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Posted by David Sherman [216.18.131.132] on Friday, September 25, 2009 at 01:26:04 :
In Reply to: Porous welds posted by David Sherman [24.32.202.83] on Thursday, September 24, 2009 at 22:52:20 :
I brazed the leaking welded up holes in the bottom till they were nice and shiny, got a nice patch of brazing about 2" in diameter all over the area (holes started out about 1/2" dia), and tried again. This time they leaked even more than before, but looking at the underside of it I discovered something. The brass had nicely wetted a number of fine cracks that went not only across my welding job, but into the base metal on the sides. The brazing didn't go all the way to the ends of those cracks and so that's what's leaking now. It's almost as if the heat of welding up the holes stretched the surrounding metal until it cracked. Either that or the surrounding metal got hot enough that it expanded and took a set in that condition, and then cracked when it cooled and shrunk. Either way, I've never seen mild steel be so temperamental about heat.
So, it looks like what I'm going to have to do is flip the tank over again, grind all the welds down until I can see every possible crack and how far it goes, and then cover them with brazing all the way to the ends. Hopefully the metal isn't so poor that the heat of brazing will make the cracks go even farther. I still can't see any cracks around the stove pipe, but I hope I'll be able to see them when I grind it.
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