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Hi Frank, I understand much better now what's what, that makes sense to me. Sounds like a good plan. There is also that rattle can spray from Diffutherm that Carsten uses to check weld zones for imperfections. I'm not sure what brands we have available here in the states, for that type of developer and penetrant. There might be some good options here. http://www.mxindustrial.com/ Szybowski From: ShellyDalg@aol.com Date: Sat, 31 Jan 2009 01:57:01 -0500 Subject: Re: [PSUBS-MAILIST] Pitting Rust against Voids To: personal_submersibles@psubs.org 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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