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pipe ram between it and the annular preventer. These components are bolted or

clamped together before being integrated into the BOP stack framework. A

mandrel is installed atop the bag-type (annular) preventer for attaching the lower

riser package (fig. 6.17).

The lower, middle, and upper support frames are flanged and bolted to four

large guide posts through which guidelines are run. When the stack is landed on

the ocean floor, these stack posts fit over the posts on the PGS. Intermediate

landing pads are sometimes located on the posts at the level of the upper stack

frame to support the stack on the moonpool or spider beams while the lower riser

package is connected. Hydraulic connectors are included, top and bottom, to

connect the stack remotely to the subsea wellhead housing and to attach the lower

riser package to the stack prior to running.

The pipe rams are operated hydraulically, when necessary, to close and seal
around the drill pipe. Their normal operating pressure is 1,500 psi. Cameron pipe

rams are equipped with hydraulic wedge locks to hold the rams in closed position.
The wedge locks must be hydraulically retracted to open the pipe rams again.

Shaffer and Hydril rams have an automatic lock incorporated in their operating
mechanisms.

The hydraulically operated blind shear rams can cut through the drill pipe to

seal off the BOP stack bore in an emergency. These rams also operate at 1,500 psi

but usually have larger operating mechanisms than the pipe rams. The blind shear

rams have a locking feature that must be released to open them again.

The annular or bag-type preventer is basically a rubber cylindrical element

with bonded metal ribs. When hydraulically actuated, a large piston compresses the

rubber element, which then closes on the drill pipe, casing, or itself. The metal ribs

help it return to the fully open position. Standard operating hydraulic line pressure

for annular preventers is 1,500 psi. Some types of annular preventers must close

against the hydrostatic pressure in the riser column; therefore, a pressure-balance

system is incorporated for counteraction. Annular preventers used in offshore
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