Apparatus for suppression of vortex induced vibration without aquatic fouling and methods of installation

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to apparatus and methods for suppressing vortex-induced vibrations (VIV). In another aspect, the present invention relates to apparatus and methods for suppressing VIV while also suppressing the growth of aquatic organisms on the VIV suppressing apparatus. In even another aspect, the present invention relates to apparatus for suppressing VIV comprised of copper for suppressing the growth of aquatic organisms on the surface of the apparatus.

2. Description of the Related Art

Whenever a bluff body, such as a cylinder, experiences a current in a fluid, it is possible for the body to experience vortex-induced vibrations (VIV). These vibrations are caused by oscillating hydrodynamic forces on the surface which can cause substantial vibrations of the structure, especially if the forcing frequency is at or near a structural natural frequency. The vibrations are largest in the transverse (to flow) direction; however, in-line vibrations can also cause stresses which are sometimes larger than those in the transverse direction.

Drilling for and/or producing hydrocarbons or the like from subterranean deposits which exist under a body of water exposes underwater drilling and production equipment to water currents and the possibility of VIV. Equipment exposed to VIV includes structures ranging from the smaller tubes of a riser system, anchoring tendons, or lateral pipelines to the larger underwater cylinders of the hull of a minispar or spar floating production system (hereinafter “spar”).

Risers are discussed here as a non-exclusive example of an aquatic element subject to VIV. A riser system is used for establishing fluid communication between the surface and the bottom of a water body. The principal purpose of the riser is to provide a fluid flow path between a drilling vessel and a well bore and to guide a drill string to the well bore.

A typical riser system normally consists of one or more fluid-conducting conduits which extend from the surface to a structure (e.g., wellhead) on the bottom of a water body. For example, in the drilling of a submerged well, a drilling riser usually consists of a main conduit through which the drill string is lowered and through which the drilling mud is circulated from the lower end of the drill string back to the surface. In addition to the main conduit, it is conventional to provide auxiliary conduits, e.g., choke and kill lines, etc., which extend parallel to and are carried by the main conduit.

Also, the newly developed spar production facilities are used in aquatic environments of great depths. Aquatic environments is used here to describe water environments of any salinity. Strong water currents often occur at these greater depths in ocean environments. The hulls of spar production facilities, therefore, can be exposed to excessive vortex-induced vibrations.

Methods to reduce vibrations caused by vortex shedding from aquatic structures can operate by modifying the boundary layer of the flow around the structure to prevent the correlation of vortex shedding along the length of the structure. Examples of such methods include the inclusion of helical strakes around a structure, or axial rod shrouds and perforated shrouds.

The use of strakes and shrouds in aquatic environments exposes them to being colonized by aquatic animals and plants that anchor themselves to these structures. Mature growth of these organisms on strakes and shrouds changes the contours of these VIV suppression devices and can diminish their effectiveness in VIV suppression, and perhaps in some instances result in greater VIV. The location of these VIV suppression devices deep in aquatic environments makes it difficult to remove aquatic organisms. Aquatic organisms can be removed from VIV suppression devices by divers working from water craft, defined herein as any vehicle that can travel on or in water. After removal, the aquatic organisms immediately begin to re-colonize the structures.

However, in spite of the above advancements, there still exists a need in the art for improved apparatus and methods for VIV suppression.

There is another need in the art for apparatus and methods for strakes and other VIV suppression devices which resist the growth of aquatic organisms on their surfaces.

These and other needs in the art will become apparent to those of skill in the art upon review of this specification, including its drawings and claims.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide for improved apparatus and methods for VIV suppression.

It is another object of the present invention to provide for apparatus and methods for strakes and other VIV suppression devices which resist the growth of aquatic organisms on their surfaces.

These and other objects of the present invention will become apparent to those of skill in the art upon review of this specification, including its drawings and claims.

According to one embodiment of the present invention, there is provided a system for suppressing VIV. The system generally includes a first flange, having a first set of two or more members, and a second flange having a second set of two or more members. The system further includes an elongated strake member with the elongated strake member connected to the first flange and the second flange. At least a portion of the system comprises copper in the range of about 1 wt % to about 100 wt %, based on the total weight of that portion. In a more specific embodiment of this embodiment, the system may also include an elongated sleeve positioned within the first and second flanges and a marine element positioned within the elongated sleeve.

According to another embodiment of the present invention, there is provided a method of modifying a structure intended to operate while at least partially immersed in an aquatic environment. The method generally includes arranging a plurality of elongated members around at least a portion of the structure, wherein at least a portion of the elongated members comprise copper in the range of about 1 wt % to about 100 wt % copper.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is a schematic illustration of a coated riser joint

7

, comprised of riser joint

3

coated with and supporting riser coating

5

.

FIG. 2

shows a schematic illustration of strake flange

25

in frontal view, comprised of top half

20

and bottom half

22

, each half defining multiple holes

24

.

FIG. 3

depicts a first clad sleeve

35

, comprised of top half

30

and bottom half

32

.

FIG. 4

shows a schematic illustration of a cross section of an additional clad sleeve

55

comprised of upper half

50

and lower half

52

.

FIG. 5

shows a schematic illustration of lateral view of additional clad sleeve

55

, comprised of upper half

50

and lower half

52

.

FIG. 6

provides a schematic overview of clad sleeves and strake flange

25

encircling coated riser

7

.

FIG. 7

provides a magnified schematic view of strake flange

25

positioned near one end of first clad sleeve

35

and supported thereby.

FIG. 8

shows a schematic illustration of strake attachment flange

115

, comprised of top half

92

and bottom half

94

with hole

80

used to anchor tubes

90

.

FIG. 9

displays a schematic representation of strake attachment flange

115

attached at both ends of tubes

90

.

FIG. 10

shows a schematic overview of riser

7

and tubes

90

are shown anchored at both of their ends to attachment flanges

92

and

94

.

FIG. 11

portrays a magnified schematic view of strake flange

25

attached to strake attachment flange

115

with tubes

90

attached to flange.

FIG. 12

provides a schematic overview of riser

7

with strake flange

25

and attachment flange

115

with tubes

90

connected and encircling clad sleeves

35

and

55

.

FIG. 13

provides a schematic overview riser joint

7

with sleeves

35

and

55

and with tubes

90

twisted into a helix.

FIG. 14

shows a schematic overview of apparatus and methods of adding additional clad sleeves

55

and tubes

90

across the abutted ends of two risers

7

.

DETAILED DESCRIPTION OF THE INVENTION

The VIV suppression apparatus of the present invention generally includes protective coverings and VIV suppression devices for aquatic elements of underwater structures or subject to VIV, including but not limited to risers. The apparatus and methods of the present invention find utility with an aquatic element either in an assembly yard or a lay vessel, prior to being installed in an aquatic environment, or with the aquatic element in situ in an aquatic environment.

Referring first to

FIG. 1

, shown is coated riser joint

7

, comprised of riser joint

3

coated with and supporting riser coating

5

. Riser joints are individual sections of tubing that can be connected end to end to create a riser of various lengths.

Referring next to

FIGS. 2 and 3

, shown is strake flange

25

, comprising a set of top half

20

and bottom half

22

, each half defining multiple holes

24

. Also shown is first clad sleeve

35

, comprised of top half

30

and bottom half

32

. Upper and lower first clad sleeves

30

and

32

are fitted around one end of coated riser joint

7

if it is the first in a series of riser joints that require VIV suppression. Upper

30

and lower

32

first clad sleeves support respectively upper strake attachment flange

92

and bottom strake attachment flange

94

.

Referring now to

FIGS. 4 and 5

, shown in cross section and laterally is additional clad sleeve

55

, comprised of upper half

50

and lower half

52

. Additional clad sleeve

55

does not support strake flange

25

. Any number of additional clad sleeves

55

may be installed adjacent to first clad sleeve

35

on the side of first clad sleeve

35

that is away from the nearest end of riser joint

7

.

Referring now to

FIGS. 6 and 7

, one additional clad sleeve

55

is installed adjacent to and in contact with first clad sleeve

35

which is installed at one end of coated riser joint

7

. More additional clad sleeves

35

may be installed down the remaining length of riser joint

7

, adjacent to and in contact with each other at abutted ends

62

, as is shown in FIG.

6

. Further shown in FIGS.

6

and

7

are strake attachment flange

25

positioned near one end of first clad sleeve

35

and supported thereby. Strake flange

25

may be assembled from top half

20

and bottom half

22

with two or more bars

70

anchored through opposite holes

24

, on each half. The bars may optionally be anchored with welding, preferably with rivets, even more preferably with bolts. Also shown in

FIGS. 6 and 7

are compression straps

60

spaced at intervals along first sleeves

35

and additional sleeves

55

to anchor those sleeves to riser

7

. In

FIG. 6

, a non-limiting example of the placement of compression straps

60

is shown with straps

60

positioned at both ends and in the middle of first sleeve

35

and additional sleeves

55

.

Referring now to

FIGS. 8 and 9

, shown strake attachment flange

115

, comprising a set of top half

92

and bottom half

94

attached at both ends of tubes

90

, which are anchored to attachment flange

115

through holes

80

defined by attachment flange

115

. Also defined by attachment

115

are multiple anchor holes

85

.

Referring now to

FIGS. 10 and 11

, shown is riser

7

supported by yard braces

100

at both ends of riser

7

. Tubes

90

are shown anchored at both of their ends to top attachment flanges

92

and to bottom attachment flanges

94

. Strake attachment flange

115

with tubes

90

attached may be connected to strake flange

25

using the same anchoring methods used to anchor the top

20

and bottom

22

halves of strake flange

25

. Optionally, bars

70

may be used to anchor strake flange

25

to strake attachment flange

115

using welding, preferably with rivets, even more preferably with bolts.

Referring now to

FIG. 12

, shown is riser

7

with strake flange

25

and attachment flange

115

connected and encircling clad sleeves

35

and

55

, which in turn encircle riser

7

, with tubes

90

attached to flange

115

at both ends of tubes

90

.

Referring now to

FIG. 13

, shown are tubes

90

twisted into a helix forming strake

130

, useful in VIV suppression. The helical arrangement of tubes

90

forming strake

130

is achieved by anchoring one strake flange

25

with tab

120

to clad sleeves

35

or

55

and applying torque to another strake flange

25

not anchored to clad sleeves

35

or

55

and supporting the other end of tubes

90

. The direction of the torque applied to tubes

90

may be either clockwise or counterclockwise.

Referring now to

FIG. 14

, shown is a method of adding additional clad sleeves

55

across the abutted ends of two risers

7

using support mandrel

140

to hold the two abutted ends of two risers

7

together. Also shown is the installation of top attachment flange

92

with tubes

90

and the installation of bottom attachment flange

94

with tubes

90

to strake flange

25

. Torque may be applied to the strake flange

25

at the end of tubing

90

opposite the end being attached to the prior torqued flange

25

along the length interconnected risers

7

. Prior to applying torque to the un-torqued tubes

90

, the strake flange

25

should be anchored to clad sleeves

35

or

55

with tab

120

to prevent the previously torqued tubes

90

from receiving additional torque being applied to the adjacent un-torqued tubing

90

. If only one strake

130

is used, it is described as being a single start strake. However, if multiple strakes

130

are attached end to end as shown, with torque applied separately to each set of straight tubes

90

, then the series of strakes

130

are described as being multiple start strakes.

Referring now to all of the previous Figures, at least a portion of the apparatus described is comprised of metal comprising copper. Preferably, at least a portion of the strake(s) comprise metal comprising copper. Most preferably, the portion of interest will be the portion of the apparatus or strake in contact with the water (i.e., the “contact surface.” The portion requiring antifouling properties may comprise metals having a wide range of copper content provided that adequate antifouling is achieved, with the lower end of the range generally about 1 weight (wt) % based on the total weight of that portion, preferably about 60 wt %, more preferably about 75 wt %, even more preferably about 90 wt %, still more preferably about 95 wt %, and yet more preferably about 98 wt %.

The upper end of the range of copper content used is selected independently of the lower end to be greater than the lower end, with the upper end of the range generally about 60 wt %, preferably about 90 wt %, more preferably about 95 wt %, even more preferably about 98 wt %, yet more preferably 99 wt %, and even still more preferably 100 wt %.

While the methods and apparatus have been illustrated herein as being used with risers, it should be understood that the methods and apparatus are believed to have applicability to any structure underwater, whether permanent or temporary, fixed or mobile, in any type of aquatic environment, whether fresh, brackish, or salt water.

Further, while the methods and apparatus have been illustrated herein with elongated tubes, circular in cross-section, forming strakes, elongated members of any shape may be used, including but not limited to those with cross-sections that are rectangular, square, triangular, oval, arc-shaped, or spoke-shaped

Finally, while the illustrative embodiments of the invention have been described with particularity, it will be understood that various other modifications will be apparent to and can be readily made by those skilled in the art without departing from the spirit and scope of the invention. Accordingly, it is not intended that the scope of the claims appended hereto be limited to the examples and descriptions set forth herein but rather that the claims be construed as encompassing all the features of patentable novelty which reside in the present invention, including all features which would be treated as equivalents thereof by those skilled in the art to which this invention pertains.