JPH02136737A - Evaluating method for remaining service life of high temperature apparatus parts - Google Patents

Abstract

PURPOSE:To predict with high accuracy a fatigue crack generation service life in high temperature apparatus parts by evaluating a fatigue remaining service life by using an X-ray diffracting method or a hardness measurement. CONSTITUTION:First of all, the inspection surface is formed on a surface layer of high temperature apparatus parts to be inspected. By irradiating this inspection surface with an X-ray, width at half max. from its diffraction line or a distribution of hardness is derived at the time point of the number of repetitions N1, N2. Subsequently, based on the drived width at half max. or hardness, a width at half max. ratio to initial width at half max. or a hardness ratio to initial hardness is derived at the time point of the number of repetitions N1, N2. Next, a rate of change beta of the width at half max. ratio or the hardness ratio between the number of repetitions N1, N2 derived by them is derived. Thereafter, the number of repetitions NC by which a microcrack is generated and a crack propagation speed da/dN (a and N denote a distance from the surface to the tip of a crack and length of the crack, and the number of repetions, respectively) are derived from an expression I and an expression II.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a method for evaluating the remaining fatigue life of high-temperature equipment parts such as a high-temperature rotor of a steam turbine using X-ray diffraction or hardness measurement. Regarding.

[Prior Art] Research on fatigue detection and remaining life evaluation methods using X-ray diffraction has a long history, for example, as described in the Proceedings of the Japan Society of Mechanical Engineers [Hirata and Honda, 2B (1'1132) 4582]. ing. Figures 10 and 11 are diagrams for explaining the contents shown in the above paper, and Figure 10 is
It shows the relationship between the X-ray diffraction intensity and the diffraction angle 2θ determined by the line diffraction method. In FIG. 10, the X-ray diffraction intensity curve H
The half width (the width of the diffraction angle 2θ at 1/2 height of the peak of the intensity curve) is measured.

Figure 11 shows the number of rupture cycles N on the horizontal axis based on numerous experiments.
Repetition number ratio N / N r when 1 repetition number is N
In addition, the vertical axis is the half-width ratio b/B between the spread b of the X-ray diffraction line (often expressed as the half-width in Figure 10) and B before the fatigue test. . As is clear from this figure, regardless of the magnitude of the repeated stress, it can be approximated by a straight line.

However, the relationship depends on the material, and Fig. 11(a) shows that
An example of annealed carbon steel, which has a repetition rate of N/N
This is a case where the half width ratio b/B increases as r increases. FIG. 11(b) is an example of carbon steel that has been previously subjected to plastic working, in which the half width ratio b/B decreases as the repetition rate ratio N/N r increases.

JP-A-56-87849 (hereinafter referred to as the known example) shows a method that develops the idea of the above paper and calculates the remaining life using the fracture of the part to be inspected as the life. . Figures 12 to 17 are for explaining known examples, and Figure 12 shows the relationship between the remaining life and the half-width ratio obtained from the above-mentioned paper, and the horizontal axis shows the remaining life N, It is on the vertical +B-bl axis, and X', Y' and Z'
show cases where the stress amplitudes are σ, σ, and σ3, respectively. The first idea is that in a range where the remaining life is short, that is, after a certain number of stress cycles have been carried out,
It is shown that the value of -b also becomes almost constant as the value of the stress amplitude changes, which indicates that it is possible to set A11J for 8 and have a margin for the remaining life. It goes like this-
b 1 The remaining life can be measured by determining the relationship between the remaining life and and creating a master curve in advance.

Figure 13 shows the master curve, for example, for 5FA55 turned material.The horizontal axis shows the remaining life N, the vertical axis shows the half-width ratio -bB, and the black circle is 10φ. , white circles are those obtained for a 20φ sample. In this way, the master curve differs depending on the heat treatment conditions and processing conditions, so
Find a master curve for each case (and, for example, by giving a program to a computer to compare the measured half-width of the test sample with the master curve of the test sample, you can calculate the remaining lifetime of the test sample. can be found from the master curve in Fig. 13.For example, in a machine part using 5FA55 that has been turned, if the half-width ratio is, for example, 0.1 from Fig. 13, the remaining life is approximately 10
If it is 5 cycles and the half width ratio is 0.04, the remaining life is predicted to be approximately 3×10 6 cycles.

FIG. 14 shows the relationship between the number of repetitions and the half width. The horizontal and vertical axes of this figure show the number of repetitions Ω, respectively.
ogN, the half width is taken, E and F indicate the case of processed material and annealed material respectively, and the number of repetitions Ωog
Between N and half width is b −AN ogN + B
The relationship (2) holds true, and the relationship between the half width change rate IAI and the number of rupture cycles N can be expressed by a single line regardless of whether the material is annealed or processed.

FIG. 15 shows the relationship between the number of rupture cycles Nr and the half-width change rate IAI during the fatigue process, which was determined for 5FA55 annealed material and turned material. When predicting the remaining life N using FIG. 15, the half-width b1 is determined by al1 at a certain number of repetitions N1, and the half-width b2 is determined by /l1ll at a certain number of repetitions N, Half width change rate A-(b-b2)/(N o
gNl-ΩogN 2 ), the number of rupture cycles N1 can be determined using FIG. 15, and the remaining life at N2 can be predicted as Nr-N, -N2, and the half-width change rate is 0. If it is less than 02, the load stress amplitude is less than the fatigue limit, and it can be determined that the remaining life is sufficient.

Fig. 16 is a diagram showing the measurement position of the half-width when a crack exists. Half-width -b is measured at the measurement position of the crack tip, and this half-width ratio is equal to the crack growth rate d.
The relationship between a/dN (where a is the distance from the surface to the crack tip and is called the crack length, and al indicates the crack length) is as shown in FIG. 17. The horizontal and vertical axes of this figure cover a wide range of crack growth rates da/dN, where m and n are clearly related to material constants. Therefore, if the half width b1 of the crack tip is measured at a certain number of repetitions N,
From the relationship shown in Figure 17, the crack growth rate (da/dN) 1
can be determined, and by measuring the half width of the crack tip several times at a certain number of repetition intervals, a crack growth curve can be created.

According to the conventional example described above, it is possible to evaluate the remaining life of a structure in which fatigue strength is a problem.

Note that half-width and hardness exhibit the same behavior when it comes to fatigue damage in high-temperature equipment, so even if the half-width described above is replaced with hardness, or the half-width ratio is replaced with hardness ratio, the results will be the same. I can say that.

[Problem to be solved by the invention] Traditionally, most thermal power generation facilities have been operated for many years with few monthly starts and stops, but very recently they have shifted to frequent starts and stops, such as daily starts and stops. ing. In such cases, it is necessary to estimate the remaining lifespan by considering the following points.

(1) The half-value width before fatigue is unknown, as it may have changed over many years of operation with few startups and stops.

(2) For unit operation, there are several starting methods as shown in Fig. 18, and the stress varies depending on the starting method, and the actual unit is operated with seven combinations of these methods.

In addition, Cr-Mo-V forged steel is used as a material for the rotor of steam turbines, and this is
As shown in the figure, during the fatigue process under constant strain cyclic conditions, there is a clear dependence on the cyclic strain range, and (3) when a small strain range is repeated, the half-width does not change in the early stage of fatigue.

(4) Half width does not change in the latter half of the process leading to rupture.

was recognized.

That is, regarding (1) above, the 13th known example mentioned above
It is difficult to determine the half-width ratio and remaining life shown in the figure. In the above-mentioned known example, it is necessary to determine B before use, but B is not measured before use of the actual machine that requires actual inspection. Therefore, it is necessary to obtain B at the current point in time when the device is in use.

Furthermore, in the event (4) above, the half-width does not change in the latter half of the process leading to fracture, so it does not occur as shown in FIGS. 12 and 14. For this reason, it is not possible to organize as shown in FIG.

On the other hand, although clear cracks are observed before rupture, the life span must be measured at the time of crack initiation, not at rupture.

As described above, in the above-mentioned known examples, the fatigue life of high-temperature equipment parts such as the rotor of a steam turbine cannot be accurately estimated.

Therefore, it is an object of the present invention to provide a method for evaluating the remaining life of high-temperature equipment parts, which can accurately predict the fatigue crack initiation life of high-temperature equipment parts.

[Means for Solving the Problems] In order to achieve the above object, the present invention is as follows. That is, step A of forming an inspection surface on the surface layer of a high-temperature equipment component to be inspected, and irradiating the inspection surface with X-rays and measuring the half-width or hardness distribution from the diffraction line over a number of repetitions N and N. Based on the half-width or hardness obtained at step B, the half-width ratio between the initial half-width or the initial hardness is determined by the number of repetitions N and N.
The half-width ratio or the hardness ratio change rate β between the process C obtained at the time point and the number of repetitions N and N2 obtained in the above steps B and C, and the Rimicro ( The number of repetitions N at which microscopic cracks occur.

and a step E of determining the crack propagation velocity da/dN.

(N −N )β −01 CO However, n and C1 are material constants, and No is the number of repetitions at which the half width ratio or hardness ratio changes from 1.0.

da/dN-C2β-C3 C, C and m are material constants.

[Function] By doing the above, the present invention makes it possible to predict the micro fatigue crack initiation life and crack propagation speed in the material change region that occurs at the initial stage of fatigue damage, leading to micro cracks. It is possible to evaluate the remaining life.

[Examples] Examples of the present invention will be described below, but first an outline of the present invention will be explained. In order to complete the present invention, fatigue tests were conducted using a tensile compression fatigue testing machine in various strain repetition modes at actual operating temperatures. Figure 3 shows the method, in which fatigue tests are carried out up to the various stages leading up to rupture, the specimen is removed, various fatigued test specimens are created, and the half value of these specimens is Width and hardness (scale was attached to the surface, so the surface was removed, but it was necessary to cut and measure at the center section), as well as cracks on the surface side of the test piece in cross section. These observations were made in detail to determine whether there are any rules for changes in half-value width and hardness due to fatigue and crack behavior.

Figure 4 shows the results. Since the half width and hardness b do not change when a crack of approximately 0.5 m11 or more occurs, the 71 p] constant results for a greater number of repetitions are omitted. In addition, in Fig. 4, 0, 01 mm and O
, the number of repetitions at which a 1 mm crack occurred is also shown.
The following can be said from Figure 4.

(b) When the half-width and hardness are plotted against the logarithm of the number of repetitions, they do not change at the initial stage of fatigue and remain flat, but after a certain number of repetitions N, changes appear and they become almost constant relative to the logarithm of the number of repetitions. Decrease linearly.

(b) In constant strain repetition, the larger the strain amplitude, the smaller the number of repetitions N, and the greater the slope (hereinafter referred to as β) of the number of repetitions with respect to the logarithm.

(c) For example, when the strain ranges Δε and Δε3 are combined, the half-width and hardness do not fall between the change lines observed in fatigue when Δε1 and Δε3 are constant, and the number of repetitions N is The number of repetitions N when the large amplitude Δεl is constant. It may become smaller than. However, the slope β is Δε1 or Δε3
It falls within the range of constant slope and remains almost constant during the process.

Therefore, the number of repetitions N at which a crack depth (0.01 mm) occurs, which is considered to be the limit that can be judged with a metallurgical microscope.

I investigated changes in the 14 value range or hardness. The half-width and hardness during this period are schematically the fifth
It will look like the figure.

At the initial stage of fatigue, repeated strain causes changes in the material structure characteristic of fatigue, but considering that it does not contribute to crack initiation, the above N is an invalid number of repetitions. Further, it is considered that the half width or the slope (rate of change) β of hardness with respect to the logarithm of the number of repetitions corresponds to the magnitude of effective strain energy contributing to crack initiation. Then, the following relationship is considered to hold.

(N - N ) β - C, (1) CO Therefore, the data were organized using equation (1), and as shown in Figure 6, the results are as follows: When n is approximately 2.5, N during various fatigue processes is estimated. It turns out it can be done. Similarly, cases with different crack depths were investigated, and although n was different, the number of repetitions of crack occurrence could be expressed using equation (1) in all cases.

Next, we investigated a formula for displaying the propagation speed da/dn (the depth of a crack that propagates in one repetition), which is a microscopic crack that is difficult to discern only with a metallurgical microscope.

The display formula was possible using formula (2). This result is the seventh
Shown in the figure.

da/dn=c β -C3 (2) Furthermore, C, m, and C3 are material constants. Here, how to obtain the constants of equations (1) and (2) will be explained.

The constant (N - N ) β0-01 in equation (1) is based on the observation results of 5 CO types of fatigue test processes. N - N and β are determined for each, and then n is Calculate (N − N ) β by changing the 5 types C
Obtain n such that the results of class O show approximately constant values.

In addition, the average value of (N - N) β0 at that time is C0 It becomes C1.

The constant da/dN-Cβ1-C3 in equation (2) was determined experimentally based on similar observation results.

From the above, there is a method to measure the half-width or hardness using an actual machine and predict the number of repetitions at which macroscopic cracks occur, which is considered to be the end of life, and the number of repetitions at which various damage conditions appear in the preceding stages. Can be provided.

Note that cracks that are difficult to identify only with a metallurgical microscope can be detected by using the replica method and the method of creating a special observation surface, which will be described later.

However, the problem lies in how to determine the rate of change β. In other words, choose an appropriate time and do it twice or more in total.
(In addition to performing 111, the half width or hardness must be displayed as a ratio to the initial value.

Regarding the latter, Japanese Patent Application Laid-Open No. 61-21 filed by the present applicant
27411 (Japanese Patent Application 1986-53796) and Japanese Unexamined Patent Application 1986
-247238 (Japanese Patent Application No. 61-90025) may be used.

That is, as shown in FIG. 8, the bottom of the outer circumferential groove is polished very shallowly and horizontally, and then subjected to electric field polishing to obtain an observation surface.

Then, both ends of the observation surface touch the hard scale of the rotor, but their positions are extremely close to the surface of the rotor base material. In addition, the central part of the observation surface exposes the base material that is deeper than the surface. The groove bottom is also a stress concentration area, and fatigue is concentrated near the surface.

Therefore, if the half-width or hardness H is measured in the horizontal direction on the observation surface, the value should be small at both ends and a horizontal distribution should be obtained at the center, as shown in FIG. 9th
The figure is a distribution diagram of the half width or hardness H with respect to the measurement position X, and explains that the center is flat and that value H is the initial value B, and that the extrapolated value H is set as b. . In other words, this shows that the central part is not subjected to fatigue, and can be set as the initial value B of the half-width or hardness obtained there. As shown in the figure, the half-width at the surface or the hardness H can be obtained by extrapolating from the data plot points.

If the above method is used, even if the half-width or hardness when not in use is unknown, the half-width ratio or hardness ratio that is desired by current measurement can be determined.

Next, examples of the present invention will be described. FIG. 1 is a flow chart for explaining the method of the present invention, and FIG. 2 is a diagram showing the relationship between the logarithm of the number of repetitions used in the method of the present invention and the half width ratio (or hardness ratio).

(1) When carrying out the method of the present invention, first create a graph of the half width ratio (or hardness ratio) on the vertical axis and the number of repetitions (logarithmic display) on the horizontal axis, as shown in Figure 2. Draw a line parallel to the horizontal axis at a position corresponding to the half value ratio (or hardness ratio) of 1.0.

(2) Next, the inspection surface shown in FIG. 8 is prepared for the high-temperature equipment component to be inspected, and the measurement shown in FIG. 9 is performed. The number of stress repetitions that this part received during this special trip is assumed to be N1 times.

From this result, the half-width or hardness B at that point and the initial half-width or initial hardness B are obtained, and their ratio b/B is determined. This is the measured value (b
/B), and plot it on the graph against the number of repetitions N1 (N2).

(3) Then, choose an appropriate time and use the same U as the first time.
j is determined (N3). This is the second measurement value (b/
B) Plot on a graph against the number of repetitions N2.

(4) Connect the first plot point and the second plot point to find the slope β (N4).

(5) Next, extend that line to make the half-width ratio of term (1) 1.0
Find the intersection with the line and set the number of repetitions to N (N4
).

N can be calculated using equation (3) from the slope β determined above, the number of repetitions N at which the change appears, and the material constant n' determined separately (N5). In addition, the crack propagation velocity after N 2 is determined from equation (4), and the crack initiation life of the defined length (for example, 0.5 mm) is determined.

(6) N2kuN. If no, please use the replica method to observe micro-cracks (S7)
, measure its length (N8), calculate the crack propagation velocity using equation (4) (N9), and estimate the remaining life up to a certain length (for example, 0.5+am) defined by the crack (S1
0).

(7) N2 × N at N6. If YES, the remaining life until crack initiation is estimated (Sll).

(8) Operation is then performed (S12), and it is determined whether N<N or not (313). At this time, if the answer is no, the process returns to step 312, and if the answer is yes, the process proceeds to S7.

According to the examples described above, when evaluating the remaining fatigue life of a steam turbine high-temperature rotor, it is possible to predict the micro fatigue crack initiation life and crack propagation speed in the material change region that occurs at the early stage of fatigue damage. This makes it possible to evaluate the remaining life at each stage up to the occurrence of severe cracks.

In other words, it is possible to determine the lifespan from when no cracks have occurred until microscopic cracks occur (e.g. 0.01 mm) and the crack growth lifespan up to a defined length (e.g. 0.5 rm). can.

In the above embodiment, the object to be inspected is a high-temperature rotor of a steam turbine, but the object to be inspected is not limited to this, but any high-temperature equipment part that is a large rotating machine and is made of a material exhibiting similar material behavior may be used.

[Effects of the Invention] According to the present invention, it is possible to provide a method for evaluating the remaining life of high-temperature equipment parts, which can accurately predict the fatigue crack initiation life of high-temperature equipment parts.

[Brief explanation of the drawing]

Figure 1 is a flowchart showing one embodiment of the method of the present invention, Figure 2 is a diagram showing the logarithm of the number of repetitions and the half value ratio (or hardness ratio) used in the method of the present invention, and Figure 3 is the same diagram. Figure 4 is a diagram showing the relationship between the half-width or hardness and the occurrence of cracking in the strain patterns of each company as an example; , a schematic diagram showing the change in half-width or hardness up to the number of repetitions N at which micro-cracks occur. FIG. indicates C
Figure 7 is a diagram showing that there is a linear relationship between the crack propagation velocity and the exponential shape of the half-width change rate or hardness change rate, as the same example, and Figure 8. Figure 9 shows the method for preparing the inspection surface for determining the initial value of the half-width or hardness used in the method of the present invention. Distribution diagrams, Figures 10 and 11 are diagrams for explaining an example of a conventional method for evaluating remaining life using X-rays, and Figure 10 is
Line explanation Diagram showing the spread of the line at half maximum and number, 1st
Figure 6 shows the measurement position of the half width when a crack exists.
Fig. 17 is a diagram showing the relationship between the half width ratio and the crack propagation speed, Figs. 18 and 19 are diagrams for explaining the problems of the conventional example, and Fig. 18 is a schematic diagram showing the difference in the starting method.
FIG. 19 is a diagram showing the relationship between the half width and the number of repetitions in the fatigue process under constant strain repetition conditions. Relationship diagrams between half-value width ratio and repetition rate ratio showing the case of carbon steel subjected to plastic working in advance, and Figures 12 to 17 are diagrams for explaining other examples of the remaining life evaluation method using X-rays. 12 is a diagram showing the relationship between the remaining life and the half width ratio, and FIG. 13 is a diagram showing the relationship between the remaining life and the half width ratio, and FIG.
B-b Diagram organized by I/B, Figure 14 is an explanatory diagram of the half price width change rate in Figure 12, Figure 15 is the half price width change rate and repeat applicant patent attorney Takehiko Suzue 10th mouth 12th douhiki (logN) 140th! splitting employment (mountain / dN) 180th 180th 13th stone 7L storage, * and number (N ↑) No. 15

Claims (1)

[Scope of Claims] Step A of forming an inspection surface on the surface layer of a high-temperature equipment component to be inspected; irradiating the inspection surface with X-rays and repeating the half-width or hardness distribution from the diffraction line; Process B obtained at the time points N_1 and N_2 and the half-width ratio with the initial half-width or the hardness ratio with the initial hardness based on the half-width or hardness obtained in this step B are repeated for the number N_1 and N_2. Step C, which calculates the rate of change in the half-width ratio or hardness ratio between the repetition numbers N_1 and N_2 obtained in steps B and C, and the micro (fine) ) A method for evaluating the remaining life of high-temperature equipment parts, comprising a step E of determining the number of repetitions N_C at which no cracks occur and the crack propagation speed da/dN. (N_C-N_O)β^n=C where n and C_1 are material constants, and N_O is the number of repetitions at which the half-width ratio or hardness ratio changes from 1.0. da/dN=C_2β^m-C_3 C_2, C_3 and m are material constants.