GB2205913A

GB2205913A - Pipe joint of fibre-reinforced resin

Info

Publication number: GB2205913A
Application number: GB08814202A
Authority: GB
Inventors: Lars Lindstrom; Kurt Olofsson
Original assignee: Asea Plast AB
Current assignee: ABB Plast AB
Priority date: 1987-06-16
Filing date: 1988-06-15
Publication date: 1988-12-21
Anticipated expiration: 2008-06-15
Also published as: GB2205913B; NO882657L; GB8814202D0; IT1219375B; SE8702503L; SE465230B; IT8867557A0; SE8702503D0; NO882657D0

Abstract

A joint of two fibre-reinforced resin pipes (10, 11) joined at their ends (13, 17). Around the pipe ends (13, 17) there is arranged a sleeve (12) of a fibre-reinforced resin, which is fixed by an internal thread to the pipe ends via portions (15, 19) thereof having cylindrical envelope surface which are provided with external threads. The confronting ends (13, 17) of the pipes meet over a surface (22) inclined to the axes of the pipes. The internal thread on the sleeve constitutes a coherent thread with a constant pitch extending over the external threads on the pipe ends. A coherent adhesive joint is formed at the surface 22 and between the thread on the sleeve and the threads on said pipe ends. <IMAGE>

Description

PIPE JOINT OF FIBRE-REINFORCED RESIN The present invention relates ' to a joint for two fibre-reinforced resin pipes and to a method of manufacturing such a joint.

In the case of lengths of pipes used for transporting gases, high demands are placed on the tightness against gas leakage of joints between such pipe lengths and on the mechanical strength of such joints, especially if the gas has a high pressure. This is the case, for example, with pipes used in connection with offshore drilling operations, such as pipelines disposed on the bottom of the sea.

US-A-3540757 discloses a joint between two lengths of fibre-reinforced resin pipe. each one of the two ends of the pipe lengths that are to be connected is externally provided, on parts having cylindrical envelope surfces, with threads of a moulded resin which is moulded onto the envelope surfaces of the pipe. Around the pipe ends there is fixed a sleeve which, in the area inside each end, has an internal thread with the' same form of thread as the moulded threads on the pipe ends. The end surfaces of the pipe ends make contact with each other in the centre of the sleeve. An adhesive is arranged between confronting parts of the pipe ends and the sleeve without threads.

A joint according to the present invention also comprises pipe ends with parts having cylindrical envelope surfaces which are provided with external threads and a sleeve, secured around the pipe ends, of fibre-reinforced resin with an internal thread, as well as an adhesive joint disposed between the sleeve and the pipe ends. However, a joint according to this invention is tighter and mechanically stronger than the prior art joint.

What constitutes a joint in accordance with this invention is defined in the following claim 1 and is characterized in that the threads are cut in the pipe ends, the confronting parts of the pipe ends which make contact with each other, comprise one part on one pipe end having an outwardly-facing bevelled surface and one part on the other pipe end having an inwardly-facing bevelled surface, the internal thread of the sleeve being a coherent thread with a constant pitch extending over the two parts of the pipe ends which are provided with external threads, and a coherent adhesive joint is formed between'the bevelled surfaces on the confronting parts of the pipe ends and between the thread on the sleeve and the threads on the pipe ends.

According to one advantageous embodiment of joint according to the invention, the thread on each pipe end extends to the end of a cylindrical envelope surface of each pipe length in the direction in which the respective pipe end makes contact with the other pipe end. Desirably the internal thread of the sleeve has at least substantially the same length as the sum of the lengths of the external threads on the envelope surfaces of the pipe ends.

Especially strong threads are achieved on the pipe ends and in the sleeve by orienting the fibres in the outer layers of the pipes and in the interior of the sleeve in helical directions relative to the axis of the pipe length or sleeve respectively.

A method aspect of the invention is set out in the following claim 7 which is characterised in that an adhesive is arranged on at least one of the bevelled surfaces on those parts of the pipe ends which are to be brought into contact with each other and on at least one of the threaded surfaces of the sleeve and on each pipe end which is to be secured to each other, the sleeve is rotated relative to the pipe ends until the bevelled surfaces make contact with each other via an intermediate layer of adhesive and this layer forms a coherent unit with layers of adhesive between the threads on the sleeve and on the pipe ends and the adhesive in the unit is thereafter solidified.

A joint of particularly good quality is attained by coating all the surfaces which are to be brought to make contact with each other with adhesive before the sleeve is rotated and by bringing the sleeve and the pipe length to rotate in one direction of rotation only. In this case, the adhesive fills up all the voids particularly well.

Such a result can be obtained, inter alia, by rotating one of the pipe lengths in one direction and by keeping one of the pipe lengths stationary. The first pipe length then brings the sleeve to rotate around this pipe length and around the other pipe length until the bevelled surfaces make contact with each other via a thin adhesive layer.

The resin used for the reinforced resin in the pipes and in the sleeve is preferably a solvent-free thermosetting resin, such as e.g. an epoxy resin, an unsaturated polyester resin, or a polyurethane resin of such kinds as are conventionally used for the manufacture of fibrereinforced resin. Both thermosetting resins and resins which are curable at room temperature can be used.

The fibre material preferably consists of glass fibre but may also consist of fibres of different natural and synthetic materials, such as cotton, polyethyleneglycol terephthalate, polyacrylonitrile, polyamide and carbon.

The fibre material can be advantageously used in the form of a thread or strand of the fibres. The application of the thread or the strand when manufacturing the pipe lengths and the sleeve, is preferably effected by winding it helically around a mandrel with a certain pitch in certain layers and with the opposite pitch in other layers, so that the fibres in adjacent layers cross each other.

Preferably, the fibres are arranged so that layers with one pitch alternate with layers with the opposite pitch. The fibre material can also be used, inter alia, in the form of a tape, such as a tape woven from a thread and/or a strand of the fibres. Such a tape can be applied by being helically wound on the mandrel with a certain pitch, preferably with a certain pitch in certain layers and with the opposite pitch in alternate layers.

The fibre material preferably constitutes 55-65% of the total volume of fibre material and resin in the reinforced resin.

The adhesive for the joint, as well as the resin, can advantageously constitute a solvent-free resin such as an epoxy resin, an unsaturated polyester resin, or a polymethane resin.

The invention will now be explained in greater detail, by way of example, with reference to the accompanying drawing, wherein Figures la and 1b show the ends of two pipe lengths to be joined together, partially in a section through the symmetry axis of the pipes and partly in side view, Figure 2 shows a sleeve to be arranged around the pipe ends shown in Figures la and ib, partially in a section through the symmetry axis of the sleeve and partly in side view, and Figure 3 shows a completed joint according to the present invention, partially through the symmetry axis of the joint and partially in side view.

Figures la and 1b show two pipe lengths 10 and 11, respectively, each made of glass-fibre reinforced resin, and Figure 2 shows a sleeve 12, also made of glass-fibre reinforced resin. In manufacturing both the pipe lengths and the sleeve, the glass fibre reinforcement consists of roving which has been wound in a plurality of close-wound helical layers on a mandrel while displacing the point of application of the roving from end to end of the mandrel while rotating the mandrel. In this way, the fibres in any one intermediate layer cross the fibres in the two adjacent layers. The pitch of the wound roving strand in each helical layer may be, for example, + 650. When being wound on, the fibre material is impregnated with an epoxy resin before being wound around the mandrel.The epoxy resin may consist of 100 parts by weight of a resin made up of bisphenol A (e.g. XB 3052 A from Ciba AG) and 38 parts by weight of a curing agent of amino type (e.g. XB 3052 B from Ciba AG). The curing of the resin is suitably carried out at a temperature of 800C for about two hours.

As is clear from Figure la, the pipe length 10 has a pipe end 13 with one part 14 having an outwardly-facing bevelled surface and one part 15 having a cylindrical envelope surface on which a thread 16 is formed. In a similar manner, as will be clear from Figure 1b1 tne pipe length 11 has a pipe end 17 with one part 18 having an inwardly-facing bevelled surface and one part 19 having a cylindrical envelope surface on which a thread 20 is formed. In the illustrated case, the parts 14 and 18 with bevelled surfaces are both frusto-conical and the threads 16 and 20 on each pipe end extend to the end of the cylindrical envelope surface in the direction in which the end of one pipe length makes contact with the end of the other pipe length.

As shown in Figure 2, the sleeve 12 is provided with a thread 21 on its internal cylindrical envelope surface.

The thread 21 has a constant pitch, for example of about 20. This pitch as well as the form of the thread are the same as for the threads 16 and 20 on the pipe ends 13 and 17. The thread 21 has the same length as the total length of the threads 16 and 20. This means that the pipe ends and the sleeve 12 become fixed in a pre-determined position. The threads 16, 20 and 21 are formed on the pipe ends and the sleeve, respectively by cutting (e.g. with diamond grinding wheels) which ensures that a fine surface structure of the threads is attained. The bevelled surfaces on the parts 14 and 18 are also cut or ground in a similar way.

When preparing the joint between the pipe lengths 10 and 11, an adhesive is applied, for example in the form of an epoxy resin of the same kind as was used as the plastic material in the construction of the pipe lengths 10 and 11 and in the sleeve 12, on the bevelled surfaces of the parts 14 and 18 which are to make contact with each other, as well as on the threads 16 and 20 of the parts 15 and 19 having cylindrical envelope surfaces on the pipe ends, and on the internal thread 21 on the sleeve 12. The sleeve 12 is suitably applied to the pipe ends 13 and 17 by being first screwed onto each pipe end a couple of turns.

Thereafter, the pipe length 11 is suitably rotated around its symmetry axis while the pipe length 10 is held stationary. This rotation results in the pipe length 11 being threaded into the sleeve 12 and in the sleeve 12 being rotated around the pipe length 10 in the same direction of rotation until the conical surfaces of the parts 14 and 18 are drawn further and further into the sleeve to make contact with each other via an intermediate adhesive layer roughly in the centre of the axial length of the sleeve 12. The spaces between the threads 21 and 16 and between the threads 21 and 20 thus become completely filled with adhesive. After curing of the adhesive simultaneously in the entire joint, and adhesive joint 22 between the frusto-conical surfaces of the parts 14 and 18, an adhesive joint 23 between the threads 21 and 16, and an adhesive joint 24 between the threads 21 and 20 are obtained. The adhesive joints 22, 23 and 24, which have a thickness of at the most 0.5 mm, form one single coherent unit which fills all the spaces between surfaces of the pipe ends 1 and 17 and between surfaces of the sleeve 12 and the pipe ends 13 and 17 which are facing each other.

A joint as described in the foregoing description is very well suited for use in connection with the exploitation of the byproducts of offshore drilling techniques, for example for transporting gas under high pressure in a pipeline at the bottom of the sea.

Claims

1. A joint between two lengths of fibre-reinforced resin pipe in which externally threaded ends of the two lengths are connected by an internally threaded bridging sleeve surrounding confronting pipe ends of the two lengths, wherein threads are cut in the pipe ends, the confronting parts of the pipe ends which make contact with each other comprise one part on one pipe end having an outwardly-facing bevelled surface and one part on the other pipe end having an inwardly-facing bevelled surface, the internal thread of the sleeve being a coherent thread with a constant pitch extending over the two parts of the pipe ends which are provided with external threads and a coherent adhesive joint is formed between the bevelled surfaces on the confronting parts of the pipe ends and between the thread on the sleeve and the threads on the pipe ends.

2. A joint according to claim 1, in which the thread on each pipe end extends to the end of a cylindrical envelope surface of each pipe length in the direction in which the respective pipe end makes contact with the other pipe end.

3. A joint according to claim 1 or 2, in which the internal thread of the sleeve has at least substantially the same length as the sum of the lengths of the external threads on the two pipe ends.

4. A joint according to any preceding claim, in which the fibre material in the external layers of the pipe lengths and in the internal layers of the sleeve is oriented essentially in helical directions relative to the axis of the pipe length or sleeve respectively.

5. A joint between two lengths of pipe substantially as hereinbefore described with reference to, and as illustrated in Figure 3 of the accompanying drawing.

6. A pipeline comprising a plurality of lengths of pipe connected by joints as claimed in any preceding claim.

7. A method of manufacturing a joint between two lengths of fibre-reinforced resin pipe, a part on a pipe end of the first pipe length, having an outwardly-facing bevelled surface which is brought into contact with a part on the pipe end of the second pipe length, having an inwardly--facing bevelled surface, a sleeve provided with an internal coherent thread with a constant pitch being arranged around the pipe ends and being secured by means of the internal thread to external threads arranged at the pipe ends on parts having cylindrical envelope surfaces and by means of an adhesive joint disposed between the sleeve and the pipe ends, wherein an adhesive is arranged on at least one of the bevelled surfaces on those parts of the pipe ends which are to be brought into contact with each other and on at least one of the threaded surfaces of the sleeve and on each pipe end which is to be secured to each other, the sleeve is rotated relative to the pipe ends until the bevelled surfaces make contact with each other via an intermediate layer of adhesive and this layer forms a coherent unit with layers of adhesive between the threads on the sleeve and on the pipe ends and the adhesive in the unit is thereafter solidified.

8. A method according to claim 7, in which all the surfaces on parts of pipe ends and sleeve which are to be brought into contact with each other are coated with adhesive before the sleeve is rotated relative to the pipe ends.

9. A method according to claim 7 or 8, in which the sleeve and the pipe lengths are rotated in one direction of rotation only.

10. A method according to-any one of claims 7 to 9, in which one of the pipe lengths is rotated and one is kept stationary, the sleeve being made to rotate by the first pipe around this pipe and around the other pipe until the parts with the bevelled surfaces make contact with each other along the bevelled surfaces via an adhesive layer of a thickness of not more than 0.5 mm.

11. A method of forming a joint between confronting ends of two fibre-reinforced resin pipes substantially as hereinbefore described with reference to Figure 3 of the accompanying drawing.