Dual rod drill pipe with improved flow path method and apparatus

A drill rod assembly including inner and outer drill rods. The drill rod assembly further including flow passages that are in fluid communication with an annular fluid flow path defined between the inner and outer drill rods. The passages preventing blockage of a drill string fluid flow path when a number of drill rod assemblies are interconnected to form a drill string.

TECHNICAL FIELD

This disclosure generally relates to a drill rod assembly used for boring. More particularly, this disclosure relates to a drill rod assembly having inner and outer, coaxial drill pipes with an improved flow path. More particularly still, this disclosure relates to such a drill rod assembly used in a horizontal directional drilling (HDD) environment.

BACKGROUND

Drill strings are typically constructed of short, individual sections of drill pipes or rods. The drill rods attach to one another to form a drill string, which can extend significant distances in some drilling applications. The drill rods used in small to medium sized horizontal drilling machines are typically either ten feet or fifteen feet in length. A drill string often extends over one hundred to three hundred feet in length. Thus, it is not unusual for a drill string to be assembled using 10 to 30 sections of drill rods, or more.

Referring now toFIG. 1, one known drill rod assembly10used in conventional drilling systems is illustrated. The drill rod assembly10includes an outer tubular drill rod30having external threads on one end and internal threads on the opposite end. The drill rod assembly10further includes a smaller, inner drill rod20. The inner drill rod20fits inside the tubular outer rod30. As previously described, typical drill rods are either ten feet or fifteen feet in length. Drill rod assemblies having inner and outer rods, however, are uncharacteristically short, to address stack-up problems described in greater detail hereinafter. The illustrated drill rod assembly10is only three feet in length.

Drill rods are typically positioned in the drilling machine, with one end higher than the other; thus, the illustrated assembly10has an up-hill end36and a down-hill end38, as shown. The inner drill rod20includes a hexagonal first end29and a hexagonal second end27. A coupling22is affixed to the first end29by a cross pin26that passes through a hole25formed in the inner drill rod20. The cross pin26has an interference fit such that the pin26remains fixed within the hole25of the inner drill rod20when properly installed. The cross pin26also passes through a slotted hole23formed in the coupling22. The coupling22has a larger diameter D1than that of an inner diameter ID1of the outer drill rod30at the up-hill end36of the assembly10. The larger outer diameter OD1of the coupling22prevents the inner drill rod20from sliding through the outer drill rod30. The inner drill rod20also includes an enlarged portion28located adjacent to the down-hill end38of the assembly10. The enlarged portion28prevents the inner drill rod20from sliding through the outer drill rod30in an opposite direction.

The drill rod assembly10is constructed by installing the inner drill rod20into the outer drill rod30at the down-hill end38of the assembly10. In particular, the inner drill rod20is installed within the outer drill rod20until the expanded portion28of the inner drill rod10contacts the outer drill rod30, and limits longitudinal movement; or until the hole25of the inner drill rod20aligns with the slotted hole23of the coupling22, so that the cross pin26can be inserted. The coupling22includes an internal hexagonal bore that mates with the hexagonal first end27of the inner drill rod to fix the coupling and inner drill rod rotationally. The mating hexagonal bore and the hexagonal first end29of the coupling and inner drill rod transmit torque, while the cross pin26simply holds the coupling22and the rod20in place.

When assembled, the inner drill rod assembly20freely moves in a longitudinal direction from the position illustrated inFIG. 1to a position where the enlarged portion28of the inner drill rod20contacts the outer drill rod30. That is, the inner drill rod20slides longitudinally between an up-hill position and a down-hill position. In the up-hill position, a gap is formed between the coupling22and the outer drill rod30at the up-hill end36of the assembly10. In the down-hill position, the coupling22is flush with the outer drill rod30at the up-hill end36of the assembly.

FIG. 2illustrates the drill rod assembly10coupled to a boring tool40. The boring tool40is connected to the down-hill end38of the assembly10. The boring tool40includes an outer casing45having an external threaded end44. The boring tool40also includes an inner rod42and an attached coupling43having an internal hexagonal bore. Unlike the drill rod assembly10, however, the inner rod42of the boring tool40is coupled to the outer casing45in a fixed position. That is, the inner rod42of the boring tool40does not longitudinally slide relative to the outer casing45. Accordingly, when the drill rod assembly10is coupled to the boring tool40, the fixed position of the inner rod42of the boring tool40determines the position of the inner drill rod20of the drill rod assembly10relative to the outer drill rod30.

More specifically, when the drill rod assembly10is threaded onto the boring tool40, the coupling43of the inner rod42engages with the second hexagonal end27of inner drill rod20. The inner drill rod20is normally positioned as shown inFIG. 1by gravity; i.e., positioned such that the coupling22is flush with the outer drill rod30at the up-hill end36of the assembly10. As the assembly10threads onto the boring tool40, the inner drill rod20of the assembly10is pushed or slides longitudinally toward the up-hill end36of the assembly. The inner drill rod20slides such that an axial gap100is created between the coupling22and the outer drill rod30, as depicted inFIG. 2. In operation, the axial gap100serves as a fluid flow path that allows fluid to enter the drill rod assembly10and pass through an annular area between the inner and outer drill rods20,30. From the annular area of the assembly10, the fluid passes through to the boring tool40to cool the boring tool and assist in the transportation of cuttings.

FIG. 3illustrates first and second drill rod assemblies10aand10bconnected to form a drill string. The same boring tool40is coupled to the down-hill end of the drill string (i.e., the down-hill end of the lowermost drill rod assembly10a). The first drill rod assembly10ais connected to the second drill rod assembly10bby threading an externally threaded up-hill end32aof the first outer drill rod30ainto an internally threaded down-hill end34bof the second outer drill rod30b. As the outer drill rods30a,30bare being coupled, the coupling22aof the first inner drill rod20aengages the hexagonal end27bof the second inner drill rod20b.

The drill string defines a fluid flow path that extends along the lengths of the drill rod assemblies10a,10b. In operation, fluid is pumped into the upper most drill rod assembly, through the fluid flow path, and into the boring tool for cooling and transporting cuttings. For example, referring specifically toFIG. 3, fluid is pumped into the annular area between the inner and outer drill rods20b,30bof the second drill rod assembly10b, through the gap100of the first drill rod assembly10a, then through the annular area between the inner and outer drill rods20a,30aof the first drill rod assembly10a, and into the boring tool40.

As previously described, the fixed position of the inner rod42of the boring tool40determines the position of the inner rod20aof the first drill rod assembly10a. That is, the position of the inner drill rod20abecomes fixed relative to the outer drill rod30awhen attached to the boring tool40. The now fixed positions of the first inner and outer drill rods20a,30aof the first drill rod assembly10aaccordingly determine the position of the second inner drill rod20brelative to the second outer drill rod30bof the second drill rod assembly10b. As the second assembly10bthreads onto the first assembly10a, the second inner drill rod20bis pushed or slides longitudinally such that an axial gap102is created between the coupling22band the second outer drill rod30b, as depicted inFIG. 3. Fluid now enters the drill string at the axial gap102of the second drill rod assembly10b, passes through to the first drill rod assembly10a, and further passes through to the boring tool40to cool the boring tool and assist in the transportation of cuttings.

The inner and outer drill rods20,30of each of the drill rod assemblies10a,10bhave unavoidable variations in length resulting from manufacturing tolerances. Because of the length variations, drill rod assemblies are designed such that the overall length of interconnected inner drill rods20a,20bis never longer than the overall length of interconnected outer drill rods30a,30b. If the interconnected inner drill rods were longer than the outer drill rods, the inner rods would collide while the outer drill rods were being threaded together, causing damage to one or both of the inner and outer drill rods. Accordingly, by design, the length of interconnected inner drill rods is slightly less than the length of interconnected outer drill rods. This design requirement, however, results in a situation where the second axial gap (e.g.,102) of an up-hill drill rod assembly (e.g.,10b) is less than the first axial gap (e.g.,100) of a down-hill drill rod assembly (e.g.,10a).

FIG. 4illustrates a drill string with a boring tool40and four drill rod assemblies10a,10b,10c, and10d. The difference in the overall lengths of the interconnected inner and outer drill rods, and the manufacturing variations of the drill rods, are depicted in an exaggerated manner to better illustrate the effect of this design limitation.

FIG. 4aillustrates the first axial gap100defined by the position of the first coupling22arelative to the outer drill rod30aof the first drill rod assembly10a. When the second drill rod assembly10bis coupled to the first assembly10a, the first end29aof the first inner drill rod20acontacts the second end27bof the second inner drill rod20bof the second assembly10b, and determines the relative positions of the second inner and outer drill rods20b,30b.

FIG. 4billustrates the second axial gap102defined by the position of the second coupling22brelative to the outer drill rod30bof the second drill rod assembly10b. The axial gap102is smaller than the first axial gap100. When the third drill rod assembly10cis coupled to the second assembly10b, the first end29bof the second inner drill rod20bcontacts the second end27cof the third inner drill rod10cof the third assembly10c, and determines the relative positions of the third inner and outer drill rods20c,30c.

FIG. 4cillustrates the position of the coupling22cof the third drill rod assembly10crelative to the third outer drill rod30c. There is no gap (shown at arrow104). Instead, the coupling22cis seated against the up-hill end32cof the third outer drill rod30c. When the fourth drill rod assembly10dis coupled to the third assembly10c, the first end29cof the third inner drill rod20cis spaced apart from the second end27dof the fourth inner drill rod20d. The space between these ends29c,27dof the inner drill rods20c,20dis caused by the fact that the coupler22d(FIG. 4d) of the fourth assembly10dhas contacted the uphill end32dof the outer drill rod30d; thereby positioning the fourth inner drill rod20drelative to the outer drill rod30d. That is, the inner drill rod20dcan no longer shift or slide down longitudinally toward the down-hill end of the assembly, but is instead stopped by contact between the coupling22dand the outer drill rod30d.

Because of the design requirement that the inner rods always be shorter than the outer rods, any drill rod assemblies subsequently added to the fourth drill rod assembly10dwill have inner and outer drill rods similarly positioned as shown inFIG. 4d. That is, the couplings22of subsequently added drill rod assemblies10will be in contact with the outer drill rods30, such that no gaps exist in the drill string. This results in a blockage of the fluid flow path of the drill string. Such blockages are a known problem in the industry.

In view of the foregoing, there exists a need for a drill rod assembly, having inner and outer coaxial drill rods, that minimizes and/or eliminates restricted fluid flow paths upon assembly into a drill string.

SUMMARY

The present invention relates to a rod assembly an outer drill rod and an inner drill rod positioned within the outer drill rod. An annular fluid flow path is defined between the inner and outer drill rods. The outer drill rod includes an internal shoulder, while the inner rod includes an external shoulder sized to engage the internal shoulder. Engagement of the internal and externals shoulders limits movement of the inner drill rod relative to the outer drill rod in a first longitudinal direction. A coupling attached to the second end of the inner drill rod limits movement of the inner drill rod relative to the outer drill rod in a second opposite longitudinal direction.

One feature of the present invention relates to providing fluid flow passages in the coupling such that the passages are in fluid communication with the annular fluid flow path when the coupling is seated against the outer drill rod. Another feature of the present invention relates to providing fluid flow passages in the external shoulder of the inner drill rod such that the passages are in fluid communication with the annular fluid flow path when the external shoulder of the inner drill rod is seated against the internal shoulder of the outer drill rod. Still another feature of the present disclosure relates to a fluid flow passage formed in the inner drill rod.

Therefore, according to one aspect of the invention, there is provided a drill rod assembly, comprising: an outer drill rod having a first externally threaded end and a second internally threaded end, the outer drill rod including: a first inner diameter and a second inner diameter, the second inner diameter being greater than the first inner diameter; and an internal shoulder located at a transition between the first and second inner diameters; an inner drill rod having a first and second hexagonal ends, the inner drill rod being positioned within the outer drill rod such that an annular fluid flow path is defined between the inner and outer drill rods, the inner drill rod including: an external shoulder sized to engage the internal shoulder of the outer drill rod to limit movement of the inner drill rod relative to the outer drill rod in a first longitudinal direction; and a coupling attached to the second end of the inner drill rod, the coupling having an outer diameter at a first end that exceeds the first inner diameter of the outer drill rod to limit movement of the inner drill rod relative to the outer drill rod in a second opposite longitudinal direction; wherein the coupling defines fluid flow passages that are in fluid communication with the annular fluid flow path when the coupling is seated against the outer drill rod.

According to another aspect of the invention, there is provided a drill rod assembly, comprising: an outer drill rod having a first externally threaded end and a second internally threaded end, the outer drill rod including: a first inner diameter and a second inner diameter, the second inner diameter being greater than the first inner diameter; and an internal shoulder located at a transition between the first and second inner diameters; an inner drill rod having a first and second hexagonal ends, the inner drill rod being positioned within the outer drill rod such that an annular fluid flow path is defined between the inner and outer drill rods, the inner drill rod including: an external shoulder sized to engage the internal shoulder of the outer drill rod to limit movement of the inner drill rod relative to the outer drill rod in a first longitudinal direction; and a coupling attached to the second end of the inner drill rod, the coupling having an outer diameter that exceeds the first inner diameter of the outer drill rod to limit movement of the inner drill rod relative to the outer drill rod in a second opposite longitudinal direction; wherein the external shoulder of the inner drill rod defines fluid flow passages that are in fluid communication with the annular fluid flow path when the external shoulder of the inner drill rod is seated against the internal shoulder of the outer drill rod.

According to yet another aspect of the invention, there is provided a drill rod assembly, comprising: an outer drill rod having a first externally threaded end and a second internally threaded end; an inner drill rod having first male hexagonal end and a second end, the inner drill rod being positioned within the outer drill rod such that an annular fluid flow path is defined between the inner and outer drill rods; a coupling attached to the second end of the inner drill rod, the coupling having a female hexagonal end; wherein the inner drill rod defines a fluid flow passage, the fluid flow passage providing fluid communication between the annular fluid flow path defined by the inner and outer drill rods and another annular fluid flow path of a second drill rod assembly when the second drill rod is coupled to one of the first and second ends of the outer drill rod.

According to another aspect of the invention, there is provided a method of forming a drill rod, comprising: forming a first outer drill rod, the first outer drill rod having a first externally threaded end and a second internally threaded end, the first outer drill rod further including: a first inner diameter and a second inner diameter, the second inner diameter being greater than the first inner diameter; and an internal shoulder located at a transition between the first and second inner diameters; forming a first inner drill rod, the first inner drill rod having a first and a second hexagonal end, the first inner drill rod being positioned within the first outer drill rod, wherein an annular fluid flow path is defined between the first inner and first outer drill rod; forming an external shoulder on the first inner drill rod, the external shoulder arranged and configured to engage the internal shoulder of the first outer drill rod to limit movement of the first inner drill rod relative to the first outer drill rod in a first longitudinal direction; and attaching a coupling to the second end of the first inner drill rod, the coupling having an outer diameter at a first end that exceeds the first inner diameter of the first outer drill rod to limit movement of the first inner drill rod relative to the first outer drill rod in a second opposite longitudinal direction, wherein the coupling defines fluid flow passages that are in fluid communication with the annular fluid flow path when the coupling is seated against the outer drill rod.

Another aspect of the invention provides for a method of forming a drill string, comprising: forming first and a second outer drill rods, the first and second outer drill rods each having a first externally threaded end and a second internally threaded end, the first and second outer drill rods further including: a first inner diameter and a second inner diameter, the second inner diameter being greater than the first inner diameter; and an internal shoulder located at a transition between the first and second inner diameters; forming first and second inner drill rods, the first and second inner drill rods having a first and a second hexagonal end, the first and second inner drill rods being positioned within the first and second outer drill rods, respectively, wherein an annular fluid flow path is defined between the first inner and first outer drill rod and the second inner and second outer drill rod; forming an external shoulder on each of the first and second inner drill rod, the external shoulder arranged and configured to engage the internal shoulder of the first and second outer drill rods, respectively, to limit movement of the first and second inner drill rods relative to the first and second outer drill rods in a first longitudinal direction; attaching a coupling to the second end of the first and second inner drill rods, the coupling having an outer diameter at a first end that exceeds the first inner diameter of the first and second outer drill rods to limit movement of the first and second inner drill rods relative to the first and second outer drill rods in a second opposite longitudinal direction, wherein the coupling defines fluid flow passages that are in fluid communication with the annular fluid flow path when the coupling is seated against the outer drill rod; and attaching the first inner drill rod to the second inner drill rod and attaching the first outer drill rod to the second outer drill rod, whereby a drill string is formed.

While the invention will be described with respect to preferred embodiment configurations and with respect to particular devices used therein, it will be understood that the invention is not to be construed as limited in any manner by either such configuration or components described herein. While particular drill pipes are described herein, the principles of this invention extend to any environment in which minimizing and/or eliminating fluid flow restrictions in a drill string. These and other variations of the invention will become apparent to those skilled in the art upon a more detailed description of the invention.

The advantages and features which characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. For a better understanding of the invention, however, reference should be had to the drawings which form a part hereof and to the accompanying descriptive matter, in which there is illustrated and described a preferred embodiment of the invention.

DETAILED DESCRIPTION

FIGS. 5-27illustrate various embodiments of drill rod assemblies having features that are examples of how inventive aspects in accordance with the principles of the present disclosure may be practiced. Preferred features are adapted for preventing blockage of a fluid flow path through a drill string formed by the interconnection of the drill rod assemblies.

Referring first toFIG. 5, a drill string made up of two drill rod assemblies100is illustrated. The two drill rod assemblies100include a down-hill drill rod assembly and an up-hill drill rod assembly. Each of the down-hill and up-hill assemblies100includes identical components. Wherever possible, the same reference numbers are used through the drawings to refer to the same or like components, however, subscripts of ‘a’ and ‘b’ are used to identify the components of the particular down-hill or up-hill rod assembly, respectively. This same reference numbering scheme is used throughout the description of the various embodiments of the present disclosure.

Each of the outer drill rod assemblies100ofFIG. 5includes an outer drill rod110having a first externally threaded end150and a second internally threaded end152. The drill rod assemblies100each further include an inner drill rod120having a first hexagonal end154and a second hexagonal end156. The inner drill rod120is positioned within the outer drill rod110such that an annular fluid flow path160is defined between the inner and outer drill rods120,110. A coupling106is attached to the second hexagonal end156of the inner drill rod120.

To create the drill string, the internally threaded end152bof the up-hill outer drill rod110bis threaded to the externally threaded end150aof the down-hill outer drill rod110a. At the same time, the first hexagonal end154bof the up-hill inner drill rod120bis received within corresponding structure of the down-hill coupling106a.

Still referring toFIG. 5, the outer drill rod110defines a first inner diameter ID2and a second larger inner diameter ID3. An internal shoulder130is located at a transition between the first and second inner diameters ID2, ID3. The inner drill rod120includes an enlarged portion138that defines an external shoulder132. The external shoulder132of the enlarged portion138engages the internal shoulder130of the outer drill rod110to limit movement of the inner drill rod120relative to the outer drill rod110in an up-hill longitudinal direction (represented by arrow X).

The coupling106of the drill rod assembly100has an outer diameter OD2that exceeds the first inner diameter ID2of the outer drill rod110. The larger outer diameter OD2of the coupling106limits movement of the inner drill rod120relative to the outer drill rod110in a down-hill longitudinal direction (represented by arrow Y).

This first drill rod assembly embodiment ofFIG. 5is adapted to prevent blockage of the fluid flow path through the drill string. The fluid flow path of the drill string is generally defined by the annular fluid flow paths160of the interconnected drill rod assemblies100. The drill rod assembly100includes a number of passages140(best seen inFIG. 6) that further define the fluid flow path of the drill string. The passages140prevent a situation where flow between the annular flow path160b(FIG. 5) of an up-hill drill rod assembly and the annular flow path (160a) of a down-hill drill rod assembly is blocked.

Referring now toFIGS. 6-8, the passages140of the drill rod assembly100include fluid flow slots102formed in a bearing surface108of the coupling106. The fluid flow slots102cooperate with slots112formed in a bearing surface104of the outer drill rod110to define the passages140that prevent flow blockage.

Although no specific number of fluid flow slots102in the coupling106is required, preferably, the number of slots102balances the need for an adequate cross-sectional flow area with the need for adequate structural area of the bearing surface108. That is, the number of fluid flow slots102in the coupling106preferably maximizes fluid flow, without jeopardizing the structural strength of the bearing surface108of the coupling106. Likewise, no specific number of slots112in the outer drill rod110is required. Yet, preferably, the number of slots112balances the need for an adequate cross-sectional flow area with the need for adequate structural area of the bearing surface104. That is, the number of slots112in the outer drill rod110preferably maximizes fluid flow, without jeopardizing the structural strength of the bearing surface104of the outer drill rod110. In the illustrated embodiment, the coupling106includes eight fluid flow slots102(FIG. 7), and the outer drill rod110includes six slots112(FIG. 8).

In an alternative embodiment, as shown inFIG. 9, the drill rod assembly100includes fluid flow slots102formed only in the coupling106. There are no slots formed in the bearing surface104of the outer drill rod110. The fluid flow slots102of the coupling106are sized and oriented such that the passages140communicate directly with the inner diameter ID3(FIG. 5) of the outer drill rod110. Similarly, in yet another alternative embodiment, the drill rod assembly includes slot112formed only in the bearing surface104of the outer drill rod110(FIG. 10). Referring toFIG. 10, there are no slots formed in the bearing surface108of the coupling106. The slots112of the outer drill rod110are sized and oriented such that the passages140communicate directly with the annular flow path (e.g.,160b) of an up-hill drill rod assembly.

While each of the passages140defined by either one or both of the slots102,112of the coupling106and the outer drill rod110is cylindrical in form, other shaped passages can be provided. For example, inFIGS. 11 and 12, the outer drill rod110of the drill rod assembly defines passages140formed by splines or slots114having a generally square shape.

FIG. 13illustrates drill rod assemblies200of a second embodiment, the drill rod assemblies200being interconnected to form a drill string. Similar to the previous embodiment ofFIG. 5, each of the drill rod assemblies200includes an outer drill rod210, an inner drill rod220, and a coupling206that is attached to the inner drill rod220. This second drill rod assembly200is also adapted to prevent blockage of the fluid flow path through the drill string. In particular, the drill rod assembly200includes passage240that prevent a situation where flow between the annular flow path260bof an up-hill drill rod assembly and the annular flow path260aof a down-hill drill rod assembly is blocked.

In the embodiment ofFIG. 13, the passages240are formed in each of the first and second ends254,256of the inner drill rod220. In particular, as shown inFIG. 14, cross-drilled holes222are formed in the first end254of the inner drill rod220. The cross-drilled holes222are in fluid communication with a bore224located at the first end254of the inner drill rod220. Referring toFIG. 15, cross-drilled holes226are likewise formed in the second end256of the inner drill rod220. The cross-drilled holes226are in fluid communication with a bore228located at the second end256of the inner drill rod220. With this arrangement, fluid passes through the bores224,228from the first end254b(FIG. 13) of the up-hill inner drill rod220bto the second end256aof the down-hill inner drill rod220a, even when the coupling206is seated against the outer drill rod210of the down-hill assembly200. That is, the present drill rod assembly200permits the coupling206to seat against the associated outer drill rod210without blocking the fluid flow path of the drill string.

FIG. 16illustrates a third embodiment wherein the inner rod320includes a flow path through its entire length, eliminating the need for cross-drilled holes of the previous embodiment.

FIG. 17illustrates drill rod assemblies400of a fourth embodiment, the drill rod assemblies400being interconnected to form a drill string. Similar to the previous embodiments, each of the drill rod assemblies400includes an outer drill rod410, an inner drill rod420, and a coupling406that is attached to the inner drill rod420. The fourth drill rod assembly400embodiment is also adapted to prevent blockage of the fluid flow path through the drill string. In particular, the drill rod assembly400includes passages440that prevent a situation where flow between the annular flow path460bof an up-hill drill rod assembly and the annular flow path460aof a down-hill drill rod assembly is blocked.

In the embodiment ofFIG. 17, the passages440are defined by cross-drilled holes442formed in the coupling406. The second end456of the inner drill rod420includes an offset hexagonal construction444. The remaining portion458of the second end456of the inner drill rod that fits within the coupling406is round. When the coupling406is affixed to the inner drill rod420, the round portion458of the second end456of drill rod420generally aligns with the cross-drilled holes442. Fluid flows through the passages440defined by the holes442and around the round portion458of the inner drill rod and into the annular fluid flow path460aof the down-hill assembly400. In the illustrated embodiment, as shown inFIG. 18, the passages440formed in the coupling406are defined by six cross-drilled holes442; although other numbers of holes442can be provided.

In an alternative coupling embodiment of the fourth drill rod assembly embodiment400, the coupling406of the drill rod assembly400can include passages440that longitudinally extend along the length of the coupling406, as opposed to being radially oriented as shown inFIG. 18. Referring now toFIGS. 19-21, the passages440can be defined by reliefs (e.g., clearance bores or clearance notches)446formed along the length of the hexagonal inner bore448of the coupling406.

In still another alternative inner drill rod embodiment of this fourth drill rod assembly embodiment400, the drill rod420can define the passages that prevent fluid flow blockage. In particular, referring toFIGS. 22-24, the inner drill rod420can include passages440formed in the first and second hexagonal ends454and456of the inner drill rod420. As shown inFIG. 24, the passages440can be defined by slots464formed in the first hexagonal end454of the inner drill rod420and slots466(FIG. 23) formed in the second hexagonal end456of the inner drill rod.

Referring now toFIG. 25, drill rod assemblies500of a fifth embodiment are illustrated. Similar to the previous embodiments, each of the drill rod assemblies500includes an outer drill rod510, an inner drill rod520, and a coupling506that is attached to the inner drill rod520. This fifth drill rod assembly embodiment500is adapted to prevent blockage of the fluid flow path through the drill string. In particular, the drill rod assembly500includes passage540that prevent a situation where flow between the annular flow path560bof the up-hill drill rod assembly and the annular flow path560aof the down-hill drill rod assembly is blocked.

In the embodiment ofFIG. 25, the inner drill rod520is oriented in an up-hill position such that a gap516is provided between the coupler506and the outer drill rod510. The gap516of a down-hill drill rod assembly500can cause the inner drill rod520of the up-hill drill rod assembly to contact the outer drill rod510. That is, an external shoulder532of an enlarged portion538of the inner drill rod520can be pushed into contact with an internal shoulder530of the outer drill rod510. This up-hill position is typically experienced in the lower down-hill drill rod assemblies of a drill string, as previously described in the background of this disclosure.

Referring now toFIGS. 26 and 27, the passages540of the drill rod assembly500are formed in the external shoulder532of the enlarge portion538of the inner drill rod520. In particular, the external shoulder532includes slots or notches534. The notches534define the passages540that prevent flow blockage between the annular flow path560b(FIG. 25) of an up-hill drill rod assembly and the annular flow path560aof a down-hill drill rod assembly.

Although no specific number of notches534in the external shoulder532is required, preferably, the specific number of notches534balances the need for an adequate cross-sectional flow area with the need for adequate structural area of the shoulder532. That is, the number of notches534preferably maximizes fluid flow, without jeopardizing the structural strength of the external shoulder532. In an alternative embodiment, passages can also be formed in the internal shoulder (not shown) to prevent flow blockage at this particular region of the drill rod assembly.

As noted above, the drill rods are typically positioned in the drilling machine, with one end higher than the other during operation of the drilling machine; thus, the description has utilized the terms up-hill end and a down-hill end. It will be appreciated, however, that the use of such terms are for the purposes of describing preferred embodiments of the present invention and should not be construed as limiting. Those of skill in the art will appreciate that the drill rods may be positioned with the ends reversed. Further, in operation once the drill rods are employed during horizontal directional drilling, the drill rods may be horizontal and/or at an angle which differs from the original angle on the drilling machine.

Various principles of the embodiments included in the present disclosure may be used in other applications. The above specification provides a complete description of the present invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, certain aspects of the invention reside in the claims hereinafter appended.