First off, good thing you spotted the weld now, rather than later, or never. The weld though looks pretty good, I mean, that's some solid skill at work there. I'd wager it's fixing a crack and doing a good job of it, but, if it's fixing rust or something then I'd want to check it out from the inside when you change the BB spindle and see what's going on. You can always chemically strip that area since you're just removing the black, not the original paint, no real loss there.