In virtually every industrial field it is desirable to be able to connect two threaded members with a predetermined torque.

In the oil industry tongs are used to threadedly connect and disconnect successive lengths of pipe, casing and tubing. In many instances, it is critical to apply the correct torque to the joint during make-up of the joint. It is also the practice to record the break¬ out torque which is applied to the joint when it is disconnected. The make-up and break-out torques are carefully recorded and kept as part of the history of each length of pipe, casing or tubing to assess its suitability for future service.

Torque is generally measured using a load cell. Although load cells are known which operate in both tension and compression these load cells presently have disadvantages which are such that load cells which operate solely in tension are generally used with tongs- It will be appreciated that if a tensile-indicating load cell is arranged to be under tension when a tong is arranged to rotate a pipe in one sense the load cell will be in compression (and inoperative) when the tong is arranged to rotate the pipe in the opposite sense. For this reason it is the current practice to either reposition the load cell so that is will be in tension each time the direction of rotation is changed or to provide tongs with two load cells, one arranged to be in tension and the other inoperative when the pipe is

rotated in one sense and the other arranged to be operative and the one inoperative when the pipe is rotated in the opposite sense.

In the former case time is spent re-positioning the load cell each time the direction of rotation is reversed whilst the later solution involves the costs associated with two load cells.

According to the present invention there is provided a load cell assembly comprising: (a) load cell mounting apparatus, and

(b) a single load indicating load cell mounted on said load cell apparatus, characterized in that, in use, said load cell mounting apparatus translates both tensile loads and compressive loads imposed on said load cell assembly to the load cell into a unidirectional force.

Preferably, the load cell mounting apparatus comprises: an outer bracket connectable to a first load- inducing device, the outer bracket having a first opening for loosely receiving a first rod secured to a first end of the single load cell and a second opening for loosely receiving a second rod secured to a second end of said single load cell, the first opening and second opening spaced apart from one another; an inner bracket disposed within the outer bracket and connectable to a second load-inducing device, the inner bracket having a first opening therein for loosely receiving the second rod and having a second opening for loosely receiving the first rod, and the inner bracket disposed partially within the outer bracket and the single load cell connected between the first rod and the second rod so that upon application of a load to the load cell assembly the load cell indicates the magnitude of the load.

Advantageously, the load cell is disposed within the inner bracket.

Preferably, the load cell assembly further comprises a cylindrical housing enclosing said inner bracket, said outer bracket and said load cell.

Advantageously, said first opening of said outer bracket and said second opening of said inner bracket comprise slots.

Preferably, said second opening in said outer bracket and said second opening in said inner bracket comprise recesses open at one end.

Said single load cell may be a tensile-load indicating load cell, a compression-load indicating load cell, or a shear-load indicating load cell. Advantageously, in the case where a shear-load indicating load cell is used, said shear indicating load cell has a central member extending through a load cell body, and the load cell mounting apparatus comprises: rod means secured to the load cell body and extending above it, an upper plate to which the rod means are secured, a top plate interposed between the upper plate and the load cell body, the top plate freely movable about the rod means, the rod means extending through openings through the top plate, a lower plate secured to the central member, a bottom plate interposed between the lower plate and the load cell body, the central member freely movable in an opening through the bottom plate, the plates disposed so that application of a tensile load on the top and bottom plates forces the top plate against the upper plate and the bottom plate against the lower plate to apply a shear load to the load cell in one sense, and the plates disposed so that application of a

compressive load on the top and bottom plates forces the top plate against the central member and the bottom plate against the load cell body to apply a shear load to the load cell in the same sense. The present invention also provides a tong assembly comprising a power tong , and a back-up tong , characterized in that said tong assembly further comprises a load cell assembly in accordance with the present invention connected between said power tong and said back-up tong.

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For a better understanding of the present invention reference will now be made, by way of example, to the accompanying drawings, in which:-

Fig. 1 is a front view of a tong assembly provided with one embodiment of a load cell assembly according to the present invention;

Fig. 2 is a perspective view, partially exploded, of a power tong provided with a second embodiment of a load cell assembly according to the present invention; Fig. 3A is a perspective view of a third embodiment of a load cell assembly according to the present invention with a tensile load on it;

Fig. 3B is a top view of the load cell assembly of Fig. 3A; Fig. 4A is a perspective view of the load cell assembly of Fig. 3A with a compressive load on it;

Fig. 4B is a top view of the load cell assembly of Fig. 4A;

Fig. 5 is a side view, partially in cross-section, of a fourth embodiment of a load cell assembly according to the present invention with a tensile load on it;

Fig. 6 is a side view, partially in cross-section of the load cell assembly shown in Fig. 5 with a compressive load on it; Fig. 7 is a front view of a load cell assembly as shown in Figs. 5 and 6 associated with a tong assembly;

Fig. 8 is a top view of a tong assembly (partially shown) and a load cell assembly similar to the load assembly shown in Figs. 3A, 3B, 4A and 4B, secured thereto;

Figs. 9A and 9C are side views of a fifth embodiment of a load cell assembly according to the present invention; and

Figs. 9B and 9D are top views of the load cell assembly of Figs. 9A and 9C respectively.

Referring to Fig. 1, there is shown a tong assembly 2 mounted on a pipe 3. The tong assembly 2 comprises a power tong 4, a back-up tong 6, and a framework 8 that interconnects the power tong 4 and the back-up tong 6 yet permits some freedom of movement between the two. Also interconnected between the power tong 4 and the back-up tong 6 is a load cell assembly 10 which has a first connection arm 12 secured to a bar 13 which in turn is secured to the power tong 4 and a second connection arm 14 secured to a bar 15 which in turn is secured to the back-up tong 6.

In use, the load cell assembly 10 reads, in tension, regardless of whether the power tong 4 is tending to. rotate clockwise or anti-clockwise. The load cell assembly 10 is disposed in a plane at substantially a right angle to the longitudinal axis 7 of the pipe and also perpendicular to a central horizontal axis (not shown, but like axis T in Fig. 2) of the tongs so that no correction for deviation from.90 degrees is needed.

A load cell assembly 20, like the load cell assembly 10 in Fig. 2, is shown in Figs. 3A, 3B, 4A and 4B. The load cell assembly 20 has an outer bracket 21 with a first connecting arm 23 secured to a vertical beam 24 from which extend a top beam 25 and a bottom beam 26. The beams 25 and 26 each have a slot 27 and a recess 28 through which pass rods 50 and 51, respectively.

An inner bracket 31 disposed generally between the top beam 25 and bottom beam 26 of the outer bracket 21 has a second connecting arm 33 secured to a vertical beam 34 from which extend an upper beam 35 and a lower beam 36. The beams 35 and 36 each have a slot 37 and a recess 38 through which pass the rods 51 and 50, respectively.

A tension-indicating load cell 40 is disposed generally within the inner bracket 31 and has one connector 42 secured about rod 50 and another connector 44 secured about the rod 51. Typical commercially available load cells such as a Hardy Instruments load cell no. 5501-0085-02 may be used.

Due to the configuration and size of the slots 27, 37 and the recesses 28, 38 (which are all larger than the rods that pass through them) the outer bracket 21 and inner bracket 31 are movable with respect to the rods 50 and 51. This arrangement ensures that regardless of whether the load cell assembly 20 is placed in tension or compression the tension-indicating load cell 40 is always in tension as indicated by arrows E, F. This is illustrated in the relative movement shown in Figs. 3A and 4A.

In Fig. 3A, when the outer bracket 21 and inner bracket 31 are pulled apart in the direction of arrows "A" and "B" respectively, the rod 50 is pulled outwardly by the inner edges of the slots 27 and the edges of the recesses 28 do not restrain the rod 51. Simultaneously, the inner edges of the slots 37 pull the rod 51 outwardly and the edges of the open recesses 38 do not restrain the rod 50. The tension-indicating load cell 40 is thus subject to tension.

When the outer bracket 21 and inner bracket 31 are pushed together in the direction of arrows "C" and "D" respectively (Fig. 4A) the reverse occurs with the inner edges of the recesses 28 and 38 acting on the rods 51 and 50 respectively while rod movement is permitted in the slots 27 and 37. Again the tension-indicating load cell 40 is subject to tension.

In summary, irrespective of whether a tensile load or a compressive load is applied to the load cell assembly 20, a tensile load is applied to the tension-

indicating load cell 40.

The slots Δ7 and 37 (which could alternatively comprise large holes) provide sufficient space for the required movement of the rods 50 and 51. A cable 62 extends from a transducer output connector 60 and carries the load indicating signal to a monitoring instrument (not shown).

An alternative load cell assembly 220 is shown in Figs. 9A, 9B, 9C and 9D. The load cell assembly 220 has an outer bracket 221 with a first connecting arm 223 secured to a vertical beam 224 from which extend a top beam 225 and a bottom beam 226. The top beam 225 and bottom beam 226 each have a slot 227 and a slot 228 through which pass rods 250 and 251 respectively. An inner bracket 231 disposed generally between the top beam 225 and bottom beam 226 of the outer bracket 221 has a second connecting arm 233 secured to a vertical beam 234 from which extend an upper beam 235 and a lower beam 236. The upper beam 235 and lower beam 236 each have a slot 237 and a slot 238 through which pass the rods 251 and 250, respectively.

A compression-indicating load cell 240 is disposed generally within the inner bracket 231 and has one connector 242 secured about rod 250 and another connector 244 secured about rod 251. Typical commercially available load cells may be used.

Due to the configuration and size of the slots 227, 228, 237 and 238 (which are all larger than the rod that passed through them) the outer bracket 221 and inner bracket 231 are movable with respect to the rods 250 and 251. This arrangement ensures that regardless of whether the load cell assembly 240 is placed in tension or compression the compression-indicating load cell 240 is always in compression as indicated by arrows P, Q. This is illustrated in the relative movement shown

in Figs . 9A and 9C.

As shown in Fig. 9A, when the outer bracket 221 and the inner bracket 231 are pushed together in the direction of arrows "K" and "L" respectively, the rod 250 is pushed outwardly by the inner edges of the slots 227 and the edges of the holes 228 do not restrain the rod 251, while the inner edges of the slots 237 push the rod 251 outwardly. The compression-indicating load cell 240 is thus subject to compression. When the outer bracket 221 and inner bracket 231 are pulled apart in the direction of arrows "M" and "N" respectively (Fig. 9C), the reverse occurs with the edges of the slots 228 and 238 acting on the rods 251, 250 respectively while rod movement is permitted within the confines of the slots 227 and 237.

In summary, irrespective of whether a tensile load or compressive load is applied to the load cell assembly 220, a compressive load is applied to the compression- indicating load cell 240. A cable 262 extends from a transducer output connector 260 and carries the load indicating signal from the load cell to a monitoring and/or recording instrument (not shown).

Fig. 2 shows a load cell assembly 61 (similar to the load cell assemblies 10 and 20 described above) with a power tong 62. The load cell assembly 61 is secured between the power tong 62 and a connecting arm 64 that is secured to another member such as a rig 66. A connection end 65 of the load cell assembly 61 (like the second connection arm 33, Fig. 3A) is connected to a holding member 67 at the rear of the power tong 62 with a bolt 69 and cotter pin 71.

The embodiment shown in Fig. 2 has a generally cylindrical outer housing 63 and the brackets within it (not shown; like the brackets of the embodiment of

Fig. 3A) are much closer together (e.g., clearance between moving parts of 1.5mm (0.06 inches)) than the brackets shown in Fig. 3A) but the same results are accomplished. Thus when the power tong 62 is used for either make-up or break-out of a tubular threaded joint 68 (i.e., when the load cell assembly is subjected to either a tensile or a compressive load) the load cell within the assembly 61 (not shown) will indicate the load. A load cell assembly 80 according to the present invention is shown in Figs. 5 - 7. A shear-indicating load cell 81 has two rods 82 and 83 secured to a load cell body 91. The rods 82 and 83 secured to a load cell body 91. The rods 82 and 83 freely extend through holes 84 in the top plate 85. The rods 82, 83 are secured to an upper plate 86. The shear-indicating load cell 81 has a central member 87 which is εlidably mounted in the load cell body 91 and is attached thereto via sensing webs Wl, W2. The central member 87 is also attached to a lower plate 88. The central member 87 freely extends through an opening 89 in a bottom plate 90. By appropriately orienting the top plate 85 and plate 90 (see e.g., Fig. 7), they can be secured to items, e.g., a tong or tongs, which will induce a load on the load cell assembly 80.

As shown in Fig. 5, a tensile load indicated by arrows G, H causes plates 85 and 90 to coact with plates 86 and 88 to induce a shear load on the shear load cell 81 in one sense. As shown in Fig. 6, a compressive load indicated by arrows "J", "K", also applies a shear load on load cell 81 in the same sense. The shear force is measured by strain gauges mounted on the sensing webs Wl, W2.

Referring now to Fig. 7, a tong assembly 2 about a pipe 3 has a power tong 4, a back-up tong 6, and a

framework 8 that interconnects the tongs and permits some freedom of movement between the two tongs. Also interconnected between the two tongs is a load cell assembly 100 which is similar to the load cell assembly 80 in Figs. 5 and 6. Plates 185 and 190 correspond to plates 85 and 90 in Fig. 5, respectively, except plate 190 extends in a different direction away from the assembly 100 than does the plate 90 from load cell assembly 80. The load cell (not shown) of the load cell assembly 100 reads, in shear, both tensile and compressive loads on the load cell assembly 80 according to the direction of rotation of the rotary (not shown) in the power tong 4. The load cell in the load cell assembly 100 is perpendicular to the central horizontal axes of the power tong 4 and back-up tong 6 and is perpendicular to the vertical axis of the pipe 3.

As shown in Fig. 8, a load cell assembly 270 (like those shown in Fig. 3A or 9A) has a side plate 272 through which extends bolts 274 securing the load cell assembly 270 to a housing 276 of a tong 278 (shown partially in Fig. 8). Such a connection of the load cell assembly 270 to a tong assembly ensures that the load cell itself in the load cell assembly 270 will be perpendicular to the tong's central horizontal axis (not shown in Fig. 8, but like the load cell in either Fig. 3A or Fig. 9A).

Various modifications to the embodiments described are envisaged. For example, the slots 27, 37, 227, 228, 237, 238 could comprise holes loosely accommodating their respective rods. The recesses 37, 38 could also comprise suitably elongated slots or holes although one side of the slot/hole would serve no useful purpose in the context of the embodiment shown in Figs. 3A, 3B, 4A, 4B.