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Tried 100 percent CO2 shielding on a root pass in Amarillo, and the inspector caught what I did not
Working a tank job outside Amarillo last month, I figured I would run straight CO2 on a 2 inch root pass to save time on the stop and start cleanup. Third weld in, the puddle went cold on me, and the bead looked fine from the outside. Inspector ran dye penetrant and found lack of fusion about 3/8 inch long, so I cut the whole section out and started over. Lost about 4 hours plus the rod I wasted, and cost myself a full redo with 75/25 mix and a preheat I should have done anyway. What got me was how clean the cap looked, nothing hinted at the trouble underneath. Anyone else run into a shielding mix that fooled you on the surface but let you down on the root?
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fisher.jessica4d ago
I remember reading a writeup from a pipeline welder about running straight CO2 on roots and he said the same thing, the bead looks great until you cut it. Something about how CO2 runs hotter and gives you that nice wet look on top but the penetration at the root can be shallow if your travel speed creeps up. He mentioned the freeze line moves faster than you expect, so you get that cold lap before you even feel it in the puddle. Surprised the cap looked that clean though, usually you see a little something on the toes.
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