[justa-hairyape]

From the Oil Drum article linked above.

The 16-inch pipe has a burst rating approximately equal to the current shut-in pressure of 6,900 psi (80% of rating), but the 22-inch pipe does not meet this standard.

[Marine_Uncle]

Don't sound good. But then the pressure has stabilized, and only creeps up well below what originally would have been expected. Perhaps the idea of doing the top kill first was to verify the soundness of the main well bore. If one successfully plugs it then the inner liner as well at the outer casings where not damaged. If one pours extremely large amount of drilling oil well beyond calculated cubic volume of the tube system, then there are cracks in the pipe down below leading to oil/gas pockets or worse.
I have to get ready for work shortly. So I will be out of things until later evening hours.