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(11) | EP 0 072 105 B1 |
| (12) | EUROPEAN PATENT SPECIFICATION |
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| (54) |
Assessment of life of duct Ermittlung der voraussichtlichen Lebensdauer einer Rohrleitung Estimation de la durée de vie d'une conduite |
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| Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). |
[0001] The present invention relates to the assessment of the overall lifetime until failure of a pipe carrying a fluid such as a gas at elevated pressures and temperatures.
[0002] Control and Instrumentation, Vol. 11, No. 11, December 1979, pages 27, 29 discloses a system for monitoring and displaying the status of up to 250 temperature sources on an ethylene compressor plant. The system incorporates means by which if any temperature source exceeds a predetermined level an alarm sounds.
[0003] Document DE-A-2 714 069 discloses a system for detecting and analysing hazards in a chemical plant, for example, a butadiene transfer process plant. The system includes a number of sensors for measuring pressure, temperatures and liquid levels in various parts of the plant which sensors input the various measurements as signals to a computer. The computer is preprogrammed to determine the hazard level represented by the various levels of the signals received and to take appropriate action to control the process if necessary.
[0004] It is an object of the present invention to determine the overall lifetime until failure of a pipe carrying fluid at elevated pressures and temperatures by sensing the pressure and temperature of the fluid at selected points in the pipe, causing signals representative of the pressure and temperature to be emitted and determining the values of the pressure and temperature represented by the signals.
[0005] According to one aspect of the present invention, there is provided a method for assessing the overall lifetime tr until failure of a pipe carrying fluid at elevated pressures and temperatures, the method comprising sensing the pressure and temperature of the fluid at selected points in the pipe, causing signals representative of the pressure and temperature to be emitted, determining the values of pressure and temperature represented by the signals, wherein the value of pressure is utilised to derive the value of hoop stress to which the pipe is subjected, the relevant value of the Larson Miller parameter (P) as herein defined is selected from a calibration curve of hoop stress against P for the pipe being tested and thence tr is determined from the equation:-
where C is a constant and T is the temperature value in °K.
[0006] According to another aspect of the present invention, there is provided an apparatus for assessing the overall lifetime tr until failure of a pipe carrying fluid at elevated pressures and temperatures, the apparatus comprising sensors for sensing the pressure and temperature of the fluid at selected points in the pipe and for emitting signals representative of the pressure and temperature of the fluid at the selected points, means responsive to the signals for determining the values of the pressure and temperature from the signals, wherein means are provided to store a calibration curve of hoop stress against the Larson Miller parameter (P) as herein defined for the pipe being tested and the signal responsive means is adapted to derive from the pressure value the value of hoop stress to which the pipe is subjected, to select from the store means the relevant value of P corresponding to the derived value of hoop stress and thence determine the value of tr from the equation:-
where C is a constant and T is the temperature value in °K.
[0007] Before the actual components of the apparatus are described in detail, it will it is believed be helpful to explain the steps required to calculate the time to failure tr of a pipe carrying fluid at elevated temperatures and pressures.
[0008] The time to failure tr of a material, usually by rupture, at a constant stress is given by the eauation-
where tr is the time to failure in hours measured from the instant when the material was first subjected to the stress, P and C are constants and T is the temperature in °K at which the material is being held while being subjected to the stress.
[0010] If for any given material, the stress required for rupture is plotted as a function of P, all the points are found to fall on a curve, the so called Larson Miller curve.
[0011] This relationship was first established by F. R. Larson and James Miller who revealed their findings for a number of steel alloys in July 1952, pages 765 to 775, in a paper published in the American Society of Mechanical Engineers. That paper contains a full explanation of the theories underlying the authors findings. The authors also empirically discovered that constant C is equal to 20 for certain materials.
[0012] The applicants have discovered that the Larson-Miller curve can be used to determine tr for a pipe carrying a fluid at elevated pressures and temperatures. To do this it is necessary first to establish a standard Larson-Miller curve for the particular material from which the pipe is constructed by plotting the stress to rupture obtained experimentally against the corresponding parameter P. Once this curve has been established, the stress to which the pipe is being subjected in service can be determined and the parameter P corresponding to this stress can be read off from the curve and tr can be calculated from equation (1) above by inserting the relevant values of T and C.
[0013] For a pipe the relevant stress is the hoop stress a, which can be determined from the equation:-
where p is the pressure of the fluid carried by the pipe in Nm-2, D is the external diameter of the pipe in metres and t is the wall thickness of the pipe in metres.
[0014] Thus the time to rupture tr can be calculated by measuring the pressure and temperature of the fluid- carried by the pipe in service, the time tr being the total time starting from the instant when the pipe first began to carry fluid.
[0015] While the pressure at any point in a fluid is constant, its temperature may vary so that in a length of pipe the temperature of the fluid may be very different at different points along the pipe length. Since the parameter P is directly dependent upon temperature, it will vary along the length of the pipe and thus the time tr will be different for different points in the pipe. It is therefore important for the temperature to be measured at as many points as possible along the pipe length to enable that point at which the rupture time is the shortest to be established.
[0016] Consequently the applicants measure temperature at a multiplicity of points along the pipe to provide an accurate overall indication of the rupture time tr.
[0017] Each calculated value oftrfor each temperature sensor point is then used to calculate the fraction of life tF(m) of the pipe used up between sequential signals samples of the same temperature sensor from the equation:-
where t1 is the time of the last or current signal sample, t2 is the time of the last but one sample, and tr1 is that value of tr derived from the current temperature signal.
[0018] tF(m) is integrated to provide an overall fraction ItF(m) of the life of the pipe which has been used up in the period during which the duct has been carrying fluid. In this case of course failure of the pipe is predicted when ItF(m) is equal to one.
[0019] As an alternative to calculating tF(m), a direct indication of the remaining useful life of the pipe can be obtained by subtracting the period during which the pipe has been carrying fluid from tri. The disadvantage with this method is that the value of tr1 will only be reliable if the fluid has been at a relatively constant pressure and temperature during the period it has been carried by the pipe. However if this method is used the point at which the highest currently derived value of tr has been calculated should be taken as the datum since this is the point at which the pipe will first rupture. To provide a margin for safety a factor is added to the value of pressure (or to the calculated stress) before tr1 is determined and the applicants have found that a factor of 10% of the measured pressure is an adequate margin.
[0020] An embodiment of the present invention will now be described with reference to the accompanying drawings in which:-
Figure 1 is a schematic block circuit diagram of the apparatus,
Figure 2 is a more detailed circuit diagram of a number of the components shown in the dotted box in Figure 1,
Figure 3a is a circuit diagram of the 2 to 4 line decoder shown schematically in Figure 2,
Figure 3b is a logic table for the decoder,
Figure 4 is a diagram of the signal selected shown in Figure 2 and,
Figure 5 is a flow sheet of the sequential operations performed by a microcomputer in assessing tr until failure.
[0021] Referring to the drawings, block 1 includes a multiplexer, amplifier and voltage to frequency converter which supply in sequence a series of amplified frequency signals analogous to voltage signals supplied to the multiplexer by a number of sensors. The frequency signals are received by and processed in the central processing unit of a microcomputer 2 together with data in the microcomputer store so as to provide inter alia information on the overall lifetime until failure tr of a duct carrying fluid at elevated temperatures and pressures. The data is supplied to the microcomputer 2 by way of a data teletype 3 and information is output to a printer 4.
[0022] Referring to Figure 2 the multiplexer comprises four analogues multiplexer chips 5 to 8 each of which is supplied with analogue voltage signals from eight sensors.
[0023] Chip 5 is connected to one pressure sensor P and to seven temperature sensors T1 to T7. Chips 6 to 8 however are each connected to eight temperature sensors T8 to T15, T16 to T23 and T24 to T31 respectively. Where the duct is a pipe or pipe-work, the pressure sensor may be located at any convenient position in the pipe and the temperature sensors at conveniently spaced intervals along the pipe so as to record the temperature at a multiplicity of points along the pipe.
[0024] The multiplexer also comprises a 2 to 4 line decoder 9 and a signal selector 10 which together form parallel input-output ports to select one of the 32 signal inputs to the multiplexer chips 5 to 8. The 2 to 4 line decoder 9 receives two input control signals which are decoded to give four "enable" signals to select one of the four multiplexer chips 5 to 8. The signal selector 10 receives three input control signals which are supplied in parallel as three input select signals to the each of the four chips so as to select one of the eight sensor signals in that chip selected by the decoder 9.
[0025] Referring to Figure 3a, the decoder 9 comprises two pairs of serially connected inverters 9', 10', 11,12 and four'NOR' gates 13 to 16 which each in turn produce a high output in dependence on the level of the two control input signals to the inverters as shown in the table in Figure 3b. As shown in Figure 4 the signal selector 10 comprises three parallel inverters 17 to 19 which respond to the eight combinations of input signals to produce eight combinations of inverted output signals.
[0026] Referring again to Figure 2, the decoder 9 enables each chip to be sampled or monitored for 4 seconds and the signal selector samples or monitors each sensor for 0.5 second so that 32 multiplexed inputs of 0.5 second duration are monitored giving a cycle time of 16 seconds.
[0027] The outputs of the multiplexer chips 5 to 8 are wired ORed to the input of a low drift instrumentation amplifier 20. The amplifier 20 is connected to the analogue input of a voltage to frequency converter 21. The output of the converter 21 is connected directly to the counter timer circuit channel of the microcomputer 2. This circuit inter alia counts the number of frequency pulses over a fixed time period and hence enable the values of sensed pressure or temperature to be measured.
[0028] The microcomputer 2 is a Zilog Z80 microcomputer which is programmed to calculate the time tr, the programme residing in 4K bytes of "read only" memory. The microcomputer 2 incorporates a teletype monitor 3 to provide teletype initialisation and a source code contained in several modules as described below.
Main module
[0029] This is the main control routine which calls the other routines. The data areas are initialised on reset (or power up) and the input parameters solicited from the teletype 3. The main programme loop is within this module, supervising the analysis of the data, the synchronisation of the calculations with the input of new readings and the output of results.
Module pressure
[0030] From the counter time count, the pressure of the fluid in the pipe is calculated and hence the pipe hoop stress o. The parameter P is calculated from pre-input values of P vs log10 σ by linear interpolation.
Module temperature
[0031] From the counter time count and the parameter P calculated by the Pressure Module, tr is calculated for each of the 31 temperature sensors. - The value of tr may be used either to calculate the fraction of life tF(m) which is integrated as previously described to provide an integral ΣtF(m) or the remaining useful life of the pipe may be directly calculated from tr. In this case tr may be calculated with the value of P or σ modified by the addition of a factor for safety.
Module results
Module interrupt
[0033] The central timer circuit is programmed to interrupt on two channels and both these interrupts are handled by routines in the main module.
(1) Timer interrupt
[0034] The timer is interrupted every 25 ms, the clock is incremented and the sensor being monitored at the particular time is read and updated every 0.5 second.
-(2) Counter interrupt
[0035] The counter is interrupted every 256 pulse counts and the total is incremented and the counter restarted.
Module PROM store
[0036] This module contains the permanent data which accurately defines the system and includes the Data Module. The Data Module contains values of log10 σ and the corresponding value of P which are input before the fluid is introduced into the pipe.
30) Start-switch on power
[0038]
31) Input M=1 where M is the temperature sensor to be sampled (normally a thermocouple).
32) Read L and N where L=number of thermocouples being sensed and N=number of data points to plot or describe the Larson-Miller curve.
33) Input tF(m) m=1, L=0 where tF(m) is the fraction of life used up between signal samples from the same temperature sensor.
34) DIMENSION σ(N); P(N).
35) (i) Input σD (I) data where σD is the stress data obtained experimentally to construct the Larson-Miller curve and I=1, 2, 3 ...N.
(ii) Input PD (I) data where PD is the Larson-Miller parameter corresponding to ao (I) and I=1, 2, 3... N.
[0040] The σD(I) and PD(I) values may be stored permanently if the system is to be dedicated to a particular component material.
37) Read σ and T (input from multiplexer) for M.
38) 1=2.
39) J=I.
40) Is stress σ<σD(I).
41) Does I=PD.
42) 1=1+1.
[0041] This equation enables the relevant value of P to be determined by linear interpolation.
44) tr=10(P/T-C).
45) Print/display rupture time tr.
where t1 is time of the present temperature measurement and t2 is the time of the
last but one temperature measurement.
47) Does Σtf(m)=1.
48) Does M=L.
49) M=M+1.
50) M=1.
51) Sound Alarm.
52) Stop.
[0042] While not shown, tr in equation 44) can be calculated from a P value derived from the pressure or stress value to which 10% of that value has been added to provide a margin for safety. The remaining useful life of the pipe can then be calculated by subtracting the period during which the pipe has been carrying the fluid from tr.
1. A method for assessing the overall lifetime tr until failure of a pipe carrying
fluid at elevated pressures and temperatures, the method comprising sensing the pressure
and temperature of the fluid at selected points in the pipe, causing signals representative
of the pressure and temperature to be emitted, determining the values of pressure
and temperature represented by the signals, wherein the value of pressure is utilised
to derive the value of hoop stress to which the pipe is subjected, the relevant value
of the Larson Miller parameter P is selected from a calibration curve of hoop stress
against P for the pipe being tested, and thence tr is determined from the equation:-
where C is a constant and T is the temperature value in °K.
where C is a constant and T is the temperature value in °K.
2. A method as claimed in Claim 1, characterised in that the temperature of the fluid
is sensed at a plurality of points in the pipe, a temperature signal is derived from
each point and a value of tr is derived for each signal.
3. A method as claimed in Claim 1 or Claim 2, characterised in that the signals are
continuously sampled sequentially and the value of tr is derived for each sampled
pressure and temperature signal.
4. A method as claimed in any of Claims 1 to 3, characterised in that each emitted
signal is an analogue signal and is converted to a digital signal to enable the value
of pressure or temperature to be determined.
5. A method as claimed in Claim 4, characterised in that the analogue signal is a
voltage which is converted to pulses of a frequency analogous to the voltage.
6. A method as claimed in Claim 5, characterised in that the pulses are counted during
the signal sampling period to provide values of the pressure or temperature.
7. A method as claimed in any of the preceding claims, characterised in that the fraction
of life tF(m) of the pipe used up between sequential signal samples of the same temperature
sensor is determined from the equation:-
where t1 is the time of the last or current signal sample, t2 is the time of the last but one sample, tr1 is that value of tr derived from the current temperature signal and tF(m) is integrated to provide an overall fraction ItF(m) of the life of the pipe which has been used up in the period during which the pipe has been carrying fluid.
where t1 is the time of the last or current signal sample, t2 is the time of the last but one sample, tr1 is that value of tr derived from the current temperature signal and tF(m) is integrated to provide an overall fraction ItF(m) of the life of the pipe which has been used up in the period during which the pipe has been carrying fluid.
8. A method as claimed in Claim 7, characterised in that failure of the pipe is indicated
when ItF(m)=1.
9. A method as claimed in any of Claims 1 to 6, characterised in that the period during
which the pipe has been carrying fluid is subtracted from the currently derived value
of tr so as to provide an indication of the period of the remaining useful life of
the pipe.
10. A method as claimed in Claim 9, characterised in that the highest currently derived
value of tr is taken as the datum.
11. A method as claimed in Claim 9 or Claim 10, characterised in that a factor is
added to the value of pressure before tr is determined to provide a margin for safety
in the currently derived value of tr.
12. A method as claimed in Claim 11, characterised in that the factor is 10% of the
value of pressure.
13. A method as claimed in any of the preceding claims, characterised in that the
value of tr is printed out and/or displayed.
14. Apparatus for assessing the overall lifetime tr until failure of a pipe carrying
fluid at elevated pressures and temperatures, the apparatus comprising sensors for
sensing the pressure and temperature of the fluid at selected points in the pipe and
for emitting signals representative of the pressure and temperature of the fluid at
the selected points, means responsive to the signals for determining the values of
the pressure and temperature from the signals, wherein means are provided to store
a calibration curve of hoop stress against the Larson Miller parameter P for the pipe
being tested and the signal responsive means is adapted to derive from the pressure
value the value of hoop stress to which the pipe is subjected, to select from the
store means the relevant value of P coresponding to the derived value of hoop stress
and thence determine the value of tr from the equation:-
where C is a constant and T is the temperature value in °K.
where C is a constant and T is the temperature value in °K.
15. Apparatus as claimed in Claim 14, characterised in that the sensors sense the
temperature of the fluid at a plurality of points in the pipe and emit a signal for
each point, the signal responsive means being adapted to derive a value of tr for
each signal.
16. Apparatus as claimed in Claim 14, characterised in that means are provided to
continuously sample the signals sequentially and the signal responsive means is adapted
to derive a value for tr for the sampled pressure and temperature signal.
17. Apparatus as claimed in Claim 16, characterised in that the sampling means is
a multiplexer (1).
18. Apparatus as claimed in any of Claims 14 to 17, characterised in that each sensor
is adapted to emit an analogue signal and means (21) are provided to convert the analogue
signal to a digital signal for processing by the signal responsive means.
19. Apparatus as claimed in Claim 18, characterised in that the analogue signal is
a voltage and the converter means (21) is adapted to convert the analogue voltage
to pulses of a frequency analogous to the voltage.
20. Apparatus as claimed in Claim 19, characterised in that the signal responsive
means includes a counter for counting the pulses during the signal sampling period
to provide values of the pressure or temperature.
21. Apparatus as claimed in any of Claims 14 to 20, characterised in that the signal
responsive means is adapted to determined the fraction of life tF(m) of the pipe used
up between sequential signal samples of the same temperature sensor (T) using the
equation:-
where t1 is the time of the last or current sample, t2 is the time of the last but one sample, tri is that value of tr derived from the current temperature signal, the signal responsive means being adapted to integrate tF(m) to determine the overall fraction ZtF(m) of the life of the pipe which has been used up in the period during which the pipe has been carrying fluid.
where t1 is the time of the last or current sample, t2 is the time of the last but one sample, tri is that value of tr derived from the current temperature signal, the signal responsive means being adapted to integrate tF(m) to determine the overall fraction ZtF(m) of the life of the pipe which has been used up in the period during which the pipe has been carrying fluid.
22. Apparatus as claimed in Claim 21, characterised in that the signal responsive
means is adapted to indicate failure of the pipe when ΣtF{m)=1.
23. Apparatus as claimed in any of Claims 14 to 22, characterised in that means (4)
responsive to the signal responsive means are provided to print out the value of tr.
24. Apparatus as claimed in any of claims 14 to 23, characterised in that means (3)
responsive to the signal responsive means are provided to display the value of tr.
25. Apparatus as claimed in any of claims 14 to 24, characterised in that the signal
responsive means and the store means comprise a computer 2.
1. Verfahren zum Ermitteln der Gesamtlebensdauer tr eines ein Strömungsmittel bei
erhöhten Drücken und Temperaturen führenden Rohres, bei dem Druck und Temperatur des
Strömungsmittels an auswählten Stellen im Rohr abgetastet werden, dem Druck und der
Temperatur entsprechende Signale ausgesandt werden und die von den Signalen dargestellten
Druck- und Temperaturwerte bestimmt werden, wobei der Druckwert dazu genutzt wird,
den Wert der Reifenbeanspruchung, der das Rohr ausgesetzt ist, abzuleiten, dann der
entsprechende Wert des Larson-Miller-Parameters P aus einer Eichkurve der Reifenbeanspruchung
gegen P für das zu prüfende Rohr ausgewählt und daraus tr bestimmt wird nach der Gleichung:
wobei C eine Konstante und T der Temperaturwert in °K ist.
wobei C eine Konstante und T der Temperaturwert in °K ist.
2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß die Temperatur des Strömungsmittels
an einer Vielzahl von Stellen im Rohr abgetastet wird, ein Temperatursignal von jeder
Stelle her abgeleitet wird und eine Wert für tr für jedes Signal abgeleitet wird.
3. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß die Signale kontinuierlich
nacheinander entnommen werden und der Wert von tr für jedes entnommene Druck- und
Temperatursignal abgeleitet wird.
4. Verfahren nach einem der Ansprüche 1 bis 3, dadurch gekennzeichnet, daß jedes ausgesandte
Signal ein Analogsignal ist und in ein Digitalsignal umgewandelt wird, um die Bestimmung
des Wertes für Druck und Temperatur zu ermöglichen.
5. Verfahren nach Anspruch 4, dadurch gekennzeichnet, daß das Analogsignal eine Spannung
ist, die im Impulse einer der Spannung analogen Frequenz ungewandelt wird.
6. Verfahren nach Anspruch 5, dadurch gekennzeichnet, daß die Impulse während der
Signalentnahmeperiode gezählt werden, um Werte für Druck und Temperatur zu erhalten.
7. Verfahren nach einem der Ansprüche 1 bis 6, dadurch gekennzeichnet, daß der zwischen
aufeinanderfolgenden Signalentnahmen des gleichen Temperatursensors aufgebrauchte
Anteil der Lebensdauer tF(m) des Rohres bestimmt wird nach der Gleichung:
wobei t1 der Zeitpunkt der letzten oder laufenden Signalentnahme ist, t1 der Zeitpunkt der vorletzten Entnahme ist, tr, derjenige Wert von tr ist, der aus dem gegenwärtigen Temperatursignal abgeleitet wird, und tF(m) integriert wird, um einen Gesamtanteil ΣtF{m) der Lebensdauer des Rohres zu erhalten, der während der Zeitdauer, in welcher das Rohr strömungsmittelführend war, aufgebraucht wurde.
wobei t1 der Zeitpunkt der letzten oder laufenden Signalentnahme ist, t1 der Zeitpunkt der vorletzten Entnahme ist, tr, derjenige Wert von tr ist, der aus dem gegenwärtigen Temperatursignal abgeleitet wird, und tF(m) integriert wird, um einen Gesamtanteil ΣtF{m) der Lebensdauer des Rohres zu erhalten, der während der Zeitdauer, in welcher das Rohr strömungsmittelführend war, aufgebraucht wurde.
8. Verfahren nach Anspruch 7, dadurch gekennzeichnet, daß ein Ausfall des Rohres ausgezeigt
wird, sobald ZtF(m)=1 ist.
9. Verfahren nach einem der Ansprüche 1 bis 6, dadurch gekennzeichnet, daß die Zeitdauer,
während welcher das Rohr strömungsmittelführend war, vom gegenwärtig abgeleiteten
Wert von tr subtrahiert wird, um eine Anzeige für die Zeitdauer der verbleibenden
nutzbaren Lebensdauer des Rohres zu erhalten.
10. Verfahren nach Anspruch 9, dadurch gekennzeichnet, daß der höchste gegenwärtig
abgeleitete Wert von tr als Bezugsgröße genommen wird.
11. Verfahren nach Anspruch 9 oder 10, dadurch gekennzeichnet, daß zum Druckwert vor
der Bestimmung von tr ein Faktor addiert wird, um eine Sicherheitsgrenze in dem gegenwärtig
abgeleiteten Wert für tr vorzusehen.
12. Verfahren nach Anspruch 11, dadurch gekennzeichnet, daß der Faktor 10% des Druckwertes
entspricht.
13. Verfahren nach einem der Ansprüche 1 bis 12, dadurch gekennzeichnet, daß der Wert
für tr ausgedruckt und/oder optisch angezeigt wird.
14. Einrichtung zum Ermitteln der Gesamtlebensdauer tr eines ein Strömungsmittel bei
erhöhten Drücken und Temperaturen führenden Rohres, mit Sensoren zum Abtasten von
Druck und Temperatur des Strömungsmittels an ausgewählten Stellen im Rohr und zum
Aussenden von Signalen, die dem Druck und der Temperatur des Strömungsmittels an den
ausgewählten Stellen entsprechen, sowie mit auf die Signale ansprechenden Mitteln
zum Bestimmen der Werte für Druck und Temperatur aus den Signalen, wobei Mittel zum
Speichern einer Eichkurve der Reifenbeanspruchung gegen den Larson-Miller-Parameter
P für das zu prüfende Rohr vorgesehen sind und die auf das Signal ansprechenden Mittel
aus dem Druckwert den Wert für die Reifenbeanspruchung, der das Rohr ausgesetzt ist,
ableiten, um aus den Speichermitteln den jeweiligen Wert für P, der dem abgeleiteten
Wert der Reifenbeanspruchung entspricht, auszuwählen und daraus den Wert für tr nach
der Gleichung
zu bestimmen, wobei C eine Konstante und T der Temperaturwert in °K ist.
zu bestimmen, wobei C eine Konstante und T der Temperaturwert in °K ist.
15. Einrichtung nach Anspruch 14, dadurch gekennzeichnet, daß die Sensoren die Temperatur
des Strömungsmittels an einer Vielzahl von Stellen im Rohr abtasten und für jede Stelle
ein Signal aussenden, wobei die auf das Signal ansprechenden Mittel einen Wert für
tr für jedes Signal ableiten.
16. Einrichtung nach Anspruch 14, dadurch gekennzeichnet, daß Mittel zum kontinuierlichen
Entnehmen der Signale nacheinander vorgesehen sind und daß die auf das Signal ansprechenden
Mittel einen Wert für tr für das entnommene Druck- und Temperatursignal ableiten.
17. Einrichtung nach Anspruch 16, dadurch gekennzeichnet, daß ein Multiplexer (1)
die Entnahmemittel bildet.
18. Einrichtung nach einem der Ansprüche 14 bis 17, dadurch gekennzeichnet, daß jeder
Sensor ein Analogsignal aussendet und daß Mittel zum Umwandeln des Analogsignals in
ein Digitalsignal zur Verarbeitung durch die auf das Signal ansprechenden Mittel vorgesehen
sind.
19. Einrichtung nach Anspruch 18, dadurch gekennzeichnet, daß das Analogsignal eine
Spannung ist und daß die Umwandlungsmittel
(21) das Analogsignal in Impulse einer der Spannung analogen Frequenz umwandeln.
20. Einrichtung nach Anspruch 19, dadurch gekennzeichnet, daß die auf das Signal ansprechenden
Mittel einen Zähler zum Zählen der Impulse während der Signalentnahmeperiode enthalten,
um Druck- und Temperaturwerte zu erhalten.
21. Einrichtung nach einem der Ansprüche 14 bis 20, dadurch gekennzeichnet, daß die
auf das Signal ansprechenden Mittel den Anteil der Lebensdauer tF(m) des Rohres, der
zwischen aufeinanderfolgenden Signalentnahmen des gleichen Temperatursensors (T) aufgebraucht
wird, bestimmen, und zwar unter Verwendung der Gleichung:
wobei t1 der Zeitpunkt der letzten oder laufenden Signalentnahme ist, t2 der Zeitpunkt der vorletzten Entnahme ist, und tr1 derjenige Wert von tr ist, der aus dem gegenwärtigen Temperatursignal abgeleitet wird, wobei die auf das Signal ansprechenden Mittel tF(m) integrieren, um den Gesamtanteil ZtF(m) der Lebensdauer des Rohres zu bestimmen, der während der Zeitdauer, in welcher das Rohr strömungsmittelführend war, aufgebraucht wurde.
wobei t1 der Zeitpunkt der letzten oder laufenden Signalentnahme ist, t2 der Zeitpunkt der vorletzten Entnahme ist, und tr1 derjenige Wert von tr ist, der aus dem gegenwärtigen Temperatursignal abgeleitet wird, wobei die auf das Signal ansprechenden Mittel tF(m) integrieren, um den Gesamtanteil ZtF(m) der Lebensdauer des Rohres zu bestimmen, der während der Zeitdauer, in welcher das Rohr strömungsmittelführend war, aufgebraucht wurde.
22. Einrichtung nach Anspruch 21, dadurch gekennzeichnet, daß die auf das Signal ansprechenden
Mittel einen Ausfall des Rohes anzeigen, sobald ΣtF(m)=1 ist.
23. Einrichtung nach einem der Ansprüche 14 bis 22, dadurch gekennzeichnet, daß eine
Vorrichtung (4) vorgesehen ist, die auf die auf das Signal ansprechenden Mittel anspricht,
um den Wert von tr auszudrucken.
24. Einrichtung nach einem der Ansprüche 14 bis 23, dadurch gekennzeichnet, daß eine
Vorrichtung (3) vorgesehen ist, die auf die auf das Signal ansprechenden Mittel anspricht,
um den Wert von tr optisch anzuzeigen.
25. Einrichtung nach einem der Ansprüche 14 bis 24, dadurch gekennzeichnet, daß die
auf das Signal ansprechenden Mittel und die Speichermittel einen Computer (2) aufweisen.
1. Procédé pour estimer la durée de vie globale tr avant défaillance d'une conduite
transportant un fluide à des pressions et températures élevées, le procédé consistant
à détecter la pression et la température du fluide en des points choisis de la conduite,
à provoquer l'émission de signaux représentatifs de la pression et de la température,
à déterminer les valeurs de pression et de température représentées par les signaux,
où la valeur de pression est utilisée pour calculer la valeur de la contrainte circonférentielle
à laquelle la conduite est soumise, la valeur associée du paramètre Larson-Miller
P est choisie à partir d'une courbe d'étalonnage de la contrainte circonférentielle
vis-à-vis de P pour la conduite testée et, de là, tr est déterminé d'après l'éauation:
où C est une constante et T est la valeur de température en °K.
où C est une constante et T est la valeur de température en °K.
2. Procédé selon la revendication 1, caractérisé en ce que la température du fluide
est détectée en plusieurs points de la conduite, un signal de température est établi
à partir de chaque point et une valeur de tr est établie pour chaque signal.
3. Procédé selon la revendication 1 ou la revendication 2, caractérisé en ce que les
signaux sont échantillonnés en continu séquentiellement et la valeur de tr est établie
pour chaque signal échantillonné de pression et de température.
4. Procédé selon l'une quelconque des revendications 1 à 3, caractérisé en ce que
chaque signal émis est un signal analogique et est converti en un signal numérique
afin de permettre la détermination de la valeur de pression ou de température.
5. Procédé selon la revendication 4, caractérisé en ce que le signal analogique est
une tension qui est convertie en impulsions d'une fréquence analogue à la tension.
6. Procédé selon la revendication 5, caractérisé en ce que les impulsions sont comptées
pendant la période d'échantillonnage du signal pour donner des valeurs de la pression
ou de la température.
7. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce
que la fraction de la durée de vie tF(m) de la conduite utilisée entre des échantillons
de signaux séquentiels du même capteur de température est déterminée d'après l'équation:
où t1 est le temps du dernier échantillon ou de l'échantillon de signal en cours, t2 est le temps de l'avant-dernier échantillon, tr1 est la valeur de tr établie d'après le signal de température en cours et tF(m) est intégré pour donner une fraction globale EtF(m)de la durée de vie de la conduite qui a été utilisée dans la période au cours de laquelle la conduite a transporté un fluide.
où t1 est le temps du dernier échantillon ou de l'échantillon de signal en cours, t2 est le temps de l'avant-dernier échantillon, tr1 est la valeur de tr établie d'après le signal de température en cours et tF(m) est intégré pour donner une fraction globale EtF(m)de la durée de vie de la conduite qui a été utilisée dans la période au cours de laquelle la conduite a transporté un fluide.
8. Procédé selon la revendication 7, caractérisé en ce qu'une défaillance de la conduite
est indiquée lorsque Σtf(m)=1.
9. Procédé selon l'une quelconque des revendications 1 à 6, caractérisé en ce que
la période pendant laquelle la conduite a transporté un fluide est soustraite de la
valeur en cours d'établissement de tr afin de donner une indication de la période
de la durée de vie utile restante de la conduite.
10. Procédé selon la revendication 9, caractérisé en ce que la valeur la plus élevée,
en cours d'établissement, de tr est prise comme référence.
11. Procédé selon la revendication 9 ou la revendication 10, caractérisé en ce qu'un
facteur est ajouté à la valeur de pression avant que tr soit déterminé pour apporter
une marge de sécurité à la valeur en cours d'établissement de tr.
12. Procédé selon la revendication 11, caractérisé en ce que le facteur est de 10%
de la valeur de pression.
13. Procédé selon l'une quelconque des revendications précédentes, caractérisé en
ce que la valeur de tr est imprimée et/ou affichée.
14. Appareil pour estimer la durée de vie globale tr avant défaillance d'une conduite
transportant un fluide à des pressions et températures élevées, l'appareil comprenant
des capteurs destinés à détecter la pression et la température du fluide en des points
choisis de la conduite et à émettre des signaux représentatifs de la pression et de
la température du fluide aux points choisis, des moyens qui, en réponse aux signaux,
déterminent les valeurs de pression et de température à partir des signaux, où des
moyens sont prévus pour mémoriser une course d'étalonnage de la contrainte circonférentielle
vis-à-vis du paramètre de Larson-Miller P pour la conduite testée et les moyens de
réponse aux signaux sont conçus pour établir, d'après la valeur de pression, la valeur
de la contrainte circonférentielle à laquelle la conduite est soumise afin de sélectionner,
à partir des moyens de mémorisation, la valeur associée de P correspondant à la valeur
établie de la contrainte circonférentielle et, de là, déterminer la valeur de tr d'après
l'équation:
où C est une constante et T est la valeur de température en °K.
où C est une constante et T est la valeur de température en °K.
15. Appareil selon la revendication 14, caractérisé en ce que les capteurs détectent
la température du fluide en plusieurs points de la conduite et émettent un signal
pour chaque point, les moyens de réponse au signal étant conçus pour établir une valeur
de tr pour chaque signal.
16. Appareil selon la revendication 14, caractérisé en ce que des moyens sont prévus
pour échantillonner en continu et séquentiellement les signaux et les moyens de réponse
aux signaux sont conçus pour établir une valeur pour tr pour le signal échantillonné
de pression et de température.
17. Appareil selon la revendication 16, caractérisé en ce que les moyens d'échantillonnage
comprennent un multiplexeur (1).
18. Appareil selon l'une quelconque des revendications 14 à 17, caractérisé en ce
que chaque capteur est conçu pour émettre un signal analogique et des moyens (21)
sont prévus pour convertir le signal analogique en un signal numérique destiné à être
traité par les moyens de réponse aux signaux.
19. Appareil selon la revendication 18, caractérisé en ce que le signal analogique
est une tension et les moyens de conversion (21) sont conçus pour convertir la tension
analogique en impulsions d'une fréquence analogique à la tension.
20. Appareil selon la revendication 19, caractérisé en ce que les moyens de réponse
aux signaux comprennent un compteur destiné à compter les impulsions pendant la période
d'échantillonnage de signaux afin de donner des valeurs de la pression ou de la température.
21. Appareil selon l'une quelconque des revendications 14 à 20, caractérisé en ce
que les moyens de réponse aux signaux sont conçus pour déterminer la fraction de durée
de vie tF(m) de la conduite utilisée entre des échantillons séquentiels des signaux
du même capteur (T) de température à l'aide de l'équation:
où t1 est le temps du dernier échantillon ou de l'échantillon en cours, t2 est le temps de l'avant- dernier échantillon, tr, est la valeur de tr établie d'après. le signal de température en cours, les moyens de réponse aux signaux étant conçus pour intégrer tF(m) afin de déterminer la fraction globale ΣtF(m) de la durée de vie de la conduite qui a été utilisée dans la période au cours de laquelle la conduite a-transporté un fluide.
où t1 est le temps du dernier échantillon ou de l'échantillon en cours, t2 est le temps de l'avant- dernier échantillon, tr, est la valeur de tr établie d'après. le signal de température en cours, les moyens de réponse aux signaux étant conçus pour intégrer tF(m) afin de déterminer la fraction globale ΣtF(m) de la durée de vie de la conduite qui a été utilisée dans la période au cours de laquelle la conduite a-transporté un fluide.
22. Appareil selon la revendication 21, caractérisé en ce que les moyens de réponse
aux signaux sont conçus pour indiquer une défaillance de la conduite lorsque ΣtF(m)=1.
23. Appareil selon l'une quelconque des revendications 14 à 22, caractérisé en ce
que des moyens (4), qui réagissent aux moyens de réponse aux signaux, sont destinés
à imprimer la valeur de tr.
24. Appareil selon l'une quelconque des revendications 14 à 23, caractérisé en ce
que des moyens (3) réagissent aux moyens de réponse aux signaux sont destinés à afficher
la valeur de tr.
25. Appareil selon l'une quelconque des revendications 14 à 24, caractérisé en ce
que les moyens de réponse aux signaux et les moyens de mémorisation comprennent un
ordinateur (2).