SHAFFER SL RAM BLOWOUT PREVENTERS
- Flat doors simplify ram changes. To change the rams, apply opening hydraulic pressure to move the rams to the full open position. Remove the door cap screws and swing the door open. Remove the ram from the ram shaft and replace it. It is not necessary to apply closing hydraulic pressure to move the rams inward to clear the door.
- Door seals on most sizes have a hard backing moulded into the rubber. This fabric and phenolic backing prevents extrusion and pinching at all pressures to assure long seal life.
- Internal H2S trim is standard. All major components conform to API and NACE H2S requirements.
- Maximum ram hardness Is Rc22 to insure H2S compatibility of pipe and blind rams. Shear rams have some harder components.
- Manual-lock and Poslock pistons can be interchanged on the same door by replacing the ram shaft, piston assembly and cylinder head.
- Wear rings eliminate metal-to-metal contact between the piston and cylinder to increase seal life d virtually eliminate cylinder bore wear.
- Lip type piston seals are long-wearing polyurethane with molybdenum disulfide moulded in for lifetime lubrication..
- Lip-type ram shaft seals hold the well bore pressure and the opening hydraulic pressure. No known failures of this highly reliable high pressure seal have occurred.
- Secondary ram shaft seals permit injection of plastic packing if the primary lip-type seal ever fails. Fluid dripping from the weep hole in the door indicates that the primary seal is leaking and the secondary seal should be energised.
- Rams are available which will support a 600,000 pounds when a tool joint is lowered onto the closed rams. These rams conform to H2S requirements.
- Shear rams cut drill pipe and seal in one operation. Most common weights and grades of drill pipe are sheared with less than 1,500 psi hydraulic pressure.
- Poslock operators automatically lock the rams each time they are closed. This eliminates the cost of a second hydraulic function to lock. It also simplifies emergency operation because the rams are both closed and locked just by activating the close function.
TYPE 72 SHEAR RAMS
Type 72 shear rams shear pipe and seal the well bore in one operation. They also function as blind or CSO (complete shut-off) rams for normal operations.
The hydraulic closing pressure required to shear commonly used drill pipe is below 1,500 psi for BOP’s with 14'’ pistons. These pistons are standard in all BOP’s rated at 10,000 psi working pressure and higher. On lower pressure preventers, optional 14" pistons can be supplied for shearing instead of the standard 10" pistons.
When shearing, the lower blade passes below the sharp lower edge of the upper ram block and shears the pipe. The lower section of cut pipe is accommodated in the space between the lower blade and the upper holder. The upper section of cut pipe is accommodated in the recess in the top of the lower ram block.
Closing motion of the rams continues until the ram block ends meet. Continued closing of the holders squeezes the semicircular seals upward into sealing contact with the seat in the BOP body and energises the horizontal seal. The closing motion of the upper holder pushes the horizontal seal forward and downward on top of the lower blade, resulting in a tight sealing contact. The horizontal seal has a moulded-in support plate which holds it in place when the rams are open.
Type 72 Shear Rams are covered by U.S. Patent No. 3,736,982. (Ref fig 6.1.16)