Patent Publication Number: US-2005141832-A1

Title: Armouring joint, an armoured cable joint and a method for jointing armouring of two armoured cables

Description:
The present invention relates to the field of cables joint and more precisely an armouring joint, an armoured cable joint and a method for jointing armouring of two armoured cables.  
      An armoured cable typically comprises: 
          one or several cable element(s) such as optical fiber element(s) sometimes disposed within a central steel tube and/or power cable element(s) and/or hydraulic steel tubes     generally an inner sheath, e.g. of extruded polyethylene, onto the central steel tube or onto the stranded elements,     one armouring which is a layer of stranded steel wires over the inner sheath,     an outer sheath, e.g. of extruded polyethylene, over the armouring.        

      For jointing of two armoured cables, it is known to use a joint box for the whole, including strain termination for armouring steel wires and, if required, a chamber for coiling excess fiber length.  
      The joint box has a larger diameter than the entire cables it is used to joint; thereby this joint box is expensive, complex to install and time consuming.  
      The invention aims at providing a cable with one armouring joint contributing to the reduction of the diameter of the total cable joint and preferably ensuring enhanced mechanical properties of cables in the joint area.  
      To this purpose, the invention provides a cable comprising first and second armoured cables respectively comprising N first armouring stranded wires and N second armouring stranded wires and an armouring joint between said first and second armoured cables, 
          characterized in that a number K lower than N of first armouring wires,     called shorter first wires, are shorter than N-K first armouring wires,     called longer first wires,     a number N-K of second armouring wires, called shorter second wires,     are shorter than K second armouring wires, called longer second wires,     and in that K shorter first wires and N-K shorter second wires are respectively abutting or nearly abutting with K longer second wires and N-K longer first wires thereby forming an armouring common zone comprising first and second armouring wires.        

      The armouring common zone forms an extension of the two armourings which maintains the same diameter in the joint area and is easy to make.  
      The invention is applicable to any armoured cable such as optical fiber cable, power cable, composite cable and is of great interest in large cable such as umbilical.  
      Advantageously, in order to reinforce the mechanical properties of the joint, the armouring joint can comprise a layer of preformed steel wires over at least said armouring common zone and an substantially equal length on each side of said armouring common zone, in order to grip both cable ends, and preferably with steel wires of larger total cross-sectional area than armouring wires.  
      The layer of preformed steel wires should combined be able to take more tension than armouring wires combined.  
      In one embodiment of the invention, said longer first wires are not adjacent and preferably are regularly spaced from each other. Identically, said longer second wires are not adjacent and preferably are regularly spaced from each other.  
      Preferably, said number K can be equal to entire part of N/2, by way of example, there is an alternance of longer first (or second) and shorter first (or second) wires.  
      In an advantageous embodiment of the invention, said armouring common zone has a so-called common length equal to at least one pitch length, and preferably with said pitch length substantially equal to the pitch length of the armouring from any of said first of second armoured cables.  
      By way of example, the common zone can be greater or equal to 0.5 m.  
      According the invention, the armoured cable joint comprises two abutting positions separated by a length substantially equal to said common length.  
      Doing this way, all shorter first (and second) wires have the same length.  
      According the invention, armouring wires can be made of steel.  
      In a preferred embodiment of the invention, each of said armoured cables comprising optical fibers within a first steel tube, said cable further comprises spliced optical fibers and a first steel tube joint under said armouring joint.  
      Said steel tube joint can preferably comprise: 
          an overlaid steel tube over said spliced optical fibers,     and two second steel tubes, 
 
 each of said second steel tubes being covered at a first end by one distinct end of said overlaid steel tube and being covered at a second end by one end of said first steel tubes, any of said tubes made of steel being end crimped. 
       

      Each of said armoured cables comprising inner and outer sheaths, said cable can comprise under said armouring joint, a heat shrunk hose welded by a polyethylene tape to inner sheaths at both the ends of said inner sheaths and, said cable can comprise, over said armouring joint, a heat shrunk hose welded by a polyethylene tape to the outer sheaths oat both ends of said outer sheaths.  
      Therefore, each polyethylene tape is not applied over the entire length of the joint, but merely at the transition between heat shrink hose and inner or outer sheaths. Heat is then applied to this area in order to weld inner or outer sheaths to heat shrink hose.  
      The above described joint is substantially as small as the diameter of the cables.  
      The invention also proposes a method for making or repairing a cable comprising first and second armoured cables respectively comprising N first armouring stranded wires and N second armouring stranded wires and an armouring joint between said first and second armoured cables characterized in that it comprises the successive following steps: 
          cut said N first and N second armouring wires so that they overlap in a certain overlapping length,     cut, over a distance substantially equal to said overlapping length, a number K lower than N of first armouring wires and N-K of second armouring wires to provide K shorter first wires and N-K shorter second wires,     lay back all said first and second armouring wires so that K shorter first wires and N-K shorter second wires are respectively abutting or nearly abutting with K longer second wires and N-K longer first wires, thereby forming a common armouring zone.        

      The overlapping length could be the same for each couple of first and second wires to joint or could be chosen individually for each of those couples.  
      Lay back can preferably be done with approximately the same pitch length as said armoured cables.  
      The method for making or repairing a cable can comprise a step of securing said common armouring zone with straps or a tape.  
      The method for making or repairing a cable can also comprise a step of directly applying a number of preformed steel wires over at least said armouring common zone. 
    
    
      Further characteristics and advantages of the invention will become clear on reading the following description of embodiments of the invention, given by way of examples only, and made with reference to the accompanying drawings in which:  
       FIG. 1  shows schematically and partially a longitudinal view (not in scale) of a cable including two armoured cables and an armouring joint of the two armoured cables according to one first embodiment of the invention;  
       FIG. 2  shows schematically and partially a longitudinal view (not in scale) of a cable with spliced optical fibers and cabled steel tube joint disposed under the armouring joint of  FIG. 1 ;  
       FIG. 3  shows schematically a cross sectioned view (not in scale) of a cable including two armoured cables and an armoured cable joint of the two armoured cables according to a second embodiment of the invention.  
    
    
      Elements performing the same functions are symbolized with the same references in the two embodiments.  
       FIG. 1  shows schematically and partially a longitudinal view (not in scale) of a cable  1000  including two armoured cables such as optical fiber umbilicals and an armouring joint  10  of the armoured cables, in first embodiment of the invention.  
      Starting from the core till the periphery, each optical fiber umbilical (partially shown) of the cable  1000  comprises: 
          cable element(s) such as optical fibers within a central steel tube (see  FIG. 2 ),     an inner sheath layer of extruded polyethylene,     an armouring which is a layer of for instance twenty stranded steel wires  1 A to  8 B (not all viewable) or  1 ′A to  10 ′B (not all viewable), giving a certain pitch length,     and an outer sheath  50 A,  50 B of extruded polyethylene.        

      In a variant (not shown), cable elements such as insulated copper conductors for power or signal transmission and/or hydraulic steel tubes could be added or replaced the optical fiber element.  
      The outer sheaths  50 A,  50 B of extruded polyethylene are removed from each cables end, along a certain distance greater than that required for armouring jointing such as 3 m, leaving each armouring  1 A to  10 B or  1 ′A to  10 ′B stripped, thereby giving a finished jointing length of approximately 5 m about 1 m of armouring wires is cut away during assembly.  
      Ten of first armouring wires  1 B to  8 B, called shorter first wires, are shorter than ten first armouring wires  1 A to  10 A called longer first wires. Shorter first wires  1 B to  10 B are preferably chosen not adjacent and regularly spaced from each other.  
      Ten of second armouring wires  3 ′B to  10 ′B, called shorter second wires, are shorter than ten second armouring wires  1 ′A to  10 ′A called longer second wires. Shorter first wires  1 B to  8 B are chosen preferably not adjacent and regularly spaced from each other.  
      Each shorter first wire  1 B to  8 B is respectively abutting, i.e. welded end to end, with a longer second wire  1 ′A to  10 ′A—or in a variant not shown nearly abutting, i.e without welding—. Each longer first wire . 1 A to  10 A is respectively abutting or nearly abutting with shorter second armouring wires  3 ′B to  10 ′B,  
      Therefore, an armouring common zone  11  with second and first wires is formed on a certain common length L.  
      In this first embodiment, the armouring common zone  11  comprises an alternance between longer first wires  1 A to  10 A and longer second wires  1 ′A to  10 ′A.  
      The common length L is equal to at least one pitch length. In a variant (not shown) it could be up to two pitch lengths or even more. Preferably, the pitch length in the common armouring zone  11  is substantially equal to the armouring pitch length in both umbilicals.  
      Two abutting positions d 1 , d 2  are referenced in a longitudinal axis d of the joint starting from one prepared first umbilical end (on the left). For example d 1  is equal to two meters and d 2  is equal to 2.5 meters.  
      In a first variant (not shown), there are more than two lengths of first (and second) wires, thereby more than two abutting positions.  
      In a second variant (not shown), there are more longer first (and second shorter) wires than shorter first ( and longer second) wires.  
      For instance the end of the cut second umbilical is at a distance d 5  equal to 5 m from the end of the cut first umbilical.  
      To make (or to repair) the cable  1000  with the armouring jointing  10 , at first, all steel wires  1 A to  10 ′B and the inner sheath have been preferably cleaned properly. At second, all steel wires are cut so that first steel wires  1 A to  10 A overlap in a given overlapping length, here equal to 50 cm, with the second steel wires  1 ′A to  10 ′A. At third, ten wires  1 B to  8 B,  3 ′B to  10 ′B which are not adjacent are cut 50 cm shorter on each cables end.  
      At fourth, all wires  1 A to  11 ′B are laid back with approximately the same pitch length. Therefore the ten shorter first wires  1 B to  8 B and the ten shorter second wires  3 ′B to  10 ′B are respectively abutting with the ten longer second wires  1 ′A to  10 ′A and the ten longer first wires  1 A to  10 A. The laid back wires could be secured with straps or tape.  
      Preferably, a layer of preformed steel wires is applied over at least the armouring common zone  11  and an substantially equal length on each side of this armouring common zone  11 .  
      For instance the ends of the layer are at d 3  and d 4  respectively equal to 0.75 m and 3.75 m. Tape and/or straps are removed as the layer is applied. The steel wires of the layer present a larger diameter than the one of the armouring steel wires.  
      The armouring joint  10  should preferably be over the individual splices  20  of the optical fibers FO of the cable  1000  and a cabled steel tube joint  30  of the cable  1000  which are shown in  FIG. 2 .  
      The cabled steel tube joint  30  comprises: 
          an overlaid steel tube  31  over the spliced optical fibers FO,     and first and second steel tubes  32 ,  32 ′.        

      The first steel tube  32  is covered at a first end  343  by a first end of the overlaid steel tube  31  and at a second end  344  by the end of the first central steel tube  33  of the first umbilical.  
      The second steel tube  32 ′ is covered at a first end  342  by the second end of the overlaid steel tube  31  and, at a second end  341 , by the end of the second central steel tube  33  of the second umbilical.  
      The ends  341  to  344  of those steel tubes  31  to  33 ′ are crimped.  
      More precisely, the armouring joint  10  is not in contact with the cabled steel tube joint  30 , the latter being covered directly by a heat shrink hose (see  FIG. 3 ).  
       FIG. 3  shows schematically a cross sectioned view (not in scale) of a cable  1000  including two armoured cables such as optical fiber umbilicals and an armoured cable joint  1000 . The cross section is made around the splices  20  of the optical fibers FO.  
      Starting from the core till the periphery, the total joint  100  comprises: 
          spliced optical fibers FO,     an overlaid steel tube  31  of cabled steel tubes joint  30      a heat shrunk hose  41  welded by a polyethylene tape to the inner sheaths of two umbilicals (not shown) for inner sheath jointing,     an armouring joint  10  with a layer longer first and second wires  1 A to  10 ′A covered by a layer  12  of larger preformed steel wires  13 ,     a heat shrunk hose  51  welded by a polyethylene tape to the outer sheaths of two umbilicals (not shown), for outer sheath jointing.        

      The armoured cable joint is exempt from external joint closure or coil chamber, has a small total diameter and good mechanical properties.  
      Of course to make the armoured cable joint  100 , all elements are cut in a sufficient distance on each side. Prior to tube jointing, the heat shrink hoses are pulled over inner/outer sheaths. Heat shrink hose and outer sheaths could be prepared to be end conical toward the tube joint, in a complementary way.