EP0122578B1 - Fatigue monitoring method of components, for example in a nuclear power station - Google Patents

Description

The invention relates to a method for monitoring the fatigue of preferably thermally and / or mechanically loaded components, such as. B. in nuclear power plants or aircraft, with sensors attached to the outside of the monitored components.

The since then fatigue analysis for individual components, such as B. for a feed water nozzle in a nuclear power plant, takes place on the basis of load case specifications, which in addition to thermal and mechanical load data contain assumptions about the frequency of mechanical load cases to be expected in each case. The disadvantage of such a specification lies in the theoretical assumptions, which often do not correspond to the stresses actually determined during operation by measurement.

On the other hand, an exact fatigue analysis is desired in order to be able to predict as precisely as possible when a certain component has reached its maximum degree of utilization and must therefore be replaced.

The object of the invention is to provide a method for monitoring the fatigue of components, for. B. in a nuclear power plant to create a continuous, based on actual measurement data operational monitoring.

According to the invention, this object is achieved by a method according to claim 1, which is characterized on the one hand in that the measured values measured by sensors on the components to be monitored arrive in a certain time cycle at a process computer which contains a first computing unit which records the measured course of the measured values dissolves into uniform elementary courses charged with different weighting factors and stores them in a first memory such that a superposition of these preferably triangular elementary courses weighted with the weighting factors approximates the actually measured course of the respective measured values, so that the values stored in a second memory for the elementary voltage profiles generated from these elementary profiles of the measured values are called up from these elementary profiles of the measured values and weights in a second arithmetic unit by superimposing them with the above-mentioned weighting factors The elementary voltage curves approximate the actual voltage curve and are stored in a third memory, and that a third arithmetic unit calculates the partial utilization factor of the component resulting from an evaluation cycle from this stored, approximate voltage curve using voltage-dependent fatigue curves and outputs it to a fourth memory in which the partial degree of utilization is added to the total degree of utilization stored therein and forms a new value for the total degree of utilization.

In the specific case, this means e.g. B. that temperature sensors are arranged along the circumference of a component, for example a feed water nozzle in a nuclear power plant. On the basis of the local temperature distribution and / or the temperature profile over time, the corresponding temperature profiles inside this component are now calculated (temperature backward analysis). On the basis of these temperatures calculated for the interior of the component, the tensile stress profiles in the wall material of the component can be calculated. This method, which is very complicated per se, is simplified in that the calculations are not carried out for the actually measured course of the measured values, but for "elementary courses _" , so-called elementary transients, as a superimposition of which - when using certain weighting factors - the actually measured temperature course can be approximated As a result of the linearity of the system of equations used to calculate the stress curves from the temperature curves, the actually occurring tensile stress curve can also be represented as a corresponding, ie provided with the same weighting factors, superimposition of elementary tensile stress curves which correspond to the elementary temperature curves is then processed with the help of the well-known rainflow or reservoir algorithm, ie converted into partial utilization rates Add up the partial utilization levels resulting from the evaluation cycles to the respective latest total utilization level, a characteristic value for the fatigue of a component.

In a similar way, as explained in the preceding paragraph on the basis of temperature measurement values, mechanical measurement values measured on the component can also be converted into partial utilization rates.

In parallel, on the other hand, it can be provided that, in addition to the measured values tapped directly on the component to be monitored, operating data which control the operating system to which the component to be monitored belongs, for example from a control room or control panel, are used for load case identification. Such load cases in a nuclear power plant are, for example, «starting», «rapid shutdown» etc. These individual load cases can now be determined

- Assign empirically determined or calculated or estimated on the basis of assumptions - reference stress curves, so that when identifying such load cases by possible additional superimposition with suitably weighted mechanical standard load cases, a reference stress curve arises, which is also converted back to a partial utilization rate with the help of the rainflow algorithm can.

The advantages of the process can be summarized as follows:

The uniform procedure leads to comparable results for all components and provides information on critical components.

The chronological recording of the individual operating processes and the continuous temperature measurements lead to the exact determination of the degrees of utilization.

If a critical tendency is identified during the monitoring, it is possible to increase the service life of individual, endangered components in good time through a newly defined gentle driving style.

Advertisements during ultrasound tests can be tracked continuously.

By monitoring the crack growth, one is able to continue operating the system even when the calculated utilization of 1.0 is reached.

This monitoring also makes it possible to carry out repair measures that are necessary in a targeted and thus economical manner.

Continuous operational monitoring leads to complete operational data acquisition (log book).

The operational monitoring system enables e.g. B. for all areas in power plants a more precise and, above all, more economical implementation of stress and fatigue analyzes.

The invention is applicable not only in the power plant area described by way of example, but also in other areas. Another example is the fatigue check of aircraft components etc.

An embodiment of the invention and its advantageous development is described below with reference to the accompanying drawings.

• Fig. 1 ein Ablaufschema des Verfahrens,
• Fig. 2 eine Ermüdungskurve für den Bauteil (materialspezifische Ermüdungskurve),
• Fig. 3 die schematische Anordnung mehrerer Temperatursensoren entlang des äußeren Umfangs eines rohrförmigen Bauteils,
• Fig. 4 den zeitlichen Verlauf einer Elementartransiente,
• Fig. 5 den örtlichen Verlauf einer Elementartransiente,
• Fig. 6 die zeitliche Überlagerung mehrerer gewichteter Elementartransienten,
• Fig. 7 eine weitere Darstellung einer Elementartransiente an einem Punkt x der Innenseite eines Bauteils,
• Fig. 8 der sich daraus als « Antwort ergebende Verlauf der Temperatur in dem dem genannten Punkt x auf der Innenseite gegenüberliegenden Punkt y an der Außenseite,
• Fig. 9 die durch Überlagerung von Antworten gemäß Fig. 8 entstehende Antwort auf überlagerte Elementartransienten nach Fig. 6,
• Fig. 10 ein Blockschaltbild eines Ausführungsbeispiels.

They represent:

• 1 is a flow chart of the method,
• 2 shows a fatigue curve for the component (material-specific fatigue curve),
• 3 shows the schematic arrangement of a plurality of temperature sensors along the outer circumference of a tubular component,
• 4 shows the time course of an elementary transient,
• 5 shows the local course of an elementary transient,
• 6 shows the temporal superimposition of several weighted elementary transients,
• 7 shows a further illustration of an elementary transient at a point x on the inside of a component,
• 8 the resultant temperature curve in the point y on the outside opposite the point x mentioned on the inside,
• 9 shows the response to superimposed elementary transients according to FIG. 6 resulting from the superimposition of responses according to FIG. 8, FIG.
• Fig. 10 is a block diagram of an embodiment.

ausgedrückt.Figure 1 shows a flow diagram for the method for monitoring the fatigue of components in a nuclear power plant. The basis for the fatigue analysis is the material-specific, empirically determined fatigue curve, e.g. B. Fig. 2 shows. In it, the individual reference _{stress ranges Δσv are assigned} the maximum permissible number N of load changes. The material fatigue caused by n equal load change fluctuations is determined by the "utilization factor"

expressed.

For different load change Δσi variations, the total utilization factor Ug of formula gives _{it j} as the sum of the individual partial utilization factors U according to

Where n _; in each case, based on the associated reference stress change Δσ _i , the number of load changes actually occurring, and N _; the maximum number of load changes resulting from the curve according to FIG. 2.

In detail, the requirements of these findings when operating reactor systems result from the ASME code, Sec. III (Stress Categories). The overall degree of utilization can be determined at a particular point in time by the monitoring method according to the invention.

The operating system symbolically marked with 1 in FIG. 1, e.g. B. a nuclear power plant, gives certain measurements. Box 2 is followed by data acquisition and weighting of the unit load cases:

The most important measured values, on the basis of which the stress distribution and then the degree of utilization are calculated, are the temperatures. B. lack of suitable long-term stable strain gauges - not possible to measure the stress curves in the material directly and to determine the degree of utilization. The calculation is therefore carried out on the basis of a temperature backward analysis, which assumes that the temperature distribution in the entire structure and, in turn, the stress distribution can be calculated from the outside temperatures, the temporal and spatial course of which can be measured by suitable sensors is.

As is shown schematically in FIG. 3, the temperatures are measured using suitable sensors (13), which in the example are arranged on a pipe section (14). The monitoring device according to the invention makes use of a particularly simple calculation of the voltage distribution, which is therefore described in detail below:

In general, the heat conduction equation applies

If a is assumed to be constant and T ₁ and T _{2 are} temperature fields, i.e. solutions of equation (3) that satisfy the boundary conditions R ₁ and R ₂ , then both T = T ₁ + T ₂ and (for constant r) also T = r · T ₁ Solutions of (3) that satisfy the boundary conditions R = R ₁ + R ₂ or R = r · R ₁ .

Das zur Oberflächentemperatur R gehörige Temperaturfeld T ist dann näherungsweise durch

gegeben.The invention makes use of this superposition principle in that it approximates complex temperature profiles from elementary triangular temperature profiles, so-called “elementary transients”, according to a modular principle. An attempt is made to present the externally measured temperature curve R (boundary condition) as a superposition of appropriately weighted elementary transients T _l ^l ... T _n '(FIG. 6) of the inner surface surface temperatures R of the inner surface, ie

The temperature field T belonging to the surface temperature R is then approximately through

given.

definiert, wie er in Fig. 4 und 5 dargestellt ist.The elementary transients T _i which are used here are due to the temperature profile occurring on the inside of the corresponding component (for example a pipe section (14) according to FIG. 3)

defined as shown in Figs. 4 and 5.

In these figures 4 to 6, i denotes the point on the inside opposite the measuring point i, E ^(I) the temperature profile on the inside and (x, t) the dependence on the coordinates of place and time.

FIG. 6 shows how a uniform, piece-wise linear internal temperature curve T ^(I) (represented by a continuous line), by means of superposition, elementary transients shifted in time and differently weighted

T _j ⁽¹⁾ , T ₂ ^(I) , T3 ^(I) , T ₄ ^(I) can be obtained, the courses of which have the shape of simple triangles on the inside, as shown in FIG. 4.

As can be seen from FIGS. 7 to 9, the “response” to an elementary transient T _E ^(I) at point x on the inside of a component (FIG. 7) is the temperature curve E ^(A) according to FIG. 8 in the opposite Point y on the outside, and by superposition of the “answers” T ₁ ^(A) -T ₄ ^(A) according to FIG. 9, an “answer” to the temperature profile according to FIG.

The temperature-backward analysis mentioned uses a measured outside temperature curve to determine the corresponding inside temperature curve according to the following scheme: First, the outside temperature T ^{(A) is} approximately represented as a superposition of answers E _i ^(A), i.e. of elementary curves or elementary transients for the outer surface at location i :

Pictured, the measured curve of the outside temperature would be replaced by a large number of overlapping, time-shifted and differently weighted triangular element temperature curves. The individual weightings r _j are determined in such a way that the best possible approximation to the actually measured profile of the outside temperature is achieved.

minimiert wird.This approximation minimizes the error in the quadratic mean. Expressed mathematically, this means that the integral

is minimized.

Due to the linearity of the heat conduction equation (3), the temperature curve on the inside can now be concluded:

Also compare FIGS. 8 and 7. From these, it is clear how an assumed elementary profile of the temperature on the inner tube wall at point x (FIG. 7) has a temporally shifted effect on a temperature profile on the outer wall.

From the temperature distribution, which is clearly determined by the internal temperature profile, the associated stress state can be determined as follows according to Hooke's generalized law:

The material values E, a and µ are assumed to be constant. If the first three equations are solved for T, the quantities u, v, w as well as the σ's and the τ's are combined into a vector s and T is also used to denote the vector (T, T, T, O, O, O), Equation (8) can be described as follows:

D is a linear differential operator. As is known, this system can be uniquely solved with given displacements or given forces in the peripheral area, taking into account the body balance conditions.

This results in: If the temperature field T can be represented as a superposition of elementary transients T according to equation (5) and if the resulting stress state s _{i is} known for each T, then equation (9) can also be solved by superposition, namely in the form

This means that the weightings of the individual elementary transients determined in the temperature backward analysis explained with reference to FIGS. 4 to 9 can also be used directly when the individual voltage profiles are superimposed. The relevant weighting factors for the individual temperature transients determined in the temperature backward analysis are determined in block 2 in accordance with the flow diagram shown in FIG. 1.

The elementary reference stress curves corresponding to the elementary transients T of the temperature of the inner surface are stored in the block-specific stress file for unit load cases, block 3 in FIG. 1. From this voltage file for unit load cases, the reference voltage curves stored for the respective temperature transient, specific to the module, are called up and multiplied in block 2 by the associated weighting factors. In block 4, the elementary voltage curves called up in the voltage file 3 and weighted in block 2 are followed by Superposition of the actual voltage curve determined.

From this voltage curve thus determined in block 4, the degree of utilization is calculated in block 5 with the aid of a specific algorithm. This algorithm is known as the "rainflow" or reservoir algorithm. It is essentially based on the fact that the determined voltage curve is broken down into a finite number of simple-period processes. (See K. Roik, lectures on steel construction, Wilhelm Ernst and Son Verlag, 1978, p. 69). A material-dependent partial utilization factor is stored in a memory FAT for each of these processes.

From the fatigue curve according to FIG. 2, which applies to the component or the material, the partial utilization factor U to be applied for the individual periodic elementary cycle is then obtained in block 5 using the rainflow algorithm _; , which is included in the determination of the total utilization factor according to equation (2). In block 6, the result is the cumulative time profile of the overall degree of utilization, which is transferred to peripheral devices.

The part of the fatigue monitoring of a certain component described up to now by continuously updating the degree of utilization can be summarized as follows: On the basis of the measurement data that record the outside temperatures, the internal temperatures are first calculated back; the internal temperature curve is broken down into weighted "elementary transients". The individual elementary transients obtained when the temperature profile is divided are individually assigned voltage transients previously calculated from a file and superimposed on a voltage profile. From the superposed stress curve, partial degrees of utilization and the degree of utilization are calculated from the rainflow method using predefined fatigue curves. The replacement of the monitored component can be planned in good time before the overall degree of utilization reaches its highest permissible limit, namely the value 1.

Parallel to the determination of the degree of utilization described so far, a second fatigue monitoring for components is running, the stress of which cannot be determined or can only be inadequately determined by outside temperature measurements. The corresponding load cases are identified in block 8 on the basis of various system-specific operating signals, which can essentially be seen in the control room 7 in the exemplary embodiment of a nuclear power plant 1. Such typical load cases are e.g. For example: slow start-up, rapid shutdown, etc. For load cases identified in this way, the voltage file shown in block 9 contains the corresponding reference voltage curves. This means: For each load case identified on the basis of certain operating signals or operating signal combinations, the associated voltages are taken from block 9 from the voltage file and compiled in block 10 to form a voltage curve. The data that are stored in the voltage file in block 9 have been determined on the basis of theoretical considerations and / or calculations, or have been measured in the past for special load cases. It is a matter of previously known - calculated or measured - voltage profiles for special load cases, from which the voltage profile is composed in block 10. The flow of information leads again from block 10 to block 5, where the associated partial utilization rate is calculated from this comparison voltage curve with the aid of the rainflow or reservoir algorithm. The calculation of the degree of partial utilization in block 5 by way of blocks 7 to 10, i.e. based on the load case identification and the voltage data determined for identified load cases based on previous processes and / or calculations, thus runs in parallel with the determination of the degree of utilization via the component to be monitored directly measured temperature and other mechanical data and their processing in blocks 2 to 5.

Both from the measured value acquisition in block 2 and from the load case identification in block 8, the operating data are recorded in a block 11 and stored in a data memory, a so-called log book, indicated by block 12 in FIG. 1. In addition, it can be provided (not shown) that the results of the calculation of the stress distribution in block 4 and the formation of the stress curve in block 10 are continuously compared on the basis of the load case identification in block 8 and that the most unfavorable value is used to determine the degree of utilization to ensure maximum security. This makes it possible to determine the superimposition of voltages for the monitored modules that occurs during certain load cases that can be identified in the load case.

The data determined in this way can be used to obtain data for module-related, life-extending operating modes of the system.

10 shows the circuit implementation of the invention.

The measured values relevant to the subject of the application come from three different sources in a nuclear power plant, namely the temperature sensors 13, 20, the mechanical sensors 15, 21 and the sensors 22, the control room 7, from which the nuclear power plant 1 is controlled.

The temperature sensors 13, 20 provide the measured values which are required for the temperature backward analysis described above. The mechanical sensors 15, 21 stand for such signal transmitters or sensors, which allow information about mechanical stresses, such as. B. measuring instruments for internal pressure, flow rate, level indicators etc. The operating signals emanating from the sensors 22 of the control room 7 can be used to determine the current operating state (load case) of the operating system 1 or power plant.

From these three units, designated 20, 21, 22 in FIG. 10, lines each go to the Process computer 33, namely after possibly necessary A / D conversion to the unit for measured value acquisition MWE 34. In the unit for measured value acquisition MWE 34, the measured values transmitted by temperature sensors 13, 20 and mechanical sensors 15, 21 or by The operating signals emitted by the sensors 22 of the control room 7 are processed, smoothed, classified, checked for plausibility. In unclear or critical cases recorded, for example, during the plausibility check, messages are output directly from there to a so-called console CO 35, which can be in the control room 7.

Within the process computer unit shown in FIG. 10, data and program memories are drawn on the left side ROM (Read Only. Memory) and RAM (random access memory) main memory on the right side. A first memory FIFO I 37 (First In / First Out) and a second memory FIFO II 38 are connected to the unit for measured value acquisition MWE 34 via a data bus 36. The data that is first read in time is also read out first in time. The memories 37, 38 are buffer memories. The first memory 37 is in alternating connection with the computing unit LCID 39 (load case identification), which is used to identify the individual load cases.

The basis for the identification of the individual load cases are the operating signals coming from the sensors 22 of the control room 7. The computing unit LCID 39 determines, based on the load cases identified in this way, from the voltage file for specified load cases LCL 9, comparison voltage values for identified load cases, and component-dependent as well as various weighting factors for these comparison voltage values, which are determined by various sensors, and places them in one of the computing units HSP / VSP 40 for later superposition not represented RAM.

The temperature and voltage measurement values prepared by the measurement value acquisition MWE 34 go directly to the second memory FIFO II 38 and from there to the voltage file for unit load cases 3, which contains the memory TLL (Thermal Load Library) 41 for thermal load cases and the memory MLL 42 (Mechanical Load Library) for mechanical load cases. In the TLL 41, those reference voltage profiles are stored that are assigned to the individual thermal elementary transients. In the memory MLL 42 those reference voltage profiles are stored which are assigned to the mechanical elementary gradient. Using the data stored by the computing unit LCID 39 and the voltage values for mechanical and thermal load cases in the MLL or TLL memories, the computing unit VSP 40 (for the main and comparative voltages) then determines the resulting voltage curve by superimposing it and stores it in the STACK HSP VSP 43 memory. This is divided into two storage units 44 and 45 for the main voltages (HSP) and the determined reference voltages (VSP).

The resulting reference stress curve stored in the memory unit 44 of the working memory STACK HSP VSP 43 is calculated in the third arithmetic unit RFL (rainflow) 46 with the aid of the material-related fatigue curves (cf. FIG. 2) stored in the memory FAT (fatigue) 47 with the rainflow mentioned above. or reservoir algorithm processed. The resulting partial utilization levels are added to the utilization level already stored in the RAM USE I 48 memory.

In addition, starting from a crack depth on the inner wall measured otherwise, for example by ultrasound testing, or on the basis of a crack depth assumed or postulated based on empirical values, on the basis of the main stresses occurring in the computing unit HSP / VSP 40 during operation of the operating system, i. H. of the stresses occurring in the three coordinate axes, the crack growth can be calculated. For this purpose, these main stresses occurring in the arithmetic unit HSP / VSP are stored in the memory unit STACK HSP 44 of the memory STACK HSP / VSP 43 and retrieved from there by a second arithmetic unit RFL 11 and processed on the basis of the stress-dependent crack growth curves stored in the memory RWK 50. The calculation result, the crack growth per load unit, is added to the crack lengths previously stored in RAM USE II 51.

The process computer 30 is connected to the console CO 35, which has the usual peripheral devices (printer, writer, etc.) and can be read in the degree of utilization and the accumulated crack lengths. The console 35, which is usually in the control room 7, allows the replacement of components that have been used in foreseeable periods to be planned in good time. It also enables the operating system to be operated in the way that is most gentle on the most vulnerable or most worn components.

Claims (8)

1. Method for monitoring the fatigue of components which are preferably thermally and/or mechanically loaded, such as, for example, those in nuclear power stations or aeroplanes, with sensors provided externally on the components to be monitored, characterised in that the measured values measured in a certain time cycle by the sensors (13, 15, 20, 21, 22) on the components (14) to be monitored reach a process computer (33) which contains a first computing unit (LCID) (39) which from the measured values and with the aid of a stress dataset (LCL) (9) for specified unit loading cases determines weighting factors to be applied to the mechanical unit loading cases or/and comparison stresses which are directly specific to loading cases and files them in a first working memory, in that, furthermore, a second computing unit (HSP VSP) (40), in accordance with the comparison stresses determined by the first computing unit (LCID) (39) and/or on the basis of the measured data filed by a measured data acquisition dataset (MWE) (34) in a second working memory (FIFO II) (38) after resolution of the same into correspondingly weighted unit values allocates to the latter using two unit loading case libraries (TLL, MLL) (3, 41, 42) comparison stress values and weights them and files them in the time cycle in a third memory (STACK VSP) (43, 45), in that, furthermore, a third computing unit (RFL) (46) controls the third memory (STACK VSP) and calculates from the comparison stress course using fatigue curves residing in a memory (FAT) (47) the part usage factor of the component resulting during an evaluation cycle and this value is added to the former usage factor residing in a fourth working memory (RAM USE I) (48), from which the current total usage factor (Ug_es) results.

2. Method according to claim 1, characterised in that the sensors (13, 20) are temperature sensors which are arranged on the outside of the component (14) which is to be monitored and is insulated in the region of the temperature sensors and in that the elementary stress courses which are stored in a fifth memory (TLL) (41) are ones which correspond to thermal unit courses.

3. Method according to claim 1, characterised in that the sensors (15, 21) are mechanical sensors and in that the elementary stress courses which are stored in a sixth memory (MLL) (42) are ones which correspond to mechanical unit loading cases.

4. Method according to claim 1 or one of the following claims, characterised in that, furthermore, the first computing unit (LCID) (39) mentioned identifies from the operating signals which are emitted from a control room (7) to the operating system (1), the constituent part of which is the component to be monitored, the respectively specified loading case of the operating system, in that, furthermore, a further (seventh) memory (LCL) (9) is associated with the first computing unit mentioned, in which memory the stress course, which can be associated with this identified loading case, is stored in a component-specific manner and in that the stress courses which can be associated with the identified loading cases in a component-specific manner reach, by way of a buffer memory, the second computing unit (HSP VSP) (40) and in that this thence through superimposition approximates the actual comparison stress course which is stored in the third memory (STACK HSP VSP) (43) mentioned.

5. Method according to claim 1, characterised in that the superimposed stress distributions which are determined in a component-specific manner during certain loading cases, which are determined by the control room (22), by means of the measured data of the sensors (13, 15, 20, 21) and are calculated by means of the second computing unit (HSP VSP) (40), are determined and stored together with the loading case.

6. Method according to claim 5, characterised in that the superimposed stress distributions, which are calculated in a component-specific manner for certain loading cases, are converted by way of the third computing unit (RFL I) (46) into component-specific part usage factors and are documented within the framework of an operating data acquisition system (11).

7. Method according to claim 5, characterised in that the superimposed stress distributions, which are documented in the operating data acquisition system (11) and are determined for certain loading cases in a component-specific manner, are stored as such and in their frequency in a separate dataset for specified loading cases.

8. Method according to claim 1 or 4, characterised in that the weighted principal stresses occurring in the second computing unit (HSP VSP) (40) are stored in an eighth memory (STACK HSP VSP) (43, 44) and are converted by a fourth computing unit (RFL II) (49) with use of stress-dependent crack growth curves which are stored in a ninth memory (RWK) (50) into crack growth values which result during an evaluation cycle and these crack growth values are added to the crack lengths stored in a tenth memory (RAM USE 11) (51).

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