Gilly,

I did ask him about your theories and he said that they were possible. He added that it might be vibration too. He really doesn't do much in the way fixing convertors. The exhaust systems he's made were for race cars and hot rod's and they don't have convertors or in lots of cases mufflers at all. He basically does custom welding not automotive related at all expect for the race cars and hot rods.

He did say that most all vehicle are subject to vibration and water and they don't have cracked convertors; of course we are aware of this fact.

He went on to explain that with these convertors being welded by machine that you can get less than ideal results because if anything goes wrong as far as the welding process or the preparation (like some kind of contamination) prior to welding there may be no human to intervene.

Bottom line he really could not tell from my convertor why it failed.
I sure hope this don't happen to that many people because if they replace the convertor, out of warranty, and the other stuff attached to it and don't do it themselves it will be quite costly.