GB2544075A

GB2544075A - Improvements relating to bend restrictors

Info

Publication number: GB2544075A
Application number: GB1519542.3A
Authority: GB
Inventors: Stuart Page Malcolm
Original assignee: Trelleborg Offshore UK Ltd
Current assignee: CRP Subsea Ltd
Priority date: 2015-11-05
Filing date: 2015-11-05
Publication date: 2017-05-10
Also published as: GB201519542D0

Abstract

A bend restrictor 50 to limit the radius of curvature of an elongate member such as a power cables, signal cable or fibre, a pipe or an umbilical. The bend restrictor has multiple units 52, 54 each having a through-going passage 64. The units are connected in a string to form a continuous passage through the bend restrictor for receiving the elongate member. Each unit has a male connector 56 and a female connector 58, with each unit being connected to the next by engagement of the male connector with the female connector of the next unit, wherein at least one of the units in the string is a clamp unit 54 adapted to clamp against the elongate member to resist movement of the bend restrictor axially along the elongate member. There are further independent claims for a clamp unit, an installation of a bend restrictor and elongate member, and a method of restricting the bending of an elongate member.

Description

IMPROVEMENTS RELATING TO BEND RESTRICTORS

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 the 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.

It is typically necessary to locate the bend restrictor against axial movement (that is, against movement along the length of the elongate member) and this is typically achieved using some form of fixed steelwork at an end of the bend restrictor string. This is appropriate for example where the bend restrictor is used in the vicinity of some fixed structure to which the member and the bend restrictor can both be secured. Refer again to W02015/104560, Figure 1 in particular, showing a metal flange for this purpose at the end of a bend restrictor string. A different challenge arises if the bend restrictor is to be mounted "mid-line" - that is, somewhere along the length of the elongate member away from its ends. In this case the bend restrictor needs in some way to engage with the elongate member in order to resist axial movement. Consider for example the use of a bend restrictor to provide protection in a region where one cable or pipeline crosses another on the sea bed. In this vicinity the cables may need physical protection from damage by one another, they may need to be separated by a certain distance (e.g. to avoid interference or unwanted electrical effects) but they may also need to be protected against excessive bending. A segmented bend restrictor may be used for these purposes if a suitable means of locating it axially on the elongate member can be provided.

There are existing segmented spacer devices used to physically separate one elongate member from another at such a crossover. One such is offered by Trelleborg Offshore U.K. Ltd. under the trade mark POLYSPACE and is depicted in Figure 1, being used at an intersection between a first cable 10 on the seabed and a second cable 12 passing over it. The spacer device comprises a string of interlocking units 14 each comprising lightweight hollow plastics mouldings which are typically free-flooding and which can be provided with internal ballast to stabilise them on the sea bed. The units have an internal cavity of annular shape for receiving a band-type clamp 16 secured to the cable 12 to prevent axial movement of the spacer device. The units 14 are assembled around both the cable 12 and the clamps 16. Each unit 14 is formed by a pair of semi-tubular parts coupled to one another by bands passed around their joint circumference. The bands are omitted from Figure 1 but they rest in shallow circumferential troughs 20.

Although the depicted spacer device is like a segmented bend restrictor in that each unit has a male connector having a flange 22 and a female connector having an annular recess 24 to receive the flange of the neighbouring unit, it is not capable of resisting large bending loads due to its lightweight construction. The function of this device is to maintain a certain distance of separation between the cables 10,12 at their crossover.

There is a need for a bend restrictor suited to mid-line installation which is simple to manufacture and to install.

According to a first aspect of the present invention there is a bend restrictor comprising multiple units each having a through-going passage, the units being connected in a string with their passages aligned to form together a continuous passage through the bend restrictor for receiving an elongate member, each unit having a male connector and a female connector and each unit being connected to the next unitin the string by engagement of the male connector of one with the female connector of the other, wherein at least one of the units in the string is a clamp unit adapted to seat upon and clamp against the elongate member to resist movement of the bend restrictor along the elongate member.

The clamp unit can thus be incorporated into the string of units forming the bend restrictor at any point along its length. Unlike the spacer device of Figure 1, the bend restrictor of the present invention does not require a separate internal clamp to resist axial movement. As a result the external diameter of the bend restrictor embodying the present invention can be relatively small, which is attractive in some installations in that it reduces drag on the elongate member in a water flow. Installation of a bend restrictor according to the invention can be straightforward since it does not require mounting of a discrete clamp followed by mounting of a further unit around the clamp, not provision of steelwork for axial restraint of the bend stiffener.

In an especially preferred embodiment, the string includes at least one bend restrictor unit, the passage in the bend restrictor unit having a larger cross-section than the passage in the clamp unit. Hence the clamp will seat upon and grip the elongate member, but the bend restrictor unit can be over-size on the elongate member.

According to a second aspect of the present invention there is a clamp unit for use in a bend restrictor, the clamp unit comprising two or more clamp parts to be assembled to one another around an elongate member, together forming a through-going passage which extends in an axial direction and which is for receiving the elongate member, the clamp unit having a male connector and a female connector which face in opposite axial directions, enabling the clamp unit to connect through the male connector to another unit of the bend restrictor on one side and to connect through the female connector to still another unit of the bend restrictor on its other side, and having an arrangement for securing the clamp parts to one another and for drawing them together to reduce a lateral dimension of the through-going passage and so exert a clamping pressure on the elongate member in use.

The clamp unit can be used with conventional bend restrictor units, such as those disclosed in W02015/104560, enabling mid-line mounting of the bend restrictor in a straightforward manner.

Specific embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:-

Figures la and lb each depict a spacer device belonging to the prior art, being used at a crossover between a pair of elongate members on the seabed. Figure la is partly sectional, showing internal details of the spacer device, and Figure 2 is a section through the device in an axial plane;

Figure 2 is a section in an axial plane through a segmented bend restrictor embodying the present invention;

Figure 3 is a section in an axial plane through a restrictor part used in the Figure 2 bend restrictor;

Figure 4 is a view along a radial direction of a clamp unit used in the Figure 2 bend restrictor, showing both external features and internal (sectional) detail;

Figure 5 is a section through the clamp unit of Figure 4 in a radial plane;

Figures 6a and 6b are perspective views of the clamp unit of Figure 4 showing a male end and a female end to the fore, respectively;

Figures 7a and 7b are perspective views of an individual clamp part of the clamp of Figure 4, showing a male end and a female end to the fore, respectively.

The segmented bend restrictor 50 depicted as an assembly in Figure 2 comprises a string formed of (a) bend restrictor units 52 and (b) clamp units 54. The clamp units 54 seat upon and clamp against the elongate member (which is not seen in Figure 2) and resist axial movement of the bend restrictor 50 along it. The bend restrictor units 52 and the clamp units 54 each have a male connector 56 facing in one axial direction and a female connector 58 facing in the opposite axial direction, so that clamp units 54 can be incorporated at any chosen position in the string.

Each bend restrictor unit 52 is circular, viewed along its axis, but is split in a plane containing this axis into two semi-tubular parts, one of which is depicted on its own in Figure 3 and is designated 60. A flat face 62 lies in the plane of this split and abuts a corresponding face of a second similarly formed bend restrictor part in the assembled bend restrictor unit. A semi-circular recess 64 is formed in the face 62. In the assembled unit this faces toward an identically formed recess of the second bend restrictor part to form a circular, through-going passage for receiving the elongate member. This passage has frusto-conical mouth 66 at a male end 68 of the bend restrictor unit, and at a female end 70 it has opposed shoulders 72, 74 on either side of an increased diameter region which forms an annular recess 76 and which leads to a mouth 78.

The outer profile of the bend restrictor unit 52 has, at the male end 68, an integral flange 80 leading to a neck 82.

The two parts 60 of the bend restrictor unit 52 are assembled to one another around the elongate member (which is not shown in Figure 3). This may be by means of connective fasteners such as bolts passed through aligned bores 83. Alternatively bands may be passed around the parts 60 to secure them to one another, the bands being joined to themselves under tension to keep them in place.

When one bend restrictor unit 52 engages with a neighbour as in Figure 2, the flange 80 of one is received in the neighbour's annular recess 76. The neck 82 of one emerges from the neighbour's mouth 78, the neck being small enough in diameter to pass through the mouth. Abutment of end faces 84, 86 of the flange 80 of the one unit against shoulders 72, 74 of its neighbour limits relative axial and radial movement of the two units. In this way an articulated coupling capable of limited angular movement is formed between them. A clamp unit 54 is depicted in Figures 4 to 7. It is generally circular in radial section (see Figure 5) but is formed by multiple parts to be assembled to one another around the elongate member. In the present embodiment the clamp unit is split into three clamp parts 88, each of them a 120 degree sector of a tube. A different number of clamp parts could be used. The clamp could for example be split into two parts or four.

An arrangement is provided for securing the clamp parts together and drawing them toward one another to exert a clamping force upon the elongate member within. In the present embodiment connective fasteners 92 pass through aligned bores in adjacent clamp parts 88 to draw them together. These fasteners are threaded, in the present embodiment, each comprising a bolt and a nut. Pockets 89 in the outer surfaces of the clamp parts enable insertion of the fasteners 92 and provide a flat face for them to bear upon.

In an alternative embodiment (not shown) the arrangement for securing the clamp parts 88 together uses one or more circumferential bands passed around the clamp parts, or through circumferential channels in the clamp parts. The band(s) are joined to themselves under tension to provide the required clamping force.

Part-cylindrical concave seating surfaces 90 of each clamp part 88 together form a substantially cylindrical passage 94 for receiving the elongate member. In use the seating surfaces 90 seat upon the elongate member (which is not seen in Figures 4 to 7) and exert the clamping force upon it, to resist movement of the clamp unit 54 along the member. Note that adjacent faces 96, 98 of the clamp parts 88 do not contact one another but are separated by a gap, so that the force applied to the clamp parts is reacted by the elongate member and not by abutment of one clamp part with another.

The clamp unit 54 is provided with male and female connectors which are respectively able to couple to the female and male connectors of bend restrictor units 52. Thus the clamp unit 54 has a flange 100 leading to a neck 102 at a male end 104. The cylindrical passage 94 leads, at a female end 106, to an annular recess 108 and then to a mouth 110.

In Figure 2 it can be seen that clamp unit 54a, for example, is coupled at its female end 106 to the male end of a first bend restrictor unit 52a and at its male end 104 to the female end of a second bend restrictor unit 52b. Any chosen sequence of bend restrictor units 52 and clamps 54 can thus be constructed. The clamps can be placed at ends of the string but they can - additionally or alternatively - be placed at intermediate positions. Three or more clamps may thus be used in a single string. A given installation may for example have more bend restrictor units 52a than clamp units, the number of clamps being sufficient to resist axial motion of the string as a whole. Clamps could for example be placed at regular intervals - say every three or five units. The number of clamps may be chosen with regard to the required bend characteristic of the restrictor as a whole.

The clamp unit 54 may be provided with a compliant feature intended to maintain its clamping force in the event of dimensional changes in the elongate member, or indeed of the clamp parts 88. Such dimensional changes may for example result from creep that takes place over a protracted design lifetime. The elongate member may be subject to such creep under the force exerted by the clamp. Dimensional change may also result form changes of temperature, for example. If the clamping system lacks compliance then a small dimensional change may result in an excessive reduction in clamping force. To combat this the clamp can be provided with a compliant feature which is elastically prestressed upon installation of the clamp and which acts in the manner of a spring to maintain clamp force. In one embodiment the compliant feature takes the form of one or more ridges or fingers upstanding from the seating surfaces 90 of the clamp parts 88. These may for example form one or more inwardly projecting rings running around the passage 94, which will be compressed somewhat upon installation. An alternative is to build compliance into the arrangement used for securing the clamp parts 88 together. For example, springs may be provided under the heads of the connective fasteners 92.

The passage through the bend restrictor unit 52 is sized to provide clearance around the elongate member being protected, when the bend restrictor parts abut through their faces 62. The passage 94 through the clamp unit 54 is smaller in lateral dimension (diameter), being sized to seat on the elongate member while the opposed faces 96, 98 of the clamp parts 88 are separated by a gap.

In the present embodiment the clamp parts 88 are moulded plastics items. Nylon is a suitable material. They are solid. The bend restrictor parts 60 are also moulded plastics items. They are solid. They may comprise elastomeric material. Polyurethane is suitable.

Claims

1. A bend restrictor comprising multiple units each having a through-going passage, the units being connected in a string with their passages aligned to form together a continuous passage through the bend restrictor for receiving an elongate member, each unit having a male connector and a female connector and each unit being connected to the next unit in the string by engagement of the male connector of one with the female connector of the other, wherein at least one of the units in the string is a clamp unit adapted to seat upon and clamp against the elongate member to resist movement of the bend restrictor along the elongate member.

2. A bend restrictor as claimed in claim 1 in which the string includes at least one bend restrictor unit, the passage in the bend restrictor unit having a larger cross-section than the passage in the clamp unit.

3. A bend restrictor as claimed in claim 1 in which the string includes at least one bend restrictor unit, the passages in the bend restrictor unit and in the clamp unit being substantially circular in cross section and the passage in the clamp unit having a smaller diameter than the passage in the bend restrictor unit.

4. A bend restrictor as claimed in any preceding claim wherein each unit comprises two or more parts to be assembled around the elongate member, the parts together defining the unit's through-going passage.

5. A bend restrictor as claimed in any of claims 1 to 3 in which the clamp unit comprises two or more clamp parts to be assembled around the elongate member to define the clamp unit's through-going passage, and an arrangement for securing the clamp parts to one another and for drawing them together to exert a clamping pressure on the elongate member in use.

6. A bend restrictor as claimed in claim 5 in which the said arrangement comprises bores in the clamp parts and connective fasteners received by the bores to draw the clamp parts together.

7. A bend restrictor as claimed in claim 5 or claim 6 in which the clamp parts are substantially sectors of a circle in cross section, except that a radially inner portion forms a seating surface for seating upon the elongate member.

8. A bend restrictor as claimed in any preceding claim in which the male connectors each comprise a flange.

9. A bend restrictor as claimed in any preceding claim in which the female connectors each comprise an annular recess.

10. A bend restrictor as claimed in any preceding claim in which the engagement of male and female connectors forms an articulated coupling which permits limited angular movement of one unit relative to its neighbour but which resists angular movement beyond a certain angle.

11. A bend restrictor as claimed in claim 4 in which the parts of the clamp unit are solid plastics mouldings.

12. A clamp unit for use in a bend restrictor, the clamp unit comprising two or more clamp parts to be assembled to one another around an elongate member, together forming a through-going passage which extends in an axial direction and which is for receiving the elongate member, the clamp unit having a male connector and a female connector which face in opposite axial directions, enabling the clamp unit to connect through the male connector to another unit of the bend restrictor on one side and to connect through the female connector to still another unit of the bend restrictor on its other side, and having an arrangement for securing the clamp parts to one another and for drawing them together to reduce a lateral dimension of the through-going passage and so exert a clamping pressure on the elongate member in use.

13. A clamp unit for use in a bend restrictor as claimed in claim 12 in which the said arrangement comprises bores in the clamp parts and connective fasteners received by the bores to draw the clamp parts together.

14. A clamp unit for use in a bend restrictor as claimed in claim 12 or claim 13 in which the clamp parts are substantially sectors of a circle in cross section, except that a radially inner portion forms a seating surface for seating upon the elongate member.

15. A clamp unit for use in a bend restrictor as claimed in any of claims 12 to 14 in which the male connector comprises a flange.

16. A clamp unit for use in a bend restrictor as claimed in any of claims 12 to 15 in which the female connectors each comprise an annular recess.

17. An installation comprising an elongate member and a bend restrictor as claimed in any of claims 1 to 11, in which the clamp units exert a clamping force on the elongate member and so resist movement of the bend restrictor along it.

18. A method of resisting overbending of an elongate member, comprising applying to the elongate member a bend restrictor comprising multiple units coupled to one another in a string by engagement of a male connector of one unit with a female connector of the next unit, each unit being formed by two or more parts assembled around the elongate member, wherein at least one of the units is a clamp which seats upon the elongate member and exerts a clamping force on it to resist movement of the bend restrictor along the elongate member.

19. A method as claimed in claim 18 in which the clamp unit has a male connector engaged with the female connector of a further unit on one side, and a female connector engaged with the male connector of still a further unit on its other side.

20. A bend restrictor substantially as herein described with reference to, and as illustrated in, accompanying figures 2 onward.

21. A clamp unit for use in a bend restrictor substantially as herein described with reference to, and as illustrated in, accompanying Figures 2 and 4-7.