WO2020156661A1

WO2020156661A1 - Bend limiter

Info

Publication number: WO2020156661A1
Application number: PCT/EP2019/052259
Authority: WO
Inventors: Peter Frost; Ion MAFTIE
Original assignee: Huawei Marine Networks Co., Ltd.
Priority date: 2019-01-30
Filing date: 2019-01-30
Publication date: 2020-08-06
Also published as: CN112970158B; JP2022510006A; CN112970158A; EP3834261A1

Abstract

A bend limiter comprising a plurality of collars arranged in a series and a plurality of couplers, 5 wherein each collar neighbours two other collars in the series and is coupled to a first one of those collars by a first one of the couplers, to which it is joined by a revolute joint having a first axis, and to a second one of those collars by a second one of the couplers, to which it is joined by a revolute joint having a second axis non-parallel to the first axis, the bend limiter being configured to accommodate bending of a conduit running through the bend limiter and to limit 10 that bending by abutment of adjacent collars on rotation about the first and second revolute joints.

Description

BEND LIMITER

FIELD OF THE INVENTION

This invention relates to bend limiters for limiting bending of a conduit running through the bend limiter, for example to act as a flexible mechanical coupling between a cable and a piece of submarine telecommunications equipment.

BACKGROUND

At the interface between typical submarine wet plants, such as submarine repeaters, and their connecting cables is a mechanical connection that allows articulation between the two components. The connection has to withstand tensile loading during deployment and recovery operations. These conditions are particularly arduous when these components are passing over the sheave of a cable laying ship, where both tensile and bending loads combine to stress the components in a complex way.

These flexible mechanical couplings between the cable and the wet plant, known as bend limiters, need to withstand and exceed the cable breaking load of heavy armoured cable and thus are made out of high-strength materials, most often out of metal.

Figure 1 shows an example of a submarine repeater 1 with cables 3 and 13 connected to the repeater 1 . A metallic bend limiter 2 is arranged at the interface between the repeater 1 and the cable 3. As shown in Figures 2(a) and 2(b), the bend limiter is formed from a series of outer yokes or collars 4 and inner rings 5 which can rotate relative to one another to accommodate but limit bending at the interface.

Of the total amount of cable used to inter-connect wet plant in the trans-oceanic systems deployed in recent years, only approximately 20% is of“armoured” construction, the remaining 80% being“light weight”. Telecommunications submerged plant manufacturers generally use a“one size fits all” high-strength bend limiter design such as that shown in Figures 1 and 2 to connect different cable types to the wet plant. This is the case for various reasons, mostly related to compatibility requirements and size constraints, such as minimum inner diameter constraint, minimum length constraint and fixed maximum bend angle constraint. Using two (or more) different designs for different cable strengths has potential drawbacks in that different interface and ancillary elements would need to fulfil different requirements for each cable type. However, bend limiters capable of withstanding armoured cable loads are often unnecessarily used for deep-water deployment situations. For most of the cable that is being deployed, high- strength and most often high-cost bend limiters are over-dimensioned. This approach limits the deployment depth, should this coupling become a significant proportion of the overall weight of the submerged equipment.

Significant savings in weight and manufacturing costs would be achieved by using lighter, lower strength bend limiters to connect“light weight” cables to the wet plant. The requirement for lighter components has increasing importance in the design of the next generation of subsea equipment. The constant demand for higher fibre count and more capacity are driving an imminent increase in size and weight, both of which have a detrimental impact on deployment and recovery depth.

It is desirable to develop a bend limiter that is able to withstand the loads and bend angles required whilst also being suitable for fabrication from different materials depending on the cable weight requirement of the application.

SUMMARY OF THE INVENTION

According to a first aspect there is provided a bend limiter comprising a plurality of collars arranged in a series and a plurality of couplers, wherein each collar neighbours two other collars in the series and is coupled to a first one of those collars by a first one of the couplers, to which it is joined by a revolute joint having a first axis, and to a second one of those collars by a second one of the couplers, to which it is joined by a revolute joint having a second axis non-parallel to the first axis, the bend limiter being configured to accommodate bending of a conduit running through the bend limiter and to limit that bending by abutment of adjacent collars on rotation about the first and second revolute joints.

This may allow for a multi-purpose bend limiter design which can be applied to both metal and composite bend limiters and is capable of a 25-year service life under steady state operation.

For each collar the respective first and second couplers may be offset along the longitudinal direction of the bend limiter and the respective collar may extend along that longitudinal direction between those first and second couplers. For each collar, the axes of the revolute joints by which it is joined to adjacent couplers may be offset along the longitudinal direction of the bend limiter. This may allow the bend limiter to accommodate bending of the conduit running through the bend limiter. Each coupler may be joined to adjacent collars by respective revolute joints, and the axes of those joints may lie in a common plane perpendicular to the longitudinal direction of the bend limiter.

Each collar may define a bearing surface configured to bear against a bearing surface of a neighbouring collar when those collars are inclined relative to each other by rotation about their joints to a coupler extending between those collars. Each collar may define two such bearing surfaces, facing in opposite directions along the longitudinal direction of the bend limiter. This may allow the bend limiter to restrict bending of the conduit and bear tensile load.

The bearing surfaces may be defined such that irrespective of the direction of inclination between two neighbouring collars, when the bearing surfaces of those collars abut each other they do so over a contact patch that is linear or two-dimensional. The geometry of the adjacent bearing faces of the collars may ensure contact between neighbouring collars while in full bend and along all axes of bending. This may result in superior bend control, contact stress optimization and reduced wear.

The bearing surfaces may be configured so as to restrict the maximum bend angle of the bend limiter to less than 70 degrees. The bearing surfaces may be configured such that the maximum angle of inclination between neighbouring collars is less than 20 degrees. This may allow a degree of flexibility for the movement of cable coupled to the bend limiter but prevent damage.

The collars and/or the couplers may be annular and define a passage for the conduit therethrough. This may allow the bend limiter to restrict the bending of the conduit.

Each collar may be attached to its respective first and second couplers by connector pins, the connector pins running parallel to the respective first and second axes. The connector pins may conveniently allow the components of the bend limiter to be assembled and disassembled as required.

The bend limiter may further comprise two end parts, each end part neighbouring a collar at respective first and second ends of the bend limiter and being joined by a revolute joint to one of the couplers that are joined to that collar. The end parts of the bend limiter may be connected to other parts of the system. The product is versatile and is compatible with various sea case diameters. Using purpose-built adaptors that connect to the internal and / or external diameter of the sea case outer collar, the design is compatible with both existing and new generation wet plant products.

The collars and the couplers may be configured to bear tensile load applied between the end parts. This may help submerged equipment to achieve a 25-year service life under steady state operation.

The collars and/or the couplers may be rigid. This may allow the components of the bend limiter to bear tensile load.

For each collar the respective first and second couplers may be located inwardly of that collar about the longitudinal axis of the bend limiter. This may result in a more compact design.

BRIEF DESCRIPTION OF THE FIGURES

The present invention will now be described by way of example with reference to the accompanying drawings. In the drawings:

Figure 1 shows a known bend limiter coupled to a submarine repeater.

Figures 2(a) and 2(b) show close-up and exploded views respectively of the known bend limiter shown in Figure 1 .

Figure 3 shows an example of a bend limiter according to the present invention coupled to a submarine repeater.

Figures 4(a) and 4(b) show close-up and exploded views respectively of the bend limiter shown in Figure 3.

Figure 5 illustrates the relative positions of the components of the bend limiter at the maximum bend angle of the bend limiter.

Figure 6 illustrates how the contact face of each collar section may be defined.

Figure 7 illustrates the connection of collars and rings using pins.

Figure 8 illustrates the retention of the pins which connect the collars and rings of the bend limiter. Figure 9 illustrates the machining of the collars of the bend limiter from a single tube.

DETAILED DESCRIPTION OF THE INVENTION

Figure 3 shows an example of a bend limiter 6 according to the present invention. The bend limiter 6 comprises a plurality of collars 7, 8, 9 arranged in a series and a plurality of couplers, two of which are indicated at 10 and 1 1 . The collars and the couplers are rigid and annular and define a passage for the cable 3 therethrough. The couplers are located inwardly of the collars about the longitudinal axis of the bend limiter, such that the couplers fit inside the collars when the collars are joined in the series. Each collar 7 neighbours two other collars 8, 9 in the series and is coupled to a first one 8 of those collars by a first one of the couplers 10, to which it is joined by a revolute joint having a first axis 20. Each collar 7 is also coupled to a second one of those collars 9 by a second one of the couplers 1 1 , to which it is joined by a revolute joint having a second axis 21 non-parallel to the first axis 20. The axes are orthogonal when projected on to a plane perpendicular to the longitudinal axis of the bend limiter when the bend limiter is in its straight configuration. Each collar is attached to its respective first and second couplers by connector pins 30, the connector pins running parallel to the respective first and second axes. The bend limiter further comprises two end parts 15, 16, each end part neighbouring a collar at respective first and second ends of the bend limiter. The ends parts 15, 16 are joined by a revolute joint to one of the couplers that are joined to the neighbouring collars. The collars and the couplers of the bend limiter 6 are configured to bear tensile load applied between the end parts 15, 16.

Figures 4(a) and 4(b) show close-up and exploded views of the bend limiter of Figure 3 respectively. For each collar 7, the respective first 10 and second 1 1 couplers are offset along the longitudinal direction of the bend limiter 6 and the respective collar 7 extends along that longitudinal direction between those first 10 and second 1 1 couplers. For each collar, the axes of the revolute joints by which it is joined to adjacent couplers are offset along the longitudinal direction of the bend limiter. The bend limiter accommodates bending of the cable 3 and limits that bending by abutment of adjacent collars on rotation about the first and second revolute joints.

Each collar 7, 8, 9 defines two bearing surfaces configured to bear against a bearing surface of a neighbouring collar when those two collars are inclined relative to each other by rotation about their joints to a coupler extending between the two collars. The two bearing surfaces face in opposite directions along the longitudinal direction of the bend limiter. The bearing surfaces are defined such that irrespective of the direction of inclination between two neighbouring collars, when the bearing surfaces of those collars abut each other they do so over a contact patch that is linear or two-dimensional.

Figure 5 shows the components of the bend limiter when it is at its maximum bend angle. The bearing surfaces are configured so as to restrict the maximum bend angle of the bend limiter. In one example, the maximum bend angle of the bend limiter is restricted to less than 70 degrees. In this example, the bearing surfaces are configured such that the maximum angle of inclination between neighbouring collars is less than 20 degrees. Other values of maximum bend angle are possible. One way of varying the maximum bend angle of the bend limiter is by repositioning the pins which connect the collars and the couplers and define the rotation axes.

The geometry of the adjacent contact faces of the collars ensures continuous contact between any two neighbouring collars while the bend limiter is at its maximum bend angles along all axes. The design of the present invention therefore maximises the contact area at full bend, resulting in superior bend control and contact stress optimization.

Figure 6 shows the definition of one of the contact faces in more detail. Each collar has a contact face directed to a first end of the bend limiter and a contact face directed to a second end of the bend limiter. It is preferred that all the collars’ contact faces directed to the first end of the bend limiter describe the same surface. It is preferred that all the collars’ contact faces directed to the second end of the bend limiter describe the same surface. It is preferred that both contact faces of each collar describe the same surface, albeit facing in opposite directions. The contact faces of adjacent collars are cooperatively configured so that when those collars are maximally inclined relative to each other about any inclination axis their contact faces make contact over a greater area than a point, preferably a line. That line may lie on a plane that runs through the central axis of one or both of those collars, so the line may be an essentially radially directed line. Since the collars extend longitudinally with respect to the bend limiter, it is convenient for each contact surface to deviate longitudinally. Each contact surface may have 180 degree rotational symmetry about the central axis of its collar. Each contact surface may be such as to be a mirror image of itself rotated by ninety degrees. Each contact surface may have an extent in a radial direction with respect to the central axis of its collar. In that extent the surface may in places be inclined with respect to the central axis of the collar. Conveniently parts of the surface that are offset by 180 degrees with respect to each other about the central axis may be inclined in one sense (e.g. with their radially outer edge closer to an end of the bend limiter than their radially inner edge) and parts of the surface that are offset by 90 degrees with respect to the aforesaid parts may be inclined in the opposite sense (e.g. with their radially inner edge closer to the end of the bend limiter than their radially outer edge). The contact surfaces of a collar may have a generally sinusoidal form on rotation about the central axis of the collar. A collar having these characteristics may conveniently permit line contact between adjacent collars when they are at full bend.

In the example of Figure 6, the geometry of the contact face comprises two convex regions or “lobes” and two concave regions or“dwellings”. This design feature allows for contact between any two neighbouring collars while the bend limiter is at its maximum bend angle, since the geometry of a“dwelling” matches the geometry of a“lobe” of an adjacent collar. Along the length of the bend limiter the lobes of each collar nest in the dwellings of the adjacent collars.

As shown in Figure 6, each contact face may be built using two spline curves. Spline curve A is located on the outer diameter of the tube forming the collar and spline curve B is located on the inner diameter of the tube of the collar. The contact face smoothly joins the two spline curves. The splines can conveniently be defined using pre-defined points. The points are located equally spaced around the outer collar circumference. Each point of spline curve A has a corresponding point on spline curve B, located at the same angular position about the collar’s central axis. All of the spline curve B points are offset with the same distance radially in relation to the spline curve A points. This distance sets the maximum bend angle. It is preferred that this is the same for all the collars within the bend limiter.

In order to define the axial offset of the points, parallel planes are defined that are perpendicular to the collar’s revolution axis. Two pairs of planes define an active contact face. The distance between each of the two planes in a pair is the bend angle distance. The first plane in the pair, labelled as the“length plane”, controls the length or depth of the“dwellingTlobe” geometry. The second plane in the pair, labelled as the“angle plane”, controls the angle.

The length and maximum bend angle are adjustable by modifying the position of the spline curves’ defining points, giving design flexibility. As a result of the parameterised design, the bend characteristics are readily adjustable by modifying the design input parameters.

Figures 7(a)-(c) illustrate how the collars and the couplers are joined together by the connector pins 30. The connector pins run parallel to the respective first and second rotation axes to allow the parts 7 and 10 to rotate relative to one another about the revolute joint. As illustrated in Figure, the swivel pins 30 that connect the outer collars 7 to the inner ring couplers 10 and allow them to rotate during the articulation may be retained against loosening at two ends using two different retention methods, as follows:

Inwards retention : A tapered geometry at the top of the pin, shown at 17, matches a complementary recess on the outside of the collar 7 and restricts the movement of the pin 30 to prevent it from moving below the outer surface of the collar 7. The pin STOP position is calculated so that the front face of the pin taper sits flush on the outer diameter chamfer of the collar 7.

Outwards retention : The pin is retained using a ring 18, a groove 19 at the bottom of the pin 30 and a corresponding recess at the bottom of the hole in the inner coupler 10. The ring is installed onto the pin and the outer collar and inner coupler are aligned so that the pin holes are concentric. The pin 30 is then inserted into the hole in the outer collar using the inwards retention recess’ chamfer to compress the ring. Once the pin is in position, the frontal faces of the ring groove of the pin and of the inner coupler’s recess become aligned, allowing the ring to sit in its “resting” position. The perpendicular frontal face of the inner ring’s recess acts as a stopper on the ring, preventing the pin from coming out under regular operating conditions.

The swivel retention pins are therefore able to be installed without the need for special tools, improving the ease of assembly and disassembly of the bend limiter.

The present construction proposes the use of a single design bend limiter that can utilise a high strength to weight ratio composite material for use in the 80% of cases where lightweight cable equipment is used and a metallic version for the remaining 20% of cases where armoured equipment is used.

The metallic bend limiter may be manufactured from a corrosion resistant, high strength metallic compound such as steel, beryllium copper, or a high strength titanium alloy. The material can be selected in line with the specific requirements of the application but should preferably be able to withstand the cable breaking load of the heaviest armoured cable that the wet plant product connects to, which is currently in the region of 550 KN.

The bend limiter for use with light weight cable may be manufactured from a carbon fibre reinforced resin composite and might only need to be able to withstand the cable breaking load of the heaviest light weight cable, which is currently in the region of 1 15 KN. Size-for-size, carbon composites offer high strength and light weight, which are two key parameters required for this application. Carbon fibre composites offer the highest specific modulus of any commercial yam, with a tensile Modulus of between 230-400 GPa and ultimate tensile strength of around 3.5-5.0 GPa. Furthermore, carbon fibre composite materials also show excellent inter-laminar shear strength, fatigue resistance and low coefficients of thermal expansion.

The key attributes when selecting the resin system are good mechanical properties, low degradation, good resistance to thermal stress, excellent resistance to corrosion, and low water absorption. The use of a matting impregnation method has been shown to obtain the best composite performance by full saturation of the pre-impregnated carbon fibre matting with resin and good fibre wet out specific to carbon tow size.

As a result of the excellent strength to weight ratios achievable when using carbon fibre composites, components can be lightweight, reduced in size, and offer increased performance over other composite materials and a genuine alternative to metal for similar applications.

The bend limiter described herein may also result in more streamlined machining. As shown in Figure 9, the collar 7 and end parts 15, 16 may be machined from the same tube of material by a tool 40. The outer collars and the inner couplers may therefore be manufactured from two tubes of pre-defined size. This may result in low manufacturing wastage. The identical geometry of the active bearing faces of the collars allows the collars to be machined by removing a small amount of material in-between the adjacent active faces of two consecutive collars from a single prefabricate tube.

The bend limiter described herein is therefore a multi-purpose design which can be applied to both metal and composite bend limiters and is capable of a 25-year service life under steady state operation.

Both embodiments of the bend limiter may share the same size (inner and outer diameters, total length, maximum full bend angle) and geometry and may be connected to the wet plant using similar solutions. The product is versatile and is compatible with various sea case diameters. Using purpose-built adaptors that connect to the internal and / or external diameter of the sea case outer collar, the design is compatible with both existing and new generation wet plant products.

The present invention may allow for improvement of the maximum deployment depth of submerged equipment by using a component of lighter weight than can be achieved with a metal equivalent of similar strength and corrosion resistance. This reduces the overall weight of deep-water submarine cable systems normally limited by metal components. It may also improve deployments and recovery limits and increase the installation capability of wet plant products. Furthermore, the lower cost and mass per unit volume for the composite bend limiter compared to the metallic version (for example when using titanium grade 5) allows for a significant cost saving in the case of light weight solutions.

Although the invention has been described above with respect to the example of a bend limiter for use with a submarine repeater, the invention is also applicable to other submarine telecommunications equipment, such as amplifiers, switches, multiplexers and demultiplexers. For example, branching units and reconfigurable optical add-drop multiplexers (ROADM).

The applicant hereby discloses in isolation each individual feature described herein and any combination of two or more such features, to the extent that such features or combinations are capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or combinations of features solve any problems disclosed herein, and without limitation to the scope of the claims. The applicant indicates that aspects of the present invention may consist of any such individual feature or combination of features. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention.

Claims

1 . A bend limiter (6) comprising a plurality of collars (7, 8, 9) arranged in a series and a plurality of couplers (10, 1 1 ), wherein each collar neighbours two other collars in the series and is coupled to a first one of those collars by a first one of the couplers, to which it is joined by a revolute joint having a first axis (20), and to a second one of those collars by a second one of the couplers, to which it is joined by a revolute joint having a second axis (21 ) non-parallel to the first axis, wherein the bend limiter is configured to accommodate bending of a conduit running through the bend limiter and to limit that bending by abutment of adjacent collars on rotation about the first and second revolute joints.

2. A bend limiter as claimed in claim 1 , wherein for each collar the respective first and second couplers are offset along the longitudinal direction of the bend limiter and the respective collar extends along that longitudinal direction between those first and second couplers.

3. A bend limiter as claimed in claim 2, wherein for each collar, the axes of the revolute joints by which it is joined to adjacent couplers are offset along the longitudinal direction of the bend limiter.

4. A bend limiter as claimed in claim 2 or 3, wherein each coupler is joined to adjacent collars by respective revolute joints, and the axes of those joints lie in a common plane perpendicular to the longitudinal direction of the bend limiter.

5. A bend limiter as claimed in any preceding claim, wherein each collar has a bearing surface which bears against a bearing surface of a neighbouring collar when those two collars are inclined relative to each other by rotation about their joints to a coupler extending between those two collars.

6. A bend limiter as claimed in claim 5, wherein each collar has two such bearing surfaces, facing in opposite directions along the longitudinal direction of the bend limiter.

7. A bend limiter as claimed in claim 5 or claim 6, wherein the bearing surfaces are shaped such that irrespective of the direction of inclination between two neighbouring collars, when the bearing surfaces of those collars abut each other they do so over a contact patch that is linear or two-dimensional.

8. A bend limiter as claimed in any one of claims 5 to 7, wherein the bearing surfaces are shaped so as to restrict the maximum bend angle of the bend limiter to less than 70 degrees.

9. A bend limiter as claimed in any one of claims 5 to 8, wherein the bearing surfaces are shaped such that the maximum angle of inclination between neighbouring collars is less than 20 degrees.

10. A bend limiter as claimed in any preceding claim, wherein the collars and/or the couplers are annular and define a passage for the conduit therethrough.

1 1. A bend limiter as claimed in any preceding claim, wherein each collar is attached to its respective first and second couplers by connector pins, the connector pins running parallel to the respective first and second axes.

12. A bend limiter as claimed in any preceding claim, wherein the bend limiter further comprises two end parts, each end part neighbouring a collar at respective first and second ends of the bend limiter and being joined by a revolute joint to one of the couplers that are joined to that collar.

13. A bend limiter as claimed in claim 12, wherein the collars and the couplers are configured to bear a tensile load applied between the end parts.

14. A bend limiter as claimed in any preceding claim, wherein the collars and/or the couplers are rigid.

15. A bend limiter as claimed in any preceding claim, wherein for each collar the respective first and second couplers are located inwardly of that collar about the longitudinal axis of the bend limiter.