I would like to hear how some of you deal with your tacks on S/S pipe. 6in sch 40 pipe, both pcs beveled, 1/8 gap, tacked in 4 places, back purge, pipe horiz ,weld vertical. Do you start at one point and weld all the way around removing your purge tape as you go, "consuming" your tacks or do you weld in 1/4's bye passing the tacks, remove your tape, grind and feather the tacks, repurge and finish welding the 4 areas where your tacks were. Hope that makes sense, any help would be great. Thanks
I grind my tacks before I start to weld up the quarters. I start on one quarter and then do the one opposite from it then repeat.
small tacks and feather them out before you get to them, weld out in opposite quarters remove the tape as neccesary. Or use a bridge tack and remove it completely.
Have you guys ever tried the method of beveling both pcs to a point, butting them up tight and using no gap?
sch 10 you can on roll out.
on std wall on a bell hole weld, i run 3/16 gap. and weld the two bottom 1/4s first. by the time u get to the top 1/4s it has sucked up and close the gap enough.
as for welding it, i drip the bead in there, just grind my tacs.
Yes...
Both ends being sharp, no gap and then pulse it.
Works like a charm :)
3.2
Inspector, when you do this what should I be looking for to know I am hot enough. I had a chance to try this once on a job site when no one was around and it didnt purge through. I think I was running to cold. Is there anything I can watch for.
Well...
Do some test on the thicknesses you are going to weld.
When pulsing you can set a pretty high "max amp"
As always with SS, if you can see that small "dot" in the weld pool, you know you are having root fusion.
Experiment a little - within the parameters of your wps :)
3.2
I use small tacks an grind them out as I go, cant really trust the tacks getting a good purge if thier going to shoot it. If theres no RT then feather my tacks an weld that ***** up.
Thats my problem exactly. Some times the tacks consume sometime they don't and they would'nt pass xray. Is grinding out your tacks an exceptable way of doing it, considering its time consuming.
If tacks are good then just feather them down and reconsume them while welding. Welding it in quarters is recommended. If your in school and just learning to get a good root in, you could start by welding bottom to top on one side then the other. If allowed to roll the pipe, then weld all the way around , alternating your starts/stops 180 degrees. Make sure you have a good purge. Watch the puddle, keep it spinning. I like to use #8 cup and walk the cup on the outside of the pipe, with the cup and tungsten pointed almost straight into the bevel.(helpfull on smaller pipe).
Practice and let us know any issues you have. There's a ton of help here, take it in and make it your own.
Thanks everybody for the info. I will try your sugestions. This site and everybody that shares their knowlege are great, Thanks you.
By scrappywelds 
Date 01-03-2010 01:33
Edited 01-03-2010 23:14
read your WPS, it should tell you all allowable ways of welding. Read it and follow it, if you have one. I personally, when I have welded SS pipe without a written WPS I use a 1/8" or 5/32" gap depending on pipe size. Welding out quartering, starting with a bottom quarter first if I am not rolling it out, removing tape as I go. Don't forget to make a vent hole before closing the last quarter up.
metalmaster,
scrappywelds is correct. WPS will give you tolerances and guidelines that you need to follow.
Are you asking this for taking a test or for production or out of curiosity for the best method?
Butting and fusing sch 40 is not typical on a job site. Typically, 1/8" gap 1/8" wire. You can tack it horiz or vert. If available you can place coupons in angles, channels or a beam (protect from contamination-carbon/stainless) Tack top about 3/4" long, rotate 180 degrees tack 1" long, oh yea, put a clear lens at one end to view every tack for purge and weld quality, tack two more times and then feather. If the tacks are too small or you remove them too much the root opening will shrink during the root and make it more difficult than it has to be. I start with a loose 1/8" gap and when the 4 tacks are in it is 1/8". Perfect for my liking.
Check purge before every tack and quarter weld. When you get it right you shouldn't have too much of a difference in the tacks and the bead. Feather them alot and slow down when tying into them. I scribe a "shiney" line at the beginning of the tacks to know exactly when to tie in.
But I need all the help I can get. lol
I use the thru feed and backfeed method,tack up with Stainless nuts or small pieces of like material flat bar, 7/32 stick rod for a gap and a slight landing and have at it in quarters,I start the purge and keep it on and take it to it.Grind the bars or nuts off as I get to them and carry on.
