IT202000017689A1 - SYSTEM FOR DIAGNOSTICS OF LEAKAGE LEAKS BETWEEN THE SEAT AND PLUG OF A VALVE - Google Patents

Description

SYSTEM FOR THE DIAGNOSTICS OF LEAKAGE DUE TO LEAKAGE

BETWEEN THE SEAT AND PLUG OF A VALVE

DESCRIPTION

Technical sector of the invention

The present invention relates to a system and the relative method for diagnosing leaks between the seat and obturator of a valve, linked to the inevitable leakage between the two components. In particular, the system and the method, according to the present invention, also allow the predictive analysis of the leakage of a valve.

Known technique

How?? known, the leakage ? a leak inside a valve that originates from the seat-plug interface. Ideally, when a valve ? when closed, there is a perfect seal, i.e. the flow rate of the process fluid between the seat and the valve obturator is equal to zero. In reality, a loss? always exists and the valves are classified according to the maximum acceptable leakage in the closed valve condition. This leak? divided into classes according to ANSI B16.104. The entity? of the leakage depends on multiple parameters such as, for example, the design of the valve, the materials that make up the seat/plug group, the quality? of the surfaces, the force with which the shutter ? pressed onto the seat, which force is typically provided by an actuator mounted on the valve. Furthermore, during the useful life of a valve, therefore also in the case of specific interest of a control valve, the leakage of the process fluid can increase over time. The increase in the leakage? due to multiple factors, for example, the progressive deterioration of the obturator and seat following phenomena of cavitation, wear, deformation, presence of particulate matter in the process fluid, etc.? The increase in the leakage pu? therefore lead to the loss of efficiency of the system and, consequently, economic losses, safety problems (e.g. in case of leakage of toxic and/or flammable fluids), as well as a greater degradation of the seat and of the obturator.

According to the prior art, maintenance interventions are carried out only following a malfunction of the system, for example when a marked loss of efficiency of the system is highlighted due to the leakage of a valve. In these cases, when the leakage becomes identifiable, is there already? in the event of significant losses that cannot be foreseen sufficiently in advance.

Furthermore, still according to the prior art, there is a widespread habit of generating the maximum force achievable by the actuator on the closed valve, or in any case a high and constant force value, in order to tighten the valve seat and obturator better. This procedure, if on the one hand at the beginning of the valve's operating life it avoids situations of incipient leakage, on the other hand it creates a contact pressure between the seat and the obturator which stresses more? due to the mechanical resistance of the components, causing the anticipated wear of the two components.

However, systems and related methods are not known to the state of the art which allow real-time diagnostics to be performed, as well as? predictive diagnostics of leakage due to valve leakage, i.e. that they are able to calculate in advance the trend of valve leakage due to valve leakage over time, so as to promptly intervene with appropriate maintenance. In this way, it would also be possible not to oversize the force delivered by the actuator and therefore put less stress on the valve seat and obturator.

There is therefore the need to define a system and the relative method for the real-time and predictive diagnostics of leakage due to leakage between the seat and the obturator of a valve which allows to obtain the above mentioned advantages.

Summary of the invention

Object of the present invention ? therefore a system applied to a valve for the execution of a diagnostic in real time as well as? valve leakage predictor, comprising an actuator, an actuator-mounted positioner, a valve-mounted sensor, and a controller. The valve, which can? be of any type, includes, how?? known, a shutter and a sealing seat and does not form part of the present invention, but represents its natural application.

The actuator determines the position of the valve plug with the force generated and, in closed valve conditions, the force exerted by the valve plug on its seat. The actuator, by way of example, can? be double-acting (balancing between two pressure chambers) as in the embodiment of the invention presented below. With the appropriate considerations on pressures and forces, this description can? also be extended to single-acting actuators (balancing between a force linked to the pressure in a chamber and a resistant force, for example an elastic force).

The positioner, how else? known, ? a component which, connected to the actuator via mechanical feedback of the position, ? able to vary the pressure in the actuator chambers in order to position the valve plug where required. In the case of a closed valve, i.e. in the event that the obturator is in contact with the seat, the positioner can? modulate the seat/plug contact force by varying the pressure in the chambers.

The sensor, what ? a normal feedback sensor according to the prior art, ? able to detect the? Entity? of the leakage directly or indirectly by means of a quantity which depends on the leakage of the valve seat itself. This size can vary according to the type of sensor used.

The controller, through the use of a software that implements a suitable control algorithm, correlates the data supplied by the sensor with those supplied by the positioner, i.e., respectively, the quantity measured on the valve (function of the seal of the valve seat) and the contact force seat/plug normally deduced from the pressure(s) in the actuator chambers. In other words, ? it is therefore possible to relate the degree of tightness or leakage of the valve seat to the force impressed by the actuator on the seat itself. Advantageously, the controller can? be integrated into the positioner itself.

Advantageously, the seat/shutter pair is not stressed unnecessarily, but the force ? limited by that generated by the positioner and sufficient to guarantee the seal, or rather an acceptable leakage limit threshold, therefore? the seat/shutter pair is subjected to less stress throughout its operating life, probably resulting in an extension of the operating life itself.

Advantageously, with the valve closed, since? the actuator generates a force lower than its capacity? maximum, ? It is possible to open the valve in reduced times, i.e. with shorter times than those necessary according to the prior art, since a lower dead time (time necessary for the separation between the obturator and the seat) is benefited.

Therefore, ? object of the present invention is a system applied to a valve for carrying out a diagnostic in real time as well as predictive of the leakage due to leakage of the valve itself, as specified in the attached independent system claim.

According to another object, the present invention also consists of a method for carrying out the predictive diagnostics of leakage due to leakage of a valve, as specified in the attached independent method claim.

The dependent claims outline particular and further advantageous aspects of the invention.

Brief description of the drawings

These and other advantages of the invention will now be described in detail, with reference to the accompanying Figures, which represent an exemplary embodiment of the invention, wherein:

- Figure 1 shows a diagram of the system object of the present invention; - Figure 2 ? a graph relating to the trend over time of the Fact force exerted by the actuator to guarantee the seal between the plug and the valve seat, during normal operation, compared to the reference force Fset necessary to guarantee optimal sealing of a valve and its range of tolerance;

- Figure 3 ? a graph like the one in figure 2 and also presents a future projection of the force values of the Fact actuator, even outside the tolerance range considered;

- Figure 4 shows a graph of the leak tests over time to obtain a correlation between the parameter measured by the sensor and the force of the actuator Fact.

Detailed description

With reference to the attached Figure 1, according to an absolutely non-limiting embodiment of the present invention, ? shown is a system 100 applied to a valve 1, of a known type and comprising a shutter and a sealing seat. The system 100 comprises an actuator 2, a positioner 3, at least one sensor 4 and a controller 5 provided with analysis software. Controller 5 can? be a component ?stand alone?, cos? how can be integrated into the positioner 3.

The actuator 2, by way of non-limiting example, is double effect. How?? known, there? does it mean that the control stem of the actuator, the part which imparts a force to the valve obturator, is? immersed between two chambers in which the relative pressures balance each other and a net force acts on the control rod which ? transmitted to the valve obturator. Naturally, with appropriate considerations on pressures and forces, the invention can be implemented also with single-acting actuators, presenting a single pressure chamber and where the balancing of forces takes place between a force linked to the pressure in the pressure chamber and a resistant force, for example an elastic force.

Positioner 3 ? a component that determines the ?behavior? of the actuator 2 as it regulates the pressure acting in the pressure chambers of the actuator 2 itself. The logical connection with the? actuator 2 ? achieved through mechanical feedback of the position of the actuator itself. Based on the feedback on the position of the actuator 2, the positioner 3 ? capable of varying the pressure in the chambers of actuator 2 in order to position the obturator of valve 1 where required. If valve 1 is? closed, therefore in the event that the obturator is in contact with the seat, the positioner 3 can? modulate the seat/plug contact force by varying the pressure in the actuator chambers 2.

Sensor 4? a normal feedback sensor capable of detecting the entity? of the leakage directly or indirectly by means of a quantity which depends on the leakage of the valve seat 1 itself. This size can vary according to the type of sensor used.

The sensors used can be, purely by way of non-limiting example, a temperature detector (for example, an infrared thermometer), a flow detector (for example, a flowmeter), an acoustic detector (for example, a microphone ultrasound) or a combination thereof.

The modulation of the seat/plug contact force by varying the pressure in the chambers of the actuator 2 ? realized through the controller 5 which implements a closed loop control (leakage->pressure->force->leakage), where the regulated quantity ? the leakage through the valve seat, taken directly or indirectly from the sensor 4 and the actuating variable ? the pressure acting in one or both of the pressure chambers of the actuator 2. In other words, the controller 5 (or directly the positioner 3, if it integrates the controller 5) ? capable of relating the seat/plug force of valve 1 and the degree of leakage of valve 1 over time.

The availability of such data allows therefore to obtain:

- an immediate datum that can be easily compared with the design values: the force value required for the seat/shutter contact (with this datum it is therefore possible to immediately check whether valve 1 is operating within the design limits);

- data emerging from historical analysis (relationship between force and leakage over time), i.e. the seat/plug seal degradation curve, which therefore allows predictive diagnostics by extrapolating the curve itself.

Furthermore, working in a closed loop (leakage->pressure->force->leakage), ? It is possible to adjust the positioner 3 to generate only the force necessary to obtain the desired seal between the seat and the obturator, plus? a desired margin.

Advantageously, therefore, according to the method described, the seat/shutter pair the seat/shutter pair ? subjected to less stress throughout its operating life. Such a result? obtained thanks to the fact that the applied force ? equal to that generated by the positioner (ie the only force required plus a freely configurable safety margin).

Advantageously, the fact that with the valve closed the actuator generates a force lower than its capacity? maximum, allows the valve to be opened in less time and with less downtime.

Various tests can be performed using this system. Those considered to be of greatest importance for the investigation of the seal on the valve seat are:

- the on-line test: for any valve ? note the reference force Fset (useful to ensure optimal sealing). During normal operation of valve 1, whenever it reaches the closed position, ? It is possible to record the Fact force exerted by the actuator 2 to ensure seat tightness. As shown in Fig. 2 , the data provided by the positioner 3 can be compiled into a graph. In particular, the controller 5 by means of the analysis software can? deduce from a historical analysis (comparing force and leakage over time) the degradation curve of the seat/plug seal allowing predictive diagnostics by extrapolating the curve itself.

In this way ? It is possible to obtain, as shown in Figure 3, a graphical projection of the future values of the Fact outside the tolerance range considered.

The sensor 4 can? moreover, it can be used for the definition of the tolerance range of the force Fset, as pu? be useful as a check and verification of the leak on the seat during the evaluation of the admissible limit forces UCL (upper control limit) and LCL (lower control limit), shown both in Figure 2 and in Figure 3. Evidently, the lower limit value LCL ? the value below which the valve does not hold, i.e. the leakage becomes sensitive; the UCL limit value ? the one above which the mechanical resistance of the components in contact (shutter and seat) is put at risk;

- the leak test: in some systems the valves must work closed most of the time. It is therefore difficult to carry out the tests during their useful life and to analyze the degree of tightness of the seat over time. In this regard, the system 100 object of the present invention can be used to carry out periodic leak tests.

During the normal functioning of the valve 1, through a command signal to the positioner 3, ? It is possible to vary the force of the actuator 2 Fact up to the appearance of a leakage of the valve seat 1, carrying out in this circumstance multiple measurements by means of the sensor 4. The recording of the data obtained from the sensor 4 and from the positioner 3 is carried out by the controller 5 using the analysis software. At the end of this phase, the initial value of the Fact force is restored in order to guarantee again the optimal seal on the seat (the leakage of the working fluid generated during the test is used exclusively for data collection and although it does not compromise the closing function of the valve itself, it can lead to the alteration of the state of the system: it is therefore necessary to carry out this test with due precautions, depending on the type of valve investigated).

As shown in Figure 4, the succession of seal tests over time leads to the achievement of a relationship between the parameter measured by sensor 1 and the Fact force of actuator 2, identifying a tolerance range of this parameter within which the seal of the valve seat 1 ? considered acceptable (therefore the tolerance range is obtained as a reference in addition to that associated with the Fact).

Advantageously, the integrated system 100 can be designed in configurations pi? complex capable of recording multiple quantities through the use of a plurality? of sensors. In this way, it is therefore possible to increase the diagnostic level of the integrated system and predict the trend of the seal of the valve seat with more? precision. When will one of the measured quantities tender? to go out of the respective tolerance range defined during the test, sar? it is therefore necessary to intervene with preventive maintenance actions.

These tests can be useful for different purposes, such as for example the control of a valve park through a statistical analysis of the data collected on a plant or on multiple plants. Additionally, remote monitoring of such data can be useful for generating a database regarding the useful life of the investigated valves.

Even if at least one exemplary realization ? been presented in the summary description and in the detailed description, it should be understood that there are a large number of variations which fall within the scope of the invention. Furthermore, it must be understood that the embodiment or embodiments presented are only examples which are not intended to limit in any way the scope of protection of the invention or its application or configurations. Rather, the summary description and the detailed one provide the expert technician of the sector with a convenient guide for implementing at least one exemplary embodiment, it being clear that numerous variants can be made in the function and in the assembly of the elements described herein, without departing from the scope of protection of the invention as established by the attached claims and their technical-legal equivalents.

Claims (10)

1. System (100) for performing a diagnostic in real time and/or predictive of leaks due to leakage of a valve (1), in which the valve (1) ? provided with a shutter and a sealing seat, the system (100) comprising an actuator (2), a positioner (3) for regulating the pressure acting in at least one pressure chamber of the actuator (2), at least one sensor (4) capable of detecting a variable depending on a leak due to leakage of the sealing seat of the valve (1) and a controller (5) provided with an analysis software, said system (100) being characterized in that the controller ( 5) ? configured to perform, via the analysis software, a closed-loop control, where the regulated quantity ? the leakage loss through the valve seat (1) and the actuating variable ? the pressure acting in said at least one pressure chamber of the actuator (2). The system (100) according to claim 1, wherein the controller (5) is integrated in the positioner (3). 3. System (100) according to claim 1 or 2, wherein the actuator (2) is a double acting actuator. 4. System (100) according to claim 1 or 2, wherein the actuator (2) is? a single acting actuator. System (100) according to one of the preceding claims, wherein the at least one sensor (4) is a temperature detector. System (100) according to one of claims 1 to 4, wherein the at least one sensor (4) is a flow detector. System (100) according to one of claims 1 to 4, wherein the at least one sensor (4) is an acoustic detector. System (100) according to one of claims 5 to 7, wherein the at least one sensor (4) is a combination of a temperature detector, a flow detector and an acoustic detector. 9. Actuation method of the system (100) according to one of the preceding claims, the method comprising the following steps: to. define the tolerance range of a reference force (Fset) predetermined and suitable for guaranteeing the optimal seal between the seat and the obturator of a valve (1) by means of a sensor (4), b1. record, with the valve (1) closed, by means of the sensor (4) a force (Fact) exerted by an actuator (2) to guarantee the tightness of the seat, c. record the data by means of a controller (5) and an analysis software implemented on the controller (5), d. obtain the force degradation curve (Fact) exerted by the actuator (2) allowing predictive diagnostics by extrapolating the curve itself. Method of implementing the system (100) according to one of claims 1 to 8, the method comprising the following steps: to. define the tolerance range of a reference force (Fset) predetermined and suitable for guaranteeing the optimal seal between the seat and the obturator of a valve (1) by means of a sensor (4), b2. vary the force (Fact) exerted by the actuator (2) until the occurrence of a leakage due to seepage of the valve seat (1) through a command signal to a positioner (3). c. record the data by means of a controller (5) and an analysis software implemented on the controller (5), d. obtain the force degradation curve (Fact) exerted by the actuator (2) allowing predictive diagnostics by extrapolating the curve itself.