JPH1019204A - Creep lifetime evaluating method for high temperature apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a creep lifetime evaluating method for a high temperature apparatus which can obtain reliable data with a small number of samples in a short test time. SOLUTION: A plurality of thermocouples 4 are mounted on a parallel portion of a test piece 3 in an axially spaced-apart manner. The temperature distribution on the entire parallel portion of the test piece 3 is estimated from temperatures monitored by these thermocouples 4. Upon completion of a rupture test, a creep damage rate on at least one portion of the parallel portion with an exception of the ruptured portion is obtained by observing a change in micro structure thereof and a change in hardness thereof. The rupture time is estimated from the creep damage rate and the creep test time, and the relationship between the rupture time and the operation temperature is obtained from the rupture portion and the change in the microstructure and hardness.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for evaluating the creep life of materials for equipment such as a boiler used at a high temperature.
In particular, the present invention relates to a creep life evaluation method for high-temperature equipment in which the life is evaluated by a creep rupture test performed by taking a sample.

[0002]

2. Description of the Related Art It is well known that materials used for a long time under high temperature and high pressure, such as thermal power plants and chemical plants, are deteriorated due to creep, fatigue or aging damage during operation. Have been. Such deterioration of the material is governed by the metal temperature of the material used, the acting stress, and the operating time. In a boiler for thermal power generation, considering these governing factors, a life of 100,000 hours is usually maintained. Designed for However, in recent years, the number of boilers operating beyond the design life has increased,
In addition, even if the operation time is within 100,000 hours, an accident that the material is damaged due to an increase in the metal temperature due to the drift of the combustion gas or abnormal deterioration of the material due to segregation in the material may occur. ing. From such a background, a technique for extending the life of a plant by accurately predicting the remaining life of the material and performing systematic replacement and repair of the material is becoming important. In particular, in high-temperature equipment that has been used for a long time, creep damage tends to progress, and damage evaluation for creep is important. Techniques for estimating the creep life of materials are roughly classified into destructive and nondestructive methods. The destruction method is a method of directly estimating the creep life by taking a sample from a site to be evaluated and performing a creep rupture test, so that a highly accurate diagnosis is possible. To estimate the remaining life by the destruction method, the parameter method and the iso-stress method are mainly used. In the parameter method, the creep rupture test is performed under different conditions of stress and temperature, and the test results are arranged by temperature and time parameters. Various temperature and time parameters have been proposed, but the Larson-Mil
The ler parameter is most often used. That is, P = T · (c + logtr) where P: Larson-Miller parameter T: absolute temperature (K) tr: creep rupture time (h) c: constant As shown in FIG.
The relationship between the Larson-Miller parameter and the stress (logarithmic representation) is plotted on a graph, and the used stress of the site where the sample is taken is substituted to obtain the Larson-Miller parameter value.
The remaining life is determined by substituting the operating temperature at the sampling position for that value.

On the other hand, in the Iso-stress method, a creep rupture test is carried out by changing the temperature conditions under the working stress of the site where the sample is taken, and as shown in FIG. 8, the temperature and the rupture time (logarithmic display) are determined. This is a method of estimating the remaining life by creating a graph and extrapolating to the operating temperature of the site where the sample was taken. It has been confirmed that the relationship between temperature and rupture time (expressed in logarithm) for ferritic materials is substantially linear (for example, R. Viswanathan: Damage Mechanisms and Life)
Assessment of High Temperature Component).

It is said that this method is a temperature accelerated test at a working stress at a sample collection site, so that the life can be evaluated more accurately than the parameter method. However, since the creep rupture test must be performed under various temperature conditions, it is necessary to collect many samples from the site to be evaluated. In addition, in order to evaluate the remaining life, it is necessary to extrapolate to the temperature, and it is preferable to collect data up to the evaluation temperature, that is, a temperature range close to the use temperature of the sample collection site from the viewpoint of improving accuracy. However, performing a creep rupture test at a low temperature means that the test time is prolonged, and a test at a low temperature close to such an evaluation temperature is not practical.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to reduce the number of samples and test time in creep life evaluation of materials used for high-temperature equipment by the Iso-stress method.
An object of the present invention is to provide a creep life evaluation method for high-temperature equipment that can collect reliable data with a small number of samples in a relatively short time test.

[0006]

The above problems can be solved by the following method. A creep rupture test piece was prepared from a sample taken from the evaluation site,
A temperature gradient is provided in the parallel part of the test piece, and a creep rupture test is performed at the working stress at the sample collection site. Heating is performed with a plurality of heating wires of three or more systems, and a temperature gradient is applied to the parallel portion of the test piece by controlling the output of each heating wire. In order to evaluate in a short time, the test temperature (the highest temperature in this case to provide a temperature gradient) is a temperature higher than the operating temperature of the site where the sample was collected. During the creep rupture test, at least five or more thermocouples are provided in the axial direction of the parallel part of the test piece, the temperature is monitored, and the temperature distribution of the parallel part of the test piece is obtained based on the monitored temperature. Since the temperature continuously changes in the parallel part of the test piece, the part without the thermocouple was
The temperature is estimated by the complementary method, and the temperature distribution of the entire parallel part of the test piece is obtained. After the fracture of the test piece, the creep damage rate of at least one portion other than the fracture portion in the parallel portion is estimated by a remaining life diagnostic method based on a change in microstructure or a change in hardness.

[0007] The remaining life diagnostic method may be any method as long as it is technically established. However, since the creep damage other than the fractured portion is widely distributed from a low damage region to a high damage region, it is possible to evaluate the remaining life. A method that can evaluate the damage in the damaged area is preferable,
A method of comprehensively determining the remaining life from the results of metal structure change, degree of crystal grain deformation, degree of cavity formation, and hardness measurement (for example, a known technique disclosed in Japanese Patent Application No. 63-142268).
Is referred to as the “comprehensive evaluation method”. FIG. 6 is a diagram showing the flow of the “overall evaluation method”. In FIG. 6, the degree of crystal grain deformation (base material), the degree of cavity formation (welded portion), and the results of measurement of the properties and hardness of carbides by observation of the replied force are ranked according to the degree of damage, and the parameters of each parameter are determined. It is a comprehensive evaluation taking into account the degree of contribution to creep damage, and it is possible to evaluate the entire damage area.

After estimating the creep damage rate, the expected rupture time in the portion where the remaining life diagnosis was performed is calculated from the test time using the following equation.

Tri = t / φci tri: Estimated rupture time of the target part (h) φci: Creep damage rate of the target part t: Test time (h) By such a method, 1 Above the point, the temperature and the expected rupture time can be known. The temperature including the fractured portion and the expected fracture time (the fracture time is the fracture time) are plotted on a graph where the horizontal axis is the fracture time (logarithmic display) and the vertical axis is the temperature, and a regression line is determined from these plots. By extrapolating this straight line to the operating temperature of the sampling site, the creep life of the evaluation site is estimated.

[0010] A method of performing a creep rupture test by providing a temperature gradient in a parallel portion of a test piece is disclosed in Japanese Patent Publication No. Hei 6-70606. The purpose of this method is to prepare a test curve for evaluating the remaining life by examining the hardness and microstructure of the prepared sample. On the other hand, an object of the present invention is to estimate the remaining life of a material used for a long time by using a real shore. In addition, in the above-described known technology, the creep damage rate of a portion having a different temperature is calculated assuming that the Larson-Miller parameter value is the same because the stress is constant.
The ler parameter value is temperature-dependent, and an accurate creep damage rate cannot be calculated. On the other hand, in the present invention, since the creep damage rate other than the fractured portion is obtained by the technically established remaining life diagnosis method, highly accurate prediction is possible.

[0011] By combining the above-mentioned cleave rupture test, remaining life evaluation, and the iso-stress method, a small number of samples and a relatively short time test enable highly accurate creep of materials used in high temperature equipment. Service life can be evaluated.

In a creep rupture test provided with a temperature gradient,
Since the stress is constant, the parallel part breaks from the hottest part, but the other parts have a low temperature and the creep damage rate is not 100%. Therefore, by estimating the creep damage rate of a portion other than the fractured portion using a technically established remaining life diagnosis method, it is possible to calculate the expected fracture time of that portion. The expected rupture time is calculated by dividing the test time by the creep damage rate because the test time and the damage rate of the portion are known. According to such a method, several points of creep rupture data having different stresses and different temperatures can be collected with one test piece, and it is actually a long time test, so that it is difficult to collect data. Data in the low temperature range can be collected in a relatively short time.

[0013] From the creep rupture data of several points taken by one test piece, the remaining life of the sample material is Iso-stre
Estimate using ss method. All the collected data have a constant stress (use stress at the evaluation site), and the relationship between the temperature under a constant stress and the rupture time can be determined. Presumed.

[0014]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic view of a boiler secondary superheater outlet header where a sample is taken, FIG. 2 is a schematic view showing a creep rupture test method provided with a temperature gradient, and FIG. 3 is a parallel view of a test piece in a creep rupture test. FIG. 4 is a diagram showing the temperature distribution of the part,
FIG. 5 is a graph showing the calculation results of the temperature, creep damage rate, and expected rupture time of the parallel portion of the test piece, and FIG. 5 is a graph showing the relationship between the temperature and the rupture test.

As shown in FIG. 1, the test sample was cut out as a boat sample from the outlet of the outlet of the secondary superheater of the boiler for thermal power generation. Two test pieces were prepared from almost the same position so that two test pieces could be produced. A sample is being taken. The material is 2.25Cr-1Mo steel and the working temperature of the sampling site is 55.
At 4 ° C., the stress was 4.2 kg / mm ² . Standard dimensions (outer diameter of parallel part: 6mm, length: 3)
0 mm) round bar creep rupture test piece was prepared,
A creep rupture test was performed at 2 kg / mm ² . Heating 3
The test was carried out in an electric furnace having a heating wire of the system, and by setting the output of the upper heating wire 5 shown in FIG. 2 to be the highest, the temperature was set to be highest at the upper part of the parallel portion of the test piece. The maximum temperature was set to 670 ° C. (test piece A) and 630 ° C. (test piece B). Thermocouples 4 were provided at five locations on the test piece, and the temperatures during the test were measured. From these temperature measurement results, the temperature distribution of the two parallel test pieces was estimated as shown in FIG. The rupture position occurred at the highest temperature part, and the rupture time was measured for the test piece A (maximum temperature 67
The temperature was 168 h at 0 ° C.) and 1,624 h at test piece B (630 ° C. maximum temperature).

Next, 660 ° C., 650 ° C., 6
620 ° C, 610 ° C, 60
A site at 0 ° C. was selected, and the creep damage rate was estimated by the above-described comprehensive evaluation method. FIG. 4 shows a chart of the creep damage rate estimated by the comprehensive evaluation method and the estimated rupture time estimated from the damage rate and the test time. FIG. 5 shows the relationship between the temperature and the rupture time based on the results. The relationship between the temperature and the rupture time (logarithmic representation) is almost a straight line, and when a regression line is determined and extrapolated to 554 ° C., which is the operating temperature of the sample material, the rupture time is 172,000 h, which is the sampling position. Is the estimated remaining life. In order to confirm the reliability of this data, a creep rupture test was performed at 650 ° C. and 4.2 kg / mm ² using samples taken from the same place, and the rupture time was 855 h. It was equivalent to the expected rupture time of 840 h.

[0017]

According to the method for evaluating creep life of high-temperature equipment of the present invention, a large amount of creep rupture data can be collected with a small number of samples, and long-term rupture data can be predicted in a relatively short time. High-accuracy remaining life evaluation becomes possible. As a result, the industrial value according to the present invention is very high, for example, the repair / replacement time of the material used for the high-temperature equipment can be estimated at low cost and in a short time.

[Brief description of the drawings]

FIG. 1 is a schematic view of a boiler secondary superheater outlet header where a sample has been taken.

FIG. 2 is a schematic view showing a creep rupture test method provided with a temperature gradient.

FIG. 3 is a temperature distribution in a parallel portion of a test piece in a creep rupture test.

FIG. 4 is a table showing calculation results of temperature, creep damage rate, and expected rupture time of a parallel portion of a test piece.

FIG. 5 is a graph showing a relationship between a temperature and a breaking test.

FIG. 6 is a diagram showing a flow of a comprehensive evaluation method.

FIG. 7 is a diagram showing a remaining life evaluation by a parameter method.

FIG. 8 is a diagram showing a remaining life evaluation by the Iso-stress method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Secondary heater outlet header 2 ... Sample collection position 3 ... Creep rupture test piece 4 ... Thermocouple 5 ... Heating wire (upper) 6 ... Heating wire (middle) 7 ... Heating wire (lower)

Claims (1)

[Claims] In a creep life evaluation method for a high temperature device, a test piece is sampled from a creep life evaluation portion of the high temperature device, and a temperature gradient is provided in an axial direction of the parallel portion of the test piece and heated. The creep rupture test is performed under the operating stress conditions of the high-temperature equipment, and the creep damage rate of at least one portion excluding the rupture portion by the creep test is estimated from the change in the microstructure and the hardness. By calculating the rupture time from the damage rate and the creep test time, by obtaining the relationship between the temperature and the rupture time of the rupture portion by the creep test, and the location where the creep damage rate was estimated from the microstructure and hardness change, Creep life of high temperature equipment characterized by calculating the rupture time at the operating temperature of the creep life evaluation part of high temperature equipment Value method.