CA2268985A1

CA2268985A1 - Method and device for connecting a flexible pipe

Info

Publication number: CA2268985A1
Application number: CA 2268985
Authority: CA
Inventors: Anh Tuan Do; Joel Le Nouveau
Original assignee: Individual
Current assignee: Technip Energies France SAS
Priority date: 1996-10-16
Filing date: 1997-10-13
Publication date: 1998-04-23
Also published as: WO1998016774A1; ZA979260B; FR2754585A1; AU725395B2; AU4709397A; FR2754585B1; EP0932788A1

Abstract

The connecting device for connecting a joining piece to the end of a flexible pipe comprises a cannula (7) and a sleeve tube (23) having over a certain length undulations (28), characterised in that the undulations are constituted by separate rings (28) which extend over a length at least equal to the internal diameter of said flexible pipe (2), and the cannula (7) has indentations (34) arranged on its external surface in a straight line with the internal sheath (3).

Description

Method and device for connecting a flexible pipe The present invention relates to a method and a device for connecting an end fitting onto one end of a flexible pipe, and more particularly a flexible pipe which is exposed to high mechanical and thermal stresses when it is transporting a fluid such as gas or crude.
Various connection devices, denoted most generally in their entirety by the term end fitting, have been proposed over several decades.
In a simplified version, a flexible pipe includes, from the inside to the outside, at least one tightness internal sheath, a pressure vault consisting of armouring, and a tightness external sheath.
An end fitting commonly used includes a certain number of components which are connected and interact with each other, and in particular a hollow internal end component whose terminal face butts against the impermeable internal sheath of the flexible pipe, a special component which is placed under, and is connected to, the pressure vault, and an external retention and pinching sleeve or cap which is placed on the outside of the flexible pipe, over an axial length, in order to surround, on the one hand, the region which joins the terminal faces of the internal component and the impermeable internal sheath and, on the 2o other hand, a part of the flexible pipe. Means are also provided for fixing the external sleeve. However, fitting such an end fitting requires partial stripping of the end of the pipe to be connected and moving the armouring of the pressure vault apart so as to insert the special component, without which it would be impossible to insert anything into the end of the flexible pipe.
Another type of end fitting, also developed by the Applicant, requires in the same way as above prior preparation of the end of the flexible pipe to be connected so as to be able to fit an internal component in the pipe.
FR-A-2,728,049 and FR-A-2,728,051 relate to a connection device for plastic pipes, which consists of a pinching sleeve, internally threaded and capable 3o of being screwed onto reverse-handed threads provided on each of the ends of the pipes to be connected. A seal is interposed between the terminal faces of the pipes and is housed in a central groove made in the sleeve.
This type of end fitting can only be used if the ends of the pipes are threaded since the connection is essentially made by screwing. In the case of pipes which do not have threads on the external protective sheath, it is essential, beforehand, to give the said pipes appropriate threads, something which is not easy when the connection has to be made at the place of operation; in addition, this type of connection requires a special tool.
FR-A-2,729,206 relates to a method for making a connection between s a rigid tubular piece and the end of a flexible pipe. The tubular piece must have two parts separated by a collar provided with a circumferential groove, one of the parts having circumferential slots into which a layer of thermoplastic enters.
A
metal sleeve, one end of which is taken out and turned over into the groove and the other end of which is turned over radially towards the inside beyond the end of 1 o the tubular piece, is mounted so as to retain the connection. The connection method consists in inserting heating means into the flexible pipe, so as to deform the latter, flaring it out before inserting the tubular piece, then in heating the tubular piece while at the same time compressing the metal sleeve so as to melt the thermoplastic and to pinch the tubular piece and the flexible pipe in their 15 joining position. Over and above the fact that the pipes capable of being connected to the tubular piece must be sufficiently flexible in order to be able to be deformed by heating and to allow the insertion of the tubular piece, it should be noted that the recommended connection fiu~ther requires either special components, such as the tubular piece (with circumferential groove and slots), or a 2o prior preparation. Finally, and above all, such a connection device cannot be used for flexible pipes which carry a fluid under high pressure, for example of about 40 bar and higher, and which develop high stresses, such as the end force which is the tensile force exerted on the end fitting-pipe connection, the end force possibly being about 10 tonnes.
25 US-A-2,262,228 discloses a method of fitting an end fitting onto quite a flexible and defonmable plastic hose so that its end can be forcibly inserted into the end fitting with a large reduction in its outside diameter; this operation is followed by a new compression of the thickness of the pipe by expanding a central sleeve. The pipe is then compressed and pinched, but not otherwise 30 deformed. Such a method cannot be applied to the pipes to which the invention relates, which are too rigid to be inserted in this manner into an end fitting having an inside diameter which is much less than the outside diameter of the pipe.
US-A-4,653,779 teaches a method of fitting an end fitting in which an external sleeve provided with internal rings compresses and deforms the pipe as 35 far as its reinforcement plies. However, in this method, the internal passage of the pipe has a diameter which varies greatly in the region of the end fitting, so that the flow may be disturbed.
Document US-A-2,146,756 relates to a permanent end fitting for a non-reinforced hose.
The object of the present invention is to remedy the aforementioned drawbacks and to propose a connection device which can be used in any type of pipe to be connected, as long as the end of the pipe is capable of being tube expanded in diameter.
The diametral tube-expansion to which reference is made in the 1 o present invention is the operation by which at least the end of a pipe is expanded over a certain length, in order to allow introduction of one component of a piece, in this case the cannula of a joining end fitting.
When reference is made to the drawing operation, this means that the piece to be drawn is subjected to squeezing by a radial compression, leading to a reduction in the external diameter.
When reference is made to the operation of hooping, this means that a mechanical connection is made between two components by means of pressure exerted on one or both of the components.
The subject of the present invention is a device for connecting a 2o flexible pipe of the type which includes at least one internal sheath, a reinforcement consisting of wound wires and an external protective sheath, the said end fitting including a cannula and a sleeve having corrugations over a certain length, and which is characterized in that the corrugations consist of separate rings which extend over a length at least equal to the internal diameter of the said flexible pipe, and in that the cannula has teeth provided on the external face opposite the internal sheath.
According to another characteristic, the sleeve is under a radial tensile stress.
According to another characteristic, the cannula is under a radial compressive stress.
According to another characteristic, the sleeve and the cannula are squeezed together through the said end of the flexible pipe, with a degree of squeezing of between 15 and 20%.

According to another characteristic, the squeezing causes the corrugations of the sleeve to penetrate into the external sheath and causes the teeth of the cannula to penetrate into the internal sheath.
According to another characteristic, the method for connecting an end s fitting onto one end of a flexible pipe is of the type in which the end fitting includes, on the one hand, a cannula, one end of which is inserted into the free end of the flexible pipe, the said cannula having an external diameter equal (to within the manufacturing tolerances of the pipe) to or slightly greater (by about 1 %) than the inside diameter of the said pipe (the cannula possibly being tapered at its end 1 o so as to act as an insertion starter), and, on the other hand, a sleeve which is placed around the external sheath of the pipe, and the method is characterized in that it consists in:
- inserting the cannula into the end of the pipe (possibly forcibly), over a predetermined length;
15 - moving the sleeve in order to bring it above the length of cannula inserted;
- radially deforming the length of cannula inserted by means of a mandrel placed beforehand in the flexible pipe until the internal diameter of the cannula is approximately equal to the internal diameter of the unflared flexible 20 pipe;
- passing the sleeve and the corresponding pipe portion into a squeezing device, in which the said sleeve is squeezed radially at the same time as the said pipe portion under the sleeve.
According to another characteristic, the sleeve and the pipe portion are 25 squeezed to a predetermined degree of squeezing.
According to another characteristic, the degree of squeezing is between 15 and 20%.
Other advantages and characteristics will appear on reading the description relating to a preferred embodiment of the invention, as well as on 3o examining the appended drawings, in which:
- Figure 1 is a diagrammatic view, in longitudinal section, of the pipe to be connected;
- Figure 2 shows the sleeve fitted around the pipe of Figure 1;
- Figure 3 shows the cannula fitted into the pipe of Figure 2;

- Figure 4 shows the result of the diametral expansion of the pipe of Figure 3;
- Figure 5 shows the sleeve fitted around the diametrally expanded part of the pipe of Figure 4;
- Figure SA shows an enlargement of the section of the pipe of Figure 5;
- Figure 6 shows the pipe of Figure 5 after die-drawing;
- Figure 6A shows an enlargement of the section of the pipe of Figure 6;
- Figure 7 is a partial sectional view of the connection end fitting; and - Figures 8 to 10 are views, in partial elevation, of the apparatus used to carry out the various steps in connecting the end fitting onto a flexible pipe.
The pipe 2 to be connected (Figure 1 ) has an inside diameter DI and an outside diameter Do. Its thickness is e, and consists of at least one internal sheath, layers of armouring and an external sheath.
Passed around the pipe 2 is a sleeve 23 (Figure 2), the inside diameter DMO (taken level with the teeth 28) of which is at least equal to the outside diameter D, of the pipe after diametral tube-expansion (Figure 4).
A cannula 7, of inside diameter D~IO and outside diameter D~EO equal 2o to or slightly greater than the inside diameter D1 of the pipe, is inserted into the end of the pipe 2 over a length L which is preferably greater that the width of the sleeve 23 (Figure 3).
In order to aid its penetration into the pipe 2, the cannula 7 preferably terminates in a tapered shape 20 (shown here in simplified form, but more precisely in Figure 7). The outer surface of the cannula 7 has corrugations or indentations, not shown in this figure. After inserting the cannula 7 into the pipe 2, the outside diameter Do of the latter is not significantly modified.
The cannula 7 (at least its end) is forcibly enlarged (Figure 4), by means of a tube-expansion mandrel, which is not shown, so that its new internal 3o diameter D~I1 is equal to or very close to the diameter DI of the undeformed pipe 2, its outside diameter becoming D~Ei. The outermost part 2' of the pipe is therefore enlarged in order to take on an internal diameter equal to D~E1 and a new external diameter D1. The additional degree of expansion, by tube-expansion, [(Dl - Do)/Do], is greater than 1% and preferably greater than or equal to 3%.

During this widening by tube-expansion, a dog-leg 2a is formed between the widened part 2' and the non-widened part; the thickness a of the pipe is not very appreciably different between the part 2' and the part 2, and the dog-leg 2a itself has this thickness. In other words, the slight reduction in thickness results only from the perimeter of the pipe being increased but not from the thickness of the pipe being compressed.
Next (Figure 5), the sleeve 23, which was in readiness, is moved so that it surrounds the tube expanded part 2', this being possible because of the sufficient diameter DMO of the sleeve 23. Alternatively, it would have been 1o conceivable, depending on the tool chosen, to place the sleeve immediately around the part 2'.
The pipe has, in this region 2', the shape which may be seen in Figure 5A, namely that the inner sheath 3 and outer sheath 5 and the armouring ply 4 are not appreciably deformed (apart from their widening as a result of the tube-expansion). There was, approximately, merely a displacement of material, but no compression.
By means of a drawing operation (Figure 6), the diameter of the sleeve 23 is reduced, resulting in its internal diameter (and the outside diameter of the part 2') adopting a value D2 which is less than D1 and less than DMO. During this operation, the cannula 7 is designed to withstand the drawing and its new inside diameter DC~ is very slightly different from DI. Optionally, the tube-expansion tool may be kept in the cannula 7 in order to prevent it from collapsing during the drawing. It is also possible to pass the tube-expansion tool back in if the diameter Dci2 was too small.
During the drawing operation, it should be noted that the dog-leg 2a remains, even if it is slightly reduced.
As shown in Figure 6A, the pipe 2' deforms locally under the effect of the penetration of the teeth 28 of the sleeve 23 (and additionally of the reliefs 34 on the cannula 7, the function of which is essentially to prevent the pipe from 3o slipping) so that the armouring ply 4 is corrugated.
A more detailed description will now be given of a particular application which is that of connecting an end fitting 1 onto a flexible pipe through which a pressurized fluid, for example a gas or crude, flows. The flexible pipe 2 generally includes, from the inside out, at least one impermeable internal sheath 3, of a given internal diameter DI, one or more armouring plies 4 wound _7_ around the impermeable internal sheath 3, which is made of a material identical to or different from that of an external protective sheath 5 placed around the armouring 4. The structure of such a pipe is well known to experts and will not be described in detail. Nevertheless, the application relates more particularly to a pipe in which the armouring plies 4 each consist of a winding of "Kevlar"
tapes, which form the subject of Documents WO 97/13091 and WO 97J12753 in the name of the Applicant.
The end fitting 1 includes, on the one hand, a vault comprising in particular the cannula 7 intended to be inserted into the end 14 of the pipe 2 and, on the other hand, the sleeve or cap 23 placed around the end of the pipe 2 to be connected (Figure 7).
The vault includes a rear part 6 and a distal part or cannula 7 proper.
The rear part 6 is fixed and centred by a centring ring 9 in a traction fixture 8 integrally fastened to a thrust or traction member 10 which can move on a frame 11 of the drawing rig 12 (Figure 8). Mounted in the cannula 7 is a tube-expansion rod 13 which is integrally fastened to the traction fixture 8. The flexible pipe 2 is held in place in a support denoted in its entirety by the reference 15 and including, in particular, a support plate 16, a spacer 17 and a clamping collar 18. In a first step, the cannula 7 of the vault is inserted into the end 14 of the pipe 2 so as to 2o enlarge (very slightly) the said end 14 over a predetermined length L, for example 250 mm, such a deformation in fact being very limited (if not, a considerable force would be necessary to thrust the cannula 7 into the pipe 2). The end 14 of the pipe 2, as shown in Figure 1, may have a chamfer 14a to make it easier to insert the tip of the cannula 7 into the said end 14. This insertion is carried out without any prior preparation of the pipe 2, i.e. without separating and/or removing part of the constituent components of the structure of the pipe 2.
This insertion is carned out by means of the cannula 7, which is also thick enough to withstand the residual stresses resulting from the drawing. Tests carned out have shown that a thickness of 5 mm of the cannula 7 was perfectly acceptable for a 3o flexible pipe having an inside diameter equal to three inches. The cannula includes a thick cylindrical part 19 which is extended towards the front by a tapered tip 20. The dotted line 21 is an imaginary line which divides the thickness of the distal part 7 into two regions, the upper region approximately 3 mm in thickness corresponding to the diametral expansion and the lower region corresponding to that which will be hooped subsequently so as to ensure that the inside diameter Dc~ of the cannula 7 is, after hooping, equal to the inside diameter Dl of the pipe 2.
In the second phase, shown in Figure 9, the cannula is unfastened from the traction fixture 8 in order to be moved forward and integrally fastened to the support 1 S by means of bolts 22. In this forward position of the cannula 7 and of the pipe 2, the sleeve or cap 23 fitted beforehand on the pipe 2 is positioned opposite the cannula 7, which sleeve or cap, referring to Figure 7, includes a region 24 raised up with respect to the main body 25, the difference in thickness in the cap being portrayed by an imaginary dotted line 26. Provided on the lower 1o face 27 of the cap 23 are corrugations in the form of separate rings 28 which, during the subsequent squeezing, have to penetrate into the external sheath 5.
An end part 29 of the cap rests on a flat 30 made on the rear part 6 of the vault. The rings 28 are made over a predetermined length of the sleeve, which is at least equal to the internal diameter DI of the pipe and more particularly equal to approximately 250 mm, and they are spaced apart with a pitch of at least 4 mm.
The height of each ring is approximately 8 mm so that the rings can penetrate into the external sheath 5 and, during the subsequent drawing, cause the armouring wires to become corrugated.
When the cap 23 is fitted, a mandrel 33, positioned beforehand in the 2o pipe, is moved so as to force it into the cannula 7. Such an insertion of the mandrel 33 deforms the cannula 7 of the vault until the sections of the said cannula 7 and of the pipe 2 are aligned, that is to say that there is continuity between the pipe 2 and the cannula 7 since the diameters DI and Din are equal.
This is the tube-expansion operation.
On its external face, the cannula 7 has teeth 34, which differ in structure from the rings 28, a few of which have been shown in Figure 7. The function of the teeth 34 is to provide hooping between the cannula 7 and the facing internal sheath 3 as well as hooping between the cannula 7 and the armouring 4. After hooping, the end of the pipe lies in a confined space, which 3o makes it possible to limit the creep over time of the internal sheath 3 and consequently to ensure that there is a lasting seal at the end of the pipe. In an illustrative embodiment, the pitch between the teeth is about one millimetre and the height of each tooth is about 0.5 mm.
In a following step, the end fitting-pipe assembly is retracted towards 3s the rear position on the frame 11 and a die 31 with its die-holder 32 is fitted into _ g _ the die-drawing rig 12. Having done this, the above assembly is moved through the die 31, this die-drawing operation having the effect of pinching the cap onto the external sheath 5 and of completing the hooping of the cannula 7 onto the internal sheath 3 and the armouring 4 of the pipe 2, so that, on leaving the die 31, the diameters DI and D~a are equal, thereby ensuring continuity between the connected components and avoiding any obstacle for flow of the fluid.
The tests carried out have shown that a thickness of 5 mm for the cannula 7 was sufficient to withstand the traction, during insertion, of the diametral expansion and the residual compression effect after the drawing, for the 1o pipe's internal diameter in question.
With regard to the degree of squeezing, it has been determined empirically that this was between 15 and 20% and more particularly about 16.5%, i.e. approximately 2 to 3 times the conventional pinching employed in the prior art.
The degree of squeezing is defined by the ratio of the difference between the thickness of the free pipe and the thickness of the flared end of the pipe to the thickness of the free pipe.
Likewise, the die-drawing length is related to the internal diameter DI
of the pipe and depends essentially on the end force which is known in principle, on the coefficients of internal friction of the structure of the pipe (about 0.2) and on the nature of materials used for making the pipe (the impermeable sheaths and armouring) as well as on the material from which the cap is made. The tests have shown that this drawing length is at least approximately 3 times the internal diameter DI of the pipe.
On leaving the die, the cap 23 is under a radial tensile stress and the cannula 7 is under a radial compressive stress, the stress state a of the cap and of the cannula being able to be expressed by the relationship:
a = Ethermoplastic x degree of pinch in which ~er,~.,oplastic is the Young's modulus of the external thermoplastic sheath of the pipe.
It should be noted that the die-drawing action makes it possible, furthermore, to ensure keying of the armouring 4 because of the rings 28 of the cap 23 which, by compressing the external sheath 5 of the pipe 2 non-uniformly, causes corrugation of the plies of wires making up the said armouring 4, combined with compression between the two, external and internal, thermoplastic sheaths of the pipe 2.

-1~-In summary, the method for connecting an end fitting onto a flexible pipe consists in:
a) - inserting a mandrel 33, the diameter of which is equal to the internal diameter DI of the pipe, into an end 14 of the flexible pipe 2;
b) - placing a sleeve or cap 23 around the pipe 2;
c) - introducing the cannula 7 of the vault of the end fitting, the nominal internal diameter DCio of which is less than the internal diameter DIl of the pipe and the external diameter D~EO of which is slightly greater than or equal to the internal diameter DI of the flexible pipe 2, into the end 14;
to d) - continuing the said insertion over a defined length of pipe L, optionally with a slight flaring of the said end 14 along the said length;
e) - moving the cap 23 in order to bring it over or opposite the cannula 7 of the vault;
f) - moving the mandrel 33, inserted beforehand, in order to bring it into the cannula 7 of the vault, thereby causing, by tube-expansion, radial deformation of the said cannula 7 until the nominal diameter D~IO becomes Din, equal to the internal diameter DI of the unexpanded pipe, this tube-expansion operation ensuring hooping between the cannula 7 and the internal sheath 3 and therefore sealing between the end fitting and the flexible pipe; and g) - drawing the cap 23 and the corresponding pipe end 14 so as to reduce the outside diameter of the said cap and to compress that pipe portion lying between the cap and the distal part with a defined degree of pinch.
As was seen earlier, step e) could come before step f).
Finally, it should be noted that the effects of the hooping and the drawing are long-lasting. This is because relaxation of the plastics will tend to cancel out the initial stresses imposed by the hooping and drawing. The fact that the pipe is a reinforced pipe considerably increases the relaxation times of the layers of the thermoplastic sheaths; in addition, after drawing, the end of the pipe thus compressed between the cannula and the sleeve is, after compression, in a 3o confined space which has the effect of making the relaxation times of the thermoplastic sheaths virtually infinite and therefore of virtually eliminating the phenomena of creep. Permanent sealing and bonding of the pipe to the end fitting are thus obtained.

Claims

1. End fitting (1) for connecting one end (14) of a flexible pipe (2) comprising at least one internal sheath (3) having a diameter D I, an armour (4) consisting of wires and an external protective sheath (5) having a diameter D0, said fitting including a vault composed of a rear part (6) and a cannula (7) having teeths (34) on its external side and a sleeve (23) having corrugations (28), said cannula (7) and said sleeve (23) being designed for undergoing deformation in order to pinch therebetween the end of the flexible pipe, said deformation comprising at least tube-expanding of the cannula (7), characterized in that said cannula (7) has, before deformation, a portion with an external diameter D CEO equal to or slightly greater than the diameter D I and an intrenal diameter D CIO less than said diameter D I, said sleeve (23) having before deformation an internal diameter D MO greater than the external diameter D0 and greater than or equal to the new diameter D1 after tube-expanding of the portion (2') of pipe (2) which surrounds the cannula (7) and being capable of withstanding a drawing operation that gives thereto after deformation a diameter D2 less than D1, and in that the cannula (7) has a thickness permitting both its being tube-expanded and its resistance to compression during the drawing operation of the sleeve (23).

2. End fitting (1) for connecting one end (14) of a flexible pipe (2) comprising at least one internal sheath (3) having a diameter D I, an armour (4) consisting of wires and an external protective sheath (5) having a diameter D0, said fitting including a vault composed of a rear part (6) and a cannula (7) having teeths (34) on its external side and a sleeve (23) having corrugations (28), said cannula (7) and said sleeve (23) being designed for undergoing deformation in order to pinch therebetween the end of the flexible pipe, said deformation comprising at least tube-expanding of the cannula (7), characterized in that said cannula (7) has after deformation a portion with a external diameter D CE1 greater than the diameter D I and an internal diameter D CI1 equal to said diameter D I or substantially equal thereto plus or minus about 1%, in that said tube expanding of the cannula (7) enlarges the portion (2') of the pipe (2) which surrounds the cannula (7) from an external diameter D0 to a new external diameter D1, in that the enlarged portion (2') of the pipe is connected to the remaining portion of the pipe (2) by a dogleg (2a), said dogleg (2a), the pipe (2) and the enlarged portion (2') having substantially the same thickness (e), and in that the sleeve (23) has after deformation an internal diameter D2 less than said new diameter D1.

3. End fitting according to anyone of Claims 1 or 2, characterized in that the cannula (7) has a tapered portion (20).

4. Method for connecting an end fitting (1) to one end (14) of a flexible pipe (2) comprising at least one internal sheath (3) having a diameter D I, an armour (4) consisting of wires and an external protective sheath (5) having a diameter D0, said fitting including a vault composed of a rear part (6) and a cannula (7) having teeths (34) on its external side and a sleeve (23) having corrugations (28), said method comprising inserting the cannula into the end of the pipe (2), over a predetermined length L, deforming said cannula (7) and said sleeve (23) in order to pinch therebetween the end of the flexible pipe, said deformation comprising at least tube-expanding of the cannula (7) by means of a mandrel (33) placed beforehand in the flexible pipe, characterized in that tube-expanding of the cannula (7) enlarges enlarges the portion (2') of the pipe (2) which surrounds the cannula (7) from an external diameter D0 to a new external diameter D1, in that said method comprises moving the sleeve (23) in order to bring it above the length of cannula inserted, and, after the tube-expanding, drawing the sleeve (23) and the corresponding portion of pipe in a drawing device (31, 32) in which said sleeve is radially squeezed at the same time as said pipe portion under the sleeve, the enlarged portion (2') of the pipe being connected to the remaining portion of the pipe (2) by a dogleg (2a), said dogleg (2a), the pipe (2) and the enlarged portion (2') having substantially the same thickness (e).

5. Method according to Claim 4, characterized in that during the drawing operation the cannula (7) is maintained by the tube-expanding mandrel (33).

6. Method according to anyone of Claims 4 or 5, characterized in that the squeezing ratio of the pipe after tube-expanding and drawing is comprised between 15% and 20%.

7. Method according to anyone of Claims 4 to 6, characterized in that the step of moving the sleeve (23) is performed after the tube-expanding step.