Torque reduction assembly

Abstract

A torque reduction assembly for a drill string has a mandrel for connecting two sections of drill pipe, the mandrel comprising a first annular shoulder and a plurality of radial retention slots arranged circumferentially around an outer surface of the mandrel, including a first retention slot and a second retention slot; an outer sleeve for rotatably mounting on the mandrel; a retaining ring for retaining the outer sleeve between the retaining ring and the first annular shoulder, the retaining ring comprising a first aperture and a circumferential groove about an inner surface of the retaining ring, the first aperture aligned with the circumferential groove, the retaining ring being rotatable about the mandrel so as to progressively align the first aperture with each retention slot; a first retention element for locating in the first retention slot via the first aperture to axially fix the retaining ring relative to the mandrel such that the retaining ring is still rotatable about the mandrel; and a second retention element for locating in the second retention slot via the first aperture to rotationally fix the retaining ring relative to the mandrel.

1 . A torque reduction assembly for a drill string, the torque reduction assembly comprising:
 a mandrel for connecting two sections of drill pipe, the mandrel comprising a first annular shoulder and a plurality of radial retention slots arranged circumferentially around an outer surface of the mandrel, including a first retention slot and a second retention slot;   an outer sleeve for rotatably mounting on the mandrel;   a retaining ring for retaining the outer sleeve between the retaining ring and the first annular shoulder, the retaining ring comprising a first aperture and a circumferential groove about an inner surface of the retaining ring, the first aperture aligned with the circumferential groove, the retaining ring being rotatable about the mandrel so as to progressively align the first aperture with each retention slot;   a first retention element for locating in the first retention slot via the first aperture to axially fix the retaining ring relative to the mandrel such that the retaining ring is still rotatable about the mandrel; and   a second retention element for locating in the second retention slot via the first aperture to rotationally fix the retaining ring relative to the mandrel.   
     
     
         2 . The torque reduction assembly of  claim 1 , wherein the first retention element is shorter than the second retention element. 
     
     
         3 . The torque reduction assembly of  claim 2 , wherein the first retention slot is the same depth as the second retention slot. 
     
     
         4 . The torque reduction assembly of  claim 3 , wherein the first retention slot is identical to the second retention slot. 
     
     
         5 . The torque reduction assembly of  claim 1 , wherein the first retention element is the same length as the second retention element. 
     
     
         6 . The torque reduction assembly of  claim 1 , wherein the first retention element is identical to the second retention element. 
     
     
         7 . The torque reduction assembly of  claim 5 , wherein the first retention slot is deeper than the second retention slot. 
     
     
         8 . The torque reduction assembly of  claim 1 , wherein:
 the plurality of radial retention slots further comprises a plurality of first retention slots; and   the torque reduction assembly further comprises a plurality of first retention elements, each first retention element for locating in a respective first retention slot via the first aperture to axially fix the retaining ring relative to the mandrel such that the retaining ring is still rotatable about the mandrel.   
     
     
         9 . The torque reduction assembly of  claim 1 , wherein:
 the plurality of radial retention slots further comprises a plurality of second retention slots;   the retaining ring further comprises a second aperture, the second aperture aligned with the circumferential groove, the retaining ring being rotatable about the mandrel so as to align the first aperture and the second aperture with respective second retention slots simultaneously; and   the torque reduction assembly further comprises a plurality of second retention elements, each second retention element for locating in a respective second retention slot via the first aperture and the second aperture to rotationally fix the retaining ring relative to the mandrel.   
     
     
         10 . The torque reduction assembly of  claim 1 , wherein the plurality of radial retention slots are arranged with N-fold rotational symmetry, where N is the number of retention slots. 
     
     
         11 . The torque reduction assembly of  claim 1 , further comprising a bearing sleeve for mounting on the mandrel between the mandrel and the outer sleeve. 
     
     
         12 . The torque reduction assembly of  claim 11 , wherein the bearing sleeve further comprises a second annular shoulder, wherein the second annular shoulder is positionable between the first annular shoulder and the outer sleeve. 
     
     
         13 . The torque reduction assembly of  claim 11 , wherein the mandrel comprises an external thread and the bearing sleeve comprises an internal thread for screwing onto the external thread to mount the bearing sleeve on the mandrel. 
     
     
         14 . A method of assembling a torque reduction assembly comprising the steps of:
 (i) providing a mandrel for connecting two sections of drill pipe, the mandrel comprising a first annular shoulder and a plurality of radial retention slots arranged circumferentially around an outer surface of the mandrel, including a first retention slot and a second retention slot;   (ii) sliding an outer sleeve on the mandrel;   (iii) sliding a retaining ring on the mandrel such that the outer sleeve is between the first annular shoulder and the retaining ring, the retaining ring comprising a first aperture and a circumferential groove about an inner surface of the retaining ring, the first aperture aligned with the circumferential groove, the retaining ring being rotatable about the mandrel so as to progressively align the first aperture with each retention slot;   (iv) rotating the retaining ring to align the first aperture with the first retention slot;   (v) inserting a first retention element into the first retention slot via the first aperture to axially fix the retaining ring relative to the mandrel such that the retaining ring is still rotatable about the mandrel;   (vi) rotating the retaining ring to align the first aperture with the second retention slot; and   (vii) inserting a second retention element into the second retention slot via the first aperture to rotationally fix the retaining ring relative to the mandrel.   
     
     
         15 . The method of  claim 14 , wherein the first retention element is shorter than the second retention element. 
     
     
         16 . The method of  claim 15 , wherein the first retention slot is the same depth as the second retention slot. 
     
     
         17 . The method of  claim 16 , wherein the first retention slot is identical to the second retention slot. 
     
     
         18 . The method of  claim 14 , wherein the first retention element is the same length as the second retention element. 
     
     
         19 . The method of  claim 18 , wherein the first retention element is identical to the second retention element. 
     
     
         20 . The method of  claim 18 , wherein the first retention slot is deeper than the second retention slot. 
     
     
         21 . The method of  claim 14 , wherein:
 the plurality of radial retention slots further comprises a plurality of first retention slots; and   the method further comprises between steps (v) and (vi) the steps of:   (v-1) rotating the retaining ring to align the first aperture with a further first retention slot;   (v-2) inserting a further first retention element into the further first retention slot via the first aperture to axially fix the retaining ring relative to the mandrel such that the retaining ring is still rotatable about the mandrel.   
     
     
         22 . The method of  claim 21 , wherein steps (v-1) and (v-2) are repeated until a first retention element is inserted into each first retention slot, before proceeding to step (vi). 
     
     
         23 . The method of  claim 14 , further comprising a step of sliding a bearing sleeve on the mandrel between steps (i) and (ii), wherein step (ii) further comprises sliding the outer sleeve over the bearing sleeve such that the bearing sleeve is between the mandrel and the outer sleeve. 
     
     
         24 . The method of  claim 14 , further comprising the step of:
 (viii) welding the second retention element to the retaining ring.