Control device for controlling a valve arrangement and method for controlling a safety arrangement comprising said control device and said valve arrangement

Abstract

A safety arrangement of at least one of a marine and an offshore application includes a control device and a valve arrangement configured to be positioned in a flow path between a hydraulic cylinder and a pressure accumulator. The control device is configured to control the valve arrangement according to at least one function, in particular a safety function. The valve arrangement includes a main valve that is operable to control a flow along the flow path. A method of controlling the safety arrangement includes controlling the valve arrangement with the control device.

Claims

1. A method of controlling a safety arrangement for at least one of a marine and an offshore application, comprising: controlling a valve arrangement positioned in a flow path between a hydraulic cylinder and a pressure accumulator via a control device according to at least one function, the at least one function including a safety function; monitoring at least one physical quantity of the valve arrangement on at least one of a cylinder side and an accumulator side of the valve arrangement; signaling the monitored at least one physical quantity to the control device; and comparing at least one cylinder side quantity with at least one accumulator side quantity via the control device, wherein the controlling of the valve arrangement via the control device is performed with reference (i) to the signaled and monitored at least one physical quantity, and (ii) to the comparison between the at least one cylinder side quantity and the at least one accumulator side quantity.

2. The method of claim 1, wherein the controlling of the valve arrangement via the control device with reference to the comparison includes at least one of: controlling the valve arrangement so that the flow path is open in response to the comparison indicating that a cylinder side pressure is substantially equal to an accumulator side pressure; and controlling the valve arrangement so that the flow path is closed in response to the comparison indicating that one of the cylinder side pressure and the accumulator side pressure is substantially less than the other.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Preferred embodiments of the disclosure are explained in the following by means of schematic drawings, wherein:

(2) FIG. 1 shows a safety arrangement, comprising a valve arrangement with a control device according to a first embodiment of the disclosure,

(3) FIG. 2 shows a safety arrangement, comprising a valve arrangement with a control device according to a second embodiment of the disclosure,

(4) FIG. 3 shows a safety arrangement, comprising a valve arrangement with a control device according to a third embodiment of the disclosure, and

(5) FIG. 4 shows a flow chart of the method according to the disclosure.

DETAILED DESCRIPTION

(6) In FIG. 1 there is shown a control device 1 according to the disclosure, provided with a valve arrangement 2 between a hydraulic cylinder 4 and a pressure accumulator 6. Said control device 1 and said valve arrangement 2 forming a safety arrangement 3.

(7) Said valve arrangement 2 comprises a single main valve 8 arranged in a flow path 10 between said hydraulic cylinder 4 and said pressure accumulator 6, wherein said main valve 8 is formed as a proportional shut off valve with a position sensor 12 arranged thereon, by which a position of said main valve 8 is detectable and signalable to said control device 1 as an input value.

(8) Said pressure accumulator 6 contains gas and liquid, especially a hydraulic fluid, separated by a medium separator (not shown).

(9) On an accumulator side of said main valve 8 two accumulator pressure sensors 14, 16 are arranged in said valve arrangement 2, by which an accumulator pressure is detectable and signalable to said control device 1 as an input value.

(10) On a cylinder side of said main valve 8 two cylinder pressure sensors 18, 20 are arranged in said valve arrangement 2, by which a cylinder pressure is detectable and signalable to said control device 1 as an input value. Further, there are two velocity sensors 22, 24 and two displacement sensors 26, 28 arranged on said hydraulic cylinder 4, by which a cylinder velocity and a cylinder displacement are detectable and signalable to said control device 1 as an input value.

(11) In said valve arrangement 2 two pilot valves 30, 32 are provided to operate said main valve 8 via a switchover valve 34, arranged fluidically between said pilot valves 30, 32 and said main valve 8 for switching between a first pilot valve 30 and a second pilot valve 32. On each of said two pilot valves 30, 32, formed as proportional valves, there is arranged a position sensor 12, by which a position of said main valve 8 is detectable and signalable to said control device 1 as an input value.

(12) Said control device 1 comprises a first control device 36 and a redundant second control device 38, controlling said two pilot valves 30, 32 and said switchover valve 34 by output signals sent to said two pilot valves 30, 32 and said switchover valve 34.

(13) In FIG. 2 there is shown a control device 1 according to a second embodiment the disclosure, comprising a second main valve 40 arranged in said flow path 10 between said hydraulic cylinder 4 and said pressure accumulator 6, wherein said second main valve 40 is formed as a switching valve, especially as a switching flow shut off valve, with a closed position sensor 42 arranged thereon, by which a closed position of said second main valve 40 is detectable and signalable to said control device 1 as an input value.

(14) Said position sensors 12 of said two pilot valves 30, 32 are not shown in FIG. 2, wherein here a closed position sensor 42 is used on said first pilot valve 30 which is here formed as a switching valve.

(15) Further, said switchover valve 34 of the first embodiment is omitted in the second embodiment.

(16) The other features of this second embodiment are the same as described above for the first embodiment shown in FIG. 1.

(17) In the following, a short description of the operating mode of the disclosure with reference to the above mentioned embodiments shall be made:

(18) To ensure a riser anti recoil function at a marine riser tensioner provided with said control device 1 according to the present disclosure and installed on a drilling vessel, during normal drilling operation the riser is connected to a blowout preventer (BOP) stack.

(19) Due to heave movements of the drilling vessel and a compressibility of said gas volume in said pressure accumulator 6, said fluid flows between said pressure accumulator 6 and said cylinder 4. Said main valve 8, 40, especially formed as a flow shut off valve, is enabled to protect this system against overspeed in case of a wire rope failure and said main valve 8, 40 is kept open.

(20) Said main valve 8, 40 shall be operated in the event of a riser disconnect, and/or a riser failure, and/or a tension wire failure and/or a cylinder failure to eliminate or minimize a riser recoil effect.

(21) Such operation is controlled by said control device 1, especially by a program executable on said control device 1. To realize said riser anti recoil function, said main valve 8 or said two main valves 8, 40 control said flow to assure that said pressure does not drop below a preset level and thus assuring that said wire rope of said tensioner does not slack. During this operation said main valve 8 or said two main valves 8, 40 is/are disabled, that is, kept open.

(22) To ensure a tensioner and compensator isolation function at a marine riser tensioner provided with said control device 1 according to the present disclosure and installed on a drilling vessel, a pressure of said pressure accumulator 6 and a pressure of said hydraulic cylinder 4 is detected by said respective pressure sensors, that is said two accumulator pressure sensors 14, 16 and said two cylinder pressure sensors 18, 20. Said detected pressures are signaled to said control device 1 and compared with each other by said control device 1 and/or a suitable program running on said control device 1. As shown in the respective figures of other shown embodiments, the sensor arrangement can vary.

(23) During normal operation said cylinder pressure is substantially equal to said accumulator pressure and said main valve 8, 40 is kept open.

(24) A sudden pressure drop due to a failure will cause said control device 1 to send a signal to at least one of said pilot valves 30, 32 to control said main valve 8, 40 closed.

(25) To ensure a tensioner and compensator overspeed protection function with said control device 1 according to the present disclosure and installed on a drilling vessel, said cylinder pressure and said pressure accumulator pressure are detected as described above to the tensioner and compensator isolation function. A vertical movement of said drilling vessel due to a motion of the sea and corresponding change in wire rope tension and pressure accumulator pressure is recognized by said control device 1 as a pressure difference from said cylinder pressure to said pressure accumulator pressure. This pressure difference causes said control device 1 and/or said suitable program running on said control device 1 to control said main valve 8, 40 closed if critical flow rates are exceeded.

(26) A flow direction in case a failure occurs is always from said pressure accumulator 6 to said hydraulic cylinder 4 regardless of a vertical direction of travel of said drilling vessel. A resultant pressure differential created by an explosive discharge of said pressure accumulator 6 causes said control device 1 and/or said suitable program running on said control device 1 to control said main valve 8, 40 closed.

(27) FIG. 3 shows a safety arrangement 3 comprising a valve arrangement, formed as a valve manifold 2, and a control device 1 according to a third embodiment of the disclosure.

(28) The valve manifold 2 is connected at one side to the high pressure liquid compartment of said hydraulic cylinder, formed as a compensator/tensioner cylinder 4. For pushing type cylinders this at the bottom side and for pulling type cylinders this is at the rod side. The other side of the manifold 2 is connected to a medium separator 60 of said gas accumulator, containing a piston accumulator 62, and the opposite side of this medium separator 60 is connected to a high pressure gas vessel 64 of said gas accumulator 6. In some applications the use of a medium separator 60 is omitted and a pressure vessel pressure accommodates both liquid and gas.

(29) The main component on the valve manifold 2 is a hydraulic operated main valve, formed as a cartridge valve 8, of which the valve opening is controlled by a first solenoid operated control valve 66 a second solenoid operated control valve 68. Depending on the application and the required performance level, this can be done by a single solenoid operated control valve 66 or an additional redundant second solenoid operated control valve 68. In order to improve robustness with respect to common cause failures CCF score>65, according 18013849 both valves may be of a different type.

(30) Also dependent on the application a fully closed valve position may be replaced by a slightly open position using an orifice (not shown); this to realize an automatic pressure equalizing function.

(31) As the compensator is a closed circuit with a fixed fluid volume, leakage via the control valves 66, 68 is avoided by pilot operated check valves 70, 72 which are opened when the control valves 66, 68 are operated and remain close otherwise. Compressed fluid to operate the main valve 8 is obtained from the closed circuit via check valves 74, 76 and the displaced volume from the main valve 8 is routed via check valves 70, 72 and control valves 66, 68 towards an external reservoir 78. In order to avoid that the valve manifold 2 drains empty and that the control valve 66, 68 operation is affected in a negative way, a preloaded check valve 80 is installed. Multiple operation of the main valve 8 causes fluid from the closed circuit to drain to the external reservoir 78 and to avoid that the compensator gets out of calibration, the drained volume needs to be replenished into the closed circuit using a hydraulic pump 82. A level measuring device 84 may be used to detect whether replenishment is required.

(32) Said control device 1 commands the control valves 66, 68 and the check valves 70, 72 in order to control the opening of said main valve 8. A displacement sensor 26, 28 measures the main valve 8 opening and the signal is used to allow for closed loop control.

(33) Depending on the application and the required performance level this can be done by said control device 1 that may contain a first control device 36 and a redundant control device 38. In order to improve robustness according 18013849 both control devices 36,38 may be of a different type.

(34) Depending on the application, sets of sensors 18, 20, 86, 88 are installed at an upstream side of the main valve 8 and at a downstream side. Depending on the application and the required performance level this can be done by one set or an additional redundant set of sensors 18, 20, 86, 88. In order to improve robustness according IS013849 transducers may be of a different type. Each set of sensors 18, 20, 86, 88 comprises a pressure sensor 18, 20 and a temperature sensor 86, 88.

(35) The pressure sensors 18, 20 are used to determine the absolute pressures at each side of the main valve 8, as well as the pressure difference across the main valve 8. In this way the cylinder load, gas pressure and medium flow through the main valve 8 can be determined. As the medium viscosity is temperature dependent, also temperature is measured by means of the temperature sensors 86, 88 to calibrate the medium viscosity. As an alternative to flow measurement by differential pressure, also the position and or velocity of the cylinder rod can be measured by velocity sensors and position sensors (not shown). Depending on the application and the required performance level this can be done by one set or an additional redundant set of sensors.

(36) For a number of functions, for example anti-recoil function, the actual cylinder rod position is to be measured, this can be obtained from the position sensor(s). This signal can also be used to prevent that the cylinder 4 bottoms out during normal operation.

(37) In addition the position of the piston accumulator 62 can be measured by a single position measuring device 900r an additional redundant position measuring device 92, providing information on the correct calibration of the fluid volume in the closed circuit. This is to prevent that the piston accumulator 62 bottoms out during normal operation.

(38) Signals from the aforementioned sensors are processed by the control device 1. In case redundant control devices 36, 38 are used, both control devices 36, 38 monitor each other in order to obtain required control category and diagnostic coverage according, preferably to the definition of ISO 13849.

(39) Also both control devices 36, 38 can provide an interface (not shown) with external supervisory control systems which may be required for operation, monitoring and safeguarding of the tensioner/compensator installation. This includes also all means installed to perform condition monitoring other than the safety valve arrangement itself.

(40) In case electrical power supply fails, a battery backup (not shown) is provided to keep control devices powered as long as required to bring the safety valve arrangement 3 to a safe state. This safe state can be: Remain open Remain closed Finish controlled closing cycle and remain closed when anti-recoil cycle has been initiated

(41) As long as electric power is removed, the safety valve arrangement 3 is to maintain its current state.

(42) To all embodiments of the disclosure applies in general:

(43) For realizing said tensioner and compensator isolation function and/or a valve isolation function, said main valve 8, 40 is to close as quickly as possible at loss of load or cylinder over-speed. Loss of load, especially due to rope failure or rupture of hydraulic/air pipe, can be detected by measuring a resulting pressure pulse, for example by a pressure transducer, and/or measuring resulting cylinder over-speed as described further below.

(44) For realizing said tensioner and compensator overspeed protection function and/or to prevent overspeed of a cylinder 4, especially due to loss of load or high speed of the load attached, said overspeed can be detected by measuring a cylinder speed by either measuring a pressure drop across said main valve 8, 40 (using pressure transducers, for example) and/or a cylinder rod speed (using position/velocity transducers, for example). Also the speed of a piston in a piston accumulator can be used as a measure, if said pressure accumulator 6 is formed as said piston accumulator. If said pressure drop across said main valve 8, 40 is used as detection method, also temperature sensors are required to calibrate for the effect of medium viscosity on the pressure drop measured.

(45) For realizing said overload protection of said hydraulic cylinder 4 if said main valve 8, 40 is closed, said main valve 8, 40 needs to open enough to relief pressure towards said pressure accumulator 6. Cylinder overload is detected by measuring the cylinder pressure.

(46) Realizing said riser anti recoil function is described in more detail in the following:

(47) Disconnecting a tensioned riser from a well head will lead to a series of events. At the moment the riser disconnects at the lower end, an elastic pulse travels up the length of the riser and the elastic elongation is removed. This causes the lower end to clear the well head almost immediately.

(48) As the force equilibrium is disturbed, the mass of the riser is subjected to the force imbalance causing an upward acceleration of the riser. As the vessel supporting the riser moves vertically up and down due to wave induced motion, it is essential that the riser has an upward movement that is sufficient to keep clear of the well head and to avoid colliding into it. The riser is allowed to accelerate to an upward speed that is higher than the (downward) vertical speed of the vessel. During this phase a safety valve, i.e. said main valve of said safety arrangement, remains fully open.

(49) Having sufficient vertical speed (speed detection by position/speed sensors and/or pressure difference across said main valve), the force imbalance is corrected by controlling the opening of the safety valve. Creating a preferably constant pressure drop across the safety valve will result in a tension force that equals the weight of the riser and a low rope tension. The riser continues moving upwards at a slowly increasing speed, preferably caused by the minimum tension, in order to increase clearance with the well head.

(50) When the tensioners near reach their end of stroke limit, the riser needs to be slowed down to avoid impact into their end stops. The opening of the safety valve is decreased further creating a, preferably constant, pressure drop (measured by pressure sensors) across the safety valve resulting in a tension force that is just high enough to avoid slackening of the wire lines. Now the riser is slowed down with an acceleration ad by its own weight minus the low tension force. This situation is maintained until the upward speed has dropped sufficient low. When the tensioners reach their end of stroke limit (detected by position sensors) or when the cylinder speed is sufficient low, said main valve is closed completely.

(51) FIG. 4 shows a flow chart of the method according to the disclosure-realizing at least one or several functions, especially safety functions, with said valve arrangement 2 by means of a control device 1, comprising a monitoring step 44.

(52) In said monitoring step 44 relevant physical quantities of said valve arrangement 2 on a cylinder side and/or on an accumulator side are monitored and/or measured.

(53) After said monitoring step 44, a signaling step 46 is provided, wherein said relevant physical quantities are signaled to said control device. During said signaling step 46 a detection of a difference between a desired position of said main valve 8, 40 and an actual position of said main valve 8, 40 can be executed.

(54) According to said detection of said position of said main valve 8, 40, a controlling step 48 is provided, wherein said valve arrangement 2 is controlled by means of said control device 1 by providing an output to actuation devices required to operate said main valve 8, 40 towards its desired position. Said actuation devices can enclose said first pilot valve 30 and/or said second pilot valve 32, controlled by said control device, which can enclose said first control device 36 and/or said second control device 38.

(55) Preferably if redundant control devices like said first control device 36 and said second control device 38 are used, a further decision step (not shown) can be executed, wherein said redundant control devices 36, 38 are monitoring each other and, based on predetermined criteria, a decision is made which of said redundant control devices 36, 38 is to perform said controlling step 48.

(56) During said controlling step 48, said valve arrangement 2 can be controlled by means of said control device 1 according to a result of a comparison of said cylinder side relevant physical quantities with said accumulator side relevant physical quantities by means of said control device 1. If said cylinder side pressure is substantially equal to said accumulator side pressure, controlling of said valve arrangement 2 can be executed so as to keep said flow path open, or if one of said cylinder side pressure or said accumulator side pressure is significantly less than the other, controlling said valve arrangement 2 so as to close said flow path can be executed.

(57) Further, preferably before said monitoring step 44 a checking step (not shown) can be provided, wherein a monitor and self check of the safety related parts of the valve arrangement (check reliability according to ISO 13849, for example) is executed.

(58) Where applicable, a communicating step (not shown) can be provided to receive commands from and/or provide status feedback to an external supervisory control system via an interface to said supervisory control system.

(59) Further, a condition monitoring step (not shown) can be provided for executing a condition monitoring task by said control device 1, 36, 38, involving a measurement of other physical quantities of said safety arrangement, including a compensator/tensioner arrangement for example. Said thus collected data can be relayed via said interface to external equipment.

(60) Disclosed is a safety arrangement comprising a control device and a valve arrangement, preferably formed as a valve manifold, with a minimum of hydraulic components and containing a controllable main valve, especially for isolating a hydraulic cylinder from a pressure accumulator. Said control device providing the required functions by controlling the aforementioned main valve as well as additional hydraulic components on the manifold.

(61) The typical application of the safety arrangement is the use in linear heave compensator or wire rope tensioning systems. Here a fluid filled hydraulic cylinder is used in combination with a compressed gas volume of which the pressure is in balance with the load applied to the compensator/tensioner.

(62) As mostly large loads and large volumes of compressed gas are involved, there is a risk that accumulated energy is released suddenly when the load balance is disturbed, for example by a rope failure. In other cases a controlled closing may be required to obtain a predefined speed profile.

(63) The safety arrangement can be applied for following offshore drilling and production applications (ref. DNV Offshore specification E101): Direct riser tensioners Wire line tensioners for risers

(64) Guide line and Pod line tensioners And also for: Swell compensators on trailing suction hopper dredgers Other compensators/tensioners requiring similar safety provisions The Safety Valve arrangement is suitable for installation in an open deck space in a salty and marine environment and is suitable for installation in explosive atmospheres according to the definition of A TEX and IEC-Ex regulations.

(65) Required functions are: Quick isolation at sudden load loss to avoid cylinder rod to accelerate to excessive speeds; Over-speed protection: Isolating a hydraulic cylinder from a gas volume when said cylinder exceeds a predefined speed; Overload protection: To avoid a cylinder overloading when said main valve is closed and an external load is applied to the cylinderexcessive pressure in said cylinder is relieved across said closed main valve; Controlled closing to obtain predefined speed profile (applicable to riser tensioners at riser disconnect: For realizing said anti-recoil function; Hold open function: To avoid said main valve to close under any condition (overrule safety function); Hold close function: To avoid said main valve to open under any condition; Pressure equalizing function: When said main valve is closed, pressures at both sides may differ. Pressure equalization can either be obtained by opening said main valve creating a small flow passage or by implementing an orifice which automatically equalizes pressure;

(66) An advantage of the present disclosure is providing a safe and reliable isolation between an actuator, preferably a hydraulic cylinder, and an energy source, preferably an oil-gas spring, dependent on the required functionality for its application.

(67) The reliability of operation of the safety arrangement complies with requirements as set forward by ISO 13849 with respect to required performance level PLr and actual obtained performance level PL. Dependent on the application and resulting hazard and/or failure effects determined by Severity S, Frequency of exposure F and probability of avoidance P, the required performance level may be as high as PLr=d.

(68) Depending on the application said main valve has to have a number of functions which differ per application. In order to keep the number of hardware variants as low as possible, the functions are realized by a processor based control system. In this way each arrangement can be easily configurable by means of software instead of hydraulic hardware.

(69) By applying a processor based control device including relevant instrumentation, means are available to monitor the condition of the safety valve arrangement as well as to perform self test and self diagnostics. Having sufficient redundancy (Control Category 2 or 3) and means to detect failures (diagnostic Coverage 60%<DCavg<99%) is required to obtain at least a performance level PL=d according to the definition of IS013849.

(70) Having a processor based control device also allows for conditioning monitoring of adjacent components like compensator/tensioner cylinder, piston accumulator and gas volume.

(71) Further, it is disclosed is a control device for controlling a valve arrangement and thus a flow between a hydraulic cylinder and a pressure accumulator. Advantageously, said control device is retrofitable to existing valve arrangements. In case of a failure on a cylinder side and/or on a accumulator side a main valve, especially formed as a flow shut off valve, is controllable by said control device to decrease or shut down said flow, based on detection of specific hydraulic data of said valve arrangement and/or said hydraulic cylinder and said pressure accumulator. Said main valve is to perform required functionsespecially safety functionsand is controlled by a redundant control system, especially said control device according to the present disclosure, involving monitoring of required physical quantities (for example velocity, displacement, pressure and/or temperature) required to realize such a required function. Especially by providing redundant sensors for detecting said specific hydraulic data and/or redundant valves for controlling said flow and/or redundant control devices for controlling said valves, a better reliability and/or safety is achieved, which is useful or even necessary for meeting requirements of, especially international, security standards like ISO 13849. Especially said control of said valve arrangement is done by means of a program, executable on said control device.

(72) Further, it is disclosed a safety arrangement, especially for a marine and/or an offshore application, comprising a control device for controlling a valve arrangement, and comprising said valve arrangement, which is arrangeable in a flow path between a hydraulic cylinder and a pressure accumulator. Said safety arrangement further comprises a main valve for controlling a flow in said flow path.

(73) Further it is disclosed a method for controlling a safety arrangement, arrangeable in a flow path between a hydraulic cylinder and a pressure accumulator, comprising a step of realizing at least one or several functions, especially safety functions, with said valve arrangement by means of a control device.

LIST OF REFERENCE SIGNS

(74) 1 control device 2 valve arrangement 3 safety arrangement 4 hydraulic cylinder 6 pressure accumulator 8 main valve 10 flow path (between hydraulic cylinder and pressure accumulator) 12 position sensor 14 accumulator pressure sensor 16 accumulator pressure sensor 18 cylinder pressure sensor 20 cylinder pressure sensor 22 velocity sensor 24 velocity sensor 26 displacement sensor 28 displacement sensor 30 first pilot valve 32 second pilot valve 34 switchover valve 36 first control device 38 second control device 40 second main valve 42 closed position sensor 44 monitoring step 46 signaling step 48 comparing step 50 controlling step 52 first controlling step 54 second controlling step 60 medium separator 62 piston accumulator 64 gas vessel 66 first solenoid operated control valve 68 second solenoid operated control valve 70 first pilot operated check valves 72 second pilot operated check valves 74 first check valve 76 second check valve 78 external reservoir 80 preloaded check valve 82 pump 84 level measuring device 86 first temperature sensor 88 second temperature sensor 90 first position measuring device 92 second position measuring device