Welding Problems

[fossyant]

My mate broke two gas pipe Raleigh frames he had on his winter trainer, and he wasn't a powerful lad, quite a 'climber'. Both frames replaced under warranty.

 

[gbb]

Has anyone had the bottom bracket snap completely away from the rest of the bike? I was giving it some wellie and all of a sudden the weld around the crank/bottom bracket gave way. It was starting to feel like a bolt was coming loose, then the bike snapped in two, and the seat tube is no longer connected! It's a Claude Butler Urban 500, only a year old, and the weld joint has separated. END OF BIKE. :-( Is this common?

Not quite, but a couple more weeks perhaps ?..

That crack developed over maybe a couple weeks. I wasnt aware of it of course, but was aware of an occasional creak i couldnt track down....till i upturned the bike to fix a puncture.
I suspect a catastrophic and instant failure is unlikely in a healthy frame, its a process that starts from a small defect and slowly or quickly develops...its just down to luck whether you have any idea somethings wrong in the first place if there are no symptoms..
Minewas circa 2.5 years old..replaced under warranty, no problem.