ENGINEERED WEAK POINT FOR RISER SYSTEMS

Abstract

A joint assembly allows a riser system to have a weak point that can fail at a known location and tension value without reducing the riser pressure containment capacity. The joint assembly includes a standard riser pipe machined to remove material, for example, to form a groove. The joint assembly also comprises means for restoring pressure capacity. For example, the means for restoring pressure capacity include a combination of a thick-bodied clamp and a split insert ring. The split insert ring can bridge between the groove and the clamp, at least partially transferring the pressure load contained inside the machined pipe to the clamp.

Claims

1. A joint assembly for providing a weak point that allows a riser having a longitudinal axis to sever at a predetermined longitudinal tension rating without reducing a predetermined pressure containment rating of the riser, comprising: an upper body including a pipe, the pipe having a first longitudinal tension rating that is larger than the predetermined longitudinal tension rating; a middle body, the middle body having a second longitudinal tension rating that is equal to the predetermined longitudinal tension rating and a pressure containment rating that is smaller than the predetermined pressure containment rating; a lower body including a pipe, the pipe having a third longitudinal tension rating that is larger than the predetermined longitudinal tension rating; and means for restoring pressure capacity; wherein the middle body connects the pipe of the upper body to the pipe of the lower body; wherein the means for restoring pressure capacity is sized to at least partially surround and contact a perimeter of the middle body; and wherein a sub-assembly including the middle body and the means for restoring pressure capacity surrounding and contacting the middle body has a fourth longitudinal tension rating that is equal to the predetermined longitudinal tension rating and a pressure containment rating that is equal to or larger than the predetermined pressure containment rating.

2. The joint assembly of claim 1 wherein the means for restoring pressure capacity is shaped to not hinder relative longitudinal movement of at least one of the upper body or the lower body.

3. The joint assembly of claim 1 wherein the means for restoring pressure capacity is more rigid in flexion than the middle body.

4. The joint assembly of claim 1 wherein the means for restoring pressure capacity does not include a seal.

5. The joint assembly of claim 1 wherein the upper body, the middle body, and the lower body form a unitary pipe, and wherein the middle body includes a groove forming a closed loop around the perimeter of the middle body or perforations distributed around the perimeter of the middle body.

6. The joint assembly of claim 5 wherein the middle body includes an outer groove.

7. A method of using a joint assembly, comprising: providing a joint assembly having a weak point that allows the riser to sever at a predetermined longitudinal tension rating without reducing a predetermined pressure containment rating of the riser, wherein the joint assembly comprises: an upper body including a pipe, the pipe having a first longitudinal tension rating that is larger than the predetermined longitudinal tension rating; a middle body, the middle body having a second longitudinal tension rating that is equal to the predetermined longitudinal tension rating and a pressure containment rating that is smaller than the predetermined pressure containment rating; a lower body including a pipe, the pipe having a third longitudinal tension rating that is larger than the predetermined longitudinal tension rating; and means for restoring pressure capacity; wherein the middle body connects the pipe of the upper body to the pipe of the lower body; wherein the means for restoring pressure capacity is sized to at least partially surround and contact a perimeter of the middle body; and wherein a sub-assembly including the middle body and the means for restoring pressure capacity surrounding and contacting the middle body has a fourth longitudinal tension rating that is equal to the predetermined longitudinal tension rating and a pressure containment rating that is equal to or larger than the predetermined pressure containment rating; incorporating the joint assembly into the riser; and applying the predetermined longitudinal tension to the riser to cause the middle body to sever.

8. The method of claim 7 wherein the means for restoring pressure capacity is shaped to not hinder relative longitudinal movement of at least one of the upper body or the lower body.

9. The method of claim 7 wherein the means for restoring pressure capacity is more rigid in flexion than the middle body.

10. The method of claim 7 wherein the means for restoring pressure capacity does not include a seal.

11. The method of claim 7 wherein the upper body, the middle body, and the lower body form a unitary pipe, and wherein the middle body includes a groove forming a closed loop around the perimeter of the middle body or perforations distributed around the perimeter of the middle body, the method further comprising severing the groove or perforation.

12. The method of claim 11 wherein the middle body includes an outer groove.

13. A method of making a joint assembly, comprising: providing an upper body including a pipe, the pipe having a first longitudinal tension rating that is larger than a predetermined longitudinal tension rating; providing a middle body, the middle body having a second longitudinal tension rating that is equal to the predetermined longitudinal tension rating and a pressure containment rating that is smaller than a predetermined pressure containment rating; providing a lower body including a pipe, the pipe having a third longitudinal tension rating that is larger than the predetermined longitudinal tension rating; wherein the middle body connects the pipe of the upper body to the pipe of the lower body; providing means for restoring pressure capacity; wherein a sub-assembly including the middle body and the means for restoring pressure capacity surrounding and contacting the middle body has a fourth longitudinal tension rating that is equal to the predetermined longitudinal tension rating and a pressure containment rating that is equal to or larger than the predetermined pressure containment rating; and forming a joint assembly having a weak point that allows a riser to sever at the predetermined longitudinal tension rating without reducing the predetermined pressure containment rating of the riser by at least partially surrounding and contacting a perimeter of the middle body with the means for restoring pressure capacity.

14. The method of claim 13 wherein the means for restoring pressure capacity is shaped to not hinder relative longitudinal movement of at least one of the upper body or the lower body.

15. The method of claim 13 wherein the means for restoring pressure capacity is more rigid in flexion than the middle body.

16. The method of claim 13 wherein the means for restoring pressure capacity does not include a seal.

17. The method of claim 13 wherein the upper body, the middle body, and the lower body form a unitary pipe, and wherein the middle body includes a groove forming a closed loop around the perimeter of the middle body or perforations distributed around the perimeter of the middle body, the method further comprising forming the groove or the perforations by removing material of a cylindrical pipe.

18. The method of claim 17 wherein the middle body includes an outer groove.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] For a more detailed description of the embodiments of the disclosure, reference can now be made to the accompanying drawings, wherein:

[0015] FIG. 1 is a sectional view of an example joint assembly;

[0016] FIG. 2 is a sectional view of a portion of the joint assembly shown in FIG. 1;

[0017] FIG. 3 is a perspective view side view of the joint assembly shown in FIG. 1; and

[0018] FIG. 4 is an exploded view of the joint assembly shown in FIG. 1.

DETAILED DESCRIPTION

[0019] The joint assembly described in the disclosure can solve the problem of allowing a riser system to have a weak point that can fail at a known location and tension value without reducing the riser pressure containment capacity. This joint assembly may be made using a standard riser pipe without the need to have a seal be part of the joint assembly, although a seal can also be provided.

[0020] The standard riser pipe can be machined to remove material (e.g., to form a groove) either on the Outside Diameter only or on both the Outside and Inside Diameters. The advantage of removing material on the OD only is that the required machining operations can be simpler than removing material on both the ID and OD, but a disadvantage can be that an amount of local bending should be expected due to tension. Machining both the Inside and Outside Diameters can reduce or eliminate the local bending.

[0021] By machining down the effective wall thickness of the standard riser pipe, the point at which the machined pipe fails in tension is reduced to the desired tension capacity. As an example, a riser pipe that would otherwise fail at a rating of 2.0 MM lbs can be downrated to 1.0 MM lbs by machining out approximately half of the wall thickness (or, more precisely, half of the cross-section). This machining operation, however, can reduce the pressure capacity of the machined riser pipe to an unacceptably low value.

[0022] Referring to FIGS. 1-4, the pressure capacity can then be restored to its intended value by adding a thick-bodied clamp 12 to the outside of the machined riser pipe 10, with a split insert ring 14 that is designed to interface directly with the machined profile 16 (e.g., a groove) and the ID of the clamp 12. The split insert ring 14 can bridge between the machined profile 16 and the clamp 12, partially transferring the pressure load contained inside the machined pipe 10 to the body and bolts of the clamp 12. The split insert ring 14 may be formed by ring segments that are stacked radially and/or along the machined riser pipe 10. The split insert ring 14 preferably surrounds the entire length of profile 16 or a substantial portion of the height of profile 16. Alternatively, segments similar to the ring segments of the split insert ring 14 are integral to (e.g., braised to) the thick-bodied clamp 12.

[0023] This combination of thick-bodied clamp 12 and split insert ring 14 can be used to make a joint assembly that has a pressure capacity greater than or equal to the original, standard riser pipe but a tension capacity that is as low as the riser designer would like it to be in order to suit the weak point requirements of the riser system.

[0024] Alternatively, the standard riser pipe could be machined to remove material across or through the wall thickness (e.g., form perforations) that are then filled by ring segments that seal the perforations. Other known ways of reducing tension capacity can also be used.

[0025] By making the body of clamp 12 long enough, the machined profile 16 can also be isolated from bending stresses. The ends of the body of clamp 12 are preferably profiled in order to reduce any compression hotspots that are due to the bending. In some embodiments, it may be advantageous to also introduce a preloaded elastomer (not shown) between each of the two ends and the machined riser pipe 10, which can allow a smooth stiffness transition and thereby reduce any hotspots.

[0026] The disclosure is susceptible to various modifications and alternative forms. Specific embodiments thereof are shown by way of examples in the drawings and description. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the scope of the invention to the particular form disclosed. However, on the contrary, the intention is to cover all modifications, equivalents, and alternatives enabled by the disclosure.