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Welding Pipe with smooth seams on the inside ?

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Welding Pipe with smooth seams on the inside ?

Postby mikejwoodnz » Wed Jan 25, 2012 6:01 pm

I know nothing about welding, as it is not in my skill set, but I have just read this :

"You may know this already,but make sure you weld the joints from the inside out so you have a sanitary weld on the inside of your pipe.Do this by taping the gas to the top of the tubing and tig the weld.The gas will come out the joint to be welded and produce a smooth seam on the inside of the pipe."

comments please :idea:
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Re: Welding Pipe with smooth seams on the inside ?

Postby Dan P. » Wed Jan 25, 2012 6:07 pm

I think he is talking about filling the pipe with gas (inert), so that the interior of the pipe does not suffer from porosity (bubbles).
Why anyone would worry about sanitation in a system whose basic nature is to act as conduit for high proof alcohol/vapour I don't know.
As it happens, filling your pipe with argon is just one of a number of varying requirements you need to meet to get a smooth inside seam on a pipe weld.
I wouldn't worry about it, personally.
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Re: Welding Pipe with smooth seams on the inside ?

Postby Dan P. » Wed Jan 25, 2012 6:12 pm

On a second reading, he may be talking about actually welding from the inside (of what?). The situation being presented is not clear.
If you can reach "inside", go for it. Again, I wouldn't bust my sack over it, we are talking about distilling here, not processing unpasteurized milk
or anything.
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Re: Welding Pipe with smooth seams on the inside ?

Postby fastill » Wed Jan 25, 2012 6:15 pm

I worked as a pipefitter when I was much younger and one of the welders I was paired up with could weld from the outside and when he was done, it looked like he ran the bead on the inside as well. Good tapered joints, keep the gap the same thickness as the filler rod and watch him work his magic. I think the gap would allow the shielding gas inside the pipe enough to keep things clean. Hard to tape off the end of a 18" piece of stainless.
I have a tig welder and have been using it for about 6 years and I am not nearly as good as this guy was.
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Re: Welding Pipe with smooth seams on the inside ?

Postby mikejwoodnz » Wed Jan 25, 2012 6:31 pm

It was a comment by this guy (not the author of the page) "trushing1" which seemed make sense

on this page (which I wouldn't recommend to anybody). http://www.instructables.com/id/Build-a-Whisky-Still/ :cry:
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Re: Welding Pipe with smooth seams on the inside ?

Postby SuburbanStiller » Wed Jan 25, 2012 11:11 pm

If you're going to do it, might as well do it as best you can. Nobody else will ever know unless you break your kit down and show them. But it's always nice to work with first rate gear.
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Re: Welding Pipe with smooth seams on the inside ?

Postby olcarguy » Thu Jan 26, 2012 9:50 am

When welding a pipe, the oxygen on the inside causes oxidation to occur. By putting inert gas inside you prevent the corrosion, there by producing a better looking weld. You can plug the pipe ends with duct tape, keeping a steady flow of gas will take care of any leaking.....
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Re: Welding Pipe with smooth seams on the inside ?

Postby Seb » Sat Feb 18, 2012 4:02 pm

I'm a pipe fitter by trade, Yes when working on metal's with nickel content to prevent sugaring and porosity on the inside bead you need to elemental the oxygen with the same process gas your working with on your torch, typicality argon. It dose make for a clean looking weld but you still have a bead with texture on it.
True brewery piping, dairy piping any food process piping is sanded or polished on the inside to make the weld bead smooth and texture free to stop any things that could get stuck on the bead and be a source of infection.

There is flux that you can paint on the inside called solar flux that prevents sugaring. But you do not want to get this stuff near any thing that has to do with human consumption its a carcinogen, or any process that the glass which the flux turns in to could damage.
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Re: Welding Pipe with smooth seams on the inside ?

Postby Marshwalker » Sat Jun 02, 2012 9:53 pm

I never understood the science behind it but have done this very technique when building gas and oil tanks. A welder I worked with back in the day told me to run Argon in the tanks when welding the lids and/or bottoms because it would ensure a better weld...so I did it then and still do it now...seems to work!
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Re: Welding Pipe with smooth seams on the inside ?

Postby Marshwalker » Sat Jun 02, 2012 9:55 pm

Don't know what happened there...?? Sorry :doh:
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Re: Welding Pipe with smooth seams on the inside ?

Postby Bayou-Ruler » Sat Jun 02, 2012 10:59 pm

good old double post..lol :doh:
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Re: Welding Pipe with smooth seams on the inside ?

Postby olcarguy » Mon Jun 04, 2012 5:01 am

just a case of sticky finger...... :D
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Re: Welding Pipe with smooth seams on the inside ?

Postby Spud1700 » Wed Jun 06, 2012 7:09 am

I would fuse, no penetration into the tube, 1.2mm - 1.4 mm of penetration will give plenty of strength. numerous ways of getting a good result.

Edit: discolouration will clean up with sandpaper or you could pickle it but there is no need.
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Re: Welding Pipe with smooth seams on the inside ?

Postby hambwild » Mon Jan 06, 2014 7:29 pm

fastill wrote:I worked as a pipefitter when I was much younger and one of the welders I was paired up with could weld from the outside and when he was done, it looked like he ran the bead on the inside as well. Good tapered joints, keep the gap the same thickness as the filler rod and watch him work his magic. I think the gap would allow the shielding gas inside the pipe enough to keep things clean. Hard to tape off the end of a 18" piece of stainless.
I have a tig welder and have been using it for about 6 years and I am not nearly as good as this guy was.


You would be correct sir! as an AWS certified pipe welder {6in sch80 6g position} proper fitting coupled with correct technique and temp settings on your machine should produce a smooth "root pass" that looks as if you made a weld from the inside. this is done by fusing both sidewalls with conjunction of the filler metal. if done properly, it should pass the cotton ball test.

under normal circumstances purging the base metal with an inert gas {co2/argon/ect} is not necessary unless you are in an extreme environment or you are dealing with something that has had a volatile product inside of it. example: when ga/fla railway called me to weld some cracks in the fuel cell on one of their engines, I purged the tank with CO2 then did a continuous purge with CO. this was done to remove the presence of oxygen in the cell. I was providing the spark, the steel had diesel residue, but without oxygen... no boom.
there are certain circumstances when purging pipe fittings is useful, but that is normally when mig is used, and the finished product is under high stress. in some extreme cases you can purge stainless to reduce "sugaring" but more often than not, that is merely a case of the welder running his machine too hot.
hope this helped! if in doubt, practice some more!!!!!
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Re: Welding Pipe with smooth seams on the inside ?

Postby pintoshine » Mon Jan 06, 2014 9:45 pm

When welding things onto plate, I use a copper backing plate to keep the ox from the weld. Careful amperage control is the most important part though. I walk the cup around a 5 mm screw when making mounts for my displays on 14 gauge and have no issue other than removing heat discoloration. So the key things here are. Careful current control, careful current placement, and a backing of copper or argon. Duct tape is a cap of choice when making caps for flooding pipes with argon.
I've done it up to 3 inches with no problem.
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