Lifting Device Having Hinged Segments

Abstract

Lifting devices for use with drilling risers, where the lifting devices have a plurality of segments, some of which are hinged to facilitate handling and provide multiple shear points between the hinged segments. One embodiment comprises a lifting device for a drilling riser, where the device includes a collar and a lifting lug. The collar has a cylindrical ring with one or more annular ribs connected to corresponding circular edges of the ring. The lifting lug is connected to the collar and the ribs. The collar has a plurality of segments, and at least a first one of the segments is pivotally connected to another one of the segments by a hinge. Each rib may taper smoothly from a smaller thickness at a top edge of the rib to a greater thickness at a base of the rib.

Description

BACKGROUND

1. Field of the Invention

The invention relates generally to oilfield equipment and more particularly to drilling risers and apparatus for lifting drilling risers.

2. Related Art

Subsea drilling operations (also referred to as “offshore drilling”) are often carried out to recover hydrocarbons (e.g., oil and gas) from geological formations that lie beneath the seabed. In these operations, a pipe is typically installed between a floating drilling platform and a wellhead at the seabed. This pipe consists of a series of pipe segments called drilling risers, which are connected end-to-end. Drilling mud that is pumped into the well through a drill pipe flows out of the well between the drill pipe and the drilling risers, carrying cuttings out of the well.

A typical drilling riser may be 90 feet long and weigh 20,000-50,000 pounds. The size and weight of the riser may cause difficulty in positioning and installing or removing the riser. Consequently, buoyancy modules are normally coupled to the drilling riser to increase its buoyancy and thereby facilitate handling of the riser underwater, although they complicate handling of the riser out of the water. The buoyancy modules are typically cylindrical units that are positioned around and secured to the drilling riser. Thrust collars are secured near each end of the riser to transfer the axial buoyancy load of the buoyancy modules to the riser. The thrust collars may include lifting lugs to which cables can be attached to allow the riser to be suspended for purposes of moving or positioning it.

Conventional thrust collars have a cylindrical ring portion and a rib which extends outward from the collar. The ring portion encircles the drilling riser and secures the thrust collar to the end of the riser. The thrust collar is positioned adjacent to a buoyancy module at one end of the drilling riser with the rib facing the buoyancy module. When the thrust collar is secured to the riser, the rib transfers the axial force from the buoyancy modules to the drilling riser, while also preventing the modules from slipping off the end of the riser.

A conventional thrust collar typically consists of three segments that are bolted together to secure the thrust collar to the drilling riser. Each segment includes a corresponding section of the cylindrical ring portion and the rib. In thrust collars that have a lifting lug, the lug is normally welded to one of the segments (the lug segment) at the ring portion and the rib. When the lifting lug is used to lift the drilling riser, the lifting force is transferred through the lug to the ring portion and rib of the lug segment, through the connecting bolts to the other segments, which support the drilling riser.

Because the load of the drilling riser is transferred through the bolts, they are an important part of the design of the thrust collar and must be sufficient to withstand the load. Typically, multiple (e.g., four) bolts are used to connect each pair of segments. Even if the load could be safely borne by a single bolt, multiple bolts are preferred because they provide multiple points of failure. In other words, multiple bolts (rather than a single bolt) would have to fail (due to bending or tensile stresses) before the connection between the segments would fail.

While the use of multiple bolts to connect each pair of segments provides a level of redundancy and resulting safety, they may also complicate assembly and disassembly of the thrust collar. The more bolts there are, the more time it takes to install and properly tension the bolts when installing the thrust collar. Similarly, when removing the thrust collar, it takes more time to loosen and remove more bolts. Further, the more bolts that are used, the greater the likelihood that one of the bolts may be lost.

It would therefore be desirable to provide improved lifting devices that provide redundancy in their fastening means without the inconvenience of having to tighten/loosen and keep track of multiple bolts.

SUMMARY OF THE INVENTION

This disclosure is directed to systems for lifting drilling risers that solve one or more of the problems discussed above. One particular embodiment comprises a lifting device for a drilling riser, where the device includes a collar and a lifting lug. The collar has a cylindrical ring with a first annular rib connected to a first circular edge of the ring. The lifting lug is connected to the collar and the first rib. The collar has a plurality of segments, and at least a first one of the segments is pivotally connected to another one of the segments by a hinge. In one embodiment, the collar comprises a lug segment, and two hinged segments. The lug segment has the lifting lug connected to it, and each of the hinged segments is pivotally connected to the lug segment by a corresponding hinge. The hinged segments may be connected to each other by bolts. Spherical washers and seats may be employed to reduce bending stresses on the bolts when the hinged segments are coupled together. In one embodiment, the lifting device may include a second annular rib connected to a second circular edge of the ring. The annular ribs may taper from a smaller thickness at a top edge of the rib to a greater thickness at a base of the rib. The thickness at the base of each annular rib may, for example, be at least half of a height of the annular rib. The inner surface of each rib (which faces the other rib) may have a minimum radius of curvature of at least half of a height of the rib. An elastomeric layer may be provided on a cylindrical inner surface of the collar to cushion the collar against the drilling riser.

An alternative embodiment comprises a drilling riser assembly which includes a pipe section, one or more buoyancy modules and a pair of lifting devices. The buoyancy modules are annularly shaped and are positioned around the pipe section. The two lifting devices are secured to the ends of the pipe section to retain the buoyancy modules on the pipe section. Each of the lifting devices includes a collar and a lifting lug. The lifting lug is connected to the collar, which has a plurality of segments. At least one of the segments is pivotally connected to another one of the segments by a hinge. In one embodiment, the segments include a lug segment and two hinged segments. The lug segment has the lifting lug connected to it, and each of the hinged segments is pivotally connected to the lug segment by a corresponding hinge. The hinged segments are may be connected to each other by bolts. Spherical washers and seats for the washers may be employed to reduce bending stresses on the bolts when the hinged segments are coupled together. The collar has a cylindrical ring with one or two annular ribs connected to the circular edges of the ring. The thickness of each rib may vary as a function of height or angular position. An elastomeric layer may be provided on a cylindrical inner surface of the collar to cushion the collar against the drilling riser.

Numerous other embodiments are also possible.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention may become apparent upon reading the following detailed description and upon reference to the accompanying drawings.

FIG. 1 is a diagram illustrating a conventional drilling riser suspended from a pair of cables.

FIG. 2 is an illustration of a conventional thrust collar having a lifting lug.

FIG. 3 is a perspective view of an exemplary embodiment of an improved lifting device incorporating a hinged thrust collar and a lifting lug.

FIG. 4 is a first plan view of an exemplary embodiment of an improved lifting device incorporating a hinged thrust collar and a lifting lug.

FIG. 5 is a first plan view of an exemplary embodiment of an improved lifting device incorporating a hinged thrust collar and a lifting lug.

While the invention is subject to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and the accompanying detailed description. It should be understood, however, that the drawings and detailed description are not intended to limit the invention to the particular embodiment which is described. This disclosure is instead intended to cover all modifications, equivalents and alternatives falling within the scope of the present invention as defined by the appended claims.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

One or more embodiments of the invention are described below. It should be noted that these and any other embodiments described below are exemplary and are intended to be illustrative of the invention rather than limiting.

As described herein, various embodiments of the invention comprise improved thrust collar devices that are configured to enable drilling risers to be lifted using lifting lugs that are attached to the thrust collars. The improved thrust collars incorporate features that increase their ease-of-use. More particularly, the thrust collars have multiple segments as in conventional devices, but at least some of the segments are connected to each other using hinges instead of bolts. Because the segments are connected by hinges, it is not necessary to install or remove bolts, so the effort conventionally required to do so is eliminated, and there is no possibility of losing any of the bolts. Further, because the segments remain connected, they may be easier to handle than if they had to be separately positioned, aligned and then connected.

Referring to FIG. 1, a diagram illustrating a conventional drilling riser suspended from a pair of cables is shown. Drilling riser 100 includes a pipe section 110 that has a plurality of buoyancy modules 120 mounted on it. Each of the buoyancy modules is generally annular, having a cylindrical outer surface and a cylindrical aperture therethrough to allow the buoyancy module to be placed around the pipe section. A thrust collar (e.g., 130) is secured near each end of pipe section 110 to prevent the buoyancy modules from slipping off pipe section 110.

Each of the thrust collars (e.g., 130) has a lifting lug (e.g., 131) which extends outward from the collar to allow a cable (e.g., 140) to be attached to it. In this example, each of the cables is connected at its upper end to a lifting member 150. The purpose of the lifting member is to apply the lifting force of the cables attached to the two thrust collars perpendicularly to the axis of the riser, thereby minimizing the bending stresses that can be created by forces that are not perpendicularly applied. If a lifting member is not used, and the upper ends of the cables are attached to a single point, some of the lifting force applied to the lifting lugs will be directed toward the center of the riser, causing the thrust collars to undergo bending stresses.

Referring to FIG. 2, an illustration of a conventional thrust collar having a lifting lug is shown. In this embodiment, it can be seen that thrust collar 200 includes a cylindrical ring portion 210, a rib 220 and a lifting lug 230. Rib 220 is welded to one of the circular edges of ring portion 210. Lifting lug 230 is welded to the outer surface of ring portion 210 and to rib 220. Thrust collar 200 is sectioned into three segments to facilitate installation and removal of the thrust collar on a drilling riser. Each of the segments has a flange portion (e.g., 211) at each end which allows it to be bolted to the adjacent segments.

In a conventional thrust collar that does not have a lifting lug, the rib at the edge of the cylindrical ring typically has a constant height (the distance from the cylindrical ring to the outermost or maximum-diameter edge of the rib). In the thrust collar depicted in FIG. 2, the height of the rib is extended near the lifting lug to facilitate load transfer from the lifting lug, through the rib, to portions of the cylindrical ring farther from the lifting lug. This extended portion of the rib (221) may be referred to as a “web”. Regardless of whether the rib is extended in this manner, the lifting force is not evenly transferred to both ends of the cylindrical ring, and the device is subject to bending stresses that often exceed API-specified limits.

Referring to FIGS. 3-5, an exemplary embodiment of an improved lifting device incorporating a thrust collar and a lifting lug is shown. FIG. 3 is a perspective view of the improved lifting device, while FIGS. 4 and 5 are plan views of the device.

Lifting device 300 includes a cylindrical ring portion 310, a pair of generally annular ribs 320 and 330 and a lifting lug 340. Although lifting lug 340 is depicted in FIGS. 3 and 5 as having an eye 341 by which a cable can be attached to the lug, the lifting lugs in alternative embodiments may have hooks, as shown in the conventional device of FIG. 2, rather than eyes. Each of ribs 320 and 330 is joined to a corresponding one of the circular edges of cylindrical ring 310. A layer of elastomeric material (e.g., 360) is provided on the inner surface of cylindrical ring 310 to prevent slippage and to provide some cushioning between the device and a drilling riser on which the device may be installed.

Cylindrical ring portion 310 and annular ribs 320 and 330 are divided into three segments. A first one of the segments (301) has the lifting lug connected to it and will therefore be referred to herein as the “lug segment”. The other two segments (302 and 303) are connected to lug segment 301 by hinges 350 and 351, respectively, and will therefore be referred to herein as “hinged segments”. Hinged segments 302 and 303 are connected to each other by threaded bolts or studs.

It can be seen from FIGS. 3 and 5 that each hinge has a plurality of interleaved knuckles (e.g., 352, 353). The knuckles are positioned at the ends of the respective segments and form a passageway through which a hinge pin (e.g., 354) is inserted. The knuckles of each segment rotate around the hinge pin, allowing the segments to pivot with respect to each other. It should be noted that, in the embodiment of FIGS. 3 and 5, each hinge has 7 knuckles, three of which are part of the hinged segment, and four of which are part of the lug segment. When the knuckles are interleaved with each other, there are six interfaces between adjacent knuckles. Consequently, in order for this hinged joint to fail, the hinge pin would have to be sheared at six points. By comparison, in the conventional thrust collar of FIG. 2, the bolted connection between the lug segment and an adjacent segment has only four failure points—one at each of the four bolts in the connection. The hinged connection between the segments of the present device therefore has more redundancy than the bolted connection of the conventional device, even though it uses a single hinge pin instead of four bolts.

It should be noted that, while the embodiment of FIGS. 3-5 has six shear points, other embodiments may employ hinges that have different numbers of knuckles and different numbers of shear points. These variations are contemplated to be within the scope of the appended claims.

As noted above, the connection between hinged segments 302 and 303 is secured by bolts. Since this connection is opposite the lifting lug and applies horizontal tension to hold the lower ends of the hinged segments together, it does not have to be as strong as the hinged connections, which must support the weight of the drilling riser. Consequently, bolts are used here, where connection loads are smallest, thereby providing a more inherently secure attachment to the riser. The bolted connection is also more conveniently secured after the device is positioned around the riser, particularly if the segments are designed to be pre-stressed.

Lifting device 300 has two annular ribs (320, 330) instead of a single rib. The use of two ribs—one joined to each circular edge of the cylindrical ring portion of the device—serves to strengthen the device against bending and the resulting stresses. Conventional thrust collars such as the one illustrated in FIG. 2 only have a single rib because the purpose of the rib is to retain the buoyancy modules on the drilling riser. When a lifting lug is added to the conventional thrust collar, the single rib is extended to form a web (221) in order to more evenly distribute the lifting load across the rib, but no effort is made to address the bending stresses on the device. Ribs 320 and 330 include extended web portions 321 and 331 to improve load transfer from the lifting lug to the ribs.

In the embodiment of FIGS. 3-5, annular ribs 320 and 330 are generally planar rings that are welded to cylindrical ring 310. Consequently, the ribs have essentially the same thickness, both as a function of the distance from the centerline of the device, and as a function of angular position (angular distance from lifting lug 340). In other embodiments, however, the thickness of the ribs may vary. In one embodiment, The thickness of each rib changes from the base at which the rib is joined to the cylindrical ring, to the top of the rib (the edge farthest away from the centerline of the cylindrical ring). Each rib is relatively thin at its top, and the width tapers to a greater thickness at the base. The inner wall of the rib (the surface that that faces the other rib) may be rounded, with a radius of curvature that is, for example, approximately the same as the height of the rib. The inner wall may have different curvatures in different embodiments, but will preferably be a smooth curve, rather than having corners (such as in a welded joint) that will cause stress risers. The curve will preferably have a minimum radius of curvature of at least half of the height of the rib. The thickness at the base of the rib may also vary, but will preferably be at least half of the height of the rib.

In one embodiment, the lifting device is forged and machined. A forging for each segment may be produced and then machined to the specific dimensions of the segment. The forging causes the metallurgical grain structure of the metal to flow along the contours of the forging die, which strengthens the segment. The machining of the segment ensures that the dimensions of the segment can meet very strict tolerances that are very difficult to meet when welding different components together. The additional strength may then allow the device to use less material, reducing its weight and cost.

As noted above, the lifting device is designed to be secured around a drilling riser. The “inner surface” of the lifting device is the cylindrical surface that mates to the drilling riser. In a conventional thrust collar and lifting device, the inner surface of the device has a curvature that is the same as the drilling riser to which it will be secured. In one embodiment of the present lifting device, the curvature of the inner surface is slightly different than the curvature of the drilling riser. More specifically, the radius of curvature of the inner surface is greater than the radius of curvature of the riser. As a result, when the lifting device is installed, the midpoint of each segment of the lifting device contacts the drilling riser first. Then, as the segments are secured to each other, the remainder of the segments' inner surfaces are brought into contact with the drilling riser. This is referred to for the purposes of this disclosure as pre-loading or pre-stressing the lifting device. The pre-stressing of the lifting device against the drilling riser reduces stresses in the device when it is used to lift the riser. This also distributes the stresses more evenly, and reduces alternating stresses when the device is put under load, thereby increasing the fatigue life of the device. It should be noted that the differing curvature of the lifting device's inner surface may, but does not necessarily, take into account the thickness of the layer of elastomeric material that may be applied to the inner surface.

The embodiment of FIGS. 3-5 uses bolts to connect the ends of the hinged segments to each other. Bolt holes are provided in flanges at the ends of each segment. A threaded bolt or stud is inserted through each of the bolt holes and is secured by nuts that are threaded onto the stud. Spherical washers are positioned between the nuts and the flanges, and spherical seats which are complementary to the washers are provided on the flanges. The spherical washers and seats allow the studs to pivot slightly with respect to the flanges. Consequently, the flexing of the segments and the resulting misalignment of the flanges with respect to each other does not place any bending stress on the studs which might cause them to fail. The bolt holes are slightly oversized with respect to the studs so that the studs can pivot slightly within the bolt holes.

It should also be noted that, in other embodiments, the hinged segments can be coupled together by means other than bolts. For instance, in one embodiment, the hinged segments may have flanges that are configured to be clamped together. In another embodiment, the segments may be coupled together by hinges.

The benefits and advantages which may be provided by the present invention have been described above with regard to specific embodiments. These benefits and advantages, and any elements or limitations that may cause them to occur or to become more pronounced are not to be construed as critical, required, or essential features of any or all of the claims. As used herein, the terms “comprises,” “comprising,” or any other variations thereof, are intended to be interpreted as non-exclusively including the elements or limitations which follow those terms. Accordingly, a system, method, or other embodiment that comprises a set of elements is not limited to only those elements, and may include other elements not expressly listed or inherent to the claimed embodiment.

While the present invention has been described with reference to particular embodiments, it should be understood that the embodiments are illustrative and that the scope of the invention is not limited to these embodiments. Many variations, modifications, additions and improvements to the embodiments described above are possible. It is contemplated that these variations, modifications, additions and improvements fall within the scope of the invention as detailed within the following claims.

Claims

1. A lifting device for a drilling riser, the device comprising: a collar having a cylindrical ring and a first annular rib connected to a first circular edge of the ring; anda lifting lug connected to the collar;wherein the collar has a plurality of segments; andwherein at least a first one of the segments is pivotally connected to at least a second one of the segments by a hinge.

2. The lifting device of claim 1, wherein the collar comprises a lug segment, a first hinged segment and a second hinged segment, wherein the lug segment has the lifting lug connected thereto, wherein the first hinged segment is pivotally connected to the lug segment by a first hinge, and wherein the second hinged segment is pivotally connected to the lug segment by a second hinge.

3. The lifting device of claim 2, wherein the first hinged segment is configured to be connected to the second hinged segment by one or more bolts.

4. The lifting device of claim 3, further comprising one or more spherical washers positioned between each of the one or more bolts and the first and second hinged segments, wherein a plurality of spherical seats for the spherical washers are provided on the first and second hinged segments.

5. The lifting device of claim 1, further comprising a second annular rib connected to a second circular edge of the ring.

6. The lifting device of claim 1, wherein each of the first and second annular ribs tapers from a smaller thickness at a top edge to a greater thickness at a base of the annular rib.

7. The lifting device of claim 6, wherein the thickness at the base of each annular rib is at least half of a height of the annular rib.

8. The lifting device of claim 6, wherein for each rib, an inner surface that faces the other rib has a minimum radius of curvature of at least half of a height of the rib.

9. The lifting device of claim 1, further comprising an elastomeric layer positioned against a cylindrical inner surface of the collar.

10. A drilling riser assembly comprising: a pipe section;one or more buoyancy modules, wherein each of the buoyancy modules is annular and is positioned around the pipe section; anda pair of lifting devices, wherein a first one of the lifting devices is secured to a first end of the pipe section and a second one of the lifting devices is secured to a second end of the pipe section, thereby retaining the one or more buoyancy modules on the pipe section;wherein each of the lifting devices includes a collar and a lifting lug connected to the collar, wherein the collar has a cylindrical ring and a first annular rib connected to a first circular edge of the ring, wherein the collar has a plurality of segments, and wherein at least a first one of the segments is pivotally connected to at least a second one of the segments by a hinge.

11. The drilling riser assembly of claim 10, wherein the collar comprises a lug segment, a first hinged segment and a second hinged segment, wherein the lug segment has the lifting lug connected thereto, wherein the first hinged segment is pivotally connected to the lug segment by a first hinge, and wherein the second hinged segment is pivotally connected to the lug segment by a second hinge.

12. The drilling riser assembly of claim 11, wherein the first hinged segment is configured to be connected to the second hinged segment by one or more bolts.

13. The drilling riser assembly of claim 12, further comprising one or more spherical washers positioned between each of the one or more bolts and the first and second hinged segments, wherein a plurality of spherical seats for the spherical washers are provided on the first and second hinged segments.

14. The drilling riser assembly of claim 10, further comprising a second annular rib connected to a second circular edge of the ring.

15. The drilling riser assembly of claim 10, wherein each of the first and second annular ribs tapers from a smaller thickness at a top edge to a greater thickness at a base of the annular rib.

16. The drilling riser assembly of claim 15, wherein the thickness at the base of each annular rib is at least half of a height of the annular rib.

17. The drilling riser assembly of claim 15, wherein for each rib, an inner surface that faces the other rib has a minimum radius of curvature of at least half of a height of the rib.

18. The drilling riser assembly of claim 10, further comprising an elastomeric layer positioned against a cylindrical inner surface of the collar.

19. The drilling riser assembly of claim 10, wherein a radius of curvature of an inner surface of each lifting device is greater than a radius of curvature of the pipe section, and wherein each lifting device is pre-stressed when installed on the pipe section.