Abstract:
Methods and apparatus for the installation of VIV suppression during the S-Lay installation of a subsea pipeline. A locking member will be interposed between a pipe and a fairing rotatably mounted on the pipe, sufficient to bias the fairing against rotating. Upon marine application, the locking member will degrade, thereby releasing the fairing.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to apparatus, systems and methods for reducing vortex-induced-vibrations (“VIV”), current drag, low frequency drift oscillations due to random waves, and low frequency wind induced resonant oscillations. In another aspect, the present invention relates to apparatus, systems and methods comprising enhancement of VIV suppression devices for control of vortex-induced-vibrations, current drag, low frequency drift oscillations due to random waves, and low frequency wind induced resonant oscillations. In even another aspect, the present invention relates to apparatus, systems and methods comprising modified and improved performance fairings for reducing VIV, current drag, low frequency drift oscillations due to random waves, and low frequency wind-induced resonant oscillations. In still another aspect, the present invention relates to methods and apparatus for the “S-Lay” installation of pipe. In even still another aspect, the present invention relates to methods and apparatus installation of VIV suppression during the “S-Lay” installation of pipe.  
         [0003]     2. Description of the Related Art  
         [0004]     When a bluff body, such as a cylinder, in a fluid environment is subjected to a current in the 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 direction transverse to flow, however, in-line vibrations can also cause stresses which are sometimes larger than those in the transverse direction.  
         [0005]     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 the smaller tubes and cables of a riser system, umbilical elements, mooring lines, anchoring tendons, marine risers, lateral pipelines, the larger underwater cylinders of the hull of a minispar or spar floating production system.  
         [0000]     a minispar or spar floating production system.  
         [0006]     There are generally two kinds of water current induced stresses to which all the elements of a riser system are exposed. The first kind of stress as mentioned above is caused by vortex-induced alternating forces that vibrate the underwater structure in a direction perpendicular to the direction of the current. These are referred to as vortex-induced vibrations (VIV). When water flows past the structure, vortices are alternately shed from each side of the structure. This produces a fluctuating force on the structure transverse to the current. If the frequency of this harmonic load is near the resonant frequency of the structure, large vibrations transverse to the current can occur. These vibrations can, depending on the stiffness and the strength of the structure and any welds, lead to unacceptably short fatigue lives. Stresses caused by high current conditions have been known to cause structures such as risers to break apart and fall to the ocean floor.  
         [0007]     The second type of stress is caused by drag forces which push the structure in the direction of the current due to the structure&#39;s resistance to fluid flow. The drag forces are amplified by vortex induced vibrations of the structure. For instance, a riser pipe which is vibrating due to vortex shedding will disrupt the flow of water around it more so than a stationary riser. This results in greater energy transfer from the current to the riser, and hence more drag.  
         [0008]     Many methods have been developed to reduce vibrations of subsea structures. Some of these methods 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 use of helical strakes around a structure, or axial rod shrouds and perforated shrouds. Other methods to reduce vibrations caused by vortex shedding from subsea structures operate by stabilization of the wake. These methods include use of fairings, wake splitters and flags.  
         [0009]     VIV is also a common problem for subsea pipelines, especially the portions of the pipe line that span canyons or trenches on the ocean floor. These canyons or trenches can act as conduits and magnify the effects of currents at or near the ocean floor. As with vertical risers/tendons, the solution is to install VIV suppression such as fairings, wake splitters and flags.  
         [0010]     Installation of VIV suppression after the laying of the pipe line very expensive, laborious, and dangerous. Ideally, VIV suppression would be installed on the pipe at the lay vessel as it is being laid.  
         [0011]     There as two main methods of laying pipe, the “J-Lay” and “S-Lay.” 
         [0012]     With “J-Lay,” a vertical lay vessel is utilized, in which pipe leaves the traveling vessel vertically, with the pipe essentially forming a “J” as it is being laid on the ocean floor. With J-Lay installation, VIV suppression is easily applied to the pipe at the vessel during installation.  
         [0013]     With “S-Lay,” pipe leaves the lay vessel in an essentially horizontal position, and rolled off of a radially shaped “stinger” mounted aft, with the pipe essentially forming an “S” as it is being laid on the ocean floor. The stinger cross-section is a “V” shaped trough conveyor comprising a series of rollers across with the pipe passes. As the stinger is “V” shaped, only a portion of the pipe engages rollers. The problem with installing VIV during an S-Lay, is that the stinger will tend to shear off anything that extends radially from the pipe at those places where it engages the pipe.  
         [0014]     Thus, there is a need in the art for apparatus, systems and methods for suppressing VIV and reducing drag of a marine element.  
         [0015]     There is another need in the art for apparatus, systems and methods for suppressing VIV and reducing drag of a subsea pipeline, which can be installed during the laying of the pipeline.  
         [0016]     There is even another need in the art for apparatus, systems and methods for laying a subsea pipeline with VIV.  
         [0017]     These and other needs of the present invention will become apparent to those of skill in the art upon review of this specification, including its drawings and claims.  
       SUMMARY OF THE INVENTION  
       [0018]     It is an object of the present invention to provide for apparatus, systems and methods for suppressing VIV and reducing drag of a marine element.  
         [0019]     It is another object of the present invention to provide for apparatus, systems and methods for suppressing VIV and reducing drag of a subsea pipeline, which can be installed during the laying of the pipeline.  
         [0020]     It is even another object of the present invention to provide for laying a subsea pipeline with VIV.  
         [0021]     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.  
         [0022]     According to one embodiment of the present invention, there is provided a fairing for reducing vortex-induced-vibrations in a cylindrical marine element. The fairing includes a main body defining a circular passage for receiving the marine element, and comprising a tail section. A locking member is supported by the main body, wherein the member is positionable and lockable in the circular passage against any marine element in the passage to move the tail section away from any marine element in the passage, wherein at least a portion of the locking member comprises material that will degrade in a marine environment and upon degradation disengage from the marine element.  
         [0023]     According to another embodiment of the present invention, there is provided a modified pipe, which includes a pipe section, a fairing having a tail section, and rotatably mounted on the pipe. Also included is a locking member interposed between the pipe section and the fairing, biasing the fairing against rotating, and positioning the tail section radially away from the pipe section, wherein at least a portion of the locking member comprises material that will degrade in a marine environment and upon degradation will no longer bias the fairing against rotating, and no longer position the tail section away from the pipe section.  
         [0024]     According to even another embodiment of the present invention, there is provided a method of modifying a pipe having a fairing rotatably mounted thereon. The method includes positioning a locking member between the pipe and the fairing sufficient to bias the fairing against rotating, and position a portion of the fairing radially away from the pipe section, wherein at least a portion of the locking member comprises material that will degrade in a marine environment and upon degradation will no longer bias the fairing against rotating, and no longer position the fairing radially away from the pipe section. A further embodiment of this embodiment includes, placing the pipe, fairing and locking member in a marine environment, and allowing the locking member to degrade.  
         [0025]     According to still another embodiment of present invention, there is provided a method of passing a pipe with a rotatably mounted fairing over a roller, wherein the fairing comprises a tail section. The method includes (A) positioning the fairing such that the tail section will not touch the roller as it passes over the roller. The method also includes (B) passing the pipe and fairing over the roller. A further embodiment of this embodiment includes, in step (A), further comprising positioning a locking member between the pipe and the fairing sufficient to bias the fairing against rotating, wherein at least a portion of the locking member comprises material that will degrade in a marine environment and upon degradation will no longer bias the fairing against rotating.  
         [0026]     According to yet another embodiment of the present invention, there is provided a collar for securing a fairing rotatably mounted on a pipe. The collar includes a circular segment of less than 2Π radians, and a circular shaped band positioned around the segment.  
         [0027]     Other embodiments include modifying a pipe by applying the collar to the pipe, passing a pipe with the collar over a roller by positioning the circular segment so that it clears the rollers.  
         [0028]     Even other embodiments include modifying a pipe by applying both the collar and fairing of the present invention to the pipe, and passing a pipe with both the collar and fairing over a roller.  
         [0029]     Still other embodiments include S-laying of pipe by utilizing the fairing and/or collar.  
         [0030]     These and other embodiments of the present invention will become apparent to those of skill in the art upon review of this specification, including its drawings and claims.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0031]      FIG. 1  is a schematic representation of a “J-Lay” installation of a subsea pipeline, showing vessel  10  moving in direction  5  at ocean surface  18 , laying pipe  12  onto ocean floor  16 .  
         [0032]      FIG. 2  is a schematic representation of an “S-Lay” installation of a subsea pipeline, showing vessel  20  moving in direction  5  at ocean surface  18 , laying pipe  12  utilizing stinger  22  onto ocean floor  16 .  
         [0033]      FIG. 3  is a cross-sectional representation of stinger  22  of  FIG. 2 , showing pipe  12  positioned and rolling across rollers  25 .  
         [0034]      FIG. 4  is an isometric representation, showing pipe  12 , having VIV fairing  15  and collar  13 , positioned and rolling across stinger  22  in direction  7 .  
         [0035]      FIG. 5  is a cross-sectional representation of  FIG. 4 . taken at  5 - 5 , showing pipe  12 , having VIV fairing  15  and collar  13 , positioned and rolling across stinger  22 .  
         [0036]      FIG. 6  is a cross-sectional representation showing fairing  15  mounted on pipe  12 , showing gap  3  formed as a result of gravity.  
         [0037]      FIG. 7  is a cross-sectional representation showing fairing  15  mounted on pipe  12 , showing a substantially smaller gap  3  that can be achieved by lifting fairing  15  in direction  7 .  
         [0038]      FIGS. 8 and 9  are a cross-sectional representations showing fairing  15  mounted on pipe  12 , showing fairing  15  lifted and held in place by positioning lock  30 .  
         [0039]      FIGS. 10 and 11  are cross-sectional representations of stinger  22 , showing collar  13  mounted on pipe  12 .  
         [0040]      FIG. 12  is a cross-sectional representation of stinger  22 , showing fairing  15  mounted on pipe  12 .  
         [0041]      FIG. 13  is an isolated representation of collar  13 .  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0042]     The present invention is best understood by first making reference to the prior art, and understanding the problem of installing VIV suppression during an S-Lay installation of pipe.  
         [0043]     Referring to  FIG. 1 , there is shown a schematic representation of a prior art “J-Lay” installation of a subsea pipeline, showing vessel  10  moving in direction  5  at ocean surface  18 , laying pipe  12  onto ocean floor  16 . The name “J-Lay” comes from the “J” shape made by pipe  12  during installation. As shown, VIV suppression is being installed at those locations where pipeline  12  will span channels/trenches  17 . Fairings  15  and collars  13  are very easily added during installation.  
         [0044]     Referring now to  FIG. 2 , there is shown a schematic representation of a prior art “S-Lay” installation of a subsea pipeline, showing vessel  20  moving in direction  5  at ocean surface  18 , laying pipe  12  utilizing stinger  22  onto ocean floor  16 . The name “S-Lay” comes from the “S” shape made by pipe  12  during installation.  
         [0045]     Referring additionally to  FIG. 3 , there is shown a cross-sectional representation of stinger  22  of  FIG. 2 , showing pipe  12  without suppression positioned and rolling across rollers  25 .  
         [0046]     Referring additionally to  FIGS. 4 and 5 , there are shown, respectively, an isometric representation and a cross-sectional representation, of pipe  12 , having VIV fairing  15  and collar  13 , with pipe  12  positioned and rolling across stinger  22  in direction  7 .  
         [0047]     The problem with the prior art is best understood as follows. As pipe  12  rolls across stinger  22  in direction  7 , any attached suppression, i.e., collar  13  and fairing  15 , will encounter stinger  22  at point  40 , resulting in such collar  13  and fairing  15  either being broken or sheared off of pipe  12 , or held back at point  40  while pipe  12  passes through the collars and fairings.  
         [0048]     According to the present invention, if the tail end of the fairing could be oriented to avoid stinger  22 , then it could pass over stinger  22  intact.  
         [0049]     However, in addition to the fairing tail engaging the stinger, gravity will tend to pull the fairing away from the pipe allowing that portion of the fairing to fall below the pipe and also engage the stinger. This problem can be seen by reference to  FIG. 6 , which is a cross-sectional representation showing fairing  15  mounted on pipe  12 , showing gap  3  formed as a result of gravity. Obviously, as this fairing  15  approaches the stinger, the portion of the fairing sagging below the pipe will engage the stinger, and the fairing will either be sheared/knocked off, or held back while the pipe passes through.  
         [0050]     Thus, the present invention additionally provides that if the portion of the fairing that sags below the pipe and engages the stinger could be abutted firmly against the pipe, that portion of the fairing could pass easily over the stinger.  
         [0051]     Referring now to  FIG. 7 , there is shown a fairing with its tail oriented to avoid the stinger, and that has been abutted firmly against the pipe.  FIG. 7  is a cross-sectional representation showing fairing  15  mounted on pipe  12 , showing fairing tail  15 T oriented to avoid stinger  22 , and showing that a substantially smaller gap  3  that can be achieved by lifting fairing  15  in direction  7 .  
         [0052]     Of course, once fairing  15  has been lifted in direction  7  is must be held in place so that it can pass safely over stinger  22 . The present invention utilizes a positioning lock  30  to keep fairing  15  abutted in place. It should be understood that any suitable positioning lock  30  may be utilized.  
         [0053]     One non-limiting embodiment of positioning lock  30  can be seen by reference to  FIG. 9 , in which a wedge  39  has been inserted into the upper gap between fairing  15  and pipe  12  to minimize gap  30  and abut fairing  15  against pipe  12 . It is envisioned that any suitable number of wedges may be utilized, and that such wedges may comprise any suitable shape.  
         [0054]     Another positioning lock embodiment utilizes a set screw/bolt, with two non-limiting embodiments shown in  FIG. 8 . Referring now to  FIG. 8  there is shown a cross-sectional representations showing fairing  15  mounted on pipe  12 , showing fairing  15  lifted and held in place by positioning lock  30 . Threaded passages  33  are provided in fairing  15  for receiving set screws/bolts  35  and  37 . As shown, set screw/bolt  37  engages pipe  12  directly, whereas, set screw/bolt  35  engages a pipe contact member  38 , which in turn engages pipe  12 .  
         [0055]     Once fairing  15  passes over stinger  22 , fairing  15  must now be made to freely rotate around pipe  12 . Of course, positioning lock  30  prevents such free rotation. According to another embodiment of the present invention, position lock  30  will comprises materials which will degrade in the aquatic environment and allow free rotation of fairing  15  around pipe  12 . The materials are selected to degrade in the aquatic environment at a rate slow enough to allow for installation, but fast enough so that the fairing come properly operate not too long after installation. The materials must have physical properties suitable to allow fairing  15  to be locked into place, and to withstand the rigors in pipe installation, and travel across the stinger.  
         [0056]     Not all of positioning lock  30  need be comprised of degradable materials. As one non-limiting example, pipe contact member  38  comprises a degradable material. As another non-limiting example, set screw/bolt  37  comprises a degradable material. It should be easy to see, that even bolt  37  does not have to be made entirely of degradable materials. As non-limiting examples, only the tip of set screw  37  in contact with pipe  12  need comprises degradable material, or perhaps the threads of screw/bolt  37  will degrade. Alternatively, the threads of threaded passages  33  can be made to degrade, freeing set screw  38 . As even another non-limiting example, a positioning lock  30  with a degradable locking pin can be easily envisioned.  
         [0057]     Materials that will degrade in marine environments and that will have adequate physical properties are well known to those of the materials art. Preferably, such materials will be degradable thermoplastics and theermosets, most preferably biodegradable thermoplastics and thermosets.  
         [0058]     The present invention utilizes unique collars  13  to secure fairings  15  to pipe  12 . Specifically, the collars of the present invention are designed to avoid colliding with stinger  22 . Referring now to  FIGS. 10 and 11 , there are shown cross-sectional representations of stinger  22 , showing two embodiments of collar  13  mounted on pipe  12 . More clearer details are provided by additional reference to  FIG. 13 , which is an isolated representation of collar  13 . Point  63  is the center of pipe  12  cross-section and of collar  13  cross-section. Assuming a uniform circular collar  13 , the interfering radial portion  65  of collar  13  is that portion which would engage stinger  22 , and is that portion  65  of collar  13  between points  61  and  62 , defining angle Θ. Within this Θ radius, collar  13  must be made thin enough to pass over stinger  22 , and in a preferred embodiment is merely a thin band  51 . Interfering portion  65  of collar  13  that does not engage stinger  22  defines an angle 2Π-Θ radians. Thus, in the present invention, for a stinger having an interference angle with a collar of Θ radians, the main body of collar of the present invention is less than or equal to 2Π-Θ radians, with at least a Θ radian portion of the collar comprising a thin section having a thickness that will not interfere with passage over the stinger. The main body of collar  13  must extend radially away from pipe  12  sufficient to secure fairing  15  in place. It is preferred that collar  13  be provided with a band groove  54  for receiving band  51 . In some embodiments, a band locking/tightening mechanism, such as locking bolt/nut  55  are provided.  
         [0059]     Referring now to  FIG. 12 , there is shown a cross-sectional representation of stinger  22 , showing fairing  15  mounted on pipe  12 .  
         [0060]     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.