Method of manufacturing spacers for pipe-in-pipe systems and spacer for a pipe-in-pipe structure

Abstract

A method manufacturing a spacer for a pipe-in-pipe system includes mixing aerogel particles with a polymer to form a mixture in which the particles are dispersed in the polymer. The resulting mixture is moulded and the polymer is solidified to form the spacer or a component of the spacer, in which the dispersed, particles are suspended in a matrix of the solidified polymer.

Claims

1. A method of manufacturing a spacer for a pipe-in-pipe system, the method comprising: mixing a filler of aerogel particles with a polymer to form a mixture in which the aerogel particles are dispersed in the polymer; and moulding the mixture and solidifying the polymer to form the spacer or a component of the spacer, in which the dispersed aerogel particles are suspended in a matrix of the solidified polymer, wherein the polymer is a thermoset and is solidified at a temperature of from 30 C. to 250 C.

2. The method of claim 1, comprising injection-moulding the mixture.

3. The method of claim 1, comprising pouring the mixture into a mould cavity.

4. The method of claim 1, comprising mixing the aerogel particles with the polymer when the polymer is in a liquid form.

5. The method of claim 4, comprising heating and/or catalysing the polymer when solidifying the polymer after moulding the mixture.

6. The method of claim 4, comprising melting the polymer and mixing the aerogel particles with the molten polymer.

7. The method of claim 1, comprising mixing the aerogel particles with the polymer when the polymer is in a granular form, and then melting the polymer.

8. The method of claim 6 comprising cooling the mixture when solidifying the polymer after moulding the mixture.

9. The method of claim 1, wherein the aerogel particles comprise polyimide aerogel particles.

10. The method of claim 1, wherein the aerogel particles have a diameter of between 5 m and 50 m.

11. The method of claim 10, wherein the aerogel particles have a diameter of between 25 m and 125 m.

12. The method of claim 1, wherein the aerogel particles constitute between 5% and 50% of the mixture by volume.

13. The method of claim 12, wherein the aerogel particles constitute between 10% and 30% of the mixture by volume.

14. The method of claim 1, wherein the filler is mixed with the polymer at a temperature of from 50 C. to 400 C.

15. The method of claim 14, the filler is mixed with the polymer at a temperature of from 50 C. to 200 C.

16. The method of claim 1, wherein the filler is mixed with the polymer at a pressure of from 110.sup.7 MPa to 350 MPa.

17. The method of claim 16, wherein the filler is mixed with the polymer at a pressure of from 110.sup.7 MPa to 0.101 MPa.

18. The method of claim 1, wherein the polymer is solidified at a pressure of from 110.sup.7 MPa to 350 MPa.

19. The method of claim 18, wherein the polymer is solidified at a pressure of from 110.sup.7 MPa to 0.101 MPa.

20. The method of claim 1, wherein the polymer is selected from: epoxy, nylon, polyester, vinyl ester, polypropylene, or dicyclopentadiene.

21. A pipe-in-pipe structure made by a method as defined in claim 1.

Description

(1) In order that the invention may be more readily understood, reference will now be made, by way of example, to the accompanying drawings in which:

(2) FIG. 1 is a schematic diagram of a mixing and injection-moulding system for use in the invention;

(3) FIG. 2 is a schematic sectional side view of a mixing receptacle that is part of the system of FIG. 1;

(4) FIG. 3 is a schematic sectional side view of the mixing receptacle of FIG. 2, while mixing a mouldable thermally-efficient material of the invention;

(5) FIG. 4 is a schematic sectional side view of a mould that is part of the system of FIG. 1;

(6) FIG. 5 corresponds to FIG. 4 but shows a cavity of the mould now filled with a charge of material mixed in the mixing receptacle as shown in FIG. 3, to form a thermally-efficient spacer component of the invention;

(7) FIG. 6 is a schematic side view of the spacer component now removed from the mould cavity;

(8) FIG. 7 is a schematic part-sectional view of two spacer components as shown in FIG. 6 being brought together in mutual opposition around an inner pipe of a PiP structure;

(9) FIG. 8 is a schematic cross-sectional view on line VIII-VIII of FIG. 9 of the spacer components shown in FIG. 7 clamped together around the inner pipe of a PiP structure and within an outer pipe of the PiP structure;

(10) FIG. 9 is a schematic view in longitudinal section of the PiP structure, taken on line IX-IX of FIG. 8;

(11) FIG. 10 is a schematic view in longitudinal section of a mould that encircles an inner pipe of a PiP structure;

(12) FIG. 11 corresponds to FIG. 10 but shows a cavity of the mould now filled with a charge of material mixed in the mixing receptacle as shown in FIG. 3, to mould a thermally-efficient spacer of the invention in situ around the inner pipe;

(13) FIG. 12 is an enlarged sectional view of a thermally-efficient material of the invention, showing aerogel particles suspended in a polymer matrix; and

(14) FIG. 13 corresponds to FIG. 12 but shows heat flowing through the matrix and being reflected at interfaces between the particles and the matrix.

(15) In FIG. 1 of the drawings, a mixing and injection-moulding system 10 for use in the invention comprises a mixing receptacle 12, an injection moulding machine 14 and a mould 16.

(16) FIGS. 2 and 3 show the interior of the mixing receptacle 12. In each case, the mixing receptacle contains a mass of polymer 18.

(17) In FIG. 2, the mixing receptacle 12 shown on the left contains a liquid polymer 18, which may be either a thermoplastic polymer heated to a molten state or a thermoset resin that has not yet been cured or solidified. Conversely, the mixing receptacle 12 shown on the right of FIG. 2 contains grains or beads of a thermoplastic polymer 18 that has not yet been heated to melting point.

(18) Centrally, FIG. 2 shows a filler 20 that comprises an aerogel or aerogel-based material in a particulate, powder or granular form. The aerogel material of the filler 20 may, for example, be a polyimide aerogel as disclosed in PCT/US2016/55775 or in U.S. Pat. No. 9,963,571. Polyimide aerogel is preferred for the filler 20 as it disperses well with other polymers, in particular an embedding matrix of the polymer 18, and has good mechanical strength. Particles of the filler 20 may, for example, have a diameter of between 5 m and 500 m and preferably of between 25 m and 125 m.

(19) The filler 20 is poured into the mixing receptacle 12 and then is mixed with the polymer 18 in the mixing receptacle 12 at a temperature between 50 C. and 400 C. and at a pressure between 110.sup.7 and 350 MPa, as shown in FIG. 3, to form a mixture 22 in which the particles of the filler 20 are dispersed evenly through the mass of polymer 18. The filler 20 may, for example, constitute between 5% and 50% of the mixture 22 by volume and preferably constitutes between 10% and 30% of the mixture 22 by volume.

(20) The mixture 22 is pumped or poured from the mixing receptacle 12 into the injection moulding machine 14. If the polymer 18 was initially in granular form, the polymer 18 could be melted in the mixing receptacle 12 or in the injection moulding machine 14, which further mixes the filler 20 with the polymer 18 before the mixture 22 is injected into the mould 16.

(21) FIGS. 4 and 5 show the interior of the mould 16. The mould 16 defines a mould cavity 24, shown empty in FIG. 4, that in this example is substantially semi-annular to define a substantially semi-annular spacer component 26 as shown in FIG. 6. The mould cavity 24 communicates with the injection moulding machine 14 via a sprue 28, through which a charge of the mixture 22 is pumped into the mould 16 to fill the mould cavity 24 as shown in FIG. 5.

(22) When the mould cavity 24 has been filled completely with the mixture 22, the mixture 22 is cured or solidified in the mould 16 to solidify the polymer 18. Where the polymer 18 is a thermoplastic, solidification may be achieved by cooling the mould 16 to cool and freeze the polymer 18 at a temperature between 50 C. and 200 C., and at a pressure between 1=10.sup.7 and 350 MPa. Where the polymer 18 is a thermoset resin, solidification may be achieved by heating the mould 16 to a curing temperature between 35 C. and 250 C. and at a pressure between 110.sup.7 and 0.101 MPa and/or by allowing a pre-mixed hardener or catalyst component to solidify the resin at a temperature between 20 C. and 250 C. and at a pressure between 110.sup.7 and 0.101 MPa. The mould 16 is then opened or disassembled to extract the spacer component 26 as shown in FIG. 6.

(23) The spacer component 26 shown in FIG. 6 has part-circular curvature, in this example being substantially semi-circular so that two opposed spacer components 26 can be brought together as shown in FIG. 7 to encircle an inner pipe 30 of a PiP structure. When assembled around the inner pipe 30 in this way, the spacer components 26 are clamped together by bolts 32 that extend through integral flanges 34. The spacer components 26 thereby cooperate to form an annular spacer 36 that extends substantially continuously around the inner pipe 30 and within an outer pipe 38 in the PiP structure 40 shown in FIG. 8.

(24) It will be apparent that an inner face 42 of each spacer component 26 has a radius of curvature that is the same as, or slightly larger than, the external radius of curvature of the inner pipe 30. Conversely, an outer face 44 of each spacer component 26 has a radius of curvature that is slightly smaller than the internal radius of curvature of the outer pipe 38 of the PiP structure 40.

(25) The spacer 36 defined by the spacer components 26 extends radially across almost the full width of the annulus 46 between the inner pipe 30 and the outer pipe 38.

(26) However, a small clearance or gap is preferably left between the spacer 36 and the outer pipe 38 to reduce heat transmission by conduction.

(27) The longitudinal sectional view of the PiP structure 40 in FIG. 9 shows that the annulus 46 may also contain thermal insulation material 48, such as insulating blankets that encircle the inner pipe 30.

(28) Turning next to FIGS. 10 and 11, these drawings show a variant of the invention in which like numerals are used for like features. In this variant, a spacer 36 is moulded in situ around an inner pipe 30 of a PiP using a mould 16 that encircles the inner pipe 30. The mould 16 is in two or more parts to allow its removal from the inner pipe 30 after the spacer 36 has been moulded and solidified. However, the parts of the mould 16 cooperate to define a continuous mould cavity 24 that encircles the inner pipe 30 and so defines an integral one-piece annular spacer 36 as shown in FIG. 11.

(29) When the mould 16 has been removed from the inner pipe 30 to leave behind the spacer 36, the mould 16 may be moved along and reassembled around the inner pipe 30. In this way, the same mould 16 can be used repeatedly to mould other spacers 36 at respective positions spaced longitudinally along the inner pipe 30.

(30) When the required spacers 36 have been moulded onto the inner pipe 30, the inner pipe 30 can be wrapped with insulating material between the spacers 36 like that shown in FIG. 9. The resulting assembly can then be inserted into an outer pipe of a PiP structure like that shown in FIGS. 8 and 9.

(31) Turning finally to FIGS. 12 and 13 of the drawings, these enlarged detail views show the microstructure of the thermally-efficient material of the invention that results when the mixture 22 is solidified to make a spacer 36. It will be apparent that embedded particles or granules of the aerogel filler 20, of various sizes, are suspended in a solid, dense matrix of the polymer 18.

(32) In use of the spacer 36 in a PIP structure, heat will typically flow from a radially inner side of the spacer 36 to a radially outer side of the spacer 36. Such a flow of heat is represented by the arrows in FIG. 13, which generally point upwardly as illustrated. It will be apparent that the heat transfer paths through the matrix of the polymer 18 around and between the particles of the aerogel filler 20 are convoluted, indirect and therefore lengthy, as shown by arrows 50. It will also be apparent that some heat radiation is reflected back, or at least substantially diverted, by reflection at the interfaces between the polymer 18 and the particles of the filler 20, as shown by arrows 52. Both of these factors hinder the flow of heat through the spacer 36 and so are to the benefit of thermal insulation.

(33) The particles of the filler 20 could have irregular shapes and so need not have the spherical shapes that are shown schematically in FIGS. 12 and 13. Nor is it essential that the particles of the filler 20 are of substantially different sizes as shown. However, if those particles are of substantially different sizes, interstices between larger particles may be filled more effectively with smaller particles so as to optimise the volume ratio of the filler 20 to the polymer 18.

(34) Many other variations are possible within the inventive concept. For example, mixing between the filler and the polymer matrix material could be effected solely within an injection moulding machine. A separate mixing receptacle upstream of the injection moulding machine is therefore optional.

(35) The spacer could be moulded by a process other than injection moulding, such as casting involving pouring a liquid mixture into a mould cavity under no, or low, pressure rather than injecting the mixture into the cavity under high pressure.

(36) Three or more spacer components could be assembled together to form a spacer that encircles the inner pipe of a PiP system.