Drill string joint design

Abstract

A drill string rod (1) forming part of an assembly (10) of connected drill string rods (1, 1b), comprising an elongated central rod portion (2) extending axially between a male end (3) and a female end (4), wherein said central rod portion (2) has an inner first diameter (d rod ) and outer second diameter (D rod ), the male end (3) comprises a spigot (5) having a base (6) projecting axially from a shoulder (7) axially separating the spigot (5) from the central rod portion (2), the female end (4) comprises a sleeve portion (8) configured to mate with the spigot (5), the base (6) being externally threaded and the sleeve portion (8) being internally threaded, the internal thread corresponding to the external thread of the sleeve portion (8) such that the internal thread of the sleeve portion (8) is attachable to the external thread of the base (6) of the spigot (5) of a further drill string rod (1b) of the assembly (10), and the base (6) of the spigot (5) has an outer third diameter (D spigot ) and the inner fourth diameter (d spigot ) and the sleeve portion (8) is defined by an outer fifth diameter (D sleeve ) and the inner sixth diameter (d sleeve ) and the second diameter (D rod ) is 30-60 mm, and the six diameters mentioned are selected within certain constraints, drill string rod (1).

Description

[Technical Field]

[0001] The present invention relates to drill string rods for use with percussive rock drill bits, and in particular to improving the reliability and life of such drill string rods. [Background technology]

[0002] Percussion drilling is used to create long boreholes via multiple elongated drill string rods joined end-to-end by interconnected male and female threaded ends. An established technique involves driving impacts transmitted from a rock drill bit attached to one end of the drill string into the rock at the bottom of the borehole, thereby breaking the rock. Typically, the energy required to break the rock is generated by a hydraulically driven piston that contacts the end of the drill string (via a shank adapter), generating stress (or shock) waves that propagate through the drill string and ultimately into the rock. Conventional male and female threaded connections are described in U.S. Pat. Nos. 4,332,502, 4,398,756, 4,687,368, and German Patent No. 2,800,887.

[0003] The male and female threaded ends of adjacent drill rods are joined to form a drill string, and the joint is typically subjected to large forces during drilling. These forces fatigue the joint, resulting in wear and breakage within the threaded portion of the joint. Typically, it is the threaded male spigot that fails and determines the operational life of the joint. U.S. Pat. No. 6,767,156 discloses a threaded joint between two striking drill rods having conical guide surfaces at the axial ends of the male and female portions in an attempt to achieve a secure joint and prevent damage to the threads.

[0004] EP 2845992 of the present applicant aims to alleviate the above-mentioned drawbacks.

[0005] One problem with known drill string joint designs is that failure can occur due to bending resulting from a non-linear hole, which can cause cracks in the spigot or sleeve portion, thereby reducing the reliability and lifespan of the drill string rod.

[0006] Therefore, there is a need for drill string joint designs that have reduced stresses and increased bending resistance, thus improving reliability and extending the life of the drill string rods. Summary of the Invention

[0007] It is an object of the present invention to provide a drill string rod having improved reliability and life span. According to a first aspect of the present invention, this object is achieved by the drill string rod of the present invention as defined in the accompanying independent claim 1, with alternative embodiments defined in the dependent claims. The drill string rod forms part of an assembly of connected drill string rods. The drill string rod comprises an elongated central rod section extending axially between a male end and a female end. The central rod section has an inner first diameter (d rod ) and outer second diameter (D rod ) The male end includes a spigot having a base that projects axially from a shoulder that axially separates the spigot and the central rod portion. The female end includes a sleeve portion configured to mate with the spigot. The base is externally threaded and the sleeve portion is internally threaded, the internal threads corresponding to the external threads such that the internal threads of the sleeve portion are attachable to the external threads of the base of a spigot of a further drill string rod of the assembly. In a radial plane relative to the longitudinal axis of the drill string rod, the base of the spigot defines an outer third diameter (D spigot ) and the inner fourth diameter (d spigot ) and the sleeve portion is defined by an outer fifth diameter (D sleeve ) and the inner sixth diameter (d sleeveThe present invention is defined by an outer second diameter (D ) of 30 to 60 mm, preferably 40 to 60 mm. rod ) is limited to drill string rods with C sleeve and C spigot is related to the diameter of the drill string rod as defined by the following equation: TIFF0007774617000001.tif38170

[0008] C sleeve must be greater than 2.0, or C spigot must be greater than 0.6.

[0009] Those skilled in the art understand that diameters cannot be freely selected. For example, the outer diameter of the spigot is naturally limited by the inner diameter of the sleeve portion. The outer diameter of the sleeve portion is also typically limited by the size of the bore being drilled and the requirement for sufficient space between the sleeve portion and the inner wall of the bore to flush drill cuttings past the sleeve portion. Similarly, the inner diameter of the spigot cannot be too small, as this limits the rate at which flushing fluid can be pumped through the drill string rod. Drill string rod design is clearly a difficult balance to strike, and the present invention guides those skilled in the art in selecting a combination of parameters that will reduce the risk of material failure in a drill string rod with sustained flushing performance. Solving this problem has proven more difficult than it might appear.

[0010] The inventors of the present invention have recognized that failure of drill string rods is due to a combination of increased stiffness in the central rod section and forced bending of the drill string caused by harder layers or cracks in the rock. Bending of the drill string rod occurs while the rod is rotating, which creates both additional stresses due to bending and fatigue due to the constant change in the bending axis caused by rotation of the rod within the bore while in a bent state.

[0011] The proposed solution is to dimension the spigot and sleeve portions such that their calculated maximum bending stresses are each related to the calculated maximum bending stress of the central rod portion. However, to account for commonly occurring differences in strength due to local material variations that may arise, for example, due to uneven hardening and / or machining during manufacture of the drill string rod, the inventors have determined that the calculated maximum stresses of the sleeve and spigot portions will not be equal to the calculated maximum bending stress of the central rod portion, but rather will be related by a factor C sleeve or C spigot It was recognized that the calculated maximum bending stress of the central rod section multiplied by .

[0012] In some embodiments, C sleeve >2.0 and C spigot >0.6. This balance of the first, second, third, fourth, fifth and sixth diameters involved provides high reliability and life of the drill string rod.

[0013] In some embodiments, the base of the spigot is conical.

[0014] In some embodiments, the base of the spigot is cylindrical.

[0015] In some embodiments, the first diameter (d rod ) is 30 mm, and the second diameter (D rod ) is 57 mm, and the third diameter (D spigot ) is 48 mm, and the fourth diameter (d spigot ) is 21 mm, and the fifth diameter (D sleeve ) is 76 mm, and the sixth diameter (d sleeve ) is 51mm.

[0016] In some embodiments, the drill string rod has an outer seventh diameter (D hole ), and the fifth diameter is suitable for use with a drill bit having a seventh diameter (D hole) is less than 0.90 times.

[0017] A further aspect relates to a system comprising a plurality of drill string rods according to the first aspect above.

[0018] In some embodiments, the drill string rod of the system has an outer seventh diameter (D hole ) and the fifth diameter is of the type described above suitable for use with a drill bit having a seventh diameter (D hole ) is less than 0.90 times the drill bit, and the system further comprises a drill bit.

[0019] The diameter difference between the hole and the outer diameter of the sleeve portion allows for efficient flushing of the drill cuttings past the sleeve portion while providing a robust drill string rod capable of handling the forces involved.

[0020] In some embodiments, the seventh diameter is greater than 89 mm. The drill string rod has a second diameter of 30 to 60 mm, preferably 40 to 60 mm, and sleeve and C spigot The specific constraints on the diameters involved of the drill string rods, governed by, provide a robust drilling system.

[0021] In some embodiments, the threads on the base and sleeve portions are both straight.

[0022] In some embodiments, the threads on both the base and sleeve portions are arcuate. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 is a perspective view of two identical connected drill string rods. [Figure 2] FIG. 2A is an enlarged perspective view A of the male end of the drill string rod shown in FIG. 1; [Figure 3]2B is an enlarged perspective view B of the female end of the drill string rod shown in FIG. 1 connected to the male end of another drill string rod; [Figure 4] FIG. 2 is a cross-sectional side view of the sleeve portions and spigots of two connected drill string rods also shown in FIG. 1, said cross section being taken in a plane passing through the central longitudinal axes of the drill string rods.

[0024] TIFF0007774617000002.tif73170 DETAILED DESCRIPTION OF THE INVENTION

[0025] A first embodiment of the present invention is shown in Figures 1 to 4. As shown in the figures, a plurality of identical drill string rods 1, 1b are connectable to form a system / assembly 10. The drill string rod 1 comprises an elongated central rod section 2 extending axially between a male end 3 and a female end 4. As shown in Figure 4, the central rod section 2 has an inner first diameter d rod and outer second diameter D rod The male end 3 comprises a spigot 5 having a base 6 that projects axially from a shoulder 7 that axially separates the spigot 5 and the central rod portion 2. The female end 4 comprises a sleeve / sleeve portion 8 configured to mate with the spigot 5. The base 6 is provided with an external thread and the sleeve portion 8 is provided with an internal thread that corresponds to the external thread such that the internal thread of the sleeve portion 8 is attachable to the external thread of the base 6 of the spigot 5 of a further drill string rod of the assembly. In a radial plane P relative to the longitudinal axis of the drill string rod, the base 6 of the spigot 5 has an outer third diameter (D spigot ) and the inner fourth diameter (d spigot ), and the sleeve portion 8 is defined by an outer fifth diameter (D sleeve ) and the inner sixth diameter (d sleeve ) is defined by D spigot and d sleeveAlthough both are mentioned in relation to the same arrow, in reality, the diameters are slightly different, d sleeve D spigot Note that the drawing scale is such that the difference in diameter cannot be indicated using separate arrows in FIG. 4. The diameters may vary along the length of the spigot and sleeve portions, respectively, but a radial plane P passing through both the spigot and sleeve portions is used, if necessary, to clearly define the relationship between the diameters. The present invention is limited to drill string rods having an outer diameter of 30 to 60 mm, preferably 40 to 60 mm, for example drill bits having a diameter of 54 to 127 mm. Therefore, the second diameter (D rod ) is 30 to 60 mm, preferably 40 to 60 mm. sleeve and C spigot can be derived from / related to the diameter of the drill string rod using the following formula:

[0026] These formulas are derived from calculations of the section modulus of hollow cylindrical beams / bodies, which provide a good approximation for the cross-sectional shapes currently involved. Specifically, the section modulus equation for a hollow cylindrical cross section is: TIFF0007774617000003.tif61170

[0027] Figure 5 shows the section modulus of a hollow circular center in neutral.

[0028] Our assumptions are as follows: TIFF0007774617000004.tif27170

[0029] Similarly, TIFF0007774617000005.tif24170

[0030] In this embodiment, the first diameter d rod is 30 mm, and the second diameter D rod is 57 mm, and the third diameter D spigot is 48 mm, and the fourth diameter d spigotis 21 mm, and the fifth diameter is D sleeve is 76 mm, and the sixth diameter d sleeve is 51mm.

[0031] This embodiment of the drill string rod 1, 1b is suitable for use with drill bits (not shown) having a specified diameter (diameter not including drilling inserts) of 54, 57, 64, 70, 76, 89, 102, 115, or 127 mm. The actual diameter of the drill hole is slightly larger because the drill bit protrudes radially. The first through sixth diameters are, in other embodiments, relative to a second diameter D that defines the outer diameter of the central rod portion 2. rod The above constraints are met, and other diameters are sleeve is greater than 2.0, or C spigot can be chosen differently as long as it satisfies the constraint that C is greater than 0.6. sleeve is greater than 2.0, and C spigot is greater than 0.6.

[0032] The drill string rods are made from a suitable material, such as steel, and are hardened if necessary.

[0033] The drill string rod 1, 1b is sized based on the size of the drill bit to be used. However, care must be taken to provide sufficient space around the sleeve portion 8 to allow the drill cuttings to wash past the sleeve portion 8. To this effect, the drill string rod 1, 1b may in some embodiments have an outer seventh diameter D hole and the outer fifth diameter D of the sleeve portion 8 may be suitable for use with a drill bit having sleeve is the seventh diameter D hole is less than 0.90 times.

[0034] A number of identical drill string rods 1, 1b may be provided together as part of a system / assembly 10 of drill string rods 1, 1b. The system 10 may alternatively comprise a drill bit. The drill string rods 1, 1b of the system 10 have an outer seventh diameter D hole and the fifth diameter may have a seventh diameter D hole and the system further comprises a drill bit.

[0035] A fifth diameter D outside the hole and sleeve portion 8 sleeve The difference in diameter between allows efficient flushing of the drill cuttings over the sleeve portion 8 while providing a robust drill string rod 1, 1b that can cope with the forces involved.

[0036] In some embodiments, the seventh diameter D hole As mentioned above, all drill string rods of the present invention have a second diameter of 30 to 60 mm, preferably 40 to 60 mm. sleeve and C spigot The particular constraints on the diameters involved given by: provide a robust system / assembly 10.

Claims

1. A drill string rod (1) forming part of an assembly (10) of connected drill string rods (1, 1b), an elongated central rod portion (2) extending axially between a male end (3) and a female end (4); and said central rod portion (2) has an inner first diameter (d ｒｏｄ ) and the outer second diameter (D ｒｏｄ ) a hollow cylindrical shape defined by The male end (3) is provided with a spigot (5), the spigot (5) comprises a base (6) projecting axially from a shoulder (7) axially separating the spigot (5) and the central rod portion (2); the female end (4) comprising a sleeve portion (8) adapted to fit onto the spigot (5); The base (6) is provided with an external thread and the sleeve portion (8) is provided with an internal thread; the internal thread corresponds to the external thread such that the internal thread of the sleeve portion (8) is attachable to the external thread of the base (6) of the spigot (5) of a further drill string rod (1b) of the assembly (10); In a radial plane (P) relative to the longitudinal axis (9) of the drill string rod (1), the base (6) of the spigot (5) has an outer third diameter (D ｓｐｉｇｏｔ ) and the inner fourth diameter (d ｓｐｉｇｏｔ ) and said sleeve portion (8) is defined by an outer fifth diameter (D ｓｌｅｅｖｅ ) and the inner sixth diameter (d ｓｌｅｅｖｅ ) and the second diameter (D ｒｏｄ ) is 30 to 60 mm, wherein C ｓｌｅｅｖｅ >2.0 or C ｓｐｉｇｏｔ >0.6, the drill string rod (1).

2. C ｓｌｅｅｖｅ >2.0 and C ｓｐｉｇｏｔ 2. The drill string rod (1) according to claim 1, wherein the σ is > 0.

6.

3. 3. A drill string rod (1) according to claim 1 or 2, wherein the base (6) of the spigot (5) is conical.

4. 3. A drill string rod (1) according to claim 1 or 2, wherein the base (6) of the spigot (5) is cylindrical.

5. The first diameter (d ｒｏｄ ) is 30 mm, and the second diameter (D ｒｏｄ ) is 57 mm, and the third diameter (D ｓｐｉｇｏｔ ) is 48 mm, and the fourth diameter (d ｓｐｉｇｏｔ ) is 21 mm, and the fifth diameter (D ｓｌｅｅｖｅ ) is 76 mm, and the sixth diameter (d ｓｌｅｅｖｅ 5. The drill string rod (1) according to claim 1 or 4, wherein the length of the first and second ends ...

6. Outer seventh diameter (D ｈｏｌｅ ) and the fifth diameter (D ｓｌｅｅｖｅ ) is the seventh diameter (D ｈｏｌｅ 6. The drill string rod (1) according to any one of claims 1 to 5, wherein the R s is less than 0.90 times the R s.

7. A system (10) comprising a plurality of drill string rods (1, 1b) according to any one of claims 1 to 6.

8. The system (10) of claim 7 when dependent on claim 6, comprising the drill bit.

9. The seventh diameter (D ｈｏｌｅ 9. The system (10) of claim 8, wherein the distance between the first and second electrodes is 54 to 127 mm.

10. The second diameter (D ｒｏｄ 10. The system (10) according to any one of claims 7 to 9, wherein the distance between the first and second electrodes is 40 to 60 mm.

11. A system (10) as described in any one of claims 7 to 10, wherein the threads of the male screw and the threads of the female screw are both straight.

12. A system (10) as described in any one of claims 7 to 10, wherein the threads of the male screw and the threads of the female screw are both arcuate.

13. The system (10) of claim 8, wherein the seventh diameter (D hole ) is 54, 57, 64, 70, 76, 89, 102, 115, or 127 mm.

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