CA2129470A1

CA2129470A1 - Diagnostic system for control and shut-off valves

Info

Publication number: CA2129470A1
Application number: CA 2129470
Authority: CA
Inventors: Hans O. Engel
Original assignee: Honeywell Inc
Current assignee: Honeywell Inc
Priority date: 1993-08-05
Filing date: 1994-08-04
Publication date: 1995-02-06
Also published as: DE4326343A1; EP0637713A1

Abstract

DIAGNOSTIC SYSTEM FOR CONTROL AND SHUT-OFF VALVES

ABSTRACT
A diagnostic system for control and shut-off valves uses a processor of an intelligent position controller as a digital signal processor which is connected to sensors monitoring the operation of the valve and measuring working parameters of the valve so that any deviation of measured values from initial values taken and stored is compared and analyzed to predict impending error/failure conditions. Early preventive maintenance is indicated and alarm signals are outputted for objectionable valveoperation.

Description

-~ 2 ~ ~' v~

Dk~GNO~TI~SY~El~fEQ~Q~ ND SHUT-O~E V.~LYE~

13ACK~QIJ~11) OF 1~ TNVF~O~I-l~he present invention relates to control and shut-o~f valves, and more 5 particularly, to a diagnostic system for the testing and diagnosing of these valves to indicate early~n when failures occur or are about to occur.
Pe~nanently increasing competition within thc economy necessirates cost reduction and an improvement of efficiency. This request most easily can be fulfilled by a better rate of utilization of existing install&tions and by sn wgmentation of the 10 installation perforrnance~ Unpredictable shut-downs of the ins~llations or of parts of a~
installation caused by failing components as e.g., control v3Lves, measuring transducers.
flow meters, etc. reduce the production capacir, and the possible rate of utilization of an installation. A reduction of periods of disuse and an increased reliability of the installation necessitates the knowledge about the zctual condition of the installation and l; of its components. In the f~ line ~his concen~s the unavoidable pnenomena of wear of the installation components.
Strict requirements of the authorities (tec~ica} rnonitoring au~onties, trade supervising authorities etc.) with respect to the env.ronmental protection in order to keep the a~r and waters clear, request avoidance of any leakage of chemical or O petrochemic~l plants or to recogn!ze such le~age in an early state.
Within closed pressurized installations which may be encountered in the chemical or petrochemical industries, in convcntional and nuclear power plants, as well as in refineries and petrol~um processing plants, a judgment of the degree ot` wear is ex~emely difficult because a darnage de~errnination and accompanying maintenance2 5 me~qu~es nonnaliy are not possible withou,t a shut down of ~e installation and the I removal of the cornponents of the installation.
Essentisl eomponents in such installations are control and shut-off valves, i.e., ~; 1 valves which in com~ination ur~th a pnewnatic actuator and an electro-pneumatic positioner are used as xgulating un~ts. Commorl damages of control valves in th~ order i`~ 3 o of their appearance frequency are the following:
., . 1. Lealy glands resulting in environmental con~amin~tion, :~

. ~

JUL-29-19~4 09:28 hO~E`~WEI L G~NE~RL COUNSEL 512 ~51 ~3649 P.a0.1/02' 21'~9 I~

2. High or changeable friction forces resulting in hysteresi~., 3. ~ncreasing residual leaka~e of the valve sn the closed position, 4. Disturbar.ces or breakdown of the vasve positioner~

5. D~mages at the valve actuator (e.g., rupture of the diaphragm), 6. Erosion or wear of inner parts due to permaneM cavitation, 7. Corrosion damages due to ~se selection of non-appropriate material, 8. Erosion of the trsm consistsng of plug and seat in coMection with a disturbed characteristic, 9. Fatigue fracrare of inner parts, ~d 0 10. Wornguidebushings, rattl~g,insuf~icientreproducibiity.
From the periodical ''Olhydraulik und Pneumatik", 1981, pages 568-573 it is :.
already krlown to implement an ea~ly recognition at hydraulic components by measur.ng of sound conducted through solids in ~vhich sound spectru~ns are recorded at the non-usedi stnrus of the hydraulic component and during t'heir later operation, both spoctrums are compared to each other, and with a deviation by a certain level a conclusion is made ~ ~
with respect to an arising or already existin~, damage. ~he examinations are made with ~ ' respect to rotating pumps in which particular mechanical we~r and cavitation can be detected. Departing from this technique, the same or similar methods could also be applied to control as~d shut-offvalves 3nd the damages listed under points 3, 6, 7, and 9 2 0 above could be ~ndicated esrly.
rhUs, thcre is providcd by the psesent snvention, a system for mon~tonng controlshut-off valves to provide an early indication of impending problerns such tha~ effecth~
preventive maintenance can be perforrned.

2 5 SUMMAI~Y OF l'H~ ~VEN~
Therefo~o, these i~ provided by the presont inventios~, a system for monstoring control and shut-offvalves to prov~de an e~rly sndication of impending problesns w~th the valves such that efl~cti~ pre endve mai~tenancc can be perfosmet. A diagnosdc system for control and shut-offvalves uses a psocessor of an intel~igent position 3 o controller as a digital signal processor which is connected to sensors monitoling the ope tbor of tlte ve ve e td meerudrg worhr 1: pe~meters ot tlte velve so ttrt etty JUL-29-1994 09:29 ~O~EYWELL GENERf~L CCUNSEL 612 951 ~649 P.005/023 `1 7 0 deviation of measured values from initial vahles talcen and stored is compared and analyzed to predict impending error/failure conditions. Early preventive maintenance is indicated and alann sign~ls are outputte i for objectionable valve operation.
Accordingly, it is an object of the present in ~ention to provide a syste2n for monitoring control and shut-off valves to indicate impendirlg fiailures of the valves such that effective preventi~e maintenance can be perfonned.
It is anothsr object of the present invention to implement a nearly complete monitoring and early indication of cases of loss at control and shut-off valYes so that a preventive maintenance is possible.
It is still another object of the present .nvention to provide a diagnostic sys~em for control and shut-off valves.
These and other objects of the present invention will become more apparent when taken in conjunction with the following description and attached drawings, wherein like characters indicate like parts, and which drawings forrn a part of the present application.

RRIEF DFS~RIPTION OF THE~ D~AwnyGs Ftgure 1 shows the basic arrangement of a conttol valve comprising a ~ alve bodya pneumatic actuator and a positioner;
2 ~ Figure 2 shows essential components of an intelligent positioner;
Figure 3 shows a portion of the control valve having a special gland and a pressure sensor for leakage sensing;
Figure 4 shows portions of a control valve having a special gland and with a mechanical exploradon of leakages;
2 5 Figurc 5 shows the typical basic ch~ractenstic of a control valve;
Figure 6 shows a degeneration of this basic characteris~c at a daTnage of the actuator;
Figure 7 shows an operational chaTacterisdc of the control valve;
Figure 8 shows a degeneration of this operational characteristic at heavy wear of 3 0 the throttling plug~

~ . , : .- - . : :

JL!L-29-1~194 39:29 HONEY~IELL 5ENER~L COlJNSEL 612 951 06~9 P.026i023 , 7la Figure 9 shows a typical reproducible sound spectrum under normal conditioas of the control valve; and Figure l O shows a third band of the integrated sound oscillations of an unused control valve and of an already darnaged control valve.
S
DETAIT ~DFSCI~Q~
According to Fi~ure 1, a regulating unit is shown which essentially comprises a valve body l O, a pneumatic diaphragm actuator ~2 and an " intelligent" position 14. The intelligent positioner 14 functions as a position controller having processin~ capabilitics o which is capable of taki:~g ic and processin~ certain values in order to take action or to control according displays.
The valve l O is mounted within a pipe 16 and by a change in the regulating distance ~stroke) of a closing body (not shown) acting together ~vith a val~,e seat (not shown), controls the ~hroughput of a medium. With a certain pressure or differential pressure, a certain flow quamity results as a function of the valve strol~e.
The pneum~t{c diaphragm actuator 12 i9 connected to a bonnet of the valve ] O
by means of spacer bolts 18 and nuts 20 are tightcned to a packing flange 22 (not shown is a packing follower and a valve stem 24 within the bonnet). A stem connector ~6 connects the valve stern 24 to a rod 28 of the pneumatic diaphragm actuator 12. A le~rer 2 o 30 is coMected to tho stem connector 26 which acts upon a position indicator 32 whieh is preferably a poten~iometer of the position controller 14. The inhereM ~sk of the position controller 14 is to convert an electric standard signal of e.g., 4 to 20 mA. into pncumatic pressure signal which is fed to the pneumatic aetuator 12 and which results in a corresponding position of the val~e stem 24. By means of the shown potentiometer 32 2 5 the measured value may be electrically cornpared to the electrical set value.
A processor (not shown) contained within the position control5er 1~ is implemented as B digital signsl processing unit and is coMected to different sensors.
Those sensors include a position sensor 32, a sensor 34 monitoring the tightness of the gland which is preferabl~ a pressure sensor, a sensor 36 mea~unng sound conducted 3 o through solids which is arranged at a yoke connected to the bonnet, and a flow sensor 38 which can be added to the regulating unit or could be arranged in the form of a Vortex JUL-29-1994 0~ 9 HOI`I~ ELL GE:`JERRL COW`ISEL 612 951 a64~ P. ~1~7~023 , ~, ~23 ~73 sensor 38' which may be integrated within a bore in a flan~e of the valve body 10. The feedback of the measured value which is provided by the position sensor 32 also could be replaced by a pressure sensor within the pnewnatic acn~tor 12. Further pressure sensors could be provided in order to measure the pressure of the medium or the differential pressure of the medium. The position controller 14 is provided with a standard interface in order to cornmunicate via a field bus with a central station cf a digital process central system (DCS) or to provide a cormection for a portable personal computer (not shown). Furtheron, a PID controller usually provided within the central station may be integrated within the position controller.
Figure 2 shows the circuit connections of th~ processor contained w~thin the position controller 14 as far as they are required for the irnplementation of the present ~ -invention. The different analog sensors 32-38 are cormected via a rnulriplexer 40 and alternatively via an arnplifier ~ to an analog/digital (A~'D~ conver~er 44. The output of ~'D converter 44 is fed to a digital signal processing (DSP) uni~ 46 wi~ich is connected to a read only memo~,v RVM 18 and to a random access memory RAM-SO. The DSP
unit 46 processes and analyzes ~he di~itized measured values according to a prograrn within the ROM and compares them w~h predetennined standard and level values. inorder to set a fault indication at a non-permissible devi~tion or to control ~aadigital/analog Go,nverter 52 an analog displa,v 54.
2 0 Figure 3 shows an embodiment for monitoring the tightness of the gland by means of a pr~ssure sensor 34. The valve shm 24 is centered within the bor~ne~ S6 by means of a guiding sleeve ~8 and is sealed with respect to the exterior by means of an adjuseable packing which consists of a plurality of packing rir.gs 60. In the ideal condition herewith a compe~e tightness with a minimurn of fricdon and hysteresis i9 reached. However in practice a penDanent'tightness cannot be achieved. Thereforefrom time to time a readjustment of the packing is necessary in which the nuts 20 of .he packing flange 2~ according to Figure I must be tighten~d. This results in a movement of the packing follower 62 into the bonnet and in compression of the partly elastical packagc rings which hereby are tightened against ~e valYe stem 24 and to the 'oor~
3 o within dle bonnet ~6 so that sealing is again achieved. In order to pre~ ent a periodical readju~trnent special packiTlg configurations have been developed so far which e,g., by S ', JU~-29-1394 09: 30 HONEYWELL GENER~L COUhlCEL 612 ~51 l36L19 P. 0OE; '023 ~ 12 ~J -~ 7 3 means of springs guarantees an automatic readjus~nent of the packing. An ~ctual monitonng of the tightness however does not take place.
Such an examination also car~ot be implementod by the maintenance personal in a sirnple manner. With liquids an exarnination of the tightness is relatively simple 5 because leakages easily can be indicated by wetted surfaces. Also, with stearn as a process fluid a leaking valve stem packing may be easily detected by the occurrence of steam or at least by collected condenser water. With gases, a monitoring becomes very difficult in the even~ where the gases do not have a stron~ odor. By the use OI a special packing follov-er which cornprises ~vo O-rings 64 and ~6 a ;nonitoring of the tightness -0 as shown - however is easily possible. The O-ring 64 is statically arranged between the packing follower 62 and the bonnet j6 and the O-ring 66 is dynarn~cally a~anged between the valve stem 24 and the package foilower 62. 1 hus. the fact that the static sealing by means of the O-ring 6~ is completely tight and the dynamic sealing by means of the O-ring 66 retains at least the larger portion of a leakage then wiihin the pac~ing 15 follower 62 a pressure arises which is sensed by the mirliature pressure sensor 34 and con~erted into sn elec~rical sign~l. Thl9 signal is eYaluatcd by the processor of Lhe position controller 14.
Figure 4 shows the modified design for monitoring the tiBhtness of a packing follow~r, Here, the special packing follower 68 contains a spAng 70, which is biased by 2 o a plate 72. The spring rnakes sure that in the absence of a leakage a leakage qu~
indicator 74 in ~e fonn of a piston permanently takes an extremely lower repo~ition. A
the occurTence of a packing leakage, the piston-shaped indicator 74 which consists of a corrosion resistant materisl with good gliding capabilitics as e.g., fro;n PTFE, slides to an upper position such tha~ it contacts an actuadrlg plate 76 of a microswitch 7~ and 2 5 initiates a sign~l. Tightening lips at the lo~er portion of the piston-shaped indicator are biased by an expanding ring 80 a~ainst the valve stem 24 as well as against the irmsr bore of the special packing follower 68 and providc for a ti~ht seal. The signal of the microswitch 78 agairl is fed to the processor within ~,hc position con~roller 1~.
For monitorin~ of a too large frietion (hysteresis) and for the operational test of 3 0 the pneumatic actuator according to Figure S before putting ill operation the complete control valve under conditions according to the practice the basic charactenstic . ,, ,~, ,;., ~ -- , : ,. . -. , . , ~ : . :

JUL-29-1394 ~19: 3~ HO~E`.'~J'_L GENERQL COW`ISEL ~12 ~51 ~6~1g P. 00~:3/132~
9 ~L~a includin~ the re~ersal span U and the hysteresis H is evaluRt~d by recording theregulating distance, i.e., the stroke of the actuator as a function of the input signal X.
This is possible in a sirnple marmer by means of the position indicator 32 according to Figuse 1. The recorded charactenstic is memori2ed within the memory connectcd to the rnicroprocessor. During the running operation of the control valve exceeding of the rnaximum hysteresis H or of the nosrnal re~ersal span U indicates an increa~ed friction of the control val~e which e.g., may be due to a too strongly tightcned packing ~ollower or to an increased inn~r friction of the valve. Also those deviations from the stan~ard values are signalled by the micropmcessor bec3use ignormg those occurrences causes the controllability of the regulating unit to suffer and also a seLzing in the guidance, and therefore a total failure of the regulating unit may appear.
Another frequently encountered case of loss is a rupture or lea~age of the diaphragm within the pneurnatic actuator. T'nis ;esults necessarily in a de~enera~ion of the onginally recorded and mernorized characteristic of the control vaive as shown in Figu~e 6 In such a case v~thin the intesior of the diaphragrn actuator the filll operatio~l pressure is not further built-up so that f.he regulating distance according to the counteraction of tshe biasing springs is shortened. By a periodical and "esmanent monitoring of the basic characteristic of the control valve such errors and cases of loss become detectable and diagnosable.
2 0 Clcarance on matiny, parts or a partial wcar of the tslsottling element, i.e., of the closing body of the valve imp~ir the controllability of ~he control valve and therefGre have to be prevemed in ally event. The throttling elernent normally provides a changeable cross sectiou within the interior of the valve. Comrnomy a concen~icai seat rin~ and a so-called plug as a closmg body are used with the plug shifling into the seat 2 5 ring and as a function of the regulating distance. Thus~ the cross section within the interior valve changes as a function of the stroke of the throttle element. A cosn~non operational ch~racteristic is shown in Figure 7, the cont~ol variable, i.e., in the present case the flow, i9 shown with ~espect to the input si~nal X.
Clearance on nnating parts and wear result in an discontinuous behavior of this 3 0 operational characte~istic. Hereu~th the gain of the control loop may excessively change which results in an unst~ble operation as this is shown in Figure 8. In the e~ent . , . . ... ~ . . .

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~ .

JUL-2!~1-1994 09: 31 HONEYWELL GENERQL OOUl`iCEL 612 ~51 05~5 P. 0~ 0~0Z3 , ~2 Q:1 7~ -where the operational characteristic as a fl nction of the controller input signal X has been recorded under norrnal process conditions according to Figure 7, putting the control valve in operation (where this characteristic is memorized wi~hin the memory cor~nected to the processor), then in the event where a flow meter is present it i.s possible 5 to deterrnine any deviation from this nonnal operational characteristic. Ho~vever, since changed operational conditions, as e.g., with a lower input pressure, the operational characterislic of the rate of flow is changed and an exact jud~ment of the condition requires taking into account filrther parameters as e.g., requires considering the input pressure or the differential pressures,....
1 O Also. ~he average or local gain of the control valve which is evaluated from Ihe steepness dX/dQ of the characteri3tic rnay be talcen into consideration in which dQ
represents the change of flow, e.g., in kg/h at a change of the input signal dX, e.g., in rnA or as a digilal Yalue. Since with ~n integr~ted solution, i.e., with the process controller within the housing of the position controller 14 the last indicated value is 15 identical wlth the controller output signal Y, the setting parameters of the PID co~troller which usually are not changed aher ~e basic adjustment and after its putting into opcration rnust be taken ioto corlsideration.
With respect to the perrnissible behavior of the basic characteristic according to Figure S and 6 as well as with respect to the behavior of the operational characteristic 2 0 according to Figure 7 and 8, a tolerance band is determine~ and limit values for the differential quotient WdQ (which stands for the steepness of the operational characteris~ic) arc evaluated. As soon as ~his tolerance band or the limit values of the steepness of the operstional characteristic are exceeded an alarm is outputted in the diagnostic status. Hints with respect to possible causes fallure/error result from the 2 5 direction and the amount of the deviations from ~e output cha~acteristics.
Figure 9 shows a typical and reproducible spectrum recorded by a sensor fo~
measuring sound conducted through solids in the normal operational ~ondition of the valve. Hereby the oscillatiors of the valvc evaluated by means of an acceleration sensor Qre recorded with respect to the frequency, in particular ~,hithin a ran~e firom 2 to 10 30 kHz.

JUL-29--lq94 139:.1 hONE`~l,JELL GENERflL CCUNS_L 61~ 951 13649 P.011/023 7`,1 In Figure 10, the third band of the oscillations are shown with respect to a newvalve in dotted lines and with respect to an already damage~l valYe in solid lines. By forrning the area integral and by the provision of a tolerable deviation, a darnaged valve also may be recognized ~vith this measuring technique, in particular wear may be5 detected which is due to corrosion, cavitation and erosion.
All diagnoses are either implemented periodical by means of a provided timer or perrllanently at particuiar critical controls A comparison to output characteristics is always made, and deviation by a certain amount causes an aiarm to be ~nitiated. This alarm can be signalled to the central station via a fie!d bus. AlternatiYely, ~he diagnosis 10 can be initiated manually from the central station at the operation within a process control system.
As a matter of course further processing and registration of the measured valuescan be performed by a ~ersonal computer having the corresponding so~vare directly at the place of the control valve. Herewi~h a graphical recording and display of al! mea-15 sured values and characteristics can also be achieved.
While there has been shown what is consid~red the preferred embodiment of thepresent invention~ it will be manifest that many changes and modifications can be made t~erein without departing from the essen~ial spirit and scope of the in~ention. lt is intended, therefore, in the annexed clauns, to cover all such changes and modifiçations 2 o which fail wit~in the t~e sc3pe of ~e invention.

Claims

I. A system for monitoring a control and shut-off valve, said valve including a gland, and said system including a position controller, said valve permitting a flow of a fluid through said valve, said system comprising:
a) a first sensor for detecting first information data which identifies working parameters and operational characteristics relating to said valve:
b) a second sensor for detecting second information data, said second information data being a spectrum of sound made by the flow of said fluid through said valve;
c) a third sensor for monitoring third information data, said third information data being a tightness of said gland of said valve; and d) a processor, operatively connected to each of said first second and third sensors, for receiving said first, second, and third information data to analyze said first, second, and third information data thereby providing an early indication of a potential valve problem permitting effective preventive maintenance.
2. A system for monitoring a control and shut-off valve according to Claim 17 further comprising:
a memory, operatively connected to said processor, for storing parameters and characteristics which have been taken by the sensors at an unobjectionable operation of said valve.
3. A system for monitoring a control and shut-off valve, said valve having a valve stem, according to Claim 17, wherein at least one of said plurality of sensors comprises:
a position sensor to determine the position of said valve stem.
4. A system for monitoring a control and shut-off valve, said valve including a and, according to Claim 17, wherein at least one of said plurality of sensors comprises:
a pressure sensor for determining the tightness of said gland
5. A system for monitoring a control and shut-off valve, said valve having fluid flowing through said valve, according to Claim 17, wherein at least one of said plurality of sensors comprises:
a flow meter for sensing the volume flow through said valve
6. A system for monitoring a control and shut-off valve, according to Claim 21wherein at least one of said sensors comprises:
a pressure sensor for sensing the input pressure of the fluid flowing through said valve.
7. A system for monitoring a control and shut-off valve, according to Claim 19, further comprising:
information coupled to said processor from the position sensor being stored in said memory, the information bring valve stem stroke with respect to an input value.
8. A system for monitoring a control and shut-off valve, according to Claim 22, further comprising:
information coupled to said processor from the flow meter being stored in said memory, the information being fluid flow with respect to an input value.
9. A system for monitoring a control and shut-off valve, according to Claim 24, further comprising:
information coupled to said processor from one of said sensors being the steepness of the characteristic for said value.
10. A system for monitoring a control and shut-off valve, said valve including avalve housing, according to Claim 17, wherein at least one of said plurality of sensors comprises:

a sound sensor, operatively connected to the valve housing, for evaluating cavitation within the valve to determine wear caused by said cavitation
11. A system for monitoring a control and shut-off valve, according to Claim 20, further comprising:
information stored in said memory, the information being limit values of pressure for said valve.
12. A system for monitoring a control and shut-off valve, according to Claim 20, said valve including a packing follower sealed against a bonnet of the valve and against a valve stem by O-rings, and wherein at least one of said plurality of sensors comprises a pressure sensor for sensing pressure in a chamber of said valve, the chamber being formed by the O-ring and the valve stem.
13. A system for monitoring a control and shut-off valve, according to Claim 20, further comprising:
a) a packing follower;
b) a piston;
c) a spring the packing follower receiving the piston which is displaceable against the force of the spring (70) and which is guided in a sealed manner with respect to the valve stem and the packing follower; and d) a switch, activated by the piston, when a packing leak is present.
14. A system for monitoring a control and shut-off valve, according to Claim 25, further comprising:
information stored in said memory which is a tolerance band with respect to the measured values and the characteristics taken at the operation of the valve, andwherein the processor makes a comparison with the stored measured values and characteristics signal an alarm in the event where the deviation exceeds the tolerance band.
15. A system for monitoring a control and shut-off valve, according to Claim 30, further comprising.
a standard interface at the position controller for the connection of a personalcomputer or for the connection to a field bus to a central station of a process control system for remote diagnostic.