Jacket for offshore structure

Abstract

A jacket 4 for an offshore structure comprises a plurality of jacket modules 6 stacked one above the other, each of the jacket modules having multiple hollow legs 10; and a plurality of piles 8 passing through the hollow legs 10 for securing the jacket 4 to the sea-bed; wherein the piles 8 include: foundation piles 8 a passing through legs 10 of a lowermost jacket module 6 a, with a lower part of each foundation pile extending downward below the lowermost jacket module 6 a into the sea-bed, and an upper part of each foundation pile extending upward out of the tops of the legs 10 of the lowermost jacket module 6 a and into legs 10 of a second jacket module 6 b located atop the lowermost jacket module 6 a such that the upper parts of the foundation piles 8 a extend into the legs 10 of the second jacket module 6 b by a height less than the height of the jacket modules 6; and follower piles 8 b within the legs 10 of the second jacket module 6 b located atop the upper parts of the foundation piles 8 a and extending upward out of the tops of the legs 10 of the second jacket module 6 b.

1 . A jacket for an offshore structure, the jacket comprising:
 a plurality of jacket Modules stacked one above the other; each of the jacket modules having multiple hollow legs; and   a plurality of piles passing through the hollow legs for securing the jacket to the sea-bed;   wherein the piles include:   foundation piles passing through legs of a lowermost jacket module, with a lower part of each foundation pile extending downward below the lowermost jacket module into the sea-bed, and an upper part of the each foundation pile extending upward out of the tops of the legs of the lowermost jacket module and into legs of a second jacket module located atop the lowermost jacket module such that the upper parts of the foundation piles extend into the legs of the second jacket module by a height less than the height of the jacket modules; and   follower piles within the legs of the second jacket module located atop the upper parts of the foundation piles and extending upward out of the tops of the legs of the second jacket module.   
     
     
         2 . A jacket as claimed in  claim 1 , wherein the piles are arranged to extend upwardly out of the legs of the jacket module by different amounts, such that there is a first guide pile that extends upwardly by a greater length than the other piles, and a second guide pile that extends upwardly by a length less than the first guide pile but greater than the remaining piles. 
     
     
         3 . A jacket as claimed in  claim 1 , comprising: a third jacket module atop the second jacket module, with the follower piles in the legs of the second jacket module being a first set of follower piles and extending upward into the legs of the third jacket module; and a second set of follower piles within the legs of the third jacket module located atop the first set of follower piles and extending upward out of the tops of the legs of the third jacket module. 
     
     
         4 . A jacket as claimed in any of  claims 1 ,  2 , or  3 , wherein the piles are secured within the legs of the jacket modules by grout. 
     
     
         5 . A jacket as claimed in any preceding claim, comprising a transition piece for mounting a tower, such as a wind turbine tower, the transition piece being mounted on the exposed parts of the uppermost follower piles above the uppermost jacket module. 
     
     
         6 . A jacket as claimed in  claim 5 , wherein the transition piece is pre-fabricated onshore and comprises: a central structure for supporting a tower or the like and outer connecting parts for coupling to the exposed parts of the uppermost follower piles. 
     
     
         7 . A jacket as claimed in  claim 6 , wherein the outer connecting parts are hollow tubes placed on the exposed parts of the uppermost follower piles, and grout is used to secure the transition piece to the jacket modules. 
     
     
         8 . A jacket as claimed in any preceding claim, wherein the jacket modules include connectors for providing a seal about the joint between adjacent hollow legs. 
     
     
         9 . A jacket as claimed in any preceding claim, wherein the hollow legs include internal lugs for locating the piles at the centre of the legs and spacing the piles away from the walls of the legs. 
     
     
         10 . A jacket as claimed in any preceding claim, wherein the ends of the piles are shaped for interlocking fit with the next follower pile. 
     
     
         11 . A jacket as claimed in any preceding claim, wherein the upper ends of the upper parts of the foundation piles comprise a shoulder around a protruding conical or frustoconical element. 
     
     
         12 . A jacket as claimed in  claim 11 , wherein the follower piles include a female coupling at their lower end to accommodate the protruding part of the upper ends of the preceding piles. 
     
     
         13 . A jacket as claimed in  claim 12 , wherein the other, upper, end of the follower piles comprise a shoulder around a protruding conical or frustoconical element. 
     
     
         14 . A jacket as claimed in any preceding claim, wherein the jacket modules are designed with an arrangement of legs that is rotationally symmetrical about an axis extending parallel with the legs. 
     
     
         15 . A jacket as claimed in any preceding claim, comprising a J-tube with an angled section comprising a lower generally horizontal part for receiving a cable running generally horizontally along the floor, a bend that turns the cable through about a right angle, and an upper generally vertical part so that the cable exits the angled section running generally vertically, wherein the J-tube does not include a vertical tube extending up the entire height of the jacket. 
     
     
         16 . A jacket as claimed in  claim 15 , wherein the J-tube is located adjacent to a leg of the lowermost module and can be rotated in order to direct the lower generally horizontal part of the angled section in any desired direction. 
     
     
         17 . A jacket as claimed in  claim 15  or  16 , comprising two J-tubes mounted adjacent to two opposite legs of the lowermost jacket module. 
     
     
         18 . An offshore wind turbine comprising a jacket as claimed in any preceding claim. 
     
     
         19 . A method of installation of a jacket for an offshore structure, the jacket comprising: a plurality of jacket modules, each of the jacket modules having multiple hollow legs; and a plurality of piles; wherein the method comprises:
 locating a first, lowermost, jacket module on the sea-bed;   installing foundation piles through the legs of this lowermost jacket module such that lower parts of the foundation piles extend downward below the lowermost jacket module into the sea-bed and upper parts of the foundation piles extend upward out of the tops of the legs of the lowermost jacket module by a height less than the height of the jacket modules;   locating a second jacket module atop the lowermost jacket module such that the upper parts of the foundation piles extend into the legs of the second jacket module; and   installing follower piles within the legs of the second jacket module such that the follower piles are located atop the upper parts of the foundation piles and extend upward out of the tops of the legs of the second jacket module.   
     
     
         20 . A method as claimed in  claim 19 , the jacket being as claimed in any of  claims 1  to  17 . 
     
     
         21 . A method as claimed in  claim 19  or  20 , wherein the piles are installed such that they extend upwardly into the legs of the next jacket module by different amounts. 
     
     
         22 . A method as claimed in  claim 21 , wherein the jacket comprises a first guide pile that extends upwardly into the legs of the next jacket module by a greater length than the other piles and a second guide pile that extends upwardly into the legs of the next jacket module by a length less than the first guide pile but greater than the remaining piles, and the method comprises locating a subsequent jacket module by landing a first leg of the next jacket module on the first guide pile, aligning a second leg of the jacket module with the second guide pile and landing the second leg on the second guide pile so that the remaining legs and piles are aligned. 
     
     
         23 . A method as claimed in any of  claims 19  to  22 , comprising grouting about the piles inside the hollow legs in order to thereby secure the piles within the legs, wherein the grout is pumped into the legs around the piles after assembly of all the jacket modules and piles is completed. 
     
     
         24 . A kit of parts for a jacket, the kit of parts comprising:
 a plurality of jacket modules arranged to be stacked one above the other, each of the jacket modules having multiple hollow legs; and   a plurality of piles arranged for passing through the hollow legs for securing the jacket to the sea-bed;   wherein the piles include: foundation piles for passing through legs of a lowermost jacket module, the foundation piles including lower parts for extending downward below the lowermost jacket module into the sea-bed and upper parts for extending upward out of the tops of the legs of the lowermost jacket module and into legs of a second jacket module located atop the lowermost jacket module such that the upper parts of the foundation piles extend into the legs of the second jacket module by a height less than the height of the jacket modules; and   follower piles for installation within the legs of the second jacket module located atop the upper parts of the foundation piles and extending upward out of the tops of the legs of the second jacket module.   
     
     
         25 . A kit of parts as claimed in  claim 24 , wherein the jacket modules and/or piles are as claimed in any of  claims 1  to  17 .