Establishing abort criteria for partial stroke testing of fluid-actuated safety valves and determining the functional capability of fluid-actuated safety valves

Abstract

The invention relates to a method for establishing a termination criterion for a partial stroke test on a safety valve, comprising the following steps: a) performing a partial stroke test at the moment of activation of the safety valve; b) recording the position of the valve core and the pressure in the driving fluid; c) deriving a first relationship therefrom, which relates the valve core position and / or time and / or the pressure of the driving fluid and / or a mutual deviation; d) the relationship is defined as a reference curve for the safety valve; e) defining a second relationship, which has a predetermined gap relative to the reference curve; f) determining the following as a termination criterion: if the partial stroke test is repeated for the same valve and the same data are recorded, and a third relationship is derived from the data as with the reference curve, the partial stroke test is deemed to be unqualified when the third relationship has a larger gap relative to the reference curve than the second curve.

Description

Technical Field

[0001] The present invention relates to a method for establishing an abort criterion for a partial stroke test of a fluid-actuated safety valve. The abort criterion determines whether the test is evaluated as a pass or a fail and thus has a serious impact on the maintenance of the fluid-actuated safety valve.

[0002] The invention also relates to a method for determining the functional capacity of a fluid-actuated safety valve.

[0003] If the valve core remains in one position for a long time, the static friction and thus the starting force required for the valve core movement may increase significantly due to deposits, corrosion and / or adhesion. As a result, the drive energy may no longer be sufficient to reliably drive the valve core movement.

[0004] However, in safety valves, it must be ensured that the drive energy is sufficient to move the valve core to the safety position. In order to ensure that the valve core can also move against the increased friction after a long period of inactivity, a partial stroke test is performed regularly. This test can be used to check the basic movement capacity of the valve core.

[0005] The typical process of partial stroke testing can be combined with Figure 1 to understand. The relative stroke and pressure of the valve core are shown relative to the time during the partial stroke test on the safety valve. The safety valve has a one-way acting pneumatic drive with a spring return mechanism. The safety position is connected without current. The theoretical value 210 represents the ideal frictionless stroke curve when the valve is closed under uniform exhaust. The pressure is reduced and the spring force of the drive device is released and the valve core moves toward the closed position. The actual pressure curve 220 first shows that the pressure is significantly reduced, and then the stroke (actual stroke) 230 changes. This shows that the valve core starts to leave its open position, it stays in the open position, that is, encounters static friction. The difference between the maximum pressure at the beginning and the pressure at the time of starting is called the starting pressure 240. The starting pressure is the following pressure or force, which is sufficient to overcome static friction and loosen the valve. If it is higher than 0 bar, the pressure in the driving fluid at the time of starting is retained as a reserve 250. If not, the safety valve may no longer meet its function. The pressure is readjusted after starting, that is, it is increased again to avoid or reduce overshoot. After the static friction has been overcome and the stroke movement has been accelerated, the drive is evenly vented (slowly decompressed) until 90% of the stroke has been reached. The actual stroke curve 230 changes approximately linearly and parallel to the target stroke curve 210 in the sliding friction region, so that the sliding friction value is shifted in parallel. After reaching 90%, the pressure in the drive is increased again so that the valve core is fully opened again, overcoming the spring force. The partial stroke test is concluded.

[0006] By eliminating time and plotting pressure 220 versus travel 230, Figure 2The closing pressure reserve 320 is the pressure reserve left after the safety valve is closed. The closing pressure reserve 320 that occurs when the motion remains unchanged (sliding friction) can be calculated based on Figure 2 To do this, we will Figure 2 The stroke-pressure curve is further extrapolated to the closed position (stroke = 0). Background Art

[0007] The publication WO 2009 / 013205 A1 describes an adjusting mechanism for an on-off valve with a pneumatic drive, in which a position controller is provided which includes a routine for carrying out a partial stroke test.

[0008] The publication DE 10 2011 052 901 A1 also describes how the drive energy for carrying out a partial stroke test can be adjusted in order to prevent excessive overshoot after overcoming the static friction.

[0009] During the partial stroke test, the stroke-pressure curve is recorded. For example, the pressure reserve of the drive can be determined based on the stroke-pressure curve. This approach is described in the publication DE 10 2018 103 324 B3. The pressure reserve can be used to infer whether the valve is reliably closed in a safe situation.

[0010] In order to establish the criteria for a partial stroke test to be assessed as unacceptable, the following approach is usually proposed:

[0011] The reference curve is recorded for a fully functional control valve. It is known from experience which deviations of the travel-time curve or travel-pressure curve still ensure safe operation. These values ​​are permanently stored as abort limit values ​​and apply to the entire course of the travel-pressure curve and to all such valves.

[0012] If the position control or regulation of the regulating valve is a proportional regulation (also called P regulation), the regulation deviation (difference from the theoretical position) and the pressure are used as termination criteria. During the partial stroke test, it is determined when the pressure chamber is slowly exhausted whether the driving force of the spring is sufficient to start or move the valve core as expected. A pressure sensor or a pressure based on the IP converter signal is required for this purpose. For example, when the regulation deviation is greater than 3-5% or the pressure in the valve drive is less than 2.5 bar, the test is considered to be erroneous. That is, the final test position must be reached at a pressure exceeding 2.5 bar in order for the test to be qualified. Here, the deviation of the final position from the final position in the reference curve should not exceed 3-5%. The fixed termination criteria are the same for all test parts and all the time.

[0013] These fixed abort limit criteria mean that at the time of abort it is not clear how much the functional reliability state measured previously (during the last qualified partial stroke test) has changed. Changes in the physical properties caused by interfering parameters such as stopping time, medium pressure and / or medium temperature, which do not fundamentally prevent the safety valve from functioning, are also not taken into account. Summary of the invention

[0014] Task

[0015] The object of the present invention is to provide a method for providing an improved termination criterion for a partial stroke test and a method by means of which the functional capacity of a fluid-actuated safety valve can be determined more reliably.

[0016] Solution

[0017] The use of the singular shall not exclude the plural and vice versa, unless otherwise indicated.

[0018] Some method steps will be described in detail below. The steps do not necessarily have to be performed in the order described, and the method to be described may also have other steps not mentioned.

[0019] In order to accomplish this task, a method is proposed to establish a stop criterion for a partial stroke test on a fluid-actuated safety valve, which has a valve core and a spring return mechanism. The valve core should be moved to a safe position by the spring return mechanism when the driving fluid pressure is completely reduced, where the driving fluid pressure reacts against the spring. The safety valve has a mechanism for determining the driving fluid pressure and a mechanism for determining the valve core position. The method comprises the following steps:

[0020] a) A first partial stroke test is performed on the safety valve using a pressure change in the drive fluid, wherein the partial stroke test is performed at a time when the safety valve is now functional, for example when the safety valve is put into service.

[0021] b) At least the position of the valve spool and the pressure within the actuating fluid are recorded during the first partial stroke test.

[0022] c) deriving a first relationship from the record, which relates the valve core position and / or the time and / or the drive fluid pressure and / or another parameter recorded during the partial stroke test to one another, which can be a stroke-pressure curve, for example.

[0023] d) This relationship is defined and stored as a reference curve for the safety valve in a functional state.

[0024] e) defining at least one second relationship having a predetermined difference from the reference curve. The at least one second relationship may be, for example, a tolerance band centered on the stroke-pressure curve.

[0025] f) As a termination criterion for a repeated partial stroke test to be carried out at a later time, for example during a future periodic inspection of the same safety valve, it is to be determined that: if a repeated partial stroke test is carried out on the same valve and the same data are recorded this time and a third relationship is derived from these data in the same way as in the case of a reference curve, the repeated partial stroke test is deemed to be unacceptable if the third relationship has a greater deviation from the reference curve at at least one point than the second relationship.

[0026] In this way, abort criteria for future partial stroke tests on respective specific safety valves can be established which allow for flexible consideration of valve performance. Thus, whether a valve passes a partial stroke test depends primarily on changes in the valve maintenance state and has little to do with how much that particular valve differs from any ideal valve.

[0027] Preferably,

[0028] ·Valve cone travel based on time or

[0029] ·Time-dependent pressure in the valve drive or

[0030] ·Valve cone travel according to driving pressure

[0031] is used as the first relationship. The first relationship to be adopted generally depends on the control or regulation of the valve position when performing the partial stroke test.

[0032] If the valve has a position controller which is used for partial stroke measurement and if the position controller is a proportional controller with a control deviation, an embodiment of the method is preferred in which the first relationship is the sum of a setpoint curve for the valve cone position controller and the control deviation.

[0033] If, however, the valve has a position controller which is used in the partial stroke test and which is not a pure proportional controller, then an embodiment of the method is preferred in which the first relationship is a time-dependent manipulated variable of the position controller.

[0034] If the fixed difference of the second relationship from the reference curve is, for example, 2%, a very simple design of the stop criterion for the partial stroke test is obtained. For the sake of simplicity, this difference can apply not only to the upper side, but also to the lower side.

[0035] If the second relationship for different positions of the valve spool has a different deviation from the reference curve, the abort criterion is closer to the specific situation of the valve in question.

[0036] It is particularly suitable here that different deviations of the second relationship from the reference curve apply to different regions of the valve cone movement curve during the partial stroke test. Therefore, the curve is generally divided into four regions:

[0037] The starting area, beyond which static friction prevails;

[0038] The area where sliding friction is dominant, where the valve core has no other specific movement;

[0039] The reversal of movement, when the valve core has reached 10% of its closing travel determined by the hysteresis;

[0040] The valve core returns to the fully open position where sliding friction dominates.

[0041] This division is appropriate because in some areas, larger deviations from the ideal curve of the partial stroke test can occur without affecting the functional capacity of the safety valve, while in other areas such large deviations inevitably lead to suspension and failure. Thus, for example, a relatively large pressure drop can easily be required during startup, so that the valve core lags significantly behind the reference curve. This is not so important if the valve core approaches the reference curve significantly again during further movement. Therefore, in typical applications, larger deviations can be tolerated in the startup area.

[0042] In certain valve types or device configurations, it may also be advantageous to determine different gaps and regions in such a way that the stick-slip effect is taken into account. This generally occurs immediately after the start of the movement and is expressed in the travel curve over time, similar to a step function. While the valve core adheres (sticks), its position remains unchanged. Subsequently, it is followed by a sudden change in position (slip). The height of the step can be considered as a criterion for the design of at least one second relationship. In the region where the step occurs, the at least one second relationship will deviate more from the reference curve. In particular, it is conceivable that under the conditions described, the tolerance range above the reference curve must be selected to be larger than the tolerance range below the reference curve.

[0043] Preferably, the second relationship has different deviations from the reference curve for upper and lower, respectively. This is particularly advantageous when the reference curve is a travel-pressure curve. In this case, a larger deviation for upper than for lower relative to the reference curve is generally expected, since in common wear phenomena a greater reduction in the actuation pressure is required than in the case of an ideal valve.

[0044] In a very preferred development of the method, the deviation of the second relationship from the reference curve is determined dynamically at the time of carrying out the partial stroke test, depending on the current conditions on the valve and / or the system. Influences such as standstill time, temperature, process pressure which are irrelevant or almost irrelevant to the basic functional capacity of the valve can thus be taken into account. For example, it is possible to allow greater deviations after a long standstill of the valve and to adopt correspondingly stricter criteria if the valve has already moved shortly before the partial stroke test.

[0045] It is also advantageous that the partial stroke test is also considered to be unqualified when the pressure in the drive fluid is below a predetermined value. In principle, it is possible to set limit values ​​for the starting pressure and / or the pressure at the movement turning point of the partial stroke test and / or the pressure during the entire test.

[0046] In addition, in order to achieve this task, a method for determining the functional capacity of a fluid-driven safety valve is proposed, which has a valve core and a spring return mechanism. The valve core should be moved to a safe position by the spring return mechanism when the driving fluid pressure is completely reduced, wherein the driving fluid pressure acts on the spring. The safety valve has a mechanism for determining the driving fluid pressure and a mechanism for determining the valve core position. The method comprises the following steps:

[0047] -Perform a partial stroke test on the safety valve.

[0048] - Carrying out the method as described above at an earlier point in time on the same safety valve.

[0049] - Determining whether the valve has passed the partial stroke test and can also be classified as functional according to the abort criteria for the valve defined in the manner described above.

[0050] The method described makes it possible to determine more precisely whether a safety valve is still functional than is generally known. In particular, the result is better adapted to the particular valve in question and, in the case of a failure, it is possible to infer which standard was violated and perhaps even the type of valve that was adversely affected. Both the maintenance intervals of the valve and the scope of the maintenance measures can be optimized in this way.

[0051] The object is also achieved in that in the method described above, the method steps are expressed as program code, which can be executed on at least one computer by means of the program code. The object is also achieved by a computer program, which contains executable instructions that, when executed on a computing unit, a microcontroller, a DSP, an FPGA or a computer or a networked plurality thereof, perform the method described above.

[0052] In addition, the object is achieved by a computer program with a program code medium for executing the method according to one embodiment of the invention when the program is run on a computing unit, a microcontroller, a DSP, an FPGA or a computer or a plurality thereof that are networked together. In particular, the program code medium can be instructions stored on a computer-readable data carrier.

[0053] In addition, the task is accomplished by means of a data carrier on which a data structure is stored, which, after being uploaded to a memory and / or main memory of a computing unit, a microcontroller, a DSP, an FPGA or a computer or a plurality thereof networked together, is capable of executing the method according to the invention according to one of its designs.

[0054] The object is also achieved by a computer program product having a program code medium stored on a machine-readable carrier for carrying out the method according to the invention according to one of its embodiments when the program is run on a computing unit, a microcontroller, a DSP, an FPGA or a computer or a plurality thereof networked together. In this case, a computer program product is understood to be a program that is a commercially available product. It can in principle be present in any form, thus for example on paper or a computer-readable data carrier and can be distributed in particular via a data transmission network.

[0055] Finally, the task is accomplished by a modulated data signal containing instructions for performing the above method that can be executed by a computing unit, a microcontroller, a DSP, an FPGA or a computer or a plurality of them networked together.

[0056] As a computer system for executing the method, not only a single computer or microprocessor, DSP or FPGA is considered, but also a plurality of microcontrollers, DSP, FPGA or computers connected to a network, such as a home closed network, or computers connected via the Internet. In addition, the computer system can be implemented in a client-server configuration, wherein a part of the present invention runs at the server and another part runs at the client.

[0057] Further details and features are derived from the following description of preferred embodiments in conjunction with the accompanying drawings. In this case, the respective features can be implemented individually or in combination with one another. The possible ways of achieving the described tasks are not limited to the described embodiments. Therefore, range descriptions, for example, always include all unmentioned intermediate values ​​and all conceivable subranges. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Several embodiments are schematically shown in the figures. Here, the same reference numerals in these figures represent the same or functionally identical or corresponding components with respect to their functions, specifically:

[0059] Figure 1 shows the stroke-time curve and the corresponding pressure-time curve during a partial stroke test on a typical safety valve;

[0060] Figure 2 The corresponding stroke-pressure curve is shown;

[0061] Figure 3 The travel-time curves for two possible variations during a partial stroke test are shown, including the corresponding theoretical value curves;

[0062] Figure 4 Shown with Figure 3 Tolerance band associated with the travel-time curve;

[0063] Figure 5 Shown with Figure 3 Area-dependent tolerance bands associated with the travel-time curve;

[0064] Figure 6 An exemplary stroke-time curve of a partial stroke test in a regulating valve is shown. DETAILED DESCRIPTION

[0065] Figure 3 The curve course of the stroke-time curve of a typical partial stroke test of a control valve is shown. The theoretical curve (dashed line) slowly reduces the valve stroke from 100%, i.e. fully open, to 90%, in order to then fully open the valve again. The return to the open position can be carried out more quickly here. Test 1 (dotted line) and Test 2 (solid line) are possible real processes (i.e. actual curves) in such a partial stroke test. In the case of Test 2, the starting torque is large, so the drive must apply a large force, which causes the valve core to vibrate at the beginning of the movement until the control system starts the movement again. Test 2 also generally shows a large deviation from the theoretical curve.

[0066] In order to solve the problem on which the invention is based, the termination criteria for the partial stroke test must be adjusted so that they are adapted to the situation, for example, in test 1 or test 2, respectively. For this purpose, a reference curve is recorded in a new or technically compliant valve state and the termination criteria for the valve are determined based on this reference curve. In the case of pure proportional regulation, as with position regulators for valves, for example, the control deviation (difference between the theoretical position and the actual position of the valve core) can be considered. A tolerance (typically 2%) is then added to the maximum control deviation occurring in the reference measurement (for example 1% or 4%), so that a maximum permissible control deviation (for example 3% or 6%) is obtained as the termination criterion. This general condition forms a tolerance band in the stroke-time curve, which is centered on the theoretical value curve. Such a tolerance band is, for example, in Figure 4 Based on test 2 (as reference case), a wider tolerance band is obtained than based on test 1, because in test 2 already a larger adjustment deviation can be seen, which represents a situation where the valve still functions normally.

[0067] Obviously the criteria may be designed to be different for upward and downward deviations (not shown).

[0068] The pressure in the safety valve drive system can be processed accordingly. The partial stroke test is terminated when it falls below a predetermined pressure value. For example, a minimum drive pressure of 1900 mbar can be achieved in test 1 and a minimum drive pressure of 1500 mbar can be achieved in test 2. Assuming that this corresponds to a fully functional state of the respective valve, for example, when assuming a maximum permissible pressure deviation of 400 mbar relative to the normal state, a pressure termination limit of 1500 mbar can be defined for the valve of test 1 and a pressure termination limit of 1100 mbar can be defined for the valve of test 2. The pressure condition is therefore significantly more stringent for the valve of test 1 than for the valve of test 2.

[0069] In order to obtain better situation-dependent stop criteria for the partial stroke test, the criteria can also be designed to be region-dependent. This allows a description of the exact test process and possibly changes at the valve, and differential fault diagnosis can be carried out. Thus, for example, different stop criteria apply in the starting area than in the uniform movement area. Overall, 4 or 5 areas can be determined, namely starting torque, sliding friction, hysteresis when reversing direction, sliding friction when returning and possibly stick-slip effects. This is in the Figure 5 . There, the theoretical curve is again shown as a dashed line. For an overview of the illustration, only the lower tolerance band of the stop criterion is shown. The limits of the valve for test 1 are plotted as dotted lines (sliding friction area, front and back) and thin dashed lines (starting area and hysteresis in the reversal of movement), the limits of the valve for test 2 are plotted as thick dashed lines (sliding friction area, front and back) or solid lines (starting area and hysteresis in the reversal of movement).

[0070] The start-up is the point at which the static friction is overcome and the valve core begins to move. At this point, the transition to sliding friction takes place. In typical valves, deposits between the valve stem and the sealing seat or an increase in friction in the valve assembly cause the start-up torque to increase over time. This can even lead to the termination of the partial stroke test, for example, if the tolerance of the adjustment deviation is exceeded or the pressure falls below a minimum value. Therefore, when the stop occurs in this area, it can be inferred that the static friction has changed due to long-term changes in the structural machinery (for example, changes in the packing friction and / or changes that only occur during the first movement after a long rest period). This could be, for example, a hardening of the oil. Corresponding maintenance measures can be planned here.

[0071] The constant friction in the sliding process that is related to the direction of movement is called sliding friction. A constant friction force always occurs here, which resists the relative movement of the two contact surfaces and is independent of the speed of the relative movement. In valves, packings (such as graphite or PTFE) used to prevent dust ingress or to apply liquid or vapor pressure can lead to relatively high sliding friction. This is due to the fact that the packing is compressed by means of screws or springs and therefore has a large contact area. If the test is terminated in this area, a change in the sliding friction or a change in the spring constant of the drive spring can be inferred.

[0072] The hysteresis here refers to the difference in the change in the setpoint value (after a reversal of the setpoint value) until the valve position changes, or to the change in pressure required to stop the valve movement after the setpoint value changes. The causes of the hysteresis are primarily the effects of mechanical (static) friction in the valve (especially in the case of ball valves, for example) and / or flow forces (especially in the case of butterfly valves, for example). If a test stop occurs in the hysteresis region, it can be inferred that the static friction has changed over a long period of time due to mechanical changes in the structure (such as changing packing friction). If the changing friction in the breakaway torque region and the hysteresis region is now observed, it is possible to determine the torques that have occurred, for example, due to downtimes.

[0073] Sliding friction when returning: After overcoming the hysteresis, the valve plug switches from static friction to sliding friction again. When returning to the initial position, the movement is usually faster to keep the partial stroke test as short as possible.

[0074] These areas are Figure 5 In particular, the different designs of the corresponding tolerance bands for the valves of Test 1 and Test 2 are shown.

[0075] The stick-slip effect can occur when the static friction between two solid bodies is greater than the sliding friction. Due to the seals on the piston rod and the piston, relatively strong static and sliding friction occurs in pneumatic or hydraulic cylinders. As soon as the piston is set in motion, the air expands. The stick-slip effect is therefore particularly noticeable in slow movements that can only be driven with a small pressure difference. The stick-slip effect also occurs when the seal is subjected to dynamic loads, when it becomes difficult to disengage from the sealing seat due to high pressure loads, high temperatures and long standstill times. When the test is terminated beyond the position control deviation termination criterion or when the pressure is interrupted in this area, a change in the ratio of sliding friction to static friction can be inferred. The area in which the stick-slip effect occurs is not shown here, but it usually occurs immediately after the start of the valve core movement.

[0076] exist Figure 6The typical course of the stroke-time curve for a partial stroke test of a safety valve of the butterfly valve type is shown in FIG (solid line), still together with the corresponding theoretical value curve (dashed line). It can be seen that in principle the same effects occur here as in the case of a regulating valve, and therefore the approach of the invention also makes sense in this case. It is also appropriate that the dynamic adjustment of the stop criterion can be carried out as a function of the respective current process conditions. Thus, for example, the current stop time, the medium temperature or also the process pressure can be incorporated into the stop criterion for the partial stroke test. For example, the criteria may behave more leniently in the starting area after a longer stop, while they must be more stringent when the valve has only been moved a short time ago, because deviations in this case are more likely to be caused by valve defects, which inevitably lead to corresponding maintenance measures.

[0077] Glossary

[0078] Fluid actuation of valves

[0079] When the valve's actuating stem is moved by a diaphragm that is pressurized and positioned by a fluid, usually compressed air, it is called a fluid-actuated valve.

[0080] Stroke-pressure curve

[0081] A valve travel-pressure curve or partial stroke test indicates the valve plug position, in other words the travel, in relation to the pressure in the actuating fluid of a fluid-actuated valve.

[0082] Partial stroke test

[0083] PST: See Partial Stroke Test

[0084] relation

[0085] Here, a relation refers to a mathematical relationship that, unlike a function (or mapping), is not bijective. Here, we are interested in total-linked relations. That is, in a relation between sets A and B, for every element from A there is at least one element from B, but not necessarily exactly one, but completely possible multiple elements.

[0086] Safety valve

[0087] Control valves with an on / off operating mode and safety-related applications are referred to herein as safety valves. Control valves consist of a (usually fluidic) drive and a movable valve core and are used to regulate the flow of fluids. The valves can be rotary valves and poppet valves. In the field of safety-related valves, one-way-acting pneumatic drives are usually used. The drive, which is preloaded on one side by spring force, automatically moves to a safe position when the drive is exhausted, i.e. when compressed air escapes from the drive chamber. This occurs, for example, when a current-pressure (I / P) converter or a solenoid valve is no longer energized.

[0088] In the case of a safety valve, the safety valve is normally open in normal operation and automatically closes in the event of a fault (e.g. power failure). The compressed air always acts against the spring force. If the drive is now vented, the valve begins to close because the spring force is released. In the stroke-pressure curve, the configuration causes the valve to disengage by overcoming static friction when the pressure in the drive drops.

[0089] The safety position can also be open when de-energized (the drive device is depressurized) and closed when energized (the drive device is pressurized).

[0090] Stick-slip effect

[0091] The stick-slip effect, also known as the stick-slip effect or (self-excited) friction vibration, describes the stick-slip phenomenon of solid bodies moving relative to one another, i.e., the periodic alternation of sticking and sliding. Known examples are blackboard chalk on a writing board, squeaking doors, screeching brakes, squeaking windshield wipers and a wet fingertip moving unevenly over a latex balloon or vibrating the rim of a drinking glass.

[0092] Partial Stroke Test (PST)

[0093] In order to ensure safe operation of the valve, it is tested regularly or periodically whether the actuator also moves. In these tests, it is not desirable to move the valve completely to a safe position in order not to interfere with the ongoing work. In the partial stroke test, the actuator is only moved as far as is necessary to ensure that the actuator moves part of the stroke without significantly affecting the working process of the equipment. Here, it is also tested whether the actuator still disengages or breaks free from its position. After the partial stroke test, the actuator returns to its initial position. With this test, the basic mobility of the actuator can be checked.

[0094] Valve core

[0095] The valve plug is the element that closes the valve when pressed against the valve seat.

[0096] Reference numerals

[0097] 210 Theoretical stroke

[0098] 220 Actual pressure value

[0099] 230 Actual stroke value

[0100] 240 Starting pressure

[0101] 250 Starting pressure reserve

[0102] 310 Starting Reserve

[0103] 320 Close pressure reserve

[0104] 330 Two points used to determine the interpolation line

[0105] 340 interpolation straight line

[0106] 350 Pressure value when the stroke is 0

[0107] 360 90% of the trip, ends at PST

[0108] Citations

[0109] Patent Literature Cited

[0110] WO 2009 / 013205A1

[0111] DE 10 2011 052 901A1

[0112] DE 10 2018 103 324 B3

Claims

1. A method of establishing an abort criterion for a partial stroke test on a fluid actuated safety valve having a valve plug and a spring return mechanism; in, When the pressure of the driving fluid drops completely, the valve core will move to a safe position through the spring return mechanism; wherein the safety valve has a mechanism for determining the pressure of the driving fluid; wherein the pressure of the driving fluid reacts on a spring; Wherein, the safety valve has a mechanism for determining the position of the valve core; wherein the safety valve has a position regulator which is used in the partial stroke test, and The position controller is a proportional controller with a control deviation. Wherein, the method comprises the following steps: performing a first partial stroke test on the safety valve by means of the change in the pressure in the actuating fluid; wherein the first partial stroke test is performed at a time when the safety valve is capable of functioning; recording at least a position of the valve core during the first partial stroke test; deriving a first relationship from the record, the first relationship correlating the position of the valve spool and / or the time and / or the pressure of the actuating fluid and / or the parameter recorded during the first partial stroke test; Wherein, the sum of the theoretical curve of the position regulator of the valve core and the regulation deviation is adopted as the first relationship; The first relationship is defined and stored as a reference curve for the safety valve in a functional state; defining at least one second relationship, the second relationship having a predetermined gap relative to the reference curve; The following are determined as abort criteria for a repeated partial stroke test to be performed later on the same safety valve: performing said repeated partial stroke test on the same safety valve; The same data is recorded during the period; and A third relationship is derived from this data in the same manner as the reference curve, The repeated partial stroke test is deemed to have failed when the third relationship has a greater deviation from the reference curve than the second relationship at at least one point.

2. The method according to claim 1, characterized in that: The at least one second relationship has a difference of 2% relative to the reference curve, wherein the difference applies both upward and downward.

3. The method according to claim 1, characterized in that: The at least one second relationship has different deviations from the reference curve for different positions of the valve spool.

4. The method according to claim 3, characterized in that: The different deviations of the at least one second relationship from the reference curve respectively apply to different regions of the movement curve of the valve element during a partial stroke test.

5. The method according to claim 4, characterized in that: The different gaps and the different areas are determined taking into account a stick-slip effect.

6. The method according to claim 1, characterized in that: The at least one second relationship has different gaps with respect to the reference curve both upward and downward.

7. The method according to claim 1, characterized in that: The deviation of the second relationship from the reference curve is determined dynamically at the moment of execution of the partial stroke test depending on current conditions on the safety valve and / or the device.

8. The method according to claim 1, characterized in that: The partial stroke test is also deemed to have failed when the pressure within the drive fluid is below a predetermined value.

9. A method of determining the functional capacity of a fluid-actuated safety valve having a valve core and a spring return mechanism, in, When the pressure of the driving fluid drops completely, the valve core will move to a safe position through the spring return mechanism; wherein the safety valve has a mechanism for determining the pressure of the driving fluid; wherein the pressure of the driving fluid reacts on a spring; Wherein, the safety valve has a mechanism for determining the position of the valve core; Wherein, the method comprises the following steps: performing a partial stroke test on the safety valve; The method according to any one of claims 1 to 8 has been performed on the same safety valve at an earlier time; In conjunction with the abort criteria for the safety valve defined in the method according to any one of claims 1 to 8, it is determined whether the safety valve is qualified and also classified as functional.

10. The method according to claim 1 or 9, wherein: The method steps are expressed as program codes, and the method can be executed on at least one computer using the program codes.

11. A data carrier having a data structure stored thereon, which, after being uploaded to a memory and / or main memory of a computing unit, a microcontroller, a DSP, an FPGA or a plurality of them networked together, executes a method according to any one of claims 1 to 10.

12. A computer program product having a program code medium stored on a machine-readable carrier, for executing all the steps of the method according to any one of claims 1 to 10 when the program is run on a computing unit, a microcontroller, a DSP, an FPGA or a plurality of them networked together.

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