[marbeia]

Hello,

I'm new in this forum and this my first topic.

I'm trying to TIG weld a structural pipe with unknown composition.
It is magnetic and most probably steel or I'm suspecting cast iron, because I'm unable to get a stable puddle.
When the arc start it burn the part with black and the puddle is popping.
See some pictures here under:

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I've control my grounding and my gas flow, I can get my arc and puddle without problem on the counterpart that is structural steel.

I can see that this part was previously welded with MMA.
What alloy it can be ?
Could it be cast Iron ?

Thank you for your feedback

[ekbmuts]

It doesn't LOOK like cast iron to me. But you never know.

Did you clean the daylights out of it? No residue? No left over paint?

Wipe it with acetone?

Your welding with DC negative, right? Not AC.

I'm not an expert on grinding colors but the sparks coming off the metal when you grind it are an indicator of what it is - I.e. stainless, mild steel, etc. and its content.

Probably cj737 or tweake will have better answers. I'm sure you'll hear from them separately. Two super-helpful people.

The above is what I would do.

Good luck.

[ekbmuts]

And welcome to the forum! It's a terrific resource for learning welders and welders who want to improve their skills.

[cj737]

It looks to me that some type of coating was applied to that part and you are encountering it impregnated in the base metal. Can you zoom out a bit and show more of the total part? It’s not cast iron from the picture that I can see…

[tweake]

how big is the part?
i wonder if its free machining steel.

[marbeia]

Hi,

Thank you for your feedbacks.
I had no notification so I'm a bit late to answer.

I can try to grind a bit more, but as you can see on the picture It seems not that bad.
It is an umbrella pole and if I read the supplier datasheet it says "metal with powder-coated epoxy finish"

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I tried today with MMA cast iron positive electrode but that not better.

I've manage to weld the end of the pipe with TIG by doing a "dirty pass" (popping and messing) all around the perimeter and doing a second pass that went properly at 200A.
You can see on the picture here under

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But the inside join has a weird finish

20240629_224545.jpg (2.71 MiB) Viewed 5963 times

My problem is that on the other side of the flange I cannot do the same cause my puddle is not stabilizing.
And the stiffeners will be the same problem.
I need to weld those parts as the scheme here under

a8f2bfc4-7201-4cc9-805e-4cd77ba30515.jpg (62.75 KiB) Viewed 5963 times

[cj737]

You will never know the exact composition of that metal. Umbrella poles are not likely to be made from high carbon steel, rather they’re often junk “pot metal”. And since it’s been factory coated, fully removing it inside and out (because the wall is very thin) will be nearly impossible.

If it were me, I’d braze it with TIG and Silicon Bronze (100% argon, DCEN). If that cause further problems, I’d revert to gas welding it with bronze rods. It should be more than strong enough as long as you bevel the stiffeners/pole intersection.

[tweake]

yeah it looks like mystery metal or part of the coating process has soaked in.
for welding this is where 309 or 312 stick rods can come in handy.
however brazing it is most likely the best bet.

[marbeia]

Thanks for your feedbacks.

I've never braze with TIG and I don't really want to mess the assembly cause the umbrella is huge.

I think I have no choice than to bring it to a professional company.

[cj737]

Brazing with TIG is easy. Buy a Silicon Bronze TIG rod. Use less amperage because the filler melts from the base metal temp. Treat it like TIG steel, just don’t puddle the base metal.

As long as the filler bead is wetted in on the toes of the weld, it’s good. Brazing has been around for centuries and there still many automotive and motorcycle frames (custom made) that are fully braze welded and hold up to much greater forces than an umbrella stand. Plus, bronze is far more ductile and less prone to stress fractures.

[marbeia]

Thanks cj737,
I will try to find silicone bronze rod and have a try

[marbeia]

Hello,

I'm still waiting my Bronze Silicone rod, but by curiosity I tried again to grind the part and what I didn't pay attention earlier is that there are even no sparks while grinding, but the part is ferromagnetic.

What kind of material can it be ?