GB2458110A

GB2458110A - Mould for forming vortex inducing suppression features on an elongate member

Info

Publication number: GB2458110A
Application number: GB0803922A
Authority: GB
Inventors: Philip Michael Walsh
Original assignee: Trelleborg CRP Ltd
Current assignee: CRP Subsea Ltd
Priority date: 2008-03-03
Filing date: 2008-03-03
Publication date: 2009-09-09
Also published as: GB0803922D0; WO2009109776A3; WO2009109776A2

Abstract

The invention relates to a mould 10 for forming vortex inducing suppression features or strakes (16 figure 8e) directly onto an elongate member (13 figure 8), such as a riser or jumper for deployment underwater. A cladding (14 figure 8e) insulates the elongate member and protects it from vortex induced vibration (VIV). Features such as helical strakes (16 figure 8e) are formed along the exterior of the cladding to disrupt flow over it and so guard against vortex induced vibration. The mould is formed from multiple sections (18 figure 5) adapted to be assembled to one another upon the member (13 figure 8) and thereby define a mould cavity around the elongate member. The cavity is shaped to mould a cladding section having a sheath portion (15 figure 8c) which surrounds and embraces the elongate member, as well as the aforementioned strake or strakes. The mould has male and female ends wherein the male end is shaped to form a mating portion (38 figure 8e) of the cladding section, and the female end is shaped to receive and be closed b the mating portion of an existing section of cladding. The female end is closed by a blanking plate (50 figure 8a) to form the first section of the cladding and the mould re-mounted with its female end closed by the inserted male portion of the adjacent cladding section. A second cladding section can thereby be formed which is continuous with the first. By repeatedly re-mounting the mould in this way, a cladding section of arbitrary length can be formed.

Description

DESCRIPTION

MOULD FOR FORMING A CLADDING UPON AN ELONGATFM3JR The present invention is concerned with cladding for elongate members deployed underwater, and particularly with a mould and a method for moulding cladding directly onto such members.

There are many practical situations in which elongate conduits must be deployed underwater. In sub-sea oil extraction, for example, elongate conduits referred to as "jumpers" lead from wellheads to a valve manifold, and thence to a riser leading to a surface platform. A potential problem with any elongate member in a flow of water (e.g. a tidal or "cold loop" current) is vortex induced vibration ("V IV"). Vortices are created downstream of the member, and VIV happens when shedding of vortices is coherent along a sufficient length of the member and takes place alternately from opposite sides of it, creating a fluctuating force across the direction of flow. If the member has a natural frequency of oscillation close to the shedding frequency of the vortices, resonance can occur. The resulting vibration can be damaging to the structure.

It is known to protect underwater members against VIV by providing them with external features which disrupt the pattern of vortex shedding. Helical strakes fbr this purpose are disclosed for example in GB 2335248 (filed in the name of CRP Group Ltd.) That document contained a suggestion that the cladding could be formed directly on the pipe, but gave no details about how this could be achieved.

Low water temperatures can give rise to the separate problem of unwanted cooling of the contents of an underwater conduit. In sub-sea oil extraction the crude oil emerges from the welihead at an elevated temperature. If cooled sufficiently it becomes viscous and waxy and can restrict or prevent flow. The problem is most severe when flow is interrupted, e.g. due to maintenance or modification. For example flow through the jumper leading &om a wellhead may he closed off by valves for protracted periods for repair or maintenance and there is the risk that oil in them will he cooled enough to create a problem when the valves are subsequently opened.

GB2419171 (filed in the name of CRP Group Ltd.) discloses a pipe assembly having an insulating layer moulded in-situ upon it and formed by a mixture of high density polyethylene and density-reducing microspheres.

According to a first aspect of the present invention there is a mould for use in moulding a cladding directly onto an elongate member, the mould comprising at least two mould sections adapted to be assembled to one another upon the elongate member to define a mould cavity around it which is shaped to mould a cladding section having a sheath portion which surrounds and embraces the elongate member and at least one VIV suppression feature extending along the length of the cladding section, the mould having male and female ends, the male end being shaped to form a mating portion of the cladding section and the female end being shaped to receive and be closed by the mating portion of an existing cladding section, so that after moulding of a first cladding section the mould can be re-mounted with its female end closed by the mating portion of the first cladding section to form a second cladding section which is continuous with the first.

The sheath portion of the cladding can serve to provide thennal insulation. The cladding also provides protection against VIV. The mould according to the present invention allows a cladding performing both functions to be straightforwardly moulded directly onto the member being protected.

The mould can of course be re-mounted an arbitrary number of times to form a continuous cladding of a desired length.

The WV suppression feature need not extend along a precisely axial direction with respect to the elongate member. Preferably it extends along a helix about the elongate member. While it could for example be a female shape such as a trough, its preferred form is an outwardly projecting strake.

Strakes create potential problems with mould release -i.e. with the removal of the mould sections after the moulding has cured. In a preferred embodiment of the present invention, the mould sections are separable from one another along the line of at least one strake. In this way mould release problems are avoided. The lines of separation between two mould sections may for example be helical, where the strakes have this shape.

The mould preferably has the same internal section at (a) its female end and (h) a region adjacent the mating portion. Hence the part of the cladding section formed by region (h) is insertable into the female end of the mould.

The male end of the mould is preferably shaped to form a mating section of reduced lateral dimension compared with the mould's female end. I-fence when moulding the second and successive sections, material of the new moulding can overlap the mating section of the existing one and adhere to it to form a joint between one cladding section and the next.

The male end of the mould is preferably formed by an end cap secured to the mould sections. The end cap may be in two or more parts to enable it to be assembled around the elongate member.

According to a second aspect of the present invention there is a mould for use in moulding a cladding directly onto an elongate member, the mould comprising at least two mould sections adapted to be assembled to one another upon the elongate member to define a mould cavity around it which is shaped to mould a cladding section having a sheath portion which surrounds and embraces the elongate member and at least one strake projecting outwardly from the sheath portion and extending helically along the length of the cladding section, the mould sections meeting one another along the line of the said strake.

Preferably the mould sections each have helical peripheral surfaces which abut one another in the assembled mould.

Preferably surfaces through which the mould sections meet each other are at the outermost extremity of the strake.

Preferably the mould sections incorporate heating elements to aid curing. The heating elements arc preferably at or adjacent the outer extremity of the strake.

It is particularly preferred that the mould cavity is shaped to form three helical strakes, there being three mould sections each of which meets the two neighbouring sections along the line of a respective strake.

Preferably the mould further comprises an end cap detachably securable to the mould sections to close one end of the mould cavity. The end cap may be formed from two or more parts for assembly around the elongate member. It preferably has a through-going opening to receive the elongate member.

Specific embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:-Figure 1 is a perspective view of a mould embodying the present invention; Figure 2 is a side elevation of the same mould; Figure 3 is an end elevation of the mould along lines B-B of Figure 2; Figure 4 is an end elevation of the mould along lines A-A of Figure 2; Figure 5 is a perspective view of a mould section forming part of the mould of Figures 1 to4; Figure 6 is an enlarged perspective view of part of the mould section seen in circle D of Figure 5; Figure 7 shows a vent/nozzle for use with the mould; and Figures 8a-e illustrate successive stages in the fabrication of cladding embodying the present invention.

The mould 10 seen in Figures 1 to 4 is for moulding a cladding 14 directly onto an elongate cylindrical member such as a sub-sea jumper 13 (Figure 8). As Figures 8d and 8e show, the cladding 14 comprises a continuous annular sheath 15 about the member 13 with integrally formed strakes 16 projecting from it. In the particular embodiment illustrated herein there are three strakes 16, although a different number could be chosen. The strakes extend along the length of the cladding 14. In the illustrated embodiment they each form a shallow pitched helix, which has been demonstrated to be an effective shape for VIV suppression.

Nonetheless the strakes could be differently shaped. The strakes 16 of the present embodiment project radially outwardly from the sheath 15 and are continuous that is, they are without breaks or interruptions. However to simplify the moulding process, breaks in the strake profile could be formed between cladding sections.

The mould 10 comprises three identically formed mould sections 18 (see Figure 5) shaped to be assembled to one another about the member 12 to define around it a mould cavity for forming the cladding 14. Each mould section 1 8 comprises a part-cylindrical portion 20 whose two longitudinal edges are helical and meet respective upstanding helical fin portions 22, 24. The fin portions of adjacent mould sections 18 together define the helical strake portions of the mould cavity.

Their section is best seen in Figure 6. Each has at its radially outermost region an abutment surface 22 for contacting and sealing against a similarly formed surface of the adjacent mould section 18. The abutment surfaces 22 are helical, and are outboard of the outer hips of the strakes. Location features 24 are provided for ensuring alignment of neighbouring mould sections 18. They may, for example, take the form of pips in one section and complementary recesses in the other, or may be holes for receiving bolts to secure the mould sections together. A shoulder 26 forming the inner edge of the abutment surface 22 ensures that the strakes 16 have blunt outer tips. Outer strips 23 incorporate electrical heater elements to promote curing.

One end of the mould 10 (to be referred to below as the female end) has a first outwardly projecting flange 28 defined by part-annular portions of the three mould sections 18. The other end of the mould (to be referred to below as the male end) has a smaller outwardly projecting second flange 30 again defined by part-annular portions of the three mould sections 18. To form a closed mould cavity, both ends of the mould need to be closed. The front end is closed by means of an end cap 32 formed in two semi-annular parts securable to one another around the cylindrical member 12. It has a cap flange 34 lhroLlgh which it is releasably securable to the second flange 30, and a reduced diameter portion 36 which forms a mating feature (item 38 in Figure 8e) on the end of the moulded cladding 14. In more detail, the reduced diameter portion has a chamfer 40 leading to a reduced diameter constant diameter region 42 which in turn leads to a irustro-conical portion 44 terminating in an annular collar 46 which forms a seal against the cylindrical elongate member 13.

The rear end of the mould 10 can he closed by securing an end plate 50 to the first flange 28, the end plate having a bore, which receives and seals against the elongate member 13.

Steps in the process of moulding the cladding 14 on the jumper 13 will now be explained with reference to Figure 8.

The mould 10 is first assembled around the elongate member 13 with its end plate and end cap 32 in place (Figure 8a). Settable resin is injected into the mould to fill it and then cures. Heat may be applied by means of the aforementioned heating elements to promote curing. Disassembling and removing the mould 10 leaves a section olcladding 14 (Figure 8b) which lies around and is bonded to the member 13. To form the next section of cladding, the mould lOis re-assembled upon the member 1 3 as seen in Figure 8c, with its rear end overlapping and embracing the first section, and forming a seal against it. The end plate 50 is thus not required. The fins 22, 24 of the mould 10 locate upon and seal against the strakes 16 of the first cladding section 14, and hence the result of moulding the second cladding section is the continuous strakes 16 seen in Figure 8d. Note also that the mating feature 38 of the first cladding section projects into and is embraced by the rear end of the next, as seen in Figure 8e. In this way the cladding's cylindrical sheath forms a continuous layer about the member 1 3 without excessive weakening or discontinuity between separately moulded sections. Clearly the moulding process can be repeated any number of times to provide a required length of cladding. Curing time can be as little as five minutes so the process need not be excessively time consuming.

Venting of air from the mould as the resin material is injected prevents a potential problem. A vent needs to he provided at the mould's uppermost point to avoid inclusion of air bubbles which could impair the cladding's quality. Note however that the mould needs to be rotated, between one section and the next, through an angle determined by the formation of the strakes 16. Hence a vent correctly placed to serve its function when moulding the first cladding section may be too low to do so when moulding the next. The solution adopted in the illustrated embodiment is to provide multiple vents at angular intervals around the mould 1 0, and to selectively blank these off when they are not required. The vents are in outer regions of the fins 22, 24. Their positions can be appreciated from Figures 1, 2, 4 and 5, in which blanking plates 60 covering the vents can be seen. In use one of these (preferably the lowermost vent) is replaced with a nozzle port 62 seen in Figure 7, which is coupled to a conduit for receiving the resin, and another (the uppermost vent) is left open to release air. -10-

The preferred material of the cladding 14 is a glass syntactic polyurethane -a mixture of settable polyurethane resin with density reducing hollow glass microspheres. Other suitable materials could be used. -Il-

Claims

CLMMSI. A mould fir use in moulding a cladding directly onto an elongate member, the mould comprising at least two mould sections adapted to be assembled to one another upon the elongate member to define a mould cavity around it which is shaped to mould a cladding section having a sheath portion which surrounds and embraces the elongate member and at least one VW suppression feature extending along the length of the cladding section, the mould having male and female ends, the male end being shaped to form a mating portion of the cladding section and the female end being shaped to receive and be closed by the mating portion of an existing cladding section, so that after moulding of a first cladding section the mould ean be re-mounted with its female end closed by the mating portion of the first cladding section to lbrm a second cladding section which is continuous with the first.
2. A mould as claimed in claim I, in which the VW suppression feature extends along a helix about the elongate member.
3. A mould as claimed in claim 1 or claim 2 in which the VIV suppression fbature is an outwardly projecting take.
4. A mould as claimed in claim 3 in which the mould sections are separable from one another along the line of at least one strake.

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5. A mould as claimed in claim 4 in which the sirakes and the lines of separation between two mould sections arc helical.
6. A mould as claimed in any preceding claim which has the same internal section at (a) its female end and (b) a region adjacent the mating portion.
7. A mould as claimed in any preceding claim in which the mating portion is of reduced lateral dimension compared with the mould's female end.
8. A mould as claimed in any preceding claim whose male end is formed by an end cap secured to the mould sections.
9. A mould as claimed in claim 8 in which the end cap is made in two or more parts to enable it to be assembled around the elongate member.
10. A mould for usc in moulding a cladding directly onto an elongate member, the mould comprising at least two mould sections adapted to be assembled to one another upon the elongate member to define a mould cavity around it which is shaped to mould a cladding section having a sheath portion which surrounds and embraces the elongate member and at least one strake projecting outwardly from the sheath portion and extending helically along the length of the cladding section, the mould sections meeting one another along the line of the said strake.

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11. A mould as claimed in claim 10 in which the mould sections each have helical peripheral services which abut one another in the assembled mould.
12. A mould as claimed in claim 10 in which surfaces through which the mould sections meet each other are at the outermost extremity of the strake.
13. A mould as claimed in any of claims 10 to 12 in which the mould sections incorporate heating elements to aid curing.
14. A mould as claimed in any of claims 10 to 13 in which the mould cavity is shaped to form three helical strakes and the mould comprises three mould sections, each of which meets the two neighbouring sections along the line of a respective strake.
15. A mould as claimed in any of claims 10 to 14 which further comprises an end cap (letacliably securable to the mould sections to close one end of the mould cavity.
16. A mould substantially as herein described with reference to and as illustrated in the accompanying drawings.