Abstract:
A modified strongback for laying pipeline offshore that utilizes a movable clamp. One end of the strongback is modified to include a travel mechanism. A pipe clamp is mounted on the travel mechanism to allow movement of the clamp as necessary to accommodate different pipe joint lengths. A mechanism for locking the clamp in the desired position is provided on the strongback.

Description:
FIELD AND BACKGROUND OF INVENTION 
       [0001]    The invention is related to offshore pipe laying equipment and more particularly to equipment for handling long lengths of pipe. 
         [0002]    Near vertical laying of pipeline offshore utilizes specialized equipment for handling lengths of pipe (pipe joints). U.S. Pat. Nos. 5,421,675 and 5,464,307 are directed to equipment for near vertical laying of pipeline offshore and provide descriptions of the handling steps required for pipeline lay operations. Near vertical laying of pipeline requires equipment capable of picking up a pipe joint from the horizontal position and moving it into a near vertical position for adding it to the pipeline being installed. This equipment positions the pipe joint in alignment with the pipeline so that the pipe joint can be welded to the pipeline. Existing arrangements utilize a strongback, typically a triangular frame with clamps for gripping the pipe joint and moving it into a tower for welding to the pipeline. Depending on the vessel arrangement, the strongback or tower may be used to hold the pipe joint in position during the welding step. 
         [0003]    To align the pipe joint coaxially with the pipe line for welding, the clamps in the strongback or tower have been adjustable in the radial direction. 
         [0004]    In the past, four forty foot pipe sections welded together at a fabrication facility on shore has been the standard length of one pipe joint. The clamps in the strongback have been in fixed positions that are spaced specifically to handle this length pipe joint. The required number of pipe joints for a pipeline job was fabricated on shore, loaded on a barge, and transferred to the pipe lay vessel as required during the laying operation to add the pipe joints to the pipeline. 
         [0005]    Recent changes in pipeline requirements have led to varied pipe joint lengths. The result is that the prior standard clamp spacing in the strongback is no longer able to clamp one end of the pipe joint and provide the required support over the full length of the pipe joint. 
         [0006]    The near vertical tower in some pipe laying arrangements uses a gripper around the pipe that moves in the axial direction of the pipe for paying out the pipeline after a pipe joint has been welded to the pipeline or for purposes of aligning pipe joints for welding. However the applicants are not aware of any strongback modifications that address the need for accommodating different pipe joint lengths that allow the use of a single strongback on a vessel no matter what the current variation in pipe joint length may be. It should be kept in mind that a single pipe joint of steel pipe may weigh several tons, depending upon the diameter and wall thickness of the steel pipe. Thus, the strongback and associated equipment for handling the pipe is large, heavy, expensive and should be capable of multiple duties to provide the most cost efficient pipe laying vessels and equipment. 
       SUMMARY OF INVENTION 
       [0007]    The present invention is drawn to a modified strongback that utilizes a movable clamp. One end of the strongback is modified to include a travel mechanism. A pipe clamp is mounted on the travel mechanism. Means for locking the clamp in a desired position is provided on the strongback. 
         [0008]    The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming part of this disclosure. For a better understanding of the present invention, and the operating advantages attained by its use, reference is made to the accompanying drawings and descriptive matter, forming a part of this disclosure, in which a preferred embodiment of the invention is illustrated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    In the accompanying drawings, forming a part of this specification, and in which reference numerals shown in the drawings designate like or corresponding parts throughout the same: 
           [0010]      FIG. 1  is an elevation view of the invention. 
           [0011]      FIG. 2  is a plan view of the invention. 
           [0012]      FIG. 3  is an enlarged view of the area indicated in  FIG. 1 . 
           [0013]      FIG. 4  is an enlarged view of the area indicated in  FIG. 2 . 
           [0014]      FIG. 5  is an elevation view similar to that of  FIG. 3  that illustrates the range of the movable clamp. 
           [0015]      FIG. 6  is a sectional elevation view as indicated by lines  6 - 6  in  FIG. 4 . 
           [0016]      FIGS. 7 and 8  are elevation views that illustrate the invention in operation with the movable clamp in different positions. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0017]    The invention is generally indicated in  FIG. 1  by numeral  10 . The improved strongback  10  is generally comprised of a strongback  12 , a modified section  14  on the strongback  12 , and a movable clamp  16  on the modified section  14 . 
         [0018]    The strongback  12  is generally triangular in cross section, which is typical in the industry to provide the required strength and means for mounting clamps  18 . Clamps  18  are fixed in their position relative to the length of the strongback  12 . Clamps  16  and  18  are extendible along the longitudinal axis of the clamps (radially relative to the strongback  12 ) for gripping pipe  20  ( FIGS. 7 &amp; 8 ) or adjusting the position of pipe  20  as required when welding a new pipe joint to the existing pipeline. 
         [0019]    As best seen in  FIG. 4-6 , the modified section  14  is provided with means  22  for moving and securing clamp  16  along the length of the modified section  14 . Movable clamp  16  is shown in different possible positions in  FIG. 5 . Means  22  for moving and securing clamp  16  is comprised of a top rail  24 , a gear arrangement  26  (preferably rack and pinion), brake units  28 , and a locking mechanism  30 . 
         [0020]    Instead of being triangular as in a standard strongback, the modified section  14  is rectangular. The gear arrangement  26  is mounted on the top rail  24  of the modified section  14 . The top of the movable clamp  16  is movably engaged with the gear arrangement  26  such that the movable clamp  16  moves on the gear arrangement  26  along the longitudinal axis of the modified section  14  as the gear arrangement  26  is turned. 
         [0021]    As best seen in the sectional view of  FIG. 6 , the locking mechanism  30  is comprised of the lower rails  32  on the modified section  14  being provided with a plurality of apertures  34  along the length of the lower rails. At the lower portion of the clamp  16 , a guide pin, not shown, allows for easy alignment of the locking pin, not shown. The guide pin also adds redundant support for the clamp  16  in the event the brake units  28  fail to properly function. A locking pin, not shown, is inserted through an aperture in the movable clamp  16  and the desired apertures  34  in the lower rails to lock the clamp  16  in the desired position. Brake units  28  are positioned at the upper end of clamp  16  and hold the upper portion of the clamp  16  in the desired position on the gear arrangement  26 . 
         [0022]    In operation, the movable clamp  16  is unlocked and moved on the gear arrangement  26  by turning the gear arrangement  26  until the clamp  16  is in the desired position. The brake unit  28  is used to lock the upper portion of the clamp  16  to the gear arrangement and a pin is inserted through the apertures  34  in the lower rails  32  of the modified section  14  and the clamp  16  to lock the lower portion of the clamp  16  in position at the lower rails  32 . The movable clamp  16  and fixed clamps  18  are then used to grip a pipe section as illustrated in  FIGS. 7 and 8 .  FIGS. 7 and 8  illustrate the movable clamp  16  in different positions along the modified section  14  of the strongback  10 . 
         [0023]    The invention provides several advantages over the prior art fixed clamp arrangement. 
         [0024]    The traveling clamp allows a wider range of pipe lengths to be handled on the near vertical pipe lay vessel without loss of operational efficiency. This is accomplished through selective positioning of the clamp along the longitudinal axis of the pipe joint. 
         [0025]    The traveling clamp engage/disengage arrangement is designed to minimize the time required for clamp engagement. 
         [0026]    The traveling clamp engagement lock-off arrangement is designed for fail safe operation (i.e., does not require hydraulic or air power for maintaining engagement during pipe lay operations). 
         [0027]    A rack and pinion gear arrangement is used for moving/repositioning the traveling clamp along the clamp rails. 
         [0028]    Overall cycle time efficiency is maintained by keep time required for disengaging/moving/repositioning of the traveling clamp to a minimum. Controls for repositioning and engagement of the traveling clamp are operated remotely. 
         [0029]    The traveling clamp allows handling of pipe joints of an increased range of lengths without any loss of operational efficiency. By allowing an increased range of pipe lengths, the cost of supplying the pipe lengths is reduced, thereby lowering the overall cost of the project. 
         [0030]    While specific embodiments and/or details of the invention have been shown and described above to illustrate the application of the principles of the invention, it is understood that this invention may be embodied as more fully described in the claims, or as otherwise known by those skilled in the art (including any and all equivalents), without departing from such principles.