JPH07174681A - Method for evaluating damage of high-temperature structural member - Google Patents

Abstract

PURPOSE:To accurately evaluate the superposed damage of fatigue by forming the database of relationship between the creep damage for each material state and due to accumulated the fatigue damage, and the presence probability in advance and then creating the damage map of presence probability distribution for an actual machine measurement value. CONSTITUTION:The relationship between the creep damage for each material state and the fatigue damage is optimally approximated by a polynomial in advance, the relationship between the approximation coefficient and a material state absolute value is obtained, and then the presence probability near the approximation line is calculated to form a database. Then, the presence probability distribution corresponding to the amount of material state which is measured from an actual machine is obtained for the types of the amount of material state. All presence probabilities on the damage map of the amount of all material states plotting the presence probability distributions are added to obtain an addition damage map. Points with the same presence probability on the map are connected by a contour line, a damage map considering the scattering in data is completed, and then the coordinates at a part with the highest presence probability result in creep and fatigue damages, thus accurately evaluating damage based on the evaluation of a subject.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a damage evaluation method for high temperature structural members used at high temperature for a long time.

[0002]

2. Description of the Related Art Structural members of equipment such as steam turbine boilers and casings that are used for a long time at high temperatures are subject to both creep damage accumulated mainly in steady operation and fatigue damage accumulated during start-up and shutdown. receive. Accurate estimation of these damage amounts is very important for stable operation of high temperature equipment.

One of the conventionally established damage evaluation methods is one in which the damage rate and the remaining life are calculated and calculated based on the amount of use condition such as the temperature and pressure indicating the use condition of the equipment and the number of start and stop times. -27377, Japanese Patent Publication No. 1-27
It is disclosed in Japanese Patent No. 378.

In order to obtain a highly accurate damage evaluation result by calculation, it is necessary to complete measurement data such as material data structure member operation history, temperature, pressure, etc. It is difficult to obtain reliable measurement data due to the limited number of measurement points. In addition, there are various assumptions at the stage of calculation, the evaluation tends to be uniform, and it is difficult to obtain the damage characteristics peculiar to structural members. Moreover, the damage evaluation takes too much time and cost.

Therefore, in recent years, attention has been focused on a method of estimating the degree of damage to a material from the change in the material state quantity measured nondestructively. For example, the entity evaluation method based on the change in the amount of material state in the metallographic structure is that the technique of the replica method for nondestructively observing the metallographic structure is improved, and the accuracy of the image processing technology is improved.
As a result of the simplification, reliability and simplicity are dramatically improved.

Therefore, a method has been proposed in which hardness or void is used for creep damage evaluation and microscopic crack length of several microns to several millimeters is used for fatigue damage evaluation. For example, there is a creep damage evaluation diagram showing the relationship between Vickers hardness decrease amount and creep damage rate, and a fatigue damage evaluation diagram showing the relationship between maximum crack length and fatigue damage rate. There has also been proposed a method of diagnosing the degree of damage by using information obtained non-destructively from a structural member using sound, etc.

[0007]

However, the damage evaluation method based on the calculation described above requires complete measurement data such as operation history, temperature, and pressure of the material data structure member. It is difficult to obtain reliable measurement data due to problems such as measurement accuracy and limited measurement points. In addition, there are various assumptions at the stage of calculation, and there is a problem that it is difficult to obtain damage characteristics peculiar to structural members. Moreover, damage evaluation takes too much time and cost.

In addition, there is a problem that the damage state of each plant is hard to appear in the figures in the damage evaluation by the calculation of the large-sized computer from the data such as the past operation history and the design state quantity.
In addition, the plant user's resistance to not taking samples from the actual machine entity is strong.

Further, the above-described method of diagnosing damage by associating only one non-destructively measured material state quantity with creep damage or fatigue damage is an index that originally depends on both creep and fatigue, and one damage amount is used. Because it only relates to
The application is limited only when the effect of the other damage amount is small.

In other words, although it is possible to perform damage diagnosis and residual life evaluation of a material that has been experimentally given only one of the damages, it is possible to evaluate accumulated damages such as creep damages and fatigue damages as in the actual machine. Is insufficient. In other words, in the damage evaluation of the high temperature structural member of the actual machine, even if the change in the material state quantity is caught, whether it is due to creep,
There is a problem that it is difficult to surely evaluate whether it is due to fatigue.

By the way, recently, as a method for evaluating a wide range of creep damage, fatigue damage and creep superimposed damage caused by the interaction of both of them, as shown in FIG. 5, in indication (I) and indication (II), , The different material state quantities a and b measured non-destructively, and the relationship between the creep damage amount (φc) and the fatigue damage amount (φf) are obtained by an experiment in advance, and for each difference of the predetermined material state amount. Display the relationship between creep damage amount and fatigue damage amount as a contour map,
Further, a band A surrounded by contour lines a ₃ , a ₄ and b ₄ , b ₅ sandwiching the measured values of the material state quantities a, b of the actual structural member,
B is displayed, and further, in the display (III), among the displays (I) and (II), the bands A and B of the material state quantities a and b of the actual structural member and the region R where they intersect are displayed. Region R
A damage evaluation method for a structural member, which evaluates the amount of creep damage and the amount of fatigue damage of an actual structural member from the coordinates of, has been proposed by the applicant as Japanese Patent Application No. 5-106291.

[0012] In this creep fatigue superimposed damage evaluation method using damage mapping, since it is displayed that the existence probabilities in the region R are exactly the same, there are many errors in obtaining the optimum damage value. Existence probability in region R is 100%, region R
The existence probability outside is 0%, which is not a flexible and practical evaluation.

The present invention has been made in consideration of the above-mentioned circumstances, and provides a damage evaluation method for a high-temperature structural member capable of highly accurately evaluating creep fatigue superimposed damage based on nondestructive measurement directly on an actual machine. The purpose is to

[0014]

In order to achieve the above-mentioned object, the inventors of the present invention firstly conducted in advance in a laboratory a creep damage amount φ.
Several kinds of test pieces with known c and fatigue damage amount φf are created, and the material state quantity αi is measured by two or more kinds of nondestructive methods for each test piece. Next, the abscissa represents the relationship between the creep damage amount φc and the fatigue damage amount φf for each material state amount α.
Plotted for each i, and the same value αij of each material state amount αi
The plot point of the combination of the creep damage amount φc and the fatigue damage amount φf in (1) is approximated by the curve of the equation 1.

[0015]

[Equation 1] For example, n values α11, α12, ..., α of the material state amount α1
When h = 3 for 1n, creep damage amount φc
And the amount of fatigue damage φf are obtained as shown in Equation 2.

[0016]

[Equation 2] Subsequently, the relationship between Kh (αi) and αi is approximated by Equation 3 from Kh (αij) and αij thus obtained.

[0017]

[Equation 3] For example, in the above example of the material state quantity α1, the coefficient Kh of Equation 1 is
Becomes Equation 4.

[0018]

[Equation 4] The determination factors Kh1 and Kh2 of Kh (αi) are obtained for each of these material state quantities αi and are stored in a database.

Further, the distribution form of the measured quantity of the material state quantity is investigated in advance by a preliminary test, and the probability on the damage map is calculated over the entire damage map so that the points on the equation 3 are assumed to be 100%. Then, it is stored in the computer as an α damage map, and the material state quantities β, γ, and
... and β damage map, γ damage map, etc. for all material state quantities are calculated, stored on a computer, the stored damage maps are added over the entire map to create an additive damage map, The high part is set as 100% and the whole is represented by a number from 0 to 100. Points showing the same existence probability on the additive damage map are connected by a smooth curve, and the coordinates showing the highest existence probability are covered as a contour line display of the existence probability. It is characterized by creep damage and fatigue damage in the diagnostic department.

According to a second aspect of the present invention, the distribution of the state quantity data, which is different for each material and for each exposure temperature, is checked in advance for the variation of the material state quantity investigated when the laboratory deteriorated material was prepared.
The feature is that the optimum distribution type is selected from the distribution database.

[0021]

In the present invention having the above-mentioned structure, the most probable creep damage amount and fatigue damage amount can be determined in consideration of the damage in which creep and fatigue are superimposed by the material state amount measurement of the material to be evaluated, In addition, the existence probability distribution in the vicinity can be obtained. In other words, it is possible to perform highly accurate damage evaluation based on physical evaluation, unlike the conventional damage evaluation method, which does not require a high-level calculation device and is completely nondestructive for damage evaluation of creep fatigue superimposed damage load part. It can be performed.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

In the following examples, a case will be described in which the consumption life of a steam turbine high pressure casing (CrMoV cast steel) material, in which many forms of superimposed damage of creep and fatigue have been recognized in the past, is estimated.

FIG. 1 is a diagram showing a procedure for creating a master database according to this embodiment. In FIG. 1, step S1
Then, the creep damage known in the laboratory and the fatigue damage known in advance are applied as a creep fatigue superposition test (tensile holding fatigue test).

Next, in step S2, the material structure of the test piece is sampled by a nondestructive investigation using a replica, and the A parameter, which is one of the quantified indexes of voids that reflects the damage accumulation state of creep alone, from this sampled structure. (Number of damaged grain boundaries / total number of grain boundaries) The value α is measured. Various creep damages and fatigue damages are given by changing the above-mentioned superposition test conditions, and the A parameter values are measured respectively.

In step S3, this measurement result is plotted on a damage map of abscissa: creep damage, ordinate: fatigue damage, and all points showing the same A parameter value are optimally approximated by a quadratic expression to obtain expression 5. (Step S4).

[0027]

[Equation 5]

In the present embodiment, a quadratic equation is adopted as a polynomial equation, but it is generally expressed in the form of equation 1.

Next, in step S5, the relationship between the A parameter α value and the quadratic approximation coefficients A, B, and C shown in equation 5 is approximated by a linear equation to obtain equation 6.

[Equation 6]

In parallel with this work, step S6
Then, we investigated the dispersion of measurement data from the deteriorated materials in the laboratory, constructed a distribution database, applied statistical theory,
Identify the distribution of data. Above steps S1
Up to S6 is one database construction procedure.

In step S7 and step S8 in the same procedure, a database is constructed for other material state amount maximum crack length (β) and Vickers hardness reduction amount ratio (γ).

FIG. 2 is a flow chart showing the procedure of a method for evaluating damage to the actual machine diagnosed portion using the master database constructed in FIG.

First, in step S11, the material state quantities α , β , γ of the portion to be diagnosed are measured. The letters underlined mean that they are measured values from the part to be diagnosed. Substituting the measured values α 1 , β 2 , and γ into Equation 5, φc and φf
The correlation coefficients A, B, and C with and are calculated for all three types of material state quantities (step S12).

Then, the relationship between φc and φf is drawn from the correlation coefficient calculated in step S12 (step S13). The thick line in the figure represents the calculated relational expression between φc and φf. In addition, the existence probability in consideration of the distribution form of the data investigated in advance is shown in the figure. That is, when a certain material state quantity is measured from the measured portion, if the absolute value is input, a diagram showing the damaged state of the measured portion is drawn together with the existence probability distribution.

Finally, if the existence probabilities represented in the damage map for each material state quantity are added on the computer, one added damage map is obtained (step S14). The point with the highest existence probability on this additive damage map is 100
%, The entire map is displayed as a numerical value from 0 to 100, and points having the same existence probability are connected by a smooth curve in a contour line to complete a damage map in consideration of data variations. The coordinates of the part with the highest existence probability are the creep damage (φc) and fatigue damage (φ) of the measured part of the actual machine.
f) (step S15).

When a single creep damage is imparted to this material, the creep damage is accumulated in the grain boundaries to form a structure in which minute voids are generated in the crystal grain boundaries, and the voids are connected and grow into a crack, which finally becomes a crack. Breaks. Therefore,
In the case of creep independent damage, it can be arranged by the A parameter which is an evaluation index of grain boundary damage. However, when fatigue is added to the creep independent damage, the degree of increase in the A parameter is larger than that in the case of the creep independent damage due to the influence of fatigue.

In FIG. 3, the horizontal axis represents the amount of creep damage (φc) and the vertical axis represents the amount of fatigue damage (φf), showing the difference between the correlation curves of the two depending on the type of damage applied. In other words, it cannot be said that even a material state quantity that correlates with a single damage of creep or fatigue, or even creep fatigue superimposed damage, can be accurately evaluated. As typified by this example, there is no single material state metric for assessing creep fatigue superimposed damage.

In fact, it was not possible to accurately evaluate the creep damage and the fatigue damage by using the material state quantity used in this example as the A parameter, the maximum crack length, and the Vickers hardness reduction ratio alone.

FIG. 4 shows CrM according to the damage evaluation method of this embodiment.
It is a result of evaluating an actual deterioration material of oV cast steel. Also,
The results obtained by calculating the damage based on the usage state quantities such as the temperature and pressure indicating the usage state of the equipment and the number of times of starting and stopping are shown by black circles in FIG. From this figure, the damage evaluation result by careful calculation and the damage evaluation result of this embodiment are in agreement, and the method of this embodiment can accurately estimate the superimposed damage of creep and fatigue. Moreover, if future operation schedules are taken into consideration, remaining life diagnosis can be performed only by nondestructive measurement.

[0040]

As described above, according to the damage evaluation method for a high temperature structural member according to the present invention, the relationship between creep damage and fatigue damage for each material state quantity is optimally approximated in advance by a multi-dimensional equation, and The relationship between the approximation coefficient and the absolute value of the material state quantity is calculated, and the existence probabilities in the vicinity of the approximation line are calculated and stored in a database, and the existence probability distribution corresponding to the material state quantity measured from the actual machine is calculated. Number of types, the existence probabilities of all material states on the damage map are added, and the same points of the total existence probabilities on the additive damage map are connected by smooth contour lines. By setting the coordinates with high coordinates as the creep damage and fatigue damage of the part to be diagnosed, it is possible to evaluate the creep by the two or more kinds of material state quantities measured from the part to be evaluated of the material to be evaluated without needing to perform evaluation by calculation. Can be evaluated by separating the damage scratches and fatigue damage is superimposed respectively, it can also diagnose simultaneously accurate remaining life. Moreover, since the evaluation is performed in consideration of the existence probability, it is possible to make the evaluation more flexible than the evaluation by calculation.

The present invention also improves the nondestructive measurement method,
By constructing a database, it can be applied to all structural materials. Furthermore, the damage evaluation method of the present invention has shown a direction from conventional component management by one-dimensional damage evaluation to component management by multi-dimensional damage evaluation.

[Brief description of drawings]

FIG. 1 is a diagram showing a procedure for creating a master database in an example of a damage evaluation method for a high temperature structural member according to the present invention.

FIG. 2 is a flowchart showing a procedure of a method for evaluating damage to a real machine diagnosed portion using the master database constructed in FIG.

FIG. 3 is a diagram showing the relationship between creep independent damage, creep fatigue superimposed damage, and material state quantity (A parameter).

FIG. 4 is a diagram showing damage of the same actual machine by comparing the damage evaluation result according to the present embodiment and the damage evaluation result by calculation.

FIG. 5 is an explanatory diagram showing a method for evaluating creep fatigue superimposed damage of an actual machine diagnosed portion by a damage map area division method.

[Explanation of symbols]

 φc Creep damage amount φf Fatigue damage amount

Claims (2)

[Claims] 1. A damage evaluation method for a high-temperature structural member, comprising: a non-destructive measuring method for damage to a damage evaluation site where damages due to both creep and fatigue of a structural member used at high temperature are accumulated and accumulated. The relationship between creep damage and fatigue damage for each state quantity is optimally approximated by a multi-dimensional formula, the relationship between the approximation coefficient and the absolute value of the material state quantity is determined, and the existence probabilities near the approximation line are calculated respectively. Then, the existence probability distribution corresponding to the material state quantity measured from the actual machine is obtained by the number of types of material state quantity, and all the existence probabilities on the damage map of all material state quantities that describe those existence probability distributions are added. Then, the points with the same total existence probabilities on the additive damage map are connected by smooth contour lines, and the coordinates with the highest probability are the creep damage and fatigue damage of the part to be diagnosed. Method. 2. The determination of the existence probability distribution is characterized in that the distribution type of state quantity data that differs for each material and each exposure temperature is investigated in advance, and the optimum distribution type is selected from the distribution database. Item 1. A method for evaluating damage to a high temperature structural member according to item 1.