Complete failure of a TIG weld...

Ignoramus8601 · 2009-12-08T03:31:38+00:00

I tried to TIG weld a 1/2" pipe nipple, to a 16 gauge sheetmetalpiece, so that the pipe nipple is perpendicular to the sheet metal. The objective was to make a little stand on which I would mount aVFD. I used about 100 amps of current, DCEN, and ER70 filler rod. The temperature in the garage was about 40F. The result was a decent looking TIG weld, nothing to brag about, butpassable. However, as soon as I stopped welding, the weld zone began to cooland started making little popping noises. After a minute or two, Iwhacked the 16 ga sheet to straghten it, as it was warped a little. After just one or two whacks, the sheetmetal piece FELL OFF, basicallycleanly, with the entire weld remaining attached to the pipe nipple. I was completely shocked. After looking at the failure area, I had animpression that some cracks developed UNDER the weld and a part of thesheetmetal stuck to the weld, so the weld, sort of, tore off a part ofthis sheetmetal piece, as if it cracked in the middle.I feel kind of fortunate that this was never meant to be a structuralpiece, but I get some jitters just thinking about what would happen ifit was. Would anyone have any clue as to what it could have been. i

Dec 08, 2009 27 Replies

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Jim Wilkins 16 years ago

I posted a simple demo of hardness vs elastic modulus once that involved bending hard and annealed bugle head screws held by their points in a vise. The difference was very obvious between the two, but without an identical reference it's difficult to compare. In this case you could cut three pieces, harden two and anneal one of those, then bend all three. The annealed one represents what you can do to fix it after welding.

jsw

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Ed Huntress 16 years ago

Good to see you here, Ken. You might be interested in this brief piece on hot-shortness. It's all a little fuzzy:

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fran...123 16 years ago

would you consider doing exactly the same thing an inch or so away with some of your tig compatible bronze and tell us if you get the same failure? Seems there was a thread with that in it just lately around here.

not everything is weld able. There are ways to make sparks off metals and examine what you get but sometimes just the four and a half inch grinder and a piece of known structural mild steel as a control can give you an idea if what you have isn't mild steel. The first guy also told you how heat it quench it bend it.

Fran

not cross posted

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F Murtz 16 years ago

The fact that the weld stayed with the heavy piece suggests that the nipple was hot enough.Was the sheet on a steel bench that would take the heat from the sheet. Barring that it could be two dissimilar metals.

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Ernie Leimkuhler 16 years ago

Was the nipple cast or machined? Most pipe is made overseas with very poor quality control as to metallurgy. As long as the pipe holds pressure, it passes.

My suspicion is the pipe was bad steel.

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Ignoramus20864 16 years ago

machined (cut threads).

Maybe, but the weld clung to pipe very well, and broke off near where it made contact with the sheet metal.

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Bruce L. Bergman 16 years ago

Heck, just the 40-F room temperature could have been a major contributor to the failure, especially if there was a breeze. When in doubt, preheat the workpiece before welding, and let it anneal and cool slowly after...

Iggy: Got a small blacksmiths's forge? A propane weed-burner and a stack of firebricks is all you need for a makeshift forge. Two layers for the floor and base, two walls, and a little arch over the center, aim the weed burner in one end and stick your work in the other with fireplace tongs. It will concentrate the heat nicely.

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