METHOD FOR TESTING THE FUNCTIONALITY OF A SOLENOID VALVE FOR TRIGGERING A SAFETY VALVE

Abstract

The disclosure provides a method for testing a solenoid valve for triggering a safety valve having a single-acting fluidic drive and a positioner. The drive fluid pressure is increased by a first pressure difference. An attempt is made to switch the solenoid valve to the safety position. The drive fluid pressure is measured at a specified point in time that is selected such that the pressure in the drive fluid lowers at most by the first pressure difference. If the pressure in the drive fluid is higher than a reference pressure at the specified point in time, the functionality test of the solenoid valve is failed. The lowering of the pressure in the drive fluid is monitored over a defined period of time to make conclusions regarding the pressure generating system. The pressure does not fall below the operating pressure so the position of the valve member remains constant.

Claims

1. A method for testing the operability of a solenoid valve for triggering a safety valve having a valve member; wherein the safety valve has a single-acting fluidic drive for the valve member, which is driven by a drive fluid; wherein the safety valve has a positioner that determines the pressure in the drive fluid and controls the position of the valve member; wherein the valve member assumes a safety position when the pressure in the drive fluid corresponds to an ambient pressure; wherein the valve member assumes an operating position when the pressure in the drive fluid corresponds to an operating pressure; wherein the solenoid valve leaves the pressure in the drive fluid unaffected in an operating position; wherein the solenoid valve lowers the pressure in the drive fluid in a safety position; wherein the method comprises the following steps: if the valve member is not in the operating position, moving the valve member to the operating position; increasing the pressure in the drive fluid above the operating pressure by a first pressure difference; moving the solenoid valve to the safety position in response to a triggering event; measuring the pressure in the drive fluid continuously and/or at a predetermined point in time after the triggering event; choosing the predetermined point in time such that the pressure in the drive fluid drops at most by the first pressure difference; and either considering the test of the operability of the solenoid valve to be failed if the pressure in the drive fluid at the predetermined point in time is higher than an associated reference pressure; or considering the test of the operability of the solenoid valve to be passed and aborting the test of the operability of the solenoid valve as soon as the pressure during continuous measurement before or at the predetermined point in time is lower than the reference pressure.

2. The method according to claim 1, wherein the first pressure difference is the difference between a maximum possible pressure in the drive fluid and the operating pressure.

3. The method according to claim 2, further comprising: determining the first pressure difference after the drive was pressurized to the maximum possible pressure and this pressure was measured.

4. The method according to claim 1, further comprising forming a second pressure difference by multiplying the predetermined first pressure difference by a factor; wherein the factor being greater than zero and less than 1; and wherein that the at least one predetermined point in time is selected such that the pressure in the drive fluid decreases at most by the second pressure difference.

5. The Method according to claim 1, wherein the drive for the valve member is pneumatic.

6. The method according to claim 1, further comprising: using a first execution of the method on the solenoid valve of the safety valve as a reference measurement; measuring or setting the operating pressure and the first pressure difference in the drive of the safety valve and storing the operating pressure and the first pressure difference as reference values; determining and storing as a reference value the time required for the pressure in the drive to drop by the first pressure difference; and obtaining a maximum value for the at least one predetermined point in time.

7. The method according to claim 1, further comprising: considering the test of the operability of the solenoid valve as passed if the pressure in the drive fluid is lower than the reference pressure at the at least one predetermined point in time.

8. The method according to claim 4, wherein the reference pressure is higher than the operating pressure and is determined with the aid of the second pressure difference.

9. The method according to claim 1, further comprising: considering the test of the operability of the solenoid valve as passed when, in addition, an acoustic signal or a current curve of the solenoid valve proves the operability thereof.

10. The method according to claim 1, further comprising: running the method on the positioner.

11. The method according to claim 1, wherein pressure sensors for measuring the pressure in the drive fluid are provided in the positioner.

12. The method according to claim 1, comprising the following further steps: after testing the operability of the solenoid valve, moving solenoid valve to the operating position in response to a triggering event; and wherein the positioner again controls the position of the valve member, and returning the pressure in the drive fluid to the operating pressure.

13. The method according to claim 1, comprising the following further step: performing a partial stroke test on the safety valve.

14. The method according to claim 1, wherein the method steps are formulated as program code, with which the method is executable on at least one computer.

15. A non-transitory computer-readable medium having stored thereon program instructions that upon execution by a processing unit, a microcontroller, DSP, FPGA or computer or on a plurality thereof in a network cause performance of a set of steps according to the method claim 1.

16. The non-transitory computer-readable medium according to claim 15, wherein the first pressure difference is the difference between a maximum possible pressure in t d and the operating pressure.

17. The non-transitory computer-readable medium according to claim 15, the set of steps further comprising determining the first pressure difference after the drive was pressurized to the maximum possible pressure and this pressure was measured.

18. The non-transitory computer-readable medium according to claim 15, the set of steps further comprising: forming a second pressure difference by multiplying the predetermined first pressure difference by a factor; wherein the factor being greater than zero and less than 1; and wherein that the at least one predetermined point in time is selected such that the pressure in the drive fluid decreases at most by the second pressure difference.

19. The non-transitory computer-readable medium according to claim 15, wherein the drive for the valve member is pneumatic.

20. The non-transitory computer-readable medium according to claim 15, the set of steps further comprising: using a first execution of the method on the solenoid valve of the safety valve as a reference measurement; measuring or setting the operating pressure and the first pressure difference in the drive of the safety valve and storing the operating pressure and the first pressure difference as reference values; determining and storing as a reference value the time required for the pressure in the drive to drop by the first pressure difference; and obtaining a maximum value for the at least one predetermined point in time.

Description

[0049] Embodiments are shown schematically in the figures. Identical reference numerals in the individual figures denote identical or functionally identical elements or elements that correspond to one another in terms of their functions. Specifically:

[0050] FIG. 1 shows a schematic representation of a safety valve with solenoid valve, for which a method according to the invention can be used;

[0051] FIG. 2 shows a curve schematically illustrating the pressure over time in the actuator of a safety valve when a variant of the method according to the invention is performed; and

[0052] FIG. 3 shows a curve schematically illustrating the pressure over time in the actuator of a safety valve when a simplified variant of the method according to the invention is performed.

[0053] FIG. 1 shows the schematic structure of a typical safety valve 100. This includes the actual valve 110 with the valve member, which is actuated by means of a pneumatic actuator 130. In an emergency, the pressure conditions in the actuator are controlled by the solenoid valve 140. The solenoid valve is energized during normal operation (the power supply is not shown). If the power supply to solenoid valve 140 is interrupted, it switches to its safety position and releases a connection from the actuator to the atmosphere, causing the pressure in the actuator to drop to ambient pressure and moving valve 110 to the safety position. This condition can be seen in the schematic diagram of FIG. 1: the left valve position is active, in which the control line 160 between the positioner 120 and actuator 130 is interrupted and instead a connection of the actuator to the atmosphere is switched, indicated by the arrow at the bottom left of the solenoid valve 140. If the solenoid valve 140 were in its operating position, the right half would be active, releasing the control line 160 between the positioner 120 and actuator 130.

[0054] The positioner 120 is mounted on the safety valve 100 and controls the stroke position of the valve member and the pressure 180 in the actuator. The positioner 120 is capable of briefly interrupting the power supply to the solenoid valve 140 in order to perform a test of the operability of the solenoid valve 140. A compressed air supply to the positioner 120 is shown by a supply air line 150. The actuator 130 is connected to the positioner 120 via the control connection line 160. Downstream of the solenoid valve 140, the pressure is further fed to the measuring port 180 of the positioner 120. The pressure in the supply air line 150 is determined by means of the pressure sensor 170.

[0055] Since the supply pressure fluctuates and the actuator pressure can also change as a result of changes in the process or due to friction, the first implementation of the method according to the invention on a specific safety valve is used as a reference for this safety valve. This means that a pressure difference and the associated time required to reduce this pressure difference are stored as reference values. Thus, the time for this defined pressure drop is determined. With each further execution, the occurring pressure differences are always compared with the stored reference values.

[0056] Each time the method according to the invention is performed, the starting or operating pressure p.sub.start is first measured via sensor 180. An exemplary pressure curve is shown schematically in FIG. 2. From the start time t.sub.start, the actuator 130 is completely pressurized by the positioner to the maximum supply pressure p.sub.1. Subsequently, the maximum pressure difference

dp=p.sub.1−P.sub.start

and the modified pressure difference f*dp is calculated. Here, f<1, e.g. f=0.8. After the actuator 130 has been fully ventilated, the power supply to the solenoid valve 140 is interrupted from time t.sub.1. Thereby the solenoid valve should switch from its operating position to the safety position. This interrupts the compressed air supply to the actuator 130 via the control line 160 and opens a connection to the atmosphere, so that the pressure in the actuator 130 should drop to ambient pressure.

[0057] At this point, two cases can occur:

[0058] Either the pressure difference dp or, preferably, f*dp is reached and the pressure in the actuator 130 has been decreased to an appropriate level

p.sub.r=p.sub.1−f*dp

(the specified reference pressure, shown by the dotted line). This means that the solenoid valve is working as required, so the test is considered passed.

[0059] Or a predetermined point in time is exceeded without the pressure level p.sub.r being reached. Then the test is considered failed.

[0060] After one of these cases occurs, the solenoid valve is energized again, causing it to switch to the operating position.

[0061] FIG. 2 shows the first case—test passed—for the variant of the process in which the pressure is continuously monitored. The required pressure level p.sub.r has already been reached at time t.sub.2. At this point, the test is aborted, i.e. it is not continued until the predetermined point in time. The abort pressure p.sub.2, which is reached at the end of this test procedure, is therefore (if passed) equal to the reference pressure p.sub.r. The predetermined point in time is determined from the stored reference values for the reduction of the pressure difference—if any are available—as indicated above.

[0062] The schematic pressure curve of a simplified variant of the method according to the invention can be seen in FIG. 3. Continuous pressure measurement is not used here. The pressure is measured only at the predetermined point in time t.sub.2 (dashed line in FIG. 3), at which the test ends. The pressure p.sub.2 at this time is—in the case that the test was passed—lower than the reference pressure p.sub.r, which was already undercut before. However, the specifications for the time t.sub.2 and the relevant pressure differences still ensure that the final pressure p.sub.2 is above the operating pressure p.sub.start.

[0063] The position of the valve member remains unchanged during this process, especially because p.sub.2 is above p.sub.start. This is ensured by the factor f. The time period during which the solenoid valve was switched to the fail-safe position is measured. The test is performed until the pressure in the actuator 130 has dropped by the required difference f*dp (then it is considered passed), or until a time limit defined by the predetermined point in time has been exceeded—then it is considered failed.

[0064] In this case, but also if the air flow rate should have changed by a specified amount, a warning signal can be output.

[0065] Further diagnostic information can be provided by acoustic signals (e.g. clacking or hissing) and/or a recorded current curve of the solenoid valve. In particular, the recorded current curve when the solenoid valve is switched to the safety position can provide information about the state of wear of the solenoid valve.

[0066] After the solenoid valve 140 is switched back to the operating position, the pressure in the actuator 130 increases again because the control line 160 is still connected to the compressed air supply 150. After the test of the operability of the solenoid valve has been completed, the positioner 120 regulates the pressure in the actuator back to the operating pressure p.sub.start in order to control the position of the valve member again in a normal manner. This is indicated in FIG. 2 for times after t.sub.3.

[0067] In a practical application, for example, the compressed air system can provide a supply pressure of 4 bar. The operating pressure in the actuator would then be 2 bar, for example. The pressure difference is then dp=2 bar. As already described, this pressure difference is multiplied by a factor smaller than 1 in order to particularly reliably prevent movement of the valve actuator during the test. For example, the factor f=0.8. Then f*dp=1.6 bar and thus 0.4 bar pressure reserve is available up to the range in which a movement of the valve actuator—e.g. in case of further pressure fluctuations or other disturbances—could begin.

[0068] The positioner can receive the command to initiate the solenoid valve operability test according to the invention by means of a communication protocol (e.g. HART signals, radio signals, Advanced Physical Layer/APL, Profibus, etc.) or by means of a binary signal or by local operation.

Glossary

Fluidic Drive of a Valve

[0069] A valve is referred to as fluidically actuated or driven if the actuator stem of the valve is moved by a diaphragm which is pressurized by a fluid, typically compressed air, and is thus positioned.

Partial Stroke Test (PST)

[0070] To ensure the safe operation of a valve, tests are performed regularly or cyclically to determine whether the valve member does in fact move. For these tests, it is undesirable that the valve moves completely to the safety position in order not to disturb the running operation. In a partial stroke test, the valve member is moved only as far as necessary to ensure that the valve member moves part of the distance without significantly affecting the process of the plant. This also includes testing whether the valve member still disengages from its position or breaks loose. After the partial stroke test, the valve member moves back to its initial position. This test can be used to check the basic movability of the valve member.

Reference Pressure

[0071] This is to be understood as a predetermined pressure below which the pressure must fall within a certain time when the method according to the invention is performed.

Safety Valve

[0072] Safety valves are control valves with an open/close mode of operation and safety-relevant application. Control valves consist of a—typically fluidic—actuator and a movable valve member and are used to regulate a fluid flow. The type of valves can be either rotary valves or globe valves. In the field of safety-related valves, single-acting pneumatic actuators are generally used. The actuators, which are preloaded on one side by spring forces, move independently to a safe position when the actuator is vented, i.e. when the compressed air escapes from the chamber of the actuator. This happens, for example, when a current/pressure (I/P) transducer or a solenoid valve is no longer energized.

[0073] In safety valves, the safety valve is often open during normal operation, and in the event of a fault (e.g. power failure), the safety valve closes independently. The compressed air always acts against the spring force. If the actuator is now vented, the valve begins to close as the spring forces are released. The safety position can also be de-energized open (actuator vented) and energized closed (actuator vented). In the safety position, therefore, only the ambient pressure is present in the actuator.

[0074] Safety valves are often configured to reach the operating position (e.g. fully open) at an operating pressure that is below the maximum possible pressure in the actuator. This is particularly useful because the maximum available pressure is often subject to greater fluctuations due to the characteristics of the pressure-generating equipment.

Solenoid Valve

[0075] A solenoid valve is a valve with an electromagnetic drive. Depending on their design, solenoid valves can switch very quickly.

Valve Member

[0076] The valve member is the element that closes the valve when it is pressed onto the valve seat.

REFERENCE SYMBOLS

[0077] 100 safety valve [0078] 110 actual valve; valve housing with valve member [0079] 120 positioner [0080] 130 drive [0081] 140 solenoid valve [0082] 150 compressed air supply [0083] 160 control line [0084] 170 pressure sensor for air supply line [0085] 180 pressure sensor for drive pressure [0086] p pressure [0087] p.sub.1 maximum pressure [0088] p.sub.2 pressure at end of test [0089] p.sub.start operating pressure [0090] p.sub.r reference pressure [0091] t time [0092] t.sub.1 point in time for switching solenoid valve [0093] t.sub.2 end of testing period [0094] t.sub.3 transition to regulation for operating pressure [0095] t.sub.start begin of test

Cited Literature

Cited Patent Literature

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