WO2011084920A1

WO2011084920A1 - Spacers having restraint mechanisms to restrain subsea tubular structure

Info

Publication number: WO2011084920A1
Application number: PCT/US2011/020038
Authority: WO
Inventors: Donald Wayne Allen; Michalakis Efthymiou; Dean Leroy Henning; Guido Leon Kuiper; Li Lee
Original assignee: Shell Oil Company; Shell Internationale Research Maatschappij B.V.
Priority date: 2010-01-05
Filing date: 2011-01-03
Publication date: 2011-07-14

Abstract

There is disclosed a system comprising a support structure in a flowing fluid environment; a spacer plate connected to the support structure, the spacer plate comprising at least one retention mechanism movable from an open to a closed configuration, the retention mechanism comprising an opening; wherein the opening of the retention mechanism is adapted to receive a structure when in the open configuration.

Description

SPACERS HAVING RESTRAINT MECHANISMS TO

RESTRAIN SUBSEA TUBULAR STRUCTURE

Field of the Invention

The present invention relates to systems and methods for restraining and releasing tubular structures.

Background Information

Floating vessels may be used to liquefy and gasify natural gas. Sea water may be used to cool or heat the natural gas. It may be desired to separate the water inlet from the water outlet due to the temperature differences. A plurality of risers may be used to collect or deposit water at a depth from the floating vessel. These risers may be exposed to VIV.

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 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 mini spar or spar floating production system (hereinafter "spar") .

Traditionally, a bundle of risers or other tubulars are lowered and installed from a structure at the surface of a body of water and threaded through a number of templates at different depths. The templates are provided to keep a minimum distance between the risers and to keep them from interacting with each other. One problem with this arrangement is the difficulty in threading the risers through multiple holes in the templates, particularly if there are joints, junctions, VIV suppression devices, or other items extending out from a circumference of the riser. U.S. Patent Number 6,161,620 discloses a deepwater riser assembly for a riser connecting subsea equipment to a surface wellhead. A buoyancy can assembly provides an open ended buoyancy can tube which surrounds the upper end of the riser and an upper seal which effectively closes the annulus between the riser and the buoyancy can tube. A load transfer connection in the buoyancy can assembly then connects the riser to buoyancy can tube. A pressure charging system communicates with the annulus between the riser and the buoyancy can tube below the upper seal. Injecting gas into this annulus then provides support to the riser. U.S. Patent Number 6,161,620 is herein incorporated by reference in its entirety .

U.S. Patent Number 7,398,697 discloses sensors, including fiber optic sensors and their umbilicals, which are mounted on support structures designed to be retro-fitted to in-place structures, including subsea structures. The sensor support structures are designed to monitor structure conditions, including strain, temperature, and in the instance of pipelines, the existence of production slugs. Moreover the support structures are designed for installation in harsh environments, such as deep water conditions using remotely operated vehicles. U.S. Patent Number 7,398,697 is herein incorporated by reference in its entirety.

U.S. Patent Number 5,697,447 discloses a process comprising organizing the top of the risers; organizing the bottom of the risers; and twisting the risers to impose tension in the risers. A system comprising an organizer of the top of the risers; an organizer of the bottom of the risers; and a twister the risers to impose tension in the risers. U.S. Patent Number 5,697,447 is herein incorporated by reference in its entirety. WO Publication Number 2008/152369 discloses a reinforcing system for reinforcing tubular conduits such as those used in pipelines, comprising: a clamshell housing connectable around a tubular conduit so as to form a gap around such a tubular conduit between the housing and a portion of an external face of such a tubular conduit which clamshell housing comprises a first housing part; an expandable cushion comprising a central portion mounted within the first housing part and two side portions extending from the first housing part; wherein when the cushion is in an unexpanded state the cushion is adapted to be wrapped around such a conduit with at least partially overlapping side portions and when the cushion is so wrapped and in an expanded state the cushion is adapted to fill the gap. WO Publication Number 2008/152369 is herein incorporated by reference in its entirety.

There are needs in the art for one or more of the following: apparatus and methods for installing and removing structures in flowing fluid environments, which do not suffer from certain disadvantages of the prior art apparatus and methods; apparatus and methods for reducing VIV and/or drag on multiple structures in flowing fluid environments; apparatus and methods for installing, servicing, removing, and/or replacing a riser array or bundle; apparatus and methods for reducing VIV and/or drag on a riser array or bundle which allows the riser array or bundle to be easily installed, removed and/or serviced.

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

One aspect of the invention provides a system comprising a support structure in a flowing fluid environment; a spacer plate connected to the support structure, the spacer plate comprising at least one retention mechanism movable from an open to a closed configuration, the retention mechanism comprising an opening; wherein the opening of the retention mechanism is adapted to receive a structure when in the open configuration .

Advantages of the invention may include one or more of the following: improved installation, removal, servicing, and/or replacement of a plurality of structures; improved drag and/or VIV reduction of a plurality of structures; lower cost installation, removal, servicing, and/or replacement of a plurality of structures; and/or installation, removal, servicing, and/or replacement of a plurality of structures with VIV suppression devices.

These and other aspects of the 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

The invention may best be understood by referring to the following description and accompanying drawings that are used to illustrate embodiments of the invention. In the drawings:

Figure 1 illustrates an example marine system in which embodiments may be implemented.

Figures 2A-2B show two common types of VIV suppression devices or structures suitable for one or more embodiments.

Figure 3 shows a top planar view of a possible design for a spacer that has internal holes for tubular structures.

Figure 4 is a top planar view of a spacer that has a restraint mechanism for a tubular structure, according to one or more embodiments.

Figure 5 is a top planar view of a spacer that has a restraint mechanism for a tubular structure, in which a body of the spacer has an open structure, according to one or more embodiments .

Figures 6A-6B are top planar views that illustrate introducing a tubular structure into an opening of a restraint mechanism, and closing the opening of the restraint mechanism around the tubular structure to restrain the tubular structure, according to one or more embodiments.

Figure 7 is a top planar view of a restraint mechanism that includes a pressure sensor, according to one or more embodiments.

Figure 8 is a top planar view of a restraint mechanism that includes a protective, soft material or element, according to one or more embodiments.

Figure 9 is a side view of a tubular structure having a protective collar, according to one or more embodiments.

Figures lOA-lOC are top planar views that illustrate extending a restraint mechanism toward a tubular structure, introducing the tubular structure into an opening of the restraint mechanism, closing the restraint mechanism around the tubular structure to restrain the tubular structure, and retracting the restraint mechanism and the tubular structure, according to one or more embodiments.

Figure 11 is a side view of a camera, such as a video camera, proximate a restraint mechanism to obtain images or video of the restraint mechanism restraining a tubular structure, according to one or more embodiments.

Figure 12A-12B illustrates alternate restraint mechanisms, according to embodiments.

Figure 13 is a block flow diagram of a method of assembling two or more joined tubular structures, according to one or more embodiments. Figure 14 illustrates an example marine system including a Floating Liquified Natural Gas plant, in which embodiments may be implemented.

Figure 15 is a top planar view of an example spacer for nine tubular structures, according to one particular embodiment .

Detailed Description

In the following description, numerous specific details are set forth. However, it is understood that embodiments may be practiced without these specific details. In other instances, well-known structures and techniques have not been shown in detail in order not to obscure the understanding of this description.

Figure 1 :

Figure 1 illustrates an example marine system 100 in which embodiments may be implemented.

The marine system includes surface structure 102 at or near water surface 104, for example a surface of the ocean. By way of example, the surface structure may include a ship, a barge, a vessel, an offshore rig such as a spar, semisub, TLP, or other rigs, an offshore platform, a floating plant, a floating liquefied natural gas plant, or other floating or surface structure known in the arts.

At least two tubular structures 106 are connected to the surface structure. By way of example, the tubular structures may be connected to the surface structure through a marine riser tensioner, a swivel joint, a ball joint, or the like. In one embodiment, a tubular structure has a circular or oval cross-section. In another embodiment, a cross-section of a tubular structure need not be circular or oval, but can include other shapes such as, but not limited to, square, rectangular, etc. In one or more embodiments, the tubular structures may have outer diameters of at least six inches, often at least one foot, and may have lengths of at least 50 feet, often at least 100 feet, or more.

In the illustration of Figure 1, two tubular structures 106A, 106B are visible. More tubular structures may optionally be included, such as, for example, at least three, at least four, at least six, at least nine, or more. Examples of suitable tubular structures include, but are not limited to, risers, marine risers, riser pipes, marine pipes, pipes, tubes, tendons, umbilicals, or the like, or combinations thereof. The tubular structures may extend all the way to seafloor 108, or only part way to the seafloor. In some cases, mud, crude oil, natural gas, water, cold water from depth, and/or other fluids may be conveyed through the tubular structures.

The tubular structures are physically connected together, or held in a position relative to one another, with interconnected guide sleeves or other spacers 110A, HOB. The spacers connect the tubular structures together or hold them in position as a grouping, bundle, array, other ordered arrangement, or other joined plurality. The spacers may help to keep the tubular structures relatively close together, but separated so that they do not significantly strike into one another or otherwise damage one another. In one aspect, several spacers located at various depths and intermittently spaced apart along the length of the tubular structures may be used to restrain the tubular structures, and help prevent the tubular structures from contacting each other.

Referring again to Figure 1, it is not uncommon that the tubular structures will be disposed in water having current 112. Current 112 may tend to cause hydrodynamic drag and/or vortex-induced vibration (VIV) of the tubular structures. Further, in an array of tubular structures connected or positioned together with a spacer (e.g., spacer 110A) , VIV directly induced by current 112 on one tubular structure of the array may be imparted to other tubular structures of the array. Such VIV is generally undesirable, and if not suppressed, may tend to result in damage, fatigue, or even premature failure of the tubular structures. Accordingly, it is generally desirable to reduce the VIV of the tubular structures .

In one or more embodiments, some or all of the tubular structures may have VIV suppression devices or structures in order to help suppress such VIV, although this is not required. Examples of VIV suppression devices or structures include, but are not limited to, strakes, fairings, Henning devices, shrouds, wake splitters, and other types of VIV suppression devices or structures known in the arts.

Figures 2A-2B:

Figure 2A is a cross-sectional top view illustrating one or more representative strakes 216 installed along a length of tubular structure 206 as VIV suppression device (s) . The strake(s) may be helical strakes, which are helically wrapped or coiled around the tubular structure and may be described as connected thereto.

Figure 2B is a cross-sectional top view illustrating representative fairing 218 installed along a length of tubular structure 206 as a VIV suppression device and may be described as connected thereto. The fairing has nose 220 and tail 222. The fairing may swivel around the tubular structure based on the ocean current .

The VIV suppression devices may optionally be conventional, and may be constructed of conventional materials. If desired, protective materials or structures, such as, for example, covers, caps, bumpers, or the like, may optionally be included on the VIV suppression devices to help prevent damage. The protective structures may comprise pliable or soft materials, such as, for example, rubber.

Referring again to Figure 1, the rightmost tubular structure 106B has one or more VIV suppression devices or structures 114A, 114B connected thereto. Conventional collars may be used to keep the VIV suppression devices from moving along the length of the tubular structures. In the illustration, leftmost tubular structure 106B does not have any VIV suppression devices or structures connected thereto. In some cases, VIV of an array or other plurality of joined tubular structures may be sufficiently suppressed if only a subset of the tubular structures have VIV suppression devices .

Omitting VIV suppression devices from some of the tubular structures (so that only a subset of the tubular structures have the VIV suppression devices) may help to reduce the equipment cost. In addition, it tends to be more difficult, time consuming, and/or more expensive to install tubular structures with VIV suppression devices as compared to tubular structures without VIV suppression devices. The VIV suppression devices may tend to make the tubular structures more bulky, difficult to maneuver, difficult to align, and/or difficult to assemble with the spacers. It likewise tends to be more difficult, time consuming, and/or more expensive to retrieve tubular structures with VIV suppression devices, such as, for example, for cleaning, inspection, and/or repair.

Figure 3 :

Figure 3 shows a top planar view of a possible design for spacer 310. The spacer has body 324. By way of example, the body may include a sheet of a metal, such as, for example, stainless steel, which has a thickness sufficient to provide the desired strength (e.g., often from about one quarter to three quarters of an inch) . Multiple generally cylindrical internal holes or other openings 326 are formed or defined within the body. In the illustration, five openings are shown, although fewer or more openings may be used. Each of the internal openings may accommodate a tubular structure. One of the openings, such as, for example, the central opening, may accommodate a structural support tubular structure.

However, installation of arrays or other pluralities of joined tubular structures utilizing a spacer like spacer 310 of Figure 3 may tend to be difficult, time consuming, and/or expensive. A representative method of assembling joined tubular structures may include initially threading a support tubular structure through an internal opening of spacer 310, such as, for example, the central opening. The support tubular structure may also be thread through several other similar spacers. The spacers may be fixedly attached to the support tubular structures at different locations along its length. The support tubular structure having the fixedly attached spacers may be submerged in the ocean at the appropriate depth.

The assembly of the remaining tubular structures may be performed underwater in the ocean. One by one, each of the other tubular structures may be vertically threaded or otherwise introduced through an internal opening in each of the spacers along the length of the support tubular structure. Due to the ocean current, and the relatively large sizes and weights of the tubular structures, it tends to be challenging to align and thread the tubular structures through the openings. This is particularly true when some or all of the tubular structures have VIV suppression devices, since the VIV suppression devices may tend to make the tubular structures more bulky, difficult to handle, difficult to maneuver, difficult to align, and/or difficult to assemble with the spacers. In addition, some VIV suppression devices, such as fairings, may tend to move with the ocean current. Similar challenges may be encountered when tubular structures are retrieved and in some cases reinstalled, such as for cleaning, inspection, repair, or the like.

Accordingly, there would be certain advantages to a spacer that would reduce or eliminate one or more of the challenges with installation or assembly of tubular structures, especially when one or more of the tubular structures have VIV suppression devices.

Figure 4 :

Figure 4 is a top planar view of spacer 410, according to one or more embodiments. The spacer is operable to connect, join, or otherwise group or associate two or more tubular structures 406A, 406B.

Spacer 410 includes body 424. As shown, the body may have a shape of a rectangle. Alternatively, the body may have the shape of a circle, oval, star, or triangle, to name just a few examples.

In one aspect, the body may include a solid sheet or plate of a sufficiently strong material. Examples of suitable materials include, but are not limited to, metals (e.g., stainless steel, copper, aluminum, etc.), fiber reinforced plastics (e.g., fiberglass), carbon fiber materials, and the like. The sheet or plate may have a thickness sufficient to provide a desired strength. By way of example, the body may include a stainless steel sheet having a thickness ranging from about one-quarter of an inch to one inch. It will be appreciated by those skilled in the art, that the appropriate thickness may depend on a number of factors, such as, for example, the number of spacers, the amount of separation between the spacers, the amount of current or vibration expected, etc.

In this embodiment, hole or other optional opening 426 is formed or otherwise defined within the body. The opening may accommodate first tubular structure 406A. As shown, the opening may have a generally circular shape to accommodate a circular cross section of first tubular structure 406A. Alternatively, the opening may have an oval, rectangular, triangular, or other shape, to accommodate a correspondingly shaped tubular structure. Such an opening is optional and not required (for example, the opening may be replaced with another restraint mechanism as will be discussed further below . )

In one or more embodiments, first tubular structure 406A may serve as a structural support for spacer 410. Spacer 410 may be in direct contact with and fixedly attached to the first tubular structure. Although illustrated as slightly smaller, the outer diameter or other cross-sectional dimension of first tubular structure 406A (with or without a VIV suppression device) may be similar to a diameter or other cross-sectional dimension of internal opening 406, so that first tubular structure 406A, or a VIV suppression device on first tubular structure 406A, and spacer 410 may be in direct contact (e.g., a force fit) . In the case of support tubular structures, bolts, rivets, welding, or the like may be used to strengthen the connection. In one or more embodiments, spacer 410 may be fixedly attached to the first support tubular structure before they are introduced into the water, alternatively spacer 410 may be attached after tubular 406a has been installed in the water. Threading the first tubular structure through the opening in the spacer tends to be easier on land than it would be in the ocean. Spacer 410 also includes restraint mechanism 430. Restraint mechanism 430 has opening 432. The opening, in at least one configuration, is operable to receive second tubular structure 406B. For example, the opening, in at least one configuration, may be sized and shaped sufficiently to receive the second tubular structure. In this particular illustration, the opening is a c-shaped opening, which is suited to receive a cylindrical tubular structure, although this is not required.

Arrow 434 indicates a direction in which second tubular structure 406B may be introduced into the opening of the restraint mechanism. Notice that second tubular structure 406B may be introduced into the opening from the side. As discussed above, there are challenges with threading a tubular structure vertically through an interior hole or opening in a spacer. Introducing a tubular structure from the side tends to be less challenging than threading the tubular structure vertically through the interior opening, especially when VIV suppression devices or other protuberances are present. Additionally, the opening of the restraint mechanism may be made relatively larger during insertion of the tubular structure in order to facilitate insertion .

Once second tubular structure 406B has been introduced into opening 432, restraint mechanism 430 is operable to restrain second tubular structure 406B within the opening. As used herein, restraining a tubular structure includes at least partially restricting or limiting the movement of the tubular structure, and does not necessarily imply completely restricting the movement of the tubular structure. In one aspect, restraining the tubular structure may include allowing the tubular structure to move slightly, although restricting the movement of the tubular structure enough that the tubular structure does not contact other tubular structures in a way that results in appreciable damage. The restraint mechanism and the tubular structure it restrains may be, but need not be, in direct physical contact.

As used herein, the term "mechanism", as in restraint mechanism, implies more than a mere static hole or other opening defined within a solid. In one or more embodiments, restraint mechanism 430 may include at least one component part that is capable of mechanical operation, actuation, or movement associated with the restraint of second tubular structure 406B. In one or more embodiments, restraint mechanism 430 may include two or more component parts that work together to restrain the second tubular structure. In one or more embodiments, the restraint mechanism may take the form of a clasping device, a clutching device, a clamp, or another type of device that applies inward pressure or force. By way of example, the restraint mechanism may be actuated hydraulically or pneumatically.

Referring again to Figure 4, arrow 435 is used to show that at least a portion of restraint mechanism 430 may be operable to move. For example, restraint mechanism 430 may open to allow the second tubular structure to be introduced therein, and may then close around the second tubular structure to restraint the second tubular structure.

In the illustration, restraint mechanism 430 has two opposable jaws, parts, or other members 442, 444. Restraint mechanism 430 also has open and/or close mechanism 433. Open and/or close mechanism 433 is operable to allow at least a portion of restraint mechanism 430, such as, for example, one or both of members 442, 444, to move in conjunction with insertion and/or restraint of tubular structure 406B. In various embodiments, open and/or close mechanism may include one or more hinges, pivots, other rotation bearings, other rotation joints, other joints, or other mechanisms capable of allowing at least a portion of restraint mechanism to move in conjunction with opening and/or closing. Actuation of open and/or close mechanism 433 may be accomplished with hydraulics or pneumatics, for example. In the illustration, open and/or close mechanism 433 is connected to ends of members 442, 444, although this is not required. In alternate embodiments, open and/or close mechanism 433, such as, for example, a hinge or other rotation bearing, may be connected at an intermediate position along a length of one of both of members 442, 444. As shown in Figures 6A and 6B, which will be discussed further below, a joint 646 representing one possible embodiment of movement mechanism 433 may allow restraint mechanism 630 to open and close.

In one or more embodiments, restraint mechanism 430 may be controlled from a surface structure, such as surface structure 102. The surface structure may have a control system for restraint mechanism 430. One or more control lines or umbilicals may run from the control system of the surface structure to restraint mechanism 430 and/or spacer 410. Alternatively, or in addition, a button, switch, or like local control system may optionally be provided locally at a restraint mechanism, which a diver or ROV, for example, may use to control the opening and closing of the restraint mechanism. Alternatively, tubular 406b may actuate the closing mechanism when it's moved into opening 432. Alternatively, closing mechanism 433 may include a cam surface that acts to close mechanism 430 when tubular 406b is pushed into opening 432. A locking mechanism may be provided at the ends of jaws 442, 444.

In one or more embodiments, restraint mechanism 430 may receive power from a surface structure. One or more power lines or umbilicals may run from the surface structure to restraint mechanism 430. Alternatively, or in addition, a local power source, such as, for example, a battery, fuel cell, generator, or the like, may optionally be provided local to the restraint mechanism. The power may be used to actuate the restraint mechanisms, such as, for example, through local hydraulics or pneumatics. The body may accordingly have a hydraulic or pneumatic system to actuate the restraint mechanism. Alternatively, restraint mechanism 430 may have a biasing mechanism such as a spring or gas piston which is held in an open position, but forces restraint mechanism 430 to a closed position when tubular 406b is located within opening 432.

The lines or umbilicals may run along the length of a tubular structure, such as, for example, a structural support tubular structure and be secured or fastened to the tubular structure. If desired, conduits may be included to help protect the lines or umbilicals, especially near the surface where there are waves. If desired, various quick underwater connections may be used to facilitate changing out a line or umbilical with a diver or remote operated vehicle (ROV) , for example for maintenance or when there is damage.

In some embodiments, restraint mechanism 430 may have a liner on its inner surface to minimize stresses on structure 406b. The liner may be elastic or a softer material than the rest of the restraint mechanism 430 structure such that the liner fits around structure 406b. Suitable materials for the liner include elastomers, rubber, a liquid or gas filled bladder structure, and other materials as are known in the art .

Figure 5 :

It is not required that the body of a spacer include a solid sheet or plate. Figure 5 is a top planar view of spacer 510 having body 524 that has an open structure, according to one or more embodiments. Body 524 has an open structure, rather than a solid sheet or plate as does body 424 of Figure 4. As shown, the open structure of the body may include a frame having four sides and two diagonal corner-to-corner braces. The open structure may be integrally formed, or may be separate components connected together, for example, by bolts, rivets, welding, or the like. By way of example, the open structure may be made of rectangular strips, pipes, rods, or other tubular structures.

While a specific open structure has been described, it is to be appreciated that other open structures of a wide variety of different shapes, sizes, and constructions are also suitable. For example, alternate open structures may have circular, oval, triangular, hexagonal, or other shapes, and utilize various different bracing structures.

In the embodiment illustrated in Figure 5, spacer 510 has a central internal opening to receive a tubular. Spacer 510 has four restraint mechanisms 530A, 530B, 530C, and 530D. Each of the four restraint mechanisms is on a different one of four sides of body 524. Each of the four restraint mechanisms may receive and restrain a different tubular structure from the side. Each of the restraint mechanisms has a corresponding open and/or close mechanism 533A, 533B, 533C, 533D.

Spacer 410 and spacer 510 of Figures 4 and 5, respectively, each include only one internal opening and, in the case of Figure 4 one restraint mechanism and, in the case of Figure 5, four restraint mechanisms. In alternate embodiments, one or more additional internal openings and/or one or more additional restraint mechanisms may optionally be included. Tubular structures, other than the structural support tubular structure, may be, but need not be, in direct physical contact with the spacer. For example, in the case of a tubular structure with a circular or oval cross section, the tubular structure may have an outer diameter (with or without a VIV suppression device) that is less than a diameter of the opening in the spacer through which the tubular structure is inserted. Furthermore, it is not required that a spacer have an internal opening. In an alternate embodiment, the internal opening may be replaced by a restraint mechanism.

Figures 6A-6B:

Figures 6A-6B are top planar views that illustrate introducing tubular structure 606 into opening 632 of restraint mechanism 630 and closing the opening of restraint mechanism 630 around tubular structure 606 to restrain the tubular structure, according to one or more embodiments.

Figure 6A shows restraint mechanism 630 in an open position to receive tubular structure 606, according to one or more embodiments.

Restraint mechanism 630 has base portion 640 and a head portion. The base portion is fixedly attached or connected with body 624 of a spacer. The head portion includes two opposable jaws, parts, or members 642, 644. In particular, restraint mechanism 630 has first jaw, part, or member 642, and second, opposed jaw part, or member 644. The first and second members project outward from the spacer. In this particular case, the head portion comprises a c-shaped head portion, which is well suited to accommodate a cylindrical tubular structure, although this is not required.

The first and second members are opposable, moveable members that are connected together at leftmost ends thereof (as viewed) by joint 646. Joint 646 represents one example embodiment of an open and close mechanism. Examples of suitable joints include, but are not limited to, hinges, pivots, other rotation bearings, and other rotation joints, to name a few examples. The first and second members are capable of rotating or otherwise moving, about an axis of rotation of the joint, between a fully open position and a fully closed position. In the illustration, the axis of rotation is into the plane of the page. Arrows 635 show that the first and second members may rotate or otherwise move about the joint.

In Figure 6A, restraint mechanism 630 is in an open position. Opening 632 opens to the right (as viewed) . As shown, in one aspect, the opening may be significantly wider than a diameter or other cross sectional dimension of the tubular structure. This may facilitate insertion of the tubular structure into the opening. This ability for the restraint mechanism to open wide is one additional advantage over a static or fixed hole or other opening.

Arrow 634 shows that tubular structure 606 may be introduced into opening 632. Notice that tubular structure 606 may be introduced into the opening from the side, as opposed to being threaded vertically through the opening from the top. In one or more embodiments, the ends of sections of VIV suppression devices (if any), or other portions of the VIV suppression devices corresponding in position to the spacers, may optionally be tapered to a smaller diameter or cross-sectional dimension in order to help to facilitate insertion.

Figure 6B shows restraint mechanism 630 in a closed position around and restraining tubular structure 606, according to one or more embodiments. Restraint mechanism 630 may clasp, clutch, grasp, clamp, apply inward pressure, or otherwise restrain the tubular structure.

In one or more embodiments, hydraulics or pneumatics may actuate the members 642, 644. As shown, the body of the spacer may include a tube, pipe, or other channel 668 to convey a hydraulic or pneumatic fluid to the restraint mechanism. In some embodiments, a mechanical lock may be provided between the distal ends of arms 642 or 644, such as a clasp, pin, bolt and nut, or other locks as are known in the art .

The first and second members may be sized and shaped so that collectively an inner surface of the first and second members conforms to, or substantially conforms to, the size and shape of the tubular structure, when the first and second members are in a closed or partially closed position. In the illustration, for purposes of illustration, the first and second members are separated from the tubular structure by a small space. It is to be appreciated that the first and second members may either be separated from the tubular structure by such a small space, or alternatively may be in direct contact with the tubular structure. In one or more embodiments, pins, bolts, latches, other fasteners, locks, or other devices may optionally be included to help keep the restraint mechanisms in a closed position around the tubular structure, such as, for example, in the event of hydraulic or pneumatic failure, although this is not required.

In one or more embodiments, the first and second members may apply inward pressure on the tubular structure. The inward pressure may help to restrain the tubular structure. The first and second members may be fitted with a deformable liner that deforms around the tubular structure that provides for a larger surface area of the tubular structure that engages with the first and second members. A deformable liner may also allow a larger inward pressure to be applied from the first and second members without creating stress concentrations .

In one or more embodiments, the amount of pressure applied on the tubular structure by the restraint mechanism may be changed dynamically, such as, for example, based on changing conditions and/or to reduce vibrations. For example, the amount of pressure applied on the tubular structure by the restraint mechanism may be changed dynamically based on factors such as the amount of vibration on the tubular structure, the amount of ocean current, the amount of wind, the current weather, weather forecasts, or the like. Generally, the greater the amount of vibration and/or the greater the potential for vibration (e.g., high wind or current, or bad weather, etc.), the greater the pressure applied on the tubular structure by the restraint mechanism. As one specific example, in the event of a hurricane or other severe storm, the amount of pressure on the tubular structures may be increased. This increased pressure may help to dampen or suppress vibrations and may help to maintain restraint over movement of the tubular structure in adverse conditions.

It would be advantageous to more accurately know the amount of pressure exerted on the tubular structure by the restraint mechanism.

Figure 7 :

Figure 7 is a top planar view of restraint mechanism 730 that includes pressure sensor 748, according to one or more embodiments. As shown, pressure sensor 748 may be connected with an inner surface of restraint mechanism 730. Pressure sensor 748 may sense or measure a pressure exerted on tubular structure 706 by restraint mechanism 730. The sensed or measured pressure may be communicated to the surface structure via an umbilical or other line. The sensed or measured pressure may be used at the surface structure to control restraint mechanism 730, such as, for example, to open or close to decrease or increase the pressure, respectively. Examples of suitable pressure sensors include, but are not limited to, piezoelectric pressure sensors, strain gauge pressure sensors, variable capacitance pressure sensors, and the like.

When pressure is applied, metal or other hard surfaces of the restraint mechanism may potentially damage the tubular structure and/or protective coatings on the outside of the tubular structure. Damage may also potentially occur during periods of high ocean currents or high vibration, during installation, or at other times. It would be advantageous to help protect against such damage.

Figure 8 :

Figure 8 is a top planar view of restraint mechanism 830 that includes protective material or element 850, according to one or more embodiments. Protective material or element 850 may help to prevent or at least reduce the potential for damage to the tubular structure, or a coating thereof, by the restraint mechanism.

As shown, protective material or element 850 is connected or attached with inner surface 852 of restraint mechanism 830. Protective material or element 850 would be disposed between the inner surface of restraint mechanism 830 and a tubular structure.

Protective material or element 850 is softer than a material of the inner surface of the restraint mechanism and softer than a material of an exterior surface of the tubular structure. Examples of suitable soft materials in this regard include, but are not limited to, rubbers and other elastomers, soft polymers, solid foams, fibrous cushioning, woven materials, and the like which are generally more pliable or giving than a material for restraint mechanism 830, for example stainless steel or a hard polymer.

Referring to Figure 8, protective material or element 850 is included over substantially all the inner surface of the restraint mechanism. In this manner, there is limited or no contact between the generally hard surfaces of restraint mechanism 830 and the generally hard surfaces of the tubular structure, although this is not required. In alternate embodiments, discrete pads or other portions of the protective material or elements may be included over only a portion of the inner surface. Advantageously, such a protective material or element may help to reduce damage to the tubular structure and/or restraint mechanism 850.

Other ways of protecting the tubular structure from damage are also contemplated.

Figure 9 :

Figure 9 is a side view of tubular structure 906 having protective collar 954, according to one or more embodiments. The protective collar is located at a position where restraint mechanism 930 is to restrain tubular structure 906. In this embodiment, protective collar 954 is disposed around, in this case surrounding, the outside surface of a segment of tubular structure 906.

In one or more embodiments, a protective collar may include a reinforcing collar. The reinforcing collar may include an additional thickness of a sufficiently strong or structural material. Examples of suitable materials include, but are not limited to, metals, plastics, fiber reinforced plastics, carbon fiber materials, and the like, and combinations thereof. Such a reinforcing collar may help to provide additional mechanical strength and may help to distribute stresses or pressures exerted on the tubular structure by the restraint mechanism.

Alternatively, in one or more embodiments, a protective collar such as protective collar 954 may include a soft or pliable material. The types of soft materials discussed above are also suitable for the collar. To further reduce the potential for damage, the contact area between a restraint mechanism and a tubular structure may be increased. For example, the surfaces of a restraint mechanism that contact the tubular structure may be extended or elongated in the axial direction of the tubular structure. As shown in Figure 9, restraint mechanism 930 has an elongated dimension (d) in an axial direction of tubular structure 906. In one or more embodiments, the elongated dimension may be more than six inches, in some cases more than eight inches, and in some cases more than a foot. Advantageously, this can help to distribute stresses or pressures exerted on the tubular structure by the restraint mechanism.

In one or more embodiments, a restraint mechanism may be capable of extending and retracting.

Figures lOA-lOC:

Figures lOA-lOC are top planar views that illustrate extending restraint mechanism 1030 toward tubular structure 1006, introducing the tubular structure into opening 1032 of the restraint mechanism, closing the restraint mechanism around the tubular structure to restrain the tubular structure, and retracting the restraint mechanism and the tubular structure, according to one or more embodiments.

Figure 10A shows restraint mechanism 1030 in an open and retracted position, according to one or more embodiments. As before, the restraint mechanism has a head portion that includes first jaw, part, or member 1042, and second, opposed jaw part, or member 1044. The first and second members are connected together by joint 1046. Opening 1032 opens to the right (as viewed) , and is significantly wider than a diameter of the tubular structure to facilitate insertion of the tubular structure. Restraint mechanism 1030 is located a short distance away from tubular structure 1006. Notice that the restraint mechanism has extender portion 1060. The extender portion has a first, left end fixedly connected or attached with body 1024 of a spacer, and a second, right end fixedly connected or attached with the head portion. The extender portion is capable of extending away from the body of the spacer, and retracting back toward the body of the spacer. In Figure 10A, arrow 1062 shows that the extender portion may extend.

Figure 10B shows restraint mechanism 1030 in an extended position with members 1042, 1044 closed around and restraining tubular structure 1006, according to one or more embodiments. Extender portion 1060 has extended until the tubular structure has been introduced into the opening of the restraint mechanism. The restraint mechanism has closed to clasp, grasp, or otherwise hold or restrain the tubular structure, as previously described. Advantageously, the extender portion may allow the restraint mechanism to reach out and grab onto the tubular structure, which may be useful during installation.

As best viewed in Figure 10B, in one or more embodiments, the extender portion may include a telescoping portion. The telescoping portion may include telescoping parts 1063, 1064, 1065. Some of the telescoping parts may slide out from other of the telescoping parts in order to lengthen the extender portion. In the illustration, there are three telescoping parts, although this is not required. In one or more embodiments, the telescoping portion may be extended and retracted by hydraulic or pneumatic actuation. As shown, the body of the spacer may include a tube, pipe, or other channel 1068 to convey a hydraulic or pneumatic fluid to actuate the telescoping portion. Arrow 1069 shows that the extender portion may retract back toward body 1024 of the spacer.

Figure IOC shows restraint mechanism 1030 in a retraced position with members 1042, 1044 closed around and restraining tubular structure 1006, according to one or more embodiments. In retracting, the tubular structure may be drawn back toward the body of the spacer along with the restraint mechanism.

In Figure IOC, arrow 1062 shows that the extender portion may extend again, if desired. In one or more embodiments, the extender portion and/or the restraint mechanism may be capable of restraining the tubular structure at an extended or partially extended position for prolonged periods of time. This may be useful for various reasons. For one thing, additional extension provided by an extended or partially extended extender portion may provide additional distance separating the tubular structure from other hardware (e.g., other tubular structures) . This additional separation distance may help to prevent the tubular structure from being damaged through contact with other hardware. In one or more embodiments, the tubular structure may be held at an extended or partially extended position for prolonged periods of time during installation, during periods of high current, during periods of high vibration, or when periods of high wind, current, or bad whether are expected, to name just a few examples. In one or more embodiments, the extender portion may be dynamically controlled to extend or retract based on current or forecasted conditions. For example, the extender portion may be extended when the amount of vibration is high and retracted when the amount of vibration is low.

Since the tubular structure and the restraint mechanism are typically underwater during installation, sometimes at great depth, it tends to be difficult to accurately know the relative positions of the tubular structure and the restraint mechanism during installation.

Figure 11:

Figure 11 is a side view of first tubular structure 1106A, spacer 1110 connected to the first tubular structure and having restraint mechanism 1130, second tubular structure 1106B, and camera 1170, such as a video camera, to obtain images, or video, of the restraint mechanism restraining the second tubular structure, according to one or more embodiments.

Figure 11 is a side view showing that camera 1170, such as a video camera, may be used to obtain images or video of restraint mechanism 1130 restraining second tubular structure 1106B, according to one or more embodiments. Conventional cameras suitable for underwater use or deep-sea use are suitable .

Spacer 1110 is connected to first tubular structure 1106A. The spacer has the restraint mechanism. In this case, camera 1170 is also connected to first tubular structure, although this is not required. The camera may receive power locally, for example, from a battery, or may receive power from the surface structure via an umbilical cable .

The camera is positioned to obtain images or video of a region in which the restraint mechanism may restrain the second tubular structure. The camera is proximate (i.e., within 15 feet of) the restraint mechanism. The camera is often within ten feet of the restraint mechanism, sometimes within five feet of the restraint mechanism.

The camera may provide images or video of the region to a surface structure over one or more lines or umbilicals. An operator or other practitioner on the surface structure may view the images or video. These images or video may help the practitioner to know the relative positions of the second tubular structure and the restraint mechanism, which may be useful when aligning and introducing the second tubular structure into the opening of the restraint mechanism.

In alternate embodiments, a remotely operated vehicle

(ROV) may have a camera that may be used to view the region.

The particular restraint mechanisms described above are not required. A wide variety of other restraint mechanisms are also contemplated. Two further examples will be briefly described in order to illustrate certain concepts.

Figure 12A & 12B:

Figure 12A illustrates one alternate restraint mechanism 1230A to restrain tubular structure 1206, according to one or more embodiments. The restraint mechanism includes a c- shaped opening 1232A in body 1224A. The opening opens to the side of the spacer. The tubular structure is within the c- shaped opening. The mechanism also includes a gate 1272 having a cylindrical c-shaped indent 1273A. The c-shaped indent corresponds in position to the c-shaped opening in the body. The gate is coupled with the body by a joint 1246. The joint may allow the gate to rotate to close the tubular structure in a cavity formed between c-shaped opening 1232A and mating c-shaped indent 1273A. The gate may optionally be fastened or locked in this position to close or restrain the tubular structure.

Figure 12B illustrates another alternate restraint mechanism 1230B to restrain tubular structure 1206, according to one or more embodiments. The restraint mechanism includes a c-shaped or deeper u-shaped opening 1232B in body 1224B. The opening opens to the side of the spacer. The tubular structure is within the c-shaped or u-shaped opening. The mechanism also includes a sliding door 1274 optionally having a slight c-shaped indent 1273B. The door is slideably coupled to slide in front of the c-shaped or u-shaped opening after the tubular structure is introduced therein. The door may optionally be fastened or locked in this position to close or restrain the tubular structure.

Still other restraint mechanisms are contemplated and will be apparent to those skilled in the art, and having the benefit of the present disclosure.

Figure 13 :

Figure 13 is a block flow diagram of a method 1275 of assembling two or more joined tubular structures, according to one or more embodiments.

A first tubular structure may be introduced into an opening of a spacer, at block 1276. The spacer, as well as potentially other spacer, may be coupled with a second tubular structure. By way of example, the second tubular structure may serve as a structural support for the spacer apparatus. In one aspect, the introduction of the first tubular structure into the opening may be performed while the spacer apparatus and the second tubular structure are disposed within a body of water, such as, for example, the ocean. In one or more embodiments, the first tubular structure may be introduced into the opening from a side of the spacer apparatus, instead of from vertically above.

Then, the opening of the spacer apparatus may be at least partially closed in order to restrain the first tubular structure, at block 1277. In one or more embodiments, this may include moving one or more component parts of the spacer apparatus, such as, for example, hydraulically or pneumatically. In one or more embodiments, this may include clasping, grasping, clamping, or otherwise actively applying inward pressure on the first tubular structure.

In some cases, normal control of a restraint mechanism may potentially fail (e.g., a control line may be broken) . In one or more embodiments, a restraint mechanism may be capable of being controlled acoustically. By way of example, an acoustic signal may be generated at the surface and transmitted toward the restraint mechanism. For example, an operator at the surface structure may submerse an acoustic signal generating apparatus into the ocean to transmit the acoustic signal. A hydrophone or other acoustic signal detector may be proximate or local to the restraint mechanism and may detect the acoustic signal. Detection of the acoustic signal by the hydrophone or other acoustic signal detector may trigger, induce, or result in an action by the restraint mechanism. For example, detection of the acoustic signal may trigger actuation of the restraint mechanism to either open or close. In one aspect, restraint mechanisms corresponding to all hydrophones receiving the signal may either open or close. In the event of the restraint mechanisms all opening, this may provide an acoustic release. Advantageously, such acoustic actuation may help to provide a backup system in the event of a failure of the main control mechanism.

Figure 14 :

Figure 14 illustrates an example marine system 1400 in which embodiments may be implemented. The marine system includes Floating Liquefied Natural Gas (FLNG) plant 1402 on/in ocean surface 104. The FLNG plant may cool and liquefy natural gas or regasify natural gas. Alternatively, arrays or groups of tubular structures may be used as drilling riser arrays, production riser arrays, TLP tendons, anchor lines, etc .

Marine system 1400, in this embodiment, includes a number of risers or other tubular structures 1406 (e.g., nine tubular structures) . The tubular structures each have first ends and second ends. The first ends are connected to the FLNG plant. The second ends project generally downward into the ocean but not necessarily to the seafloor. In one particular example, the second ends may have depths of around 130 to 170 meters. Due to the ocean current, the tubular structures may deflect from vertical by around 40 degrees or so (not shown) . To accommodate for such deflection, the tubular structures may be connected with the FLNG plant through a swivel joint, a ball joint, a riser hanger, or other pivotable coupling.

In this implementation, some or all of the tubular structures may serve as water intake risers. The water intake risers may take in cooling water 1478 at depth, and convey the cooling water upward to the FLNG plant. The cooling water may be input to heat exchangers of the FLNG plant in order to cool natural gas to help liquefy the natural gas. The heated ocean water from the outlet of the heat exchangers may be discharged back into the ocean at the surface .

If desired, filters may optionally be attached to each of the bottoms of the tubular structures. The filters may help to prevent soil, marine life (e.g., seaweed, algae, fish, etc.), and the like, from entering the tubular structures. Over time, the filters may tend to become clogged. Advantageously, it is believed that the restraint mechanisms disclosed herein may help to reduce the cost, labor, and/or time associated with removing tubular structures from the array in order to clean the filters.

The tubular structures are physically associated or connected together with guide sleeves or spacers 1410A, 1410B, 1410C. In one or more embodiments, the guide sleeves or spacers may have one or more restraint mechanisms as disclosed elsewhere herein. In one embodiment, enough spacers may be provided interspersed along a length of the tubular structures to keep the tubular structures from striking into one another.

Figure 15 :

Figure 15 is a top planar view of an example spacer 1510 for nine tubular structures (e.g., risers) suitable for a FLNG implementation, according to one particular embodiment. This top planar view may be taken along section line 15--15 of Figure 14 directly above spacer 1410C and through the tubular structures.

In this particular embodiment, the nine tubular structures 1506 are arranged in a three-by-three rectangular array. Eight tubular structures are along the periphery of the array, and one tubular structure is at the center of the array. The eight tubular structures along the periphery may serve as water intake risers to provide cold water to the FLNG plant. It may not be necessary that all of the tubular structures operate at any one time to provide sufficient cooling water to the FLNG plant (e.g., one or more may be surplus or reserve water intake risers) . The tubular structure at the center may serve as a structural support tubular structure (riser) for the spacers. The tubular structure at the center may, or may not, convey water to the surface (i.e., may or may not serve as a water intake riser) .

In one particular embodiment, the eight tubular structures along the periphery may have outer diameters of about 42 inches and wall thicknesses of about 1 inch, while the structural tubular structure at the center may have an outside diameter of about 24 inches and a thickness of about 0.75 inches. The eight tubular structures along the periphery may be equally spaced apart by a distance of about one outer diameter or about 42 inches.

The structural support tubular structure at the center of the array is inserted through a central internal opening in the spacer. The eight tubular structures are along the periphery of the array are each restrained by a corresponding one of eight restraint mechanisms 1530. The restraint mechanisms may be similar to or the same as those described elsewhere herein. Notice that the restraint mechanisms are disposed around the perimeter of the spacer. The restraint mechanisms have openings to receive the tubular structures that face outward from the center of the spacer. During installation, the eight tubular structures may be inserted into the openings from the sides of the spacer instead of being threaded vertically from above the spacer. In one or more embodiments, restraint may begin with the bottommost spacer, and proceed upward to the topmost spacer.

In one example, only the tubular structures at the four corners may have VIV suppression devices. As previously mentioned, the restraint mechanisms disclosed herein are useful for tubular structures with or without VIV suppression devices. The restraint mechanisms tend to be particularly advantageous for tubular structures having VIV suppression devices, or other appurtenances (e.g., anodes, couplers, etc.), since these appurtenances tend to make it more difficult to thread the tubular structures through holes or openings in a spacer. As shown in this design, in one or more embodiments, most or all of the tubular structures that have VIV suppression devices may be restrained with restraint mechanisms as disclosed herein. Either restraint mechanisms or simple holes or openings in the body of a tubular structure (e.g., as shown in Figure 3) may be used for tubular structures that do not have VIV suppression devices or like appurtenances, since threading through such holes or openings is easier if the VIV suppression devices or appurtenances are not present. In the current design, in one or more embodiments, the central tubular structure may not have VIV suppression devices and notice that it is inserted through an internal hole instead of having a restraint mechanism.

Small holes or openings 1580 near the central internal opening are provided through the spacer to allow for the routing of umbilicals or other lines. As previously mentioned, the umbilicals or lines may provide control, and often power from the FLNG plant to the restraint mechanisms. In some cases, the umbilicals or other lines may optionally provide images or video and/or pressure measurements from the restraint mechanism to the FLNG plant, as previously described .

The restraint mechanisms may either be controlled individually or some or all of the restraint mechanisms may be controlled together. In addition, the pressures exerted by the restraint mechanisms on the corresponding tubular structures may either be controlled individually or some or all may be controlled together to exert substantially the same pressure on their respective tubular structures.

In alternate embodiments, the connected tubular structures be arranged in various other shapes (e.g., circular, star, triangular, etc.), and/or have various other numbers of tubular structures.

The spacer and restraint mechanisms disclosed herein may be made of any materials suitable for their intended uses in an underwater, in some cases high-pressure environment, and as long as they are sufficiently strong to handle the vibrations and mechanical forces involved. A few examples of suitable materials include, but are not limited to, certain metals (e.g., stainless steel, coated steel, copper, etc.), certain sufficiently strong and/or sufficiently thick plastics, fiber reinforced plastics (e.g., fiberglass), and carbon fiber materials, and combinations thereof, to name just a few illustrative examples.

It is to be kept in mind that not all of the tubular structures of an array need to be restrained at a given spacer. For example, the tubular structures that are not restrained at the given spacer may be restrained at other spacer intermittent along the length of the tubular structures. For example, there may be five spacer along the length of a tubular structure and the tubular structure may be restrained at only three of the spacer.

Suitable VIV suppression devices are disclosed in U.S. Patent Publication Number 2006-0021560 Al, having attorney docket number TH1433; U.S. Patent Number 7,406,923, having attorney docket number TH0541; U.S. Patent Publication Number 2006-0280559 Al, having attorney docket number TH2508; U.S. Patent Publication Number 2007-0003372 Al, having attorney docket number TH2876; U.S. Patent Publication Number 2007- 0003372 Al having attorney docket number TH2969; WIPO Publication Number 2007/149770, having attorney docket number TH1500; WIPO Publication Number 2008/064104, having attorney docket number TH3112; WIPO Publication Number 2008/064102, having attorney docket number TH3190; U.S. Patent Number 5,410,979; U.S. Patent Number 5,410,979; U.S. Patent Number 5,421,413; U.S. Patent Number 6,179,524; U.S. Patent Number 6,223,672; U.S. Patent Number 6,561,734; U.S. Patent Number 6,565,287; U.S. Patent Number 6,571,878; U.S. Patent Number 6,685,394; U.S. Patent Number 6,702,026; U.S. Patent Number 7,017,666; and U.S. Patent Number 7,070,361, which are herein incorporated by reference in their entirety.

Suitable methods for installing VIV suppression devices are disclosed in U.S. Patent Number 7,578,038, having attorney docket number TH1853.04; U.S. Patent Publication Number 2005-0254903 Al, having attorney docket number TH2463; U.S. Patent Publication Number 2008-0056828 Al, having attorney docket number TH2900; U.S. Patent Publication Number 2007-0125546 Al, having attorney docket number TH2926; U.S. Patent Publication Number 2007-0140797 Al, having attorney docket number TH2875; WIPO Publication Number 2008/008728, having attorney docket number TH2879; WIPO Publication Number 2008/070245, having attorney docket number TH2842; U.S. Patent Number 6,695,539; U.S. Patent Number 6,928,709; and U.S. Patent Number 6,994,492; which are herein incorporated by reference in their entirety.

In the description above, for the purposes of explanation, numerous specific details have been set forth in order to provide a thorough understanding of the embodiments. It will be apparent however, to one skilled in the art, that one or more other embodiments may be practiced without some of these specific details. The particular embodiments described are not provided to limit the invention but to illustrate it. The scope of the invention is not to be determined by the specific examples provided above but only by the claims below. In other instances, well-known structures, devices, and operations have been shown in block diagram form or without detail in order to avoid obscuring the understanding of the description. Where considered appropriate, reference numerals or terminal portions of reference numerals have been repeated among the figures to indicate corresponding or analogous elements, which may optionally have similar characteristics.

It should also be appreciated that reference throughout this specification to "one embodiment", "an embodiment", or "one or more embodiments", for example, means that a particular feature may be included in the practice of the invention. Similarly, it should be appreciated that in the description various features are sometimes grouped together in a single embodiment, Figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects may lie in less than all features of a single disclosed embodiment. For example, unless specified or claimed otherwise, the floating structure or floating liquefied gas plant shown in a Figure is not intended to be a part of the invention. Thus, the claims following the Detailed Description are hereby expressly incorporated into this Detailed Description, with each claim standing on its own as a separate embodiment of the invention.

Claims

C L A I M S

1. A system comprising:

a support structure in a flowing fluid environment;

a spacer plate connected to the support structure, the spacer plate comprising at least one retention mechanism movable from an open to a closed configuration, the retention mechanism comprising an opening;

wherein the opening of the retention mechanism is adapted to receive a structure when in the open

configuration .

2. The system of claim 1, wherein the spacer plate and the retention mechanism are within a body of water.

3. The system of one or more of claims 1-2, wherein at least one end of the support structure is connected to a floating vessel .

4. The system of one or more of claims 1-3, further

comprising a plurality of retention mechanisms connected to the spacer plate.

5. The system of claim 4, further comprising a plurality of tubular structures, wherein each tubular structure is within an opening of one of the retention mechanisms.

6. The system of one or more of claims 1-5, further

comprising a plurality of spacer plates at a plurality of locations along a length of the support structure.

7. The system of one or more of claims 1-6, wherein the support structure comprises an internal structure, wherein the spacer plate and the at least one retention mechanism form a periphery about the internal structure.

8. The system of one or more of claims 1-7, further

comprising the structure within the opening of the retention mechanism, and at least one vortex induced vibration

suppression device connected to the structure.

9. The system of claim 8, wherein the vortex induced

vibration suppression device is selected from henning

devices, smooth sleeves, strakes, and fairings.

10. The system of one or more of claims 8-9, wherein the vortex induced vibration suppression device comprise at least two different types of devices.

11. The system of one or more of claims 1-10, wherein the structure comprises at least one tubular, each tubular comprising an opening therethrough for transportation of a fluid.

12. The system of one or more of claims 1-11, wherein the retention mechanism comprises a clamshell device with two arms and an open/close mechanism.

13. The system of one or more of claims 1-12, wherein the retention mechanism comprises an internal surface with a protective coating.

14. The system of one or more of claims 1-13, further comprising an extension mechanism connected between the spacer plate and the retention mechanism.

15. The system of one or more of claims 1-14, wherein the retention mechanism opening is adapted to receive the

structure from a side direction.

16. A method of holding a subsea structure comprising:

providing a floating structure at a surface of a body of water ;

connecting a support structure to the floating

structure, the support structure having a first end at the surface and a second end at first depth in the body of water; connecting a spacer plate to the support structure at a second depth between the surface and the first depth;

connecting a retention mechanism to the spacer plate, the retention mechanism comprising an opening; moving the retention mechanism into an open configuration;

loading the subsea structure into the opening of the retention mechanism; and then moving the retention mechanism into a closed open configuration to limit movement of the subsea structure.

17. The method of claim 16, further comprising connecting a plurality of spacer plates to the support structure, each spacer plate at a different depth.

18. The method of one or more of claims 16-17, further comprising providing a plurality of retention mechanisms connected to the spacer plate.

19. The method of claim 18, further comprising feeding at least one subsea structure into each of the openings in the retention mechanisms.

20. The method of one or more of claims 16-19, further comprising connecting a plurality of spacer plates to the support structure, each spacer plate at a different depth, and then connecting at least one retention mechanisms to each spacer plate, then loading the subsea structure into an opening of a first retention mechanism connected to a first spacer plate; and loading the subsea structure into an opening of a second retention mechanism connected to a second spacer plate.