ESTABLISHING TERMINATION CRITERIA FOR A PARTIAL-STROKE TEST OF A FLUID DRIVEN SAFETY VALVE, AND DETERMINING THE PROPER FUNCTIONING OF A FLUID DRIVEN SAFETY VALVE

20220390324

17/773453

October 30, 2020

A method is proposed for establishing termination criteria for a partial stroke test on a safety valve, including: a) A partial stroke test is carried out when the safety valve is operational. b) Position of the valve member and pressure in the drive fluid are recorded. c) A first relation is derived, which relates position of the valve member, time, pressure of the drive fluid, and/or control deviation to one another. d) This relation is defined as a safety valve reference curve. e) A second relation is defined, which has a predetermined distance from the reference curve. f) Termination criterion include: If the partial stroke test is repeated on the same valve, the same data are recorded and a third relation is derived for the reference curve, the partial stroke test is not passed if the third relation has a greater distance to the reference curve than the second relation.

1. A method for establishing termination criteria for a partial stroke test of a fluidically driven safety valve having a valve member and a spring return; wherein the valve member is configured to be moved into a safety position by the spring return in case of a complete loss of pressure of the drive fluid; wherein the safety valve has means for determining the pressure of the drive fluid; wherein the pressure of the drive fluid acts against the spring; wherein the safety valve has means for determining the position of the valve member; wherein the method comprises the following steps: performing a first partial stroke test of the safety valve by variation of the pressure in the drive fluid; wherein the first partial stroke test is performed at a point in time at which the safety valve is operable; recording at least the position of the valve member during the first partial stroke test; deriving a first relation from the recorded data, which puts at least two of the position of the valve member, the time, the pressure of the drive fluid, and a further parameter recorded during the first partial stroke test in relation to one another; defining and saving this relation as a reference curve for this safety valve while operable; defining at least one second relation having a predetermined distance from the reference curve; establishing the following as termination criterion for a repeated partial stroke test of the same valve to be performed at a later time: if the repeated partial stroke test is performed at the same valve; and if the same data is recorded thereby; and if a third relation is determined from said data in the same manner as the reference curve, then the repeated partial stroke test is considered failed if the third relation has a greater distance to the reference curve than the second relation at at least one point.

2. The method according to claim 1, wherein the stroke of the valve member as a function of time or the pressure in the drive of the valve as a function of time or the stroke of the valve member as a function of pressure in the drive is used as the first relation.

3. The method according to claim 1, wherein the valve has a position control which is used during the partial stroke test, and wherein the position control is a proportional control with a control deviation, wherein the sum of the target curve for the position control of the valve member and the control deviation is used as the first relation.

4. The method according to claim 1, wherein the valve has a position control which is used during the partial stroke test, and wherein the position control is not a purely proportional control, wherein the output variable of the position control as a function of time is used as the first relation.

5. The method according to claim 1, wherein the at least one second relation has a distance of 2% to the reference curve; wherein this distance applies upwards and downwards.

6. The method according to claim 1, wherein the at least one second relation has different distances to the reference curve for different positions of the valve member.

7. The method according to claim 6, wherein the different distances of the at least one second relation to the reference curve respectively apply to different ranges of the movement of the valve member during a partial stroke test.

8. The method according to claim 7, wherein the different distances and ranges are determined such that stick-slip effects are taken into account.

9. The method according to claim 1, wherein the at least one second relation has different respective upward and downward distances to the reference curve.

10. The method according to claim 1, wherein the distances of the second relation to the reference curve are dynamically determined depending on current conditions at one or more of the valve and the plant at the time at which the partial stroke test is performed.

11. The method according to claim 1, wherein the partial stroke test is additionally considered failed if the pressure in the drive fluid falls below a predetermined value.

12. A method for determining the operability of a fluidically driven safety valve having a valve member and a spring return; wherein the valve member is configured to be moved into a safety position by the spring return in case of a complete loss of pressure of the drive fluid; wherein the safety valve has means for determining the pressure of the drive fluid; wherein the pressure of the drive fluid acts against the spring; wherein the safety valve has means for determining the position of the valve member; wherein the method comprises the following steps: performing a partial stroke test at the safety valve; performing the method according to claim 1 on the same safety valve at a previous point in time; based on the termination criteria defined for this the safety valve by the method according to claim 1, deciding whether or not the safety valve has passed the partial stroke test and whether or not the safety valve is still to be considered operable.

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

14. 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 a plurality thereof in a network cause performance of a set of steps according to the method of claim 1.

15. The non-transitory computer-readable medium according to claim 14, wherein one of (i) the stroke of the valve member as a function of time, (ii) the pressure in the drive of the valve as a function of time, or (iii) the stroke of the valve member as a function of pressure in the drive is used as the first relation.

16. The non-transitory computer-readable medium according to claim 14, wherein the valve has a position control which is used during the partial stroke test, and wherein the position control is a proportional control with a control deviation, wherein the sum of the target curve for the position control of the valve member and the control deviation is used as the first relation.

17. The non-transitory computer-readable medium according to claim 14, wherein the valve has a position control which is used during the partial stroke test, and wherein the position control is not a purely proportional control, wherein the output variable of the position control as a function of time is used as the first relation.

18. The non-transitory computer-readable medium according to claim 14, wherein the at least one second relation has different distances to the reference curve for different positions of the valve member.

19. The non-transitory computer-readable medium according to claim 14, wherein the different distances of the at least one second relation to the reference curve respectively apply to different ranges of the movement of the valve member during a partial stroke test.

20. The non-transitory computer-readable medium according to claim 14, wherein the distances of the second relation to the reference curve are dynamically determined depending on current conditions at one or more of the valve and the plant at the time at which the partial stroke test is performed.

01; 15; 16; 16

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