CA2027969A1 - Drill tube - Google Patents

Abstract

Abstract A method of manufacturing a drill tube (10) for drilling operations, involving centrifugally casting a plurality of tube lengths (11) and welding the tube lengths together to form welds (12), whereafter threaded end fittings (13, 15) are welded to form welds (14, 16) at opposite ends of the drill tube. Alternatively the threaded end fittings are partially formed during centrifugal casting of the tube lengths to form the ends of the drill tube and completed by appropriate machining and thread forming operations.

Description

2027~9 DRILL TUBE

Technical Field This invention relates to the manufacture of drill tubes of the type adapted to be progressively ~oined end to end to prod-~ce a string of drill tubes rotatably driven on a drilling rig to drill oil wells, bore holes and liXe drilling applications.
Backqround Art Drill tubes for such applications are conventionally formed by a piercing process resulting in a seamless tube, and can also be formed by rolling flat steel sheet into a tube and welding the abutting longitudinal edges together to form a seamed tube. In both cases the necessary internally and externally threaded components at opposite ends of the tube, which are used for the purposes of stringing thè tubes together in a drilling rig, are subsequently inserted into the ends of the tube and welded thereto.

2~7~69 The main disadvantages with such tube forming techniques is their high cost due basically to the relatively complex manufacturing techniques and associated equipment, and the relatively small number of suppliers. It is, therefore, an object of the present invention to provide a method of manufacturing a drill tube for drilling operations which is less costly than the piercing and fabricating techniques referred to above, and which also utilizes manufacturing facilities which are more readily available. The problem with the prior art technique involving a piercing process is likely to become greater as general steel prices increase, particularly as such the piercing technique requires as starting stock wrought round steel rod.
Disclosure of the Invention In accordance with the invention there is envisaged a method of manufacturing a drill tube for drilling operations, comprising centrifugally casting a plurality of tube lengths and ~oining said tube lengths together end to end to form a drill tube of the desired length.
Centrifugal casting of tube is generally cheaper than the piercing and fabricating technigues discussed previously, whilst the availability of manufacturing facilities is greater. In addition, since the present invention can utilize scrap steel, further significant cost savings can be achieved. Furthermore, because the present invention involves a casting technique, there is the possibility to change the alloy composition of the steel allowing for a lower wear rate and thus longer life.
Pierced tubes in particular have limitations with regard to variations in the alloy composition as the piercing process requires limitation on the alloy composition which may be used. Currently tubes now in use are operational for approximately three months, after which time they have to be retracted from the drill hole and removed to a workshop where their diameter is built up to replace worn material by continuous welding process, involving further costs. Use of - 202796g the correct high wear resistant alloys, made possible by the present invention, leads to an increase in the life span of the tube. If the costs envisaged can be reduced sufficiently it may be possible to discard a worn tube rather than rebuild its circumferential diameter.
The threaded end fittings for the tube may be subsequently joined to the respective ends of the manufactured drill tube at the same time as it is manufactured, or connected later by the end user of the drill tube. Alternatively, the production of the end fittings could be incorporated as part of the centrifugal casting operation and completed by appropriate machining and thread forming techniques.
The invention also envisages a drill tube manufactured in accordance with the method defined above.
Descri~tion of the Drawinq One preferred embodiment of the invention will now be described by way of example, with reference to the accompanying drawing. The drawing represents a longitudinal view, partially in section, of a completed drill tube manufactured in accordance with the method of the present invention.
Best Mode for CarrYinq Out the Invention In the example of this preferred embodiment, the main length of the drill tube designated as 10 is formed from a plurality of thick wall tube lengths 11. Each tube length 11 is centrifugally cast from a suitable metallic material, using a permanent cylindrical mould which is spun at high speed whilst molten metal is poured in, and which results in the metal being flung to the inner surface of the mould to produce a hollow cylinder or tube of uniform wall thickness. The resulting tube lengths have a uniformly fine grain outer surface, and in consequence can also be expected to be sounder with fewer inclusions. The individual tube lengths 11 are then welded end to end to produce welds 12 between their ends, and collectively the tube lengths make up the desired length of the drill tube 10.

`-- 2027969 In order to complete the drilled tube for use in drilling applications, a conventional externally threaded end component 13 is welded at 14 to one end of the drill tube, and a conventional internally threaded end component 15 welded at 16 to the other end of the drill tube. The end components 13 and 15 may be welded to the drill tube at the point of manufacture or alternatively connected later by the end user of the tube. One other possible alternative is to partially form the relevant end components as part of a special centrifugally cast tube length 11. The technique involves forming the relevant end of the final drill tube, during the centrifugal casting of that tube length, with the end components being finished by machining and thread forming operations utilizing appropriate equipment.
In the example of the invention as described, a typical drill tube 10 may be formed from four centrifugally cast tube lengths 11 of 7.5 feet in length, which when welded end to end result in a drill tube of 30 feet in length.
The centrifugal casting of the tube lengths 11 should be controlled to produce uniform tube wall thickness for each length to make up the drill tube. These wall thicknesses may conform with the range of wall thicknesses normally available in respect of conventional pierced seamless and fabricated seamed drill tubes. The thicknesses are dependent on the type and depth of the drilling operation to which the drill tube will be applied.
It is expected that once full production of drill tube in accordance with the method of the present invention commences that the price (in 1990 dollar terms) of a drill tube of conventional length will be as low as AS8,500.00.
This may be compared with a drill tube length manufactured in accordance with known techniques which can be as high as AS13,000.00.

Claims (4)

1. A method of manufacturing a drill tube for drilling operations, comprising centrifugally casting a plurality of tube lengths and welding said tube lengths together end to end to form a drill tube of the desired length.

2. A method as claimed in Claim 1, wherein threaded end fittings for the tube are subsequently joined to the opposite ends of the manufactured tube.

3. A method as claimed in Claim 1, wherein threaded end fittings for the tube are partially formed during centrifugal casting of the tube lengths which are to form the ends of the drill tube, and are completed by appropriate machining and thread forming operations.

4. A method of manufacturing a drill tube for drilling operations substantially as hereinbefore described with reference to the accompanying drawing.