capacity so You don't need any input from me, but I will say one thing: you can either set the purge at 10- 20 cfh and leave a 1/4" diameter outlet port in the tape to allow argon to escape the coupon or put that hole in the tape before you do the last quarter of the coupon. If you do if (poke a hole in the tape) before you seal up the last quarter then the inside of the root pass will be cleaner, but you risk causing concavity because the pressure(of the id purge) will push the weld out especially if the gap closes up alot. Better to put the bleeder hole in the tape before hand as examiners will accept a little color, but they will not accept a sugared root.
Be well.
Hawk