While brewing in the public parking lot of Hopman's Homebrew Supply in Waterford Michigan for National Homebrew day one of the homebrewer's brew kettles (converted sankey keg) expoded with such a bang my ears are still ringing! It is my luck that I happened to be visiting his brewery when the bomb went off. The burner frame was destroyed and the keg tipped spilling 10 gallons of boiling wort onto the pavement. Luckily no one was burned by the wort. Here's what we know:
This keg was manufactured differently than every other keg we examined, the rolled steel lip at the top and bottom was welded solid with no holes drilled in it. No other keg was welded solid and all of them had 4 holes drilled in the keg rim. This is the rim that contacts the ground when the keg is in upright position.
The keg built up pressure in the rim until the rim exploded
We don't know what caused the explosion inside the enclosed rim - air expansion, moisture, maybe some unburned propane (not quite sealed in that case). It exploded after boil was well underway.
What we do know is it is dangerous and you should check your kegs! If there are no holes - drill some! Here's some pictures
NORM : Well I'm in a gambling mood, Sammy. I'll have a glass of whatever comes out of that tap.
SAM : Oh, Looks like beer, Norm.
NORM : Call me Mister Lucky.