Defining termination criteria for a partial stroke test on a fluidically driven safety valve and determining the functionality of a fluidically driven safety valve.

Abstract

Method for defining a termination criterion for a partial stroke test on a fluidically actuated safety valve with one valve element and a spring return; 1.1 wherein the valve element is to be moved into a safety position by the spring return in the event of a complete drop in the pressure of the drive fluid; 1.2 wherein the safety valve has means for determining the pressure of the drive fluid; 1.2.1 wherein the pressure of the drive fluid acts against the spring; 1.3 wherein the safety valve has means for determining the position of the valve element; wherein the method comprises the following steps: 1.4 A first partial stroke test is carried out on the safety valve by varying the pressure in the drive fluid; 1.4.1 wherein the first partial stroke test is carried out at a time when the safety valve is functional; 1.5 At least the position of the valve element and the pressure of the drive fluid are recorded during the first partial stroke test; 1.6 From the recordings, a first relation is derived which relates the position of the valve element and / or the time and / or the pressure of the drive fluid and / or another parameter recorded during the first partial stroke test to each other; 1.7 This relation is defined and stored as the reference curve for this safety valve in its functional state; 1.8 at least one second relation is defined which has a predetermined distance to the reference curve; wherein 1.8.1 which has at least one second relation for different positions of the valve element showing different distances to the reference curve; and 1.8.2 the distances of the second relation to the reference curve are dynamically determined depending on current conditions at the valve and / or at the system at the time of the partial stroke test; 1.9 The following is defined as a termination criterion for a subsequent, repeated partial stroke test on the same valve: 1.9.1 The repeated partial stroke test is performed on the same valve; and 1.9.2 The same data is recorded; and 1.9.3 A third relation is derived from the data in the same way as for the reference curve, 1.9.4 The repeated partial stroke test is deemed to have failed if the third relation has a greater distance to the reference curve at at least one point than the second relation.

Description

Field of the invention

[0001] The invention relates to a method for defining termination criteria for a partial stroke test on a fluid-driven safety valve. These termination criteria determine whether such a test is assessed as passed or failed and therefore have a decisive influence on the maintenance situation of fluid-driven safety valves.

[0002] Furthermore, the invention relates to a method for determining the functionality of a fluidically driven safety valve.

[0003] If a valve element remains in one position for a long time, deposits, corrosion, and / or adhesions can significantly increase the static friction and thus the breakaway force required to move the valve element. The drive energy may then no longer be sufficient to move the valve element safely.

[0004] However, with safety valves, it must be ensured that the drive energy is sufficient under all circumstances to move the valve element into a safety position. To ensure that the valve element can be moved against the increased frictional forces even after a long period of inactivity, a partial stroke test is regularly performed. This test can be used to check the basic mobility of the valve element.

[0005] The typical course of a partial stroke test can be described by Fig. 1. This shows the relative stroke of the valve element and the pressure over time during a partial stroke test on a safety valve. The safety valve has a single-acting, pneumatic actuator with spring return. The safety position is closed when de-energized. The setpoint 210 shows the ideal, friction-free stroke curve when the valve closes during uniform venting. The pressure is reduced and the spring forces of the actuator are released, moving the valve element towards the closed position. The actual pressure curve 220 initially shows a significant drop in pressure before the stroke (actual stroke) 230 changes. This shows the valve element breaking away from its open position, in which it may have already been stuck, i.e. subject to static friction. The difference between the initial, maximum pressure and the pressure at the moment of breaking away is referred to as the breakaway pressure 240.The breakaway pressure is the pressure or force sufficient to overcome static friction and release the valve. The pressure in the drive fluid at the moment of breakaway remains as a reserve of 250 bar, provided it is greater than 0 bar. If not, the safety valve can no longer fulfill its function. The pressure is readjusted after breakaway, i.e. increased again, to avoid or reduce overshoot. After static friction has been overcome and the stroke movement has accelerated, the actuator is vented evenly (slow pressure reduction) until 90% of the stroke is reached. The actual stroke curve 230 is approximately linear in the sliding friction range and parallel to the desired stroke curve 210, shifted by the amount of sliding friction. Once 90% is reached, the pressure in the actuator is increased again so that the valve element opens fully again against the spring forces. The partial stroke test is complete.

[0006] By eliminating the time and plotting the pressure 220 over the stroke 230, the stroke-pressure curve of the Fig. 2. The closing pressure reserve 320 is the pressure reserve that remains after the safety valve has been closed. The closing pressure reserve 320, which is set with constant movement (sliding friction), can be calculated using Fig. 2. For this purpose, the stroke-pressure curve is calculated according to Fig. 2 further extrapolated to the closed position (stroke = 0). State of the art

[0007] An actuating device for an on-off valve with a pneumatic actuator, which includes a position controller containing a routine for carrying out a partial stroke test, is described in the document WO 2009 / 013205 A1.

[0008] The publication DE 10 2011 052 901 A1 also describes how the drive energy for carrying out a partial stroke test can be controlled in such a way that excessive overshoot is prevented after overcoming the static friction.

[0009] During a partial stroke test, a stroke-pressure curve is recorded. The stroke-pressure curve can be used, for example, to determine the pressure reserve of an actuator. Such a procedure is described in publication DE 10 2018 103 324 B3. The pressure reserve can provide information about whether the valve will close reliably in a safety event.

[0010] To determine the criteria for failing a partial stroke test, it is common practice to proceed as follows: A reference curve is recorded for a fully functional control valve. Based on experience, it is known which deviations in a stroke-time curve or stroke-pressure curve are just sufficient to ensure safe operation. These values ​​are permanently stored as cut-off limits and apply to the entire stroke-pressure curve and to all such valves.

[0011] If the position control of the control valve is proportional control (also known as P control), the control deviation (difference from the target position) and the pressure serve as termination criteria. When the pressure chamber is slowly vented during the partial stroke test, it is determined whether the driving force of the springs is sufficient to break free or move the valve element as intended. This requires a pressure sensor or the pressure based on the IP converter signal. If, for example, the control deviation is greater than 3-5% or the pressure in the valve drive is less than 2.5 bar, the test is considered faulty. This means that the end test position must be reachable at a pressure greater than 2.5 bar in order to pass the test. The end position must not deviate by more than 3-5% from the end position in the reference curve. These fixed termination criteria are the same for all test sections and for all times.

[0012] These fixed termination threshold criteria mean that, in the event of a termination, it is unclear how large the change is compared to the previously measured, functionally safe condition (during the last passed partial stroke test). Changes in physical behavior caused by disturbances such as downtime, medium pressure, and / or medium temperature, but which do not fundamentally impair the functionality of the safety valve, are also not taken into account.

[0013] A device for testing a safety valve is known from US 2004 / 0093173 A1. In particular, a partial stroke test is provided, in which the pressure in the valve actuator and the control signal to the valve control system are monitored. No specific termination criteria are provided for the partial stroke test.

[0014] The published patent application DE 10 2006 003 750 A1 describes a method for verifying the functional capability of a control device with a drive and valve. In addition to evaluating the valve movement using a position sensor, a second evaluation unit with another sensor is used to independently detect the movement of the actuator. This allows for certifiable verification of the partial stroke test. No specific termination criteria are provided for the partial stroke test.

[0015] Publication US 2009 / 0222124 A1 discloses a method for determining a segment-specific estimate of a parameter in a process control loop. Data corresponding to a signal from a process control loop is received, stored, and divided into segments. A statistical analysis is performed on one of the segments, resulting in a segment-specific estimate of the parameter. There is no further reference to the performance and evaluation of a partial stroke test on a valve.

[0016] Publication WO 2008 / 122600 A1 discloses a method for testing the functionality of an actuator whose pneumatic actuator can be vented by a solenoid valve. The solenoid valve is configured so that it is activated during operation and can be deactivated to vent the actuator. During a partial stroke test, the solenoid valve is briefly deactivated to test its functionality.

[0017] Publication US 2016 / 0274598 A1 discloses a method for testing a valve actuator connected to a process control device. The process control device regulates the pressure in the actuator in a ramp-like manner up to a threshold, while monitoring the position of the valve element. If the threshold is reached or movement of the valve element is detected, the pressure is regulated back to its initial value. This method can, in certain cases, replace a conventional partial stroke test. Termination criteria for such a partial stroke test are therefore not discussed.

[0018] Publication US 2002 / 0145515 A1 discloses a system for manually executing an emergency shutdown test and collecting data in a process control environment. No provision is made for considering the specific characteristics of the valve or its controller in question, particularly with regard to the termination criteria for this test.

[0019] The publication DE 600 20 559 T2 describes a device and method for monitoring wear in the support material of valves, i.e., the material of the valve seat. Sensors measure the ranges of the valve element's positions corresponding to the open and closed states. Counters record how often these ranges are adjusted, and the wear of the valve seat material is determined from the counter readings.

[0020] German Patent Application DE 42 18 320 A1 discloses a method and device for testing a fluid-driven valve. During a valve switching operation, the temporal profiles of a system-relevant and a valve-relevant measured variable, e.g., pressure and stroke, are measured. From this, a function-specific variable, e.g., the valve's stroke factor, is derived and stored. During a subsequent switching operation, this variable is determined again, and the deviation from the stored value is monitored. Task

[0021] The object of the invention is to provide a method that provides better termination criteria for a partial stroke test and to provide a method with which the functionality of a fluidically driven safety valve can be determined more reliably. Solution

[0022] This problem is solved by the subject matter of the independent claim. Advantageous developments of the subject matter of the independent claim are characterized in the subclaims. The wording of all claims is hereby incorporated by reference into this description.

[0023] The use of the singular shall not exclude the plural, and this shall also apply in the reverse sense unless otherwise disclosed.

[0024] Individual procedural steps are described in more detail below. The steps do not necessarily have to be performed in the order given, and the procedure described may also include additional steps not mentioned.

[0025] To solve this problem, a method is proposed for defining a termination criterion for a partial stroke test on a fluid-driven safety valve with a valve member and a spring return. Upon a complete drop in the pressure of the drive fluid, the valve member is to be moved into a safety position by the spring return, with the pressure of the drive fluid acting against the spring. The safety valve has means for determining the pressure of the drive fluid and means for determining the position of the valve member. The method comprises the following steps: a) A first partial stroke test is carried out on the safety valve by varying the pressure in the drive fluid, whereby this partial stroke test is carried out at a time when the safety valve is functional, e.g. when the safety valve is put into operation. b) At least the position of the valve member and the pressure in the drive fluid are recorded during the first partial stroke test. c) A first relationship is derived from the recordings, relating the position of the valve member and / or the time and / or the pressure of the drive fluid and / or another parameter recorded during the first partial stroke test. This can be, for example, a stroke-pressure curve. d) This relation is defined and saved as a reference curve for this safety valve in the functional state. e) At least one second relation is defined, which has a specified distance from the reference curve, wherein the at least one second relation has different distances from the reference curve for different positions of the valve element. The distances of the second relation to the reference curve are dynamically determined depending on the current conditions on the valve and / or on the system at the time the partial stroke test is performed. This at least one second relation can, for example, be a tolerance band around the stroke-pressure curve that is adapted to the specific situation of the valve under consideration. f) The termination criterion for a repeated partial stroke test to be carried out at a later date, e.g. during future regular testing of the same safety valve, is defined as follows: If the repeated partial stroke test is carried out on the same valve, the same data are recorded and a third relation is derived from the data in the same way as for the reference curve, the repeated partial stroke test is deemed to have failed if the third relation has a greater distance from the reference curve than the second relation at at least one point.

[0026] In this way, termination criteria for future partial stroke tests can be defined on the specific safety valve in question, which flexibly take the valve's properties into account. Whether the valve passes the partial stroke test or fails therefore depends more on changes in the valve's maintenance condition than on how much this specific valve differs from any ideal valve. Influences such as downtime, temperatures, and process pressure can be taken into account that have little or no connection to the basic functionality of the valve. For example, it is possible to permit greater deviations after a long valve downtime and, accordingly, to apply stricter criteria in cases where the valve was moved shortly before the partial stroke test.

[0027] Preferably • the position of the valve element as a function of time or • the pressure in the valve actuator as a function of time or • The position of the valve element as a function of the drive pressure is used as the first relation. The first relation to be used typically depends on the control or regulation of the valve position when performing the partial stroke test.

[0028] If the valve has a position control which is used in the partial stroke test and if this position control is a proportional control with a control deviation, an embodiment of the method is preferred in which the sum of the target curve for the position control of the valve element and the control deviation is used as the first relation.

[0029] If, however, the valve has a position control which is used in the partial stroke test and which is not a pure proportional control, an embodiment of the method is preferred in which the manipulated variable of the position control is used as a function of time as the first relation.

[0030] It is particularly useful if the different distances of the second relation to the reference curve apply to different regions of the valve element's movement during a partial stroke test. Typically, the curve is therefore divided into four regions: • the area of ​​breakaway, which is dominated by overcoming static friction; • the area dominated by sliding friction, in which the valve element moves without any further special features; • the range of movement reversal when the valve element has reached 10% of its closing travel, which is determined by hysteresis; • and the area of ​​return of the valve member to the fully open position, which is again dominated by sliding friction.

[0031] This subdivision is useful because in certain areas, larger deviations from the ideal course of a partial stroke test can occur without jeopardizing the functionality of the safety valve, while in other areas, such large deviations must necessarily lead to abort and failure. For example, it is entirely possible that a relatively large pressure drop is required during breakaway, causing the valve element to lag significantly behind the reference curve. This is not critical if the valve element approaches the reference curve more closely during further travel. Therefore, in a typical application, a larger deviation can be permitted in the breakaway range.

[0032] For certain valve types or system configurations, it can also be advantageous to define the different distances and ranges in such a way that stick-slip effects are taken into account. These typically occur immediately after the start of the movement and manifest themselves in a stroke curve over time that is similar to a step function. If the valve element sticks, its position does not change. After that, a sudden correction of the position occurs (slip). The height of these steps can be used as a criterion for designing the at least one second relationship. In the area in which these steps occur, the distance of the at least one second relationship from the reference curve will be made larger. In particular, it is conceivable that the tolerance range above the reference curve must be selected to be larger than the tolerance range below the reference curve under these conditions.

[0033] Preferably, the second relationship has different distances from the reference curve, both upward and downward. This is particularly advantageous when the reference curve is a stroke-pressure curve. In this case, larger deviations upward than downward from the reference curve are typically to be expected, since normal wear and tear requires a greater reduction in the drive pressure than for a valve in its ideal state.

[0034] It is also advantageous if the partial stroke test is also considered failed if the pressure in the drive fluid falls below a specified value. In principle, it is possible to specify limits for the breakaway pressure and / or the pressure at the reversal point of the partial stroke test movement and / or the pressure during the entire test.

[0035] To achieve this objective, a method for determining the functionality of a fluid-driven safety valve with a valve member and a spring return is further proposed. The valve member is to be moved into a safety position by the spring return when the pressure of the drive fluid drops completely; the pressure of the drive fluid acts against the spring. The safety valve has means for determining the pressure of the drive fluid and means for determining the position of the valve member. The method comprises the following steps: - A partial stroke test is carried out on the safety valve. - A procedure as described above was carried out at an earlier time on the same safety valve. - Based on the termination criteria defined for this valve using the procedure described above, a decision is made as to whether the valve has passed or failed the partial stroke test and can still be considered functional or not.

[0036] This method allows for the determination of whether a safety valve is still functional or not with greater accuracy than usual. In particular, the result is more closely aligned with the specific valve in question, and the criterion that was violated in the event of a failure may even allow conclusions to be drawn about the nature of the valve's impairment. This allows both the valve's maintenance cycles and the scope of maintenance measures to be optimized.

[0037] The problem is also solved by formulating the method steps as program code in a method as described above, with which the method can run on at least one computer.

[0038] Furthermore, the object is achieved by a computer program which contains executable instructions which, when executed on a computing unit, a microcontroller, DSP, FPGA or computer or on a plurality thereof in a network, carry out the method according to one of the preceding method claims.

[0039] Furthermore, the object is achieved by a computer program with program code means for carrying out the method according to the invention in one of its embodiments when the program is executed on a computing unit, a microcontroller, DSP, FPGA, or computer, or on a plurality thereof in a network. In particular, the program code means can be instructions stored on a computer-readable data carrier.

[0040] Furthermore, the object is achieved by a data carrier on which a data structure is stored which, after being loaded into a working and / or main memory of a computing unit, a microcontroller, DSPs, FPGAs or computers or a plurality thereof in a network, can execute the method according to the invention in one of its embodiments.

[0041] The object is also achieved by a computer program product with program code stored on a machine-readable medium for carrying out the method according to the invention in one of its embodiments when the program is executed on a computing unit, a microcontroller, DSP, FPGA, or computer, or on a plurality thereof in a network. A computer program product is understood to mean the program as a tradable product. It can, in principle, exist in any form, for example, on paper or a computer-readable data carrier, and can, in particular, be distributed via a data transmission network.

[0042] Finally, the object is achieved by a modulated data signal which contains instructions executable by a computing unit, a microcontroller, DSP, FPGA or computer or by a plurality thereof in a network for carrying out the method according to the invention in one of its embodiments.

[0043] A computer system for executing the method can be a single computer or microcontroller, DSP, or FPGA, as well as a network of microcontrollers, DSPs, FPGAs, or computers, for example, an in-house, closed network, or even computers connected via the Internet. Furthermore, the computer system can be implemented in a client-server configuration, with parts of the invention running on the server and others on a client.

[0044] Further details and features will become apparent from the following description of preferred embodiments in conjunction with the figures. The respective features can be implemented individually or in combination with one another. The possibilities for solving the problem are not limited to the embodiments. For example, range specifications always include all intermediate values ​​(not mentioned) and all conceivable sub-intervals.

[0045] Some embodiments are schematically illustrated 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. In detail: Fig. 1 a stroke-time and the corresponding pressure-time curve during a partial stroke test on a typical safety valve; Fig. 2 a corresponding stroke-pressure curve; Fig. 3 stroke-time curves for two possible courses in a partial stroke test, including the corresponding setpoint curve; Fig. 4 tolerance bands for the stroke-time curves from Fig. 3; Fig. 5 range-dependent tolerance bands for the stroke-time curves from Fig. 3; and Fig. 6 an example stroke-time curve from a partial stroke test on a control valve.

[0046] Fig. Figure 3 shows the stroke-time curves of typical partial stroke tests for control valves. The target curve (dashed line) slowly reduces the valve stroke from 100%, i.e., fully open, to 90%, before completely releasing the valve. The return to the open position can be faster. Test 1 (dotted line) and Test 2 (solid line) represent possible real curves for such a partial stroke test (i.e., actual curves). In Test 2, the breakaway torque is higher, so the actuator must apply a greater force, which causes the valve element to oscillate when the movement begins until the control system captures this movement again. Test 2 also shows a greater deviation from the target curve overall.

[0047] In order to solve the problem underlying the invention, the termination criteria for a partial stroke test must be adapted so that they are appropriate for the situation of, for example, Test 1 or Test 2. For this purpose, a reference curve is recorded when the valve is in new or technically proper condition, and the termination criteria for this valve are determined based on this reference curve. In the case of pure proportional control, as is generally common with position controllers for valves, the control deviation (difference between the setpoint and actual position of the valve element) can be considered. A tolerance (typically 2%) is then added to the maximum control deviation occurred during the reference measurement (of, for example, 1% or 4%), so that a permissible maximum control deviation (of, for example, 3% or 6%) is obtained as the termination criteria. These general conditions form tolerance bands around the setpoint curve in a stroke-time diagram.Such tolerance bands are exemplified in . Fig. 4. Based on Test 2 (as reference case), a wider tolerance band results than on the basis of Test 1, since in Test 2 a larger control deviation already occurs, which represents the still functional normal case for the valve.

[0048] It is of course possible to design these criteria differently for upward and downward deviations (not shown).

[0049] A similar approach can be taken with regard to the pressure in the safety valve's drive system. If the pressure falls below a specified value, a partial stroke test is aborted. For example, a minimum drive pressure of 1900 mbar could be reached in Test 1 and a minimum drive pressure of 1500 mbar in Test 2. Assuming that this corresponds to the fully functional state of the respective valve, a pressure cut-off limit of 1500 mbar could be defined for the valve in Test 1 and a pressure cut-off limit of 1100 mbar for the valve in Test 2, assuming a maximum permissible pressure deviation of 400 mbar compared to the normal state. The pressure condition is therefore significantly more stringent for the valve in Test 1 than for the valve in Test 2.

[0050] In order to obtain more situation-specific termination criteria for the partial stroke test, these criteria can also be configured based on the specific area. This allows statements to be made about the exact test procedure and, if applicable, about changes to the fittings, and a differentiated diagnosis can be performed. For example, different termination criteria apply in the breakaway area than in the steady-state area. A total of four or five areas can be defined: breakaway torque, sliding friction, hysteresis during direction reversal, sliding friction during reversal, and, if applicable, the stick-slip effect. This is Fig. 5. The target curve is again shown in dashed lines. For clarity, only the lower tolerance bands of the termination criteria are shown. The limits for the valve in Test 1 are shown as dotted lines (area of ​​sliding friction, forward and backward) and as finely dashed lines (area of ​​breakaway and hysteresis during reversal of motion). The limits for the valve in Test 2 are shown as coarsely dashed lines (area of ​​sliding friction, forward and backward) and solid lines (area of ​​breakaway and hysteresis during reversal of motion).

[0051] Breakaway is the point at which static friction is just overcome and the valve member begins to move. This is where the transition to sliding friction occurs. In a typical valve, the breakaway torque increases over time, for example due to deposits between the valve stem and the seal seat or due to increased friction in the valve trim. This can even lead to the partial stroke test being aborted if, for example, the control deviation tolerance is exceeded or the minimum pressure is not reached. If the test is aborted in this area, it can be concluded that there is a change in static friction due to permanent changes to the mechanics of the design (e.g. changes in packing friction and / or changes that only occur when the valve is moved for the first time after a long period of downtime). This could be, for example, oil resinification. Appropriate maintenance measures can be provided here.

[0052] Sliding friction is the constant friction during sliding processes that depends on the direction of movement. A constant frictional force always occurs, counteracting the relative movement of two contacting surfaces and independent of the speed of the relative movement. In a valve, packings (e.g., made of graphite or PTFE) used to protect against the ingress of dirt or against the acting pressure of liquid or vapor cause a relatively high sliding friction. This is due to the fact that the packings are compressed by screws or springs and thus have a large contact area. If a test is aborted in this range, changes in sliding friction or changes in the spring constant of the actuator springs can be inferred.

[0053] The hysteresis here refers either to the difference in the setpoint change (after a setpoint reversal) until a change in the valve position occurs, or to the pressure change that is required after a setpoint change until the valve moves. The main cause of this hysteresis is the mechanical (static) friction in the valve (particularly e.g. in ball valves) and / or the influence of flow forces (particularly e.g. in butterfly valves). If a test is aborted in the hysteresis range, it can be concluded that the static friction has changed permanently due to mechanical changes to the structure (e.g. changed packing friction). If the changed friction in the breakaway torque range and in the hysteresis range is considered, the torque that occurred, for example, due to a downtime can be determined.

[0054] Sliding friction during return stroke: After the hysteresis is overcome, the valve element transitions from static friction to sliding friction. When returning to the starting position, the valve usually moves faster to keep the partial stroke test as short as possible.

[0055] These areas are in Fig. 5, in particular the different design of the corresponding tolerance bands for the valves of Test 1 and Test 2.

[0056] If the static friction between two solid bodies is greater than the sliding friction, the stick-slip effect can occur. Due to the seals on the piston rod and piston, comparatively strong static and sliding friction occur in pneumatic or hydraulic cylinders. As soon as the piston starts moving, the air relaxes. The stick-slip effect is therefore particularly pronounced during slow movements that can only be achieved with the help of small differential pressures. The stick-slip effect also occurs in dynamically loaded seals where release from the seal seat is made more difficult due to high pressure loads, higher temperatures and longer downtimes. If the test is aborted due to the abort criterion of a control deviation of the position or if the pressure is aborted in this range, it can be concluded that there has been a change in the ratio of sliding to static friction.The area where stick-slip effects occur is not shown here - these typically occur shortly after the valve element begins to move.

[0057] In Fig. Figure 6 shows the typical stroke-time curve of a partial stroke test for a butterfly-type safety valve (solid line), again together with the corresponding setpoint curve (dashed line). It can be seen that, in principle, the same effects occur here as with a control valve, and therefore the inventive approach is also useful in this case.

[0058] It is also advantageous to dynamically adjust the termination criteria based on the current process conditions. For example, the current downtime, medium temperature, or even the process pressure can be factored into the termination criteria for a partial stroke test. For example, the criteria for breakaway after a longer downtime can be more generous, while they must be more stringent if the valve has only recently been moved, as a deviation in this case is more likely to be due to a valve defect, which would necessarily require appropriate maintenance. Glossary: ​​Fluidic actuator of a valve

[0059] A valve is called a fluid-driven valve if the valve's drive rod is moved by a diaphragm that is pressurized and positioned by a fluid, typically compressed air. Stroke-pressure curve

[0060] The stroke-pressure curve of a valve or a partial stroke test indicates the position of the valve element, in other words: the stroke, as a function of the pressure in the drive fluid of the fluid-driven valve. Partial Stroke Test: see Partial Stroke TestPST: see Partial Stroke TestRelation

[0061] A relation is understood here as a mathematical relationship that, unlike a function (or mapping), is not bijective. Of particular interest here are relations that are left-total. This means that in a relation between the sets A and B, for every element of A there exists at least one element of B—not necessarily exactly one, but quite possibly several. safety valve

[0062] Safety valves are control valves with an on / off function and safety-relevant applications. Control valves consist of a – typically fluidic – actuator and a movable valve element and are used to regulate a fluid flow. The valves can be either rotary valves or globe valves. In the area of ​​safety-relevant 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. the compressed air escapes from the actuator chamber. This occurs, for example, when a current-to-pressure (I / P) converter or a solenoid valve is no longer supplied with power.

[0063] 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 automatically. The compressed air always acts against the spring force. If the actuator is then vented, the valve begins to close as the spring forces are released. In the stroke-pressure curve, this configuration causes the valve to break free against the static friction when the pressure in the actuator is reduced.

[0064] The safety position can also be open when de-energized (actuator vented) and closed when energized (actuator ventilated). Stick-slip effects

[0065] The stick-slip effect (from the English "stick" and "slip" "slide"), also known as the stick-slip effect or (self-excited) frictional vibration, describes the jerky sliding of solid bodies moving against each other, i.e., the periodic alternation of sticking and sliding. Common examples include chalk on blackboards, creaking doors, squealing brakes, rattling windshield wipers, and a wet fingertip sputtering over a latex balloon or causing the rim of a drinking glass to vibrate. Partial Stroke Test (PST)

[0066] To ensure the safe operation of a valve, regular or cyclical tests are carried out to determine whether the actuator is actually moving. During these tests, it is not desirable for the valve to move completely into the safety position in order to avoid disrupting ongoing operations. In a partial stroke test, the actuator is only moved as far as necessary to ensure that the actuator travels part of the way without significantly affecting the system process. This also tests whether the actuator even moves away from its position or breaks free. After the partial stroke test, the actuator returns to its original position. This test can be used to check the basic mobility of the actuator. valve element

[0067] The valve member is the element that closes the valve when it is pressed onto the valve seat. Reference symbol 210 Target value of the stroke 220 Actual pressure value 230 Actual value of the stroke 240 breakaway pressure 250 breakaway pressure reserve 310 breakaway reserve 320 closing pressure reserve 330 two points to determine the interpolation line 340 interpolation line 350 Pressure value at stroke = 0 360 90% of stroke, end of PST cited literature

[0068] cited patent literature DE 10 2006 003 750 A1 DE 10 2011 052 901 A1 DE 10 2018 103 324 B3 DE 42 18 320 A1 DE 600 20 559 T2 US 2002 / 0145515 A1 US 2004 / 0093173 A1 US 2009 / 0222124 A1 US 2016 / 0274598 A1 WO 2008 / 122600 A1 WO 2009 / 013205 A1

Claims

[1] Method for defining a termination criterion for a partial stroke test on a fluid-driven safety valve with a valve element and a spring return; 1.1 wherein the valve member is to be moved into a safety position by the spring return in the event of a complete drop in the pressure of the drive fluid; 1.2 wherein the safety valve comprises means for determining the pressure of the drive fluid; 1.2.1 whereby the pressure of the drive fluid acts against the spring; 1.3 wherein the safety valve comprises means for determining the position of the valve member; the method comprising the following steps: 1.4 a first partial stroke test is carried out on the safety valve by varying the pressure in the drive fluid; 1.4.1 the first partial stroke test is carried out at a time when the safety valve is functional; 1.5 at least the position of the valve member and the pressure of the drive fluid are recorded during the first partial stroke test; 1.6 a first relation is derived from the recordings relating the position of the valve member and / or the time and / or the pressure of the drive fluid and / or another parameter recorded during the first partial stroke test; 1.7 this relation is defined and stored as a reference curve for this safety valve in the functional state; 1.8 at least one second relation is defined which has a predetermined distance from the reference curve; where 1.8.1 the at least one second relation has different distances from the reference curve for different positions of the valve member; and 1.8.2 the distances of the second relation to the reference curve are determined dynamically depending on the current conditions on the valve and / or on the system at the time the partial stroke test is carried out; 1.9 The following is specified as the termination criterion for a subsequent repeated partial stroke test on the same valve: 1.9.1 the repeated partial stroke test is carried out on the same valve; and 1.9.2 the same data are recorded; and 1.9.3 a third relation is derived from the data in the same way as for the reference curve, 1.9.4 the repeated partial stroke test shall be deemed to have failed if the third relation has a greater distance from the reference curve at at least one point than the second relation. [2] Method according to the preceding claim, characterized by , that 2.1 the position of the valve element as a function of time or 2.2 the pressure in the valve actuator as a function of time or 2.3 the position of the valve element as a function of the drive pressure is used as the first relation. [3] Method according to claim 1, 3.1 wherein the valve has a position control used in the partial stroke test, and 3.1.1 where this position control is a proportional control with a control deviation, characterized by , 3.2 that the sum of the target curve for the position control of the valve element and the control deviation is used as the first relation. [4] Method according to claim 1, 4.1 wherein the valve has a position control used in the partial stroke test, and 4.1.1 whereby this position control is not a pure proportional control, characterized by , 4.2 that the first relation used is the manipulated variable of the position control as a function of time. [5] Method according to one of the preceding claims, characterized by that the different distances of the at least one second relation to the reference curve apply to different areas of the movement course of the valve member in a partial stroke test. [6] Method according to the preceding claim, characterized by that the different distances and ranges are determined in such a way that stick-slip effects are taken into account. [7] Method according to one of claims 1 to 4, characterized by that the at least one second relation has different distances upwards and downwards from the reference curve. [8] Method according to one of the preceding claims, characterized by that the partial stroke test is also considered failed if the pressure in the drive fluid falls below a specified value. [9] Method for determining the functionality of a fluid-driven safety valve with a valve member and a spring return; 9.1 wherein the valve member is to be moved into a safety position by the spring return in the event of a complete drop in the pressure of the drive fluid; 9.2 wherein the safety valve comprises means for determining the pressure of the drive fluid; 9.2.1 wherein the pressure of the drive fluid acts against the spring; 9.3 wherein the safety valve comprises means for determining the position of the valve member; the method comprising the following steps: 9.4 a partial stroke test is carried out on the safety valve; 9.5 a method according to any one of the preceding claims was carried out at an earlier time on the same safety valve; 9.6 Based on the termination criteria defined for that valve by that method according to any one of the preceding claims, it is decided whether the valve has passed or failed the partial stroke test and can still be classified as functional or not. [10] Method according to one of the preceding claims, wherein the method steps are formulated as program code which can run on at least one computer. [11] Computer program, characterized by that it contains executable instructions which, when executed on a computing unit, a microcontroller, DSP, FPGA or computer or on a plurality thereof in a network, carry out a method according to one of the preceding method claims 1 to 10. [12] Computer program with program code means for carrying out a method according to one of the preceding method claims 1 to 10, when the computer program is executed on a computing unit, a microcontroller, DSP, FPGA or computer or on a plurality thereof in a network. [13] Data carrier on which a data structure is stored which, after being loaded into a working and / or main memory of a computing unit, a microcontroller, DSPs, FPGAs or computers or a plurality thereof in a network, executes a method according to one of the preceding method claims 1 to 10. [14] Computer program product with program code means stored on a machine-readable carrier to carry out all the steps according to one of the preceding method claims 1 to 10 when the program is executed on a computing unit, a microcontroller, DSP, FPGA or computer or on a plurality thereof in a network.

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