CA1195520A - Drill rod coupling system - Google Patents

Abstract

DRILL ROD COUPLING SYSTEM

ABSTRACT

Improvements in a drill string such as used for earth drilling wherein the elongated drill steel sections and cooperable couplings include improved means for securing the drill steel sections together end-to-end to form the elongated drill string.

Description

j5~1 BACKGROUND OF THE INVENTION

In the earth drilling arts it is cornmon practice to provide a drilliny rig with an elongated boom or mast and a drill such as a rotary percussion drill which is supported on the mast For controlled movement longitudinally thereof by a powered feed means~ An elongated drill string having a drilling bit secured to its forwardmost end extends longitudinally of` the mast and is operably engaged by the drill motor whereby a percussive or impact drilling action, or a combined impact and rotary drilling action may be imparted to the drill string as it is driven endwise into an earth formation.
In practice, the limit of drill motor movement along the mast often is less than the desired hole depth.
Therefore, earth drilling operations are often carried out by assembling the drill string from a number of elongated drill steel sections and cooperable coupling members as drilling progresses.
Many drill steel coupling systems are shown in the prior art. By way of illustrative example, U.S. patent 3,211,484 discloses an elongated drill steel having alternate external threaded and nonthreaded sections wherein a threaded section is located adjacent one end of the drill steel and is intended to be secured to the cooperating end of a similarly threaded drill steel by an internally threaded coupl:ing member as shown in figure 1 of the ~ S5~1~

patent. In figure ~ o-F the same patent there is illustrated a pair of connected drill steels having internal threaded and nonthreaded sections including internally threaded end sections which are engageable by a suitable externally threaded coupling member to secure two such drill steels together. In U.S. patent 3,~2~,479 there is disclosed a drill steel having external threads extending over substantially the entire axial length thereo-f. In U.S.
patent 3,567,254 a drill steel is disclosed which includes alternate external threaded and nonthreaded sections wherein the threaded portions located adjacent an end of the drill steel are engageable by an internally threaded coupling member to secure a pair of the drill steels together. The nonthreaded portions of the drill steels include collars which cooperate with the couplings to preclude coupler migration in either direction along the threaded end portions of the connected drill steels. In U.S. patent 3,822,952 and in the above mentioned patents the drill steel and coupling system permits worn threads adjacent the drill steel end to be cut off for further use of the drill steel by employing a new threaded portion thereof adja~cent to the worn portion.
It is also well known in the art to provide conventional drill steels with stress relieving means for the purpose of reducing the incidence of fatigue failure or the occurrence of stress risers in the drill steel structure. For example, ;2~9 U.S~ patent ~,966,341 discloses a dr.ill steel provided with a threaded end portion which is suitable for engagement with a coupler to couple a pair of such drill steels together end to end. A stress relief means is provided adjacent the threaded end section of the drill steel and as shown includes a serial plurality of axially spaced 9 circumferential undercuts or grooves.
The present invention offers improvemen-ts over heretoFore known drill steels ancl coupling systems such as lû those described hereinabove, including but not limited to a drill steel having an axially extending threaded portion for engagement with a coupling member and an axially extending stress relief portion wherein a stress relieF means is axially coextensive with the threaded portion of the drill steel. In a preferred embodiment of the invention a tubular drill steel has internal threads extending throughout a substantial length thereof whereby an externally threaded coupling is cooperable with a portion of such internal threads to secure pairs of the drill steels together end-to-end. In the event of thread failure the affected drill steel end may be cut off to provide new threads for engagement with the coupling member.
One object of the instant invention is to provide an improved drill steel for earth drilling.
Another object oF the invention is to provide an improved drill steel coupling system.

-A Further more specific object of the invention is to provide a drill steel having axially coextensive coupler engaging means and stress relief means.
A still further object of the invention it to provide a tubular drill steel having threads provided internally thereof and extending from one end thereof a distance greater than the thread engagement length of a cooperable coupler.
Yet another object of the invention is to provide a tubular drill steel having coupler engaging means provided internally thereoF which is axially coextensive with stress relief means provided externally thereof.
These and other objects and advantages of the instant invention are more fully described in the following specification with reference to the accompanying figures, in which:
Figure 1 is a fragmentary longitudinal section of a drill steel constructed according to one presently preferred embodiment of the instant invention;
Figure 2 is a fragmentary longitudinal section simi.lar to figure 1 showing an alternate embodiment of the instant invention;
Figure 3 is a fragmentary side elevation, partially in longitudinal section, showing yet another embodiment oF the invention;

Figure ~ is a fragmentary side elevation similar to a portion of Figure 3 showing one embodiment of a stress relief means of the instant invention;
Figure 5 is a longitudinal section showing one manner of coupling a pair oF drill steels of the embodiment of Figure l;
Figure 6 is a longitudinal section similar to Figure 5 showing one means for coupling a pair of drill steels of' the embodiments of Figures 2 or 3; and Figure 7 is a longitudinal section showing an alternate means f'or coupling a pair of drill steels of the embodiments of Figures 2 or 3.
Figure 8 is a longitudinal section showing another alternate means for coupling a pair of drill steels of the embodiments of Figures 2 or 3.
Referring to Figures 1 through 4, there is generally indicated at 10 a longitudinally extending portion of a drill steel according to certain presently pref'erred embodiments of the instant invention. The drill steel 10 is formed from any suitable material such as hardened steel and has a tubular form which provides an internal periphery 12 and an external peri,phery 1~ as shown. Although the description hereinbelow refers only to one end portion of the drill steel, it will be appreciated that in general the description applies to both longitudinal ends of any given drill steel of the present invention.

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The inner periphery 12 has formed the:reon any suitable force bearing thread such as a rope thread 16 extending a distance L thereon from one axial end 18 of -the drill steel 10 to an undercut 20 where L ordinarily would be about two or three times the internal thread root diameter or major diameter9 D of thread 16. Thread 16 may be either a single or multiple start thread, as desi:red, and the length of thread 16 may be the length of th:read engaqement by a suitable drill steel coupling member (to be described hereinbelow) or alternatively may be a multiple, XL, of such engagement length as shown in Figure 2. Alternatively, drill steel 10 may have in-ternal threads 16 extending continuously from one axial end 18 thereof to the other (Figure 3), in which case undercut 20 is not provided.
The undercut 20 provides for convenient thread runout so that the thread length may be readily controlled during the thread forming process. If precise enough control over the threading process is exercised through such techniques as cycle control or numerical control, the thread forming process may be su~iciently precise that thread runout at the proper point could be accomplished without r-esorting to use of the undercut 20.
The internal threads 16 may be formed by a hammer swedginy process in which drill steel 10 is swedged down on a threaded mandrel (not shown). Undercut 20 also may be formed to provide a shoulder of smaller diameter than the .

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coupling whereby the coupling will be constrained against migration in the axial direction, as described hereinbelow.
Also illustrated in Figures 1 through 3 is a stress relief means shown as a serial plurality of axially spaced 9 circumferential grooves 22 formed on exterior periphery 14 of drill steel 10. In the case of the construction of Figures 1 and 2, circumferential grooves 22 preferably are coextensive with thread 16 from the axial end 18 of drill steel 10 to a point 24 spaced beyond the terminus of thread 16 by a distance approximating D/2 where D is the root diame-ter of thread 16. One purpose in having the stress relief grooves 22 extend beyond the run of thread 16 is to minimize the e~fect of undercut 20 as a stresC riser.
As will be seen from Figure 3, in the case of a drill steel 10 having an internal thread 16 extending continuously from one axial end 18 thereof to the other~ the serial plurality of circumferential grooves 22 also extends continuously from one axial end 18 to the other.
In an alternate embodiment of the stress relief means of this invention as shown in Figure 4, the stress relief is provided by a helical groove means 26 extending along the exterior periphery 14 of drill steel 10 through the desired distance as described hereinabove. Helical groove means 26 may be either a single start or multiple start groove, as deemed desirable. For the embodiments of Figures 1 or 2 such a helical stress relief groove or grooves may taper out ~5~

to -full drill steel outside diameter or may run out to a blind end. The depth of the external groove 2~ or 26 at -the root should be at leas-t .01 inches to assure that it will be deeper than expected surface damage which might ordinarily be inflicted upon the full diameter lands 28 located between adjacent grooves 22 or between the turns of the helical groove 26. Of course, the stress relief grooves 22, 26 may be as deep as .05 or .1 inches or more as deemed necessary or desirable, consistent with overall drill steel strength considerations.
The stress relief grooves 22 provide a multiplicity of axially distributed stress risers along a length of the drill steel 10 to thereby distribute stress concentrations along the drill steel. In addition, as the stress concentrations are located in the recessed grooves 22 which are protected frorn physical damage by the intervening full diameter lands 28, any damage to the exposed exterior surfaces of the intervening lands 28 such as might result from contact with the bore hole wall or from detritus impingement will not produce serious stress risers. Of course, helical groove 26 functions in the same way.
Referring now to Figures 5 through 7, there are shown several embodiments of couplings to secure together the drill steels 10 described hereinabove. Each coupling 30 for the drill steels 10 includes an elongated, externally threaded member 31 having an axially extending through bore s~

32. The exterior threads 34 of the couplings 30 are cooperable with the interior threads 16 oF drill steels 10 for threaded engagemen-t therewith. In Figure 5 the coupling member 31 is of a length slightly less than the distance between respective shoulders 36 in undercuts 20 oF two drill steels 10 abutted end-to-end whereby, when the drill steels 10 are screwed together onto the coupliny 30, the coupling is captively retained between shoulders 36 and is thus constrained against migration in the axial direction. In this confiyuration the drill steel ends 18 abut di~ectly on one another whereby the impact drilling forces are conducted from one drill steel to the next through a single interface. Drilling fluid is passed through the tubular drill steels 10 and the axial bores 32 in couplings 30 for the purpose oF bit cooling and bore hole cleaning as is well known.
In Figures 6 and 7 the drill steels 10 to be coupled are threaded throughout a distance XL or threaded continuously as desc~ibed hereinabove whereby, if the joint were to loosen, a coupling 30 such as that shown in Figure 5 would be free to migrate away from the jointO Accordingly, the coupling to be used, labeled 30' in fig. 6, includes intermediate the threaded ends thereoF a circumferentially extendiny land 38 of enlaryed diameter which presents oppositely Faciny shoulders 40 against which the axial ends 18 of the respèctive clrill steels 10 to be coupled are butted when the joint is -tightened down. The shoulders thus fixedly loca-te -the coupler 30' axially with respect -to the drill steels 10 and prevent coupler migration. This is not the most desirable arrangement as the impact drilling Forces must be transmitted through two abutting interfaces at each coupling. A more preferable app:roach is illustrated in Figure 7 wherein a coupling 30" includes a circumferential land 42 of enlarged diameter formed on the coupling 30'' intermedia-te its threaded ends. The diameter of land 42 is substantially smaller than the exterior diame-ter of the drill steel 10 and each drill steel 10 has an interior, annular groove 44 formed adjacent the respective axial ends 18 such that when the drill steels 10 are screwed on to the coupling 30'' the axial ends 18 of the drill steels directly abut one another and the impact drilling forces are conducted through only a single mechanical interface from one drill steel 10 to the next. The annular grooves 44 formed in the adjacent end portions of the connected drill steels 10 form an undercut 45 which surrounds and captively retains the annular land 42 of coupling 30'' to prevent coupling migration.
In an alternative embodiment illustrated in Figure 8 the coupling 30" ' includes a circumferential conical portion 52 of enlarged diameter formed outwardly of the coupling 30" ' intermediate its threaded ends. The outside diameter oF the conical portion 52 is smaller than the exterior diameter of the drill steel 10, and each drill steel 10 has an in-terior camber 54 -formed inwardly and adjacent the respective axial ends 18 such that when the drill steels are screwed onto the coupling 30''' the axial ends 18 of the adjacent drill steels directly abuts on another and the impact drilling forces are conducted through only a single mechanical interface from one drill steel to the next. The interior camber 54 formed in the adjacent end portions of the connected drill steels 10 form an undercut 55 which surrounds and captively retains the conical portion 52 of the coupling 30''' to prevent coupling migration. An advantage of the embodiment illustrated in Figure 8, is the relative ease with which the camber 54 may be formed in the drill steel initially or in instances where the rod might break.
The advantages of the described drill steel and coupling system are manifold. In order to provide efficient and economical drilling operations, practitioners of the art have continuously sought ways to assure quick and easy refurbishing of a broken or damaged end portion of a drill steel for further use thereof. The embodiments of Figures 2 and 3 provide such capability in that if the threads engaged by a coupling have been damaged, the damaged thread portion may be quickly cut off and the end of the drill steel dressed to provide new threads and permit further use of the drill steel. Ey iocating the threads inside the tubular 5~

drill steel the potential for thread damage is minimized 9 most particularly due to the elimination of thread contact with the bore hole wall during drilling. An additional advantage is provided by the stress relief rneans being coextensive with the coupler engaging portion of the drill steel. In this context it is noteworthy that the described stress relief means may be other constructions than radial or helical grooves, and may be coex-tensive with other Forms of coupler engaging means than threads. For example, the disclosed stress relief means are believed to offer the same benefits as described hereinabove with respect to threads if the coupling means were instead an unconventional coupling arrangement such as a tape:r Fit or a bayonet lock.
Another advantage to be noted is that the interior passage through the tubular drill steel constitutes the flow path for blow air or fluid which is utilized for bit cooling and to clear detritus from the bottom of the bore hole.
This may be a reduced flow rate compared to the flow rate available for prior, externally coupled drill steels because the through bore in the couplings is necessarly of limited size; however, even such reduced flow rate will be effective for the following reasons. For a given air or fluid pressure, the available air or Fluid Flow rate is limited by the cross sectional area of the coupling through bores as noted. However, as the improved drill string carries its coupling members inside, the outer diameter of ~ss~

the drill string tends to fill the borehole more completely than do prior drill string systems in which the outside diameter of the coupling is the limiting factor in bore hole diameter and the major part of -the drill string is much smaller than the bore hole diameter. Accordingly, for the present invention the annular space between the drill steel and the bore hole wall tends to be much smaller and more uniform than for conventional drill strings, and this provides for greater blow air or fluid flow velocity for a given flow rate through the interior of the drill string.
As greater flow velocity produces better detritus removal From the bore hole, the present lnvention improves -the efficiency of detritus removal for a given blow air or drilling fluid pressure.
Other advantages of the invention include improved stiffness of the tubular drill steels as compared to conventional drill steels The stiffer drill steel tends to bore a straighter, truer hole. In addition, the impact drilling stress waves propagate along the tubular drill steel and therefore are delivered to the outer periphery of the drilling bit. This is believed to provide a more efficient drilling action than does the delivery of stress waves centrally of the bit as occurs in smaller diameter, conventional drill steels. It may be additionally noted that as the tubular drill steel is stiffer, energy propagation along the drill steel is more efficient because ~13-the drill steel has less tendency to bend under the Force of Feed pressure.
According -to the descrip-tion hereinabove there is provided by the instant invention an improved drill steel and coupling system For impac-t earth drilling operations ~herein a drill steel comprises a tubular structure having coupler engaging means such as rope threads extending about the interior periphery thereof anci stress relief means formed on the exterior periphery oF the drill steel and coextending with the coupler engaging means. The stress relief means preFerably extends further along the drill steel than the extent of the thread run along the interior periphery thereof. Preferably the internal threads of the drill steel extend a distance greater than the length of thread engagement for the coupling to be used whereby, in the event that the threads near the end oF the drill steel are damaged in use, that end of the drill steel may be conveniently cut off and dressed to provide previously unused threads thereby permitting further use of the drill steel.
Not intending to be limited to those specific embodiments described hereinabove, the inventors believe -the invention is capable oF other constructions within a wide design latitude without departing from the broad spirit thereof. For example, the specific dimensions and proportions mentioned hereinabove are capable of some variation, the specific cross sectional shape of the stress relief grooves as illustrated may be alte:red in various ways so long as dangerous stress risers are not produced thereby, the central lands of the couplers may instead be radially projecting lugs or other forms which do not have a continuous circumferential extent at a uniform diameter, and the like. In addition, it will be appreciated that the coextensive stress relief means and drill steel coupling threads may be utilized, in modified form, in -those structures utilizing integral pin and box threaded connections or other connection systems which do not require a separate coupler element. These and other embodiments and modifications having been envisioned and anticipated by the inventors, it is intended that the invention be interpreted as broadly as permitted by the scope of the claims appended hereto.

Claims (17)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In an elongated drill steel section for use in making up an elongated drill string wherein said drill steel section includes an internal threaded section adjacent at least one axial end thereof for cooperating with an externally threaded coupler member for coupling said drill steel section end-to-end with another drill steel section, the improvement comprising:
said drill steel section including stress relief means formed on the exterior periphery of said drill steel and extending longitudinally thereof and longitudinally co-extending with at least a major portion of said internal threaded section.

2. The improvement as claimed in claim 1 wherein said stress relief means includes a serial plurality of axially spaced circumferential grooves.

3. The improvement as claimed in claim 1 wherein said stress relief means includes a helical groove means.

4. The improvement as claimed in claim 2 or 3 wherein the longitudinal extent of the internal threads on said drill steel section is greater than the extent of thread required for fully coupling said drill steel section to another drill steel section.

5. The improvement as claimed in claim 2 or 3 wherein the longitudinal extent of said threads is at least twice the extent necessary for fully coupling said drill steel section to another drill steel section.

6. The improvement as claimed in claim 2 or 3 wherein said stress relief means has a longitudinal extent along said drill steel section greater than the longitudinal extent of the internal threads therealong.

7. The improvement as claimed in claim 2 or 3 wherein said stress relief means has a longitudinal extent along said drill steel section which is greater than the longitudinal extent of the internal threads therealong by approximately 1/2 the root diameter of said threads.

8. The improvement as claimed in claims 2 or 3 wherein said grooves extend to a depth of at least .01 inches below the full diameter of the exterior peripheral surface of said drill steel section.

9. The improvement as claimed in claim 2 or 3 wherein said grooves extend to a depth in the range of .01 inches to approximately .1 inches below the full diameter of the exterior peripheral surface of said drill steel section.

10. The improvement as claimed in claim 1 wherein said drill steel section includes means cooperable with another drill steel section coupled thereto to prevent axial migration of said coupler member.

11. The improvement as claimed in claim 10 wherein said means to preclude axial migration includes undercut means formed within interior peripheral portions of said drill steel section.

12. The improvement as claimed in claim 10 wherein said means for precluding axial migration includes enlarged diameter means formed on said coupler member.

13. The improvement as claimed in claim 12 wherein said drill steel section axially abuts said enlarged diameter means.

14. The improvement as claimed in claim 12 wherein said drill steel section axially abuts another drill steel section connected thereto and includes means whereby said enlarged diameter means is captively retained to preclude axial migration of said coupler member.

15. In a drill steel section of a type adapted for selective coupling end-to-end with other drill steel sections to form an elongated drill string, the combination comprising:
said drill steel section including an elongated generally tubular portion located adjacent one axial end thereof and having an internal peripheral portion and an external peripheral portion;
coupler engaging means formed on said internal peripheral portion and extending axially of said tubular portion; and stress relief means formed on said external peripheral portion, said stress relief means extending axially of said tubular portion and axially coextending with at least a major portion of said coupler engaging means.

16. The combination as claimed in claim 15 wherein said stress relief means extends longitudinally of said tubular portion from said one axial end of said drill steel section and said coupler engaging means extends longitudinally of said tubular portion from said one axial end and is coextensive wth at least a longitudinally extending portion of said stress relief means.

17. The combination as claimed in claim 16 wherein said stress relief means includes circumferential groove means and said coupler engaging means includes thread means.

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