Patent Publication Number: US-6334739-B1

Title: Stinger for J-Lay pipelaying system

Description:
RELATED APPLICATIONS 
     This application claims the benefits of application 60/083,964 filed May 1, 1998, incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to laying underwater pipelines in relatively deep water using a J-Lay method from a floating vessel and, more particularly, to installing underwater pipelines on the seabed and/or connecting the same to floating terminals at the surface. 
     2. Description of the Related Art 
     Subsea pipelines have most often been laid on the ocean floor by connection of welding on the deck of a barge, lowering off the back of the barge down a stinger, and then laying on the ocean floor. The curve down off the barge and then reverse curve onto the ocean floor gives a “S” bend in the pipeline during the lay process. The stinger allows the pipeline and its associated weight to be curved down toward the ocean floor without kinking or damaging the pipeline. As water depths become greater; the size, weight, and cost of the stinger become prohibitive. 
     In deeper water, it is advantageous to connect the pipeline vertically and lower it directly into the water, with a single bend at the ocean floor. This gives the shape of a “J” for a system known as J-Laying pipe. The “J” cannot be vertical at the top, but rather must have an angle with a horizontal component to be able to pull horizontal tension on the pipeline as it is being laid onto the ocean floor. If it does not have horizontal tension, it will buckle as it is laid on the ocean floor and be damaged beyond use. 
     Previous J-Lay Towers have lowered the pipe vertically and required that the pipe be bent around a cone shaped stinger to gain the required exit angle, or have had fixed angle towers with the ideal exit angle approximated. Bending the pipe around a stinger from a vertical tower makes the connections difficult and induces a high degree of stress in the pipeline. 
     The fixed angle towers require that the vessel drive along the pipe route in order to lay the pipeline. In cases where there is a cross wind or cross current, it can be advantageous to turn the vessel into the weather move the vessel somewhat sideways down the pipeline route. In some cases, the vessels will not have the power to hold course when being broadsided by the weather but could hold course if it could face the weather. In other cases, the stability of the vessel is simply better when facing the weather. 
     Additionally, as water depths and pipeline tension requirements change, the necessary angle of departure of the pipeline can change. Past J-Lay towers have had limited capability at best for changing the angle of the tower to facilitate laying the pipelines. 
     Rigidly installed, vertical towers engender a number of problems caused by an inability to respond in real time to the dynamic forces encountered during pipe laying operations. For instance, welding and assembly operations are performed at the working floor on pipe with a substantial imposed moment. Other deficiencies include the fact that they do not allow: 1) control of the bending stress and tension within the pipe string as it is deployed in an arc to the sea bed; 2) the laying vessel to weather vane or rotate about the pipe and thereby prevent torsional wind-up of the pipe string; and 3) precise control of the pipe lay envelope. Further, current J-Lay tower designs omit any means for precise and accurate alignment of the pipe string and new pipe joints during the welding process. 
     Current stinger designs have a problem in that the internal geometry of the stinger is usually fixed at the diameter of the pipe string being deployed. In order to allow the passage of large diameter packages integrated into the pipe string, the stinger must be dismantled or removed from around the hanging pipe string. Additionally, such stingers only act as guide conduits for the pipe and do not stabilize, i.e., control the alignment of, the pipe as it emerges from the weld floor. 
     An additional alternative to the laying of steel pipelines for this type service has been to lay flexible pipelines. As the pipeline is basically a long pressure vessel, it is inherently obvious that a simple steel tube pipeline would be substantially more economical to manufacture and more reliable than a multi-part flexible pipeline or hose of the same internal diameter and the same high pressure rating. These flexible pipelines have found a place in the market due to the difficulties in the field installation of the lower capital cost steel tube pipeline. The J-Lay Tower attempts to enhance the cost effectiveness of the installation of the steel tube pipeline alternative. 
     The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above. 
     SUMMARY OF THE INVENTION 
     The object of this invention is to provide a tower which can be gimbaled to different angles while facilitating the welding of pipeline sections for laying pipelines on the ocean floor from a floating vessel. 
     A second object of this invention is to provide guidance and stabilizing means for the pipe sections while the connection by welding processes are being done. 
     A third object of this invention is to provide means for accurately aligning the ends of the pipelines for welding and laying. 
     Another object of this invention is to limit the bending radius of the pipeline exiting the J-Lay tower to limit the maximum stresses imposed upon the tower. 
     Another object of this invention is to provide means for the support of the pipeline while lowering it as new sections are added by welding. 
     Another object of this invention is to provide means to fold guidance rollers out of the central area of the stinger when required to pass packages which are of a larger diameter than the pipeline. 
     Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon referring to the drawings which follow. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates the apparatus for assembling and deploying pipe string underwater, mounted on the rear of a floating vessel and deploying a pipeline. 
     FIG. 2 shows a section of pipeline which has a shoulder at the upper end for handling and weld preparations at each end. 
     FIG. 3 shows a half section enlargement of the shoulder at the top of the section of pipeline of FIG.  2 . 
     FIG. 4 shows a half section of a double collar which is used to wrap around the shoulder of FIG. 3 for the purpose of providing two independent shoulders for handling. 
     FIG. 5 shows a top view of the double collar of FIG.  4 . 
     FIG. 6 shows a more detailed perspective view of the apparatus. 
     FIG. 7 is a partial cross-sectional, side view of part of the tower system. 
     FIG. 8 is a front view of the clamp assembly which will engage and lower the double collar and therefore the pipeline. 
     FIG. 9 shows a top view of the clamp assembly of FIG. 8 with the doors open for accepting the double collar. 
     FIG. 10 shows the clamp assembly of FIG. 9 with the doors closed around the double collar and pipeline. 
     FIG. 11 shows a half section of the swivel bearing 
     FIG. 12 shows the clamp assembly at the top of its stroke between the main drums or pulleys, with the double collar engaging the pipeline and clamp shoulder on the right side of the centerline and also the swivel bearing inserted between the double collar and the clamp shoulder on the left side of the centerline 
     FIG. 13 is a half section view of a screw jack as employed in the articulating joint. 
     FIG. 14 illustrates the stinger of the apparatus which minimizes the bending radius of the exiting pipeline. 
     FIGS. 15 illustrates the erector system of the embodiment. 
     FIG. 16 illustrates the tongs which are used to handle the pipeline. 
     FIG. 17 illustrates tongs which are used to handle the pipeline, having rollers rather than pads to allow moving the tongs along the pipe section under load. 
     FIG. 18 shows a partial section through the weld alignment and placement system. 
     FIG. 19 shows a half section through section  18 . 
     FIG. 20 illustrates a bootstrap mechanism as may be used in some alternative embodiments to erect the articulated tower. 
     FIG. 21 illustrates a top view of FIG.  20 . 
     FIG. 22 illustrates the installation of the bootstrap mechanism of FIGS. 20 and 21 onto the tower. 
    
    
     While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover ail modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS 
     Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort, even if complex and time-consuming, would be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. 
     Referring now to FIG. 1, the j-lay tower  10  is shown on a floating vessel  12  in a body of water  14  with a pipeline  16  extending below the j-lay tower  10  around a bend  18  and onto the ocean floor  20 . The j-lay tower  10  is shown with a mast  21  including a lower section  22 , a middle section  24 , and an upper section  26 ; a working table  28 ; and a skid  30 . A new pipeline section  32  is shown on the erector  34  with cable  36  attached for pulling the erector up to the mast sections. Jib cranes  38  and  40  are provided for handling of the new pipe section  32  up to the erector  34 . As can be noted, the tower is inclined at an angle convenient to the laying of the pipeline. Jack assemblies,  42  as will be described later, assist in the changing of the tower angle as required. Stinger  44  provides internal rollers whose inner diameter provide a curvature to prevent overbending of the pipeline. The preferred running style is with the tower perfectly aligned to the pipeline, while using the angle gained around the curvature of the stinger as a margin of error if unforeseen events occur. 
     Referring now to FIG. 2, a pipe section  32  shows upper weld preparation  50 , lower weld preparation  52 , shoulder  54 , and buttweld  56 . Buttweld  56  is made on shore to attach the j-lay collar  58  to a plain section of pipe so that the plain section of pipe can be conveniently handled offshore. 
     Referring now to FIG. 3, an enlarged view of the j-lay collar  58  is shown. 
     Referring now to FIG. 4, a double collar  60  is shown which is made in two halves and can be wrapped around the shoulder  54  on j-lay collar  58 . After welding a new section of pipeline to the pipeline  16  hanging from the tower, two shoulders are required as will be discussed later. The double collar  60  engages the j-lay collar with a groove  62  and provides an upper shoulder  64  and a lower shoulder  66 . Hinge  68  allows the double collar  60  to open and latch  70  holds it closed during operations. Handles  72  are provided for handling. 
     Referring now to FIG. 5, a top view of the double collar  60  is shown. 
     Referring now to FIG. 6, a perspective view of the apparatus is shown with the erector  34  shown partially raised toward the mast sections  22 ,  24 , and  26 . Main cylinders  80 , with cables  82  over drums  84  are used to lift the travelling table  86  to power the system. Outriggers  88  are used to distribute the weight of the system over a large deck area. Notch  90  in the top of the upper mast section  26  allows longer sections of new pipe to be added to the pipeline by having intermediate j-lay collars in place. Bushings  92  are provided for the support of the pipeline at the working table  28 . 
     Referring now to FIG. 7, a half section thru the working table  28  area is shown with the  62 ″ bowl  100  forming the internal portion of the working table  28 , the  62 ″ split bushing  102  landed in the  62 ″ bowl  100 , the  26 ″ split bushing  104  landed on the  62 ″ split bushing  102 , and the double collar  60  landed on the  26 ″ bushing  104 , in turn supporting the pipeline  16  upon shoulder  54 . 
     Attached to the bottom of  62 ″ bowl  100  by bolts  110  is a stinger swivel  112  including an upper flange  114 , a lower flange  116 , a central barrel  118 , and a spherical section  120 . The spherical section  120  fits closely within a cylindrical bore  122  which is attached by conical member  124  to skid  30  by welding. Spherical section  120  has a spherical center  126 . Bolts  130  connect stinger  44  to the lower flange  116  of the stinger swivel  112 , and will be further described later. 
     Each of three Jack assemblies  42  includes a spherical center  132 . Each of the three jack assembly spherical centers  132  and the stinger swivel spherical center  126  are approximately in a common plane. Three jack assemblies are shown as they can be used at the bottom of their stroke for a horizontal working table, and only be extended up for tilting the table. An alternative embodiment would be to use  2  jacks and one rigid leg. This would simplify the construction from the fact that only two powered jacks would be required, but would complicate it in that the jacks would need to start in mid stroke for a horizontal plane and would each require a longer stroke. 
     The working table  28 , stinger swivel  112 , and the jack assemblies  42  are shown in their lowest position with respect to the skid  30 . If any one of the three jack assemblies  42  are actuated to move upwardly, the portion of the working table  28  above that jack assembly will be raised, tilting the working table and all parts attached to the working table including the mast, stinger swivel, and stinger. The mast is intended to operate in a near vertical mode, i.e. +/−15 to 25 degrees from vertical. 
     If there is a high pipeline load, i.e. 1,000,000 lbs., along the pipeline  16  and the working table and pipeline are tilted, one can readily see that there would be a vertical and horizontal component to the 1,000,000 lbs. The jack assemblies  42  are tall and slender and adapted to support a vertical load, but not well adapted to support a horizontal load. A slip plane  140  is established in the jack assembly  42  to prevent a horizontal or side load from being imparted into the jack assemblies  42 . With the jack assemblies  42  having little ability to support a horizontal force, the tendency to move horizontally is blocked by the engagement of the spherical section  120  with the cylindrical bore  122 . With the cylindrical bore  122  having no capacity to support a vertical load, the components of force are divided into the vertical force to the jack assemblies and the horizontal force to the stinger swivel. 
     Mast  21  is connected to the working table  28  by a pivot pin  142  and a locking pin  144 , which will be discussed later in conjunction with erecting the mast. 
     Referring now to FIG. 8, a front view is seen of the travelling table  86  showing the main clamp section  150 , two doors  152  and  154 , and two wing portions  156  and  158  with lower bearing surfaces  160  and  162 . The travelling table  86  itself is fabricated of a top plate  164 , a bottom plate  166 , a left plate  168 , a right plate  170 , a left guide  172  and a right guide  174 . Wing portions  156  and  158  bear and support on left plate  168  and right plate  170  respectively. 
     Refer now to FIG. 9 showing a top view of the travelling table, doors  152  and  154  are swung open to allow the insertion of the pipeline. 
     Referring now to FIG. 10, the doors  152  and  154  are closed as if to accept the pipe for support, with pin  180  installed to keep the doors closed. Hinge pins  182  and  184  allow for the opening of the doors  152  and  154  and cylinders  186  and  188  power the movement of the doors. Cylinders  190  and  192  provide means to slide the clamp assembly backwards and forwards to allow the shoulder  194  to be moved away from or under the shoulder on the double collar  60 . (See FIG. 12) 
     Plates  196  and  198  provide attachment holes for the cables  82  as seen in FIG. 6 to lift the travelling table  86  and therefore the pipeline  16 . The holes in plates  196  and  198  are a substantial distance apart which is difficult to bridge safely by a single member because of the high moment generated by the overall distance. The method of this construction allows the main clamp section  150  to only be required to bridge between the support of plates  168  and  170 , and therefore substantially reduce stresses on the parts generated by this first moment. Additionally the second moment established in the travelling table is a function of the distance between the support of plate  168  and  170  areas and the holes for the cables on the outside. Therefore, the stress in upper plate  164  and lower plate  166  is generated by the second moment in which is again substantially smaller than the moment which would be generated by similar forces across the full distances from plates  196  and  198 . By this means the division of distances provides lower stresses than might otherwise be seen and allows a workable system at lower overall cost and weight. 
     Referring now to FIG. 11, a rotating bushing  200  is shown which allows the rotation of the pipeline  16  relative to the floating vessel  12 . The unit is made of a lower non-rotating body  202 , an upper rotating body  204 , several low friction bearing rings  206 , and a retaining screws  208 . 
     Referring now to FIG. 12, the travelling table is shown near its uppermost position between the drums  84 . On the right side of the centerline a double collar  60  is shown around the j-lay collar  58 , with the upper shoulder  64  landed on the shoulder  194  within the main clamp section  150 . The left side of the centerline shows the rotating bushing  200  landed over the end of the pipeline  16  and the double collar  60  clamped around the j-lay collar  58 . Picking up on the travelling table  86  causes the weight of the pipeline  16  to be carried on the low friction bearings  206  within the rotating bushing  200 , conveniently allowing the pipeline  16  to be rotated relative to the floating vessel  12 . 
     Referring now to FIG. 13, a jack assembly  42  is shown in detail. The upper end has a flange  210  for interconnecting to the bottom of the working table  28  and a spherical section  212  around the spherical center  132  as previously discussed. A slip plane  140  is established by having upper and lower low friction bearings  214  and  216  and a flange  218  positioned between the bearings. The flange  218  is a part of a male threaded shaft  220  which is rotated by gear  234  to move the upper portion of the jack assembly  42  up and down. 
     Side gaps  222  and  224  allow for the slip plane  140  to provide horizontal freedom in addition to rotary freedom. A square shaft  226  engages a square hole  228  and causes the male threaded shaft  220  to be rotated in response to the input of motors (not shown), which drive worm gears  230  and  232 , wheel gear  234 , and interconnecting pieces  236 . Internally threaded base  240  utilizes bolts  242  to secure the jack assembly  42  to skid  30 . 
     Referring now to FIG.14, stinger  44  is shown comprised of six stations  250 ,  252 ,  254 ,  256 ,  258 , and  260  which include multiple rollers  262  to restrict the bending radius of the pipeline. All stations are equipped with cylinders  264  to swing the arms  266  and rollers  262  of the stations out of the bore to allow large object to pass through the stinger and into the bore to provide the preferred bending radius. Stations  250  and  252  have four arms  266  at 900 apart. Two adjacent arms  266  fold down to a fixed position at a distance from the centerline of the stinger approximately equal to the radius of the pipeline  16 . The other two arms  266  include cylinders  264  which press the rollers  262  on the arms  266  tightly against the pipeline  16  after being folded into the bore of the stinger  44 . In this manner, the pipeline  16  is immobilized against movement during the welding process. 
     Each of the additional stations  254 - 260  have arms  266  which fold down to a fixed position of a progressively larger radius from top to bottom. At the bottom of the stinger  44 , a camera  270  or similar viewing device is installed to monitor the position of the pipeline  16  within the stinger  44 . 
     Referring now to FIG. 15, the erector  34  with new pipeline section  32  is shown in the horizontal position. Erector boxes  271  and  272  provide clamps  273  and  274  for securing new pipeline section  32  to erector  34 . Additionally, erector boxes  271  and  272  may provide rollers  275  and  276  for supporting new pipe section  32  and the rollers may be powered with hydraulic motors or the such like to rotate the new pipe section  32 . This can be beneficial when the new pipe sections are not perfectly round and the out of roundness of one joint is desired to be matched with the out of roundness of the next joint to simplify the welding process. 
     The erector  34  is attached to the working table  28  by hinge  280 . Item  282  is the erector  34  shown pulled partially to the mast by cable  284 . The erector  34  and new pipe section  32  is represented fully up in the mast by item  286 . As the working table  28  can be gimbaled up to 15° in any direction by operation of the jack assemblies  42 , the required position of the erector  34  to properly engage the mast sections  22 ,  24 , and  26  is difficult to predict. By hinging the erector on the working table itself at  280 , the erector will automatically track the position of the mast sections and automatically be correctly engaged when erected to the position shown at  286 . 
     Within the mast, a centralizer  287  and a straightener  288  are shown which cooperate with the travelling table  86  in making the weld between the current pipeline  16  and the new pipeline section  32  at  289 . These will be discussed further detail later. 
     Referring now to FIG. 16, tongs  290  are shown which are utilized by the jib cranes  38  and  40  to handle the new pipe sections  32 . The tongs have pads  292  to engage the pipeline while protecting the coating, a link  294  at the top which when pulled causes linkages  296  to close, automatically locking onto the new pipe section  32 , and a hydraulic cylinder  298  to release the tongs  290  when desired. 
     Referring now to FIG. 17, an alternate style of tong  300  is shown which provides rollers  302  which can move along the new pipeline section  32  to accommodate the arcuate swing of the jib cranes. 
     Referring now to FIG. 18, a partial section thru a centralizer  287  is shown which is used to align the bottom of the new pipeline section  32  near the bottom with the top of the already welded pipeline in at the working table at  296  (see FIG.  15 ). Four hydraulic cylinders  310 ,  312 ,  314 , and  316  press on pivot arms  320 ,  322 ,  324 , and  326  to load rollers  330 , 332 ,  334 , and  336  against new pipe section  32 . By adjustment of the pressures and positions of the cylinders, the lower end of new pipeline section  32  can be properly aligned with the top of the pipeline  16  for welding. 
     A similar device referred to as a straightener  288  is positioned near the center of the new pipeline section  32  to push the center of the new pipeline section while the upper and lower ends are restrained by the travelling table  86  and the centralizer  287  respectively. This imparts a bending moment to the new pipeline section  32  which can promote better angular alignment of the faces of the ends of the pipe sections for welding. 
     Referring now to FIG. 19, a half section of the straightener  287  or centralizer  288  is shown with the cylinder  340  for folding the units up and out of the way to allow passage of the travelling table  86  when required. 
     Referring now to FIGS. 20 and 21, bootstrap mechanism  350  is shown which is bolted to the top of the working table  28  with bolts  352 , and provides a heavy chain  354  attached to a dummy double collar  356 . As shown, the heavy chain  354  is wrapped around a reinforced curved member  358 . 
     Referring now to FIG. 22, the bootstrap mechanism  350  is installed on the working table  28 , the mast  21  is attached at pivot pin  142  and the dummy double collar  356  is connected into the travelling table  86 . When the main cylinders  80  are pressured for extension, the cables pull on the travelling table  86 , which pulls on the dummy double collar  356 , which pulls on the heavy chain  354 , which pulls on the floor of the working table  28 . Rather than lifting the working table (lifting oneself by your bootstraps), the mast  21  itself is erected with its attachments. In this way the power of the system can be used to advantage to self erect itself when adequate cranes are not available. 
     The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.