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Re: [PSUBS-MAILIST] Pitting Rust against Voids



Hi Brent. Blasting down to clean metal is good, but seeing some of the weld pictures tells me that the welder was in a big hurry, not "filling in behind" as he went ( leaving unfilled "undercuts" )  and the spacing on the weld waves is so far apart there's a good chance of weld "inclusions" being present. These are things like slag, impurities, scale, and even just dirt getting into the weld puddle. With the puddle moving that fast, these bits of crap don't get a chance to "boil" to the surface while the puddle is molten. An Xray would be the ultimate tool/test but very expensive. If you blast the beads down to clean metal, put some dye on there and inspect with a magnifier. I know it's a slow process, but at least it's cheap. It won't show any deep inclusions, but will show MOST flaws and then you can take those down a little more before welding back. Often times an inclusion will barely show on the surface, like a very tiny hole, but can have a relatively large "pocket" of shit inside the bead where it got buried. Most foreign materials are off-gassing during welding, as they are incompatible with the surrounding alloys. Think of a tiny volcano, with a magma chamber and a hole to the surface. As the puddle solidifies, the metal cools and shrinks on the surface first, closing the volcano's "chimney" and trapping the inclusion below. The hole or "chimney" can be VERY small. Dye will accentuate any holes that reach the surface.
I've taught a lot of young guys how to weld, and it's a very common result when the beads look like that.
It probably isn't a big problem as George made good subs generally, but if you're going to put your life on the line, it's not that much work to check these welds. I would.
Best of luck. Frank D.
 


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