JP7576279B2 - Bend Limiter - Google Patents

Description

The present invention relates to a bend limiter for limiting the bending of a conduit passing through the bend limiter, for example to function as a flexible mechanical coupling between a cable and a submarine telecommunications facility.

The joints between typical subsea wet equipment (e.g. subsea repeaters) and their connecting cables have a mechanical connection that allows a hinged connection between the two parts. This connection needs to withstand tensile loads during laying and retrieval operations. The conditions become particularly severe when the parts pass over the pulleys of the cable laying vessel, where both tensile and bending loads are combined to stress the parts in a complex manner.

Because the flexible mechanical coupling between the cable and the wet equipment (called a bend limiter) must withstand the cable breaking loads of heavily armored cables in excess of these limits, the bend limiter is made of high strength materials, typically metal in most cases.

Figure 1 shows an example of a submarine repeater 1 with a cable 3 and a cable 13 connected to it. A metallic bend limiter 2 is placed at the junction 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 each other to accommodate the junction while limiting bending at the junction.

In recent transoceanic systems, only about 20% of the total number of cables for connecting wet installations are "armoured" and the remaining 80% are "lightweight". Manufacturers of telecommunication underwater equipment usually use "one size fits all" high strength bend limiter designs, such as the designs shown in Figures 1 and 2, to connect different types of cables to wet installations. This situation has various causes, mainly related to compatibility requirements and size limitations, such as minimum inner diameter limitations, minimum length limitations and fixed maximum bend angle limitations. Since different joints and auxiliary elements need to meet different requirements for each cable type, using two (or more) different designs for different cable strengths has potential disadvantages.

However, for deep water installations, the use of bend limiters capable of withstanding the loads of armored cables is usually unnecessary; high strength and typically high cost bend limiters are oversized for many installed cables. This method limits the installation depth when such couplings represent a significant percentage of the total weight of the underwater installation.

The use of lighter and less strong bend limiters to connect "light" cables to wet installations can result in significant weight and manufacturing cost savings. The requirement for relatively light components is becoming increasingly important in the design of next generation subsea installations. The continuing demand for higher fiber counts and greater capacity leads to exponential increases in volume and weight that adversely affect installation and recovery depths.

It is desirable to develop a bend limiter that can withstand the required loads and bend angles, and that is also suitable for manufacture from different materials depending on the applied cable weight requirements.

According to a first aspect, a bend limiter is provided that includes a plurality of collars arranged in series and a plurality of couplers, each collar being adjacent to two other collars in series and connected to a first one of the collars through a first one of the couplers and to a second one of the collars through a second one of the couplers, each collar being connected to the first one of the couplers through a rotary joint having a first axis and to the second one of the couplers through a rotary joint having a second axis not parallel to the first axis, the bend limiter being adapted to accommodate bending of a conduit passing through the bend limiter and limiting the bending by abutment of adjacent collars as it rotates about the first and second rotary joints.

This allows for the design of a versatile bend limiter that can be applied to both metallic and composite bend limiters and can have a service life of 25 years in steady state operation.

For each collar, the respective first and second couplers can be offset along the length of the bend limiter, and each collar can extend along the length between the first and second couplers. For each collar, the axis of the rotary joint can be offset along the length of the bend limiter, and each collar is connected to an adjacent coupler via the rotary joint. This allows the bend limiter to adapt to bending of the conduit passing through the bend limiter.

Each coupler may be connected to an adjacent collar via a respective rotary joint, the axes of which may lie in a common plane perpendicular to the longitudinal direction of the bend limiter.

Each collar can define a bearing surface configured to abut the bearing surface of an adjacent collar when the collars rotate about their respective joints to be connected to a coupler extending between the collars and tilted relative to one another. Each collar can define two such bearing surfaces facing in opposite directions along the length of the bend limiter, thereby allowing the bend limiter to limit bending of the conduit while also withstanding tensile loads.

The bearing surfaces may be defined such that the bearing surfaces of the collars abut with a linear or two-dimensional contact surface, regardless of the tilt direction between the two adjacent collars. The geometry of the adjacent bearing surfaces of the collars ensures that the adjacent collars are in contact and fully bent along all bending axes. This allows for excellent bending control, optimized contact stresses, and reduced wear.

The bearing surfaces can be configured to control the maximum bend angle of the bend limiter to less than 70 degrees. The bearing surfaces can be configured to provide a maximum tilt angle between adjacent collars of less than 20 degrees. This allows some flexibility in the movement of the cable connected to the bend limiter to prevent damage.

The collar and/or coupler may be annular and may define a passage for the conduit to pass therethrough, thereby allowing the bend limiter to limit bending of the conduit.

Each collar may be attached to a respective first and second coupler via a connector pin extending parallel to the respective first and second axes, the connector pin allowing easy assembly and removal of the components of the bend limiter as needed.

The bend limiter may further have two ends, each adjacent to a collar at a corresponding first and second end of the bend limiter and connected via a rotary joint to one of the couplers that is connected to the collar. The ends of the bend limiter may be connected to other parts of the system. This product is versatile and adaptable to a variety of sea state diameters. With the use of dedicated adapters that connect to the inner and/or outer diameter of the outer collar of the sea state, this design is compatible with previous next generation wet equipment products.

The collars and couplers can be constructed to withstand tensile loads applied between their ends, contributing to a service life of 25 years for underwater equipment in steady state operation.

The collar and/or coupler are rigid, allowing the bend limiter components to withstand tensile loads.

For each collar, the respective first and second couplers are housed inside the collar about the longitudinal axis of the bend limiter, allowing for a more compact design.

The present invention will now be described with reference to the drawings.

1 shows a known bend limiter coupled to an undersea repeater. 2(a) and (b) show a close-up view and an exploded view, respectively, of the known bend limiter shown in FIG. 1; 1 shows an example of a bend limiter according to the present invention coupled to an undersea repeater. 4(a) and (b) show a close-up view and an exploded view, respectively, of the bend limiter shown in FIG. 3. 1 illustrates the relative position of the bend limiter at its maximum bend angle. 1 illustrates how the contact surface of each color section is defined. Shows which collars and rings are connected using pins. 1 shows the retention of the pin connecting the collar and ring of the bend limiter. 1 shows the machining of a bend limiter collar from a single piece of tube.

3 shows an example of a bend limiter 6 according to the invention. The bend limiter 6 comprises a number of collars 7, 8, 9 and a number of couplers arranged in series, two of which are indicated at 10 and 11. The collars and couplers are rigid and annular, and define a passage for passing the cable 3. The couplers are housed inside the collars about the longitudinal axis of the bend limiter, such that when the collars are connected in series, the couplers are located inside the collars. Each collar 7 is adjacent to two other collars 8, 9 in series and is connected to a first one of the collars 8 via a first one of the couplers 10, which is connected to the first one of the couplers 10 via a rotary joint having a first axis 20. Each collar 7 is further connected to a second one of the collars 9 via a second one of the couplers 11, which is connected to the second one of the couplers 11 via a rotary joint having a second axis 21 that is not parallel to the first axis 20. When the bend limiter is in a straight configuration, the axes are orthogonal when projected onto a plane perpendicular to the longitudinal axis of the bend limiter. Each collar is attached to a respective first and second coupler via a connector pin 30 extending parallel to the respective first and second axes. The bend limiter further has two ends 15, 16, each adjacent to a collar at the corresponding first and second ends of the bend limiter. The ends 15, 16 are connected to a coupler via a rotary joint, which coupler is connected to the adjacent collar. The collars and couplers of the bend limiter 6 are configured to withstand a tensile load applied between the ends 15, 16.

4(a) and (b) show a close-up view and an exploded view, respectively, of the bend limiter shown in FIG. 3. For each collar 7, the respective first and second couplers 10 and 11 are offset along the length of the bend limiter 6, and each collar 7 extends along the length between its first and second couplers 10 and 11. For each collar, the axes of the rotary joints connected to adjacent couplers are offset along the length of the bend limiter. The bend limiter accommodates bending of the cable 3 and limits this bending by abutment as it rotates about the first and second rotary joints of the adjacent collars.

Each collar 7, 8, 9 defines two bearing surfaces that are configured to abut against the bearing surface of an adjacent collar when the two collars are tilted relative to each other by rotating about their respective joints and connected to a coupler extending between them. These two bearing surfaces face in opposite directions along the longitudinal direction of the bend limiter. The bearing surfaces are defined such that the bearing surfaces of the collars abut on a linear or two-dimensional contact surface, regardless of the direction of tilt between the two adjacent collars.

FIG. 5 shows the part when the bend limiter is at its maximum bend angle. The bearing surfaces are configured to limit the maximum bend angle of the bend limiter. In one example, the maximum bend angle of the bend limiter is controlled to less than 70 degrees. In this example, the bearing surfaces are configured such that the maximum tilt angle between adjacent collars is less than 20 degrees. The maximum bend angle can be other values. One way to change the maximum bend angle of the bend limiter is to reposition the pin that connects the collar and the coupler and defines the axis of rotation.

The geometry of the adjacent contact surfaces of the collars ensures that any two adjacent collars are in continuous contact with each other while the bend angle limiter is at its maximum bend angle along all axes. Thus, the design of the present invention maximizes the contact area at full bend, providing superior bend control and optimized contact stresses.

FIG. 6 shows the definition of one of the contact surfaces in more detail. Each collar has a contact surface facing towards the first end of the bend limiter and a contact surface facing towards the second end of the bend limiter. Preferably, the contact surfaces of all collars facing towards the first end of the bend limiter describe the same surface. Preferably, the contact surfaces of all collars facing towards the second end of the bend limiter describe the same surface. Preferably, the two contact surfaces of each collar face in opposite directions but describe the same surface. The contact surfaces of adjacent collars are cooperatively configured such that, when the collars are maximally tilted relative to each other about any tilt axis, they come into contact over an area larger than one point (preferably a straight line). This line may be essentially a radially oriented line, since it is located on a plane passing through the central axis of one or both of the collars. The collars extend longitudinally relative to the bend limiter, which facilitates longitudinal displacement of each contact surface. Each contact surface may have a rotational symmetry of 180 degrees around the central axis of the collar. Each contact surface may be a mirror image of itself rotated 90 degrees. Each contact surface may have a range in the radial direction of the central axis of the collar. Within this range, the surface may be inclined at multiple positions relative to the central axis of the collar. Conveniently, the portions of the surface that are offset 180 degrees from one another about the central axis may be inclined in one sense (e.g., their radially outer edges are closer to the end of the bend limiter than their radially inner edges) and the portions of the surface that are offset 90 degrees from said portions may be inclined in the opposite sense (e.g., their radially inner edges are closer to the end of the bend limiter than their radially outer edges). The contact surfaces of the collars may have a generally sinusoidal form when rotated about the central axis of the collar. A collar having such features may easily allow line contact between adjacent collars when it is fully bent.

In the example of FIG. 6, the geometry of the contact surface includes two convex areas or "lobes" and two concave areas or "dwellings". This design feature allows any two adjacent collars to contact and for the bend limiter to be at its maximum bend angle because the geometry of one "lobe" matches the geometry of one "lobe" of the adjacent collar. The lobes of each collar fit into the dwells of the adjacent collar along the length of the bend limiter.

As shown in FIG. 6, two spline curves may be used to construct each contact surface. 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 said collar. The contact surface smoothly connects the two spline curves. The splines can be conveniently defined using predetermined points. The points are equally spaced around the circumference of the outer collar. Each point of spline curve A has a corresponding point on spline curve B located at the same angular position around the central axis of the collar. All spline curve B points are radially offset the same distance relative to the points of spline curve A. This distance sets the maximum bend angle. Preferably, this is the same for all collars in the bend limiter.

To define the axial offset of the point, a parallel plane perpendicular to the axis of rotation of the collar is defined. Two pairs of planes define the effective contact surface. The distance between the two planes of a pair is the bend angle distance. The first plane of the pair (denoted the "length plane") controls the length or depth of the "concave"/"convex" geometry. The second plane of the pair (denoted the "angle plane") controls the angle.

By changing the location of the spline curve's limit points, the length and maximum bending angle can be adjusted, contributing to design flexibility. As a result of parameterized design, bending characteristics can be easily adjusted by changing the design input parameters.

Figures 7(a)-7(c) show how the collar and coupler are connected via pins. The connector pins extend parallel to corresponding first and second rotation axes to allow parts 7 and 10 to rotate relative to each other about the rotation joint.

As shown in the drawings, the rotation pin 30 that connects the outer collar 7 to the inner ring coupler 10 and allows them to rotate during their hinged connection can be retained at both ends to prevent loosening in two different retention methods as described below.

Inward Retention: The tapered geometry at the top of the pin, as shown at 17, mates with a complementary groove on the outside of the collar 7 and limits the movement of the pin 30 to prevent it from moving below the outer surface of the collar 7. The stop position of this pin is calculated so that the tapered front surface of the pin is flush with the chamfer on the outer diameter of the collar 7.

Outward Retention: The pin is retained using the ring 18, the groove 19 in the bottom of the pin 30 and a corresponding recessed groove in the bottom of the hole in the inner coupler 10. The ring is attached to the pin and the outer collar is aligned with the inner coupler so that the pin and hole are concentric. The pin 30 is then inserted into the hole in the outer collar using the chamfer that holds the recessed groove inward, once the pin is in place to compress the ring, the front face of the annular groove on the pin is aligned with the front face of the recessed groove on the inner coupler, allowing the ring to be in its "rest" position. The vertical front face of the recessed groove on the inner ring acts as a stop on the ring to prevent the pin from pulling out under normal operating conditions.

The rotational retaining pin can therefore be installed without the need for special tools, improving the convenience of assembling and removing the bend limiter.

This configuration proposes a bend limiter with a single design. In 80% of cases where light cable installations are used, the bend limiter can utilize a high strength-to-weight ratio composite material, and in the remaining 20% of cases where armor installations are used, the bend limiter can utilize a metallic solution.

Metal bend limiters may be fabricated from corrosion resistant high strength metal compounds such as steel, beryllium copper or high strength titanium alloys. The material may be selected depending on the specific requirements of the application, but should preferably withstand the cable breaking load of the largest armored cable to which the wet equipment product will be connected (currently in the range of 550KN).

Bend limiters for lightweight cables can be made from carbon fiber reinforced resin composites and only need to withstand the cable break load of the largest lightweight cables (currently in the range of 115 KN). Size-wise, carbon composites offer high strength and light weight, two of the key parameters required for this application. Carbon fiber composites offer the highest specific modulus of any commercially available yarn, with a tensile modulus of 230-400 GPa and an ultimate tensile strength of about 3.5-5.0 GPa. Carbon fiber composites also offer excellent interlaminar shear strength, fatigue resistance, and a low coefficient of thermal expansion.

The key attributes when selecting a resin system are good mechanical performance, low degradation rate, good thermal stress resistance, excellent corrosion resistance, and low water absorption. The matting impregnation method is known to provide optimal composite performance due to complete saturation of the carbon fiber mat pre-impregnated with resin and the good fiber wetting inherent in the carbon fiber tow size.

The superior strength-to-weight ratio that can be achieved when using carbon fiber composites results in parts that are lighter, smaller in size, and offer higher performance than other composite materials, while providing a true alternative to metals in similar applications.

The bend limiter described here also allows for simpler machining. As shown in FIG. 9, the collar 7 and ends 15, 16 may be machined from a tube of the same material by a tool 40. Thus, the outer collar and the inner coupler may be made from tubes of two predetermined sizes. This may result in less manufacturing waste. The same geometry of the moving bearing surfaces of the collars allows the collars to be machined from a single prefabricated tube by removing a small amount of material between the adjacent moving surfaces of two successive collars.

The bend limiter described herein is therefore a versatile design that can be applied to both metal and composite bend limiters and can have a service life of 25 years in steady state operation.

The two embodiments of the bend limiter can share the same size (inner and outer diameters, total length, maximum full bend angle) and geometry and can be connected to the wet fixture using similar solutions. The product is versatile and can accommodate a variety of sea case diameters. Utilizing a dedicated adapter that connects to the inner and/or outer diameter of the sea case outer collar, the design is compatible with previous and next generation wet fixture products.

The present invention allows for improving the maximum installation depth of underwater equipment by using lighter weight components than can be achieved using metallic equivalents with similar strength and corrosion resistance. This reduces the total weight of deep sea submarine cable systems, which are typically limited by metallic components. It also improves installation and retrieval limits, as well as improves the installation capabilities of wet equipment products. The lower cost and mass per unit volume of the composite bend limiter compared to metallic versions (e.g., when using titanium alloy grade 5) also allows for a significant reduction in the cost of lightweight solutions.

Although the invention has been described above with reference to an example of a bend limiter used with an undersea repeater, the invention may also be applied to other undersea telecommunications equipment such as amplifiers, switches, multiplexers, and demultiplexers, for example branching units and reconfigurable optical add-drop multiplexers (ROADMs).

The applicant hereby separately discloses each individual feature described herein and any combination of two or more of these features, and if a person skilled in the art could realize the feature or combination as a whole based on this specification with his/her common general knowledge, regardless of whether the feature or combination of features solves any problem disclosed herein, and without being limited by the scope of the claims. The applicant indicates that each aspect of the invention may consist of such individual features or combinations of features. In view of the above description, it will be apparent to one skilled in the art that various modifications can be made within the scope of the invention.

Claims (13)

A bend limiter (6) comprising a number of collars (7, 8, 9) and a number of couplers (10, 11) arranged in series,
each color is adjacent to two other colors in series, and adjacent colors are coupled via a coupler located therebetween;
Each collar has a revolute joint at each end , one of the revolute joints having a first axis (20) and the other of the revolute joints having a second axis (21) not parallel to the first axis (20);
Each collar is connected to a coupler at one end of the collar via one rotary joint and to a coupler at the other end of the collar via the other rotary joint;
the bend limiter (6) is configured to accommodate bending of the conduit passing therethrough and to limit said bending by abutment of adjacent collars when rotating about the first axis (20) or the second axis (21) of each rotary joint;
Each collar has a bearing surface on both end surfaces thereof , and when adjacent collars rotate about the first axis (20) or the second axis (21) of the respective rotary joints and the bearing surfaces of the adjacent collars come into contact with each other, the adjacent collars are at a maximum inclination angle;
The shape of the bearing surfaces is designed so that when the bearing surfaces of the adjacent collars abut against each other and the adjacent collars reach a maximum inclination angle, the bearing surfaces of the collars abut against each other with a linear or two-dimensional contact surface, regardless of the inclination direction between the adjacent collars.
A bend limiter characterized by: couplers connected to opposite ends of each collar are offset along a longitudinal direction of the bend limiter, and each collar extends along the longitudinal direction between the couplers;
2. The bend limiter of claim 1. the first axis (20) and the second axis of a single collar are offset along the longitudinal direction of the bend limiter, and each collar is connected via its own rotary joint to couplers located on either side of the collar;
3. The bend limiter of claim 2. each coupler is connected via its rotary joint to collars located on either side of the coupler, and in both adjacent collars, a first axis (20) of the rotary joint of one collar and a second axis (21) of the rotary joint of the other collar lie in a common plane perpendicular to the longitudinal direction of the bend limiter;
4. A bend limiter as claimed in claim 2 or 3. Each collar has two bearing surfaces facing in opposite directions along the length of the bend limiter.
2. The bend limiter of claim 1. The shape of the bearing surface is designed to control the maximum bend angle of the bend limiter to less than 70 degrees.
A bend limiter according to any one of claims 1 to 5. The profile of the bearing surfaces is designed such that the maximum inclination angle between adjacent collars is less than 20 degrees.
A bend limiter according to any one of claims 1 to 6. the collar and/or the coupler are annular and define a passage for passing the conduit therethrough;
A bend limiter according to any one of claims 1 to 7. Each collar is attached to a corresponding coupler via a connector pin extending parallel to the first axis and the second axis, respectively.
A bend limiter according to any one of claims 1 to 8. the bend limiter further has two ends (15, 16) with rotary joints, each end adjacent a collar at a corresponding first end and second end of the bend limiter, respectively, and connected via its rotary joint to a coupler located between said end and its adjacent collar;
10. A bend limiter according to any one of the preceding claims. the collar and the coupler are configured to withstand a tensile load applied between the ends;
11. The bend limiter of claim 10. the collar and/or the coupler are rigid;
12. A bend limiter according to any one of claims 1 to 11. the couplers located on either side of each collar are housed in an internal space defined by the collar and the adjacent collar about the longitudinal axis of the bend limiter;
13. A bend limiter according to any one of claims 1 to 12.

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