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Stubborn Porosity Problem with Pipe End Face Weld Build-up

Stubborn Porosity Problem with Pipe End Face Weld Build-up

Stubborn Porosity Problem with Pipe End Face Weld Build-up

(OP)
The sketch below shows the configuration that is giving us porosity problems. All the usual suspects have been investigated and ruled out. GTAW welding is done orbitally, using argon shield gas.

I suspect the problem results from the absence of a shielding gas 'backstop' that the base metal provides in typical welding configurations.
I would appreciate any suggestions for cup size, gas lenses, tungsten stick-out, or some kind of barrier that could help contain the argon and prevent air entrainment.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

RE: Stubborn Porosity Problem with Pipe End Face Weld Build-up

Have you tried putting a soft seal plug into the pipe just beyond the hottest area?
That might trap enough Ar, or at least prevent the 'chimney effect' and give you chance at a better weld.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: Stubborn Porosity Problem with Pipe End Face Weld Build-up

(OP)
Thanks EdS,

Yes I'm considering such a barrier scheme. I won't see the actual set-up until tomorrow, when I will learn what might be possible access-wise.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

RE: Stubborn Porosity Problem with Pipe End Face Weld Build-up

Porosity coming from lack of gas shielding or from impurities?

If the former, a weed burner with steel gauze (to make it a giant gas lense) fed by an argon bottle might help...

RE: Stubborn Porosity Problem with Pipe End Face Weld Build-up

(OP)
I can't help but think the high density of Argon (combined with the geometry) is the culprit.

Seeing what happens to the gas would help me enormously. Does anyone know what kind of smoke they use to demonstrate gas flow through welding nozzles?

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

RE: Stubborn Porosity Problem with Pipe End Face Weld Build-up

I would tack weld a metal backing strip to the I.D. and extend it some distance beyond the root face then make your weld against the backing strip and root face. When complete, grind off backing strip to conform with I.D. requirements. If some areas are shallow hand weld to conformity.

RE: Stubborn Porosity Problem with Pipe End Face Weld Build-up

(OP)
matschka,
That is in fact now being done, and they are having better success.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

RE: Stubborn Porosity Problem with Pipe End Face Weld Build-up

Quote (ironic metallurgist)

Does anyone know what kind of smoke they use to demonstrate gas flow through welding nozzles?
I was hoping for someone to reply as this also is of interest to me, however this didn't work out...

Just for your information, I have used a commercial smoke machine (like they use at fairs and night clubs, using bottles of "liquid smoke"), in combination with a small air compressor without pressure vessel, set at minimum psi (something like 20-25 psi if I remember correctly). If you remove the air filter at the compressor intake, this works enough to make the air flow visible (however a lot of the smoke disappears during the compression cycle).

RE: Stubborn Porosity Problem with Pipe End Face Weld Build-up

(OP)
kingnero,
I am told that youtube knows, but I haven't searched there yet. Apparently they add the smoke component to standard argon bottles.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

RE: Stubborn Porosity Problem with Pipe End Face Weld Build-up

I think EdStainless's original post may be the way to go - remove the "chimney" effect.
What about a round ID insert plate just inside the end of pipe held by a couple of small tack welds ?

RE: Stubborn Porosity Problem with Pipe End Face Weld Build-up

(OP)
It now looks like the problem is contamination of the shielding gas upstream.
Thanks to all.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

RE: Stubborn Porosity Problem with Pipe End Face Weld Build-up

How did you establish that? That's hard to diagnose correctly (and very uncommon)...
I'm asking this because I'd like to learn something, not because I doubt what you say!

RE: Stubborn Porosity Problem with Pipe End Face Weld Build-up

(OP)
To be precise, moisture was forming or entering the regulator, which has since been upgraded.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

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