Abstract:
Apparatus and methods for suppressing vortex-induced vibrations (VIV) of aquatic elements of underwater structures. The system includes use of a sleeve positioned around at least a portion of an aquatic element and at least one strake positioned along at least a portion of the length of the aquatic member. The apparatus further comprises copper to suppress the growth of aquatic organisms.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to apparatus and methods for suppressing vortex-induced vibrations (VIV). In another aspect, the present invention relates to apparatus and methods for suppressing VIV while also suppressing the growth of aquatic organisms on the VIV suppressing apparatus. In even another aspect, the present invention relates to apparatus for suppressing VIV comprised of copper for suppressing the growth of aquatic organisms on the surface of the apparatus. 
     2. Description of the Related Art 
     Whenever a bluff body, such as a cylinder, experiences a current in a fluid, it is possible for the body to experience vortex-induced vibrations (VIV). These vibrations are caused by oscillating hydrodynamic forces on the surface which can cause substantial vibrations of the structure, especially if the forcing frequency is at or near a structural natural frequency. The vibrations are largest in the transverse (to flow) direction; however, in-line vibrations can also cause stresses which are sometimes larger than those in the transverse direction. 
     Drilling for and/or producing hydrocarbons or the like from subterranean deposits which exist under a body of water exposes underwater drilling and production equipment to water currents and the possibility of VIV. Equipment exposed to VIV includes structures ranging from the smaller tubes of a riser system, anchoring tendons, or lateral pipelines to the larger underwater cylinders of the hull of a minispar or spar floating production system (hereinafter “spar”). 
     Risers are discussed here as a non-exclusive example of an aquatic element subject to VIV. A riser system is used for establishing fluid communication between the surface and the bottom of a water body. The principal purpose of the riser is to provide a fluid flow path between a drilling vessel and a well bore and to guide a drill string to the well bore. 
     A typical riser system normally consists of one or more fluid-conducting conduits which extend from the surface to a structure (e.g., wellhead) on the bottom of a water body. For example, in the drilling of a submerged well, a drilling riser usually consists of a main conduit through which the drill string is lowered and through which the drilling mud is circulated from the lower end of the drill string back to the surface. In addition to the main conduit, it is conventional to provide auxiliary conduits, e.g., choke and kill lines, etc., which extend parallel to and are carried by the main conduit. 
     Also, the newly developed spar production facilities are used in aquatic environments of great depths. Aquatic environments is used here to describe water environments of any salinity. Strong water currents often occur at these greater depths in ocean environments. The hulls of spar production facilities, therefore, can be exposed to excessive vortex-induced vibrations. 
     Methods to reduce vibrations caused by vortex shedding from aquatic structures can operate by modifying the boundary layer of the flow around the structure to prevent the correlation of vortex shedding along the length of the structure. Examples of such methods include the inclusion of helical strakes around a structure, or axial rod shrouds and perforated shrouds. 
     The use of strakes and shrouds in aquatic environments exposes them to being colonized by aquatic animals and plants that anchor themselves to these structures. Mature growth of these organisms on strakes and shrouds changes the contours of these VIV suppression devices and can diminish their effectiveness in VIV suppression, and perhaps in some instances result in greater VIV. The location of these VIV suppression devices deep in aquatic environments makes it difficult to remove aquatic organisms. Aquatic organisms can be removed from VIV suppression devices by divers working from water craft, defined herein as any vehicle that can travel on or in water. After removal, the aquatic organisms immediately begin to re-colonize the structures. 
     However, in spite of the above advancements, there still exists a need in the art for improved apparatus and methods for VIV suppression. 
     There is another need in the art for apparatus and methods for strakes and other VIV suppression devices which resist the growth of aquatic organisms on their surfaces. 
     These and other needs in the art will become apparent to those of skill in the art upon review of this specification, including its drawings and claims. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide for improved apparatus and methods for VIV suppression. 
     It is another object of the present invention to provide for apparatus and methods for strakes and other VIV suppression devices which resist the growth of aquatic organisms on their surfaces. 
     These and other objects of the present invention will become apparent to those of skill in the art upon review of this specification, including its drawings and claims. 
     According to one embodiment of the present invention, there is provided a system for suppressing VIV. The system generally includes a first flange, having a first set of two or more members, and a second flange having a second set of two or more members. The system further includes an elongated strake member with the elongated strake member connected to the first flange and the second flange. At least a portion of the system comprises copper in the range of about 1 wt % to about 100 wt %, based on the total weight of that portion. In a more specific embodiment of this embodiment, the system may also include an elongated sleeve positioned within the first and second flanges and a marine element positioned within the elongated sleeve. 
     According to another embodiment of the present invention, there is provided a method of modifying a structure intended to operate while at least partially immersed in an aquatic environment. The method generally includes arranging a plurality of elongated members around at least a portion of the structure, wherein at least a portion of the elongated members comprise copper in the range of about 1 wt % to about 100 wt % copper. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic illustration of a coated riser joint  7 , comprised of riser joint  3  coated with and supporting riser coating  5 . 
     FIG. 2 shows a schematic illustration of strake flange  25  in frontal view, comprised of top half  20  and bottom half  22 , each half defining multiple holes  24 . 
     FIG. 3 depicts a first clad sleeve  35 , comprised of top half  30  and bottom half  32 . 
     FIG. 4 shows a schematic illustration of a cross section of an additional clad sleeve  55  comprised of upper half  50  and lower half  52 . 
     FIG. 5 shows a schematic illustration of lateral view of additional clad sleeve  55 , comprised of upper half  50  and lower half  52 . 
     FIG. 6 provides a schematic overview of clad sleeves and strake flange  25  encircling coated riser  7 . 
     FIG. 7 provides a magnified schematic view of strake flange  25  positioned near one end of first clad sleeve  35  and supported thereby. 
     FIG. 8 shows a schematic illustration of strake attachment flange  115 , comprised of top half  92  and bottom half  94  with hole  80  used to anchor tubes  90 . 
     FIG. 9 displays a schematic representation of strake attachment flange  115  attached at both ends of tubes  90 . 
     FIG. 10 shows a schematic overview of riser  7  and tubes  90  are shown anchored at both of their ends to attachment flanges  92  and  94 . 
     FIG. 11 portrays a magnified schematic view of strake flange  25  attached to strake attachment flange  115  with tubes  90  attached to flange. 
     FIG. 12 provides a schematic overview of riser  7  with strake flange  25  and attachment flange  115  with tubes  90  connected and encircling clad sleeves  35  and  55 . 
     FIG. 13 provides a schematic overview riser joint  7  with sleeves  35  and  55  and with tubes  90  twisted into a helix. 
     FIG. 14 shows a schematic overview of apparatus and methods of adding additional clad sleeves  55  and tubes  90  across the abutted ends of two risers  7 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The VIV suppression apparatus of the present invention generally includes protective coverings and VIV suppression devices for aquatic elements of underwater structures or subject to VIV, including but not limited to risers. The apparatus and methods of the present invention find utility with an aquatic element either in an assembly yard or a lay vessel, prior to being installed in an aquatic environment, or with the aquatic element in situ in an aquatic environment. 
     Referring first to FIG. 1, shown is coated riser joint  7 , comprised of riser joint  3  coated with and supporting riser coating  5 . Riser joints are individual sections of tubing that can be connected end to end to create a riser of various lengths. 
     Referring next to FIGS. 2 and 3, shown is strake flange  25 , comprising a set of top half  20  and bottom half  22 , each half defining multiple holes  24 . Also shown is first clad sleeve  35 , comprised of top half  30  and bottom half  32 . Upper and lower first clad sleeves  30  and  32  are fitted around one end of coated riser joint  7  if it is the first in a series of riser joints that require VIV suppression. Upper  30  and lower  32  first clad sleeves support respectively upper strake attachment flange  92  and bottom strake attachment flange  94 . 
     Referring now to FIGS. 4 and 5, shown in cross section and laterally is additional clad sleeve  55 , comprised of upper half  50  and lower half  52 . Additional clad sleeve  55  does not support strake flange  25 . Any number of additional clad sleeves  55  may be installed adjacent to first clad sleeve  35  on the side of first clad sleeve  35  that is away from the nearest end of riser joint  7 . 
     Referring now to FIGS. 6 and 7, one additional clad sleeve  55  is installed adjacent to and in contact with first clad sleeve  35  which is installed at one end of coated riser joint  7 . More additional clad sleeves  35  may be installed down the remaining length of riser joint  7 , adjacent to and in contact with each other at abutted ends  62 , as is shown in FIG.  6 . Further shown in FIGS.  6  and  7  are strake attachment flange  25  positioned near one end of first clad sleeve  35  and supported thereby. Strake flange  25  may be assembled from top half  20  and bottom half  22  with two or more bars  70  anchored through opposite holes  24 , on each half. The bars may optionally be anchored with welding, preferably with rivets, even more preferably with bolts. Also shown in FIGS. 6 and 7 are compression straps  60  spaced at intervals along first sleeves  35  and additional sleeves  55  to anchor those sleeves to riser  7 . In FIG. 6, a non-limiting example of the placement of compression straps  60  is shown with straps  60  positioned at both ends and in the middle of first sleeve  35  and additional sleeves  55 . 
     Referring now to FIGS. 8 and 9, shown strake attachment flange  115 , comprising a set of top half  92  and bottom half  94  attached at both ends of tubes  90 , which are anchored to attachment flange  115  through holes  80  defined by attachment flange  115 . Also defined by attachment  115  are multiple anchor holes  85 . 
     Referring now to FIGS. 10 and 11, shown is riser  7  supported by yard braces  100  at both ends of riser  7 . Tubes  90  are shown anchored at both of their ends to top attachment flanges  92  and to bottom attachment flanges  94 . Strake attachment flange  115  with tubes  90  attached may be connected to strake flange  25  using the same anchoring methods used to anchor the top  20  and bottom  22  halves of strake flange  25 . Optionally, bars  70  may be used to anchor strake flange  25  to strake attachment flange  115  using welding, preferably with rivets, even more preferably with bolts. 
     Referring now to FIG. 12, shown is riser  7  with strake flange  25  and attachment flange  115  connected and encircling clad sleeves  35  and  55 , which in turn encircle riser  7 , with tubes  90  attached to flange  115  at both ends of tubes  90 . 
     Referring now to FIG. 13, shown are tubes  90  twisted into a helix forming strake  130 , useful in VIV suppression. The helical arrangement of tubes  90  forming strake  130  is achieved by anchoring one strake flange  25  with tab  120  to clad sleeves  35  or  55  and applying torque to another strake flange  25  not anchored to clad sleeves  35  or  55  and supporting the other end of tubes  90 . The direction of the torque applied to tubes  90  may be either clockwise or counterclockwise. 
     Referring now to FIG. 14, shown is a method of adding additional clad sleeves  55  across the abutted ends of two risers  7  using support mandrel  140  to hold the two abutted ends of two risers  7  together. Also shown is the installation of top attachment flange  92  with tubes  90  and the installation of bottom attachment flange  94  with tubes  90  to strake flange  25 . Torque may be applied to the strake flange  25  at the end of tubing  90  opposite the end being attached to the prior torqued flange  25  along the length interconnected risers  7 . Prior to applying torque to the un-torqued tubes  90 , the strake flange  25  should be anchored to clad sleeves  35  or  55  with tab  120  to prevent the previously torqued tubes  90  from receiving additional torque being applied to the adjacent un-torqued tubing  90 . If only one strake  130  is used, it is described as being a single start strake. However, if multiple strakes  130  are attached end to end as shown, with torque applied separately to each set of straight tubes  90 , then the series of strakes  130  are described as being multiple start strakes. 
     Referring now to all of the previous Figures, at least a portion of the apparatus described is comprised of metal comprising copper. Preferably, at least a portion of the strake(s) comprise metal comprising copper. Most preferably, the portion of interest will be the portion of the apparatus or strake in contact with the water (i.e., the “contact surface.” The portion requiring antifouling properties may comprise metals having a wide range of copper content provided that adequate antifouling is achieved, with the lower end of the range generally about 1 weight (wt) % based on the total weight of that portion, preferably about 60 wt %, more preferably about 75 wt %, even more preferably about 90 wt %, still more preferably about 95 wt %, and yet more preferably about 98 wt %. 
     The upper end of the range of copper content used is selected independently of the lower end to be greater than the lower end, with the upper end of the range generally about 60 wt %, preferably about 90 wt %, more preferably about 95 wt %, even more preferably about 98 wt %, yet more preferably 99 wt %, and even still more preferably 100 wt %. 
     While the methods and apparatus have been illustrated herein as being used with risers, it should be understood that the methods and apparatus are believed to have applicability to any structure underwater, whether permanent or temporary, fixed or mobile, in any type of aquatic environment, whether fresh, brackish, or salt water. 
     Further, while the methods and apparatus have been illustrated herein with elongated tubes, circular in cross-section, forming strakes, elongated members of any shape may be used, including but not limited to those with cross-sections that are rectangular, square, triangular, oval, arc-shaped, or spoke-shaped 
     Finally, while the illustrative embodiments of the invention have been described with particularity, it will be understood that various other modifications will be apparent to and can be readily made by those skilled in the art without departing from the spirit and scope of the invention. Accordingly, it is not intended that the scope of the claims appended hereto be limited to the examples and descriptions set forth herein but rather that the claims be construed as encompassing all the features of patentable novelty which reside in the present invention, including all features which would be treated as equivalents thereof by those skilled in the art to which this invention pertains.