Clamp and insert for clamping drilling tubulars

Abstract

A clamp for drilling tubulars such as drill pipes includes a jaw which defines a cylindrical recess. A cylindrical insert is rotatably mounted within the recess. This insert defines a cylindrically symmetrical toothed surface positioned to grip and frictionally engage the clamped tubular, and a cylindrically convex positioning surface configured to cooperate with the cylindrical recess to hold the insert in place in the jaw. The insert is mounted in the jaw so as to rotate freely within a selected range of rotational positions in order to allow the insert to orient itself as necessary to maximize the area of contact between the insert and the clamped tubular over a range of tubular diameters. The insert is reversible in the recess so as to allow the insert to be positioned in the jaw as necessary to maximize frictional engagement with the clamped tubular in a selected direction of rotation. In one preferred embodiment, the toothed surface is provided with an array of asymmetrical teeth which grip the clamped tubular. Also, locking bars are provided on the jaw which cooperate with recesses in the ends of the insert to restrict the rotational movement of the insert within the recess. Alternate embodiments of the insert employ cylindrically convex, cylindrically concave, or planar toothed surfaces.