GB2582305A

GB2582305A - Bend restrictor

Info

Publication number: GB2582305A
Application number: GB1903653.2A
Authority: GB
Inventors: Hussain Bilal; Harbison Austin
Original assignee: Trelleborg Offshore UK Ltd
Current assignee: CRP Subsea Ltd
Priority date: 2019-03-18
Filing date: 2019-03-18
Publication date: 2020-09-23
Anticipated expiration: 2039-03-18
Also published as: GB201903653D0; GB2582305B

Abstract

The bend restrictor includes at least first and second bend restrictor units 10, each having: a through-going passage, a head 30, a neck 26, 28, and a socket 24. The head of the first unit is captively received in the socket of the second unit. The head comprises an engagement portion 34a having a convex profile; a first abutment face 36; an internal head-receiving portion 44 having a concave profile complementary to that of the head; an internal neck-engagement portion 48 having a convex profile; an external end face 54 and an internal second abutment face 50; a portion 26 having a concave profile complementary to portion 48; a locking shoulder 40. Angular displacement of the second unit relative to the first causes: the first abutment face to abut the second abutment face; the engagement portion of the head to contact the portion 44; the portion 48 to abut the portion 28; and the shoulder 40 to abut the end face 54 of the second bend restrictor, thereby to resist angular displacement of the second unit relative to the first beyond a predetermined angle. A method of manufacturing a bend restrictor includes providing a two-part mould with a thickness shim.

Description

BEND RESTRICTOR

The field of the present invention is bend restrictors for limiting curvature of elongate members. The invention is applicable especially, but not exclusively, in relation to bend restrictors to be deployed underwater.

Bend restrictors for limiting local curvature of elongate members are known. They are for example used in underwater applications to protect elongate members including power cables, signal cables or fibres, pipes, umbilicals etc. from being excessively tightly bent or kinked, which could cause damage. Known bend restrictors typically comprise a string of identically formed units. Each unit in the string is coupled to its neighbour through interlocking male and female features which can accommodate limited angular movement but which lock when the angle between the unit and its neighbour reaches a limit. Refer for example to W02015/104560 (Trelleborg Offshore U.K. Ltd.) which discloses a bend restrictor of this type. Each unit is formed of two parts which in use are coupled to one another around the elongate member. One end of the unit has a male connector provided with a flange. The other end of the unit has a female connector providing an annular recess. The flange of one unit is received and retained in the annular recess of the next. The annular recess is somewhat over-size relative to the flange to accommodate some angular movement, but at a certain angle the flange locks in the recess to limit this. A bend restrictor is typically somewhat over-size in relation to the elongate member to which it is fitted so that there is some play between the bend restrictor and the member.

A bend restrictor may be mounted to some receiving structure arranged to receive the elongate member, such as a "J" or "I" tube. In such installations a root end of the bend restrictor is often coupled to the receiving structure through suitable steelwork. Refer again to W02015/104560, Figure 1 in particular, showing a metal flange for this purpose at the end of a bend restrictor string. In other installations the steelwork serving to mount the bend restrictor may be fabricated by welding, which can add undesirably to manufacturing costs and necessitate quality controls on the welds themselves.

Bend restrictors deployed underwater are often subject to repeated cycles of loading and unloading by the action of the water. They often need to have a design lifetime of years or decades, with minimal inspection and maintenance. Failures can be costly. On the other hand there are powerful commercial incentives to reduce material costs and installation time. It is desirable to distribute bending loads through the parts making up the bend restrictor and to avoid creation of excessive local stresses which might give rise to material failures.

Another design consideration is thermal performance of the bend restrictor. In some applications it is desirable not to excessively inhibit dissipation of heat from the elongate member within. The member in question may for example be a conduit such as a riser for hydrocarbons extracted subsea, which may be at elevated temperature. Excessive heat build-up is undesirable, and can be controlled by dissipation of heat to the surrounding water provided that the bend restrictor does not provide excessive thermal insulation. From this point of view it is desirable to minimise material usage in the design of the bend restrictor, without compromising its structural integrity.

Tooling up for manufacture of bend restrictors can be costly. Existing bend restrictors often need to be designed and constructed to meet customer requirements in terms of minimum bend radius, diameter of the elongate member and so on. But for small orders tooling costs can make this uneconomic.

It is desirable to minimise installation time of the bend restrictor.

Where bend restrictors are formed from two half shells abutted to one another to surround the elongate member, slippage of one half shell relative to the other in the region of their abutment may compromise the rigidity of the bend restrictor and reduce its structural integrity.

The present invention is intended to solve or alleviate one or more of the above problems.

According to the present invention there is a bend restrictor comprising at least first and second bend restrictor units each having a through-going passage, a head, a neck and a socket, the head of the first bend restrictor unit being captively received in the socket of the second bend restrictor unit to couple them together with their passages aligned to receive and embrace an elongate member, wherein, viewed along a radial direction: the head comprises an engagement portion having a convex curved exterior profile; the head comprises a first abutment face; the socket comprises an internal head-receiving portion having a concave curved profile complementary to the profile of the engagement portion of the head; the socket comprises an internal neck-engagement portion having a convex curved profile; the socket comprises an external end face; the socket comprises an internal second abutment face; the neck comprises a neck portion having a concave curved exterior profile complementary to the profile of the neck-engagement portion of the socket; the neck portion comprises a neck locking shoulder facing toward the head; so that angular displacement of the second bend restrictor unit relative to the first bend restrictor part causes: the first abutment face of the head of the first bend restrictor part unit to abut the second abutment face of the socket of the second bend restrictor part unit; the engagement portion of the head to abut the head receiving portion of the socket 24; the neck-engagement portion of the socket of the second bend restrictor unit to abut the neck portion of the first bend restrictor unit; and the neck locking shoulder of the first bend restrictor unit to abut the end face of the second bend restrictor part unit, thereby to resist angular displacement of the second bend restrictor unit relative to the first bend restrictor part beyond a predetermined angle.

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 depicts a neighbouring pair of bend restrictor parts according to the present invention, viewed along a radial direction; Figure 2 depicts a bend restrictor unit formed from two of the bend restrictor parts shown in Figure 1, viewed from one end; Figure 3 depicts the bend restrictor unit of Figure 2 viewed from the other end; Figure 4 is a section in a longitudinal plane through a further, different, bend restrictor embodying the present invention, including a mounting; Figure 5 depicts steelwork used in the mounting of Figure 4; Figure 6 depicts a further bend restrictor part embodying the present invention; Figure 7a depicts still a further bend restrictor part embodying the present invention and Figures 7b and 7c depict a bend restrictor unit using the same bend restrictor part; Figure 8 is a section through a bend restrictor unit embodying the present invention in a radial plane; Figures 9 to 12 each depict a respective bend restrictor part embodying the present invention and incorporating an insert; Figure 13 depicts yet a further bend restrictor part embodying the present invention; Figure 14 depicts an end region of another bend restrictor part embodying the present invention; Figure 15 depicts yet another bend restrictor part embodying the present invention; and Figure 16 depicts still another bend restrictor part embodying the present invention.

Bend restrictor parts 10 are each formed in the present embodiment as a respective unitary plastics moulding. A tough and durable material is desirable in this context. While no particular limitation is placed on the material choice by the present invention, the present embodiment uses polyurethane.

The bend restrictor part 10 is semi-annular in cross section, providing a pair of contact faces 12, 14 on either side of an axially extending recess 18. The contact faces are flat in the present embodiment although other shapes are possible. In the assembled bend restrictor a bend restrictor part 10a is coupled to a complementarily formed part 10b (see Figure 2), their contact faces being placed against one another, to form a bend restrictor unit 16 of annular cross section. The recesses 18 of the bend restrictor parts 10a, 10b together form a circular through-going passage 20 to receive and embrace the elongate member (which is not shown in the drawings). In the present embodiment the two bend restrictor parts 10a, 10b are in fact identically formed. They are secured together through suitable mechanical means which in the present embodiment comprise threaded couplings such as bolts passed through bolt holes 22a, b in the bend restrictor parts 10. Bend restrictor parts 10 is coupled to its neighbour through just four such couplings, in the present embodiment.

Holes 23 formed through both contact faces 12, 14 are not bolt holes but lifting holes, used to facilitate deployment of the bend restrictor. A lifting line may be passed through the holes 23 of a pair of bend restrictor parts 10, to loosely couple one to the other, allowing the pair to be handled together as an assembly for placement around the elongate member.

The bend restrictor parts 10 (and the bend restrictor units 16 formed from them) have: - a socket 24; -a first neck portion 26; - a second neck portion 28; and -a head 30.

In the assembled bend restrictor the head 30 of one bend restrictor unit 16a is captively received in the socket 24 of the axially neighbouring bend restrictor unit 16b, forming a coupling between them that permits limited angular displacement of one unit relative to the other. The formation of the neck 26, 28, head 30 and socket 24 is such that when the angle between the neighbouring bend restrictor units reaches a predetermined maximum, these parts lock up to resist further angular displacement.

The bend restrictor thus defines a minimum bend radius for the elongate member protected within it.

Looking now more closely at the sectional profile of the bend restrictor parts 10, it can be seen in Figure 1 that the head 30 is not precisely part-spherical. Viewed along the radial direction its shape forms a convex but not actually circular curve. Mid-way along the head 30 this curvature is interrupted by a head locking shoulder 34 which forms a reduction in the head diameter and which faces toward the socket 24. The head 30 is divided by the head locking shoulder 34 into an engagement portion 34a and a reduced diameter portion 34b. At its free end, the head 30 has a first abutment face 36 lying almost parallel to a radial plane and having the form of a shallow truncated cone. The convex curve of the head 30 leads via a concavely curved portion 36, forming a smooth transition, to the second neck portion 28.

The interior surface 32 within the head 30 is in the present embodiment roughly part-spherical. This reduces the radial depth of the material forming the head 30 and so avoids unnecessary material usage and weight, but is otherwise not vital to the function of the bend restrictor.

The second neck portion 28 has a smooth concave curve to its outer surface (viewed along the radial direction of Figure 1) leading to a neck locking shoulder 40, which faces toward the head 30, and which forms an increase in diameter in the direction from the second neck portion 28 toward the first neck portion 26.

The outer profile of the first neck portion 26 is not crucial to the function of the bend restrictor but has a constant diameter in the present embodiment. The recess 18 takes the form a semi-cylinder 42 of constant diameter where it passes through the first and the second neck portions 26, 28.

The socket 24 has an enlarged outer (and inner) diameter relative to the neck 26, 28 and head 30. Internally, it comprises a head-receiving portion 44 leading via a socket locking shoulder 46 to a neck-engagement portion 48. The socket locking shoulder 46 faces toward the head 30. The head-receiving portion has, at its end lying toward the head 30, a second abutment face 50 which takes the form of a flat annulus in the present embodiment although it may be curved in other embodiments, and may for example take the form of a shallow truncated cone. The neck-engagement portion 48 has a convex curvature, leading to the open end of the passage 20.

The manner in which lock-up of two neighbouring bend restrictor parts/units 10a, 10b takes place can be appreciated from Figure 1. There are multiple regions of contact between the two parts: -the frusto-conical first abutment face 36 of the head 30 of first bend restrictor part 10a abuts the second abutment face 50 of the socket 24 of the second bend restrictor part lob; - the engagement portion 34a of the head 30 abuts against the head receiving portion 44 of the socket 24, on either side of the axis of the first bend restrictor part 10a; - the head locking shoulder 34 of the head 30 contacts the socket locking shoulder 46 of the socket 24; - the neck-engagement portion 48 of the socket 24 of the second bend restrictor part 10b abuts the first neck portion 26 of the first bend restrictor part 10a; and - the neck locking shoulder 40 of the first bend restrictor part 10a abuts the end face 54 of the second bend restrictor part 10b.

In the present embodiment, the abutting faces of the two bend restrictor parts are in each case of complementary curved shape, so that the contacts between the parts are not lines or narrow regions, but extend in each case over an axial (or, in the case of the shoulders, radial) distance.

The abutment of the head locking shoulder 34 with the socket locking shoulder 46 provides positive resistance to withdrawal of the head 30 from the socket 24.

The abutment of: (a) the first and second abutment faces 36, 50 and (b) the neck locking shoulder 40 of the first bend restrictor part 103 and the end face 54 of the second bend restrictor provide positive axial location of one bend restrictor part with respect to the other.

The intimate engagement of the curved neck-engagement portion 48 of the socket 24 of the second bend restrictor part 10b with the complementarily curved first neck portion 26 of the first bend restrictor part 10a enables these parts to carry their portion of any bending load without local stress concentrations which could reduce fatigue lifetime.

The curved form of all the abutting surfaces also assists in avoiding stress concentrations under load.

The design proves in finite element analysis to be capable of providing a bend restrictor which meets design requirements in terms of lifetime and load bearing capacity, whilst at the same time providing a reduction in materials usage and cost compared with prior bend restrictors.

Figure 4 depicts a bend restrictor comprising restrictor parts 100 which differ from those of Figures 1 to 3 in lacking the head locking shoulder of the head 130 and the socket locking shoulder of the socket 124. This variant is considered adequate for certain applications. Figure 4 also depicts steelwork used to couple a root end of the bend restrictor to a structure 200, formed in this example as a tubular member. In this embodiment the mounting is made through root bend restrictor parts 1003 of modified form, lacking the socket 124 of the other bend restrictor parts 100. In place of the socket 124, the root bend restrictor part 100a have a second neck portion 128 which terminates in a frusta-conical coupling portion 170 surrounded and engaged by a coupling plate 172 which has a complementary frusta-conical through-going opening. The coupling plate 172 is in its turn secured through bolts 174 to a union 176 which is in the present embodiment formed in two parts, one of which is depicted in Figure 5. It has first and second union plates 178, 180 each having a respective part-circular cut-away 182, 184, and coupled to one another through spacer plates 186. To mount the union on the tubular structure 200 its two parts are assembled to one another with the first union plates lying around 178 lying around and engaging in a circumferential recess 188 in the structure 200. The coupling plate 172 can then be bolted to the second union plate 180, with the root bend restrictor parts 100a in situ, to form the mounting.

The bend restrictor parts 10 may be provided with registration features through which one bend restrictor part 10 mechanically engages with its neighbour in order to assist in alignment of one with the other, and/or to resist slippage or other movement of one relative to the other. Figure 6 provides an example. Here, the bend restrictor part 10 has in one of its contact faces 12 a female feature, specifically a dovetail section channel 300. The other contact face 14 carries a male feature for receipt in the female feature. In the present example this comprise a dovetail section upstand 302. Coupling two such bend restrictor parts 10 together involves sliding one radially with respect to the other to introduce each of the upstands 302 to a corresponding channel 300, after which the two bend restrictor parts 10 can be bolted to one another. The engagement of the upstand 302 and channel 300 serves (a) to resist longitudinal slippage of one contact face 12 over the other contact face 14 (which would compromise rigidity of the assembly) and (b) to resist separation of the two bend restrictor parts 10, due to the dovetail sections of the channel/upstand.

Figure 7a to 7c illustrate a further embodiment having registration features of a different form. Here, the bend restrictor part 10 has on one side of its axis a slotted hasp 400 and on the other side of its axis a tongue 402 for receipt in slot 404 of the hasp. Coupling two such bend restrictor parts 10 together involves sliding one radially with respect to the other to engage the tongues 402 in the slots 404.

Registration features may be formed by features of shape of the contact faces 12, 14. Refer in this connection to Figure 8, which is a section through a bend restrictor unit 16 formed by a pair of bend restrictor parts 10. It can be seen that the contact faces 12, 14 are non-flat and are complementarily shaped so that they engage in a manner which resists radial slippage of one relative to the other. In this example each of the contact faces has a step 500. Numerous other shapes could be used to provide registration of one contact face 12 relative to the other. They may for example have complementary curves, or dovetail engagement features, or may each have a "V" section (one male, one female).

It was noted above that there is at present sometimes a need to design and manufacture custom bend restrictor parts to meet a customer's requirements in terms of the diameter of the elongate member to be protected, the minimum bend radius of the restrictor, etc. The present inventors have recognised that the cost of tooling up for custom manufacture may in many instances be avoided by adapting a basic design of the bend restrictor parts 10 to a specific application.

The embodiments depicted in Figures 9 to 12 show how a basic moulding can be adapted to provide bend restrictors for use with elongate members having a range of different diameters by the use of inserts 600. In each of these examples the insert is provided within the neck 26/28, serving to reduce the internal diameter of the bend restrictor in this region. Thus only the insert itself needs to be matched to the diameter of the elongate member-and tooling for the insert can be made on a custom basis more cheaply (or a range of different inserts may be kept for different projects).

The example provided in Figure 9 has an insert 600a whose internal profile is curved along its length. Figure 10 provides an example having multiple inserts 600b, 600c, 600d disposed one within another, so that by choosing the number of such inserts one can choose from a range of different internal diameters. In Figure 11 the insert takes the form of a set of circumferentially extending ribs 600e at intervals along the interior of the neck. In Figure 12 the insert takes the form of a set of axially extending ribs 600f at circumferential intervals about the interior of the neck.

The neck 26/28 of the bend restrictor part 10 may be provided with internal features to engage with and locate the insert 600. In Figure 13, these take the form of a set of recesses or openings 602 to receive complementary stubs on the insert 600. The insert may comprise two or more parts separated along the axial direction. The example represented in Figure 14 comprises, in addition to the insert 600 within the neck 26/28, an insert part 604 disposed in the head 30 of the bend restrictor part 10, specifically at or adjacent its open mouth 606. In this example the insert part 604 comprises a circumferentially extending spacer band.

An alternative to the use of the inserts 600 is to provide the mould itself with a replaceable insert to form the recess 18, so that merely by replacing this insert the lateral dimension of the recess 18 is able to be varied.

Figure 15 represents a variant of the bend restrictor part 10 depicted in Figure 1 and having two head locking shoulders 834a, 834b and two complementary socket locking shoulders 846a, 846b. In this way bending loads are distributed over two regions of contact in this area rather than one, reducing local stress.

The minimum bend radius permitted by the bend restrictor may be adjusted by adjusting the length of the bend restrictor parts 10. The inventors have recognised that this can be done without creating a new set of tooling, by splitting and shimming the mould in which the part is formed. The principle can be understood with reference to Figure 16. Here, a section 700 of the neck 26 has been extended.

This has been done by splitting the mould in which the bend restrictor part 10 is formed in a radial plane, and placing a shim having the required internal cross section between the two parts of the mould. Varying the width of the shim enables the length of the section 700 to be varied according to requirements.

Claims

CLAIMS1. A bend restrictor comprising at least first and second bend restrictor units each having a through-going passage, a head, a neck and a socket, the head of the first bend restrictor unit being captively received in the socket of the second bend restrictor unit to couple them together with their passages aligned to receive and embrace an elongate member, wherein, viewed along a radial direction: the head comprises an engagement portion having a convex curved exterior profile; the head comprises a first abutment face; the socket comprises an internal head-receiving portion having a concave curved profile complementary to the profile of the engagement portion of the head; the socket comprises an internal neck-engagement portion having a convex curved profile; the socket comprises an external end face; the socket comprises an internal second abutment face; the neck comprises a neck portion having a concave curved exterior profile complementary to the profile of the neck-engagement portion of the socket; the neck portion comprises a neck locking shoulder facing toward the head; so that angular displacement of the second bend restrictor unit relative to the first bend restrictor part causes: the first abutment face of the head of the first bend restrictor part unit to abut the second abutment face of the socket of the second bend restrictor part unit; the engagement portion of the head to abut the head receiving portion of the socket 24; the neck-engagement portion of the socket of the second bend restrictor unit to abut the neck portion of the first bend restrictor unit; and the neck locking shoulder of the first bend restrictor unit to abut the end face of the second bend restrictor part unit, thereby to resist angular displacement of the second bend restrictor unit relative to the first bend restrictor part beyond a predetermined angle.
2. A bend restrictor as claimed in claim 1 in which the head comprises a head locking shoulder facing toward the socket, and the socket comprises an internal socket locking shoulder facing toward the head, so that angular displacement of the second bend restrictor unit relative to the first bend restrictor part causes the head locking shoulder to abut the socket locking shoulder.
3. A bend restrictor as claimed in claim 2 in which the head further comprises a reduced diameter portion which forms a smoothly curving transition into the neck portion.
4. A bend restrictor as claimed in any preceding claim in which the first abutment face of the head is frusto-conical.
5. A bend restrictor as claimed in any preceding claim in which the first and second bend restrictor units each comprise two or more bend restrictor parts of part-annular cross section coupled to one another.
6. A bend restrictor as claimed in claim 1 in which the first and second bend restrictor units are substantially identical.
7. A bend restrictor as claimed in any preceding claim further comprising an insert disposed in the neck portion and serving to reduce the internal lateral dimension of the neck portion.
8. A bend restrictor part comprising a head, a neck, a socket, a contact face, and a recess formed in the contact face and dividing it in two, the bend restrictor part being configured to be assembled to another similarly formed bend restrictor part to form a bend restrictor unit in which, viewed along a lateral direction: the head comprises an engagement portion having a convex curved exterior profile; the head comprises a first abutment face; the socket comprises an internal head-receiving portion having a concave curved profile complementary to the profile of the engagement portion of the head; the socket comprises an internal neck-engagement portion having a convex curved profile; the socket comprises an external end face; the socket comprises an internal second abutment face; the neck portion comprises a first neck portion having a concave curved exterior profile complementary to the profile of the neck-engagement portion of the socket; and the neck portion comprises a neck locking shoulder facing toward the head.
9. A bend restrictor part as claimed in claim 8 in which the head comprises a head locking shoulder facing toward the socket, and the socket comprises an internal socket locking shoulder facing toward the head.
10. A bend restrictor part as claimed in claim 9 in which the head further comprises a reduced diameter portion which forms a smoothly curving transition into the first neck portion.
11. A bend restrictor part as claimed in any of claims 8 to 10 in which the first abutment face of the head is frusto-conical.
12. A bend restrictor part as claimed in any of claims 8 to 11 which is for use in a bend restrictor according to any of claims 1 to 7.
13. A method of manufacturing a bend restrictor part comprising a head, a neck, a socket, a contact face, and a recess formed in the contact face and dividing it in two and extending along a longitudinal direction, the bend restrictor part being configured to be assembled to another similarly formed bend restrictor part to form a bend restrictor unit, the method of manufacturing comprising: providing a mould for manufacture of the bend restrictor part, the mould being divided into a first mould part and a second mould part, the first mould part having a first mould cavity for forming at least the head of the bend restrictor part and the second mould having a second mould cavity for forming at least the socket of the bend restrictor part; providing a shim having a thickness between the two parts of the mould; and moulding the bend restrictor part in the resultant mould; so that the length of the bend restrictor part depends on the thickness of the shim.