[quote KSMountain]
Folks there who claim to be knowledgable say the bolts were tightened to about 13000 ft-lbs on land, and that now underwater, if the lubrication has degraded (which it likely has), you typically need triple the torque to get ’em off.
[/quote]
They are not torqued to 13,000ft-lbs. This could be the face pressure on the joint(in lb/sqin), not the torque of the bolts. You are off by two decimal positions. Try 130ft-lbs to 360ft-lbs. 130ft/lbs is about the same torque used on the head bolts of high performance engines with moderate ‘boost’ (superchargers/turbo chargers). If you are using a bolt with a diameter of 1 inch, and torque it to 130 ft-lbs, your clamping force is about 7,800 lbs (for only 1 bolt). Multiply this by the number of bolts.
http://www.engineersedge.com/calculators/torque_calc.htm
For face pressure, divide by surface area of the flange. Note that the above calc uses inch-lbs, to get ft-lbs to inch-lbs, multiply by 12.

A torque of 13,000lb-ft would break the bolts.

There are two real problems:
1) Removing the bolts and putting the new ones in (torquing). The problem with getting them off is that you don’t have anything to ‘push against’ when torquing the bolts. That said, an impact wrench works wonders under those conditions.
2) Putting a new valve on top with all of that flow going out of the end. That said, there is a trick to doing that. The trick can be seen in the John Wayne movie “Hellfighters”, not coincidentally a movie about people who bring out of control oil wells into control.

It does make me wonder why BP has not tried this method. If the flow is high enough to cause problems when trying to rotate the upper value assembly into position, there is a trick for that involving cutting part of the flange out to reduce pressure and using a second clamp-on flange above that one.

[quote KSMountain]
One person made the point though that one should not underestimate the flow. The flow is like 12000 PSI! Crazy. So you saw off a bolt or two, then you got these totally crazy oil jets hitting the robot, it’s gonna be kinda hard to get the other bolts out.
[/quote]

Try 2000 to 5000 psi in static pressure. Considering that the end above the bolts is ‘open’, you don’t have that kind of static pressure. A closed valve would have to withstand this type of pressure, but an open end pipe has almost no pressure on it. 5000psi on an 8inch internal diameter pipe translates into about 251327lbs of force trying to lift the valve off of the flange. What will happen though is that once the cut end gets loose, it will head off in an unknown direction due to the flow rate.

The fact that the pipe had a crimp in it that didn’t straighten when the far end was cut indicates to me that they are no-where near 5000psi. That type of pressure and the resulting flow would have instantly straightened the pipe up. It would have also likely torn the crimped and partially torn part off because the crimp and tear weakened the pipe at that point.