[BITList] The Associated Press: APINVESTIGATION:Blowoutpreventers known to fail

[HUGH]

Ron,

It's a long time since last I saw one, but a Blowout Preventer sits on the sea bottom, having been clawed (literally) from its den by hydraulic transporter and lowered through the moonpool (or so it was on the drillships I had experience of).  If memory serves me right, the casing (about 30" diameter) is attached to the BOP and both are lowered, sections of the casing being added at the drillfloor as it goes down. Everything is done through the casing and through the BOP.  In an emergency, eg, a sudden blowout of gas or whatever, the BOP can be closed, in the so doing severing everything going through it - that is what is hoped will happen.  On a non-fixed system, eg, a dynamically positioned drillship or rig, it can also be operated to sever the drill string if sea conditions, wave heights, exceed that for which the riser tensioner system was designed.  Though latched to the BOP, the casing is suspended from a set of wires going over pulleys above the drillfloor, and attached to quick response pneumatic (hydraulic?) rams.  These reel out in response to the vessel rising on a wave, and vice versa, so the load on the casing is kept substantially within limits.  I have no idea, now that I reflect on it, how the drill string is protected in such conditions.  When conditions improve they "fish" for the broken end(s).  I recall an array of specialised gadgets and tools made for that purpose. One thing about the BOP is that it is BIG.

Hope this helps.

Hugh.
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