Cylinder release arrangement

Abstract

The invention relates a cylinder release arrangement, wherein at least one cylinder is arranged with a piston within the cylinder, and a cylinder head closing off one end of the cylinder, forming a chamber between the piston and the cylinder head, wherein the cylinder is provided to arrange a leakage of fluid from one side of a piston to the other side of the piston, when the piston is in a given position within the cylinder, and release means are provided for the subsequently controlled release of the cylinder head from the cylinder. The invention also comprises a cylinder arrangement with a release mechanism.

Claims

1. A cylinder release arrangement which comprises: at least one cylinder, a piston positioned within the cylinder, and a cylinder head closing off one end of the cylinder to thereby form a chamber between the piston and the cylinder head; wherein the cylinder is configured to provide a leakage of fluid from one side of the piston to the other side of the piston when the piston is located a first distance from a sealing position in which the piston is in sealing contact with a sealing surface of the cylinder; and means for controllably releasing the cylinder head from the cylinder subsequent to the leakage of fluid from one side of the piston to the other side of the piston; wherein the means for controllably releasing the cylinder head from the cylinder comprise a release part of the piston and a number of fingers connected to the cylinder head, and wherein when the piston is moved a second distance away from the sealing position, the release part causes the fingers to move out of locking contact with the cylinder to thereby release the cylinder head from the cylinder.

2. The cylinder release arrangement in accordance with claim 1, wherein the piston is provided with a piston rod that is configured to move with the piston, and wherein the leakage of fluid from one side of the piston to the other side of the piston occurs when the piston is caused to move away from the sealing position within the cylinder.

3. The cylinder release arrangement in accordance with claim 2, wherein in the sealing position of the piston, the piston is in sealed abutment with the sealing surface in the cylinder.

4. The cylinder release arrangement in accordance with claim 2, wherein the interaction between the fingers and the release part allows for the piston, the piston rod and the cylinder head to move away from the sealing surface and release the cylinder head from the cylinder.

5. The cylinder release arrangement in accordance with claim 2, wherein when the release part is moved into interaction with the fingers, a thickened portion of the piston rod is moved out of a locking contact with the fingers.

6. The cylinder release arrangement in accordance with claim 2, wherein the fingers are configured to flex inwardly during interaction between the release part and the fingers.

7. The cylinder release arrangement in accordance with claim 5, wherein the locking contact between the thickened portion of the piston rod and the fingers locks the fingers in contact with the cylinder through engagement of the fingers with holding ridges provided on at least one of the cylinder and the fingers.

8. The cylinder release arrangement in accordance with claim 2, wherein deformation of tension rods connected between two riser parts actuates the movement of the piston rod.

9. A cylinder arrangement with a release mechanism comprising: a cylinder; a piston which is positioned within the cylinder and is connectable to a piston rod; and a cylinder head which closes off one end of the cylinder to thereby form a chamber between the piston and the cylinder head; the cylinder head comprising a number of axial extending fingers which are configured to flex radial inwardly and to be locked in locking engagement to the cylinder by a thickened portion of the piston rod; wherein the piston rod further comprises a release part which is arranged at a distance from the thickened portion and is configured to interact with the fingers such that when the piston is moved in an axial direction relative to the cylinder to a finger release position by the piston rod, the thickened portion will move out of locking interaction with the fingers and further movement of the piston rod will bring the release part into interaction with the fingers and cause the fingers to flex radially inwardly out of engagement with the cylinder to allow the cylinder head to be released from the cylinder.

10. The cylinder arrangement with a release mechanism in accordance with claim 9, wherein the piston rod comprises a first part and a separate second part on which the thickened portion and the release part of the piston rod are provided and which remains in position until the first part is connected to the second part during activation of the release mechanism.

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 is a perspective view of a safety joint in accordance with an embodiment of the invention.

(3) FIG. 2 is a cross section view of the safety joint of FIG. 1 shown in a collapsed state.

(4) FIG. 3 is a cross section view of the safety joint of FIG. 1 shown in a partly activated mode.

(5) FIG. 4 is a detailed cross section view of a manifold block of the safety joint of FIG. 1.

(6) FIG. 5 is a detailed cross section view of the connection between the first set of cylinders and the second set of cylinders in the safety joint of FIG. 1.

(7) FIG. 6 is a simplified view of an override system of the present invention.

(8) FIG. 7 is a simplified view of a third set of cylinders of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

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

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

(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 at its the upper end and a manifold, which is shown in the figures as a manifold block 6, at 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 30. 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 35, 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 at 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 is equal in length to 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 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 as an extension of the bore 10 of the riser to thereby form a continuous passage between a well and the surface. The safety joint 4 comprises a first riser part 8 and a second riser part 9 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 barrels. In the not activated mode shown in FIG. 2, a sealing system 24 seals between the inner barrel 1 and the outer barrel 2 in the lowermost part of the inner barrel 1. 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) One or a plurality of first radial bores 12 are arranged to fluidly connect 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 sides (herein after referred to as the upper and lower sides) of the floating piston 14. Which side is the upper or lower side may be changed depending on 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 the 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% their original length), before they break. These tension rods 20 may have a length of 0.5 meters to 2 meters, possibly 1 meter, depending 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 based on 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, are not exposed to any excessive forces and are 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, 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 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 will act on the downwardly working area 17A of each cylinder/piston 17. Alternatively, one may omit the bellow 11, in which case 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 will result in relative movement between the first connecting piece 3 and the manifold block 6. This situation, i.e. the situation where the tension rods 20 have begun to plastically deform, is referred to as the partly activated mode. The plastic deformation of the tension rod(s) 20 will cause numerous actions in the safety joint 4, which are shown in FIG. 3.

(17) FIG. 3 discloses the partly activated mode of the safety joint 4, where the tension rod(s) 20 have 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 given distance, the piston 17 is moved out of 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 wall of the cylinder. 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 move the fingers 22 out of engagement with the complementary holding ridges 31 in the cylinder wall, thereby allowing the piston rod 18, piston 17 and cylinder head/end cap 21 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 no forces from the first cylinder set 16 will act 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 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 around 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 inside the axial bore 13 will move in an upward direction to the second stopping sealing surface 15B, thus providing a limit of how much fluid that can be pushed up towards the bellow 11 and thereby preventing the bellow 11 from being pushed into the internal bore 10 of the riser. Additionally, bores 19A to the surroundings are provided to allow seawater to enter 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, as 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, thus allowing the pressure in the riser to enter the volume V between the inner 1 and outer 2 barrels. The pressure/fluid will then flow through the volume V towards the manifold block 6 (detailed view in FIG. 4), through a radial bore 26 in the manifold block 6, and into one or more cylinders of the second set of cylinders 27 and act on an upper part of each piston 33 in each cylinder 35 in the second set of cylinders. Similarly to the case of the first set of cylinders 16, the upwardly working force 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 in 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. by providing a 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 which creates a force pulling the piston 35 towards the collapsed state, i.e. the collapsed state of the cylinder 35, 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 the hydrostatic pressure of the seawater at the given location working on the upper side of the piston and a vacuum effect 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 creates 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 flow regulation means may be arranged in the bore 26, such as a valve, burst disc, choke valve etc. In the shown embodiment, a flow regulating means exemplified as a valve 28 is arranged 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 to be used with the safety joint or for a weak link connection between two riser parts 8, 9. The override system may be used in situations where large external forces on the system are expected, 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 accomplished by providing a separate cylinder/piston arrangement 40 connected between the first and the second parts 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 so as to provide redundancy in the system.

(23) FIG. 7 shows a simplified perspective view of a third set of cylinders. 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 are provided with at least one opening 56 to the sea in the volume 50 on the upper side of the cylinder piston 51, and have 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 telescoped 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. they provide a force that acts against the separation forces in the safety joint 4.

(24) A joint may be provided with 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 a 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 obtains 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 has now been explained with reference to the accompanied drawings. A skilled person will understand that alterations and modifications to this embodiment may be made that are within the scope of the invention as defined in the attached claims.