BACKGROUND OF THE INVENTION It is widely known, that drill pipes can be assembled with a coarse thread.

With such pipes it is possible to transport one fluid in the pipe, and such trans- port has until now been sufficient for the users on drilling rigs.

Recently, the need for transporting more than one fluid has developed, but assembling drill pipes with more than one channel for different kind of fluids has met some difficulties, as the threads often are worn differently and can never be tightened to a degree, where no leaks are present and at the same time secure, that the fluids are transported without being mixed through the proper channels in the pipes.

A pipe for more than one fluid is known from NO-B 169,797, where a main pipe is assembled using an internal lining in the joining of the main pipe, and an auxilary pipe is assembled next to the main pipe using locking and sealing rings. The assembly is held with external flanges connected to each other by bolts.

The surface of such connection is obviously not cylindrical or rotational symmetric around the centre axis and it is evidently not able to be used in a drill string, where the drill string is to be rotated during drilling operations.

In order to achieve a more smooth surface it is suggested in US-B 2,294,806 to connect external flanges with axially directed,"internal bolts"being coun- tersunk with an opening sufficient for the service crew to turn the axially di- rected screws and thereby connect the pipes.

The subject matter of that publication is, however, not suited for being used in a drill string, as the assembly is not cylindrical and the flanges in- creases the diameter and thereby make the use of the drill string not feasable.

Further. this technique is not suitable for transporting more than one fluid.

SUMMARY OF THE INVENTION On this background it is the object of the invention to provide means for axially connecting drill pipes being able to transport separate fluids in a drill string.

To this end the inventions suggests that the connecting means are axially directed bolts inserted in the outer wall of the drill rod and extending axially past the end of the drill rod into internally threaded blind holes in the next drill rod to be connected to the first drill rod, and that each terminal surface of a drill rod is made with arrangements for at least one coupling means for the transport of different kind of fluids in the drill string.

With a drill pipe according to the invention it is possible both to connect drill pipes into one drill string without outer flanges and to transport different fluids in the drill string. Such fluids can be drilling mud for the drilling, brine, and e. g hydraulic fluids. When assembling the drill rods to a drill string it is important that the connection according to the invention can be made without outer flanges or external auxilary pipes, as such protrusions would prevent the use of the drill string as a rotational device.

One preferred embodiment of the coupling for drill pipes can be found in, that the bolts are accessed through pocket openings in the outer wall of the drill rod in the proximity of the end of the drill rod, where the bolts are reach- ing into the internally threaded blind holes in the next drill rod, and that the pocket openings are of a width sufficient for screwing or unscrewing the bolts.

With such embodiment the coupling can be assembled manually under visual inspection of the coupling.

If the end surfaces of the drill rods are equipped with at the least one guide pin and/or a corresponding recess, respectively, it will be easy to establish the correct connection and reduce the shearing forces on the bolts, and if the guide pins are shaped e. g. as truncated cones or tretraedres with a cylindrical base portion. and the recesses each have a shape matching the guide pins, the con- nection can be performed with a greater precision in a faster way.

In another preferred embodiment of the flange coupling the coupling means for the fluids are made as coupling plugs provided with suitable sealing means. Thereby it will be possible in each assembling to choose, whether or not a fluid connection shall be established through the relevant fluid coupling.

In still another preferred embodiment of the flange coupling the bolts are operated with one or more fluid motors in the drill rod. Thereby it can be ad- vantageous that the fluid motors are driven from the other end of the drill rod,

where suitable fluid couplings connect the fluid motors to a pressure source with regulating and surveillance means. With such embodiment it would not be necesary to mill the pocket openings in the distal wall of a drill rod.

BRIEF DESCRIPTION OF THE DRAWINGS Further advantageous embodiments will appear in the claims. The inven- tion will be disclosed further in the following special specification with refer- ence to the drawings, in which it is shown on: fig. 1. a view of the distal end of a flange coupling according to the invention together with examples of longitudinal sections of the holes for the coupling plugs; fig. 2 a view of the proximal end of a flange coupling with ex- amples of longitudinal sections of the holes for the cou- pling plugs and the blind holes for the bolts; fig. 3 the distal end of a flange coupling in a side elevation showing the pocket holes; and fi 4 an embodiment of a coupling plug for a fluid; DETAILED DESCRIPTION A view of the distal end 1 of a flange coupling is shown in fig. 1, where the coupling means in this embodiment consist of four holes 11,12 for the bolts not shown, and the fluid couplings are an arrangement of radially stepped holes 13, 17 matching corresponding coupling plugs sealed with 0-rings. The holes 13-17 are also shown in longitudinal sections a, b, c, d, e in order to show examples of the different hole types used for the different fluids flowing through the fluid couplings, where different fluids have different needs de- pending of the flow velocity, flow capacity and viscocity of the fluid. The pocket openings 18 are shown with dotted lines around the holes 11,12. From this it can be seen. that the pocket openings 18 are sufficiently wide for the working with a tool to screw or unscrew the bolts.

In fig. 2 the proximal end of a flange coupling is shown where particu- larly the blind holes 21,22 for the bolts are shown both with a topological lo- calization and with a sectional representation 21a, 22a, thereby indicating the shape of the blind hole. Two of the blind holes are short 22a and two are long 21a. This has no direct significance in relation to the invention, but might be practical for the production.

The fluid couplings are like in fig. 1 an arrangement of radially stepped <BR> <BR> <BR> <BR> holes 23,24,25,26,27 matching corresponding coupling plugs sealed with O- rings. The holes 23-27 are also shown in different longitudinal sections in or- der to show examples of the different hole types used for the different fluids flowing through the fluid couplings like in fig. 1.

In fig. 3 the distal end of a coupling is shown with the pocket openings 18 for the bolts. The pocket openings are made by milling the opening. After use, the screws can be removed simply by rinsing the pocket openings before using the tool It shall be noted, that the length of the pocket openings 18 must at the least be sufficient for placing the bolts in the holes and using the tool all the way up to release of the bolt from the threads in the corresponding blind holes in the proximal part of the next drill rod.

Fi. 4 and 5 show each one embodiment of a coupling plug 31,33 for the fluids flowing through the drill string. The plug is equipped with a total of four grooves 32,34 for 0-rings for the sealing of the plug 31,33, thereby securing a tight coupling, that can be released when the bolts are removed.

A drill rod can be a simple unit, just performing the functions of a drill string and guiding the fluids through from one end to the other. Also, a drill rod can perform certain functions with the help of the fluids flowing through the drill rod. In that way the drill rod can e. g. be equipped with traction means mounted on pivotable arms with traction motors, or a drill motor for a drill bit.

In one of the above mentioned embodiments of the flange coupling the bolts are operated with one or more fluid motors in the drill rod, and in another embodiment guide pins and corresponding recesses are used. Theese embodi- ments are, however, not shown in the figures, as such embodiments are not es- sential for the invention.