Patent ID: 8240371

Claim:
An apparatus for use in running a string of casing into a well, comprising: a telescoping sub having a longitudinal axis and tubular first and second members that are axially and telescopingly movable relative to each other and rotatable in unison with each other; the first and second members adapted to be connected between a top drive assembly and a casing gripping device for transmitting rotation from the top drive-assembly to the casing gripping device; a piston on the second member reciprocally carried within a chamber defined by the first member; the chamber containing a pressurized fluid that acts against the piston to bias the first and second members toward the contracted position, such that while the top drive assembly is supporting the weight of the casing gripping device, the first and second members can move toward an extended position as the top drive assembly rotates a casing joint gripped by the casing gripping device into threaded engagement with a casing string; a torque measuring gage mounted on the sub for measuring torque applied by the ton drive assembly to make up the casing joint with the casing string; a spline cavity within the first member; a spline head on the second member that is carried within the spline cavity, the spline cavity and the spline head having mating splines; the spline head being axially movable in the spline cavity between upper and lower stops, allowing the telescoping movement of the first and second members; a sleeve axially spaced from the spline cavity, mounted to the first member and enclosing the chamber; an anti-rotation member that prevents rotation of the sleeve with the first and second members; the piston being reciprocally carried within the sleeve; and an external source of pressurized fluid connected by a line to a port within the sleeve during operation of the apparatus for supplying the pressurized fluid to the chamber.