Two problems with stainless TIG

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I do a lot of stainless steel (either 304 or 321) TIG and have two issues. . .Setup- Lincoln PT185.usually around 70amp 3/32" 2%thoriated ground to pencil point around 30cf/h 100%argon 16 gauge (.065) tubing.First problem: BackpurgingI'm not sure I'm doing this 100% correctly. Sometimes the inside of the weld looks perfect, sometimes it's mediocre, and rarely it looks like I didn't even purge. For a common example I have a 1.5" diameter piping about 16in long. I have to cope about a    45* degree piece to it which acts as a diversion for a turbo wastgate. I make sure fitment is perfect, all surfaces are sleaned thoroughly and finished with a ss wire wheel. I tape off the the end furthest from the weld, and the end near the weld I tape, but stick the purge hose through. I'll set the purge usually to about 50cf/h.Second problem: Arc wanderAgain, on the same pieces I experience arc wander pretty frequently. I don't have the most rock solid hands, but I'm no micheal j fox. Any tips? I can get pics if needed
Reply:Your ID purge sounds to high.  I would set it to 10-15cfh and give it a minute to purge out.  I think you only need about .5-.7"h2o of backpressure for that size tube.  All the argon flow coming out of the joint is probably causing the arc wander.  I would only run about 20 cfh and a gas lens for the OD purge.  When I back purge I tape and purge from one end and tape the other closed.  Then I put a small hole in the high side of the tube so the tube fills completly before the argon escapes.  Try a max of 60amps for that wall thickness.  Hope that helps
Reply:Your purge pressure is 50cfh !!!! WOW Lower it to 10cfh,.065 wall tubing. Make sure you tack in 3-4 places first.Set machine to 50AMPS and the foot pedal will regulate that to the proper amount,Use 308L filler on 304 tube.You have a tube NOT a pipe. Tube is measured by the OD and pipe is measured by the ID and can be +or- .025 Tube is usually within .002 on the OD.Arc wander can be caused by machining oil. The tungsten needs to be sharpened like a pencil (71º) and the sides of the angle need to be straight if the sides of the angle are slightly curved the arc will wander up the sides of the point. If the point is ragged  that will also be evident in the final look of the weld.I would not use a stainless wire brush on the weld groove. Just make sure it is clean. shiney metal. It just leaves a place for dirt etc.,. Look at the surface of the metal with a magnifying glass of a wire brushed surface, and you will see galling. Small balls of metal rolled up etc.,. A wire brushed surface also gets corrosion quicker.I spent 11 years welding .065 and .049 wall stainless tubing.BTW a .065 tube on a turbo seems little thin I think. Drilling a hole in the tube to let purge gas escape seems like a little overkill. That is usually used when building a tubular framework  and pressure can build up inside and cause diffaculty in closing the final weld.Your pruge cas can and will probably leak a little at the hose  and that should be enough.I used to weld aircraft engine mounts that were tubular chromoloy and that last purge hole is often closed with a special rivet.Last edited by Donald Branscom; 01-19-2009 at 07:17 PM.AWS certified welding inspectorAWS certified welder
Reply:I did not mean drill a hole in the tube.  I should have stated it more clearly.  I put a small hole in the tape that is used to seal the end of the tube.
Reply:I don't know how I slipped up on the pipe/tube nomenclature.... My old instructor would kill me haha.I guess I'll try lowering that purge and see how that works out. This is for subarus, which have a strange setup, and this particular pipe is after the manifold. I've never seen a problem with that thickness at least for these applications. Donald- What would you recommend cleaning with? Also, the tube that is coped to the main piece is left uncovered so I don't think the pressure is an issue.
Reply:I agree with Donald.  I would not use a wire brush.  Scotch brite and acetone work great.  At home I will use brake parts cleaner if I don't have any acetone.  I might be misunderstanding you but when I back purge I like to seal all openings and have one small opening so all the oxygen is forced out.
Reply:Originally Posted by GrimmI agree with Donald.  I would not use a wire brush.  Scotch brite and acetone work great.  At home I will use brake parts cleaner if I don't have any acetone.  I might be misunderstanding you but when I back purge I like to seal all openings and have one small opening so all the oxygen is forced out.
Reply:Boomslang,If you do a lot of this type of welding, it might be worth while to invest in a set of plugs.  They make kits with plastic and rubber pipe/tube plugs for sealing up the tube ends while purging.  These plugs are faster to install and remove than tape, and would take heat better, so you may be able to use them closer to the weld joint.  They also come fitted with hose barbs to make gas connections secure and easy.Barring that, can you leave cutting off the normally short side of the tube joint till after you weld it?  This would enable you to seal up the tube, without the heat of welding burning up the tape.I also agree that a lower gas purge rate 10-15 cfh, would work much better.  Take a minute and calculate the volume of the tube assembly you're purging.  Then, using the flow rate, back calculate the time it will take to purge the tube.  I'd add 10% to the result for some added insurance.  Chances are the small assemblies you're working with purge in just a few seconds, but it never hurts to double check.Benson's Mobile Welding - Dayton, OH metro area - AWS Certified Welding Inspector
Reply:Boomslang,Enough's been said about backpurging/gas flow to help/confuse most anyone.  Couple of the posters seem most interested in telling everyone "how great they are".No one's mentioned tungsten.  Personally, I'd recommend going down to a 1/16" 2% thoriated tungsten and a gas lens.  Use whatever cup you can get in the joint.  The smaller tungsten will give better starts and a more controlable arc.One poster in particular, spends so much time "blowing his own horn", he's hurting my ears.Syncro 250 DX Dynasty 200 DXMM 251 w/30A SG XMT 304 w/714 Feeder & Optima PulserHH187Dialarc 250 AC/DCHypertherm PM 1250Smith, Harris, Victor O/ASmith and Thermco Gas MixersAccess to a full fab shop with CNC Plasma, Water Jet, etc.
Reply:If the tube is to short to tape it without the tape melting try aluminum foil.  You can wrap the end up or ball it up and stick it in the tube.  If you put a ball of foil inside make sure it isn't so deep that it comes in contact with the weld pool.
Reply:i do aseptic pipe  and tubing purge and we use aluminum foil for capping purge  welds all the time
Reply:This may be a total noob question.... but I am new to this Whats the best way to hook up a purge line to your tank? My regulator has an output going to the welder as everyone else has no doubt. I am sure I could T-off of that line and put a valve for a purge...? Then just set the flow = 17cfh (tig) + ~10cfh (for purge purposes) = 25-30 cfh total. Is that how one would go about it?ThanksTRG
Reply:Ever thought of using solarflux B instead of backpurging? Might make life much easier.
Reply:Well complete dumba** mistake by me... I've actually been reading the flow rate gauge wron and only have had it around 20 cfm... I guess still high but not as bad. I'm going to try the alum foil for sure and if not, maybe the solarflux