Abstract:
A vortex-induced vibration (VIV) suppression system configured to accommodate a change in an underlying tubular diameter. The system including an encircling member dimensioned to at least partially encircle an underlying tubular. The encircling member may be, for example, a collar or a VIV suppression device such as a strake, or any other type of VIV suppression device. The system further including a band member dimensioned to encircle the encircling member and hold the encircling member around the underlying tubular at a desired axial position. A spring member may further be provided. The spring member may be positioned between the encircling member and the band member and dimensioned to contract in response to an increase in a diameter of the underlying tubular and expand in response to a decrease in a diameter of the underlying tubular such that the encircling member remains at the desired axial position.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional of co-pending U.S. patent application Ser. No. 13/829,478, filed Mar. 14, 2013, which application claims the benefit of the earlier filing date of U.S. Provisional Patent Application No. 61/711,987, filed Oct. 10, 2012, the disclosures of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     A difficult obstacle associated with the exploration and production of oil and gas is management of significant ocean currents. These currents can produce vortex-induced vibration (VIV) and/or large deflections of tubulars associated with drilling and production. VIV can cause substantial fatigue damage to the tubular or cause suspension of drilling due to increased deflections. 
     Two solutions for VIV suppression are helical strakes and fairings. Typically, helical strakes are made by installing fins helically around a cylindrical shell. The cylindrical shell may be separated into two halves and positioned around the tubular to helically arrange the fins around the underlying tubular. While helical strakes, if properly designed, can reduce the VIV fatigue damage rate of a tubular in an ocean current, they typically produce an increase in the drag on the tubular and hence an increase in deflection. Thus, helical strakes can be effective for solving the vibration problem at the expense of worsening the drag and deflection problem. 
     Another solution is to use fairings as the VIV suppression device. Typical fairings have a substantially triangular shape and work by streamlining the current flow past the tubular. A properly designed fairing can reduce both the VIV and the drag. Fairings are usually made to be free to weathervane around the tubular with changes in the ocean current. 
     A challenge associated with both helical strakes and fairings is their use on tubulars that have an outside diameter that shrinks due to hydrostatic pressure. This is often true of risers that have insulation or buoyancy on the outside of an inner metallic tubular. Since it is usually much cheaper to install helical strakes or fairings on a tubular while it is above the water surface (before it is lowered), this means that the tubular diameter will often be larger at the surface than at depth. Helical strakes that are banded onto the tubular risk coming loose when the diameter shrinks since the bands are typically not sufficiently compliant to accommodate the diameter change. Fairings utilize thrust collars that restrain the fairings from sliding down the tubular. These thrust collars are often banded on and suffer from the same lack of compliance that helical strakes experience. 
     SUMMARY OF THE INVENTION 
     In accordance with an embodiment of the invention, a device for supporting a vortex-induced vibration (VIV) suppression device is disclosed. The device may include a collar member having a web portion dimensioned to encircle an underlying tubular and flanges extending from opposing sides of the web portion in a direction opposite the underlying tubular. A band member may be provided which encircles the web portion and the underlying tubular so as to hold the collar member about the tubular. A resilient member may be positioned between the collar member and the web portion. The resilient member may be dimensioned to expand or contract in response to a change in diameter of the underlying tubular so that an axial alignment of the collar member about the underlying tubular can be maintained. 
     In accordance with another embodiment of the invention, a system for reducing vortex induced vibration (VIV) about a tubular is disclosed. The system may include a strake section having a shell portion dimensioned to encircle an underlying tubular and a fin extending from the shell portion. A slot may be formed through the fin portion and a band member dimensioned for insertion through the slot and around the shell portion may be provided. The system may further include a resilient member positioned within the slot portion, the resilient member dimensioned to expand or contract in response to a change in diameter of the underlying tubular so that an axial alignment of the strake section about the underlying tubular is maintained. 
     In accordance with another embodiment of the invention, a vortex-induced vibration (VIV) suppression system configured to accommodate a change in an underlying tubular diameter is disclosed. The system may include an encircling member dimensioned to at least partially encircle an underlying tubular. The encircling member may be, for example, a collar or a VIV suppression device such as a strake, or any other type of VIV suppression device. The system may further include a band member dimensioned to encircle the encircling member and hold the encircling member around the underlying tubular at a desired axial position. A spring member may further be provided. The spring member may be positioned between the encircling member and the band member and dimensioned to contract in response to an increase in a diameter of the underlying tubular and expand in response to a decrease in a diameter of the underlying tubular such that the encircling member remains at the desired axial position. 
     The above summary does not include an exhaustive list of all aspects of the present invention. It is contemplated that the invention includes all apparatuses that can be practiced from all suitable combinations of the various aspects summarized above, as well as those disclosed in the Detailed Description below and particularly pointed out in the claims filed with the application. Such combinations have particular advantages not specifically recited in the above summary. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The embodiments disclosed herein are illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and they mean at least one. 
         FIG. 1A  is a perspective view of one embodiment of a collar half. 
         FIG. 1B  is an end view of one embodiment of a collar half with springs. 
         FIG. 1C  is a cross sectional view of the collar half of b along line A-A′. 
         FIG. 1D  is a cross sectional view of the collar half of  FIG. 1B  along line A-A′. 
         FIG. 1E  illustrates the collar half of  FIG. 1D  coupled to a second collar half. 
         FIG. 1F  illustrates a side view of one embodiment of a plurality of suppression devices supported along a tubular. 
         FIG. 2A  is a side view of one embodiment of a helical strake on a tubular with a spring. 
         FIG. 2B  is a cross sectional end view of the helical strake of  FIG. 2A  along line B-B′. 
         FIG. 2C  is a cross sectional view of the helical strake of  FIG. 2B  along line C-C′. 
         FIG. 2D  is a top view of one embodiment of a spring. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In this section we shall explain several preferred embodiments with reference to the appended drawings. Whenever the shapes, relative positions and other aspects of the parts described in the embodiments are not clearly defined, the scope of the embodiments is not limited only to the parts shown, which are meant merely for the purpose of illustration. Also, while numerous details are set forth, it is understood that some embodiments may be practiced without these details. In other instances, well-known structures and techniques have not been shown in detail so as not to obscure the understanding of this description. 
     The present invention is directed to a spring system that allows a band, or other structure, used to position a VIV suppression device about a tubular to accommodate changes in the tubular outside diameter so that a position of the VIV suppression device can be maintained. In some embodiments, the spring system is a discrete spring system made up of more than one spring member that can be positioned about the band. It has been found that, in some embodiments, a discrete spring system is preferable over a system that runs most of the length of the band (e.g., a resilient liner) because such a unitary system may not be able to accommodate a significant amount of tubular shrinkage since the band pressure is low relative to the material stiffness of most practical liner materials. Even if such a spring system is hollow, it is difficult to obtain sufficient deformation of the liner so that it acts like a spring with low creep or compression set. 
     Referring now to the invention in more detail,  FIG. 1A  is a perspective view of one embodiment of a collar half. Collar half  101  may be half of a collar used to axially align a VIV suppression device about a tubular. Collar half  101  may include a web  105  and two flanges  104 . Web  105  may be used as a surface to band the collar against a tubular or other structure. In this aspect, web  105  may be, for example, a band shaped member have dimensions which conform to a curvature of an underlying tubular or other structure. Flanges  104  may extend from opposing sides of web  105  in a substantially perpendicular direction (away from an underlying tubular) such that they can be used to restrict adjacent structures, such as VIV suppression devices, from sliding past collar half  101 . Collar half  101  may be made of any suitable material including, but not limited to, thermoplastics, elastomers, metals, and composite or hybrid materials. Although a single collar half  101  is illustrated in  FIG. 1A , it is to be understood that a complete collar includes a second collar half which is substantially identical to collar half  101  such that when the two are used together, they encircle an entire circumference of the underlying tubular. 
       FIG. 1B  illustrates an end view of a collar half such as that illustrated in  FIG. 1A . Representatively, collar half  101  is again shown having a web  105  and two flanges  104 . Springs  103  are shown positioned in a widthwise direction across web  105 . Springs  103  are shown positioned directly on top of web  105  such that when bands  102  are wrapped around web  105 , springs  103  are between web  105  and bands  102 . In this aspect, when bands  102  are tightened, they apply pressure to springs  103  which, in turn, causes springs  103  to deform. Springs  103  apply pressure to web  105 , which can then apply pressure to an underlying structure (e.g., a tubular). 
     Still referring to  FIG. 1B , web  105  will typically range from ½ inch wide to 12 inches wide, but most typically will range from 1 inch wide to 6 inches wide. A single band  102  may be used, or multiple bands  102  may be used. The bands  102  will typically range in width from ½ inch to 2 inches. 
     Springs  103  may have a finite width and may, or may not, cover the entire distance between the two flanges  104  (i.e., a width of web  105 ). Springs  103  may be of any suitable size, but the total of all of the springs  103  will typically cover no more than ½ of the total circumference of collar half  101 . Springs  103  may be any type of resilient structure, for example, a hollow structure, a solid structure or made of a solid material. Springs  103  may also consist of other types of compression springs such as a coiled spring. Springs  103  may be attached to web  105  using any suitable attachment mechanism (e.g., screws, bolts, brackets, adhesives, or the like) or may be positioned on web  105  and held in place by flanges  104  and bands  102 . Still further, in some embodiments, springs  103  may be molded to web  105  and/or one or both of flanges  104  by any suitable molding technique. 
     Still referring to  FIG. 1B , collar half  101  and springs  103  may be made of any suitable material, including thermoplastics, elastomers, metals, and composite of hybrid materials. For example, springs  103  may be made of stripes of an elastomeric material. 
     Referring to  FIG. 1C ,  FIG. 1C  illustrates a cross-sectional side view of the collar half of  FIG. 1B  along line A-A′ and positioned around an underlying structure. In particular, collar half  101  is shown positioned around tubular  100 . Collar half  101  includes web  105  and flange  104  extending therefrom. From this view, it can be seen that springs  103  are positioned against web  104  and band  102  lies on top of springs  103 . Note that it is also possible for band  102  to go through one or more springs  103 . In this way, the springs may be pre-installed onto the bands. 
     Again referring to  FIG. 1C , band  102  has a substantially fixed length such that once it is secured around collar half  101  and the underlying tubular  101 , band  102  has a substantially fixed circumference. Thus, when band  102  is put into tension (such as by an expansion of tubular  101 ), it applies pressure to springs  103  which causes springs  103  to compress to accommodate the diameter change. Similarly, when a tension on band  102  is reduced (such as by a contracting tubular diameter), springs  103  expand to fill in the gap created between band  102  and the reduced tubular diameter so that collar half  101  is still held tightly around tubular  100 . 
     It is noted that by having discrete springs instead of a continuous spring or liner, the local pressure on springs  103  is higher (for a given band tension) and thus the compression of springs  103  is greater. This allows collar half  101  and band  102  to accommodate a greater change in the diameter of tubular  100  than a continuous spring or liner would allow. 
     Still referring to  FIG. 1C , web  105  may be, for example, ⅛ of an inch thick to 1 inch thick but may be of any suitable thickness. Flanges  104  may be of any suitable height. Springs  103  will be of the height and width required to accommodate the required change in diameter of tubular  100 , for example from about ¼ inch to 2 inches tall. 
       FIG. 1D  illustrates a cross-sectional side view of the collar half of  FIG. 1B  along line A-A′, which is substantially similar to the collar half of  FIG. 1C  except in this embodiment, guides are included to help holds springs in a desired position. From this view, it can be seen that collar half  101  may be substantially similar to the previously discussed collar half in that it includes web  105  and flanges  104 . Springs  103  can be positioned against web  105  and band  102  lies on top of springs  103  as previously discussed. A tubular (not shown) lies underneath collar half  101 . Optional guides  106  are adjacent to one of the springs  103  to keep the spring from sliding relative to web  105 . Guides  106  may help to prevent springs  103  from sliding along web  105 . 
     For example, in one embodiment, guides  106  may be provided on one or more sides of spring  103  to provide resistance against sliding of springs  103 . Guides  106  may be made of a single member or multiple structural members and may be of any size and shape suitable for preventing sliding of springs  103 . For example, guides  106  may be “U” shaped brackets which extend between flanges  104  and along part of the span of springs  103 . Alternatively, guides  106  may be placed on top of springs  103 . Or guides may be placed on, or under, or around band  102 . In some embodiments, guides  106  may be fastened to collar half  101  by either fastening to web  105  or to flanges  104  by any suitable mechanism (e.g., bolts, screws, bands, brackets, adhesive or the like). In still further embodiments, guides  106  may also be fastened directly to springs  103  or to band  102 . 
     Guides  106  may be of any size and shape suitable for preventing sliding of springs  103  around web  105 . Representatively, in one embodiment, guides  106  may be fastener such as a bolt or screw. Guides  106  may be used to hold up any suitable spring shape. For example, guides  106  may be used to hold a helical compression spring in place. Although two guides  106  are illustrated, it is contemplated that any number of guides  106  may be used. For example, all of the springs  103  may have guides  106 , none of the springs  103  may have guides  106 , or one or more of the springs  103  may have guides  106 . Guides  106  may also be considered housings dimensioned to house an associated spring. 
       FIG. 1E  illustrates the collar half of  FIG. 1D  coupled to a second collar half. Representatively, it can be seen from this view that collar halves  101 A and  101 B are held onto a tubular by band  102 . Collar halves  101 A and  102 B have webs  105 A and  105 B as well as flanges  104 A and  104 B, respectively. Springs  103  reside under band  102  and optional guides  106  restrain one or more springs  103  from sliding or overturning. 
     Again referring to  FIG. 1E , this figure illustrates that either one or two collar halves may be used. Also, collars whose sum of all of their segments does not cover the full circumference may be used, and any number of segments may be used to make up the collar. Any number of springs  103  may also be used and any number of these springs  103  may, or may not, have one or more guides  106 . Collar halves  101 A and  101 B may be secured together around the tubular by band  102 , or/or by other securing mechanisms (e.g., a hinge). 
       FIG. 1F  illustrates a side view of suppression devices held in place along an underlying structure by any one or more of the previously discussed collar halves. In particular, as can be seen from this view, collar halves  101  are positioned between ends of suppression devices  108  such that they prevent suppression devices  108  from sliding axially along the underlying structure  100  (e.g., a tubular). In one embodiment, suppression devices  108  may be fairings free to weathervane around the tubular  100  while collar halves  101  are clamped around the underlying the tubular. 
       FIG. 1F  illustrates an embodiment in which each of collar halves  101  support two suppression devices  108 . It is contemplated, however, that collar halves  101  can support any number of suppression devices  108  ranging from 1 to 100, for example where suppression devices  108  are fairings, each of collar halves  101  can support between 1 and 8 fairings. Collar halves  101  may also support other suppression devices such as helical strakes, Henning devices, splitter plate type devices, smooth sleeves, perforated structures, or any other device that requires support on a tubular. 
       FIG. 2A  illustrates a side perspective view of one embodiment of a suppression device positioned around an underlying structure. Representatively,  FIG. 2A  shows helical strake section  201  positioned around tubular  200 . Strake section  201  may have three fins  202  that are attached to, or part of, shell  203 . A slot  204  may be formed through one or more of fins  202 . A spring  205  for accommodating a tubular diameter change, such as any of those previously discussed, may be positioned within slot  204 . Optional fasteners  210  may assist in keeping spring  205  in place, either directly or by restraining an internal structure. 
     Helical strake section  201  may be a single piece or may consist of two or more sections around the circumference. Any number of fins  202  and/or slots  204  and/or springs  205  may be present. Each fin may or may not have one or more slots, and each slot may or may not have one or more springs. In this aspect, when a band (not shown) is placed around helical strake section  201 , through slot  204  and on top of spring  205 , spring  205  compresses as the band tightens. If a diameter of tubular  200  shrinks or otherwise changes, the spring allows the band to maintain tension even though the diameter changes. Bands may be placed on top of spring  205  or may go through spring  205 . Also, the band may reside in a channel, such as a channel to produce a gap or stand-off between the main strake body from the underlying tubular. 
     Spring  205  may be of any suitable shape but will typically fit into part of slot  204  and/or fins  202 . Spring  205  may be of any suitable height, and of any suitable cross section or even spring type. The helical shape of the fins  202  may sufficiently keep springs  205  in place. Optional fasteners  210  for keeping spring  205  in place my further be provided. Fasteners  210  may be any type of fastener of any size suitable for retaining spring  205  within slot  204 . For example, fasteners  210  may be bolts, screws, brackets, adhesives or the like. Helical strake section  201 , including fins  202 , shell  203 , and spring  205 , may be made of any suitable material such as those previously discussed. 
       FIG. 2B  illustrates a cross-sectional view of the helical strake section of  FIG. 2A  along line B-B′.  FIG. 2B  shows helical strake section  201  having shell halves  203 A and  203 B which are banded together using band  207 . Shell halves  203 A and  203 B meet at a gap  206 , which may in some embodiments, extend along a length of fin  202 . Helical strake section  201  has fins  202  that are attached to shell half  203 A or shell half  203 B. Springs  205  are shown positioned through slots within each of the fins  202 . In this aspect, when band  207  is put into tension, it compresses springs  205  and puts pressure onto shell halves  203 A and  203 B which, in turn put pressure on an inner tubular (not shown). Gap  206  may get smaller as the band tension is increased. 
     Springs  205  may be of any suitable size, shape, material, or type such as those previously discussed, provided they are able to compress when band  207  is tightened. Springs  205  will typically each cover less than 20% of the helical strake section  201  circumference. The total of springs  205 , for a give point along the length of strake section  201 , will cover less than 50% of the circumference of strake section  201 . 
       FIG. 2C  illustrates a cross-sectional view of the helical strake section of  FIG. 2B  along line C-C′. From this view, it can be seen that fin  202  includes a first portion  202 A and a second portion  202 B which extend from shell  203  such that a hollow channel  212  is formed within fin  202 . In this aspect, slot  204  is formed through both of the first portion  202 A and second portion  202 B such that spring  205  and band  207  go through both sides of fin  202 . Band  207  is positioned on top of spring  205 . In some embodiments, spring  205  may include a middle portion  208  which rests within hollow channel  212  and is dimensioned to keep the spring from slipping out through the slot. For example, middle portion  208  may extend out of the plane such that it is wider than slot  204 , and in some cases, is wider than opposing ends of spring  205 . In this aspect, when the tension of band  207  is increased, spring  205  compresses onto shell  203 . Spring section  208 , which is part of spring  205 , will in turn partially compress. 
       FIG. 2D  illustrates a top view of the spring of  FIG. 2C . From this view, it can be seen that spring  205  includes middle portion  208  which is wider than the rest of spring  205  and wider than the slot within which spring  205  is inserted. With middle portion  208 , spring  205  is intentionally and significantly wider than a slot that spring  205  would be inserted into. In this fashion, middle portion  208  assist in keeping spring  205  in place and from sliding through the slot and out of the slot. 
     Although a spring having a wider middle portion  208  is shown, it is contemplated that in other embodiments, fasteners or other appurtenances may be used in place of middle portion  208 . Middle portion  208  may be made of any suitable size, shape and material. Middle portion  208  may be part of spring  205  or middle portion  208  may be separate pieces that are bonded or attached to spring  205 . 
     In the foregoing specification, the invention has been described with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes can be made thereto without departing from the broader spirit and scope of the invention as set forth in the appended claims. For example, while discrete springs for a collar and for a helical strake are shown, the spring system disclosed herein may be used for other structures that may be attached to a tubular such as Henning devices or measurement clamps. The discrete springs may also be used for a banded or bolted device (e.g. collar, or helical strake) by placing them between the device and the tubular. The springs may be put underneath the device so that the springs are located between the device and the tubular. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.