The present disclosure relates to a method for evaluating stress corrosion cracking of steam turbines.
Background technology
[0002]
It is known that in a device such as a steam turbine, stress corrosion cracking (SCC) occurs because components are exposed to wet steam in a high-temperature environment for a long period of time. As such stress corrosion cracking progresses, it causes problems in equipment. Therefore, it is required to predict the remaining life of equipment and appropriate maintenance timing by quantitatively evaluating the progress of corrosion.
[0003]
For example, in Patent Document 1, a sample (test piece) is prepared from the same material as the material of the part where stress corrosion cracking is concerned, and from the crack growth rate of the sample under the same environment as the part to be evaluated, the part to be evaluated A quantitative evaluation of stress corrosion cracking has been proposed.
prior art documents
patent literature
[0004]
Patent Document 1: JP-A-2001-305043
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0005]
In Patent Document 1 above, a sample is housed in a certain environment assumed from the operating environment of the evaluation target part, and stress corrosion cracking of the evaluation target part is evaluated based on the corrosion state of the sample. However, there is a considerable difference in temperature and humidity between the test environment of the sample and the operating environment of the part to be evaluated, which is the actual machine. Therefore, with such a method, there is a possibility that stress corrosion cracking in the evaluation target portion of the actual machine cannot be evaluated with high accuracy.
[0006]
In addition, in Patent Document 1 above, a test piece is produced from the same material as the evaluation target site. Therefore, in order to evaluate stress corrosion cracking using such a test piece, a test period equivalent to the period required for stress corrosion cracking to actually occur in the evaluation target portion, which is an actual machine, is required. .
[0007]
SUMMARY OF THE INVENTION At least one aspect of the present disclosure has been made in view of the above circumstances, and provides a method for evaluating stress corrosion cracking of a steam turbine capable of performing reliable quantitative evaluation of stress corrosion cracking quickly and accurately. With the goal.
Means to solve problems
[0008]
In order to solve the above problems, the steam turbine stress corrosion cracking evaluation method according to one aspect of the present disclosure includes:
a sample failure time acquisition step of acquiring the sample failure time of a sample that is housed in a steam turbine sample box and configured to have a higher susceptibility to stress corrosion cracking than the material to be evaluated for the steam turbine;
a failure time estimation step of estimating the failure time of the steam turbine based on the sample failure time;
Prepare.
The invention's effect
[0009]
According to at least one aspect of the present disclosure, it is possible to provide a method for evaluating stress corrosion cracking of a steam turbine that enables reliable quantitative evaluation of stress corrosion cracking to be performed quickly and accurately.
Brief description of the drawing
[0010]
1 is a schematic cross-sectional view of a steam turbine; FIG.
2A is a schematic diagram showing an example of a sample contained in the sample box of FIG. 1; FIG.
2B is a schematic diagram showing another example of a sample contained in the sample box of FIG. 1; FIG.
2C is a schematic diagram showing another example of a sample contained in the sample box of FIG. 1; FIG.
2D is a schematic diagram showing another example of a sample housed in the sample box of FIG. 1; FIG.
2E] A schematic diagram showing another example of a sample contained in the sample box of FIG. 1. [FIG.
3 is a block diagram showing the steam turbine evaluation device 100 of FIG. 1. FIG.
4 is a flow chart showing, step by step, a stress corrosion cracking evaluation method performed by the evaluation apparatus of FIG. 3. FIG.
[FIG. 5] An example of a master curve.
6 is a sub-flowchart of step S106 in FIG. 4; FIG.
7 is a diagram showing a comparison between a master curve and a corrected master curve; FIG.
8 is a diagram showing a comparison between a master curve and a corrected master curve when there are a plurality of measurement points; FIG.
9 is a diagram showing a characteristic function that defines the correlation of damage level normalized values with wetness. FIG.
MODE FOR CARRYING OUT THE INVENTION
[0011]
Several embodiments of the present invention will be described below with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of the components described as embodiments or shown in the drawings are not intended to limit the scope of the present invention, and are merely illustrative examples. No.
[0012]
FIG. 1 is a schematic cross-sectional view of the steam turbine 1. The steam turbine 1 includes a rotor 2 that rotates about an axis O, and a casing 4 that houses the rotor 2 so as to cover the rotor 2 from the outer peripheral side.
[0013]
The rotor 2 includes a rotor body 6 and turbine rotor blades 8 . The turbine rotor blade 8 is a row of rotor blades including a plurality of blade bodies 10 and a tip shroud 12, and arranged in multiple rows at regular intervals in the axis O direction. A plurality of blade bodies 10 are attached so as to extend radially from the rotor body 6 rotating about the axis O within the casing 4 , and are spaced apart in the circumferential direction of the rotor body 6 . Each of the plurality of blade main bodies 10 is a member having an airfoil-shaped cross section when viewed from the radial direction. The tip shroud 12 is an annular tip shroud that connects the tips (radial outer ends) of the plurality of blade bodies 10 .
[0014]
The casing 4 is a substantially cylindrical member provided so as to cover the rotor 2 from the outer peripheral side. A plurality of stationary blades 16 are provided on an inner peripheral surface 14 of the casing 4 . A plurality of stationary blades 16 are arranged along the circumferential direction of the inner peripheral surface 14 and along the axis O direction. Further, the turbine rotor blades 8 are arranged so as to enter the regions between the adjacent stator blades 16 .
[0015]
The casing 4 also includes a steam supply pipe 18 that supplies steam S as a working fluid from a steam supply source (not shown) to the steam turbine 1, and a steam discharge pipe that is connected to the downstream side of the steam turbine 1 and discharges the steam. 20 are connected. Inside the casing 4 , a region in which the stationary blades 16 and the turbine rotor blades 8 are arranged forms a main flow path 22 through which the steam S supplied from the steam supply pipe 18 flows. The steam S flowing through the main flow path 22 is received by the turbine rotor blades 8 to rotationally drive the rotor 2 (see arrow R). Rotation of the rotor 2 is output to the outside via a rotating shaft 24 connected to the rotor body 6 . The rotating shaft 24 is rotatably supported with respect to the casing 4 by a bearing portion 26 .
[0016]
A sample box 28 is also provided in the casing 4 . The sample box 28 includes a space 30 for containing the sample 50 used in the evaluation method described later, and an opening/closing portion 32 (for example, manhole or handhole) for putting the sample 50 in and out of the space 30 . The sample box 28 can be placed at any position on the casing 4, but for example, when the steam turbine 1 is in operation, the sample box 28 may be placed at a position that is in the same or close environment to the part of the steam turbine 1 to be evaluated. good. For example, the space 30 in which the sample 50 is housed is placed at a position where the temperature and humidity are the same or close to each other by communicating with the site to be evaluated. In the example of FIG. 1, the sample box 28 is arranged at a position adjacent to the main channel 22 through which the high-temperature steam S flows, so that the sample 50 contained in the sample box 28 is transferred to the steam S flowing through the main channel 22. It is configured to be placed in the same or similar environment as the exposed parts (turbine rotor blades 8 and stator blades 16).
[0017]
Also, the sample box 28 may be provided at a position within the casing 4 that is easily accessible from the outside so as to facilitate the loading and unloading operation of the sample 50, which will be described later. In this case, the opening/closing part 32 (for example, a manhole or a handhole installed on the flow path of the steam discharge pipe 20) is configured to be adjacent to a passage in the steam turbine 1 through which workers can enter and exit. The sample 50 can be easily taken in and out of the space 30 through the space 30 .
[0018]
Here, the samples 50 stored in the sample box 28 will be described (Samples 50A to 50E will be described below as examples of the samples 50, but these will be collectively referred to as samples 50). By using the sample 50 having such a configuration, it is possible to effectively simulate the constituent members of the steam turbine 1 in which stress corrosion cracking may occur.
[0019]
FIG. 2A is a schematic diagram showing an example of the sample 50A accommodated in the sample box 28 of FIG. Sample 50A includes two sample materials 52A, 52B in contact with each other and under stress. The sample 50A is configured such that two sample materials 52A and 52B, which are plate-like members, are bent and fixed with bolts 54, so that a stress equivalent to the yield strength can be applied to the two sample materials 52A and 52B. , so-called double U-bend specimens. In sample 50A, the two sample materials 52A, 52B are in intimate contact with each other without any gaps.
[0020]
The two sample materials 52A and 52B that make up the sample 50A include materials that make up evaluation target materials (for example, the rotor 2 and the turbine rotor blades 8) included in the steam turbine 1. The two sample materials 52A, 52B may consist of the same material as each other. For example, when the rotor 2 of the steam turbine 1 is to be evaluated, the two sample materials 52A and 52B are made of the same material as the rotor 2.
[0021]
Also, the two sample materials 52A and 52B may be made of different materials. For example, if the rotor main body 6 and the turbine rotor blades 8 constituting the rotor 2 are made of different materials, and the rotor main body 6 and the turbine rotor blades 8 come into contact with each other when combined, the dissimilar materials The contact may cause contact corrosion of different materials (galvanic corrosion), which progresses more rapidly. When such a portion is to be evaluated, the two sample materials 52A and 52B are formed from the materials constituting the rotor body 6 and the turbine rotor blade 8, respectively, so that different materials in the rotor 2 come into contact with each other. A sample 50 can be constructed that mimics the condition.
[0022]
FIG. 2B is a schematic diagram showing another example of the sample 50 housed in the sample box 28 of FIG. Sample 50B is configured as a double U-bend specimen similar to sample 50A shown in FIG. 2A, except that a gap 56 is partially provided between the two sample materials 52A, 52B. By using such a sample 50B, it is possible to perform an evaluation considering crevice corrosion that may occur in the steam turbine 1 .
[0023]
2C to 2E are schematic diagrams showing other examples of the sample 50 housed in the sample box 28 of FIG. Sample 50C shown in FIG. 2C is a tapered DCB (Double-Cantilever Beam) test piece, and crack growth can be evaluated while changing the acting stress by the thickness of the wedge. In particular, the tapered DCB test piece has the characteristic that the stress intensity factor hardly changes even if the crack length changes. A sample 50D shown in FIG. 2D is a branch-notch CT test piece, and crack initiation can be evaluated by applying a predetermined acting stress by changing the thickness of the wedge. A sample 50E shown in FIG. 2E is a pre-crack CT test piece, and crack growth can be evaluated while changing the acting stress by the thickness of the wedge. In this specimen, the stress intensity factor decreases as the crack length increases.
[0024]
Also, the samples 50 stored in the sample box 28 may contain a plurality of samples with different sensitivities. In general, the susceptibility of the sample 50 depends on the yield strength, and can be adjusted by, for example, high-strength processing or heat treatment when manufacturing the sample 50 .
[0025]
FIG. 3 is a block diagram showing the evaluation device 100 of the steam turbine 1 of FIG. Evaluation device 100 is, for example, an analysis unit for performing an evaluation of steam turbine 1 . The evaluation device 100 includes, for example, a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read
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5,000 character limit. Use the arrows to translate more.Only Memory), computer-readable storage media, etc. A series of processes for realizing various functions is stored in a storage medium or the like in the form of a program, for example, and the CPU reads out this program to a RAM or the like, and executes information processing and arithmetic processing. As a result, various functions are realized. The program may be pre-installed in a ROM or other storage medium, provided in a state stored in a computer-readable storage medium, or delivered via wired or wireless communication means. etc. may be applied. Computer-readable storage media include magnetic disks, magneto-optical disks, CD-ROMs, DVD-ROMs, semiconductor memories, and the like.
[0026]
The evaluation device 100 includes a sample failure time acquisition unit 102 that acquires the sample failure time, a storage unit 104 that stores the master curve 60, a correction master curve creation unit 106 that corrects the master curve 60, and the steam turbine 1 and a failure time estimation unit 108 that estimates the failure time of the steam turbine 1 and an evaluation unit 110 that evaluates the steam turbine 1 based on the failure time.
[0027]
Each block constituting the evaluation apparatus 100 shown in FIG. 3 is described corresponding to a function exhibited when an evaluation method to be described later is performed, and may be integrated with each other as necessary. and may be further subdivided. At least part of the configuration of the evaluation device 100 may be arranged at a position distant from the steam turbine 1 to be evaluated by being configured to be able to communicate via a network. For example, the evaluation device 100 may be arranged in a remote base station capable of network communication with the steam turbine 1, or may be configured as a cloud server.
[0028]
FIG. 4 is a flow chart showing the stress corrosion cracking evaluation method implemented by the evaluation device 100 of FIG. 3 for each process. In addition, although the stress corrosion cracking evaluation method described below is performed using the evaluation apparatus 100 described above, it may be performed by an operator without using the evaluation apparatus 100 .
[0029]
First, create a master curve 60 that defines the correlation between the susceptibility to stress corrosion cracking and the standard failure time (step S100: master curve creation process). Creation of the master curve 60 is performed by a breaking test using a plurality of test pieces. A plurality of test pieces used in the fracture test include the same material as the rotor material, which is an example of the material to be evaluated for the steam turbine 1, and have sensitivities different from each other. In this embodiment, a plurality of test pieces having the same shape as the sample 50 described above with reference to FIGS. 2A to 2E are prepared, and prepared so that each has a different sensitivity. A method of making the susceptibility of a plurality of test pieces different is generally carried out by performing strong working or heat treatment, since there is generally a correlation between susceptibility and yield strength.
[0030]
Then, by performing a rupture test on a plurality of test pieces having different sensitivities, the failure time of each test piece (hereinafter referred to as the failure time obtained in the rupture test to create the master curve 60 is the reference failure (referred to as time). A master curve 60 is created by linking the susceptibility and the reference failure time thus obtained.
[0031]
FIG. 5 is an example of the master curve 60. This master curve 60 is expressed as a function f(t, y) with susceptibility y and failure time t as variables, and shows a tendency that standard failure time t decreases as susceptibility y increases. The master curve 60 created in this manner is stored in the storage unit 104 in a readable manner. For example, the sensitivity on the vertical axis in FIG. 5 is the load stress of a test conducted by applying a stress corresponding to the proof stress using the test piece 50 with the proof stress varied. Alternatively, the material may be sensitized and used as the index on the vertical axis in FIG.
[0032]
Then, the sample 50 is stored in the sample box 28 (step S101). The samples 50 stored in the sample box 28 are configured to have a higher susceptibility to stress corrosion cracking than the steam turbine 1 to be evaluated. Specifically, the sample 50 having the shape described above with reference to FIGS. 2A to 2E is subjected to strong working or heat treatment to prepare the sample 50 whose sensitivity is adjusted. By using the sample 50 having higher susceptibility to stress corrosion cracking than the steam turbine 1 in this way, the sample 50 stored in the sample box 28 can be caused to undergo stress corrosion cracking before the steam turbine 1.
[0033]
A plurality of samples 50 may be accommodated in the sample box 28. In this case, the plurality of samples 50 may have sensitivities different from each other by adjusting the proof stress of each sample 50 by, for example, performing high-strength processing or heat treatment. The plurality of samples 50 may also include different aspects as described above with reference to Figures 2A-2E. By using such a plurality of samples 50, it is possible to consider the influence of differences in susceptibility and differences in sample shape on sample breakage time, thus enabling more detailed evaluation.
[0034]
Then, the operation of the steam turbine 1 is started with the sample 50 stored in the sample box 28 (step S102). During operation of the steam turbine 1 , corrosion of the steam turbine 1 progresses due to the steam S passing through the main flow path 22 . After the operation of the steam turbine 1 is started, the sample 50 is monitored for damage (step S103). For example, when maintenance of the steam turbine 1 can be performed at intervals sufficiently shorter than the assumed sample breakage time, the monitoring in step S103 is performed by a worker checking the state of the sample 50 in the sample box 28 during maintenance. It may be done by Alternatively, a damage state detection sensor may be attached to the sample 50 contained in the sample box 28, and the presence or absence of damage may be monitored by obtaining a detection signal from the damage state sensor. In this case, by configuring the damage state sensor to communicate with the evaluation device 100 by wire or wirelessly, the damage state of the sample 50 can be monitored without actually taking out the sample 50 from the sample box 28 . This enables real-time monitoring not only during maintenance of the steam turbine 1 but also during operation.
[0035]
When it is determined that the sample 50 is damaged (step S104: YES), the sample damage time obtaining unit 102 obtains the sample damage time (step S105: sample damage time obtaining process). The sample failure time is the elapsed time from the start of operation of the steam turbine 1 in step S102 to the discovery of failure in the sample 50 . For example, when a worker checks the condition of the sample 50 in the sample box 28 during maintenance and finds damage to the sample 50, the elapsed time from the start of operation of the steam turbine 1 to the time of checking is It may be regarded as breakage time. As described above, the sample 50 has a higher sensitivity than the steam turbine 1, so stress corrosion cracking develops sufficiently before the steam turbine 1, and it is possible to acquire the sample failure time required for evaluation. can.
[0036]
In addition, when a plurality of samples 50 are stored in the sample box 28 and damage occurs in the plurality of samples 50, the sample damage time acquisition unit 102 calculates the sample damage time for each damaged sample 50. may be obtained.
[0037]
Subsequently, the failure time estimation unit 108 estimates the failure time of the steam turbine 1 based on the sample failure time acquired by the sample failure time acquisition unit 102 (step S106: failure time estimation step). Although a specific method by the failure time estimating unit 108 will be described later, the sample failure time is obtained from the sample 50 stored in the sample box 28 of the actual steam turbine 1 to be evaluated. Effects on operating conditions, including temperature and humidity, are reflected. Therefore, by estimating the failure time of the steam turbine 1 based on such sample failure times, it is possible to evaluate the steam turbine with high accuracy.
[0038]
Subsequently, the evaluation unit 110 evaluates the remaining life or maintenance timing of the steam turbine 1 based on the damage time estimated in step S106 (step S107: evaluation step). Specifically, the evaluation unit 110 obtains the remaining life of the steam turbine 1 as the difference between the operation time of the steam turbine 1 up to the present and the damage time estimated in step S106. The evaluation unit 110 also obtains the remaining life of each component of the steam turbine 1, and obtains the implementation timing of maintenance work such as repair or replacement of each component based on the remaining life. Such evaluation results are effective in formulating a maintenance plan for preventing stress corrosion cracking in the steam turbine 1 .
[0039]
Next, the method of estimating the failure time of the steam turbine 1 in the failure time estimation process of step S106 will be described in detail. FIG. 6 is a sub-flowchart of step S106 in FIG.
[0040]
First, the failure time estimation unit 108 acquires the master curve 60 stored in the storage unit 104 (step S200). As described above with reference to FIG. 5, the master curve 60 is stored in the storage unit 104 in advance as a function that defines the correlation between susceptibility and standard failure time.
[0041]
Subsequently, the failure time estimation unit 108 corrects the master curve 60 acquired in step S200 based on the sample failure time acquired by the sample failure time acquisition unit 102 and the sensitivity of the sample 50 corresponding to the sample failure time. By doing so, a correction master curve 70 is created (step S201). Here, FIG. 7 is a diagram showing a comparison between the master curve 60 and the corrected master curve 70. In FIG. In FIG. 7, the horizontal axis indicates the failure time t, the vertical axis indicates the sensitivity y (proof stress), and the master curve 60 before correction acquired from the storage unit 104 is indicated as a function f(t, y). . FIG. 7 also shows the sample failure time acquired by the sample failure time acquisition unit 102 and the measurement point A (t1, y1) specified by the sensitivity of the sample 50 corresponding to the sample failure time. Assuming that the failure time corresponding to the sensitivity y1 on the master curve 60 is t2, the corrected master curve 70 is obtained by the following equation.
f'(t,y)=f(t*t2/t1,y)
That is, the correction in step S201 is performed to adjust the magnification of the master curve 60 in the horizontal direction so that the master curve 60 passes through the measurement point A (t1, y1). Although there are not a few differences between the environment (reference environment) in which the master curve 60 is created and the actual operating environment of the steam turbine 1, the master curve 60 is calculated based on the actual measurement points (t1, y1). By correcting the curve 60, it is possible to create a corrected master curve 70 that considers the influence of the difference between the two.
[0042]
In addition, when a plurality of samples 50 having different sensitivities are stored in the sample box 28 and there are a plurality of measurement points corresponding to each sample 50, the sample 50 corresponding to the fastest stress corrosion cracking progresses. The master curve 60 may be corrected based on susceptibility and sample failure time. FIG. 8 compares the master curve 60 and the correction master curve 70 when there are a plurality of measurement points A1 (t1-1, y1-1), A2 (t1-2, y1-2), . FIG. 4 is a diagram showing; In the example of FIG. 8, the sample 50 in which stress corrosion cracking progresses fastest is, for example, a plurality of measurement points A1 (t1-1, y1-1), A2 (t1-2, y1-2), . Among them, the measurement point A2 (t1-2, y1-2) located at the lower leftmost side is specified. Using the measurement point A2 (t1-2, y1-2) specified in this way as a reference, as in the case of FIG. can be estimated, the more reliable steam turbine 1
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5,000 character limit. Use the arrows to translate more.evaluation becomes possible.
[0043]
Next, the failure time estimation unit 108 acquires the sensitivity of the steam turbine 1 to be evaluated (step S202). Since the sensitivity generally corresponds to the strength, the sensitivity may be calculated by obtaining the strength of the steam turbine 1 in step S202.
[0044]
Subsequently, the failure time estimation unit 108 uses the corrected master curve 70 created in step S201 to obtain the failure time corresponding to the susceptibility of the steam turbine 1 acquired in step S202 (step S203). Referring to FIG. 7, when the sensitivity of the steam turbine 1 is y0, the failure time t0 of the steam turbine 1 is obtained based on the correction master curve 70. FIG.
[0045]
Subsequently, the failure time estimation unit 108 performs a first correction based on the reference temperature corresponding to the master curve 60 and the operating temperature of the steam turbine 1 for the failure time t0 obtained in step S203 (step S204: first 1 correction step). The first correction is performed by first calculating the time evaluation base value Δt based on the failure time t0 obtained in step S203. As shown in FIG. 7, the time evaluation base value Δt is obtained by combining the failure time t0 obtained in step S203 and the current sample failure time (since this step is the time when the sample failure time is obtained, the sample failure time current time).
[0046]
In the first correction, the time evaluation base value Δt is corrected based on the reference temperature corresponding to the master curve 60 and the operating temperature of the steam turbine 1 . For example, the parameters X1 and X2 corresponding to the test environment temperature T1 when creating the master curve 60 and the temperature T2 of the actual steam turbine 1 are obtained using Clark's equations (coefficients A, B, and C) below. (a is the crack length, σ0.2 is the 0.2% proof stress (or yield strength), and coefficients A, B, and C are constants defined based on conditions such as materials).
X1=ln(da/dt)=-A-B/T1+Cσ0.2
X2=ln(da/dt)=-A-B/T2+Cσ0.2
When T2>T1, the first correction value Δt' of the time evaluation base value Δt is obtained by dividing the time evaluation base value Δt by the ratio of X (X2/X1). The first correction value Δt′ calculated in this way can take into account the influence of the difference between the reference temperature of the master curve 60 and the temperature during operation of the actual steam turbine 1, and thus can evaluate the steam turbine with higher accuracy. becomes possible.
[0047]
The first correction value Δt′ of the time evaluation base value obtained in step S204 is further subjected to a second correction based on the reference wetness corresponding to the master curve 60 and the wetness during operation of the steam turbine 1 ( step S205: second correction step). In the second correction, a characteristic function f(s, D) that defines the correlation of the damage degree normalized value D with the wetness s is created in advance. FIG. 9 is a diagram showing a characteristic function f(s, D) that defines the correlation of the damage level normalized value D with the wetness level s. Here, using the test environment damage degree D1 when creating the master curve 60 and the assumed damage degree D2 of the actual steam turbine 1, the ratio between the two is evaluated. If D2>D1, the second correction value T'' is obtained by dividing the first correction value .DELTA.t' of the time evaluation base value by the ratio of D (D2/D1). By obtaining the second correction value T″ in this way, the effect of the difference between the reference wetness of the master curve 60 and the wetness during operation of the actual steam turbine 1 can be taken into consideration, and the steam can be produced with higher accuracy. Turbine evaluation becomes possible.
[0048]
In the embodiment, the case where the second correction is performed in step S205 after performing the first correction in step S204 is exemplified. Alternatively, only one of the second corrections may be performed. Further, in step S106, the damage time t0 itself calculated in step S3 may be output as an estimation result without performing the first correction and the second correction.
[0049]
As described above, according to the above-described embodiment, by using the samples 50 having higher susceptibility to stress corrosion cracking than the steam turbine 1, the samples 50 accommodated in the sample box 28 are subjected to cracking before the steam turbine 1. Stress corrosion cracking occurs. Therefore, using the sample 50 housed in the sample box 28 provided in the steam turbine 1, the sample failure time is acquired at a timing sufficiently before stress corrosion cracking actually occurs in the steam turbine 1, and the sample failure time is obtained. Based on this, the failure time of the steam turbine 1 can be estimated. Also, the sample failure time is obtained from the sample 50 housed in the sample box 28 of the steam turbine 1, which is the actual machine to be evaluated. Since the sample failure time reflects the influence of the operating conditions including the actual temperature and humidity of the steam turbine 1, the steam turbine 1 can be evaluated with high accuracy.
[0050]
In addition, it is possible to appropriately replace the components in the above-described embodiments with well-known components within the scope of the present disclosure, and the above-described embodiments may be combined as appropriate.
[0051]
The contents described in each of the above embodiments can be understood, for example, as follows.
[0052]
(1) A steam turbine stress corrosion cracking evaluation method according to one aspect includes:
A sample housed in a sample box (for example, the sample box 28 of the above embodiment) of a steam turbine (for example, the steam turbine 1 of the above embodiment) and configured to have a higher susceptibility to stress corrosion cracking than the evaluation target material of the steam turbine. a sample failure time obtaining step (for example, step S105 of the above embodiment) of obtaining a sample failure time of (for example, the sample 50 of the above embodiment);
a failure time estimation step (for example, step S106 in the above embodiment) of estimating the failure time of the steam turbine based on the sample failure time;
Prepare.
[0053]
According to the above aspect (1), by using a sample that is more susceptible to stress corrosion cracking than the steam turbine evaluation target material (for example, rotor material, moving blade material, etc.), the sample stored in the sample box , stress corrosion cracking occurs before the steam turbine. Therefore, by using the sample stored in the sample box provided in the steam turbine, the sample failure time is obtained at a timing sufficiently before stress corrosion cracking actually occurs in the steam turbine, and the steam turbine is based on the sample failure time. can be estimated. Also, the sample failure time is obtained from a sample housed in a sample box of the actual steam turbine to be evaluated. Such sample failure time reflects the effects of operating conditions including the temperature and humidity of the actual steam turbine, so it is possible to evaluate the steam turbine with high accuracy.
[0054]
(2) In another aspect, in the aspect of (1) above,
The sample has a higher strength than the material to be evaluated.
[0055]
According to the aspect (2) above, by increasing the strength of the material to be evaluated, the sensitivity of the sample can be made higher than that of the material to be evaluated.
[0056]
(3) In another aspect, in the above aspect (1) or (2),
The failure time estimation step is
By correcting a master curve that defines the correlation between the susceptibility and the standard failure time (for example, the master curve 60 of the above embodiment) using the susceptibility and the sample failure time of the sample used in the first step , a correction master curve creation step (for example, step S201 of the above embodiment) for creating a correction master curve (for example, the correction master curve 70 of the above embodiment);
a failure time identification step (for example, step S203 in the above embodiment) of identifying the failure time corresponding to the design yield strength of the steam turbine based on the corrected master curve;
including.
[0057]
According to the aspect (3) above, a master curve that defines the correlation between the susceptibility under the reference environment and the standard failure time is prepared in advance for the materials that make up the steam turbine. Due to the considerable differences between the master curve reference environment and the actual steam turbine operating environment, the master curve is corrected for the susceptibility and sample failure time of the samples contained in the steam turbine sample box. . By determining the failure time of the steam turbine based on the master curve corrected in this way, it is possible to evaluate the steam turbine with high accuracy.
[0058]
(4) In another aspect, in the aspect of (3) above,
In the sample breakage time acquisition step, the sample breakage time is acquired for a plurality of the samples with different sensitivities,
In the correction master curve creation step, the correction master curve is created by correcting the master curve based on the susceptibility and the sample failure time corresponding to the sample in which the stress corrosion cracking progresses fastest.
[0059]
According to the aspect (4) above, the sample breakage time is obtained for each of the plurality of samples housed in the sample box. Then, among these samples, select the sample with the fastest stress corrosion cracking progression speed determined by the susceptibility and sample failure time, and use the susceptibility and sample failure time corresponding to the sample to correct the master curve. conduct. As a result, the failure time of the steam turbine can be estimated with a large margin, so that the steam turbine can be evaluated with higher reliability.
[0060]
(5) In another aspect, in the above (3) or (4) aspect,
The master curve creation step (for example, step S100 in the above embodiment) of creating the master curve by performing a rupture test using a plurality of test pieces containing the same material of the steam turbine and having different sensitivities. Prepare more.
[0061]
According to the aspect (5) above, by using a plurality of test pieces with different sensitivities for the same material as the steam turbine to be evaluated, a master curve that defines the correlation between the susceptibility and the standard failure time can be created.
[0062]
(6) In another aspect, in any one aspect of (1) to (5) above,
Further includes a first correction step (for example, step S204 in the above embodiment) for correcting the failure time based on the reference temperature corresponding to the master curve and the temperature during operation of the steam turbine.
[0063]
According to the aspect (6) above, the failure time of the steam turbine estimated based on the sample failure time is corrected based on the reference temperature of the master curve and the operating temperature of the actual steam turbine. As a result, the influence of the difference between the reference temperature of the master curve and the operating temperature of the actual steam turbine can be taken into account, and the steam turbine can be evaluated with higher accuracy.
[0064]
(7) In another aspect, in any one aspect of (1) to (6) above,
Further includes a second correction step (for example, step S205 in the above embodiment) for correcting the failure time based on the reference wetness corresponding to the master curve and the wetness during operation of the steam turbine.
[0065]
According to the aspect (7) above, the failure time of the steam turbine estimated based on the sample failure time is corrected based on the reference wetness of the master curve and the operating wetness of the actual steam turbine. do. As a result, the effect of the difference between the reference wetness of the master curve and the wetness during operation of the actual steam turbine can be taken into account, and the steam turbine can be evaluated with higher accuracy.
[0066]
(8) In another aspect, in any one aspect of (1) to (7) above,
The sample includes two sample materials (eg, sample materials 52A and 52B in the above embodiment) that are at least partially in contact with each other and are stressed.
[0067]
According to the aspect (8) above, by using a sample having such a configuration, it is possible to effectively simulate a component of a steam turbine in which stress corrosion cracking occurs.
[0068]
(9) In another aspect, in the aspect of (8) above,
　The two sample materials are
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5,000 character limit. Use the arrows to translate more.Each contains different materials that are included in the turbine.
[0069]
According to the aspect (9) above, by configuring the two sample materials that constitute the sample so as to contain different materials contained in the steam turbine, contact corrosion (galvanic corrosion) that can occur in the steam turbine can be prevented. can be evaluated in consideration of
[0070]
(10) In another aspect, in the above aspect (8) or (9),
A gap (for example, the gap 56 in the above embodiment) is provided between the two sample materials.
[0071]
According to the aspect (10) above, by providing a gap between the two sample materials that make up the sample, it is possible to perform an evaluation that takes account of crevice corrosion that may occur in the steam turbine.
[0072]
(11) In another aspect, in any one aspect of (1) to (10) above,
The samples include double U-bend test pieces (e.g., samples 50A and 50B of the above embodiment), tapered DCB test pieces (e.g., sample 50C of the above embodiment), blunt notch CT test pieces (e.g., sample 50D of the above embodiment), It is a pre-crack CT test piece (for example, sample 50E of the above embodiment).
[0073]
According to the aspect (11) above, by using these test pieces as samples, the steam turbine can be suitably evaluated by the methods of the above aspects.

we claims

[Claim 1]
a sample failure time acquisition step of acquiring the sample failure time of a sample that is housed in a steam turbine sample box and configured to have a higher susceptibility to stress corrosion cracking than the material to be evaluated for the steam turbine;
a failure time estimation step of estimating the failure time of the steam turbine based on the sample failure time;
A method for evaluating stress corrosion cracking of a steam turbine, comprising:
[Claim 2]
The method for evaluating stress corrosion cracking of a steam turbine according to claim 1, wherein the sample has a higher strength than the material to be evaluated.
[Claim 3]
The failure time estimation step is
A corrected master curve for creating a corrected master curve by correcting the master curve that defines the correlation between the susceptibility and the standard failure time using the susceptibility and the sample failure time of the sample used in the first step. a creation process;
a failure time identification step of identifying the failure time corresponding to the design strength of the steam turbine based on the corrected master curve;
The steam turbine stress corrosion cracking evaluation method according to claim 1 or 2, comprising:
[Claim 4]
In the sample breakage time acquisition step, the sample breakage time is acquired for a plurality of the samples with different sensitivities,
In the correction master curve creation step, the correction master curve is created by correcting the master curve based on the susceptibility and the sample failure time corresponding to the sample in which the stress corrosion cracking progresses fastest. The method for evaluating stress corrosion cracking of a steam turbine according to claim 3.
[Claim 5]
5. The method according to claim 3 or 4, further comprising a master curve creating step of creating the master curve by performing a rupture test using a plurality of test pieces containing the same material of the steam turbine and having different sensitivities. A method for evaluating stress corrosion cracking of a steam turbine as described.
[Claim 6]
6. The method according to any one of claims 1 to 5, further comprising a first correction step of correcting the failure time based on a reference temperature corresponding to the master curve and a temperature during operation of the steam turbine. Method for evaluating stress corrosion cracking of steam turbines.
[Claim 7]
7. The method according to any one of claims 1 to 6, further comprising a second correction step of correcting the failure time based on the reference wetness corresponding to the master curve and the wetness during operation of the steam turbine. A method for evaluating stress corrosion cracking of a steam turbine as described.
[Claim 8]
The method for evaluating stress corrosion cracking of a steam turbine according to any one of claims 1 to 7, wherein the sample includes two sample materials that are at least partially in contact with each other and are stressed.
[Claim 9]
The steam turbine stress corrosion cracking evaluation method according to claim 8, wherein the two sample materials each include different materials included in the steam turbine.
[Claim 10]
The steam turbine stress corrosion cracking evaluation method according to claim 8 or 9, wherein a gap is provided between the two sample materials.
[Claim 11]
The steam turbine stress corrosion cracking evaluation method according to any one of claims 1 to 10, wherein the samples are double U-bend test pieces, tapered DCB test pieces, blunt notch CT test pieces, and pre-crack CT test pieces. .
[Claim 12]
The stress of the steam turbine according to any one of claims 1 to 11, wherein in said sample failure time acquisition step, said sample failure time is acquired based on a detection signal of a failure state detection sensor provided in said sample. Corrosion crack evaluation method.
[Claim 13]
The steam turbine stress corrosion cracking evaluation method according to any one of claims 1 to 12, further comprising an evaluation step of evaluating the remaining life or maintenance timing of the steam turbine based on the failure time.