WO2016009208A1

WO2016009208A1 - End fittings for fibre reinforced polymer matrix composite pipes

Info

Publication number: WO2016009208A1
Application number: PCT/GB2015/052053
Authority: WO
Inventors: Graeme HYSON
Original assignee: SIGMA PRECISION COMPONENTS UK Ltd
Current assignee: SIGMA PRECISION COMPONENTS UK Ltd
Priority date: 2014-07-15
Filing date: 2015-07-15
Publication date: 2016-01-21
Anticipated expiration: 2017-01-15
Also published as: GB201412515D0

Abstract

An end fitting (20, 40) for a composite pipe (10) comprising a thermoplastic matrix (14) in which is embedded reinforcing fibres braids or fabrics (15), and a method of fixing the end fitting (20), (40) to a composite pipe (10). The end fitting (20, 40) comprises a hollow barrel (21 41), that has a retaining feature (shoulder (21), teeth (45), which in use engages the bore (12) of the pipe (10) to secure the barrel (21, 41) in the pipe (10), and an external deformable collar (22, 43) which in use is capable of being swaged down onto the pipe (10) when the pipe is heated to soften the thermoplastic matrix. The pipe (10) is heated to a plastic state either by using a preheated end fitting (20, 40) or a preheated swaging tool (30).

Description

END FITTINGS FOR FIBRE REINFORCED POLYMER MATRIX COMPOSITE PIPES

THIS INVENTION relates to the end fittings for rigid fluid impermeable fibre reinforced polymer matrix composite pipes or tubes, methods of connecting such fittings to composite pipes and tube, and composite pipes and tubes fitted with such end fittings. In this specification the term "composite pipe" refers to a pipe made from a thermoplastic matrix in which reinforcing fibres, braids or fabrics are embedded.

Our co-pending International Patent Application PCT/GB/2015/050468 discloses a method of manufacturing a novel thermoplastic composite pipe, and in particular it discloses a rigid thermoplastic pipe that comprises a thermoplastic-rich layer formed at the bore of the pipe that is surrounded by a fibre-reinforced region. The inner region is substantially wholly thermoplastic and provides the preciseness of dimensions and fluid impermeability of the pipe wall whist the fibre- reinforced region provides the strength.

In PCT/GB/2015/050468 the reinforcing fibres are formed as a hollow tubular braided structure formed by weaving the braiding threads using a conventional circular braiding machine. A conventional circular braiding machine typically consists of two sets of an even number of spools carrying the braiding yarns. One set of spools rotates about a common central axis in a clockwise direction whist the other set rotates about the same axis in an anticlockwise direction. Whilst revolving in opposite directions, the spools of each set are diverted to pass alternately inside and outside one or more of the threads of the other set, so that the braiding threads pass alternately under and over one or more of the threads of the other set. In this way, the two sets of braiding threads or yarns intersect, thus producing a tubular braid. Lengths of the braid are collected off the mandrel in a direction extending along the common axis of rotation of the two sets of spools. Circular braiders are often called "Maypole Braiders" since their motion is similar to the braiding formed on a maypole during a maypole dance. The helical angles of the threads that are laid up on the supporting mandrel determine the tightness or looseness of the weave formed during braiding.

Within the aeronautical, marine and automotive industries, there is a need to be able to replace metallic pipes with much lighter weight rigid pipes that are fluid impermeable even when conveying fluids at extremely high pressures. In order to replace metal and metallic pipes in those applications where metal pipes are used, such composite pipes must have sufficient structural strength to be self-supporting and be impermeable so as to be totally interchangeable with metal or metallic pipes without impairing the strength or functionality of the pipe. With the ability to make composite pipes or tubes that are interchangeable with metal pipes or tubes as proposed by PCT/GB/2015/050468 comes the need to be able to fit end fittings that are interchangeable with end fittings normally used with metal pipes that the composite pipes are intended to replace. The problem with attaching metal end fittings to these thermoplastic materials is that they do not readily bond with metal fittings using adhesives or cements.

Furthermore where the thermoplastic pipe is reinforced with metal or electrically conductive fibres or filaments (for example carbon fibres) there is a need to avoid or at least lessen the effects of galvanic or electrolytic corrosion at interfaces between dissimilar metals or electrical conductors. An object of the present invention is to provide a mechanical way of joining metal end fittings to thermoplastic pipes without the need to chemically or adhesively bond the metal fitting to the composite pipe.

An object of the present invention is to provide an end fitting for a rigid self-supporting thermoplastic pipe that is reinforced with one or more circular braided reinforcing fabrics and which has a fluid impermeable region adjacent to, or forming, the bore of the pipe.

A further object is to provide a composite pipe that has end fittings that are interchangeable with metal or metallic pipes in most circumstances where metal or metallic pipes are used.

A further aspect of one embodiment of the invention is to provide a mechanical way of joining metal end fittings with thermoplastic pipes with means for reducing or lessening electrolytic corrosion between a metal end fitting and electrically conductive reinforcing fibres or filaments of the composite pipe.

According to one aspect of the present invention there is provided an end fitting for a composite pipe comprising a thermoplastic matrix in which is embedded reinforcing fibres braids or fabrics are embedded, the end fitting comprising a hollow barrel that has a retaining feature which in use engages the bore of the pipe to secure the barrel in the pipe, and an external deformable collar which in use is capable of being swaged down onto the pipe when the pipe is heated to soften the thermoplastic matrix and thereby secure the end fitting in the bore of the pipe.

The retaining feature may comprises a shoulder having a chamfer at its distal end and a neck portion remote from the distal end of the barrel that is of a smaller diameter than the shoulder on to which, in use, the external collar squeezes the softened thermoplastic matrix to trap and retain the shoulder and thereby secure the barrel in the bore of the pipe.

The retaining feature comprises a tapered region that has a plurality of spaced ridges on it outer surface on to which, in use, the external collar squeezes the softened thermoplastic matrix to trap and retain the tapered portion and thereby secure the end fitting in the bore of the pipe.

The collar may be provided with teeth that project radially inwards to engage and penetrate the thermoplastic matrix when the collar is swaged onto the outside of the pipe.

According to a further aspect of the present invention there is provided a method of fixing an end fitting constructed in accordance with any one of the preceding claims comprising the steps of heating the end of the pipe to a temperature at which the thermoplastic matrix softens but does not lose its shape and simultaneously swaging the bore of the pipe radially outwards, inserting into the swaged bore the retaining feature of the barrel, locating the external deformable collar around the outside of the pipe in the vicinity of the end fitting, and swaging the collar onto the pipe to deform the softened thermoplastic matrix to grip and trap the retaining feature and thereby secure the end fitting in the bore of the pipe.

The step of swaging of the bore radially outwards nay be done by inserting a tool that is preheated to a temperature at which the thermoplastic matrix will soften into the bore of the pipe to heat and soften the thermoplastic matrix.

The swaging of the bore radially outwards may be done by inserting an end fitting that is pre-heated to a temperature at which the thermoplastic matrix will soften into the bore of the pipe to heat and soften the thermoplastic matrix.

Various preferences or alternatives are set out in the attached claims.

The present invention will now be described by way of example, with reference to the accompanying drawings, in which:- Figure 1 shows schematically a cross sectional view of a thermoplastic composite rigid pipe to which end fittings constructed in accordance with the present invention can be attached to each end of the pipe; Figure 2 shows a longitudinal cross-sectional view of the pipe shown in figure 1 with a first end fitting constructed in accordance with the present invention inserted into a swaged end of the pipe prior to securing the end fitting in place;

Figure 3 shows a longitudinal cross-sectional view of the pipe shown in figure 2 with the end fitting shown in Figure 2 secured in place on the pipe;

Figures 4 show a longitudinal cross-sectional view of the pipe shown in figure 1 and shows a swaging tool for swaging the bore of the pipe to enable an end fitting to be fixed to the pipe of figure 1 prior to inserting it into the bore of the pipe;

Figure 5 shows the swaging tool shown in Figure 4 after insertion into the pipe; Figure 6 shows the swaging tool of Figures 4 and 5 after removal from the pipe, prior to inserting the end fitting of Figure 2 into the pipe;

Figures 7 to 9 show a second end fitting constructed in accordance with the present invention; and,

Figures 10 to 13 show a third end fitting for fitting to the ends of the composite pipe shown in Figure 1 in accordance with the present invention.

Referring to Figure 1 there is shown, schematically a transverse cross sectional view of a rigid composite pipe 10 to which an end fitting 20 or 40 of the type shown in Figures 2 to 13 is fitted in accordance with the method of the present invention. Fuller details of the design of this pipe 10 are set out in our co-pending International Patent application No: PCT/GB/2015/050468. Suffice it to know, that the pipe 10 has a wall structure comprising a first region 11 of 100 % thermoplastic material that defines the bore 12 of the pipe (and constitutes a fluid impermeable layer), surrounded by a circumferential zone 14 that is predominantly made of a braided fibre- reinforced fabric 15 embedded in a thermoplastic matrix. Preferably the fabric 15 is a carbon fibre braided fabric. The pipe 10 is effectively made in two steps namely, firstly by forming a semi-rigid unfinished "green" state pipe that is self-supporting, and then forming or bending the pipe 10 to the desired finished shape. The "green" state pipe is made using a heat-shrink layer 16 on the outside circumference of the pipe 10 which when heated causes the zone 14 to be squeezed into the fibre reinforcement 15 and fuse with the first zone 11. The Green pipe 10 is then fabricated into the finished shape using a modified multi-axis pipe-bending machine. A conventional pipe-bending machine of the type used for bending metal or metallic pipes is modified to provide a heating means operable to heat the pipe 10 at least in the region of where the pipe 10 is to be bent to a temperature sufficient to soften the thermoplastic material (without the pipe 10 losing its shape) and enable the pipe to be formed to a desired shape. The heating means used during pipe-bending may comprise heated bending tools, radiant heaters, induction heaters (in this case the reinforcing fibres are those (such as for example carbon fibres) that are susceptible to induction heating, by infra red heaters, or by ultrasonic or high frequency heating devices,

When the pipe 10 is bent to the desired shape the pipe 10 is allowed to cool so as to retain the formed shape. The specific method of manufacturing the composite pipe 10 is not part of the present invention except for the heating steps required to form the pipe 10 onto an end fitting 20 that enables the pipe 10 to be fitted to other pipes or structures (not shown). The specific design of that part of the end fitting 20 which is to connect to another complementary shaped end fitting 20, or other structure (not shown), is not shown.

In the above-mentioned example, the thermoplastic material of the pipe 10 is PEEK but other thermoplastic materials could be used to form the matrix. For example the thermoplastic may be selected from one or more of polyetheretherketone (PEEK), polyaryletherketone (PAEK), polyetherketone (PEK), poly oxy methylene (POM), polyphenylenesulphide (PPS), polyethyleneimine (PEI), Polyacrylamide (PA), or a mixture of two or more of these thermoplastics.

The outer diameter of the pipe 10 in the present examples is between 0.25 inches (6mm) up to 2.0 inches (50mm), but the invention is not restricted to this range of sizes.

A pipe 10 of the type shown in Figure 1 is fitted with an end fitting 20 which is preferably made of metal, in order to enable the composite pipe to be used in those applications currently using metal pipes.

Figures 2 and 3 show the longitudinal cross section view of a first end fitting 20 constructed in accordance of the present invention. Each end fitting 20 comprises a hollow metal barrel 21 that is of slightly larger outer diameter than that of the bore 12of the pipe 10 and an external sleeve or collar 22 that secures the barrel in place on the pipe 10 as shown in Figure 3. The barrel 21 has a retaining feature 23 in the form of a shoulder region 24 at its distal end that is of larger outer diameter than the bore of the pipe 10, and a neck portion 25 remote from the distal end of the barrel 21. The neck 25 is of a smaller outer diameter than the outer diameter of the shoulder 24. The retaining feature 23 secures the end fitting 20 in the bore 12 of the pipe 10 as will be explained. The shoulder region 24 has a chamfer 26 at its distal end.

For reasons of clarity, only the barrel 21 part of the end fitting 20 that forms a mechanical joint to the pipe 10 is shown. The remaining part of the end fitting 20 which is not shown is constructed to form a connector that enables the end fitting 20 to be connected to other end fittings 20, or to other structures (not shown). The specific details of all possible designs of suitable connectors are not important features of the end fitting 20.

The barrel 21 has a bore that is of the same diameter as the bore 12 of the pipe 10 and is made of a metal that is heat resistant so as to withstand being heated to a temperature in the range of 350°C to 450°C, at which the thermoplastic matrix of the zones 11 and 12 of the pipe 10 softens as will be explained below.

The external collar 22 is made of a metal that can be deformed or swaged radially inwards on the outside of the pipe 10. The collar 22 may be a separate part to the barrel 21 (as shown in Figures 2 and 3) or it may be fitted onto the barrel 21 as shown in Figures 7 to 10. The fitting 20 is secured to an end of the pipe 10 by firstly positioning the external collar 22 loosely on the outside of the pipe 10 and then offering the chamfered end 26 of a pre-heated barrel 21 up to the end of the pipe 10 and inserting it into the bore of the pipe 10. The barrel 21 is pushed firmly into the bore 12 of the pipe 10 to swage the wall of the pipe outwards. Preferably the barrel 21 is heated to a temperature (350°C to 450°C ) at which the thermoplastic matrix of the pipe 10, in at least the region 11, will soften without the pipe 10 collapsing or losing its shape. During this swaging process, a split die (not shown) is assembled around the pipe 10 to provide support to the wall of the pipe 10. With some pipes 10 the pipe may be strong enough to withstand the compression of the wall of the pipe during the swaging step, and it may not be necessary to use a split die. When the barrel 21 is fully inserted in the bore 12 of the pipe 10 (as shown in Figure 2) the collar 22 is swaged radially inwards using a rotary swage (not shown) or compression dies (not shown) to squeeze the softened thermoplastic matrix of the pipe wall down onto the neck portion 25 (as shown in Figure 3). This causes the thermoplastic matrix to mould completely around the shoulder 23 so that when the matrix cools the fitting is completely secured in the matrix of the pipe. Figures 4 to 6 shows an alternative method of securing the barrel 21 in the pipe 10. In figures 4 to 6, a non-heated barrel 21 is used, and the bore 12 of the pipe 10 is swaged by inserting a preheated forming tool 30 that has an outer diameter similar to that of the shoulder 24 of the barrel 21 into the bore 12 of the pipe 10. The tool is pre-heated to a temperature in the range of 350° C to 450°C. The tool 30 is first offered up to the end of the pipe 10 as shown in Figure 4 and plunged into the bore 9 of the pipe 10 as shown in Figure 5 to swage the bore 12 radially outward. The tool 30 is then withdrawn from the bore 12 as shown in Figure 6. To fit the end fitting 20 into the swaged bore of the pipe 10, a collar 22 is slid over the outside of the pipe 10 and positioned alongside the neck 25, the barrel 21 of an end fitting 20 is then inserted into the swaged bore and the collar 22 is then swaged onto the outside of the pipe 10 (see Figure 3) before the thermoplastic matrix hardens, to trap the shoulder 24 within the deformed thermoplastic matrix. The barrel 21 or tool 30 may be heated by radiant thermal heaters, infrared heater, halogen light source heaters, ultrasonic heaters, or electrical induction heaters (where the barrel 21 or tool 37 is an inductance susceptor).

Figures 7 to 9 show the longitudinal cross section of a second end fitting 40 constructed in accordance of the present invention. Each end fitting 40 comprises a hollow metal barrel 41 that has an externally tapered portion 42 that is of slightly larger outer diameter than the diameter of the bore 12 of the pipe 10, and an external collar 43.

The barrel 41 has a bore 44 of the same diameter as that of the bore 12 of the pipe 10. The tapered portion 42 has a plurality of spaced circumferentially extending ridges 45 spaced along its length that in use serve to grip the bore 12 of the pipe 10. Optionally, to improve bonding between the tapered region 42 and the pipe 10, a layer of thermoplastic tape (not shown), such as for example PEEK tape, is wrapped around the tapered region 42 prior to inserting the tapered portion 42 in the bore of the pipe 10 so that it melts during the heating and swaging steps.

The External collar 43 can be a separate part (see Figure 7) that is swaged onto the pipe 1, or a separate part that is swaged (or formed as an interference fit) onto an external shoulder 44 of the fitting 40 as shown in figure 8. Alternatively, the collar 43 could be machined as an integral part of the fitting 40 that is spaced radially outwards of the barrel 41 as shown in figure 9.

To join the end fitting 40 to the pipe 10, the end of the pipe 10 is first swaged as shown in Figures 4 to 6 to leave an enlarged internal diameter that will receive the distal tip of the tapered region 42 of the end fitting 40 using a pre-heated tool 30 that is heated to a temperature in the range of 350° C to 450°C to soften the thermoplastic matrix. Whilst the matrix is in the plastic state, the tapered region 42 is fully inserted into the swaged bore 12 and the collar 43 is swaged down onto the tapered region 42 to engage the ridges 45 with the pipe 10 and hold the end fitting 40 in place.

Referring to figures 10 to 13 there is shown a modification of the end fitting 20 or 40 for use with rigid composite pipes 10 that are reinforced with, or contain, electrically conductive fibres or filaments (such as for example wires, carbon fibres or the like). The external collar 22 or 43 is provided with longitudinally extending internal teeth 47 that project radially inwards sufficient to penetrate into the pipe 10 and thereby contact the electrically conductive fibres in the thermoplastic matrix. The teeth 47 ensure that electrical continuity is maintained to reduce galvanic corrosion or electrolytic corrosion due to dissimilar metal contacts. In order to enhance the electrical connectivity between the end fittings 20, 40 and the fibres or filament electrically conductive particles such as for example carbon particles or chopped carbon fibres may be provided. If desired further electrical conductors such as for example wires or continuous carbon fibres may be incorporated in the thermoplastic matrix of the pipe 10.

Claims

Claims An end fitting for a composite pipe that comprises a thermoplastic matrix in which is embedded reinforcing fibres braids or fabrics, the end fitting comprising a hollow barrel that has a retaining feature which in use engages the bore of the pipe to secure the barrel in the pipe, and an external deformable collar which in use is capable of being swaged down onto the pipe when the pipe is heated to soften the thermoplastic matrix and thereby secure the end fitting in the bore of the pipe. An end fitting according to claim 1 wherein the retaining feature comprises a shoulder having a chamfer at its distal end and a neck portion remote from the distal end of the barrel that is of a smaller diameter than the shoulder on to which, in use, the external collar squeezes the softened thermoplastic matrix to trap and retain the shoulder and thereby secure the barrel in the bore of the pipe. An end fitting according to claim 1 wherein the retaining feature comprises a tapered region that has a plurality of spaced ridges on it outer surface on to which, in use, the external collar squeezes the softened thermoplastic matrix to trap and retain the tapered portion and thereby secure the end fitting in the bore of the pipe. An end fitting according to any one of the preceding claims wherein the collar is provided with teeth that project radially inwards to engage and penetrate the thermoplastic matrix when the collar is swaged onto the outside of the pipe. A method of fixing a metal end fitting to a thermoplastic pipe that comprises a thermoplastic matrix in which is embedded reinforcing braids or fabrics an end fitting constructed in accordance with any one of the preceding claims comprising the steps of, heating the end of the pipe to a temperature at which the thermoplastic matrix softens but does not lose its shape and simultaneously swaging the bore of the pipe radially outwards, inserting into the swaged bore the retaining feature of the barrel, locating the external deformable collar around the outside of the pipe in the vicinity of the end fitting, and swaging the collar onto the pipe to deform the softened thermoplastic matrix to grip and trap the retaining feature and thereby secure the end fitting in the bore of the pipe. A method according to claim 5 wherein the step of swaging of the bore radially outwards is done by inserting a tool that is pre-heated to a temperature at which the thermoplastic matrix will soften into the bore of the pipe to heat and soften the thermoplastic matrix A method according to claim 5 wherein the swaging of the bore radially outwards is done by inserting an end fitting that is pre-heated to a temperature at which the thermoplastic matrix will soften into the bore of the pipe to heat and soften the thermoplastic matrix. A method according to claim 5 wherein the end fitting is constructed in accordance with claim 3 and a layer of thermoplastic tape is wound on to the outer surface of the tapered portion prior to inserting the tapered portion into the bore of the pipe. A method of fixing an end fitting to a composite pipe substantially as herein described with reference to the drawings.

An end fitting for a composite pipe substantially as herein described with reference to the drawings.