WO1998015865A1

WO1998015865A1 - Bend limiting boot assembly

Info

Publication number: WO1998015865A1
Application number: PCT/US1997/018117
Authority: WO
Inventors: Mohamad A. Amirkalali
Original assignee: Tyco Submarine Systems Ltd.
Priority date: 1996-10-10
Filing date: 1997-10-08
Publication date: 1998-04-16
Also published as: AU4895897A; TW354435B

Abstract

A bend limiting boot assembly (10) includes two substantially identical boots (20). Each boot (20) has a flange arrangement (90) at one end that fits into a complementing flange arrangement (90) on the other boot (20). The boots (20) are then fastened at the mated flanges (90) to secure the boot assembly over a joint assembly (75) which contains a fiber optic cable joint.

Description

BEND LIMITING BOOT ASSEMBLY

Field of the Invention

The present invention relates to the field of submarine fiber-optic communications systems and, in particular, to a device for limiting the bend at a cable joint between two fiber-optic cables.

Background of the Invention

In our truly global society, more and more people are becoming interconnected with one another through telecommunications systems. Although submarine fiber-optic cable communications systems are but one type of telecommunication system, submarine fiber-optic cables are capable of carrying a greater number of data and voice transmissions than traditional submarine cable systems or modern satellite communication systems.

Stretching thousands of miles across the oceans, submarine fiber-optic cables lie on the ocean's floor, thousands of feet below sea level. Because no one cable could be made that extended thousands of miles in length, submarine fiber-optic cable communication systems are comprised of a series of submarine fiber-optic cables that are spliced together at cable joints. In this manner, many individual cables can be connected to form a single cable of the required length.

If one were to cut open a standard "non-armored" fiber-optic cable, he would see that each cable is comprised of a series of optic fibers clustered around a steel "king" wire. Together, these wires form the fiber-optic "core" of the cable. The fiber-optic core itself is surrounded by steel strength members and two watertight, insulating jackets (an inner copper jacket and an outer polyethylene jacket) encase the entire assembly. The function of the optic fibers is to carry the data and voice transmissions sent over the fiber-optic cable; the steel wires carry any loads placed upon the cable and, in conjunction with the insulating jacket, give the cable its rigidity. Because excess residual strain on the optic fibers may result in undesirable static fatigue and crack growth in the fibers, it is important that the amount of permanent load on the optic fibers (i.e., sustained loads over long periods of time) be minimized. Minimizing the amount of permanent load will prevent excess residual strain from developing in the optic fibers and thus will protect the fibers from damage. Accordingly, it is important that the optic fibers of a fiber-optic cable be protected against permanent loading and excess residual strain.

The cable joints themselves, however, are subject to a considerable amount of potentially harmful loads. For example, when the cable is first being lowered onto the ocean floor, a large tension load is created in the cable by the weight of the many thousands of feet of additional cable below it. In addition, cables are coiled on large storage rolls for storage and transport, and are then fed from the rolls to a position on the ocean floor. The coiled storage of the cables can cause undesirable bend in the cable joints resulting in possible damage to the optic fibers. Also, during positioning of the cable on the ocean floor, the cables are subject to bending which places undesirable stress on the cable joints. Traditionally, cable joints are protected from undue bending by encasing the cable joint with a pair of bend limiting boots attached to the cable joint assembly and extending a distance back along the cable. Each boot has a different configuration at the joint end for attachment to the joint assembly. Once attached to the joint assembly, the stiffness of the boots acts to reduce bend in the cable at the joint assembly, and thus reduce the likelihood of damage to the fiber optic cable at the cable joint.

The disadvantages of this configuration, however, are that the different configurations required for the two joint ends of the boots increase the manufacturing costs and complexity of the boots. Since the boots are configured differently, they are not interchangeable, thus requiring that an appropriate number of each boot type be maintained in stock. This need to stock a sufficient number of both boot types is particularly burdensome on ships which have limited storage space. Also, having two boots with different joint end configurations increases the complexity of field assembly, increasing the likelihood of improper assembly, and increasing assembly time. Since the boots are directly attached to the outer surface of the joint assembly, there is a possibility that the boots may loosen and slip off the joint assembly. Also, since each boot is connected to an end of the joint assembly, there are two connections at the cable joint, which reduces the stiffness which can be achieved by the bend limiting boot.

Summary of the Invention

Accordingly, a bend limiting boot assembly is provided which is less expensive to manufacture, has interchangeable boots, is easier and quicker to attach, and provides improved stiffness. The boot assembly includes two identical boots which encase a cable joint and a portion of the adjacent cable. The joint ends of the boots have an arrangement of extended flanges which are designed to fit into corresponding openings of an opposing boot when the two boots are brought together at their joint ends. A clamp is positioned around a recessed radial channel on the flanges in the joint ends of the boots and tightened to secure the opposing boots together.

Brief Description of the Drawings

FIG. 1 is a perspective view of a bend limiting boot assembly according to a preferred embodiment of the invention. FIG. 2 is a cross section of a boot as illustrated in FIG. 1.

Detailed Description of the Invention

As shown in FIGs. 1 and 2, the bend limiting boot assembly 10 includes two boots 20 and two band clamps 30. The boots 20 are made of a suitably rigid material such as butyl rubber which is relatively impervious to degradation over extended periods of use in the ocean. Each boot 20 is generally an elongated cylinder approximately 5 feet long having at least one longitudinally extending, cylindrical passageway 40 having a diameter larger than the outer diameter of a fiber optic cable 45. Each boot 20 has an elongated tapered section 50 leading to a tapered end of the boot 60. The other end of the boot has a shortened, reverse tapered section 70 leading to a cylindrical section 80 having at least two extended flanges 90 which are symmetrically arranged around the circumference of the cylindrical section 80. Thus, there will be spaces 85 between the extended flanges 90 to receive the extended flanges 90 of an opposing boot. A hollow chamber 95 is defined by the inner walls of the cylindrical section 80 and a portion of the inner surface of the reverse tapered portion 70 and is configured to receive one end of a fiber optic cable joint assembly. The extended flanges 90, cylindrical section 80 and a hollow chamber 95 have inner surfaces with diameters larger than the outer diameter of a joint assembly 75 over which the bend limiting boot will be connected. Typicall, the outer diameter of a joint assembly is about 6.5 inches. The outer surfaces of the extended flanges 90 have a recessed radial channel 100 that accommodates a removable fastener 30 such as a band clamp or any other fastener that is configurable to allow a desired uniform hoop stress to be applied radially inward.

To assemble the bend limiting boot 10 over a joint assembly, two boots are provided and a fiber optic cable 45 is inserted through the narrow tapered end of one of the boots 60 and drawn through the other end of the boot. A second cable 45 is inserted in the second boot 60 in a similar manner. The free cable ends extending through two boots 60 are then joined to each other in a joint assembly 75. The flanges 90, cylindrical section 80, and hollow portion 95 of the boot are slid over the joint assembly 75 such that the extended flanges 90 of each boot 20 are disposed in corresponding intermediate spaces 85 on the opposing boot 20. When the boots 20 are properly positioned, the recessed channels 100 of the mated boot ends are aligned. A fastener 30, such as one or more band clamps is fitted over the mated boots in the recessed channels 100. The fastener 30 is then tightened to secure the mated boot ends. Still other objects and advantages of the present invention will become readily apparent to those skilled in this art from the above-recited detailed description, wherein only the preferred embodiment of the invention has been shown and described. The description of the preferred embodiment is simply by way of illustration of the best mode contemplated for carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modification in various respects, all without departing from the invention. Accordingly, the drawings and descriptions are to be regarded as illustrative in nature, and not as restrictive.

Claims

What is claimed is: 1. A bend limiting boot for attachment at a joint assembly for fiber optic cables comprising: an elongated, cylindrical boot having an internal, longitudinal passageway capable of receiving a fiber optic cable, the boot having tapered section connected to a reverse tapered section, the reverse tapered section being connected to a cylindrical section having at least two axially extending flanges which are symmetrically arranged about the circumference of the cylindrical section, each of the at least two flanges having a radial recessed channel on an outer surface of the flange, and wherein the cylindrical section and an adjacent portion of the reverse tapered section define an inner cylindrical chamber capable of receiving one end of a joint assembly.

2. A bend limiting boot assembly for attachment at a joint assembly for fiber optic cables comprising: two elongated boots, wherein each of the two boots being substantially identical and including: a) an axially aligned internal passageway extending through the boot; b) a recessed chamber at one end of the boot, the chamber being capable of receiving one end of a joint assembly; and c) at least two axially flanges extending from the boot at the opening of the chamber; and a fastener for connecting the two boots together in opposing relationship at the flanges.