EP0907820B1

EP0907820B1 - Drill tube for forming drill strings

Info

Publication number: EP0907820B1
Application number: EP97928611A
Authority: EP
Inventors: Per-Olof Liljebrand; Urban Olsson; Rainer Beccu
Original assignee: Sandvik AB
Current assignee: Sandvik AB
Priority date: 1996-06-24
Filing date: 1997-06-18
Publication date: 2004-01-02
Anticipated expiration: 2017-06-18
Also published as: SE9602472D0; AU3282197A; ZA975507B; ATE257214T1; SE9602472L; AU712137B2; EP0907820A1; WO1997049891A1; DE69727056D1; SE506855C2

Abstract

In a first aspect the invention relates to a drill-string-forming drill tube which includes a channel (15) intended for passing flushing liquid, inside of which there is a restriction which forms a seat (14) for a valve body (16) serving as a check valve. Said drill tube comprises, in addition to a partly spherical skittle member (17) for engagement in the seat (14), two or more tangentially separated blocking elements (21). The purpose of said elements is, when flushing liquid is fed from the valve seat towards a second restriction distanced therefrom, to stop the valve body against said second restriction without sealing thereagainst. Therefore, one and the same drill tube may be used for upwardly directed as well as downwardly directed drilling. In a second aspect, the invention relates to the valve body as such.

Description

Technical Field of the Invention

This invention relates to a drill tube for forming drill strings, comprising a through channel intended for passing flushing liquid, inside of which there is a restriction which forms a seat for a valve body serving as a check valve. The invention further relates to a valve body per se.

Drill strings composed of such drill tubes are in practice often used for percussive top hammer drilling, the drill string having the purpose of transferring percussion energy from a top hammer to a drill bit in the free end of the drill string. The individual drill tube usually has a female thread formed at an end intended to receive a male thread at an opposite end of another drill tube. These threads are formed at production in particular end pieces in which reduced or necked sections of the flushing liquid channel are included, the end pieces being joined to a longer tube having a larger cross-section area, by friction welding.

Prior Art

A drill tube of the kind initially referred to is previously disclosed in EP-B-0 126 740 (see particularly figures 4 to 9). In order to remove drill cuttings from the drill hole and to grease and cool the drill bit in connection with drilling, water, possibly together with certain additives, e.g. to improve the greasing, is usually used as a flushing liquid. Since the drill tubes are of a relatively large inner diameter, the channel of each tube holds a considerable amount of flushing liquid. As the length of the drilled hole is increased, the drill string is elongated by means of further drill tubes which are connected to the drill string by the above-mentioned threaded joints.

When drilling in rocks, the drill string may not only be directed downwards but also upwards as well as substantially horizontally. When drilling is effected in the direction upwards, it is necessary to see to it that the flushing liquid remains in the individual drill tube of the drill string when a new drill tube is to be connected, because otherwise the entire channel in the drill string would first have to be emptied and then be refilled with flushing liquid in connection with each shift occasion. In order to solve this problem, a check valve has previously been arranged in the type of drill tubes which are used for drilling in the direction upwards. More precisely, a ball which is allowed to abut against the lower reduction of the individual drill tube has been used for this purpose. When flushing liquid is fed in with a relatively high pressure in the lower end of the drill tube, the ball will be lifted and float in the liquid column inside the tube, the liquid being able to pass freely out through the opposite, upper end of the tube. However, an annoying disadvantage of this kind of check valve is that drill tubes with a permanent built-in valve ball can only be used for drilling in the direction upwards. Namely, if the tube is included in a drill string for downwardly directed drilling, the ball would fall down by its own weight to the lower end portion of the tube and there seal against the restriction in the thread-furnished end piece of the tube. Therefore, in practice, different kinds of tubes have to be used for upwards and downwards drilling, respectively. This leads to, among other things, stock-keeping problems.

Objects and Features of the Invention

The present invention aims at obviating the above-mentioned problems and at creating an improved drill tube. Thus, a primary object of the invention is to create a drill tube which may be used for upwardly directed as well as downwardly directed drilling and, on one side, has a reliably working check valve function at upwardly directed drilling at the same time as the tube, at downwardly directed drilling, admits a free flow of flushing liquid through the flushing liquid channel. In other words, the drill tube should be able to be used universally for drilling in all arbitrary directions.

According to the invention, this object is attained by the features defined in the characterizing portion of claim 1. Preferred embodiments of the drill tube according to the invention are furthermore defined in the dependent claims 2 to 5.

In a particular aspect, the invention also relates to a valve body for the drill tube according to the invention. The features of said valve body may be seen in claim 6.

Further Elucidation of Prior Art

A check valve arrangement at a connection between two tubes, the connection between the tubes being achieved by friction welding, is previously known in SE-B-456 269. The arrangement includes a ball and a holder which is mounted in connection with an internal welding bead which is formed in connection with the friction welding, the holder being axially locked by said bead. However, this arrangement requires a very exact check of the parameters at the friction welding so that the holder is not wedged up by the bead growing radially inwards. Said type of check valve would neither be able to be used for percussive top hammer drilling, since a clamed up ball holder would break down fairly at once because of the large percussion energy which is developed at this kind of drilling.

Brief Description of the Appended Drawings

In the drawings:

Fig 1: is a view of a drill tube according to the invention shown partly in a longitudinal section, the tube being shown in a cut state,
Fig 2: is an enlarged section A-A in Fig. 1, and
Fig 3: is a view corresponding to Fig. 1 showing an alternative embodiment of the invention.

Detailed Description of Preferred Embodiments of the Invention

In Fig. 1, reference numeral 1 generally designates a drill tube which is composed of two end pieces 2, 3 and a proper tube part 4, positioned therebetween. A cavity 5 with a schematically shown internal thread or female thread 6 is recessed in the first-mentioned end piece 2. The opposite end piece 3 has a male-like spigot 7 on the outside of which an external thread or male thread designated 8 is formed.

The end pieces 2, 3 are connected to the intermediate tube part 4 via conventional friction weldings 9. Such welding seams are produced by bringing two metal bodies adjoining each other to rotate relative to each other while gradually increasing the temperature in the interface between the bodies, the bodies being pressed together when the material in the interface has obtained an appropriate temperature (around 1 200°C). When applying friction welding on the drill tube in question, beads designated 10 and 10' respectively are formed on the inside of the tube walls. In this connection, it should be pointed out that the first end piece 2 has a cavity 11 turned towards the tube part 4 which communicates with the cavity 5 via a restricted channel section 12 delimited by a ring-formed material portion 13 on the inside of the otherwise tubular end piece 2. A cone-shaped surface 14 constitutes a transition between the cavity 11 and the channel section 12.

In an analogue way, the second end piece 3 comprises a cavity 11' turned towards the tube part 4 which, via a cone-shaped or otherwise narrowing surface 14' transform into a restricted channel section 12' having a smaller diameter than the cavity 11. Said channel section 12' extend the whole way through the male-like portion 7. In this connection, it may also be mentioned that the inner diameter of the cavities 11, 11' correspond to the inner diameter of the proper tube part 4.

In practice, the shown drill tube may have a length within the range of 1,5 - 2 meter and an outer diameter within the range of 50 - 100 mm. Then the inner diameter of the proper tube part amounts to about 2/3 of the outer diameter of the tube part (for e.g. a tube having the outer diameter 90 mm, the inner diameter is approx. 60 mm).

The through flushing liquid channel which is formed by the cavity in the tube part 4 as well as the cavities 11, 11' and the restricted sections 12, 12' in the end pieces 2, 3 is in its entirety designated 15 in Fig. 1.

As far as the shown drill tube has been described hitherto, the same is in all essentials previously known.

A check valve, in its entirety designated 16, which includes a front skittle member 17 as well as a shaft 18 extending backwards therefrom is arranged in the channel 15. The free end portion in the very front of the skittle member 17 has, in the shown example, a partially spherical surface 19 which may turn into a sealing engagement with the cone surface 14 serving as a seat. In the area behind said front end portion, the skittle member 17 is in other respects in all essentials cylinder-shaped. Instead of a partly spherical shape, the front end portion may also be cone-shaped (e.g. for a sharp-edged seat).

As may be seen in Fig. 2, the shaft 18 includes a central portion 20 from which three wings 21 serving as blocking elements protrude between which equally many grooves or cavities designated 22 are delimited. The rounded bottoms of said grooves designated 23 extend not only along the shaft but also along the major part of the cylindric skittle member 17, as may be seen in Fig. 1. The wing-formed blocking elements 21, which in the shown example have a relatively long axial extension, have an outer radius which is smaller than the inner radius of the tube channel 15. On the other side, the outer radius of each one of the blocking element is larger than the outer radius of the portion engaging in the skittle member.

In the exemplified embodiment, the shaft 18 has a plane end surface 24. However, the shape of said end surface may be modified most considerably. In particular, the surface in question may be made concave, preferably deeply concave.

In accordance with a preferred embodiment of the invention, the total cross-sectional area of all grooves 22 is at least as large as the cross-sectional area of one of the restricted sections 12, 12' of the channel. Most suitably, the total cross-sectional area of the grooves is considerably larger than the above-mentioned restricted section.

The Function and Advantages of the Invention

In Fig. 1, the drill tube 1 is shown with the end piece 2 turned downwards and the end piece 3 turned upwards. In this state, the drill tube may (when said tube constitutes a part of a composed drill string) be used for upwardly directed drilling (at arbitrary angles between the ground plane and the vertical plane). During drilling, flushing liquid is then fed in the direction from the bottom part of the drill string towards the drill bit at the upper end of the drill string. As long as the feeding of the flushing liquid is not effected, the valve body 16 will fall down by its own weight to the lower end of the wide channel section and seal against the seat surface 14. However, as soon as flushing liquid with a certain pressure is fed in the direction upwards throughout the drill tube, the valve body will be lifted from the seat and kept floating in the liquid column inside the tube (normally, the valve body is so heavy that it is kept floating in the lower half of the drill tube). When the flow of flushing liquid is disrupted in connection with coupling another drill tube at the lower end of the drill string, the valve body will automatically fall down and seal against the seat surface 14 and thereby retain the liquid in the tube. In connection with an upwardly directed drilling, the valve body 16 thus fulfils the same purpose as a conventional ball, viz. said body works as a check valve.

However, unlike the conventional valve balls, the valve body according to the invention also enables downwardly directed drilling with one and the same drill tube. Namely, if the drill tube is turned downwards in a drill string (at an arbitrary angle from the ground plane to the vertical plane), the wing-formed blocking elements 21 of the valve body will be stopped either against the welding bead 10' (if the outer radius of the blocking element is larger than the inner radius of the bead) or towards the cone-shaped surface 14' in connection with the channel section 12' (if the outer radius of the blocking element is smaller than the inner radius of the bead). In doing so, the flushing liquid may pass freely via the grooves 22 without the valve body sealing against the welding bead or the coned surface. In other words, the valve body admits a free flow of flushing liquid to the drill bit in connection with a downwardly directed drilling.

Thus, a substantial advantage of the invention is that one and the same drill tube may be used for arbitrary drilling directions without the operator having to think about the check valve body. When a check valve effect is needed, viz. at an upwardly directed drilling, the valve body automatically starts to function and as soon as the back valve would be a hindrance, viz. at a downwardly directed drilling, said valve automatically seizes to function. This means that stock-keeping and handling drill tubes is considerably facilitated and rendered more effective.

In Fig. 3 an alternative embodiment is shown according to which a valve body 16' has a skittle member with a cone-shaped sealing surface 19' for co-operation with the welding bead 10 instead of the coned surface 14 in connection with the channel section 12. Even if the welding bead 10 would be somewhat uneven, in practice a satisfactory sealing effect is achieved, as it is acceptable that a smaller amount of water percolates during the relatively short period of time which is required for connecting another drill tube on a drill string.

Feasible Modifications of the Invention

The invention is not solely restricted to the embodiments described and shown in the drawings. Thus, it is conceivable that the valve body has a different number of blocking elements than three. Thus, it is possible to use only two blocking elements as well as four or more. Furthermore, the blocking elements may be formed as relatively thin, finger-like organs which are mutually separated and extend backwards from the skittle member or a common shaft. Neither do the blocking elements need to have the same large axial length as the wings which have been exemplified in the drawings. Another feasible embodiment is to make the valve body so that it may be built-in and retained in one of the end pieces of the drill tube, more precisely between the valve seat and a welding bead or another restriction. In doing so, the skittle member sealing against the valve seat may be small (e.g. ball-like) and furnished with blocking elements in the form of fingers or tines. The total length of the valve body must then of course be at least somewhat smaller than the distance between the valve seat and the welding bead so that the valve body may move between closing and opening positions. In case the tine-formed blocking elements are made at least partly elastic, the valve body may be mounted by being pressed pass the welding bead while elastically deforming the elements, and then said elements are widened again so as to be blocked against the bead. Thus, the primary function of the elements is to stop or block the valve body against a restriction in the flushing liquid channel distanced from the valve seat and preferably also steer the valve body so that the sealing surface of the skittle member with reliability is brought into engagement with the valve seat.

Claims

Drill tube for forming drill strings, comprising a through channel (15) intended for passing flushing liquid, inside of which there is a first restriction (13,10) which forms a seat for a valve body (16;16') serving as a check valve, characterized in that the valve body (16;16'), in addition to a partially spherically or conically shaped, front skittle member (17) for engagement in the seat, includes two or more tangentially separated blocking elements (21) which at least in the mounted state thereof have an outer radius which is smaller than the inner radius of the channel, but larger than the outer radius of the portion of the skittle member (17) engaging in the seat, and the purpose of which elements is, when flushing liquid is fed from a first restriction (13, 10) towards a second restriction (10', 14) distanced therefrom, to stop the valve body against said second restriction without sealing thereagainst.
Drill tube according to claim 1, characterized in that the seat for the skittle member (17) of the valve body is a cone-shaped surface (14) at a ring-formed tube material portion (13) which delimits a restricted section (12) of the channel (15).
Drill tube according to claim 1, characterized in that the seat for the skittle member of the valve body consists of a bead (10) provided on the inside of the tube formed by friction welding.
Drill tube according to any one of the preceding claims, characterized in that the blocking elements are in the form of axially extending wings (21), which protrude from a central shaft (20) and between which cavities (22), through which the flushing liquid may pass freely, are delimited.
Drill tube according to claim 4, characterized in that the total cross-section area of the cavities (22) is at least as large as the cross-sectional area of a restricted section (12, 12') of the channel (15).