GB2378493A

GB2378493A - Cladding comprising semi-tubular sections with projections

Info

Publication number: GB2378493A
Application number: GB0225928A
Authority: GB
Inventors: David Gordon Lace; Antony Yeldrem
Original assignee: CRP GROUP Ltd; CRP Group Ltd
Current assignee: CRP GROUP Ltd; CRP Subsea Ltd
Priority date: 1998-03-07
Filing date: 1999-03-08
Publication date: 2003-02-12
Anticipated expiration: 2019-03-08
Also published as: GB2378493B; GB9905276D0; GB0225928D0; GB2335248B; GB2335248A

Abstract

The cladding comprises longitudinally staggered semi-tubular sections 12'. The assembled sections form a passage. Each section has at least one external projection 24. Preferably the identical semi-cylindrical sections 12' are offset by half their lengths. Preferably the strakes 24 form three almost continuous helices having a pitch = 4-6 times the diameter. Preferably the sections 12' are connected using projections and recesses (figure 4, 20 and 22). Preferably the projections 24 are hollow, compressible and triangular. The sections 12' may be made from polyurethane with metal securing bands 28 in slots (figure 3, 26). The cladding is used to reduce vortex induced vibrations in underwater pipes and cables.

Description

(74) Agent and/or Address for Service W P Thompson & Co Coopers Building,

Church Street, LIVERPOOL, L1 JAB, United Kingdom

-1 DESCRIPTION

PROTECTION OF UNDERWATER ELONGATE MEMBERS

The present invention relates to the protection of underwater pipes, cables or other elongate members.

When water flows past an underwater pipe, cable or other elongate member of circular cross section, vortices are shed alternately from each side.

The effect of these vortices is to induce fluctuating, across-flow forces on the structure. If the natural frequency of the structure is close to the shedding frequency of the vortex the member can be caused to vibrate with a large oscillation amplitude.

Such oscillations not only cause the pipe, cable or member to bend more than is desirable, but can also induce unwanted forces on a connector (either under water or above water) to which the pipe, cable or the like is secured. In extreme cases, the coupling between the pipe, cable or the like and the connector is damaged.

It is an object of the present invention to avoid or reduce these socalled "vortex induced vibrations".

In accordance with the present invention, an underwater cladding comprises a plurality of semi-tubular sections which are assembled to form a longitudinal through passage, each section comprising an external projection to interrupt or reduce vortex-induced vibration and wherein oppositely located sections are staggered or offset longitudinally with respect to one another.

By interrupting or reducing the vortex-induced vibrations, the damage to

-2- the pipe, cable or the like and any fitting to which it is connected, can be greatly reduced or even avoided.

Preferably, the cladding comprises a plurality of substantially identical semi-tubular sections. Preferably, oppositely located sections are staggered or offset by approximately one-half the length of a section.

The semi-tubular sections may comprise projections andlor recesses which engage with corresponding recesses and/or projections on one or more other sections. The projections and/or recesses may be located on longitudinal edges of the semi-tubular sections.

Each semi-tubular section may comprise a plurality of external projections to interrupt or reduce vortex-induced vibrations.

Preferably, the or each external projection forms part of a substantially continuous external projection when the semi-tubular sections are assembled.

For example, there may be three substantially continuous external projections.

The cladding may comprise a plurality of external projections substantially evenly spaced around the periphery of the cladding.

Advantageously, the or each substantially continuous external projection is substantially helical.

The pitch of the substantially helical projection is preferably from four to six times, and more preferably approximately five times, the external diameter of the cladding.

The or each external projection may be resiliently deformable or compressible. The or each external projection may be hollow.

Advantageously, the or each external projection is sharp-edged.

Moreover, the height of the or each external projection is preferably from 0. l to 0.15 tunes the diameter of the external diameter of the cladding.

By way of example only, a specific embodiment of the present invention will now be described, with reference to the accompanying drawings, in which: Fig. 1 is a side elevation of a section of pipe fitted with an embodiment of cladding in accordance with the present invention; Fig. 2 is a cross-section of the clad pipe shown in Fig. 1, looking in the direction of arrows II - II; Fig. 3 is a plan view to a larger scale of a section of the cladding shown in Fig. 1; and Fig. 4 is a plan view of the inner surface of one of the cladding sections illustrated in Fig. 3.

Referring to Figs. 1 to 4, a pipe to is clad in a protective ducting 12.

The ducting is generally as described in GB-A-2260590 and comprises a tubular flexible, Impervious, polyurethane casing comprising a plurality of identical, releasably engaged, semi-tubular sections 12' which are arranged with respect to one another to provide a cylindrical passage 14 thereehrough which is dimensioned and shaped to receive the pipe. In use longitudinally adjacent sections are secured to one another by fining a reduced outer diameter end spigot portion 16 of one section into a complementarily-shaped, enlarged inner diameter end socket portion 18 of the adjacent section.

Each section 12' is provided with a series of small lugs 20 along one

-4 - diametrically opposed edge 21 and a series of complementarily positioned and shaped recesses 22 in the other diametrically opposed edge 23. Diametrically-

opposed sections are secured to one another by engaging the lugs 20 in the corresponding recesses 22 in the abutting edge 23 of the diametrically-opposed section. Diametrically-opposed sections are also "staggered" by approximately half the length of a section to ensure that the vertical joints between two longitudinally adjacent sections are not aligned with the vertical joints between diametrically-opposed longitudinally adjacent sections.

Each section of ducting is also provided with three identical, parthelical strakes 24. As illustrated in Fig. 2, the strakes are angularly spaced by 120 at any cross-section through the strakes. The strakes on each section are arranged such that when the cladding is assembled from the plurality of cladding sections, the strakes thereby formed on the exterior of the cladding thus formed are substantially continuous, with the exception of regularly longitudinally-spaced slots 26 for receipt of securing bands 28 of metal or other material which are located in circumferential recesses 30 in me assembled ducting.

In use, the preformed sections 12' are located on the exterior of a section of pipe to be protected and are secured to each other around the pipe by means of the aforementioned projections 20 and recesses 22 and by means of the metal banding 28. The ducting thus formed comprises three helical, substantially continuous (with the exception of the gaps 26 provided for receipt of the securing bands) strakes. As best seen in Fig. 2, the strakes are substantially

-5- triangular in cross-section and are sharp-edged. It has been found that the pitch of the strakes should be between four and six, and preferably approximately five, tunes the external diameter of the cladding and that the height of the strake should be 0.1 to 0.15 times the external diameter of the cladding. There should also preferably be, as illustrated in the first embodiment, three helical strakes.

As can be seen in the enlarged portion of Fig. 2, the strakes are also hollow, having an elongate void 25 of substantially triangular crosssection passing therealong. This makes the strakes compressible and resiliently deformable and allows them to be deformed after installation of the cladding on a pipe after it passes, for example, through rollers. The deformable nature of the strakes also allows the pipe to be gripped more tightly after having been clad, e.g. to control its deployment. Alternatively, the strakes may be solid but may still be compressible and resiliently deformable or alternatively may be substantially rigid.

When a pipe is clad in this way and is submerged under water, the presence of the strakes prevents the formation of, or significantly reduces the intensity of, vortices and thereby eliminates or reduces vortex induced vibrations. This results in greater stability of the pipe and increases the useful life of the pipe and the connectors to which it is attached.

The invention is not restricted to the details of the foregoing embodiment. For example, the strakes may initially be omitted from cladding and instead the cladding may be provided with a plurality of helically-extending

-6 - grooves which are adapted to receive strake sections secured therein at a later date in order to form a cladding having a plurality of external strakes, in a "retrof t" manner.

Furthermore, although the strakes have been described as being compressible and resiliently deformable (whether hollow or solid) the strakes may instead be resistant to substantial deformable deformation, if desired.

Although the specific embodiments have been described with reference to the cladding of pipes, the invention is not restricted thereto but is equally applicable to underwater cables or other elongate members.

Claims

1. An underwater cladding comprising a plurality of semi-tubular sections which are assembled to form a longitudinal through passage, each section comprising an external projection to interrupt or reduce vortex-induced vibration and wherein oppositely located sections are staggered or offset longitudinally with respect to one another.

2. An underwater cladding as claimed in claim 1, comprising a plurality of substantially identical semi-tubular sections.

3. An underwater cladding as claimed in claim 1 or claim 2, wherein oppositely located sections are staggered or offset by approximately onehalf the length of a section.

4. An underwater cladding as claimed in any of the preceding claims, comprising projections and/or recesses on each of the sections which engage with corresponding recesses and/or projections on one or more other sections.

5. An underwater cladding as claimed in claim 4, wherein the projections and/or recesses are located on longitudinal edges of the semi-tubular sections.

6. An underwater cladding as claimed in any of the preceding claims, wherein each semi-tubular section comprises a plurality of external projections to interrupt or reduce vortex-induced vibrations.

7. An underwater cladding as claimed in any of the preceding claims, wherein the or each external projection forms part of a substantially continuous external projection when the semi-tubular sections are assembled.

8. An underwater cladding as claimed in claim 7, comprising three substantially continuous external projections.

-8

9. An underwater cladding as claimed in claim 7 or claim 8, comprising a plurality of external projections substantially evenly spaced around the periphery of the cladding.

10. An underwater cladding as claimed in any of claims 7 to 9, wherein the or each substantially continuous external projection is substantially helical.

1 1. An underwater cladding as claimed in claim 10, wherein the pitch of the substantially helical projection is from 4 to 6 times the diameter of the cladding.

12. An underwater cladding as claimed in claim 11, wherein the pitch of the substantially helical projection is zpproxi.mately 5 ti...es e dia... ete. of e cladding.

13. An underwater cladding as claimed in any of the preceding claims, wherein the or each external projection is resiliently deformable or compressible.

14. An underwater cladding as claimed in any of the preceding claims, wherein the or each external projection is hollow.

15. An underwater cladding as claimed in any of the preceding claims, wherein the or each external projection is sharp-edged.

16. An underwater cladding as claimed in any of the preceding claims, wherein the or each external projection is triangular in cross-section.

17. An underwater cladding as claimed in any of the preceding claims, wherein the height of the or each external projections is from 0.1 to 0. 15 times the diameter of the external diameter of the cladding.

18. An underwater cladding substantially as herein described, with reference to, and as illustrated in, the accompanying drawings.