JPH10170416A - Method for evaluating creep life of high-temperature device material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the amount of a material to be collected and evaluate a creep life in a short time accurately, by measuring an effective stress of the collected material and calculating a creep life consumption rate on the basis of a relation diagram of the effective stress and creep life consumption rate investigated and formed beforehand for the material. SOLUTION: A material collected from an optical part of a high-temperature device is processed to an effective stress test piece 1 and heated to a predetermined temperature in a test container 2. A tensile stress as an initial stress is applied to the test piece 1 (weights 3, 4 are loaded). Approximately 10% of the loaded stress is removed from the test piece 1 being deformed due to a creep (the weight 4 is removed). When a distortion of the test piece 1 is received to not smaller than a distortion immediately after the stress is rapidly reduced, approximately 10% of the load is again removed. The procedures are repeated several times. An effective stress is measured in this manner, and a creep life consumption rate is calculated on the basis of a diagram of a relation of the effective stress and creep life consumption rate investigated and formed beforehand for the martial.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method using a small number of samples.
The present invention relates to a method for evaluating the creep life of high-temperature equipment materials, which can accurately measure the creep life consumption rate in a short time.

[0002]

2. Description of the Related Art Methods for evaluating the creep life consumption rate and remaining life of high-temperature equipment materials are roughly classified into two methods: a nondestructive test method and a destructive test method. Non-destructive inspection methods include the use of dye penetrant inspection, magnetic inspection, or ultrasonic inspection to check for cracks and defects on the surface and inside, defect inspection, and the creation of creep voids by collecting replicas from the target site. And a metallographic evaluation method for estimating the life consumption rate from the distribution state and morphological change of precipitates. On the other hand, in the destructive test method, a miniature creep test piece was sampled from a portion used for a long time in a high-temperature device, and a long-term creep rupture test was performed at an arbitrary stress and temperature to estimate a remaining life.

[0003]

The problems in the creep life consumption rate and remaining life evaluation methods of these prior art high temperature equipment materials are as follows. (1) In a nondestructive inspection method such as a dye penetration inspection method, a magnetic inspection method, or an ultrasonic inspection method, it is difficult to quantify the creep life consumption rate only by investigating the presence or absence of a defect. (2) The metallographic evaluation method is the most active and useful method in creep life evaluation, but it is difficult to evaluate the life with high accuracy in the first half of the life when the number of creep voids generated is small. (3) The destructive test method of conducting a creep rupture test using a material collected from an actual machine is most useful for estimating the remaining life, but the test is performed over a long period of time and under several conditions. Therefore, a large number of materials must be collected from high-temperature equipment.

The present invention has been made in view of the above circumstances of the prior art, and has as its object to provide a creep life evaluation method for high-temperature equipment materials that requires a small amount of material to be collected from an actual machine and enables accurate evaluation in a short time. is there.

[0005]

According to the present invention, there is provided a method for evaluating the creep life using a material collected from a high-temperature device. In this method, the effective stress of a material collected from an arbitrary portion to be measured of the high-temperature device is measured. A creep life evaluation method for a high-temperature equipment material, wherein a creep life consumption rate is calculated based on a relationship diagram created by examining a relationship between an effective stress and a creep life consumption rate of a material.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION An effective stress is a stress that contributes to the deformation of a material (a stress effectively acting to move dislocations) among applied stresses. There is a relationship between effective stress = load stress−internal stress. The internal stress is a reverse stress acting in the opposite direction to the applied stress, and represents the deformation resistance of the material itself. The internal stress is determined by the distribution of the precipitates and the dislocation structure. The finer the precipitates are dispersed, the smaller the subgrain (subcrystal grain) size, and the orientation of the subgrain boundary (subcrystal grain boundary). The greater the difference, the greater the internal stress.

In the present invention, there is a certain relationship between the effective stress of the material and the creep life consumption rate. A preliminary test is performed on a specific material, and a relationship diagram (calibration curve) showing the relationship between the two in advance is shown.
Is based on the finding that creep life can be evaluated only by measuring the effective stress of the material. According to the method of the present invention, by measuring the effective stress of a material using a material collected from a high-temperature device actually operated, for example, a high-temperature device material used at a high temperature of about 500 to 650 is used. Can be evaluated.

In the method of the present invention, a sample having a creep life consumption rate of several steps for a specific material (for example, 10%
Life-consuming material, 20% life-consuming material,...).
Here, the creep life consumption rate is defined as a 10% life consumption material obtained by applying a stress for 10% of the creep rupture time at that temperature and stress.
If the material is 000 hours, 10
The sample from which the stress was unloaded at the time when 0 hour had passed was used as a sample. Then, a stress drop test described later is performed using these samples to measure the effective stress, and a relation diagram between the obtained effective stress and the creep life consumption rate of the used sample is created.

In evaluating the creep life of a sample taken from an actual machine, creep life is measured only by measuring the effective stress of the sample by using a relationship diagram between the effective stress and the creep life consumption rate prepared in advance for the material. Life evaluation can be performed. As described above, since the effective stress is a value obtained by subtracting the internal stress from the applied stress, if the stress changes, the effective stress also changes. In the present invention, the creep life is evaluated based on the increase and decrease of the effective stress due to the change of the internal stress. Therefore, it is necessary to keep the applied stress constant at the time of creating the relationship diagram and at the time of measuring the sample taken from the actual machine.

Next, a method for measuring the effective stress will be described with reference to FIG. FIG. 1A is a diagram showing dimensions and shapes of test pieces used for measurement, and FIG. 1B is an explanatory diagram showing a measurement method. The measurement is performed according to the following procedure. (1) A material collected from an arbitrary portion of a high-temperature device is processed into a test piece 1 for measuring an effective stress, and a predetermined temperature (usually a temperature near the actual use temperature or use of the actual device for an acceleration test) in the test container 2 Temperature slightly higher than the temperature). (2) An arbitrary tensile stress (usually a stress of about 50% of the proof stress of the test material at the test temperature at which the effective stress is measured) is applied as an initial stress to the heated test piece (weights 3 and 4).
Load). (3) The initial load stress from the test piece during creep deformation is 1
Instantly unload about 0% (unload one of the unloading weights 4). After unloading, the metal material starts creep deformation immediately after the elastic displacement decreases, the deformation stays, or the strain decreases for a certain period despite applying tensile stress. , Then begin to increase. (4) When the strain of the unloaded test piece recovers to a level equal to or higher than the strain immediately after the sharp decrease in stress, the stress of about 10% is unloaded again (the second unloading weight 4 is unloaded). (5) This procedure is repeated several times (that is, several steps of unloading a stress of about 10%).

FIG. 2 shows an example of a change in strain after a sharp decrease in stress of 9% Cr steel. After the stress drop, the strain on the specimen decreases for a period of time and then begins to increase. Here, the time (deformation residence time) until the strain of the test piece recovers to the strain after the stress suddenly decreases is measured. Note that the graph of FIG. 2 is a continuous graph (the magnitude of the final distortion corresponds to the starting point).
FIG. 2 shows the range up to the range where the deformation residence time can be measured. In this example, the next unloading is performed after the strain is recovered to a strain higher than the strain before unloading.

FIG. 3 shows a method for determining the effective stress. Here, the abscissa plots the 乗 power of the deformation residence time and the ordinate plots the stress reduction rate, that is, the value of (unloading stress) / (initial stress). A linear relationship is established between the two, and the stress at which the deformation residence time becomes zero is the effective stress. That is, when a part of the stress applied to the material undergoing the creep deformation is suddenly reduced, the strain behaves as follows due to the sudden decrease. (1) When the sudden decrease in stress is equal to the effective stress, the force acting on dislocations in the material becomes zero, and the deformation stays. (2) When the amount of sudden decrease in stress exceeds the effective stress, a negative force acts on dislocations in the material, and creep deformation in the opposite direction is observed (strain is reduced). (3) If the amount of sudden decrease in stress falls below the effective stress, the state in which positive force acts on dislocations in the material continues.
Immediately after the stress suddenly decreases, the strain increases. Therefore, the stress at which the deformation residence time becomes zero is the effective stress. This effective stress is the stress that actually contributes to the deformation of the material among the applied stresses.Using a material under high temperature stress reduces the internal reverse stress, that is, the deformation resistance of the material. To increase. The data in FIG. 3 corresponds to FIG. 2. Since the unloading stress / initial stress = 0.06 at the position where the deformation residence time is 0, the effective stress is 0.06 × 140.
(MPa), that is, 8.4 MPa.

Next, a description will be given of a method for creating a relationship diagram between life and effective stress. First, a creep life consuming material of several stages is produced by a constant load creep rupture tester. afterwards,
The effective stress is measured by a stress drop test using the above materials (each life consuming material) in the above-described procedure, and a relationship diagram between the effective stress and the creep life consumption rate is obtained.

FIG. 4 is a graph showing the relationship between the creep life consumption rate and the effective stress of the 9% Cr heat-resisting steel thus obtained. The experimental data shown in FIGS. 2 and 3 are experimental results of a 10% life consuming material.
This corresponds to a plot of 0%. As described above, the effective stress is the stress that actually contributes to the deformation of the material among the applied stress, and the use of the material under high temperature stress reduces the internal reverse stress, that is, the deformation resistance of the material, Effective stress increases. Therefore, by preparing such a relation diagram in advance, the life consumption rate and the remaining life of the metal can be evaluated.

The dashed line in FIG. 4 shows the effective stress of 9% Cr heat-resistant steel which has been used for a long time as a heat transfer tube of a thermal power plant boiler. Since the effective stress of the material used in the actual machine is 37 MPa, the creep life consumption rate of this material determined from the relation diagram of FIG. 4 is about 50%. 600 ° C for the same material used in the actual machine,
As a result of conducting a creep rupture test at 140 MPa, 48
It broke in 00 hours. The average fracture time at 600 ° C. and 140 MPa of an unused material of 9% Cr heat-resistant steel measured this time is about 10,000 hours, and the creep life consumption rate obtained by the most reliable fracture test method by the conventional method is 100. ×
(10000-4800) / 10000 = 52%. As described above, the creep life consumption rate obtained by the method of the present invention is substantially the same as that obtained by the conventional method, and it can be seen that the creep life evaluation can be performed with high accuracy by the method of the present invention.

[0016]

According to the method of the present invention, the following effects can be obtained. (1) Since the result is obtained in a shorter time than the conventional destructive test method, feedback to the actual machine can be performed quickly. In addition, since the test time is short, it is advantageous in terms of cost. (2) Since the measurement of the effective stress can be performed with one test piece, the amount of material collected from the high-temperature equipment target portion may be small. For this reason, work such as repair welding after material collection is simplified.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an outline of a method for measuring an effective stress.

FIG. 2 is an explanatory diagram showing an example of a result of an effective stress measurement test.

FIG. 3 is an explanatory diagram showing a method of calculating an effective stress from a measurement result of the effective stress.

FIG. 4 is a relationship diagram showing a relationship between effective stress and creep life consumption rate.

Claims (1)

[Claims] In a method for evaluating creep life using a material collected from a high-temperature device, an effective stress of a material collected from an arbitrary measurement target portion of the high-temperature device is measured, and the effective stress and the creep life of the material are measured in advance. A creep life evaluation method for a high temperature equipment material, wherein a creep life consumption rate is calculated based on a relation diagram created by examining a relation with a consumption rate.