Abstract:
A modular rotating carousel assembly for storage and unspooling of pipe or cable is provided that comprises a plurality of triangular subassemblies; each triangular subassembly comprises a base member and at least one pair of connecting members; the connecting members are connected together at one end to form an apex and are connected at the other end to the base member; the base members of the plurality of triangular subassemblies are rotatably connected together to form a first circle; wherein the apexes of the connecting members extend outwardly from said first circle; and a plurality of rotating caster members is positioned beneath the rotatable connection of a plurality of said base members. Additional sets of triangular subassemblies are built up on concentric circles until the desired size of carousel is formed. A drive mechanism is provided that includes a motor that rotates a perimeter drive chain that engages sprocket pads spaced about the circumference of the carousel. A modular hub is provided that includes a set of fixed plates arranged in a circle and a set of adjustable plates that are connected to the fixed plates. A set of segments forming a uniform circular shape is attached to the outside surface of the moveable plates and vertically oriented curved plates are positioned about the outer surface of the set of segments to provide a uniform surface for casters to rotate about.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    Not applicable. 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       REFERENCE TO MICROFICHE APPENDIX 
       [0003]    Not applicable. 
       BACKGROUND OF THE INVENTION 
       [0004]    1. Field of the Invention 
         [0005]    The field of the invention is pipe storage devices and in particular, pipe storage devices that rotate pipe or cable about a vertical axis. 
         [0006]    2. Description of the Related Art 
         [0007]    In the oil and gas industry, flexible and semi-flexible tubular goods and cables are stored and transported on spools or carousels. The rotating axes of spools are oriented either horizontally or vertically while the rotating axes of carousels are oriented vertically. 
         [0008]    Carousels have been used for many different purposes over the years. For example, U.S. Pat. No. 1,819,656 shows the use of a carousel to revolve a stage. U.S. Pat. No. 3,968,961 shows a merry-go-round carousel. U.S. Pat. No. 2,694,144 and US Patent Publication 2003/0145760 show carousels used for rotatable aircraft storage hangars. U.S. Pat. No. 6,745,699 shows a carousel used to rotate production parts on a production line. The subject of this invention relates to carousels used to store and unspool pipe or cable, as would be typically in the oil and gas industry. 
         [0009]    Most carousels rotate on uneven surfaces because it is not generally possible or practical to provide a truly flat surface. The flatness can vary from approximately ±0.10 inch to ±3 inches or more and the possible variation in surface flatness increases as the size of the carousel increases. The carousel of this invention may be either in a fixed location, such as in a manufacturing building or it may be on the deck or inside of a marine vessel. If a carousel is built and installed in a building, it would typically rotate on a concrete based, or other hard surface, which generally could be level to within ±0.25 inch, but possibly as much variation as ±0.5 inch, or more. For applications involving mounting a carousel on a marine vessel, the variation in support surface flatness can be significant. Moreover, a deck of a vessel, from which pipes or cables are deployed offshore, can be curved or can flex with the variable forces that are encountered in the offshore environment. Marine vessels typically have flexibility designed in, to prevent stress damage from the changing and considerable ocean forces. 
         [0010]    U.S. Pat. Nos. 3,804,111 and 3,941,146 show the use of a carousel for purposes of storing drill pipe. Both U.S. Pat. Nos. 3,804,111 and 3,941,146 also show the vertical displacement of wedge shaped sectors to raise the entire carousel sector in response to an uneven support surface. U.S. Pat. No. 3,965,713 shows the use of a carousel to store and unspool pipe during offshore pipe lay operations in preparation for oil or gas production. 
         [0011]    There can be substantial lengths and weights of tubular goods that are coiled onto the drill pipe and offshore pipe carousels. As the lengths and loads increase, the support structure of the carousel can become extremely important. As the lengths of the pipe to be stored increases, the overall diameter of the carousel must also increase. As the diameter of the carousel increases, it becomes probable that the underlying support surface, which supports the carousel mechanism and the weight of the pipe on the carousel, will be uneven and will not be perfectly flat. Carousels are typically supported by casters that rotate about circular rails. If the underlying support is uneven, the casters can rise up and lose contact with the supporting circular rails. If that happens, the load is transferred to an adjacent caster or a caster that is in contact with the rails. Because of the extreme loads that are carried by the carousel, the concentrated loads placed on those casters that are in contact with the rail can exceed the capacity of the casters, which can cause the load bearing casters to fail. The problem can then become aggravated because if one or more casters fail, the pipe weight can then immediately and catastrophically be transferred to other casters that are in contact with the rails. The failure cascades by then causing the remaining casters to be exposed to the load that is no longer supported by the failed casters. 
         [0012]    It may also be desirable to move flexible pipe from the manufacturing location to a pipe lay vessel, from which the flexible pipe may then be installed into the subsea water column. The decks of barges and work vessels are somewhat flexible by design, to respond to wave and hydrodynamic forces that are imposed on them when they are operating in the oceans, seas and the challenging offshore environment. The flexing causes the underlying support to become uneven, which can again cause the problem of all casters not being in contact with the circular rails. 
         [0013]    Additional problems can occur when extremely large diameter carousels are constructed. Because of the extreme transverse loads that occur when the carousel is rotated during the spooling or unspooling of pipe, it is not practical to use a conventional center “kingpin”. The transverse loads that are placed on the center kingpin would require that the kingpin be extremely large. Furthermore, the radius of the center hub must be no less than the minimum bend radius of the flexible pipe that is wound about the center of the carousel. 
         [0014]    The large diameter necessary to accommodate long lengths of relatively large diameter pipe also creates challenges related to the mechanism that is used to rotate the carousel. Motors may be attached to individual casters, as shown in U.S. Pat. Nos. 3,804,111 and 3,941,146. As the number of casters increases, and the size and weight of the carousel increases, the number of individual motors can become unwieldy and unreasonably expensive. Gears may be attached about the circumference of the carousel, with a motor engaged with the track, as shown in U.S. Pat. No. 3,965,713. This requires a very large, heavy and expensive gear to be used. A motor, attached to a rotating gear, may also be used to engage a chain that encircles the entire carousel, as shown in U.S. Pat. No. 6,745,699. Unfortunately, when a chain encircles the entire carousel, it becomes extremely heavy and expensive, and if the weight of the chain sags it can cause serious operational problems. 
       BRIEF SUMMARY OF THE INVENTION 
       [0015]    A modular rotating carousel assembly and method of constructing the assembly for storage and unspooling of pipe or cable is provided that optionally includes a plurality of concentric support rings. A plurality of triangular subassemblies comprise a base member and at least one pair of connecting members. The base members are oriented substantially tangentially to the support ring above which they are positioned. Each of the connecting members is connected at one end to the base member and connected at the other end to the other connecting member to form an apex. The apex is oriented outwardly from the center of the concentric support rings. The triangular subassemblies are rotatably interconnected at the base members about the circumference of the support rings whereby the base members form an articulating substantially circular ring above each support ring above which each base member is positioned. 
         [0016]    The base members of the plurality of triangular subassemblies may also simply be rotatably connected together to form a first circle; wherein the apexes of the connecting members extend outwardly from first circle; and then positioning a plurality of rotating caster members beneath the rotatable connections of the plurality of base members. Concentric support rings may be used to support the caster members if desired, but they are optional. 
         [0017]    The base members of additional triangular subassemblies are rotatably interconnected to the apexes of the connecting members of existing triangular subassemblies whereby the interconnected base members form an additional articulating substantially circular ring above the support ring above which each base member is positioned. 
         [0018]    Tangential support members are rotatably connected between each apex of the triangular subassemblies. The tangential support members are positioned substantially tangential to the support ring above which each tangential support member is positioned; whereby the tangential support members provide movement in the vertical direction and provide lateral support to the triangular subassemblies. 
         [0019]    Rotating casters are positioned below the triangular subassemblies at each of the three outer points of each triangular subassembly to support the triangular subassemblies and to allow the triangular subassemblies and the carousel to rotate about the plurality of concentric support rings. 
         [0020]    The resulting articulating assembly provides numerous advantages. The multiple, articulating joints, each of which typically includes a supporting caster, results in an assembly that can fully support the load of pipe that is on the carousel by keeping the rotating casters on the surface of the concentric support rings. There is articulating movement in multiple directions. First, the interconnected base members of the triangular subassemblies form an articulating substantially circular ring above the support rings above which the interconnected base members are positioned. Second, the moveable interconnection between the base members and the apexes of the triangular subassemblies allows vertical movement between adjacent sets of triangular subassemblies. The multiple ranges of motion is similar in nature to the kinematics of the motion of a manta ray, whereby the vertical motions are not limited to movements at points positioned at varying positions away from center, but also includes vertical movements at points along concentric circular paths. Such an improved range of motion for the carousel assembly improves the characteristics of the carousel by maximizing the number of supporting casters that remain in contact with the underlying support structure to thereby support the load on the carousel and prevent premature failure of one or multiple rotating casters. 
         [0021]    The modular construction of the inventive rotating carousel also provides the flexibility to expand the number of support rings and corresponding triangular subassemblies to accommodate varying required sizes and lengths of pipe or cable. If a larger carousel is needed, additional concentric support rings are installed outside of any existing support rings. Then additional triangular subassemblies are added until the desired sized carousel is completed. Also, the size of the inner support ring can be varied depending upon the minimum radius of the flexible pipe or cable to be stored on and unspooled from the carousel. 
         [0022]    A drive mechanism for rotating the carousel and method of constructing a drive mechanism is provided that includes a motor that rotates a perimeter drive chain. The perimeter drive chain is positioned to engage less than the full circumference of the outer perimeter of the carousel. Sprocket pads are positioned at spaced intervals on the outer perimeter of the carousel and the sprocket pads are configured to engage the profile of the perimeter drive chain. 
         [0023]    The perimeter drive chain typically includes a plurality of rows of chain and the sprocket pads include a corresponding number of rows to engage the profile of the perimeter drive chain. 
         [0024]    At least one of the sprocket pads is engaged with the perimeter drive chain to rotate the carousel. 
         [0025]    The drive mechanism includes a plurality of sprockets that engage the perimeter drive chain comprising at least a pair of perimeter idler sprockets configured to accept the profile of the perimeter drive chain and the perimeter idler sprockets are spaced apart sufficiently far to allow the perimeter drive chain extending between the perimeter idler sprockets to engage a portion of the perimeter and at least one of the sprocket pads on the perimeter of the carousel. 
         [0026]    At least one idler sprocket is normally positioned between each perimeter idler sprocket and the drive sprocket, and each of the idler sprockets is adjustable to impose force upon the perimeter drive chain thereby maintaining a desired tension in the perimeter drive chain. 
         [0027]    A drive mechanism according to an embodiment of the invention includes the motor connected to a motor sprocket that is connected to a primary drive chain. The primary drive chain is then connected to a primary sprocket of a stacked sprocket assembly. The stacked sprocket assembly includes an integral secondary chain sprocket that engages the perimeter drive chain to rotate the carousel. The primary drive chain may include multiple rows of rollers but does is necessarily the same size or configuration as the perimeter drive chain. 
         [0028]    An inner hub design and method of constructing the inner hub design for the rotating carousel assembly is provided that comprises a plurality of vertically oriented fixed plates arranged to form a circle. A plurality of vertically oriented adjustable plates is then moveably connected to the fixed plates. A first set of segments forming a first substantially circular shape is positioned vertically on an outer surface of the adjustable plates. A first substantially circular shape is thereby formed about the outer perimeter of the segments. A plurality of vertically oriented curved plates is positioned about the outer surface of the circular shape of the segments and the curved plates form a substantially uniform circular vertical surface to serve as a center hub of a rotating carousel assembly. 
         [0029]    A second set of segments can also be positioned about a lower, outer surface of the moveable plates wherein the second set of segments form a second substantially circular shape that is substantially similar in diameter to the first substantially circular shape, whereby the vertically oriented curved plates have a substantially circular shape upon which to be mounted. 
         [0030]    The fixed plates on the inner hub can be embedded in an underlying foundation, such as concrete, asphalt or cement or can be fixed to an underlying fixed platform, constructed of wood or metal or polymer, or the like. 
         [0031]    A plurality of horizontally oriented rolling casters is positioned about the substantially uniform circular vertical surface of the curved plates of the hub. The horizontally oriented rolling casters are connected to the rotating carousel assembly whereby at least some of said plurality of horizontally oriented casters engage the substantially uniform circular vertical surface of the curved plates as the rotating carousel rotates. 
         [0032]    The novel hub design results in a substantially uniform, vertical, circular shape upon which the horizontal casters of the inventive carousel can rotate. The hub design overcomes the inherent difficulties of attempting to construct a relatively large diameter uniform, vertical circular surface from plate material. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0033]      FIG. 1  is an overall isometric view of the inventive carousel, showing pipe wrapped thereon; 
           [0034]      FIG. 2  is an overall isometric view of the inventive carousel, without any pipe or cable wrapped thereon; 
           [0035]      FIG. 3  is a portion of the isometric view of  FIG. 2 , showing several triangular subassemblies and a portion of the inner hub; 
           [0036]      FIG. 4  is an isometric assembly view of a portion of the carousel assembly, including the hub caster and hub caster support tube; 
           [0037]      FIG. 5  is a portion of the isometric view of  FIG. 2  showing the triangular subassemblies and articulating joints; 
           [0038]      FIG. 6  is an enlarged portion of  FIG. 5  showing the triangular subassemblies and articulating joints; 
           [0039]      FIG. 7  is a detailed isometric view of an articulating joint of the invention; 
           [0040]      FIG. 8  is a detailed top view of an articulating joint of the invention; 
           [0041]      FIG. 9  is a front view of the articulating joint of  FIG. 8 ; 
           [0042]      FIG. 10  is a partial isometric view of the carousel of  FIG. 2 , including covering plates of a portion of the carousel structure; 
           [0043]      FIG. 11  is a sectional view taken from line  11 - 11  of  FIG. 10 ; 
           [0044]      FIG. 12  is a partial sectional view taken from  FIG. 11 ; 
           [0045]      FIG. 13  is a partial sectional view taken from  FIG. 11 ; 
           [0046]      FIG. 14  is a top view of the tractor drive assembly and a portion of the carousel; 
           [0047]      FIG. 15  is an isometric view of the tractor drive assembly; 
           [0048]      FIG. 16  is an isometric view of the sprocket pad; 
           [0049]      FIG. 17  is a top view of a portion of the roller drive chain; 
           [0050]      FIG. 18  is an isometric view of a portion of the roller drive chain; 
           [0051]      FIG. 19  is a top view of the hub including a portion of the carousel; 
           [0052]      FIG. 20  is an isometric assembly view of the hub assembly; 
           [0053]      FIG. 21  is an isometric view of the assembled hub; 
           [0054]      FIG. 21   a  is an isometric partial view showing an alternative embodiment of the fixed and adjustable plates; and 
           [0055]      FIG. 22  is a section view of the hub assembly taken from line  22 - 22  of  FIG. 21 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Modular Carousel Assembly 
       [0056]    The inventive modular carousel C assembly is illustrated isometrically in  FIG. 1 . The carousel C rotates about the modular hub assembly H and is driven by the tractor drive assembly D. The pipe P that is illustrated on the carousel C is contained on the carousel C with the pipe-retaining ring  24 . In  FIG. 2 , an overview of the carousel C is shown isometrically without any pipe in place. 
         [0057]    The modular carousel C assembly includes, but is not limited to, the following parts: 
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                 Element: 
                 Description: 
               
               
                   
                   
               
             
             
               
                   
                 C 
                 Carousel Assembly 
               
               
                   
                 D 
                 Tractor Drive Assembly 
               
               
                   
                 H 
                 Hub Assembly 
               
               
                   
                 J 
                 Articulating Joint 
               
               
                   
                 P 
                 Pipe 
               
               
                   
                  20 
                 Sprocket Pad 
               
               
                   
                  22 
                 Outer Perimeter 
               
               
                   
                  24 
                 Pipe-Retaining Ring 
               
               
                   
                  25 
                 Triangular Cover Plate 
               
               
                   
                  25a 
                 Trapezoidal Cover Plate 
               
               
                   
                  26 
                 Access Port 
               
               
                   
                  28 
                 Support Surface 
               
               
                   
                  30 
                 Support Ring 
               
               
                   
                  30a 
                 Raised Step 
               
               
                   
                  32 
                 Connecting Member 
               
               
                   
                  34 
                 Base Member 
               
               
                   
                  34a 
                 Rotation of Base Member 
               
               
                   
                  35 
                 Tangential Support Member 
               
               
                   
                  35a 
                 Rotation of Tangential Support 
               
               
                   
                   
                 Member 
               
               
                   
                  40 
                 Apex Hinge Base 
               
               
                   
                  41 
                 Apex Base 
               
               
                   
                  42 
                 Hinge Plate 
               
               
                   
                  44 
                 Hinge Block 
               
               
                   
                  46 
                 Tangential Hinge Base 
               
               
                   
                  48 
                 Hinge Bolt 
               
               
                   
                  50 
                 Caster 
               
               
                   
                  50a 
                 Vertical Movement of Caster 
               
               
                   
                  52 
                 Caster Mount 
               
               
                   
                  54 
                 Caster Mount Base 
               
               
                   
                  60 
                 Roller Drive Chain 
               
               
                   
                  62 
                 Perimeter Sprocket 
               
               
                   
                  62a 
                 Perimeter Sprocket Base 
               
               
                   
                  64 
                 Perimeter Drive Chain 
               
               
                   
                  64a, 64b, 64c 
                 Roller Chain Rows 
               
               
                   
                  65 
                 Idler Sprocket 
               
               
                   
                  65a 
                 Idler Sprocket Support 
               
               
                   
                  66 
                 Chain Roller 
               
               
                   
                  66a 
                 Chain Gap 
               
               
                   
                  67 
                 Motor Support 
               
               
                   
                  68 
                 Chain Link 
               
               
                   
                  69 
                 Chain Link Pin 
               
               
                   
                  70 
                 Sprocket Pad 
               
               
                   
                  70a, 70b, 70c 
                 Sprocket Pad Rows 
               
               
                   
                  72 
                 Sprocket Tooth 
               
               
                   
                  73 
                 Sprocket Gap 
               
               
                   
                  80 
                 Motor 
               
               
                   
                  81 
                 Motor Sprocket 
               
               
                   
                  82 
                 Primary Drive Chain 
               
               
                   
                  83a 
                 Primary Drive Chain Sprocket 
               
               
                   
                  83b 
                 Secondary Drive Chain Sprocket 
               
               
                   
                  85 
                 Hub Base 
               
               
                   
                  86 
                 Fixed Plate 
               
               
                   
                  86a 
                 Outer Edge of Fixed Plate 
               
               
                   
                  88 
                 Adjustable Plate 
               
               
                   
                  89 
                 Adjustment Slot 
               
               
                   
                  89a 
                 Adjustment Bolt/nut 
               
               
                   
                  90 
                 Lower Circular Segments 
               
               
                   
                  90a 
                 Lower Step 
               
               
                   
                  92 
                 Upper Circular Segments 
               
               
                   
                  92a 
                 Upper Step 
               
               
                   
                  94 
                 Hub Plates 
               
               
                   
                  96 
                 Hub Caster 
               
               
                   
                  97 
                 Hub Caster Base 
               
               
                   
                  98 
                 Hub Caster Support Tube 
               
               
                   
                  99 
                 Hub Inner Support Tube 
               
               
                   
                 100 
                 Inner Caster Support 
               
               
                   
                 101 
                 Hub Support Link 
               
               
                   
                 102 
                 Hub Base 
               
               
                   
                   
               
             
          
         
       
     
       Articulating Carousel Support Structure 
       [0058]    In  FIG. 3 , a portion of the carousel C and hub assembly H are shown. The carousel C generally includes a series of concentric support rings  30 . The number of support rings  30  can vary depending upon the length and size of pipe that is to be stored on the carousel C. The carousel C is assembled by first assembling the hub H (which will be described in more detail in the Modular Hub Assembly section). Referring to  FIG. 3 , the first support ring  30  is assembled outside of the hub H. The support ring  30  is either mounted directly to the support surface  28  (best seen in  FIGS. 11-13 ) or is mounted on timber or other material between the support surface  28  and the support ring  30 . Hub caster  50  support tube  98 , together with hub caster  96 , which rolls about hub plates  94  are assembled together with alternating hub inner support tubes  99 . 
         [0059]    The first circular row of the carousel includes the hub caster support tubes  98  connected to the hub inner support tubes  99  with inner caster supports  100  and hub support links  101 . A tangential support member  35  is also typically connected between the outer ends between the hub caster support tubes  98  and the hub inner support tubes  99 . A caster is connected beneath each inner caster support  100 . The caster support  100  is usually fixed between hub caster support tube  98  and hub inner support tube  99  but may also be rotatably connected. Hub support links  101  are rotatably connected to each hub caster support tube  98  and hub inner support tube  99  as best seen in the assembly view of  FIG. 4 . The rotatable connection is provided at hinge block  44 , which allows the casters  50 , which are attached to hub caster supports  100  to move independently, and in particular, in a vertical direction. The casters  50  are able to move up and down, even when the surface of the support ring  30  is uneven due to uneven support surface  28  upon which the support ring  30  is located. The casters  50  that are connected to the inner caster supports  100  roll on the innermost support ring  30 . Additional casters  50  are connected to caster mounts  52 , which are connected to caster mount bases  54  and are positioned at each outer end of the hub caster support tube  98  and the hub inner support tube  99 , best seen in  FIG. 4 . 
         [0060]    It is possible that no support rings  30  would be used if the carousel C is installed on a surface that is sufficiently durable to withstand the rolling stresses from the casters  50 . 
         [0061]    Referring now to  FIGS. 3-13 , the carousel C is built up from the inside working outward by adding triangular subassemblies T. Triangular subassemblies T include base member  34 , which is connected to two connecting members  32 . The two connecting members  32  are typically equal in length, thereby forming an isosceles triangle and are joined at an apex base  41 . 
         [0062]    The first set of triangular subassemblies T are assembled above the second concentric support ring  30  and are attached to the apex hinge bases  40 , which are attached to the ends of the hub inner support tube  98  and the hub inner support tube  99 , as best seen in  FIG. 3 . Tangential support members  35  are pivotally connected between the triangular subassemblies T to tangential hinge bases  46 . The tangential support members  35  provide lateral support to the apex base  41  ends of the triangular subassemblies T. The tangential support members  35  rotate about hinge bolts  48  to provide vertical movement to the casters  50  to allow the casters  50  to move up and down to stay in contact with the support ring  30 , thereby transferring the load from the carousel C to the casters  50  and then to the support ring  30 . 
         [0063]    The construction of the carousel C continues by placing additional support rings  30  outside of the existing outer support ring  30 , then assembling additional triangular subassemblies T, as explained above.  FIG. 5  shows an outermost support ring  30  and a first assembled triangular subassembly T (shown in dashed lines).  FIG. 6  shows a detail of the triangular subassembly T after it has been assembled to the existing apex hinge bases  40 . 
         [0064]    The detail of the articulating joint J of the carousel C is shown in  FIGS. 7-9 . Tangential support members  35  rotate about hinge bolts  48  and the rotational direction is indicated by the rotational arrow  35   a.  Similarly, base members  34  rotate about hinge bolts  48  as indicated by the rotational arrow  34   a.  The rotational movements of tangential support members  35  and base members  34  are determined by the vertical movement of the casters  50 , as indicated by the vertical directional arrow  50   a,  shown in  FIGS. 7 and 9 . The articulating joints J allow the individual casters  50  to move vertically to allow for an uneven support surface  28  and/or an uneven support ring  30 . As many sets of additional triangular subassemblies T can be added as desired, based on the desired pipe capacity of the carousel C. As each additional row of triangular subassemblies T is added, another series of articulating joints J is provided above the underlying support ring  30 , as best seen in  FIGS. 11-13 . 
         [0065]      FIG. 10  shows an isometric view of a portion of the carousel C of  FIG. 1 . In  FIG. 10 , covering plates  25  and  25   a  are shown covering the structure of the carousel C. The triangular cover plates  25  cover the triangular subassemblies T and the trapezoidal cover plates  25   a  cover the areas formed between the hub caster support tubes  98  and hub inner support tubes  99 . Access ports  26  are provided for purposes of assembly and inspection. 
         [0066]      FIGS. 11  shows a cross section of the carousel C including seven (7) concentric support rings  30  on a support surface  28 . The support rings may be raised above the support surface  28  with the raised steps  30   a . More or less than seven (7) concentric support rings  30  can be provided, depending upon how large of a carousel C is desired. When the final number of support rings  30  is assembled and the corresponding triangular subassemblies T are assembled about the outer support ring  30 , the triangular assemblies T are normally connected together with tangential support members  35 , for example, as shown in  FIGS. 10 ,  11  and  13 . An outer perimeter  22  is attached to the outer apex hinge bases  40 . The outer perimeter  22  comprises a series of curved plates that conform to the circumferential shape of the outer perimeter  22  of the carousel, best seen in  FIG. 10 . Also shown on the outer perimeter  22  in  FIG. 10  are sprocket pads  20 , which will be discussed as they relate to the tractor drive assembly D. 
         [0067]    After the desired number of concentric support rings  30 , corresponding triangular subassemblies T and outer perimeter  22  have been assembled, triangular cover plates  25  are assembled to cover the triangular subassemblies and trapezoidal cover plates  25   a  are assembled to cover the open trapezoids formed between the hub caster support tube  98  and the hub inner support tube  99 , as shown in  FIG. 10 . The cover plates  25  and  25   a  are removable to allow access to the structures of the carousel C, and help to prevent debris from fouling the casters  50 , the supporting rings  30 , the articulating joints J and the interconnected structures of the carousel C generally. 
       Tractor Drive Assembly 
       [0068]    The tractor drive assembly D is shown in the overview of  FIGS. 1 and 2  and in detail in  FIGS. 14-18 . The tractor drive assembly D includes a perimeter drive chain  64  that typically includes multiple rows  64   a,    64   b,    64   c  of rollers as shown in  FIG. 18 . Drive chain motor  80  drives motor sprocket  81  that turns primary drive chain  82 . Primary drive chain  82  rotates primary drive chain sprocket  83   a.  Primary drive chain sprocket  83   a  is part of a stacked sprocket that includes integral secondary roller chain sprocket  83   b.  Secondary drive chain sprocket  83   b  rotates the perimeter drive chain  64 . Perimeter sprockets  62  engage the perimeter roller drive chain  64  and space the perimeter drive chain  64  apart such that the perimeter drive chain  64  contacts the outer perimeter  22  of the carousel C. The drive motor  80  may also be coupled directly to the primary drive chain sprocket  83   a  or to the secondary drive chain sprocket if alternate gearing of the sprocket size is not desired. The larger the diameter of the primary drive chain sprocket  83   a,  the greater the torque will be transferred to the secondary drive chain sprocket  83   b  from the drive chain motor  80 . 
         [0069]    The following estimates have been made for the motor size for different carousel sizes and pipe speeds: 
         [0000]    
       
         
               
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Carousel Outer Diameter/Hub 
               
               
                   
                 Diameter/Pipe Speed 
               
             
          
           
               
                   
                 75 feet/ 
                 75 feet/ 
                 60 feet/ 
                 60 feet/ 
               
               
                   
                 20 feet at 
                 20 feet at 
                 20 feet at 
                 20 feet at 
               
               
                   
                 10 feet/min 
                 20 feet/min 
                 10 feet/min 
                 20 feet/min 
               
               
                   
                   
               
             
          
           
               
                 Motor Size 
                 40 
                 80 
                 20 
                 40 
               
               
                 (HP) 
               
               
                   
               
             
          
         
       
     
         [0070]    The calculations are estimated and will also depend upon the weight of the pipe and carousel and other factors. 
         [0071]    The perimeter sprockets  62  are positioned sufficiently far apart so that the span of the perimeter drive chain  64  between them engages the outer perimeter  22  of the carousel C. The position of the perimeter sprocket bases  62   a  can be changed to adjust the position of the perimeter sprockets  62 . Idler sprockets  65  engage the outside of the perimeter drive chain  64  on opposite sides of the secondary roller drive chain sprocket  83   b.  The position of the idler sprocket bases  65   a  can be changed to adjust the tension of the perimeter drive chain  64 . 
         [0072]      FIG. 16  shows the sprocket pad  70  used with the tractor drive assembly T. The sprocket pad  70  has a profile of teeth  72  and grooves  73  that correspond to the rollers  66  and gaps  66   a  of the perimeter drive chain  64 . Multiple rows  70   a,    70   b,    70   c  of teeth  72  and grooves  73  are provided on the sprocket pads  70  to correspond to the multiple rows  64   a,    64   b,    64   c  of the perimeter drive chain  64 . Multiple sprocket pads  70  are positioned about the outer perimeter  22  of the carousel C. The sprocket pads  70  may be connected to the outer perimeter  22  in any conventional manner, such as welding or bolting. The perimeter drive chain  64  engages the sprocket pads  70  as shown in  FIG. 14 . The sprocket pads  70  are spaced apart such that the roller drive chain is in contact with at least a minimum desired number of sprocket pads  70 . The number of sprocket pads  70  in contact with the roller drive chain  64  is shown in the drawings to be three (3), but the number of sprocket pads  70  in contact with the roller drive chain  64  can vary depending upon the amount of torque that is to be transferred by the perimeter drive chain  64  to the sprocket pads  70  and carousel C, as will be understood by a person skilled in the art. 
         [0073]    Although the primary drive chain  82  and perimeter drive chain  64  are typically similar in construction, and typically have the same number of rows  64   a,    64   b,    64   c,  it is contemplated that different numbers of rows may be included on the primary drive chain  82  than on the perimeter drive chain  64 . The stacked sprocket, comprising the primary sprocket  83   a  and the secondary sprocket  83   b  will have the same number of rows of sprocket teeth  70   a,    70   b,    70   c  that corresponds to the number of rows of rollers  64   a,    64   b,    64   c  on the corresponding primary drive chain  82  and perimeter drive chain  64 . 
         [0074]    Use of sprocket pads  70  in combination with the perimeter drive chain  64  offers significant advantages over the use of a drive chain or belt around the entire outer perimeter  22  of the carousel C.
       First, the perimeter drive chain  64  is expensive. The length of perimeter drive chain  64 , and hence the cost, is significantly reduced by driving the spaced sprocket pads  70  instead encircling the entire outer perimeter  22  of the carousel C with a full length drive chain.   Second, perimeter drive chain  64  is heavy. By using a shorter overall length of perimeter drive chain  64 , the handling of a full circumference chain can be avoided. Heavy chain wrapped around the full circumference of a carousel can fail because it tends to sag and/or stretch, either of which are undesirable.   Third, a full circumference gear generally accompanies a full circumference chain. The full circumference gear is both expensive and unwieldy. The use of sprocket pads  70  is both efficient and inexpensive relative to the conventional full circumference approaches to turning carousels.       
 
       Modular Hub Assembly 
       [0078]    Refer to  FIGS. 19-22  for details concerning the modular hub assembly H. A top view of the fully assembled hub H and a portion of the carousel C are shown in  FIG. 19 . An isometric assembly view of the modular hub assembly H is shown in  FIG. 20 . A hub base  102  is constructed from concrete or other suitable base material, for example by setting forms and pouring concrete between the forms. Alternative material and forms may also be used to provide a solid base for the hub assembly H. The hub base  102  is shown as a donut shape in  FIGS. 21 and 22 , but it may be a solid circular shape and need not necessarily be raised. 
         [0079]    It is important for the elevation of the horizontal casters  96  to correspond to the hub plates  94 , so that the horizontal casters roll about the hub plates  94 . Therefore, consideration is given during construction of the carousel C and the modular hub assembly H to the elevation of the support rings  30  relative to the hub base  102  (Refer also to  FIG. 12 ). 
         [0080]    The fixed plates  86  are positioned in the hub base  102 , while the hub base is still soft enough for the fixed plates  86  to be inserted into the hub base  102  material. In other words, the fixed plates  86  are inserted into the hub base material  102  while it is still in the formative state, and before the hub base  102  material solidifies. The fixed plates  86  are arranged such that the outer edge  86   a  of each plate faces outward from the center of the hub base  102  to generally form a circle along the outer edge  86   a  of each fixed plate  86 , as best seen in the lowermost portion of  FIG. 20 . The diameter of the hub assembly H is typically 20 feet or more, but may also be smaller. Because of the possible large diameter of the hub assembly H, it is very difficult to obtain a true, uniform circle about the outer edges  86   a  of the fixed plates  86 . Therefore, adjustable plates  88  are temporarily attached to each of the fixed plates  86  with clamps or other connecting mechanisms. The lower circular segments  90  are assembled about the adjustable plates  88  by positioning and welding or otherwise securing the lower circular segments  90  on the lower steps  90   a  of the adjustable plates  88 . The lower circular segments  90  can be cut or machined to a close tolerance to produce a very uniform circular shape about the outer edge of the assembled lower circular segments  90 . After the lower circular segments  90  have been assembled about the adjustable plates  88 , the adjustable plates are secured to the fixed plates  86  by either welding or by securing nuts/bolts  89   a  in adjustment slots  89  to secure the adjustable plates  88  to the fixed plates  86  together (See  FIG. 21   a  for a detail of the adjustment slots  89  embodiment). Alternative connections such as clamps may also be used to secure the adjustable plates  88  to the fixed plates  86 . 
         [0081]    The upper circular segments  92  are assembled about the adjustable plates  88  by positioning and welding or otherwise securing the upper circular segments  92  on the upper steps  92   a  of the adjustable plates  88 . As with the lower circular segments  90 , the upper circular segments  90  can be also cut or machined to a close tolerance to produce a very uniform circular shape about the outer edge of the assembled upper circular segments  92 . 
         [0082]    The assembled lower circular segments  90  and upper circular assembly  92  provides a very uniform, circular surface on which to assemble the hub plates  94 . The hub plates  94  are bent or otherwise formed to the same shape as the shape of the outer edges of the lower circular segments  90  and upper circular segments  92 . The hub plates  94  are then typically welded together and to the lower circular segments  90  and upper circular segments  92 , but they may also be secured with bolts or other fastening means. 
         [0083]    It is contemplated that a single set of circular segments, having a uniform shape about the outer edge of the assembled circular segments may also be used instead of a set of upper circular segments  92  and a set of lower circular segments  90 . Also, more than two sets of circular segments may also be provided, as desired. 
         [0084]    The resulting uniform, circular surface of the hub plates  94  provides an ideal surface to serve as the hub assembly H on which the hub casters  96  rotate, as best seen in  FIG. 19 . It is possible that not all hub casters  96  will engage the surface of the hub plates  94 , but the uniform surface maximizes the number of hub casters  96  that can engage the surface of the hub plates  94  at any time. It is important for as many hub casters  96  to be in contact with the hub plates  94  in order to distribute the load across as many hub casters  96  as possible. If too few hub casters  96  were to bear the load of the rotating carousel C, failure of the hub casters  96  could occur. Also, the uniform hub surface about the hub plates  94  results in a smooth movement of the hub casters  96  to prevent the casters from vibrating, bending or from suffering other undesirable stresses. 
         [0085]    The foregoing disclosure and description of the invention are illustrative and explanatory thereof, and various changes in the size, shape, and materials, as well as in the details of the illustrated construction may be made without departing from the spirit or scope of the invention.