Drilling Tools and Accessories

What the hardware does

Crossover subs join two different connections. Bit subs, box by box, take the bit. A saver sub sits under the top drive main shaft so thread wear lands on a cheap part. Lift subs and lift plugs give an elevator shoulder to collars and tools without a recess.

Kelly valves and full-opening safety valves (FOSV) are ball valves that close the drill string bore. Upper kelly valves carry a left-hand thread. An inside BOP is a one-way dart or check valve stabbed onto the string during a kick. A drill pipe float valve sits in a float sub above the bit and stops flow up the string when pumps stop.

Configurations

• Crossover subs, straight or reduced OD, in any pairing of API regular, full hole and numbered connections.
• Kelly valves and FOSVs, usually rated 10,000 or 15,000 psi (69 or 103 MPa), in standard or H2S trim.
• Inside BOPs of dart or drop-in type.
• Float valves of flapper or plunger type, solid or ported.
• Lift subs and lift plugs sized to the elevator, and bit breakers for each bit size.

Key specifications

Standards and certification

API Spec 7-1 covers drill stem subs and upper and lower kelly valves. API Spec 7-2 governs their connections. API RP 7G gives make-up torque and the bending strength ratio checks for subs between collars. For valves in sour service, the trim must be made to NACE MR0175 / ISO 15156. A certificate of conformity ties each valve to its rated pressure and trim at manufacture.

Failure modes and inspection

• Sub connections crack, gall or swell like collar connections. Ask for magnetic particle inspection of both ends, thread and shoulder gauging and the current length.
• Kelly valve balls and seats erode and score. Stem seals leak, and the operating crank seizes.
• Inside BOP darts and seats wear from flow, and their springs weaken.
• Float valve elastomers age and flappers erode.
• Lift sub shoulders wear and deform under load.

A valve is checked by a body and seat test with a low-pressure step, followed by a high-pressure step at rated working pressure with a recorded hold. Your rig's well control program sets the exact pressures and hold times. Lift subs need a load test or magnetic particle inspection of the load shoulder.

Documentation

• Certificate of conformity for each valve, with pressure rating and trim.
• The last pressure test chart, with test pressures and hold times.
• Redress records listing seal kits and parts fitted.
• Connection inspection reports and current length for each sub.
• Load rating and last load test or NDT for lift subs and plugs.

Integration with your string and rig

Build a crossover table from the bit up to the top drive and order subs to fill every gap. The FOSV on the rig floor must make up to every connection in the hole, so keep a crossover for each one with the same pressure rating. Match the saver sub to your top drive main shaft and the string connection. Size the float valve to the float sub bore. Check that the bore of a ported float valve and of every sub passes drop balls and darts.

Refurbishment and when to buy what

Subs come back into service with a recut, shoulder reface and inspection, as long as the length still allows space-out. Valves need a redress with OEM seal kits and a fresh low and high pressure test before they reach the rig floor. Unused surplus subs from a cancelled program often arrive in matched sets, which saves sourcing odd pairings one at a time. For the pipe these subs join, see Drill Pipe and Tubulars, and for the saver sub interface, Top Drives.