SUBSEA DAMPER UNIT

Abstract

A subsea damper unit comprising a cylinder body (C) equipped with an internal damper chamber (9) filled with damper oil (A), said damper chamber (9) contains a through-running piston rod (D) with a piston (7) that divides the damper chamber (9) into two chamber parts (9a,9b), and where the piston (7) is equipped with one or more valves (3) that permit fluid communication between said chamber parts (9a,9b). Mounted to each end of the cylinder body (C) is a compressible and fluid-filled chamber (F) with a fluid (B) that takes up the same pressure as the surrounding water pressure, where respective fluid chambers (F) are in fluid communication with each other, and the cylinder body (C) comprises a pressurization valve or membrane (3) that transmits the pressure from said fluid (B) in at least one of the compressible fluid chambers (F) to the damper oil (A) in the damper chamber (9).

Claims

1. Subsea damper unit, comprising a cylinder body (C) equipped with an internal damper chamber (9) filled with damper oil (A), said damper chamber (9) contains a through-running piston rod (D) with a piston (7) that divides the damper chamber (9) into two chamber parts (9a,9b), and where the piston (7) is equipped with one or more valves (3) that permit fluid communication between said chamber parts (9a,9b), characterised in that a compressible and fluid-filled chamber (F) with a fluid (B) that takes up the same pressure as surrounding water pressure is mounted to each end of the cylinder body (C), where respective fluid chambers (F) are in fluid communication with each other, and that the cylinder body (C) comprises a pressurization valve or membrane (3) that transmits the pressure from said fluid (B) in at least one of the compressible fluid chambers (F) to the damper oil (A) in the damper chamber (9).

2. Subsea damper unit according to claim 1, characterised in that the piston rod (D) is fastened to respective, compressible fluid chambers (F).

3. Subsea damper unit according to claim 1, characterised in that the compressible fluid chambers (F) are formed as rolling bellows or accordion bellows manufactured from rubber, such as reinforced rubber.

4. Subsea damper unit according to claim 1, characterised in that the compressible and fluid-filled chambers (F) are in fluid communication with each other via one or more channels (G), where the internal diameter of the channel (G) or the channels is large enough to prevent chocking of the fluid stream.

5. Subsea damper unit according to claim 1, characterised in that said one or more valves (3) in the piston (7), and which control the fluid communication between the chamber parts (9a,9b), comprises a valve to control the decompression force and another valve to control compression force.

6. Subsea damper unit according to claim 1, characterised in that the pressurization valve (3) that transmits the pressure from at least one of said fluid chambers (F) to the damper oil (A) in the damper chamber (9) comprises a watertight slide, bellows or the like to avoid mixing of the oils.

7. Subsea damper unit according to claim 1, characterised in that one end of the cylinder body (C) is fastened to a housing (E) equipped with fastening devices (5), and that the piston rod (D) at the other end is equipped with fastening devices (6).

8. Subsea damper unit according to claim 6, characterised in that the housing (E) surrounds one of said fluid chambers (F) and is equipped with openings (8) that allow ingress of the surrounding seawater.

9. Subsea damper unit according to claim 1, characterised in that for deactivation of the damper it is equipped with a valve (2) to be able to turn off damper force, where the valve (2) controls fluid communication of the damper oil (A) between the chamber parts (9a,9b) via a relief channel (H), instead of through said one or more valves (3) in the piston (7).

10. Subsea damper unit according to claim 1, characterised in that for testing of the damper it is equipped with a service port (4) for filling and removal of damper oil (A) in the damper chamber (9).

11. Subsea damper unit according to claim 1, characterised in that the compressible and fluid-filled chambers (F) that are in fluid communication with each other form a constant volume chamber that makes the damper pressure neutral with respect to the surrounding pressure.

Description

DESCRIPTION OF THE FIGURES

[0025] Preferred embodiments of the invention shall, in the following, be described in more detail with reference to the enclosed figures, in which;

[0026] FIG. 1 shows in perspective a damper unit according to the invention.

[0027] FIG. 2 shows a principle diagram of the first embodiment of a damper unit according to the invention, seen in cross section.

[0028] FIG. 3 shows a principle diagram of a second embodiment of a damper unit according to the invention, seen in cross section.

[0029] FIG. 4 shows more details of a given embodiment of the damper unit according to the invention, seen in cross section.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0030] The damper unit according to the invention can be mounted between a fastening point (anchor, the ground, a rig, something heavy) and a pipe or other technical installation that has a low frequency vibration or has a need for dampening. For example, sudden pressure blows in a pipe. The damper unit can also be mounted between pipes in a flex loop pipe (pipe in a spiral form to be able to handle movements) where low frequency vibrations can arise between the pipes because of external and internal pressures and flow phenomena.

[0031] Initially, the assembly of the damper unit shall be explained, thereafter the function of the damper unit will be explained. As shown in the principle diagram in FIG. 2, the damper unit according to the invention comprises a housing E that can be equipped with an attachment lug 5. The housing E comprises, or is connected to, a cylinder body C that has an internal piston rod D that extends out from both ends of the cylinder body C. The cylinder body C is internally hollow and filled with a damper oil A in a damper chamber 9 and which is divided into two chambers 9a,9b by an intermediate piston 7, where the piston 7 is equipped with one or more valves 1 to control the damper force.

[0032] Mounted at respective ends of the cylinder body C are two compressible fluid chambers F which, in the example shown, contain oil B for a constant volume chamber. In a preferred embodiment, these compressible fluid chambers F are formed as rolling bellows (FIG. 3) or accordion bellows (FIG. 2) in reinforced rubber, but can also be formed from another flexible material. However, the expression bellows is used in the subsequent text to describe both types of bellows. The housing E is open to the surrounding environment, i.e. the surrounding seawater, via an opening 8, so that the pressure from the seawater affects the bellows F. Two bellows F are mounted at each end of the cylinder body C and are connected to each other via a line or channel G so that said constant volume chamber is formed.

[0033] A valve 3 is equipped to at least one end of the cylinder body C to transmit the pressure to the damper oil A. Correspondingly, a service port 4 can be mounted to the damper oil chamber 9 for filling and pressurising of the chamber 9, for example, to be able to test the damper on land.

[0034] An essential feature of the invention is that by the use of a through-running piston rod D one does not get a volume change in the damper and thereby avoids a gas reservoir to handle this. But it is important to pressurise the damper oil A to avoid cavitation and this is obtained by transferring the seawater pressure that acts on the bellows F, where the pressure goes via the oil/fluid B in the bellows F and is transmitted to the damper oil A via a valve/membrane 3. This ensures that the damper is pressure neutral with respect to the seawater pressure and no gaskets/seals need to be exposed to seawater. That the two bellows F are coupled together via the channel(s) G contributes to generate no volume changes in the damper.

[0035] The Damper Piston and the Damper Valve

[0036] It is preferred that the damper is made with a large diameter for the damper piston 7 to move large amounts of oil from small movements as this increases the control of the damper force at low damper speed. The valve pack 1 that chokes the oil and decides the damper force is mounted directly on the piston 7, and there can be a valve to control the decompression force and another valve for the compression, which ensures that the damper hysteresis is very low.

[0037] Pressure Neutral Construction

[0038] Dampers with a large piston diameter move large amounts of oil and this can cause cavitation behind the piston at large speeds, but this can be overcome by pressurising the damper oil. It is not desirable to operate with a gas reservoir to achieve this and pressure from the surrounding seawater is not used either. When the damper according to the invention is lowered down to installation depth, the pressure from the seawater will press against the bellow F, and this pressurises the oil B in the bellow F, and the pressure will be transmitted into the damper oil A in the damper chamber 9 via the valve 3. In this way, the whole of the damper will be pressure neutral with respect to the seawater pressure on the outside and there will be no pressure load on the cylinder body C or the bellows F as a consequence of the damper being mounted in deep water.

[0039] The valve 3 will not see any flow, only a pressure transmission. It can therefore comprise a watertight slide, membrane or bellows to avoid mixing of oils or to be able to relieve the pressure if the damper is taken up from an extreme depth. However, in the drawings a non-return valve is mounted that opens for pressure in towards the damper oil A in the damper chamber 9. When the damper is installed at ocean depths the pressure on the damper oil A is pressurised due to the seawater pressure and no cavitation will arise.

[0040] The Internal Volume of the Damper

[0041] The piston rod D is through-running and will therefore not cause any volume changes in the cylinder body C. A bellows F made from rubber is mounted at either end of the piston rod D on the outside of the cylinder body C and this gives two chambers 10a, 10b that are filled with oil. The chambers 10a, 10b are connected to the channel(s) G. When the damper moves, the volume of one of the chambers will increase and the other decrease, where the relationship between the increase and decrease in volume is the same. The oil B will change sides via the channel(s) G when the damper moves and the volume remains constant in the damper. Therefore, there will be no pressure changes in this system. The channel(s) G should be sufficient in number and large enough so that there is no chocking effect when the oil B flows through the channel(s) G. The piston rod gaskets will not be exposed to seawater either. Because of this construction with constant volume, the damper will not provide any static pushing force with the piston rod D and the seawater pressure will not be able to push the piston rod D into the damper either because of the pressure. The housing E will be open as the seawater presses against the rolling bellows F.

[0042] Deactivation of the Damper

[0043] It is desirable to be able to turn off the damper force on the damper for servicing or moving of the equipment the damper is mounted onto while it is subsea. This can be carried out in that one opens a valve 2 which is connected via a channel H to the two damper chambers 9a,9b. The oil A will then flow through the channel H instead of through the damper valve 1 in the piston 7 when the damper moves. The valve 2 can be opened with the help of hydraulic pressure from an ROV panel that is mounted so that it can be easily accessible for an ROV. One can also have an electrical remote control or mechanical operation of the valve directly from the damper. The hydraulic valve 2 in the drawing is such that with a rupture of the hose, the valve will close so that normal damper function will be maintained.

[0044] Robust

[0045] Because of the damper being pressure neutral with respect to the seawater pressure it will not have to be dimensioned from the consideration of very high pressures at large depths. The cylinder body C, the bellows F and the piston rod gaskets around the piston rod D will not feel any difference in the load if they are mounted at, for example, 50 metres or 500 metres depths.

[0046] Testing and Maintenance

[0047] To be able to test the damper on land during production, one must pressurise the oil to avoid cavitation. This can be carried out via the service port 4. There, one can also fill and remove oil. The damper will initially not function satisfactorily at high speeds under normal atmospheric pressure without the oil A being pressurised.

EXPLANATION OF THE DRAWINGS

[0048] A: Damper oil

[0049] B: Oil for the constant volume chamber

[0050] C: Main damper body, cylinder

[0051] D: Piston rod

[0052] E: Housing with attachment lug

[0053] F: Rolling bellows or accordion bellows in reinforced rubber

[0054] G: Oil channel for the constant volume chamber

[0055] H: Oil channel to deactivate the damper function

[0056] I: Hydraulic hose to the ROV panel

[0057] 1: Valves mounted on the damper piston to control the damper force

[0058] 2: Valve to be able to turn off the damper force

[0059] 3: Valve that transmits in the seawater pressure to pressurise the damper oil

[0060] 4: Service port for the damper oil chamber to fill and pressurise the chamber to be able to test the damper on land.

[0061] 5,6: Fastening device in the form of attachment lugs

[0062] 7: Damper piston

[0063] 8: Opening for the surrounding seawater

[0064] 9,9a,9b: Damper chambers

[0065] 10a, 10b: Bellows chambers