KR100305723B1 - Method for Automatic Life Assessment of Mechanical Equipments under Complex Loads Using Strain - Google Patents

Abstract

The present invention relates to an automatic life assessment method of a mechanical equipment subjected to a complex load using a strain, and more particularly, to accurately measure the service life of a mechanical equipment subjected to a complex load to promote safe operation of the equipment and to replace the mechanical equipment. It is about making it possible to predict correctly.

The present invention continuously measures the temperature input from the thermocouple and the stress-strain input from the strain measurement sensor and digitizes it as a signal converter, and then analyzes the hysteresis loop through the plastic energy and strain division in the computer and analyzes the analyzed stress and temperature. The creep life is compared with the creep life consumption diagram.

In addition, if the creep life consumption fraction and fatigue life fraction are constant, the creep-fatigue interaction index can be used to evaluate the life of mechanical equipment that simultaneously creep and fatigue. By introducing and calculating, the service life of the mechanical equipment under the combined load is to be accumulated in real time.

Description

Automated Life Estimation Method for Mechanical Equipments under Complex Load Using Strain

The present invention relates to an automatic life assessment method of a mechanical equipment subjected to a complex load using a strain, and more particularly, to accurately measure the service life of a mechanical equipment subjected to a complex load to promote safe operation of the equipment and to replace the mechanical equipment. It is about making it possible to predict correctly.

As is well known, in the late 1990s, Korea's electricity demand growth rate is expected to be 6.2% per year due to the increase in the national level and the level of culture.

The construction of new power plants needed to expand such power supply capacity is facing difficulties as power plant location increases due to widespread funding difficulties and awareness of environmental issues. Therefore, in order to meet the ever-increasing demand for power even in the construction of new power plants, it is first and foremost to extend the service life of the power generation facilities to the design life and to improve the reliability of the equipment in use.

Developed countries use most of the thermal power plants, nuclear power plants, petrochemical plants and refineries for a long time, and the machines are being used with their original design life exceeded.

In order to dispose of these old machinery and construct new facilities, in addition to the economic burden, the legal procedures for new construction are complicated, and many of them are used for prolonging their life without disposing of the old obsolete equipment.

More than 65% of the thermal power plants currently used in Korea are over 10 years of driving experience, and more than 55% have passed more than 15 years of legal operation. In particular, heavy chemical plants and power generation facilities are operated under high temperature and high pressure, resulting in deterioration of materials and deterioration of mechanical facilities. Factors causing such deterioration of materials include high temperature operating conditions, ie excessive operating time, load conditions, equipment corrosion, etc., and most of the factors are combined to promote deterioration of equipment. In the case of thermal power plants, the deterioration of equipment due to material deterioration occurs in the steam boiler pipe, header, tube, steam turbine rotor, turbine casing, turbine blade, etc. As a result, there is a demand for technology development capable of quantitative evaluation.

Conventionally, in order to meet such demands, the conventional equipment life evaluation method is performed by a damage summation method in which creep life and fatigue life are separately calculated and summed.

Creep phenomenon is a phenomenon in which a large deformation or breakage occurs after a long time in proportion to time when a metal is subjected to a constant load (constant stress) at a high temperature (above 400 ° C). . Therefore, the whole life from the initial load to break at high temperature is called the creep life, and the creep life curve showing the relationship between the strain and the time caused by the creep phenomenon is called the creep life curve.

Fatigue is a phenomenon in which a metal is repeatedly subjected to a critical repetitive number and is destroyed when a metal is repeatedly subjected to a constant load (constant stress). The relationship between is called fatigue life.

Actual power plants are operated at high temperatures where most structures are subject to creep under constant stress, and since most power plants are fatigued under constant load through repeated daily or weekend shutdowns due to power demand, actual facilities are creep. You are being compounded with fatigue.

Therefore, as shown in (b) of FIG. 4 (b), the period of strain / time of operation of the power plant is made of a trapezoidal waveform, and the cycle is repeated. Therefore, one cycle is made of the trapezoidal waveform of FIG. Therefore, the front part (starting) and the rear part (at stopping) of the trapezoidal waveform of Fig. 4 (b) are regarded as fatigue, and the driving (straight line) is regarded as creep and the damage is calculated by adding each creep and fatigue separately. The summation method evaluates the life of mechanical equipment.

More specifically, the creep fracture life (t _f ) and the fatigue failure life until the specimen is broken by conducting the creep test and the fatigue test separately in the same environment (same material and temperature) in the laboratory. By calculating (N _f ) and calculating the creep time (normal operation time: t) and fatigue time (starting and stopping repetition number: N) of the actual power generation facility, and calculating it by the following equation (1) Evaluate the service life of the equipment.

That is, the conventional method of damage summation is the most common and common method of predicting the life when a material is subjected to fatigue and creep damage at the same time. Creep and fatigue damage act independently of each other, and the sum of the damages is the threshold value (1). It is the theory that when it reaches, it is destroyed.

N _i : Number of cycles subjected to fatigue load in state i

N _fi : Number of cycles destroyed when fatigue load in state i

t _j : time to apply creep load of j state

t _fj : Time to break when creep load in j state is applied

Q: The limit of cumulative damage allowed, usually used as 1 as a function of cycle and time,

In the above, i and j represent the state of the load applied to the material, and in actual installations, various loads vary from small creep and fatigue loads (j, i) to large creep and fatigue loads (p, q). And when such a load is divided into creep and fatigue, respectively, it becomes a form as shown in Equation (1).

In this damage summing up formula (1) Fatigue damage, Is the creep damage, and if the fatigue fatigue is 0.4, the creep damage is calculated as 0.6, and the material breaks when the sum is 1 day.

In practice, however, facilities operating in the field are subjected to cyclic creep and fatigue cycles as shown in Fig. 4 (b), and as the use time continues, the creep and fatigue do not work independently, but the synergy effect is increased. Since creep and fatigue act simultaneously in a cycle, creep-fatigue interactions must be considered for accurate life prediction.

In addition, in the conventional damage summation method, since creep and fatigue are simultaneously performed, when data is acquired from a real facility, signals appear to be mixed with each other. Therefore, a method of directly acquiring data cannot be provided. The problem is pointed out.

The present invention was devised to solve the problems of the method for evaluating the service life of a facility by the conventional damage summation method. The object of the present invention is to measure the stress and strain directly occurring in a metal using a thermocouple and a strain sensor in a facility in operation. Use of industrial equipment that is subjected to complex loads by analyzing the hysteresis loops displayed on the computer screen continuously and calculating the cumulative life consumption simultaneously with complex creep life and fatigue life, and performing life assessment in real time. It can be used to accurately measure the service life and at the same time accurately predict the replacement time of the equipment to promote safe operation of the equipment and improve the reliability of the industrial equipment.

1 is an overall system configuration of a temporary example for explaining the present invention

Fig. 2 is a split view of the elastic and plastic strain in the present invention.

(a) is the pp-type cycle

(b) the cp-type cycle

(c) is a pc-type cycle

(d) cc-type cycle

Figure 3 is a division diagram for explaining the elastic and plastic deformation energy in the present invention

Fig. 4 (a) is a graph showing the relationship between the strain division method and the life span according to the present invention.

Figure 4 (b) is a trapezoidal waveform diagram for experimentally simulating the thermal stress and strain of the actual equipment

5 is a graph illustrating the relationship between the plastic strain energy method and the lifespan according to the present invention;

6 is a graph showing creep lifespans for obtaining creep rupture life.

7 is an experimental graph for FIG. 6

FIG. 8 is a graph illustrating creep-fatigue interaction effect analysis according to the present invention.

<Description of Symbols for Major Parts of Drawings>

1: strain strain sensor 2: thermocouple

3: hardware 4: signal converter

5: computer

In order to achieve the above object, the present invention obtains data from a sensor in the field in real time, and receives stress and strain generated in a facility as a hysteresis loop on a computer screen using a signal conversion device to interact with creep and fatigue in real time. It is intended to calculate the service life of the equipment.

That is, the real-time creep temperature can be known from the temperature input from the thermocouple, and the strain measured in real time from the strain measurement sensor is also inputted in real time from the property relationship of the material (stress = elastic modulus x strain). After measuring the strain continuously and digitizing it as a signal converter, divide the creep and fatigue sections by each type and calculate the divided loops as shown in Fig.2. Is to assess the lifetime.

Technical features that can be obtained through the automatic equipment life measurement method according to the present invention;

First, as shown in FIG. 2, the lifetime can be directly evaluated by a combination from each loop represented through the division of the real-time input stress and strain trajectory (hysteresis loop).

Second, as shown in FIG. 2, the loops are calculated by dividing the trajectory (hysteresis loop) of stress and strain input in real time, thereby evaluating the life by plastic strain energy continuously accumulated in the metal. In order to calculate this plastic strain energy, when the metal is subjected to temperature and stress, the plastic strain energy, which initially represents the internal area of the hysteresis loop, is present in a small amount, and gradually increases and breaks as the threshold is reached. It is a method of evaluating the lifetime by calculating the inner area of the hysteresis loop in real time.

Third, the elastic deformation life curve and plastic deformation are expressed by using the equation that shows the life relationship by dividing each loop represented by elastic part and plastic part strain as shown by the division of the real-time input stress and strain trajectory (hysteresis loop). It is a method to evaluate the combined life of creep and fatigue by obtaining the final life curve by the sum of the life curves.

Fourth, real-time creep life can be calculated. Since the actual damage to the plant is greater than the damage to fatigue (70% of 100% of total damage), it is very important to calculate the creep life in real time. Since creep damage is a function of temperature, stress, and time, stresses are calculated from real-time measurements of temperature and strain from thermocouples, and the creep life is calculated by comparing creep life consumption diagrams.

Fifth, instead of calculating the existing creep and fatigue separately as a modified method of damage summing, the creep damage and fatigue loss of Equation (1) are introduced as an index. It is applied to the situation so that the life of the mechanical equipment with the combined load is real time and accumulated.

Hereinafter, an embodiment of an automatic life assessment method for a mechanical facility receiving a complex load using a strain according to the present invention will be described in more detail.

1 is an overall system configuration according to an embodiment of the present invention, to accurately evaluate the life of a mechanical equipment subjected to a complex load in the mechanical equipment (3) of the site where stress concentration and breakage during operation in the power generation equipment is expected The strain strain sensor 1 and the thermocouple 2 are mounted, and the current and voltage signals detected by the strain strain sensor 1 and the thermocouple 2 are converted into digital signals by the A / D signal converter 4. And then transmit the data to the computer 5 having the life analysis device and the life display device.

In the above, the life analysis device evaluates the life by calculating the inner hysteresis loop of stress and strain from the strain change input from the stress strain sensor 1 and calculating the inner area of each loop, or the elasticity and plasticity of the loop. Divide the strain and add each strain curve to calculate the final life curve.

In addition, the creep parameter (t _f = T (20 + log t) × 10 ³ ; where (t _f ) is the creep life to be obtained and (t _f ) is the operating time) It is easy to know how much creep life was consumed in real time by calculating the life span and comparing it with the creep rupture life curve of the material.

In addition, as shown in FIG. 8, the creep life and the fatigue life are calculated from the divided hysteresis loops to correct the damage summation method, which is a conventional method, and the respective slopes indicate creeps rather than the slope of the conventional damage damage method. And fatigue each have a small value. By this reduced value, the interaction between creep and fatigue shortens the lifetime. Quantifying these values, expressing them in exponents, and continuously accumulating them can calculate the lifetime due to creep-fatigue interactions in real time.

When referring to the detailed life calculation procedure to be mentioned in the present invention in addition to the device system mentioned so far as follows.

First, a method of directly evaluating life by dividing a strain input from a sensor.

The present invention obtains data by using the strain and stress obtained in real time from the mechanical equipment 3, and the data is obtained in real time in the computer 5 with the strain as the X axis and the stress as Y. According to the type of load acting as shown in Fig. 2, the load is divided in real time by the following equation. This is because when one cycle of repeated loading to compress the structure or specimen is applied, a hysteresis loop (hysteresis curve) of stress-strain is generated inside the material as shown in FIG. 3, but the hysteresis curve generated in the industrial structure is The magnitude of the cyclic load of numerous creep and fatigue is to be subjected to various cycle loads, and the computer 5 should be used to divide the strain of many creep and fatigue. This is because the internal area of the hysteresis curve becomes the small strain energy accumulated inside the material, and the small strain energy is directly related to creep and fatigue life. The relationship between the strain component and the fatigue life is explained as follows. The strain obtained in real time is tensioned and compressed by creep and fatigue at the measurement site and is divided into the following four types (a), (b), (c), and (d).

Δε _ij (N _ij ) ^m = C (2)

In Equation (2), i and j represent p (plastic-plastic-strain deformation) and c (creep deformation) received at the measurement site, and m is a material constant, which is a constant (number) that can be obtained through experiments for each material. Again, it is a constant (number) indicating the relationship between the amount of deformation and the service life, N _ij is the total number of creep and fatigue, and p and c are as follows.

(a) Δε _pp : Deformation produced by compressive plastic deformation after tensile plastic deformation

(b) Δε _cp : amount of deformation produced by compressive plastic deformation after tensile creep deformation

(c) Δε _pc : Deformation produced by compression creep deformation after tensile plastic deformation

(d) Δε _cc : Deformation amount produced by compression creep deformation after tensile creep deformation

In general, if only tensile creep is applied to the site where the sensor is attached in Equation (2), fatigue life can be calculated immediately as Δε _p (N _f ) ^m = C. Since four cases (a), (b), (c), and (d) should be summed up as shown in (3).

In formula (3), f _ij represents the divided terms of (a), (b), (c), and (d), and represents the real-time fraction of creep and litigation strain. Strain splitting has the disadvantage that the linear cumulative and actual complex loops of the parts divided from the hysteresis loop are difficult to divide, but can be solved by computer programs and have the advantage of being displayed in a temperature-independent manner.

The following is a method of calculating the life by plastic strain energy. Facilities Each metal is initially consumed as heat while being subjected to creep and fatigue loads, and is absorbed into the material by only a very small amount and appears as plastic strain energy. Is destroyed.

This plastic strain energy is the inner area of the hysteresis loop, which is the trajectory of the applied stress and strain, and the total energy consumed is the sum of these loops. Each material has a constant capacity to absorb energy, Is broken.

3, and explaining the plastic deformation energy, _p is the firing energy ΔW, ΔW _e is the elastic energy, Δεa ^e is an elastic deformation range, Δεa ^p denotes a plastic strain range. The sum of these components is the total energy ΔW _t and the total strain range Δεa ^f . As a result, ΔW _p (plastic deformation energy) in FIG. 3 represents the inner area of the curve, and the inner area is calculated in real time, and the life is evaluated using the equation (4).

ΔW _p = A (N _f ) ⁿ (4)

Where A and n are constants (numbers) according to the material and time of use, and N _f is the fatigue life, and then the life curve is calculated by dividing the hysteresis curve and the plastic strain range. It is a way of evaluating life span.

Hysteresis curve The elastic strain range and the plastic strain range are calculated, plotted, and programmed to sum each curve, and each time the number of load repetitions is counted to obtain a curve as shown in FIG. 4A. An equation representing the relationship between each such strain range amount and the lifetime is expressed by equation (5) (Δε _t is the total strain).

(5)

In the present invention, after verifying the results of each analysis method through sinusoidal low-cycle fatigue life prediction, hold time is 1, 10, and 30 minutes in trapezoidal waveforms to identify creep-fatigue interactions. Strain control was 0.2 to 0.6%. The strain rate demonstrates that the strain and the plastic energy in the case of maintaining constant (0.004 / see) for each holding time and strain have a direct functional relationship with the lifetime as shown in FIGS. 4 and 5.

In other words, Figure 4 shows the relationship between the strain amplitude (Strain amplitude) and the number of cycles (R) of the results obtained through the trapezoidal waveform experiment.

Specifically, it is possible to calculate the respective elastic and plastic strain ranges from the hysteresis curve and combine them in a program and obtain a real-time picture of FIG.

5 shows the plastic energy (Δεa ^p ) of the material, strain, and the relationship with the number of breaking cycles of the strain test, respectively, when the internal area of the hysteresis curve (FIG. 3) is calculated. If the graph is drawn using 4), a curve between the firing energy and the lifetime as shown in FIG. 5 can be made.

However, there are two ways to find the plastic energy of the inner surface of the hysteresis loop. In other words, the first method uses the equation (4) to theoretically calculate the area of the hysteresis loop, and the second method is to directly integrate the internal area of the hysteresis loop shown on the computer by using the computational processing function of the computer.

The graph of FIG. 5 shows that the results obtained using the respective methods at room temperature (20 ° C.) and high temperature (515 ° C.) are fairly consistent, and thus the plastic energy can be accurately measured using a computational processing function. Accordingly, the data of FIG. 5 are data for the above two cases.

4 and 5 show in Figs. 4 and 5 that the lifetime of the equipment in operation is directly related to the elastic and plastic strain and the fracture life of the hysteresis loop (history curve) measured in the field. 4), (5) and computational and graphing functions such as those obtained in FIGS. 4 and 5 are calculated using a computer.

Next, we want to calculate the real-time lifetime separately for creep only. Since creep damage is a function of temperature, stress, and time, stresses are calculated from real-time measurements of temperature and strain from thermocouples, and the creep life is calculated by comparing creep life consumption diagrams.

Meanwhile, the present invention analyzes the hysteresis loop and compares the analyzed stress and temperature with the creep life consumption diagram to evaluate the creep life. FIG. 6 is a graph showing the creep life consumption diagram for obtaining the creep rupture life. 7 is an experimental graph of FIG. 6.

That is, if the stress and temperature are used, the creep life (t ₅ ) of the corresponding material can be obtained using the creep parameter (t ₅ = T (20 + log t) × 10 ³ ) at the stress and temperature for each material. Service temperature and stress are input in real time from thermocouples and strain sensors to assess creep life.

The following is to change the conventional linear damage summing method. Figure 8 is a graph of the creep-fatigue interaction effect by the experiment. As mentioned earlier, the sum of creep damage and fatigue damage must be maintained at 1 according to the damage summation method, which takes the sum of each damage. However, the actual creep and fatigue damage mutually affect each other's lifespan so that failure occurs faster than the failure life of the sum of the damages. Therefore, the correction factor (interaction index) can be used to accurately measure the lifetime of creep-fatigue interactions that are broken early. That is, if the creep life consumption fraction and the fatigue life fraction are constant, the life-reduced effect of creep-fatigue interaction indexes is calculated by introducing the creep-fatigue interaction indexes a and b according to the material according to the following equation (6). Accurate measurement of the lifetime of early creep-fatigue interactions can be achieved.

(6)

In Equation (6), EXP = exponential means e ^x , N is fatigue time, t is creep time, Q is cumulative damage coefficient, and the same meaning as in (1), but the damage summation method is always 1 However, when creep and fatigue are combined, they always appear below 1, shortening their lifespan.

More specifically, referring to FIG. 8, for example, when a plant is operated at a strain of 0.004, the damage life of the plant is 0.6 when the damage damage is 0.4, and the creep damage is 0.6. It is thought to break at, but when the fatigue damage is 0.4 at a strain of 0.004 (a = 3.08, b = 1.39), the creep damage breaks at about 0.35, reducing the lifespan by about 25% by interacting with each other than the damage summing method. Will occur.

As described above, the automatic life assessment method for a mechanical facility receiving a complex load using the strain according to the present invention is to obtain data directly from the sensor in the field and to automatically evaluate the life of the facility accurately and in real time. The method of evaluating the life by dividing, the method of evaluating the life by plastic strain energy, the method of evaluating the life by summing the elastic strain range amount and the plastic strain range amount, and the method of evaluating the life of creep only in real time. As mentioned above, it is possible to improve the accuracy of the life assessment by adding the interaction index to the existing damage summing method for the composite load of creep and fatigue, and to improve the accuracy of the life assessment. It will automatically evaluate the lifespan.

As described above, the present invention is stressed among the important elements of the mechanical equipment, and attaches a strain measuring device to a selected part of the weak area, and obtains a hysteresis loop of one cycle leading to starting and stopping of the industrial equipment such as a power plant and creep- By allowing the fatigue interaction evaluation to be performed in real time, the remaining life of the equipment in operation is constantly monitored, which greatly contributes to improving the reliability of the equipment.

Claims (6)

In a power plant, a strain measuring sensor (1) and a thermocouple (2) are attached to a mechanical facility (3) at a site where stress concentration and breakage are expected during operation, and the temperature and strain measurement detected and input from the thermocouple (2). The stress-strain detected and input from the sensor 1 is continuously measured and digitized by the signal converter 4, and then the computer 5 analyzes the hysteresis loop by dividing the plastic energy and strain and creep from the hysteresis loop. And evaluating fatigue life (N _f ) using the real-time fraction (f _ij ) and the total number of deformations Evaluating fatigue life (N _f ) using plastic deformation energy (ΔW _p ) Evaluating the fatigue life (N _f ) using the total strain (Δε _t ) of the elastic and plastic strains of the loop Evaluating the creep life (t _f ) using the creep parameters and the creep life consumption plots from the stresses and temperatures analyzed from the loop; and An automatic life assessment method for a mechanical facility subjected to a compound load using a strain, characterized by calculating the creep-fatigue interaction index to real-time and cumulatively process the life of the mechanical facility under the combined load. The fatigue life (N _f ) is calculated by the relationship between f _ij , the real-time fraction of creep and plastic strain, and N _ij , the total number of creep and fatigue, from a hysteresis loop detected from a machine under complex loading. Automatic life assessment method of a mechanical equipment subjected to a compound load using the strain characterized in that consisting of. The plastic strain energy (ΔW _p ) is a fatigue life (N _f) using a constant A, n calculated according to the material and the use time as the real-time internal area of the hysteresis loop detected from a mechanical load subjected to a compound load. Automatic Life Assessment Method for Mechanical Equipments under Complex Loads Using Strains Equation ΔW _p = A (N _f ) ⁿ The method according to claim 1, wherein the strain-life curves are constants A, B, and a obtained from the hysteresis loop detected from a machine under a complex load according to the total strain (Δε _t ) and the material and the number of repetitions in the elastic strain and the plastic strain. A method for automatically evaluating a life span of a mechanical equipment subjected to a compound load using a strain, characterized by the equation A (2N _f ) ^a + B (2N _f ) ^b for calculating the fatigue life (N _f ) using ^b . The creep parameter (t _f = T (20 + log t)) according to claim 1, wherein the creep parameter (t _f = T (20 + log t)) is a relationship between the creep life (t _f ) and the use time (t) through the temperature and stress detected and input from a mechanical load subjected to a compound load. X10 ³ ) to determine the creep life (t _f ) of the material of the plant, using an automatic strain assessment method for a mechanical plant subjected to a complex load using strain. The method according to claim 1, wherein the creep life consumption fraction and the fatigue life fraction are constant in order to evaluate the service life of a mechanical equipment in which creep and fatigue work simultaneously. An automatic life assessment method of a mechanical equipment subjected to a complex load using a strain, characterized by introducing a fatigue interaction index (a, b) to be expressed as follows.