DRILL STRING JOINT DESIGN.

Abstract

Drill string rod (1) to form part of an assembly (10) of such connected drill string rods (1, 1b), the drill string rod (1) comprising: an elongated center rod portion (2) extending axially between a male end (3) and a female end (4), wherein the center rod portion (2) is hollow-cylindrically defined by a first inner diameter (drod) and a second outer diameter (Drod), wherein the male end (3) comprises a tang (5), wherein the tang (5) comprises a base (6) projecting axially from a flange (7) axially separating the tang (5) and the center rod portion (2), wherein the female end (4) comprises a sleeve portion (8) configured to fit the tang (5), wherein the base (6) is provided with an external thread and wherein the portion (8) The sleeve is equipped with an internal thread,wherein the internal thread corresponds to the external thread such that the internal thread of the sleeve portion (8) can be joined to the external thread of the base (6) of the pin (5) of an additional drill string rod (1b) of the assembly (10), wherein, in a radial plane (P) with respect to the longitudinal axis (9) of the drill string rod (1), the base (6) of the pin (5) is defined by a third outside diameter (Pin) and a fourth inside diameter (Pin) and the sleeve portion (8) is defined by a fifth outside diameter (Dsleeve) and a sixth inside diameter (Dsleeve), wherein the second diameter (Drod) is between 30 and 60 mm, and wherein the six diameters mentioned are selected within specific limits.

Description

DRILL STRING JOINT DESIGN FIELD OF INVENTION The present invention relates to drill string rods for use with drill bits for percussion rock drilling. Specifically, the invention relates to improving the reliability and lifespan of such drill string rods. BACKGROUND OF THE INVENTION Percussion drilling is used to create a long borehole by means of a plurality of elongated drill string rods coupled end-to-end by interconnected male and female threaded couplings. The well-established technique breaks rock by hammer impacts transferred from a rock drill bit, mounted at one end of the drill string, to the rock at the bottom of the borehole. Typically, the energy required to break the rock is generated by a hydraulically driven piston that contacts the end of the drill string (by means of a stem adapter) to create a stress (or shock) wave that propagates through the drill string and ultimately to the rock. Conventional male and female threaded couplings are described in US patents 4,332,502, 4,398,756, 4,687,368, and DE 2800887. The male and female threaded ends of adjacent drill rods are mated to create the drill string, and the joint is typically subjected to high forces during drilling. These forces fatigue the joint and lead to wear and breakage within the threaded portion. Typically, the male threaded stud is the part that is damaged and determines the service life of the joint. US Patent 6,767,156 discloses a threaded joint between two percussion drill rods having tapered guide surfaces provided on the forward axial ends of the male and female portions in an attempt to achieve a secure mating and prevent damage to the threads. The purpose of document EP2845992B1 from the present applicant is to mitigate the aforementioned drawbacks. A problem with known drill string joint designs is that failure occurs due to flexing in non-straight wells. Cracks can develop in the shank or sleeve portion, thus reducing the reliability and lifespan of the drill string. Therefore, there is a need for a drill string joint design that has reduced stress and greater bending strength, thereby improving reliability and increasing the service life of the drill string rods. BRIEF DESCRIPTION OF THE INVENTION An object of the invention is to provide a drill string rod with improved reliability and durability compared to other drill string rods. According to a first aspect of the invention, this object is achieved by the inventive drill string rod as defined in appended independent claim 1, with alternative embodiments defined in the dependent claims. The drill string rod is intended to form part of an assembly of such connected drill string rods. The drill string rod comprises an elongated center rod portion extending axially between a male end and a female end. The center rod portion is hollow-cylindrically defined by a first inner diameter (dvaniia) and a second outer diameter (Dvariiia).The male end comprises a spigot, wherein the spigot includes a base projecting axially from a flange axially separating the spigot and the central rod portion. The female end comprises a sleeve portion configured to fit the spigot. Furthermore, the base is provided with an external thread and the sleeve portion is provided with an internal thread, wherein the internal thread corresponds to the external thread such that the internal thread of the sleeve portion can engage with the external thread of the spigot base of an additional drill string rod of the assembly. In a radial plane with respect to the longitudinal axis of the drill string rod, the spigot base is defined by a third outer diameter (Spigot) and a fourth inner diameter (Spigot), and the sleeve portion is defined by a fifth outer diameter (Sleeve) and a sixth inner diameter (Sleeve).The present invention is limited to drill string rods with a second outside diameter (Dvariiia) of between 30 and 60 mm, preferably between 40 and 60 mm. Cmanguito and Cespiga refer to the diameters of the drill string rod as defined by the following formulas:. _ ^rod ' (^sleeve ~ ^-sleeve') '-'sleeve ~ ~_ j4 I^sleeve ^roduvarillaJ _ ^rod (Despiga ~ d-spike) ^spike ~ TTñ4— ti4Ίuespiga \uvarillauvarillaJ Cmanguito must be greater than 2.0 or Cespiga must be greater than > 0.6. The person skilled in the art understands that diameters cannot be chosen freely. For example, the outer diameter of the shank is naturally limited by the inner diameter of the sleeve portion. Furthermore, the outer diameter of the sleeve portion is typically limited by the size of the drilled borehole and the need for sufficient space for washing drilling debris beyond the sleeve portion, between the sleeve portion and the borehole wall. Similarly, the inner diameter of the shank limits the rate at which washing fluid can be pumped through the drill string and therefore should not be too small.The design of drill string rods is clearly a difficult balancing act, and the present invention guides the skillful practitioner toward selecting a combination of parameters that allows for a reduced risk of material failure in the drill string rod with extended flushing performance. Solving this problem has proven to be more difficult than it appears. The inventors of the present invention have realized that failures in the drill string are due to a combination of the increased stiffness of the central rod portion and the forced bending of the drill string induced by harder layers or cracks in the rock. The bending of the drill string occurs while the rod is rotating, thereby creating both additional stress due to the bending itself and fatigue due to the constant change in the bending axis caused by the rod's rotation in the borehole while it is in its bent state. qj LPnn / cznz / E / YiAi The proposed solution is to dimension the shank and sleeve portion such that the maximum calculated bending stress in the shank and sleeve portion, respectively, is referenced to the maximum calculated bending stress in the center rod portion. However, the inventors have realized that the maximum calculated stresses in the sleeve portion and shank, respectively, should not be equal to the maximum calculated bending stress in the center rod portion, but rather should be referenced to the maximum calculated bending stress in the center rod portion multiplied by the factor Csleeve or Cshank, respectively, in order to compensate for differences in strength that commonly occur, for example, due to local material variations likely resulting from uneven hardening and / or machining during the manufacture of the drill string rods. In some models, Cmanguito > 2.0 and Cespiga > 0.6. This balance of the first, second, third, fourth, fifth and sixth diameters involved provides high reliability and durability of the drill string rod. In some varieties, the base of the spike is conical. In some varieties, the base of the spike is cylindrical. In some versions, the first diameter (dvariiia) is 30 mm, in which the second diameter (Dvariiia) is 57 mm, in which the third diameter (Despiga) is 48 mm, in which the fourth diameter (despiga) is 21 mm, in which the fifth diameter (Dmanguito) is 76 mm and in which the sixth diameter (dmanguito) is 51 mm. In some embodiments, the drill string rod is suitable for use with a drill bit having a seventh outside diameter (Dwell), wherein the fifth diameter is < 0.90* the seventh diameter (Dwell). An additional aspect relates to a system comprising a plurality of drill string rods according to the first aspect described above. In some embodiments, the drill string rods of the system are of the type mentioned above that are suitable for use with a drill bit having a seventh outside diameter (Dpozo), wherein the fifth diameter is < 0.90* the seventh diameter (DpoZo), and wherein the system further comprises the drill bit. The difference in diameter between the wellbore and the outer diameter of the sleeve portion allows for efficient washing of drilling debris beyond the sleeve portion, while providing robust drill string rods that can absorb the forces involved. In some configurations, the seventh diameter is > 89 mm. The drill string rods have a second diameter between 30 and 60 mm, preferably between 40 and 60 mm, where the specified limits of the involved drill string rod diameters governed by Cmanguito and Cespiga provide a robust drilling system. In some models, the threads on the base and the sleeve portion are both straight. In some models, the threads on the base and the sleeve portion are both warped. q; LPnn / cznz / E / YiAi BRIEF DESCRIPTION OF THE FIGURES Fig. 1 shows a perspective view of two identical connected drill string rods. Fig. 2 shows an enlarged perspective view A of the male end of the drill string rod as shown in Fig. 1. Fig. 3 shows an enlarged perspective view B of the female end of the drill string rod as shown in Fig. 1, which is connected to the male end of the other drill string rod. Fig. 4 shows a cross-sectional side view of the sleeve portion and the spigot of the two connected drill string rods also shown in Fig. 1, said cross-section being taken in a plane through the longitudinal centerline of the drill string rod. Fig. 5 shows a neutral hollow center round section module. DETAILED DESCRIPTION OF THE INVENTION Figures 1 to 4 illustrate a first embodiment of the invention. As shown in the figures, a plurality of identical drill string rods 1, 1b can be connected to form a system / assembly 10. The drill string rod 1 comprises an elongated center rod portion 2 extending axially between a male end 3 and a female end 4. As shown in Figure 4, the center rod portion 2 is hollow-cylindrically defined by a first inner diameter dvariiia and a second outer diameter Dvariiia. The male end 3 comprises a pin 5, and the pin 5 comprises a base 6 projecting axially from a flange 7 axially separating the pin 5 and the center rod portion 2. The female end 4 comprises a sleeve / sleeve portion 8 configured to fit the pin 5.The base 6 is provided with an external thread, and the sleeve portion 8 is provided with an internal thread, wherein the internal thread corresponds to the external thread such that the internal thread of the sleeve portion 8 can be joined to the external thread of the base 6 of the pin 5 of an additional drill string rod of the assembly. In a radial plane P with respect to the longitudinal axis of the drill string rod, the base 6 of the pin 5 is defined by a third outside diameter (Dpin) and a fourth inside diameter (Dpin), and the sleeve portion 8 is defined by a fifth outside diameter (Dsleeve) and a sixth inside diameter (Dsleeve). It should be noted that in Fig. 4, both Dpin and Dsleeve are referred to in relation to the same arrow, although in reality the diameters are slightly different, Dsleeve being larger than Dpin. The scale of the figure is such that the difference in diameter cannot be shown in Fig. 4.4 using independent arrows. Although the diameters may vary along the length of the shank and the sleeve portion respectively, the radial plane P, which necessarily passes through both the shank and the sleeve portion, is used to define the relationship between the diameters in an unambiguous manner. The present invention is limited to drill string rods with an outside diameter of between 30 and 60 mm, preferably between 40 and 60 mm, such as drill bits having a diameter of 54–127 mm. Therefore, the second diameter (Dvariiia) is between 30–60 mm, preferably between 40–60 mm. Csleeve and Cshank can be derived from / refer to the diameters of the drill string rod using the following formulas: o? LPnn / cznz / E / YiAi These formulas arise from the calculation of section moduli for hollow-cylindrical beams / bodies, which provide a good approximation of the cross-sectional shapes involved. Specifically, the section modulus equations for hollow-cylindrical cross-sections are: „ _ ^rod ' fbmanguito^manguito') L sleeve — 77 / E — <74Y ^sleeve ¿'rod “rod! o? LPnn / cznz / E / YiAi , ^rod ' (.^spike ^-spike^ •spike ~ n . , (r\4 — d4Ί ^spike ¿'rod “rod! vfá-rfi Tr(í^-dJ) 4r232^2 Fig. 5 shows a neutral hollow center round section module. The hypothesis is that: Sespiga = Cespiga *Svarilla ^n(Despigadesplga) _ ^D^arilla-d^arilla) 22*D , 32*Drod spike , _ Drod ' (j^spike ^-spike} •spike ~ . / ()4 _ j4 Iuespike '.rodrodrodJ And similarly to Smanguito—Cmanguito*Svar¡lla é D (D4— d4j _ '-'rod (''sleeve ''sleeveJ ' '-sleeve ~ ñ m4_ ,4 I '-'sleeve (.'-'rod ^rodJ In this modality, the first diameter dvariiia is 30 mm, in which the second diameter Dvariiia is 57 mm, in which the third diameter Desp¡ga is 48 mm, in which the fourth diameter desp¡ga is 21 mm, in which the fifth diameter Dmanguito is 76 mm and in which the sixth diameter dmanguito is 51 mm. This 1.1 b drill string configuration is suitable for use with a drill bit (unpolished) having a specified diameter (not including the diameter of the drill inserts) of 54, 57, 64, 70, 76, 89, 102, 115, or 127 mm. The actual diameter of the drilled wells is slightly larger because the drill bits protrude radially. The first through sixth diameters may be selected differently in other configurations, provided that the second diameter, Dvar¡iia, which defines the outside diameter of the center rod portion 2, meets the above limit of being between 30 and 60 mm, and the other diameters meet the limits that Cmanguito is greater than 2.0 or Cespiga is greater than 0.6. Preferably, Cmanguito is greater than 2.0 and Cespiga is greater than 0.6. Drill string rods are made of a suitable material, such as steel, and are hardened as needed. Drill string 1, 1b is sized based on the size of the drill bit for which it will be used. However, care must be taken to provide sufficient space around the sleeve portion 8 for washing away drilling debris beyond the sleeve portion 8. For this purpose, drill string 1, 1b may be suitable in some configurations for use with a drill bit having a seventh outside diameter DpOzo, where the fifth outside diameter Dsleeve of the sleeve portion 8 is less than 0.90 times the seventh diameter DpOzo. A plurality of identical drill string rods 1,1b may be provided together as part of a drill string rod system / assembly 10. The system 10 may alternatively comprise a drill bit. The drill string rods 1,1b of the system 10 may have a seventh outside diameter Dwell, wherein the fifth diameter is < 0.90* the seventh diameter Dwell, and wherein the system further comprises the drill bit. The difference in diameter between the wellbore and the fifth outer diameter Dsleeve of the sleeve portion 8 allows for efficient washing of drilling debris beyond the sleeve portion 8, while providing robust 1.1 b drill string rods that can absorb the forces involved. In some embodiments, the seventh diameter Dwell can be 54–127 mm. As mentioned above, the drill string rods of the present invention all have a second diameter of between 30 and 60 mm, preferably between 40 and 60 mm. The specified limits of the diameters involved, given by Csleeve and CsPig, provide a robust system / assembly. References o? LPnn / cznz / E / YiAi 1 drill string rod Q longitudinal axis of drill string rod I drilling and drilling 1b additional drill string rod of the same type 10 system / assembly of a plurality of drill string rods 2 center rod portion P plane defining cross sections to determine CesPiga and Cmanguito 3 male end drod rod inside diameter of rod / first diameter 4 female end Drod rod outside diameter of rod / second diameter 5 dowel Dedoga outside diameter of dowel / third diameter 6 base (of dowel) dedoga inside diameter of dowel / fourth diameter 7 flange Dmanguito outside diameter of sleeve portion / fifth diameter 8 sleeve portion dmanguito inside diameter of sleeve portion / sixth diameter Dwell diameter of drilled well / seventh diameter (Dvariiia) is 57 mm, in which the third diameter (DeSp¡ga) is 48 mm, in which the fourth diameter (despiga) is 21 mm, in which the fifth diameter (Dmanguito) is 76 mm and in which the sixth diameter (dmanguito) is 51 mm. 6. The drill string rod (1) as claimed in any of claims 1 to 5, wherein the drill string rod (1) is suitable for use with a drill bit having a seventh outside diameter (Dwell), wherein the fifth diameter (Dsleeve) is < 0.90* the seventh diameter (Dwell). 7. A system (10) comprising a plurality of drill string rods (1, 1b) in accordance with any one of the preceding claims. 8. The system (10) according to claim 7 when dependent on claim 6, further characterized in that said system (10) comprises the drilling auger. 9. The system (10) according to claim 8, further characterized in that the seventh diameter (Dwell) is 54-127 mm or greater, such as 54, 57, 64, 70, 76, 89, 102, 115 or 127 mm. 10. The system (10) in accordance with any of the preceding claims, further characterized in that the second diameter (Dvariiia) is between 40-60 mm. 11. The System (10) in accordance with any of the preceding claims, further characterized in that the threads on the base (6) and the sleeve portion (8) are both straight. 12. The system (10) according to any of claims 1 to 10, further characterized in that the threads on the base (6) and the sleeve portion (8) are both curved. o? LPnn / cznz / E / YiAi SUMMARY OF THE INVENTION Drill string rod (1) to form part of an assembly (10) of such connected drill string rods (1,1b), the drill string rod (1) comprising: an elongated center rod portion (2) extending axially between a male end (3) and a female end (4), wherein the center rod portion (2) is hollow-cylindrically defined by a first inner diameter (dvariiia) and a second outer diameter (Dvariiia), wherein the male end (3) comprises a tang (5), wherein the tang (5) comprises a base (6) projecting axially from a flange (7) axially separating the tang (5) and the center rod portion (2), wherein the female end (4) comprises a sleeve portion (8) configured to fit the tang (5), wherein the base (6) is provided with an external thread and wherein the portion (8) The sleeve is provided with an internal thread,wherein the internal thread corresponds to the external thread such that the internal thread of the sleeve portion (8) can be joined to the external thread of the base (6) of the pin (5) of an additional drill string rod (1b) of the assembly (10), wherein, in a radial plane (P) with respect to the longitudinal axis (9) of the drill string rod (1), the base (6) of the pin (5) is defined by a third outside diameter (DSpig) and a fourth inside diameter (Dpin) and the sleeve portion (8) is defined by a fifth outside diameter (Dsleeve) and a sixth inside diameter (Dsleeve), wherein the second diameter (Dsleeve) is between 30 and 60 mm, and wherein the six diameters mentioned are selected within specific limits.

Claims

1. A drill string rod (1) for forming part of an assembly (10) of such connected drill string rods (1, 1b), characterized in that the drill string rod (1) comprises: an elongated center rod portion (2) extending axially between a male end (3) and a female end (4), wherein the center rod portion (2) is hollow-cylindrically defined by a first inner diameter (dvariiia) and a second outer diameter (Dvariiia), wherein the male end (3) comprises a tang (5), wherein the tang (5) comprises a base (6) projecting axially from a flange (7) axially separating the tang (5) and the center rod portion (2), wherein the female end (4) comprises a sleeve portion (8) configured to fit the tang (5), wherein the base (6) is provided with an external thread and in in which the sleeve portion (8) is provided with an internal thread,wherein the internal thread corresponds to the external thread such that the internal thread of the sleeve portion (8) can be joined to the external thread of the base (6) of the pin (5) of an additional drill string rod (1b) of the assembly (10), wherein, in a radial plane (P) with respect to the longitudinal axis (9) of the drill string rod (1), the base (6) of the pin (5) is defined by a third outside diameter (Pin) and a fourth inside diameter (pin) and the sleeve portion (8) is defined by a fifth outside diameter (Sleeve) and a sixth inside diameter (Sleeve), wherein the second diameter (Drod) is between 30-60 mm, wherein: _ ^rod · (Dsleeve ^sleeve') '-sleeve ~ 77ñi _ '-'sleeve ('-'rod rod rod ^rod ' Respiga ~ ^-spiga) ^spiga ~ y. ' yTjCi —[i 7 '-'spiga {'-'rod “rod in which, and in which Cmanguito > 2.0 O Cespiga > 0.6., 2. The drill string rod (1) according to claim 1, further characterized in that Cmanguito > 2.0 and Cespiga > 0.

6.

3. The drill string rod (1) according to any one of claims 1 to 2, further characterized in that the base (6) of the tenon (5) is conical.

4. The drill string rod (2) according to any one of claims 1 to 2, further characterized in that the base (6) of the pin (5) is cylindrical.

5. The drill string rod (1) according to claim 1 or 4, further characterized in that the first diameter (dvariiia) is 30 mm, wherein the second diameter

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