GB1071720A - Method and apparatus for coupling tubes and rods - Google Patents

Abstract

1,071,720. Assembling force-fits. KOBE Inc. Dec. 16, 1963, No. 49537/63. Heading B3U. [Also in Division F2] A method of making a friction joint consists in putting inner 44 and outer tapered surfaces 44, 42 together so that their central regions are in engagement and there are sealing regions at their ends, injecting pressure fluid into the central region through a port 46 sufficient to expand the outer (44) and contract the inner (42) surfaces whilst they are being relatively moved into further inserted positions whilst still maintaining the seals at their ends, then venting by way of the port 46 to relieve the pressure so that the surfaces respectively contract and expand to engage together under high pressure. Fig. 1 shows tapered tube ends 32, 34 joined by an external coupling sleeve 22 which is internally tapered. An annular groove 48 may be provided centrally and seals 52 at the outer ends. In Fig. 2 (not shown) the coupling 122 is inside the tubes and the tapers are correspondingly arranged. The former method is suitable for joining rods. Alternatively the two pipe ends may have complementary tapers. To control the stressdistribution the ends of the untapered surfaces may be chamfered. The material of the coupling is of higher strength than that of the members it joins. Steel or tungsten carbide is used normally for couplings for joining steel rods or tubes, but if space permits aluminium alloy couplings may be used. Steel couplings may be used to join aluminium tubes. The frctional grip may be improved by turning a shallow sharp-crested, buttress thread on one or both of the mating tapered surfaces, or a thin film which includes a fine wire of diamond cross-section may be interposed between them, or fine particles of hard material may be used similarly. As an alternative to pushing the members together whilst the engaged regions are under pressure they may be screwed together, for which purpose shallow trapezoidal threads 72c and 74c may be cut in the mating tapered surfaces. To accommodate the pressure fluid the threads are allowed a relatively large flank clearance. An equation for calculating the minimum axial length of the contacting tapered surfaces is discussed in the Specification. Taper angles may vary from 0 degrees 30 minutes to 18 degrees according to circumstances. It may be desirable to improve the mechanical properties of the mating portions of the tubes or rods by cold work. Means for assembling and separating the joints other than the screwed version is illustrated in Fig. 16. The tube 34 is at the top of a string which is to be run into, or out of an oil-well below the apparatus and is shown already attached to a coupling 22 with the apparatus operating on the joint between the same coupling and another pipe 36. Hydraulic pistons 360 in a base 356 are actuated by a tubular slide valve 378 by the operation of which pressure is applied to one side or the other of the pistons whilst the opposite side is exhausted. The hollow piston-rods 382 are connected to a crosshead 384 in which hydraulically operated jaws 388 grip the pipe 36 whilst similar jaws in the head of the base 356 grip the pipe 34, both sets of pistons being fed with pressure by way of a rotary valve 392. An open-sided yoke 404 is supported on the upper end of the coupling 22 and is located by a tapered key fitting into a V-notch to align a spring-loaded nozzle with the channel 46 in the coupling. An alternative design of yoke is in the form of a split collar. Whilst a high pressure is applied to the coupling through the nozzle the pistons 360 are operated to press the pipe 36 further into it for assembly or alternatively to withdraw the pipe for breaking-down. Fig. 25 (not shown) illustrates an apparatus for use with screwed pipes and couplings. The apparatus is similar in all respect to the one just described except that a rotor is mounted on top of the lower crosshead plate (386 of Fig. 16) and carries the upper jaws 484, which are three in number. Whilst pressure is applied to the coupling the rotor is rotated by an hydraulic motor and the threads co-operate to draw the two parts together. The opposite procedure is used when breaking down the string of pipes.