Patent ID: 8167340

Claim:
A length of drill stem used in horizontal directional drilling operations, the length of drill stem comprising: a first pair of joined elongate tubular members which terminate in first and second opposing outer ends, the elongate tubular members each having an internal bore and a selectively sized external diameter, the elongate tubular members being joined together by a pin and box threaded connection located between the opposing outer ends thereof; wherein at least a selected end of one of the elongate tubular members has a threaded pipe coupling which connects the selected end of the one elongate tubular member to a further tubular member used to make up the length of drill stem, the further tubular member having an internal bore and an external diameter which is less than the external diameter of the first pair of elongate tubular members so that, upon connection of the further tubular member to the first pair of elongate tubular members, the external diameter of the first pair of elongate tubular members forms an upset region in the pipe, the upset region containing the pin and box threaded connection; and wherein the threaded pipe coupling comprises an internally threaded box end on the selected end of the one elongate tubular member which mates with an externally threaded pin end on the further tubular member, wherein the pin end terminates in an exposed pin face, and wherein an internal stiffener ring is received within the internal bore of the pin end and which underlies and extends along a portion of the length thereof, the stiffener ring having an innermost extent terminating in an exposed end which is received upon an internal shoulder provided in the internally threaded box end, the stiffener ring also having an external shoulder formed at the innermost extent thereof which traps the pin face between the ring exterior and the box threaded interior; wherein the exposed end of the internal stiffener ring forms an obtuse angle α with respect to a centerline of the connection and of the stiffener ring, the internal shoulder provided in the internally threaded box end being tapered at a complementary angle to the angle of the stiffener ring exposed end, and wherein the stiffener ring external shoulder which traps the pin face slopes at an acute angle β with respect to the centerline of the connection and of the stiffener ring, the pin face being sloped at a complementary angle so as to contact and mate with the external shoulder of the stiffener ring; whereby, upon make up of the drill stem, and initial contact is made between the pin exposed face and the external shoulder of the stiffener ring, the make up forces tend to force the pin nose radially in the direction of the internal diameter of the stiffener ring thereby trapping the pin and stiffening the further tubular member, rather than allowing the pin nose to disengage from the internally threaded box end of the coupling or climb the shoulder of the ring.