JPH09195795A - Remaining life evaluation method for gas turbine stationary blade and device thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reasonably evaluate the remaining life of a member by predicting growth of a crack generated on the member based on stress estimated from structural analysis, carrying out a breakdown test by the use of a micro-test- piece picked from the member in use, and obtaining critical crack length. SOLUTION: For evaluating the remaining life of a gas turbine stationary blade having possibility of generating a crack on the surface of the member in use, a parameter used for crack development analysis is computed by a breakdown dynamic parameter computer 2 based on stress computed by structural analysis 1, and a crack development curve is obtained from the parameter and material data 4 by a crack development analysis computer 3. The maximum crack length as the object of evaluation is obtained from inspection data 5, and the developing quantity in the depth direction is obtained from it and the result of crack development analysis. Further based on the breakdown test data 7 obtained from a micro-test-piece picked from the stationary blade, critical crack length is obtained by a critical crack length evaluation device 8, and the remaining life is obtained by a remaining life evaluation device 9 by totalling them.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for evaluating the remaining life of a stationary blade in a gas turbine, which is damaged by fatigue and creep and requires inspection and repair.

[0002]

2. Description of the Related Art A stationary blade of a gas turbine is used for starting a plant
Due to repeated thermal strain associated with the stoppage, a crack is generated on the surface of the member during use. Further, since it is used at high temperature for a long time, the material is deteriorated. Therefore, in order to prevent the plant from being stopped for a long time due to an accident or failure, the plant is stopped at an appropriate time and the members are inspected in order to maintain the safety of operation and the reliability of the equipment. With respect to the stationary vanes, investigations have been conducted on damage such as crack length and surface loss that occur on the surface. A standard value is set for each damage, and if it exceeds the standard value, measures such as replacement and repair can be taken. However, in order to ensure stable operation and reliability of equipment, it is necessary to understand the progress of future damage and deterioration, and some methods for predicting the progress of damage such as cracks and deformation have been proposed. .

[0003]

As described above, some methods for predicting the progress of damage have been proposed, but the limit value of damage is often empirically determined, and in some cases it may be excessive. In some cases, it is evaluated as safe. Further, since the inspection is regularly performed over several weeks by stopping the plant, there is also a demand for rationalizing the inspection work and shortening the inspection period in order to increase the operation rate of the plant.

The object of the present invention is to evaluate the deterioration of the material of a gas turbine stationary blade at the same time as the crack propagation analysis observed at the time of inspection, and obtain the maximum allowable crack length.
An object of the present invention is to provide a method and a device capable of performing a reasonable remaining life evaluation.

[0005]

As described above, since the allowable crack length decreases with the deterioration of the material, it is necessary to evaluate the deterioration.

The present invention is characterized by the following.

(1) In a method of evaluating the life of a gas turbine stationary blade, the growth of cracks occurring in a member is predicted based on the stress estimated from structural analysis, and a small test taken from the member in use. A fracture test is performed using a piece, the limit crack length is determined from the amount of decrease in the fracture energy, and the remaining life of the component is determined from the results and the crack length observed during inspection.

In (2) or (1), the parts are divided into several parts, the maximum crack length at each part is measured, and the remaining life is evaluated based on the crack length. And

In (3) or (1), the stress generated at the position where the crack exists is estimated from the crack length observed at the time of inspection and the operation history up to that time, and the stress value is estimated based on the stress value. The feature is that crack extension analysis is performed and the remaining life is obtained.

In (4) or (1), the relationship between the fracture energy obtained from the fracture test and the amount of change in the structure such as the amount of carbide precipitation is obtained, and the maximum length of the parts not subjected to the fracture test is It is characterized by observing the microstructure change in the vicinity of the crack, estimating the fracture energy from the above relation, and determining the critical crack length.

In (5) or (1), the relation between the decrease amount of the fracture energy obtained in the destructive test and the temperature and time is obtained in advance, and it is used from the result of the destructive test conducted at the time of inspection and the above relation. It is characterized by estimating the temperature of the member inside.

(6) Alternatively, in the residual life evaluation system for a gas turbine stationary blade, the crack growth analysis and the limit crack length can be analyzed by inputting the maximum crack length generated in the member and the result of the fracture test. It is characterized in that the amount of decrease in the data is estimated, the result is displayed, the input data is recorded in the database, and it is used as the data at the time of the next and subsequent inspections.

In the present invention, a minute test piece is sampled from the surface of the vane, and a destructive test is carried out to evaluate the deterioration and obtain the critical crack length. Further, considering damage to the stationary blade, when a crack penetrates the member and propagates until it opens, cooling air leaks through the crack, leading to loss of function. If even one crack penetrates, it is thought that such a thing will occur, so the problem is that the crack propagates to the deepest, and such a crack also has the maximum surface length. it is conceivable that. Therefore, at the time of inspection, it is only necessary to detect the maximum length crack and the crack that merges with the maximum length, and by doing so, it becomes possible to rationalize the inspection work.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. FIG. 1 is a basic block diagram of the present invention. Fracture mechanics parameter calculator 2 calculates the parameters used for crack growth analysis such as stress intensity factor and J-integral based on the stress calculated by structural analysis 1. A crack growth curve is required. On the other hand, the maximum crack length to be evaluated is obtained from the inspection data 5, and at that time, the amount of propagation in the depth direction is obtained from the crack growth analysis result. Furthermore, destructive test data obtained from micro test pieces collected from the vane 7
Based on the above, the limit crack length evaluation device determines the limit crack length. The remaining life is obtained by the remaining life evaluation device 9 by combining them.

FIG. 2 is a characteristic diagram of remaining life evaluation. By performing both damage growth evaluation and material deterioration evaluation due to long-term use, the remaining life evaluation is achieved and the remaining life is obtained. FIG.
The damage growth curve 10 is obtained by the flow from the structural analysis 1 to the crack growth analysis calculator 3 in FIG. 1, and the fracture test data 7 and the limit crack length evaluation device 8 obtain the curve 11 representing the decrease in the critical damage dimension. By evaluating together, the remaining life of the parts can be obtained. A detailed explanation of each of these tasks is given below.

FIG. 3 shows the procedure for obtaining the damage growth curve in FIG. First, the stress value of the problematic portion is obtained by the structural analysis 1 by the finite element method or the like. Since the problem here is the crack growth in the depth direction of the member, the stress distribution 12 inside the member is obtained. The stress intensity factor K, which is a fracture mechanics parameter, can be obtained by the polynomial approximation of such a stress distribution.

[0017]

[Equation 1]

Here, F ₀ , F ₁ , F ₂ , ... are the shape factors of the crack, A ₀ , A ₁ , A ₂ , ... are the coefficients of each term when the stress distribution is polynomial approximated, and a is The crack length, t is the plate thickness, and σ ₀ is the stress value on the outer surface of the member. Although the crack growth evaluation is performed based on this K value, in some cases, the stress intensity factor obtained by the equation 1 is converted into the J integral value J by the following equation, and the crack growth evaluation is performed based on the J value. It may be done.

[0019]

[Equation 2]

Several other formulas for the J-integral have been proposed, and other formulas may be used when the evaluation by the equation 2 is difficult. The K value or J value is destroyed by the above calculation. A relationship 13 between the dynamic parameter and the crack depth is obtained. For crack growth analysis, the relationship between this K value or J value and the crack growth rate da / dN

[0021]

(Equation 3)

It is necessary to experimentally obtain Number 3
C and m in the figure are constants obtained by experiments. Also, Δ in the formula is K value (J value) during one load cycle.
It shows that the fluctuation range is. The crack growth curve 15 can be obtained by substituting the K value and the J value obtained by the equation 1 or the equation 2 into the equation 3 and integrating them.

The actual damage of the vane varies depending on the vane because the operating conditions such as the combustion gas temperature vary depending on the mounting position. In structural analysis, it is very difficult to determine the stress value generated in the vane in consideration of them. Therefore, if the horizontal axis of the crack growth curve is standardized by an appropriate life such as the number of repetitions of a crack penetrating a member, the crack growth curve obtained analytically will be one curve regardless of stress. Therefore, the life ratio is obtained from the crack length observed at the time of inspection. Further, as shown in FIG. 4, crack growth curves are obtained for some stress values,
By estimating the stress generated in the member from the crack length at the time of inspection and the number of times of starting and stopping until then, it is possible to cope with the variation in the load condition for each stationary blade.

The data obtained during inspection is the surface length of the crack, and it is difficult to directly determine the actual crack depth.
The load generated on the stationary blade is a so-called thermal shock load, and the stress variation on the outer surface is larger than that on the inner surface. Therefore, the shape of the crack is also flat with the amount of propagation in the depth direction being smaller than the surface length. Therefore, the relationship between the crack surface length and the depth is obtained in the form as shown in Fig. 5 by performing the crack growth analysis and cutting the discarded blades, etc., and by using the relationship, at the time of inspection. From the observed crack surface length, the amount of propagation in the depth direction can be obtained.

Many cracks are generated in the stationary blade of the actual machine, but if there is even one crack that penetrates and is open, it will lead to a decrease in efficiency and reliability. It becomes a problem. It is considered that such a crack also has the largest surface length. Currently, all cracks that occur during inspection are measured and recorded, but the maximum length of crack is required for damage evaluation. Therefore, it is possible to reduce the amount of work at the time of inspection by measuring only a crack having a maximum length or a length close to it without measuring a minute crack. Note that the stress distribution and the like will differ somewhat if the parts within the vane are different, so as shown in FIG. 6, the vane was divided into several parts and attention was paid to the maximum crack length in each part. Progress evaluation is required.

FIG. 7 is an explanatory diagram of a destructive test conducted for evaluation of the limit crack length. The test piece 22 is typically 10 mm
The corner and the thickness of 0.5mm are used. Since the outer surface of the vane is exposed to the high temperature gas and the inner surface is cooled, it is considered that the deterioration of the material is concentrated near the outer surface. Therefore, for a stationary blade, evaluation using a test piece having such a small plate thickness is effective. A load-displacement curve as shown in FIG. 8 is obtained by applying a load to the puncher 19 and breaking the test piece. As the material deteriorates with use time, the maximum load of the load-displacement curve and the displacement at breakage become small. The fracture energy is obtained from the area under the load-displacement curve up to the maximum load, which is indicated by the diagonal lines in the figure. As shown in FIG. 9, if the relationship between the fracture energy and the fracture toughness value is obtained in advance, the reduction amount of the fracture toughness value is obtained by this fracture test, and the critical crack length is determined. In the critical crack length evaluation device of FIG. 1, the critical crack length is determined from the relationship shown in FIG. 9 and the stress and temperature obtained by structural analysis or the like.

Since this destructive test is performed by collecting test pieces from the actual machine vanes, it cannot be performed on all the vanes, and it is a sampling test with several vanes taken out, and no destructive test is conducted. With respect to the stationary blade, it is necessary to estimate the fracture energy by another method. FIG. 10 shows a schematic diagram near the surface of the vane where the material deterioration has occurred. Oxide layer 23 on the surface
It has been confirmed that not only is formed, but also carbides 24 are precipitated at the grain boundaries 25. It is considered that the precipitation of carbides is a major factor in material deterioration. Therefore, the relationship between the precipitation amount of this carbide and the fracture energy was obtained during the fracture test.For blades that were not subjected to the fracture test, the structure around the crack with the maximum length was observed by the replica method, etc. The fracture energy is estimated from the obtained carbide precipitation amount. Note that it takes a considerable amount of time and labor to observe the structure over a wide area, but in reality, the influence of deterioration on the growth of cracks poses a problem. Only the tissue observation should be performed. In addition, it is necessary to estimate the amount of decrease in the fracture energy after long-term use. Therefore, as shown in FIG. 12, the relationship between the aging time and the fracture energy is obtained under some temperature conditions, and the results of the fracture test are obtained. The temperature of the member is estimated from the operating time until then, and the amount of reduction in the fracture energy after long-term use is obtained based on that temperature.

FIG. 13 is a diagram showing the results of the residual life evaluation of the stationary blade based on both the crack growth evaluation and the material deterioration evaluation as described above. The crack growth curve can be obtained by obtaining the stress value from the crack length observed at the time of structural analysis or inspection, calculating the fracture mechanics parameter, and performing the crack growth analysis. Further, the reduction amount of the critical crack length is obtained from the fracture energy obtained by the fracture test. The intersection of these curves becomes the life, and the remaining life is obtained from it and the current damage amount. The remaining life evaluation apparatus 9 of FIG. 1 performs the work shown in FIG. The critical crack length is obtained from the fracture toughness value at that time, and the fracture toughness value is a function of temperature, stress and crack length. That is, the critical crack length is determined from the crack length observed during structural analysis or inspection and the stress and temperature values estimated by the fracture test and the fracture toughness value. Since the amount is much smaller than the surface length, it is necessary to evaluate the critical crack length considering both depth and surface length.

In the present embodiment, some material data on crack growth and material deterioration are required, and these data will basically be obtained by experiments, but based on the crack length observed at the time of inspection and it. The estimated stress, the fracture energy obtained from the fracture test, the number of times of starting and stopping, the operating time, etc. are recorded as a part of the data in the material database 4 and are used at the time of the next inspection.

[0030]

As described above, according to the present invention, it is possible to evaluate the growth of damage by the crack propagation analysis observed at the time of inspection and the critical crack length by the fracture test for the gas turbine stationary blade, and the accurate remaining life can be evaluated. It will be possible. Also, by paying attention to the maximum crack length, the inspection work can be rationalized and the operation rate can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram of the method of the present invention.

FIG. 2 is a characteristic diagram of remaining life evaluation.

FIG. 3 is a flowchart of crack growth analysis.

FIG. 4 is a characteristic diagram showing a change in a crack growth curve due to stress.

FIG. 5 is a characteristic diagram showing a relationship between a crack surface length and a depth in a stationary blade.

FIG. 6 is an explanatory view showing an example of partial division of a stationary blade at the time of inspection.

FIG. 7 is an explanatory diagram of a destructive test.

FIG. 8 is a characteristic diagram showing a load-displacement curve obtained in a destructive test.

FIG. 9 is a characteristic diagram showing the relationship between fracture energy and fracture toughness value.

FIG. 10 is an explanatory view of the structure of the stationary blade after being used for a long time.

FIG. 11 is a characteristic diagram showing the relationship between fracture energy and carbide precipitation amount.

FIG. 12 is a characteristic diagram showing a change in a breaking energy decrease curve with temperature.

FIG. 13 is a characteristic diagram showing the result of evaluation of remaining life of a stationary blade.

[Explanation of symbols]

1 ... Structural analysis, 2 ... Fracture mechanics parameter calculator, 3 ... Crack growth analysis calculator, 4 ... Material database, 5 ... Inspection data, 6 ... Crack depth evaluation device, 7 ... Fracture test data, 8
... Limit crack length evaluation device, 9 ... Remaining life evaluation device.

Claims (6)

[Claims] 1. A method of evaluating the life of a gas turbine vane, in which a crack growth occurring in a member is predicted based on a stress estimated from a structural analysis, and a micro test piece collected from a member in use. A gas turbine characterized by conducting a destructive test using a crack energy, determining the limit crack length from the amount of decrease in the fracture energy, and calculating the remaining life of the component from the results and the crack length observed during inspection. A method for evaluating the remaining life of a stationary blade. 2. The component according to claim 1, wherein the part is divided into several parts, and the maximum crack length at each part is measured,
A method for evaluating the remaining life of a gas turbine stationary blade, which evaluates the remaining life based on the crack length. 3. The crack growth analysis according to claim 1, wherein the stress generated at the position where the crack exists is estimated from the crack length observed at the time of inspection and the operation history until then, and the crack growth analysis is performed based on the stress value. A method for evaluating the remaining life of a gas turbine stationary blade by performing the above. 4. The relationship between the fracture energy obtained from the fracture test and the amount of change in the structure such as the amount of carbide precipitation obtained in the fracture test according to claim 1, and the parts not subjected to the fracture test are tested in the vicinity of the maximum length crack. A method for evaluating the remaining life of a gas turbine stationary blade by observing the microstructural change, estimating the fracture energy from the above relationship, and determining the critical crack length. 5. The member in use according to claim 1, wherein the relationship between the amount of decrease in the breaking energy obtained in the destructive test, the temperature, and the time is previously obtained, and the result of the destructive test performed at the time of inspection and the above relationship are used. Life Residue Evaluation Method for Gas Turbine Stator Blades that Estimates the Temperature of Engines. 6. A crack propagation analysis and a reduction amount of a limit crack length by inputting a maximum crack length generated in a member and a result of a fracture test in a residual life evaluation apparatus for a gas turbine stationary blade. The gas turbine stationary blade residual life evaluation device is characterized in that the estimated results are displayed, the input data is recorded in a database, and the data is used as data for the next and subsequent inspections.