Ram and annular BOPs: what each one seals, and the spares that wear

A blowout preventer has one job — to close the well when the well will not stay closed by itself — and it does that job in two different ways. The annular preventer seals around almost anything; the ram preventers seal around a particular thing, or cut it, and hold more firmly. A stack is built from both, and the spares that keep it ready are mostly rubber.

/01The annular preventer.

An annular BOP contains a doughnut-shaped elastomer packing element reinforced with steel inserts. Hydraulic pressure drives a piston that squeezes the element inwards until it seals around whatever is in the bore — drill pipe, a tool joint, a casing string or a kelly — which is why it is usually the first preventer closed on a kick. Our annulars are listed in the GK style at 11" and 13-5/8", 5,000 and 10,000 psi, and in the GX style at 18-3/4" and 10,000 psi for subsea stacks, all for sour service.

/02Ram preventers and ram types.

Ram BOPs close two steel ram blocks from opposite sides of the bore, each faced with an elastomer packer and top seal. They seal more firmly than an annular element, and pipe rams can hang off the drill string, but each pair seals only what it was made for. Bodies house one or more ram cavities: our listings run from double-cavity U-style preventers at 11" and 13-5/8" (5,000 and 10,000 psi), a UII-style 13-5/8" at 15,000 psi with HPHT trim to 350 °F, and T-81-style 7-1/16" workover preventers at 3,000 and 5,000 psi, to a triple-cavity 18-3/4" 15,000 psi subsea preventer and quadruple snubbing and coiled-tubing stacks.

/03The spares that wear.

The parts that are replaced are the elastomers and the joint hardware. Annular packing elements are listed in GK and spherical styles at 13-5/8", in the GK style at 11", and in the GX style at 18-3/4" for subsea, all in HNBR; ram redress kits cover one cavity, and bonnet seal kits the doors of a U-style preventer. Each nipple-up needs new ring gaskets and the right studs and nuts — for sour service, B7M studs and 2HM nuts — and a test plug lets the stack be pressure tested against the wellhead bowl. Between the stack and the wellhead sit drilling spools, double studded adapters and adapter flanges — ours are a 13-5/8" 10K drilling spool, a 13-5/8" × 11" 10K double studded adapter and an 11" × 7-1/16" 10K crossover, all for sour service. Control units have their own soft goods: our Koomey-style five-year kit covers seals, diaphragms, bladders and pilot hoses, to API 16D.

/04Matching spares to the stack.

Every spare is specific to the preventer design, bore and pressure: a 13-5/8" 10,000 psi U-style ram block will not fit a 5,000 psi body of another design. Order by preventer style, bore, pressure, service and — for pipe rams — the pipe size, and quote the serial or assembly number where it is available. Flanged connections take BX rings at these pressures, covered in R, RX and BX ring joint gaskets, and the control lines in BOP control hose fire resistance.