Rolled, milled, or machined surface finishes are available. New drill collar connections are manufactured to API Specification 7. Thread roots are cold-rolled on API and H-90 connections, increasing fatigue resistance. Slip and elevator recesses are designed to cut drill collar handling time by eliminating lift subs and safety clamps. Cold-rolling the radii at the upper shoulder of each recess also extends the fatigue life of the drill collar.
An API stress-relief groove on the pin and an API bore back box are available on request, and are recommended for drill collars and all downhole tools where fatigue can occur as a result of bending. Drill collar hardbanding is the most effective way to retard OD wear.
DRILCO drill collar applications
- Provision of drilling weight is the most universal application of drill collars.
- Hole size integrity results from proper drill collar sizing, enabling the desired casing size to be run to bottom. The drill collar accomplishes this integrity by limiting the lateral movement of the drill bit in the absence of larger-diameter drilling tools.
- Drill collar stiffness is important to drill and maintain a straight borehole.
- Spiral drill collars reduce the area of contact between the drill collar and the hole wall, a helpful feature when differential sticking is a problem.