Purging

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I am tig welding a 3" polished stainless 304 pipe with a .65 wall thickness for a milk line for my dairy.  I am cutting holes every 27" for a 3/4 ID nipple that is 1 1/2 " long. I need to weld on 60 of theses.  The joints of pipe I am working with are 20' long.  Do I need a seperate regulator and argon bottle to purge the line?  Or can I use a flow meter on my tig welding argon bottle?  What amount of pressure should I use when purging the pipe?  These welds have to be sanitary welds.
Reply:I weld the same tubing all day, we just use a t-junction at the flow meter which has an inline valve that lets us adjust the flow.  Now since your purging so much you may want an extra bottle just for that.As for how much pressure, it has to be enough to keep the welds from sinking in, but not enough to push them out.Im no expert, but that gets the job done for us.Are you doing something to fishmouth the fittings or do they sit inside the holes?Have we all gone mad?
Reply:I am going to make some test welds and then cut them open to make sure I am doing right.  If I do not weld correctly our bacteria counts could go up do to insufficient cleaning.  I am really worried about the inside weld looking like the outside weld.  I did not know which way to go on the nipples butting to the 3" pipe or sitting inside the bored hole.  Which way is the best?  I am interested in keeping my bacteria counts down.  What is the best way to stop up the 3/4" ID nipples because I have so many of them?
Reply:Let me get this straight..Your doing 20 foot sections at a time..You need a way to keep the purge gas in each area of the bung itself..No need to do the whole pipe at a time when you need 6" of sealed area..Smooth enough on the inside as is...Fab up a round 6" sealed chamber out of thin plate and slide it in between the middle of the weld area..Put a small hose in one plate and feed the argon in that way..Its not like it has to be sealed 100% either..Weld away and move to the next bung and fill the chamber...You should not need that much heat anyway to create a problem..How are you gonna connect all those 20 footers anyway?...zap!I am not completely insane..Some parts are missing Professional Driver on a closed course....Do not attempt.Just because I'm a  dumbass don't mean that you can be too.So DON'T try any of this **** l do at home.
Reply:I do a lot of sanitary welds in juice plants on 2"  304 pipe, I would not recommend the fittings to be recessed into the parent tube as you always have the chance of bacterial buildup with improper clean out. The way I do it is take and make all of you holes for your fittings and cover them with masking tape and also the far end of the tube, place your argon hose into the near end and stuff a rag around the purge hose to prevent leakage, poke a small relief hole in the tape covering the far end. You do not need a lot of argon pressure in the tube, just crack the valve and wait till you have a stream of gas exiting the far end of the tube, untape each hole as you weld each fitting in place. Also the best way to avoid sugaring on the inside is to do a real good fit up and if at all possible only fuse the fitting to the parent tube, only use filler where needed and keep your heat down and work quickly. I've attached a couple of pics of the set ups I use when purging juice pipe. The first pic is when I'm running two rigs off of one bottle, but can be used for purging as well. The third pic is the setup I use when purging most often. Dave Attached ImagesI am what I am, Deal with it!If necessity is the Mother of Invention, I must be the Father of Desperation!
Reply:as for getting the fit right, we have a wheel for our belt sander that lets us cope the fittings to 2.5" and 3" dia tube, if we do it right they fit on the tube with a perfect fit every time.It might be worth looking into one with the amount of fittings your doing, or find a shop that can do the job.I would recommend adding wire, if your purging you shouldnt sugar the weld and not using wire will really suck away from the thin .065 wall.  If you have a bit of a gap, that .065 will be .01 when your done and cracks very easy.Have we all gone mad?
Reply:I am going to join the 20' sections with a 3" Tri clamp weldable  flange, then clamp them together with a 3" Tri clamp.  The next question is how am I going to plug the 3/4" X 1 1/2 long nipple.  If I put tape on the nipple how am I going to keep the tape from melting?
Reply:All you need is a 1" ball from a big ball bearing..Position ball on bung..Weld away!If you need one I got em'.....zap!I am not completely insane..Some parts are missing Professional Driver on a closed course....Do not attempt.Just because I'm a  dumbass don't mean that you can be too.So DON'T try any of this **** l do at home.
Reply:There goes ZAP again.Bragging about having "big balls".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:get rubber stoppers, thats what we use.  Have them in sizes from 3.5" to 1", and they are tapered so the get a snug fit and fit a wider ranger of sizes.  most hardware stors carry them in the parts bins.Ours have a small hole in the middle so that the pressure doesnt build up to high.Zap, wouldnt the ball bearing only work if he can weld it with the nipple vertical?  Probably not the easiest position to weld it in.Have we all gone mad?
Reply:1)  You do NOT want any pressure in the pipe.  You want FLOW, not pressure.2)Use a ball of aluminum foil to cap the nipples.  From there, it's just a matter of the technique you choose..  there's several ways to get it to work.What I'd do:1)  Put the purge hose in end A, using tape or something similar that will seal..not a rag.2) Tape up ALL the holes that you drilled for the nipples.  3)  Purge pipe.4)  Put aluminum foil on your nipples.5)  Start with the nipple closest to end A.  Untape the hole and fit/tack your nipple on.6)  Tape it up to completely seal the pipe at the nipple and fitup area, and go to the next nipple.7)  Work your way to the other end, fitting each nipple one at a time.8)  Go back to nipple 1, and pop a small hole in the end of it, so that you will not build any pressure when you weld up your last quarter of it.  9)  Weld.  (you can check my webpage for a nice jig that will help you keep from making the pipe look like a banana when you're done.)10) Reseal the nipple and go to the next one.In short, I always vent from the nipple I'm welding.  That guarantees that I'm getting flow up inside it.  Remember that argon is heavier than air.
Reply:Originally Posted by Engloid4)  Put aluminum foil on your nipples.
Reply:Originally Posted by sn0border88 What does that have to do with welding?
Reply:I was joking, sounded like you were suggesting for him to put tin foil on HIS nipples. Have we all gone mad?
Reply:Originally Posted by sn0border88I was joking, sounded like you were suggesting for him to put tin foil on HIS nipples.
Reply:only if your into those kind of things.  Have we all gone mad?