GB2413976A

GB2413976A - Manufacture of pipes

Info

Publication number: GB2413976A
Application number: GB0410828A
Authority: GB
Inventors: Graeme John Collie
Original assignee: FMC TECHNOLOGIES; FMC Technologies Inc
Current assignee: FMC TECHNOLOGIES; FMC Technologies Inc
Priority date: 2004-05-14
Filing date: 2004-05-14
Publication date: 2005-11-16
Also published as: GB0410828D0; WO2005110637A1

Abstract

A method for manufacturing a multi-walled pipe by inserting a second pipe 2 into a first pipe 1, bending the first and second pipes and expanding the first pipe into contact with the second pipe.

Description

BP-09-0441 2413976

MANUFACTURE OF PIPES

Field of the Invention

The present invention relates to a method for manufacturing lined and multi-walled pipes s and tubes, and to novel pipes which may be manufactured by that method.

Background of the Invention

In many applications pipes need to convey corrosive, erosive, extreme temperature/pressure or otherwise aggressive fluids. This often means that the pipe must be made from expensive 0 materials. It is therefore known to use a double-walled or lined pipe where an inner pipe is made of a special material to protect against the fluid. The composite pipe so formed can also have inbuilt residual stresses which help to increase its bursting strength. Since the outer pipe or pipes are made to withstand internal pressures the innermost pipe can be made very thin and therefore inexpensive. The inner pipes can be press-fitted into the outer pipes but, more commonly, are initially of a lesser diameter and expanded into contact with the outer pipe after insertion in it, by passing a suitable expansion tool or mandrel through the inner pipe.

However, many applications call for pipes with a complicated three dimensional geometry, for example for use in chemical plants, fuel injection or subsea Bowlines. The bending of double- or multi-walled pipes is a difficult process, necessitating special provisions, e.g. to prevent separation or kinking of the inner pipes. It also makes the passage of expansion tools through the inner pipe more difficult.

2s In US Patent No. 4,784,31 l there is described a method for manufacturing a double-walled pipe where a straight inner pipe is inserted into a straight outer pipe. The inner pipe has a smaller outer diameter than the inner diameter of the outer pipe and both pipes are press fitted together using a mandrel and a drawing process. This ensures an integrated bonding thereof involving disappearance of the boundary interface at least in part of the inner and outer tubular members. The resultant pipe can afterwards be bent into a final shape.

German laid open patent application No. 39 27 989 discloses a method for manufacturing a double-walled pipe where a straight inner pipe is inserted into a straight outer pipe and bending the combination in at least one place with a mechanical bender. The inner pipe is BP-09-044 1 press-fitted or pulled into the outer pipe as an interference fit, before bending. When bending the pipe a mandrel is inserted into the inner pipe for support.

Both of these techniques if used improperly can result in the creasing of the inner pipe on s the inside of the bend.

Summary and Objects of the invention

The object of the present invention is to provide a simpler and more costefficient method of manufacturing a lined or double- or multi-walled pipe or tube that can be bent into different 0 shapes. The process enables thin-walled pipes to be used as the inner pipes and eliminates the problems of creating local stresses or deformities of the pipe during the bending process.

In accordance with the invention, a method for manufacturing a lined or multi-walled pipe comprises the steps of: IS providing a first straight pipe and a second straight pipe; inserting the second straight pipe into the first straight pipe; bending the first straight pipe and the inserted second straight pipe, and expanding the second pipe into contact with the first pipe.

Further, the invention provides a method for manufacturing a lined or multi-walled pipe comprising the steps of: donning a first pipe around a second pipe which has previously been bent to a desired shape, and expanding the second pipe into contact with the first pipe. 2s

More than one second pipe may be provided within the first pipe.

Correspondingly, the invention may provide a pipe bundle tor conveying a plurality of separate fluid flows, comprising an outer pipe and a plurality of generally parallel inner pipes received within the outer pipe and in pre-stressed contact with the outer pipe.

Further, the invention may provide a pipe bundle for conveying a plurality of separate fluid flows, comprising an outer pipe and a plurality of generally parallel inner pipes received BP-09-044 1 within the outer pipe, in which transverse cross sections of adjacent inner pipes have wall parts extending generally parallel to each other.

Other advantages will also be apparent from the dependent claims and from the following s description of illustrative embodiments, made with reference to the drawings.

Brief description of the Drawings

The invention will now be described with reference to the accompanying drawing where Fig. I shows a standard thick-walled pipe; lo Fig. 2 shows the first step of a process embodying the invention where an inner pipe is inserted into the outer pipe; Fig. 3 shows a second step of the process; Fig. 4 shows a third step of the process; Fig. 5 shows a fourth and final step of the process; Fig. 6 shows an assembly of an outer pipe and multiple nested inner pipes prior to processing in accordance with a second embodiment of the invention, and Figs. 7 and 8 show an assembly of an outer pipe and multiple parallel inner pipes prior to processing in accordance with a second embodiment of the invention.

Description of the preferred Embodiments

The pipe I shown in the figures is a relatively thick-walled pipe made e. g. from iron, carbon steel or standard stainless steel. The pipe can be rolled, welded or made in any standard pipe manufacturing process. The minimum thickness of the pipe must be designed to withstand the intended internal pressure and should conform to accepted industry standards for its pressure class. It is also possible to make the pipe from plastic, such as PVC, PTFE or other plastic material, as long as it can be made to withstand intended internal pressure.

The pipe can also be formed from composite materials, such as glass or carbon fibre filament wound or otherwise reinforced plastics, if necessary formed (laid up) with the required bends prior to curing.

As shown in Fig. 2 a second pipe 2 is inserted into pipe 1. Pipe 2 is made from a material that is corrosion resistant or resistant to chemicals or otherwise compatible with the properties of the fluid that will be conveyed through the resultant pipe.

BP-09-044 1 The combination is now bent into its final shape as shown in Fig. 3. The shape may be any two- or three-dimensionally bent shape fit for the purpose. The bending may be done in a conventional way by placing the pipe between rollers 3, 4, 5 and 6 and applying pressure at points 7 to 12 such that the pipe is bent into its final shape. Heat may also be applied during the bending process. This both reduces the forces required for bending, eliminates potential problems of work-hardening of the outer pipe and an provides a post-work heat treatment so minimizing undesired residual stresses. As can be seen from Fig. 2 the inner pipe 2 will also be bent at certain points in the process. During this stage the inner pipe may just be held loosely in position, taking no special care except to keep the inner pipe inside the outer pipe.

0 In the case of outer pipes (e.g. of composite materials) having preformed bends, the inner pipe may likewise be pre-bent, with e.g. a sectional, temporary, internal former placed around the bent inner pipe for subsequent layup of the outer pipe. When the outer pipe has cured the temporary fonder can be removed if necessary, e.g. by dissolution, melting or breaking it up.

Next, as shown in Fig. 4, pressure is applied to the inner pipe interior to expand the inner pipe into engagement with the inner wall of the outer pipe. This is done by attaching pressure fittings to each end of the inner pipe and pressurising to expand the pipe beyond yield, so generating plastic deformation. Preferably the pressure is then increased to cause so temporary elastic deformation of the outer pipe. The degree of expansion of the two pipes must be such that the outer pipe remains within its elastic limit. Once the pressure is removed, the outer pipe recovers elastically so as to remain in continual contact with the inner pipe. Particularly if the yield stress of the outer pipe is higher than that of the inner pipe, residual compressive hoop stress can be left in the inner pipe as a result of the outer pipe's elastic recovery. This may increase the bursting resistance of the finished assembly, and helps to maintain a good joint between the inner and outer pipes.

The gap between the inner and outer pipes shown in Figs. 2 and 3 has been considerably exaggerated for clarity of illustration. In practice, the inner pipe OD is preferably kept as close as possible to the outer pipe ID as is allowed by the pipe geometry. The material of the inner pipe is preferably ductile, such as copper or annealed Inconel 625. However other materials are also suitable, depending for example on the properties of the fluid to be conveyed by the pipe in service.

BP-09-044 1 Alternatively, the inner pipe can be expanded to a tight fit within the outer pipe before bending.

Any tail ends can now be removed from the inner pipe and flanges 13, 14 welded on, as shown in Fig. 5, to give the finished product. The flanges may be manufactured entirely from a corrosion resistant alloy, or from e. g. carbon steel overlaid with a corrosion resistant alloy.

Using hydraulic pressure to expand the inner pipe enables precise and controlled application lo of the internal pressure, ensuring complete plastic deformation of the inner pipe.

Temporarily causing elastic deformation of the outer pipe ensures good bonding between the two pipes. Expansion of the inner pipe can be further controlled by differentially work hardening or heat treating it or slightly varying its wall thickness along its length, to correspondingly vary its yield strength such that expansion starts at a predetermined point or points and propagates along the inner pipe away from those points. In this way, the amount of trapped air between the two pipes can be minimised. Additionally or alternatively, the annulus between the two pipes can be evacuated prior to the expansion step.

Any trapped air between the pipes can be vented by having vent holes at critical points, JO which will typically be at the apex of the bends, or perhaps along the bend inside radius, depending upon the configuration adopted by the inner pipe prior to and during expansion.

The holes can later be capped by a weld or plug.

To prevent kinking, the inner pipe can be filled with sand or like relatively incompressible material which binds together or resists flow under pressure, or a removable flexible internal support such as a bending spring or springs can be used during bending. Such a support if hollow can be left in place during the expansion step, after which it will be easier to recover from inside the now larger diameter inner pipe.

While it is not deemed necessary to keep the inner pipe centered during bending of the outer pipe it may be advantageous to control its position somewhat by holding each end firm and/or employing distance holders. Since these will most probably break during bending they will be easily removed before expanding the inner pipe. The pipe annulus could for example be filled (particularly at or near the regions to be bent) with a semi-rigid, preferably BP-09-044 1 open-celled, plastics foam, such as PA foam, which is later removed using a suitable solvent. Other temporary centering supports which are later removable e.g. by dissolving, melting, breaking or burning will be readily apparent.

s To ensure that trapped air between the two pipes is minimised an HNBR or other elastomeric "sleeve" can be located between the OD of the inner pipe and ID of the outer pipe. The elastomer can also be fitted to the inner pipe or the outer pipe can be lined with the elastomer before inserting the inner pipe. The size and material characteristics of the elastomer can be selected in order that the trapped elastomer provides a pressure tight barrier 0 should the inner pipe leak in operation. Alternatively one of the pipes can be coated with a material such as an adhesive that will cure during bonding, or a setting or non-setting mastic, to ensure a leak-tight end product. The pipes may be heat treated after the expansion step, to promote fusion between the inner and outer pipes, as disclosed in US47843 1 1, with or without an interposed layer of brazing material.

Fig. 6 shows a cross-section through an outer pipe I and plural nested pipes 2a, 2b which can be successively or simultaneously expanded into firm or pre-stressed contact with the outer pipe 1, using substantially the same methods and variants as discussed above in relation to Figs. I to 5. Although only two inner pipes 2a, 2b are shown, larger numbers will permit a higher pre-stress to be built up, resulting in a higher strength assembly. The intermediate pipe 2a may also be metallurgically more compatible with each of the pipes 1, 2b than these are with each other, permitting more effective diffusion bonding, or reducing electrolytic corrosion effects. The material of pipe 2a may additionally or alternatively have a lower melting point than those of the other pipes, to serve as a brazing layer to bond the 2s pipes together on heating.

Fig. 7 shows an arrangement in which two inner pipes 2c, 2d extend parallel to one another inside an outer pipe 1, as may be usctul for conveying multiple separate fluids in a pipe bundle. The pipes 2c, 2d are separated from each other by a stiffening member or wall 16 and together the inner pipes and stiffening wall are initially a clearance or sliding fit within the outer pipe 1. The wall 16 is stiff in comparison to the walls of the inner pipes 2c, 2d, so that it is not subjected to any significant plastic deformation when the inner pipes 2c, 2d are expanded into contact with it and the inner surface of the outer pipe I using pressurized fluid in the manner described above. Expansion preferably takes place in a controlled way, with BP-09-044 1 the larger inner pipe 2c interior being pressurised first, sufficient to hold the stiffening wall 16 in place against the inside of the outer pipe I and to fully expand the inner pipe 2c. The fluid pressure in the inner pipe 2c is maintained whilst the smaller inner pipe 2c is next also expanded into contact with the outer pipe I and stiffening wall 16. The pressure in both s inner pipes may then be increased substantially equally and simultaneously so as to elastically deform the outer pipe I and lock in a compressive prestress on the inner pipes 2c, 2d and stiffening wall 16, on release of the internal pressure. Although the wall 16 is stiff compared to the walls of the inner pipes 2c, 2d and serves to control and even out expansion of the inner pipes, it is nevertheless relatively flexible in comparison to the 0 overall pipe assembly and so does not hinder the bending operations. This is particularly so if the inner pipes 2c, 2d and wall 16, optionally together with the outer pipe 1, are twisted around the axis of the outer pipe, so that the stiffening wall 16 presents its minimum second moment of cross-sectional area to the local bending direction (i.e. the major plane of the wall 16 lies substantially perpendicular to the bend radius). The transverse section of the wall 16 also remains relatively flat during the bending operation, so that the cross-sections of the expanded inner pipes 2c, 2d maintain their proper shapes. As shown in Figure 2, the unexpanded cross-sections of the inner pipes 2c, 2d are generally D- shaped so as to follow the contours of the adjacent interior wall of the outer pipe I and of the adjacent surfaces of the stiffening wall 16. Alternatively, where the material of the inner pipes is sufficiently malleable, dissimilar (e.g. oval, trapezoidal or even circular) inner pipe cross sections can be used. In any of the previously described embodiments, the inner pipes 2, 2a, 2b, 2c, 2d may be provided with one or more longitudinally extending pleats, concavities or the like which straighten out on internal pressurization of the pipes, to aid their expansion.

2s The embodiment shown in Fig. 8 is generally similar in structure and in its expansion and bending operations to the embodiment shown in Fig. 7. Three parallel inner pipes 2e, 2f, 2g and two intervening stiffening walls 16a, 16b are received within an outer pipe 1. The cross-section of outer pipe I is oval rather than circular and if necessary is orientated (twisted) to the local bending radius direction together with the stiffening walls 16a, 16b to provide the lowest overall second moment of cross sectional area, or to minimise the second moments of cross sectional area of the stiffening walls 16a, 16b alone, as desired. The middle inner pipe 2f is pressurised and expanded first, followed by the other inner pipes 2e, 2g, and then all three inner pipes together to elastically deform the outer pipe 1. Other numbers and arrangements of inner pipes can be readily accommodated, including parallel BP-09-044 1 and nested inner pipes within the same outer pipe. Although the stiffening walls are shown as separate members in Figs. 7 and 8, they could be combined with the inner pipes 2c - 2e, e.g. as a thicker wall of these pipes that does not yield as the remainder of the pipe is hydraulically expanded. Where the inner pipes are provided with expansion pleats, concavities, etc., stiffening walls may not be necessary. The pipe assemblies with generally parallel inner pipes may be provided with end flanges having the appropriate number and configuration of flow apertures, for use with an appropriately configured sealing gasket or gaskets. Pipe bundles as shown for example in Figs. 7 and 8 are particularly compact, transverse cross sections of adjacent inner pipes having wall parts extending generally lo parallel to each other. Thus a large proportion of the interior crosssection of the outer pipe can be used as a flow area. This minimises the surface area to volume ratio of the pipe bundle, which can help in reducing heat losses.

The tern "pipe" as used throughout this specification, including the claims, is to be broadly construed and includes any hollow elongate member, including members whose cross sectional areas and/or cross sectional shapes vary along their lengths.

Claims

BP-09-044 1 CLAIMS

1. A method for manufacturing a lined or multi-walled pipe comprising the steps of: providing a first straight pipe and a second straight pipe; s inserting the second straight pipe into the first straight pipe; bending the first straight pipe and the inserted second straight pipe, and expanding the second pipe into contact with the first pipe.

2. A method according to claim 1, wherein the bending step is performed before the lo expanding step.

3. A method according to claim 1, wherein the expanding step is performed before the bending step.

is

4. A method according to any preceding claim, wherein the second pipe is temporarily supported in the first pipe for the bending step.

5. A method for manufacturing a lined or multi-walled pipe comprising the steps of: forming a first pipe around a second pipe which has previously been bent to a desired shape, and expanding the second pipe into contact with the first pipe.

6. A method according to any preceding claim, wherein the second pipe is expanded by hydraulic pressure. 2s

7. A method according to any preceding claim, wherein the second pipe is filled with an incompressible medium prior to the bending step.

8. A method according to any of claims I - 6, wherein a flexible support is inserted into the second pipe prior to the bending step.

9. A method according to any preceding claim, wherein the second pipe is of a corrosion, erosion' dissolution and/or temperature resistant material.

BP-09-044 1

10. A method according to any preceding claim, wherein the second pipe is coated with a material that bonds to the first pipe.

11. A method according to any preceding claim, wherein the second pipe is a clearance or sliding fit within the first pipe prior to the expansion step.

12. A method according to any preceding claim, wherein a plurality of said second pipes is received in the first pipe.

lo

13. A method according to claim 12 wherein the second pipes are nested.

14. A method according to claim 13 wherein the second pipes are generally parallel.

15. A method according to claim 14 wherein the second pipes are separated by or IS comprise longitudinally extending stiffening members.

16. A pipe bundle for conveying a plurality of separate fluid flows, comprising an outer pipe and a plurality of generally parallel inner pipes received within the outer pipe and in pre-stressed contact with the outer pipe.

17. A pipe bundle for conveying a plurality of separate fluid flows, comprising an outer pipe and a plurality of generally parallel inner pipes received within the outer pipe, in which transverse cross sections of adjacent inner pipes have wall parts extending generally parallel to each other.

18. A pipe bundle according to claim 16 or 17 comprising a stiffening member received in the outer pipe.