Composite tendon

Abstract

A composite tendon comprises a main body of rope type construction. The ends of the tendon body terminate in eye splices for connection to termination connectors. Component strands of the composite tendon may form separate eye splices for connection to the termination connectors. Multiple composite tendons of rope type construction may be joined to a single termination connector. The termination connectors secure one end of the tendon to the seabed and the opposite end thereof to a floating platform.

Description

BACKGROUND OF THE DISCLOSURE

The present invention relates to mooring systems for floating platforms, and more particularly to a composite tendon for anchoring a floating platform to the seabed.

Offshore floating platforms, such as Tension Leg Platforms (TLPs), are held in place in the ocean by means of vertical mooring elements called tendons, which are typically fabricated from high strength, high quality steel tubulars, and include articulated connections on the top and bottom (tendon connectors) that reduce bending moments and stresses in the tendon system. Many factors must be taken into account during the design of the tendon system to keep the floating platform safely in place including: (a) limitation of stresses developed in the tendons during extreme storms and while the platform system is operating in damaged conditions; (b) avoidance of any slackening of tendons and subsequent snap loading of tendons as wave troughs and crests pass the platform hull; (c) allowance for fatigue damage which occurs as a result of the stress cycles in the tendons system throughout its service life; and (d) vibrations in the platform system arising from vortex-induced vibrations.

As water depth increases beyond about 4,000 ft, the platform system cost begins to be dominated by the cost of the tendon system due to the length and wall thickness of tendons and by fatigue considerations. To limit the amount of fatigue damage caused by each wave cycle, it is necessary to limit the vertical natural resonance periods of the platform system (heave, pitch and roll) to the 3-4 second range for a steel tendon by increasing the cross-sectional area of the tendon, i.e. by stiffening the “spring” since the “mass” of the platform is set mainly by operational considerations. The increasing requirement for more steel cross-sectional area causes the tendon system to become heavier, thus reducing the payload carrying capacity of the platform system, i.e. more and more platform buoyancy is ‘consumed’ merely supporting its own mooring system. This combination of increasing tendon length and tendon wall thickness causes the tendon system to dominate total installed cost of the entire platform system in ultra-deepwater.

Various methods have been suggested to reduce the weight of tendon systems, including the utilization of composite tendons of various materials. It is known, for example, that carbon fiber, glass fiber, aramid fiber and other like fibers provide high tensile strength with less weight than metallic materials.

It is therefore an object of the present invention to provide a composite tendon of rope type construction.

It is another object of the present invention to provide a composite tendon having eye splice termination ends.

It is yet another object of the present invention to provide a composite tendon that may be rolled on drums for transportation to the installation site.

SUMMARY OF THE INVENTION

In accordance with the present invention a composite tendon comprises a main body of rope type construction. The ends of the tendon body terminate in eye splices for connection to termination connectors. Component strands of the composite tendon may be formed into component eye splices for connection to the termination connectors. Multiple composite tendons of rope type construction may be joined to a single termination connector. The termination connectors secure one end of the tendon to the seabed and the opposite end thereof to a floating platform.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features, advantages and objects of the present invention are attained can be understood in detail, a more particular description of the invention briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings.

It is noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

FIG. 1 is a side elevation view of a tendon in accordance with the present invention;

FIG. 2 is a partial side view of a tendon of the invention illustrating the crossover termination of the upper end of the tendon;

FIG. 3 is a partial side view of a tendon of the invention taken along line 3-3 of FIG. 2;

FIG. 4 is a partial side view of another preferred embodiment of a tendon of the invention;

FIG. 5 is a partial side view of another preferred embodiment of a tendon of the invention;

FIG. 6 is a partial side view of a tendon of the invention taken along line 6-6 of FIG. 5; and

FIG. 7 is a side view of another preferred embodiment of a tendon of the invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Referring first to FIG. 1, the composite tendon of the invention is generally identified by the reference numeral 10. The tendon 10 is of rope type construction and includes a main body 12. The ends of the tendon 10 are spliced to form eye splices 14, as best shown in FIGS. 2 and 3. The eye splices 14 are wrapped with a polyurethane cover 16 or similar material.

Referring again to FIG. 1, a bottom crossover connector 18 secures the lower end of the tendon 10 to an anchor pile 20 embedded in the seabed 22. Various methods known in the art may be employed to secure the crossover connector 18 to the anchor pile 20. A crossover connector 24 secures the upper end of the tendon 10 to the floating platform 26 at a point below the water line 28.

Referring now to FIGS. 2 and 3, the top crossover connector 24 is shown joined to the tendon 10 of the invention. The crossover connector 24 terminates in an integrated clevis 30 at the lower end thereof. The bottom crossover connector 18 likewise includes an integrated clevis (not shown in the drawings) for connection with the lower end of the tendon 10 in the same manner hereinafter described. The clevis 30 includes two downwardly extending clevis extensions 32 defining an open-ended gap or slot 34 formed in the clevis 30. The extensions 32 are parallel and spaced from each other. Each extension 32 includes a hole extending therethrough. The holes are aligned for receiving a load pin 36 bridging the clevis extensions 32 perpendicular to the longitudinal axis of the crossover connector 24. Upon connection with the tendon 10, the tendon eye splice 14 is advanced into the clevis slot 34 and the load pin 36 passes through the holes in the extensions 32 and the eye splice 14. Lock bushings 38 secure the load pin 36 to the clevis 30. Load cells may be embedded in the load pin 36 to monitor the tensile load on the tendon 10.

In FIG. 4, another embodiment of the composite tendon of the invention is generally identified by the reference numeral 40. The composite tendon 40 includes a main body 42 of rope type construction. The rope body 42 comprises a plurality of strands braided to form the rope body 42. The strands at the ends of the rope body 42 terminate in eyes splices 44. The component strands forming the tendon body 42 are separated at the ends thereof and an eye splice 44 for each tendon strand is formed. The crossover connectors 18 and 24 include an integrated clevis 46 having spaced, downwardly extending clevis plates 47 provided with aligned holes for receiving a plurality of load pins 48 extending therethrough. The load pins 48 correspond to the number of eye splices 44. The eye splices 44 may or may not be wrapped with a polyurethane cover or the like. The eye splices 44 are of different lengths to compensate for the location of its corresponding load pin 48 on the clevis plates 47 so that the tendon tensile load is equally shared by the component strands of the tendon 40.

In another embodiment of the invention shown in FIGS. 5 and 6, the crossover connectors are adapted to carry multiple composite tendons. The composite tendon of the invention illustrated in FIGS. 5 and 6 is similar to that described in FIG. 1 with the exception that the crossover connectors include hang off plates 50. Therefore, like reference numbers are used to designate like components.

Referring still to FIGS. 5 and 6, the crossover connector 24 terminates in integrated hang off plates 50 extending downwardly from the lower end thereof. The plates 50 are arranged in pairs and include aligned holes for receiving the load pins 36 therethrough. The plates 50, like the clevis extensions 32 of the embodiment shown in FIG. 1, define a gap therebetween for receiving the eye splice 14 of the tendons 10. The multiple tendons 10 are secured to the crossover connectors by passing the load pins 36 through the holes in the plates 50 and the eye splices 14 of the tendons 10. Roll keepers 52 are mounted about the load pins 36 against the lateral sides of the eye splices 14.

In FIG. 7, another embodiment of the composite tendon of the invention is generally identified by the reference numeral 60. The tendon 60 comprises a body 62 having the ends thereof spliced together at a single splice 64. The body of the tendon body 62 is bent to form eyes 66 of the desired size at opposite ends thereof. A protective cover or binding 68 is wrapped around the full length of the tendon body 62 between the eyes 66. The tendon 60 is secured to the crossover connectors in the manner described above.

While a preferred embodiment of the invention has been shown and described, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims which follow.

Claims

1. A composite tendon, comprising:

a) a tendon body of rope type construction having two ends;

b) each end of said tendon body terminating in an eye splice; and

c) termination connectors adapted for connection to said ends of said tendon body.

2. The composite tendon of claim 1 wherein said tendon body comprises two or more tendon components.

3. The composite tendon of claim 2 wherein said tendon components are separated at said ends of said tendon body, said tendon components forming separate eye splices.

4. The composite tendon of claim 1 wherein said termination connectors include an integrated clevis at one end thereof adapted for connection with said eye splice of said tendon body.

5. The composite tendon of claim 4 including a load pin coupling said termination connectors with said eye splice of said tendon body.

6. The composite tendon of claim 3 wherein said termination connectors include an integrated clevis at one end thereof, and further including two or more load pins coupling said termination connectors with said eye splices of said tendon components.

7. The composite tendon of claim 1 including two or more tendon bodies secured to said termination connectors.

8. The composite tendon of claim 7 wherein said termination connectors include integrated clevis plates for connecting at least four tendon bodies to said termination connectors.

9. The composite tendon of claim 1 including a load pin connecting said termination connectors with said eye splice of said tendon body and wherein said load pin includes load cells operatively connected for monitoring tensile load variations in said composite tendon.

10. The composite tendon of claim 1 wherein said tendon body forms a continuous loop spliced at a single point.