Abstract:
Systems and methods for coupling a topside to a fixed or floating substructure during float-over installation of the topside are disclosed. Some system embodiments include a first plate coupled to a leg of the substructure and a retaining wall coupled to the first plate and extending substantially normally therefrom, wherein the retaining wall and the first plate form a recess. The system embodiments further include a second plate disposed at an end of a leg of the topside, the second plate received within the recess and engaging the first plate, and a plurality of shims disposed between the second plate and the retaining wall, wherein the plurality of shims are configured to inhibit translational movement of the second plate relative to the first plate.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims benefit of U.S. provisional application Ser. No. 60/946,647 filed Jun. 27, 2007, and entitled “Big Foot and Docking Probe,” which is hereby incorporated herein by reference in its entirety for all purposes. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       BACKGROUND OF THE INVENTION 
       [0003]    Embodiments of the invention relate to systems and methods for installing a topside or deck on a substructure to form a fixed or floating offshore platform. More particularly, embodiments of the invention relate to a novel system and method for coupling the topside with the substructure during float-over installation of the topside. 
         [0004]    Float-over installations offer opportunities to install heavy topsides beyond the lifting capacity of available crane vessels on offshore substructures located in remote areas. A float-over installation includes four primary procedures. The first procedure involves transporting the topside or deck to the offshore substructure. Typically, the topside is placed on a barge or heavy transport vessel and towed to the substructure. 
         [0005]    The second procedure involves docking the transport barge to the installed substructure. The barge is maneuvered into the slot of the substructure, such that the topside is floated over and substantially aligned with the substructure. Once in the slot, mooring lines, sometimes in combination with a fendering system, are utilized to suppress surge and sway motions of the barge. After the mooring lines are set, deballasting of the substructure commences. 
         [0006]    The third procedure involves transferring the load of the topside from the barge to the substructure, and is a critical phase of the float-over installation. Deballasting of the substructure continues as the substructure rises toward the topside. Once the topside and the substructure reach close proximity, the two bodies may impact each other repeatedly due to wave action. Such impacts may damage the structures when the relative motion between the two bodies is not controlled. As deballasting of the substructure continues, the weight of the topside is gradually transferred from the barge to the substructure. After a critical fraction of the weight is transferred, the relative motion between the two bodies ceases. At that point, the two structures move as a single unit, and the possibility of damage due to hard impact is eliminated. Therefore, it is desirable to complete the load transfer up to the critical fraction as quickly as possible. 
         [0007]    After the topside is fully supported by the substructure, the legs of the two structures are coupled by welding legs extending downward from the topside to legs extending upward from the substructure. To achieve the high quality welds required to withstand the harsh load regimes of offshore environments, proper alignment of the topside with the substructure during the float-over operation is critical. 
         [0008]    The final procedure involves separating the barge from the topside, and is also a critical phase of the float-over installation. The substructure is deballasted further until the topside separates from the barge. At and immediately after separation, the relative motions between barge and topside pose a danger of damage due to impact between these bodies. That danger can be minimized by rapid separation of the barge and the topside. To promote such rapid separation, the topside may be supported on the barge by a number of loadout shoes. At the appropriate time, the loadout shoes are actuated to quickly collapse or retract, thereby providing rapid separation between the barge and the topside. These systems, however, have a propensity to malfunction and permit hard contact between the loadout shoes and the topside. In any event, hard contact between the barge and the topside may continue until the substructure is deballasted to provide sufficient separation between the barge and the topside. After which point, the barge is towed from the installation site. 
         [0009]    Thus, embodiments of the invention are directed to apparatus and methods that seek to overcome these and other limitations of the prior art. 
       SUMMARY OF THE PREFERRED EMBODIMENTS 
       [0010]    A system and method for coupling a topside to a fixed or floating substructure during float-over installation of the topside are disclosed. Some systems embodiments include a first plate coupled to a leg of the substructure, a retaining wall coupled to the first plate, and a second plate disposed at an end of a leg of the topside. The retaining wall extends substantially normally from the first plate, such that the retaining wall and the first plate form a recess. The second plate is received within the recess and engages the first plate. The system embodiments may further include a plurality of shims disposed between the second plate and the retaining wall, wherein the shims are configured to inhibit translational movement of the second plate relative to the first plate. 
         [0011]    The system embodiments may further include a tensioning system. The tensioning system includes a connector coupled to the first plate and disposed within the second plate, wherein the second plate is annular. The tensioning member further includes a support plate coupled to the topside, a rod extending between the connector and the support plate, and a securing device coupled to an end of the rod. The securing device is configured to apply a tension load to the rod. 
         [0012]    Some method embodiments for coupling a topside to a fixed or floating substructure during float-over installation of the topside include coupling a receptacle to a leg of the substructure. The receptacle includes a first plate coupled to the leg of the substructure and a retaining wall coupled to the first plate. The retaining wall extends substantially normally from the first plate, wherein the retaining wall and the first plate form a recess. The method embodiments further include disposing a second plate at an end of a leg of the topside, receiving the second plate within the recess, wherein the second plate engages the first plate, and installing a plurality of shims between the second plate and the retaining wall. The plurality of shims are configured to inhibit translational movement of the second plate relative to the first plate. 
         [0013]    Thus, the embodiments of the invention comprise a combination of features and advantages that enable substantial enhancement of float-over installation systems and methods. These and various other characteristics and advantages of the invention will be readily apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments of the invention and by referring to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    For a detailed description of the preferred embodiments of the invention, reference will now be made to the accompanying drawings in which: 
           [0015]      FIGS. 1A and 1B  are cross-sectional and top views of weldless topside coupling system in accordance with embodiments of the invention; 
           [0016]      FIG. 2  is a cross-sectional view of an installed substructure including some components of the coupling system of  FIG. 1 ; 
           [0017]      FIG. 3  is a cross-sectional view of a topside including the remaining components of the coupling system of  FIG. 1  floated over the substructure of  FIG. 2 ; 
           [0018]      FIG. 4  is a cross-sectional view of a tensioning member coupled between a topside and a substructure; and 
           [0019]      FIG. 5  is a cross-sectional view of a weldless coupling system and tensioning member coupled between the topside and the substructure of  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0020]    Various embodiments of the invention will now be described with reference to the accompanying drawings, wherein like reference numerals are used for like parts throughout the several views. The drawing figures are not necessarily to scale. Certain features of the invention may be shown exaggerated in scale or in somewhat schematic form, and some details of conventional elements may not be shown in the interest of clarity and conciseness. 
         [0021]    Preferred embodiments of the invention relate to a weldless system and method for coupling a topside with an installed substructure to form a fixed or floating platform. The invention is susceptible to embodiments of different forms. There are shown in the drawings, and herein will be described in detail, specific embodiments of the invention with the understanding that the disclosure is to be considered an exemplification of the principles of the invention and is not intended to limit the invention to that illustrated and described herein. It is to be fully recognized that the different teachings of the embodiments discussed below may be employed separately or in any suitable combination to produce desired results. 
         [0022]    As described above during a conventional float-over installation of a topside on an installed substructure, the topside is floated over and substantially aligned with the substructure using a barge. The substructure is then deballasted to engage and lift the topside from the barge, thereby assembling the fixed or floating platform. The topside is then coupled to the substructure by welding. Embodiments of the invention are directed to a system and method for coupling the topside to the substructure without the need for precise alignment of the topside relative to the substructure and subsequent welding. 
         [0023]      FIGS. 1A and 1B  depict representative cross-sectional and top views, respectively, of a topside or deck installed via float-over on a representative cross-section of a substructure  105  for a semi-submersible offshore platform, such as a multicolumn floating (MCF) platform. More specifically, a leg  110  of the topside is shown coupled to a leg  115  of the substructure by a weldless topside coupling system  120 . Coupling system  120  includes an annular plate  125  disposed at the lower end  130  of leg  110 . In this exemplary embodiment, plate  125  is formed separately from leg  110  and then coupled to leg  110  as shown. In other embodiments, however, plate  125  may be formed integrally with leg  110 . After the topside is landed on the substructure, as shown, leg  115  of the substructure supports leg  110  of the topside. By disposing annular plate  125  at end  130  of leg  110 , the area or footprint of leg  110  in contact with leg  115  is significantly increased, in comparison to the footprint of leg  110  that would otherwise contact leg  115  in the absence of plate  125 . Because annular plate  125  increases the footprint of leg  110 , annular plate  125  is also referred to the big foot. 
         [0024]    Weldless coupling system  120  further includes a receptacle or bucket  135  disposed at the upper end  140  of leg  115 . Bucket  135  includes a base plate  145  having an upper surface  155  and a retaining wall  150  coupled thereto. Retaining wall  150  extends substantially normally upward from upper surface  155 . As shown in  FIG. 1B , retaining wall  150  is generally circular in shape. Further, the inner envelope of retaining wall  150  is selected such that annular plate  125  may be received therein. 
         [0025]    For additional support, one or more small gusset plates  160  are coupled to bucket  135  between upper surface  155  of base plate  145  and the outer surface  165  of retaining wall  150 . Plates  160  provide support to retaining wall  150  when lateral force is applied to the inner surface  170  of wall  150 , where the lateral direction is substantially parallel to base plate  145 . Also for additional support, one or more large gusset plates  175  are coupled to bucket  135  between the lower surface  180  of base plate  145  and the outer surface  185  of leg  115 . Plates  175  provide support to base plate  145  when an asymmetric vertical load, defined relative to a longitudinal centerline  190  through leg  115 , is applied to upper surface  155  of base plate  145 . 
         [0026]    In some embodiments, weldless coupling system  120  further includes two or more pairs of tapered or wedge-shaped shims  200  disposed on upper surface  155  of base plate  145  between the outer surface  205  of plate  125  and inner surface  170  of retaining wall  150 . When installed, shims  200  prevent translational movement of plate  125  relative to base plate  145 , and thus lateral movement of leg  110  relative to leg  115 . In at least some embodiments, shims  200  are formed of steel. Each pair of shims  200  comprises an inner shim  210  proximate plate  125  and an adjacent outer shim  215  proximate retaining wall  150 . The adjacent surfaces of inner shim  210  and outer shim  215  form a non-slip taper  220  configured to prevent sliding of shims  210 ,  215  relative to each other. 
         [0027]    Weldless coupling system  120  may further include a coating  225  disposed between retaining wall  150  and plate  125  and covering shims  200 . Coating  225  is configured to prevent corrosion of shims  200  and potential slippage of inner shims  210  relative to outer shims  215 . Coating  225  may include an epoxy resin material, such as chalk-fast, tar, or other equivalent material known in the art. 
         [0028]    Alternatively, weldless coupling system  120  may include a hardenable material  455  ( FIG. 5 ) in place of shims  200  and coating layer  225 , if present. Hardenable material  455  is disposed within bucket  135  surrounding and covering plate  125 . Further, hardenable material  455  is applied in liquid form but subsequently hardens into solid form. Like shims  200 , material  455 , once hardened, prevents slippage of plate  125  relative to base plate  145 , and thus lateral movement of leg  110  relative to leg  115 . Hardenable material  455  may include a grout, epoxy resin, or other equivalent material. 
         [0029]    With the exception of shims  200 , coating layer  225  and hardenable material  455 , components of docking system  110  are coupled to leg  110  of the topside or leg  115  of the substructure, as appropriate, prior to transport of the topside and the substructure to the desired offshore installation site. Bucket  135  and plates  160 ,  175  are coupled to leg  115  of the substructure, for example, by welding. Similarly, annular plate  125 , if formed separately from leg  110 , is coupled to leg  110 , for example, by welding. 
         [0030]    The substructure, with leg  115  and components of weldless coupling system  120  coupled thereto, is then towed to the installation site, as shown in  FIG. 2 . Upon reaching the installation site, the substructure  105  is ballasted to the desired depth. The topside  100 , with leg  110  and components of weldless coupling system  120  coupled thereto, is next towed to and floated over substructure  105  by a barge  107 , as previously described and shown in  FIG. 3 . 
         [0031]    After topside  100  is aligned over substructure  105 , substructure  105  is deballasted to engage topside  100 . More particularly, substructure  105  is deballasted to allow bucket  135 , coupled to upper end  140  of leg  115 , to receive annular plate  125 , coupled to lower end  130  of leg  110 , such that plate  125  lands on upper surface  155  of base plate  145  within retaining wall  150 , as shown in  FIG. 1A . Continued deballasting of substructure  105  enables load transfer of topside  100  from barge  107  to substructure  105 . In other words, substructure  105  begins to lift topside  100  from barge  107 . 
         [0032]    When the load of topside  100  is completely supported by substructure  105 , shims  200  may then hammered into position between annular plate  120  and retaining wall  150 . Once installed, shims  200  prevent subsequent sliding of plate  125 , and leg  110  coupled thereto, relative to bucket  135 , and leg  115  coupled thereto. Lateral loads exerted by leg  110  in response to the surrounding water are instead transferred through shims  200  to retaining wall  150 , which resists these loads with support from gusset plates  160 . If desired, coating  225  is then applied between plate  125  and retaining wall  150  to cover shims  200 . Alternatively, hardenable material  455  may be applied to fill bucket  135  and cover plate  125  and allowed to harden. Finally, barge  107  is released from topside  100 . 
         [0033]    Weldless coupling system  120  does not require welding to couple the topside to the substructure. Analysis has shown that welding is unnecessary because the dynamic motions of the substructure, even during expected hurricane conditions, will not cause plate  125  to separate or lift off of bucket  135  due to the weight of installed topside  100 . Further, when weldless coupling system  120  is utilized to couple a topside to a substructure, precise alignment of the topside prior to deballasting the substructure to engage and lift the topside is also unnecessary for a number of reasons. For one, the topside will not be welded to the substructure once engaged. Also, bucket  135  provides a significantly increased area upon which leg  110  may land, relative to that available during conventional float-over procedures in the absence of coupling system  120 . Thus, the topside may be misaligned to a degree and leg  110  will still land within the inner envelope of bucket  135  as the substructure is deballasted. Further, the structural integrity of base plate  145  in combination with support from gusset plates  175  is capable of supporting leg  110  with annular plate  125  coupled thereto of withstanding asymmetric vertical loading, such as those resulting when leg  110  lands within bucket  135  off-center of centerline  190  of leg  115 . Similarly, annular plate  125  is also capable of withstanding asymmetric vertical loading resulting from off-center engagement of plate  125  with bucket  135 . 
         [0034]    If desired, weldless coupling system  120  may be supplemented with a positive tie-down means coupled between topside  100  and substructure  105  in case of an unforeseen extreme event, such as an atypical hurricane or an earthquake. For example, and referring now to  FIG. 4 , one or more tensioning members  400  may be coupled between topside  100  and substructure  105 , as shown. Tensioning member  400  includes a support plate  405 , a connector  410  and a tie rod  415  extending therebetween. Support plate  405  is coupled to an upper surface  420  of topside  100 . Support plate  405  includes a throughbore  435  configured to receive the upper end  440  of tie rod  415 . Connector  410  is coupled to an upper surface  430  of substructure  105 . Tie rod  415  is coupled to connector  410  and extends upward through throughbore  435  of support plate  405 . In some embodiments, tie rod  415  extends within a deck column member  425 , as shown. Upper end  440  of tie rod  415  is coupled to support plate  405  by a tensioning and securing device  445  seated on plate  405 . Device  445  is configured to apply a tension load to tie rod  415 . 
         [0035]    Like those of coupling system  120 , components of tensioning member  400  are coupled to topside  100  or substructure  105 , as appropriate, prior to transport of topside  100  and substructure  105  to the desired offshore installation site. After topside  100  is landed on substructure  105  as described above, meaning leg  110  of topside  100  with plate  125  thereto is landed within bucket  135  coupled to leg  115  of substructure  105 , tie rod  415  is inserted through throughbore  435  of support plate  405  and lowered to engage connector  410 . Securing and tensioning device  445  is then disposed over upper end  440  of tie rod  415  and seated on support plate  405 . Device  445  is next operated to apply a tension load to tie rod  415 . Once tie rod  415  is tensioned to the desired load, installation of tensioning member  400  is complete. 
         [0036]    In some embodiments, tensioning member  400  may be installed between legs  110 ,  115  of topside  100  and substructure  105 , respectively, coupled using weldless topside coupling system  120 , shown and described above with reference to  FIGS. 1-3 . In such embodiments, connector  410  of tensioning member  400  is coupled to upper surface  155  of base plate  145  of weldless coupling system  120 , as shown in  FIG. 5 . Also, support plate  405  of tensioning member  400  is coupled to an upper surface  115  of topside  100  from which leg  110  extends. Otherwise, the remaining components of tensioning member  400  are positioned and installed as described above in reference to  FIG. 4 . 
         [0037]    While preferred embodiments have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teachings herein. The embodiments described herein are exemplary only and are not limiting. Many variations and modifications of the systems are possible and are within the scope of the invention. For example, the relative dimensions of various parts, the materials from which the various parts are made, and other parameters can be varied. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims.