Carbonation in pressure barrel Is there a reason why yeast sugar and water will not create enough pressure to explode a pressure barrel With enough sugar will the yeast create pressure indefinitely?
Actually, this does happen - but, perhaps 'explode' is a bit of a dramatic term to use... 'Spring a leak' is more like it; because the building pressure would pop the seal of the barrel in order to off-gas.

Check out this thread from the Homebrewing beta:
Flat beer after priming in a pressure barrel


  That's probably the main culprit (CO2 leak).


Also, this brewer describes the exact same scenario occurring during a couple of his brews due to a specific yeast:

Pressure Barrel Blues