well I am making turbo headers and am using 304 stainless.
I understand the necessity for purging the back of the weld, however I wondered how much damage i would be doing by simply tacking the pipes together without a purge, for reference sake, and then when I go back to completely weld the runners, use a purge. Will the spots that I tacked without a purge loose their carbon if I go back over them while purging?
I have heard many different things about stainless, one thing was that welding over an existing stainless weld makes it very weak, is this true?
Another alternative I thought about was using this stuff called solar paste, I saw it on burnsstainless site, but was wondering if anyone here has had any experience with it?
thanks
tom
If you tack (it's better if you have a foot pedal or remote) and leave your tig torch gas on a few seconds after the tack, then you will have a clean enough tack so that when you go and weld (with the purge) you should have a clean weld when you are finished.
I have made repairs of stainless welds where I only groud out the defective part of the joint and re-welded that section. Because of this, I would say it is not true that a weld is weakened if you re-weld it. Why else would it be allowed?
AS long as a tack is not blackened (contaminated) then you would be alright to weld over it with a purge.
Solar paste should only be used if it is not feasable with a standard purge as it does not work very well.
the tack wont hurt anything, as long as its gold or blues not black. if you are really anal you can cut the tacks off as you approach them during the final weld {you good at stops and starts?} . when you build headers you dont seem to get total penetration {from what ive noticed} a gas lens could be handy here, as it really improved the weld quality of my work on thin stainless.
I have used solar flux on stainless pipe with acceptable results. I have also worked with a company that would tack up an open butt stainless weld using a small section of 1/4" dia. SS Tubing about 1/2" long. You lay the small peice of tubing in the bevel, and tack it to the pipe on both sides. When you go back to make the weld later, and you get a good purge on it, You can get some better tacks with complete penetration, Then grind the small peices of tubing out of your way.It is alot of work, But it worked well on large bore SS pipe. If you are working on something that is going to be X-rayed, I would make sure my tacks were properly purged and the walls of the pipe broken down. good luck.
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