Safety joint

Abstract

The invention relates to a safety joint and a method of operation, the safety joint comprising: a first riser part and a second riser part overlapping in an axial direction and having end connections to be connectable as part of a riser, a release unit, locking the two riser parts together in a not activated mode, the release unit having other modes comprising a partly activated mode and fully activated mode, where the release unit comprises at least one axial extending tension rod connected between the two riser parts, which tension rod is configured to deform plastically before breaking, thereby activating the partly and fully activated modes.

Claims

1. A safety joint comprising: a first riser part and a second riser part which overlap in an axial direction, each riser part having a respective end connection which is connectable to a corresponding section of a riser; a release unit which includes at least one axially extending tension rod connected between the first and second riser parts; wherein the release unit is configured such that, in a not activated mode of the release unit the at least one tension rod locks the first and second riser parts together, in a partly activated mode of the release unit the at least one tension rod plastically deforms and thereby allows the first and second riser parts to move apart an initial distance, and in a fully activated mode of the release unit the at least one tension rod breaks and thereby allows the first and second riser parts to move apart an additional distance before the first and second riser parts separate from each other.

2. The safety joint according to claim 1, further comprising at least one cylinder arrangement which is connected between the first and second riser parts and is configured to compensate the safety joint and the at least one tension rod for internal pressure in the riser in the not activated mode and the partly activated mode and to compensate the safety joint for internal pressure in the riser in the fully activated mode.

3. The safety joint according to claim 2, wherein the cylinder arrangement is adapted to increase the forces acting against release of the first and second riser parts in the fully activated mode.

4. The safety joint according to claim 2, wherein the cylinder arrangement comprises one cylinder set which is configured to compensate the at least one tension rod for internal pressure in the riser in the not activated mode and the partly activated mode and to increase the forces acting against the release of the first and second riser parts in the fully activated mode.

5. The safety joint according to claim 2, wherein the cylinder arrangement comprises a first set of cylinders and a second set of cylinders, and wherein the first set of cylinders is adapted to compensate the at least one tension rod for the internal pressure in the riser in the not activated mode, the second set of cylinders is adapted to compensate the at least one tension rod for the internal pressure in the riser in the partly activated mode, and the second set of cylinders is adapted to increase the forces acting against the release of the first and second riser parts in the fully activated mode.

6. The safety joint according to claim 5, wherein the first set of cylinders is shorter in length than the second set of cylinders.

7. The safety joint according to claim 5, wherein the first set of cylinders is connected to the second set of cylinders through a mechanical link, and wherein pistons in the first and second sets of cylinders move equally in the not activated mode and the fully activated mode.

8. The safety joint according to claim 5, wherein the cylinder arrangement comprises a third set of cylinders which is adapted to be activated during the fully activated mode of the release unit.

9. The safety joint according to claim 8, wherein the third set of cylinders comprises a piston and is in communication with seawater on one side of the piston and with a fluid on the other side of the piston, and wherein the third set of cylinders is adapted to contribute to the force acting against release of the first and second riser parts in the fully activated mode.

10. The safety joint according to claim 5, further comprising a manifold which is adapted to distribute a fluid to the different cylinders in the cylinder arrangement in order to compensate for the internal pressure within the riser, the manifold comprising at least one flow regulating means which is adapted to regulate to which of the cylinders the fluid is distributed.

11. The safety joint according to claim 10, wherein the manifold comprises at least one bore which leads to a cylinder comprising a floating piston.

12. A method of operating a safety joint in a riser, the safety joint comprising first and second riser parts which overlap in an axial direction and a release unit which includes at least one axially extending tension rod connected between the first and second riser parts, the method comprising: connecting the first and second riser parts to corresponding lengths of the riser to make the safety joint form part of the riser; in a not activated mode of the release unit, keeping the riser parts connected together and pressure compensating the tension rods for internal pressure within the riser; increasing the tension in the riser to activate a partly activated mode of the release unit, thereby causing plastic deformation of the tension rods and allowing the first and second riser parts to move relative to each other over a small distance; further increasing the tension in the riser to activate a fully activated mode of the release unit, thereby breaking the tension rods; and allowing controlled disconnection of the riser at another joint in the riser in each of the not activated, partly activated and fully activated modes; or in the fully activated mode, further increasing the tension in the riser to thereby separate the first and second riser parts from each other.

13. The method according to claim 12, further comprising: after the step of increasing the tension in the riser to a fully activated mode and thereby breaking the tension rods, activating a set of cylinders in a cylinder arrangement to create a force in the safety joint acting against the release of the two riser parts, said cylinders being connected between the first and second riser parts; and allowing further telescopic action in the safety joint.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other characteristics of the invention will be clear from the following description of an embodiment, given as a non-restrictive example, with reference to the attached drawings wherein;

(2) FIG. 1 discloses a side-view of a safety joint according to the invention.

(3) FIG. 2 discloses a cross section of a safety joint according to the invention in a collapsed state.

(4) FIG. 3 discloses a partly activated mode of a safety joint according to the invention.

(5) FIG. 4 discloses a detailed view of a manifold block in the safety joint according to the invention.

(6) FIG. 5 discloses a detailed view of the connection between the first set of cylinders and the second set of cylinders according to the invention.

(7) FIG. 6 shows a simplified perspective view of an override system according to the invention.

(8) FIG. 7 shows a simplified perspective view of a third set of cylinders according to the invention.

(9) FIGS. 1 and 2 show an embodiment of a safety joint 4 according to the invention. The safety joint 4 is adapted to make part of a riser extending from a floating platform to a wellhead or similar.

(10) The safety joint 4 comprises a release unit, locking two riser parts 8, 9 together in a not activated mode. The release unit also has a partly activated mode and fully activated mode, as will be explained in the following.

(11) The release unit of the safety joint 4 comprises at least one axial extending tension rod 20 connected between the two riser parts 8, 9, which tension rod 20 is configured to deform plastically before breaking, thereby activating the partly and fully activated modes. The at least one tension rod 20, is axially arranged along the longitudinal direction of the safety joint 4. The tension rod(s) 20 is connected to a first connection piece 3 in the upper end and a manifold shown in the figures as a manifold block 6 in its lower end. In between the tension rods 20 there is arranged a first set of cylinders 16. The first set of cylinders 16 may comprise one or a plurality of cylinders. The first set of cylinders 16 may have perforations 16A to the sea. A second set of cylinders 27, which set may comprise one or a plurality of cylinders, is arranged below the first set of cylinders 16. The cylinders of the second set of cylinders 27 are connected to the manifold block 6, which manifold block 6, through an outer barrel 2, is connected to a second connection piece 7. The manifold block 6 and the connection piece 7 are arranged in a fixed distance, while an inner pipe 1 and the cylinder rod of the second set of cylinders 27 may telescope. The cylinder rods of the cylinders of the first set of cylinders 16 are connected to the cylinder rods of the cylinders of the second set of cylinders 27. In an alternative embodiment the positioning of the first set of cylinders 16 and the second set of cylinders 27 may be switched, whereby the connections between the different parts may be similar to the described embodiment. In between the second set of cylinders 27, there may be arranged a third set of cylinders 32, which third set of cylinders 32 may comprise one or a plurality of cylinders. In the shown embodiment the third set of cylinders 32 has equal length as the second set of cylinders 27. The different sets of cylinders 16, 27, 32 will be described in more detail below.

(12) FIG. 2 shows a cross-sectional view of the safety joint 4 according to the invention, where the safety joint is in the not activated mode (collapsed state), which mode is the normal operation mode for the safety joint 4. An inner bore 10 is formed in the safety joint 4 and extends through the whole length of the safety joint 4 in the extension of the bore 10 of the riser, for a continuous passage between a well and a surface. The safety joint 4 comprises a first 8 and a second 9 riser part arranged in a telescopic connection. The first riser part 8, i.e. possibly the upper part of the safety joint 4, is arranged in an overlapping manner in relation to the second riser part 9. The first riser part 8 has an inner barrel 1 movably arranged inside the outer barrel 2 of the second riser part 9, forming a volume V between the inner 1 and outer 2 barrel. A sealing system 24 seals between the inner barrel 1 and the outer barrel 2 in the lowermost part of the inner barrel 1, in the not activated mode of FIG. 2. The inner barrel 1 is connected to the first riser part 8 via the first connecting piece 3. The outer barrel 2 is connected to the second riser part via the second connection piece 7. It is possible to arrange these elements in the opposite manner.

(13) It is arranged one, or a plurality of, first radial bores 12 fluidly connecting the inner bore 10 with one, or a plurality of, axial bores 13 arranged on the radial outside of the inner bore 10. Furthermore, each axial bore 13 is connected to a cylinder of the first set of cylinders 16. A fluid-tight floating piston 14 floats inside each axial bore 13, which floating piston 14 can move between a first stopping surface 15A and a second stopping surface 15B in the axial bore 13. The floating piston 14 moves in the axial bore 13 as a response to pressure differences between the first and second side herein after referred to as upper and lower side of the floating piston 14. Which side is the upper and lower may be changed dependent of the configuration of the safety joint. The pressure from the inner bore 10 acts on the upper part of the floating piston 14, while the pressure of each cylinder in the first set of cylinders 16 acts on the lower part of the floating piston 14. In the not activated mode, the first set of cylinders 16 will pressure compensate the safety joint 4, as the total downwardly working area 17A (best shown in FIG. 5) of the piston(s) 17 in the first set of cylinders 16 is similar to the upwardly working end cap area in the bore 10 of riser in order to compensate the internal pressure in the inner bore 10, as the sum of the areas 17A of the pistons 17 equals the area of the end cap.

(14) A number of axial tension rod(s) (not shown in FIG. 2, element 20 in FIG. 1) may be arranged in between the first set of cylinders 16. The tension rods 20 may deform axially plastically (up to 10% its original length), before they break. These tension rods 20 would possibly have a length of 0.5 meter to 2 meter, possibly 1 meter, dependent on the material in the tension rods and the configuration of the safety joint 4. The extension of the tension rod will initiate the different modes of the safety joint. The operator can choose the strength of the tension rods as a result of the demands of different projects. During normal operating conditions, i.e. when the safety joint 4 is in the not activated mode, the tension rod(s) are intact and not exposed to any excessive forces and pressure compensated in relation to internal pressure within the riser.

(15) On the inside of the inner bore 10, covering the first radial bores 12, it is arranged a bellow 11 allowing pressure communication between the inner bore 10 and the axial bores 13. The bellow 11 separates the riser fluid from a clean hydraulic fluid in the axial bore 13. Each of the axial bore(s) 13 is as said fluidly connected to one cylinder of the first set of cylinders 16, such that the clean hydraulic fluid in the axial bore(s) 13 is the same hydraulic fluid as in the first set of cylinders 16. Thus, a downward movement of the floating piston 14 in the axial bore (as a response to a pressure increase of the fluid inside the riser) will result in a pressure increase in the clean hydraulic fluid, which pressure in the fluid will act on the downwardly working area 17A of each cylinder/piston 17. Alternatively, one may have a solution without a bellow 11, where the floating piston 14 will act as the dividing unit between the riser fluid and the clean hydraulic fluid.

(16) If the safety joint 4, i.e. the tension rods 20, experiences excessive tension forces, as a result of e.g. excessive tension in the riser, the tension rods 20 will start to deform plastically in the axial direction and that will give a relative movement between the first connecting piece 3 and the manifold block 6. This situation, i.e. the situation where the tension rods 20 has begun to plastically deform, is referred to as the partly activated mode. The plastically deformation of the tension rod(s) 20 will cause numerous actions in the safety joint 4, disclosed in FIG. 3.

(17) FIG. 3 discloses the partly activated mode of the safety joint 4, where the tension rod(s) 20 has started to deform due to excessive tension. In the disclosed partly activated mode, the compensation of the tension rods in relation to the internal pressure in the bore 10 of the riser is transferred from the first set of cylinders 16 to the second set of cylinders 27.

(18) The deformation of the tension rods 20 will actuate a movement of the piston rod 18, including the piston 17, of the first set of cylinders 16. When the relative movement has reached a distance the piston 17 is moved out of a sealed abutment with a sealing surface 19 (see detailed view in FIG. 5) in a cylinder 30. One will then have a leakage across the piston 17, and this piston 17 will no longer compensate the tension rods 20 for internal pressure within the riser. This compensation is then transferred to the second set of cylinders 27. This movement also moves a thickened portion of the piston rod 18 out of locking contact with radial extending fingers 22 connected to the cylinder end cap/cylinder head 21. This locking contact locks the fingers 22 in contact with holding ridges 31 in the inner cylinder wall. When the piston 17 continues to move as the tension rods 20 are plastically deformed further, the radial extending fingers 22 of the cylinder end cap/cylinder head 21 interact with a release part 23 of the piston 17 and moves the fingers 22 out of engagement with complementary holding ridges 31 in the cylinder wall, allowing the piston rod 18, piston 17 and end cap of the cylinder to move upwardly in the cylinder. The piston(s) 17 of the first set of cylinders 16 are provided with the release part 23, which release part allows for flexing the fingers 22 inwardly when the piston 17 moves upwards in the cylinder. This releases the cylinders 30 in the first set of cylinders 16 into two separate parts and there are no forces from the first cylinder set 16 acting on the safety joint 4. As the piston 17 moves upwardly with the piston rod 18 in the initial extension of the tension rods 20, a smaller and smaller area of the sealing surface 19 seals between the piston 17 and the cylinder 30. And, when the piston 17 has moved out of sealing engagement with the cylinder through sealing surface 19, the hydraulic fluid on the upper part of the piston 17 (working on the working area 17A) will be allowed to flow on the radial outside of the piston 17 due to the increased diameter of the cylinder. Until the leakage across the piston 17, the floating piston 14 that is floating inside the axial bore 13 will move in an upward direction to the second stopping sealing surface 15B providing a limit of how much fluid that can be pushed up towards the bellow 11, and thereby preventing the bellow 11 to be pushed into the internal bore 10 of the riser. Additionally, it is also arranged bores 19A to the surroundings allowing seawater to enter through said bores 19A and act on the lower part of the floating piston 14 when the system is in the partly activated mode. At this time the first set of cylinders 16 is no longer pressure compensating the safety joint 4 and the pressure compensation is transferred to the second set of cylinders 27, which is described below.

(19) Simultaneous with the movement of the piston rod 18 and piston 17, the inner barrel 1 will move axially upwards relative the outer barrel 2 because of the axial deformation of the tension rods 20, such that the sealing system 24 will no longer seal between the inner barrel 1 and the outer barrel 2, allowing the pressure in the riser to enter the volume V between the inner 1 and outer 2 barrels. The pressure/fluid will then transfer through the volume V towards the manifold block 6 (detailed view FIG. 4) and into a second radial bore 26, through the manifold block 6, and flow into one or more cylinders of the second set of cylinders 27, acting on an upper part of each piston 33 in each cylinder 35 in the second set of cylinders 27. Similarly as was the case of the first set of cylinders 16, the upwardly working forces of the riser fluids inside the bore 10, i.e. the end cap force, is balanced out by providing a downwardly working area that is the same or similar size as the end cap area of the riser bore 10. The second set of cylinders 27 will also work against the separation of the first and second riser parts 8, 9 by a vacuum effect in each cylinder 35, i.e. that there is vacuum or a fluid with 1 bar pressure on the lower side of each piston 33 in the cylinders 35. When the piston 33 is moved in the cylinder 35, this fluid will have a larger volume to fill, thereby creating an even lower pressure creating a force pulling the piston 33 towards the collapsed state, i.e. the collapsed state of the cylinder, into the cylinder again. Additionally, the hydrostatic pressure of the seawater will act on the top area of each piston rod 34 adding an additional force in the downward direction of the system. At this point the second set of cylinders 27 will provide the pressure compensation of the safety joint 4 in relation to internal pressure within the riser.

(20) One or more of the cylinders in the second set of cylinders 27 may be replaced by a third set of cylinders 32. This third set of cylinders 32 is not connected to the inner bore 10 of the riser, but is open to the sea, resulting in that the hydrostatic pressure of the seawater at the given location is working on the upper side of the piston, and a vacuum effect is working on the lower side of the piston. At large water depths this third set of cylinders 32 may provide quite a substantial additional force working against separation of the first and second riser parts 8, 9 due to the large hydrostatic column of seawater.

(21) FIG. 4 shows an embodiment of the manifold block 6 mounted to the outer barrel 2. At least one second radial bore 26 extends in the radial direction of the manifold block 6 and create a connection between the internal fluid in the riser and the second set of cylinders 27. The second bore 26 may be fully open, or it may be arranged flow regulation means in the bore 26, such as a valve, burst disc, choke valve etc. In the shown embodiment, it is arranged flow regulating means exemplified as a valve 28 in the second bore 26. The second bore 26 is connected to the volume V between the inner barrel 1 and the outer barrel 2 on one side, leading to the volume(s) of the cylinders of the second set of cylinders 27 on the other side. The safety joint 4 may be provided with access to this bore 26 from the outside of the safety joint 4 making it possible to change out any element positioned in this bore 26 without disassembling the whole safety joint 4.

(22) FIG. 6 shows a perspective view of an override system according to the invention. The override system may be used in situations where it is expected large external forces on the system, i.e. to provide a system that increases the connection force between the first and second riser parts 8, 9 and to make sure that the tension rods 20 are kept undamaged. This might be done by providing a separate cylinder/piston arrangement 40 connected between the first and the second part of the riser 8, 9, or alternatively by using the first set of cylinders 16, or a combination of the first set of cylinders 16 and the separate cylinder/piston arrangement 40 for this function. The volume 41 above the pistons 42 in the override cylinders 47 making up the separate cylinder/piston arrangement 40 is then fluid filled and locked in a set position. The fluid may be locked/trapped in the override cylinders 47 by means of a valve (not shown) which may be remotely operated. The locked/trapped fluid within the override cylinders 47 may be released to an active receiver 43 with for instance 1 bar pressure or to the sea 44. Valves 45, 46 may be provided between the sea 44 and the override cylinders 47 and between the active receiver 43 and the override cylinders 47. Alternatively, one may add an additional pressure to the fluid in the override cylinders 47 by a connection to a pressure cylinder 48 with for instance 700 bar pressure. This override system may comprise a set of cylinders 47, including one cylinder, but preferably two or more separate cylinders such as to provide redundancy in the system.

(23) FIG. 7 shows a simplified perspective view of a third set of cylinders according to the invention. In one embodiment one may also provide the safety joint 4 with an additional third set of cylinders 32, which third set of cylinders 32 may comprise one or a plurality of cylinders, and which are activated during the fully activated mode of the release unit. The cylinders of the third set of cylinders 32 is provided with at least one opening 56 to the sea in the volume 50 on the upper side of the cylinder piston 51, and has a fluid on the lower side 52 of the piston 51. The figure shows that the cylinder rod 57 is mechanically linked to the first riser part 8 and the cylinder is mechanically linked to the second riser part 9. This is the situation after the safety joint has telescoped a minor predetermined distance, whereby it should be understood that the cylinder rod 57, in appropriate ways, will be connected to the first riser part 8 after the minor telsecoped distance. When the safety joint 4 is extending, the pressure from the seawater acting on the upper side of the cylinder piston 51 and the vacuum effect (low pressure) on the lower side of the piston 51 both assist in forcing the two riser parts 8, 9 to a collapsed state, i.e. it provides a force that acts against the separation forces in the safety joint 4.

(24) According to an aspect of the invention it the may be provided a joint with a first and second overlapping riser parts allowing telescopic movement between the two different parts, to which two parts there may be connected a cylinder arrangement comprising at least one cylinder as described in relation to the third set of cylinders above. This will give a possibility of having heave compensating system with the seawater as the accumulator bank. In another possible configuration one may have such a joint with the addition of at least one cylinder as described in relation to the second cylinders above. One thereby gets a pressure compensated telescopic joint with the seawater as the accumulator bank in the system.

(25) In an alternative embodiment of the safety joint one may use another element to be plastically deformed as the safety joint is extended in the partly activated state. It is possibly to provide a sleeve in the joint and have this plastically deformed, for instance widened to get a somewhat controlled extension of the safety joint before it reaches the fully activated state.

(26) The invention is now explained with reference to the accompanied drawings. A skilled person will understand that there may be made alterations and modifications to this embodiment that are within the scope of the invention as defined in the attached claims.