Re: TIG welding of Large dia SS Pipe

The Hypodermic Needle Trick

Start with a trip to the local veterinarian and get the biggest needles he's got
Go to the hardware store and devise a tubing manifold to feed Argon through the needles.
After you have your contraption damn up the piping as normal with cardboard, film, paper, etc.
Insert the needles through the root opening, (the root may need to be widened in spots to allow for the needles.) and tape the joint. As the welder progresses his helper pulls the tape and removes the needles just in front of the puddle.
When you get to the last needle draw it up so it is just inside the pipe and run the bead over the top of it. The needles are 316 so they flow right in. What is left of the needle is incorporated in to the root or if too much is left inside the pipe it melts and falls loose in the pipe.

If any needle is left inside the pipe a start up screen will normally catch it. I would not however recommend this procedure on sanitary tubing except as a last resort.

I have also heard of damning up the pipe and inserting dry ice before the ends are mated together. I have not however tried it. The CO2 should keep out the oxygen but would probably make for a poor arc. If any one has tried it let me know how it works.

Thanks
Austin M. Finke
Lion Heart Welding
620.275.8058

On Friday, July 6, 2001, at 12:34 AM, A. M. Finke wrote:

> What makes the areas hard to purge?
> Have you tried the hypodermic needle trick?
> On Sunday, July 1, 2001, at 03:44 AM, Tin Soe Thein wrote:
>
> > We are using KOBELCO TGX-308L or TGX-316L filler rod for large
> diameter
> > SS
> > pipe where difficult to purge. This fillers are flux cored filler rod
> > which
> > produce slag to protect reverse side bead from oxidation by the
> > atmosphere.
> >
> > Don't forget, slags will be inside the pipe.
> >
> > Tin Soe Thein
> >
> >
> > ----- Original Message -----
> > From: "Paul Bowers" <pbowers@pipingdesign.com>
> > To: <PipingDesign@yahoogroups.com>
> > Sent: Thursday, June 28, 2001 7:19 PM
> > Subject: Re: [PipingDesign] TIG welding of Large dia SS Pipe
> >
> >
> > > For thin-wall (Sch. 10 and under) cryogenic service, we used to
> > > reinforce the piping at intervals inside the cold boxes to help
> > > correct out-of-roundness.
> > >
> > > Slip-ons were always used, since greater mass during cooldown was
> > > a startup heat-retaining problem.
> > >
> > > This probably doesn't help for the specific problem and it's a bit
> > > more complicated than that, but at least it's a reference point.
> > >
> > > Paul
> > >
> > >
> > >
> > > > this is fine Geoff. But please note the the lenght of those
> > > bladder are
> > > > quite long for large bore piping (SOCAP from Italy). Beside u
> > > stiil have to
> > > > find a way to insert the hose near the weld area pass the
> > > ballon.
> > > >
> > > > We've acutally tried quite a number of technique. We built a
> > > cage, inserted
> > > > the welder to perfrom back weld , then from the outside we
> > > ground/clean the
> > > > root then do the hot pass. If we're really in hurry, we put two
> > > welders -
> > > > one inside and one from the outside. Weld are perform almost
> > > simultaneouely
> > > > with the welders from the inside slightly ahead.
> > > > The 3rd method is to install the hat or dam fabricated out of
> > > carboard and
> > > > fitted from the inside around te weld joint. we then tape a
> > > masking on the
> > > > outside and perform the weld. The last is the use of dissolving
> > > paper to
> > > > create a dam around the pipe.
> > > > The first 2 tecnique actually eliminated the need for backing
> > > gas.- its the
> > > > oxiadation that you worry about with this type of welding.
> > >
> > >
> > >
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[Non-text portions of this message have been removed] Received on Sat Jul 07 00:14:00 2001