Evaluation Method of Stress Corrosion Cracking in Steam Turbines

Abstract

In a method for evaluating stress corrosion cracking of a steam turbine, a sample with high sensitivity is stored in a sample box of the steam turbine, and the sample damage time is obtained. Then, the damage time of the steam turbine is estimated based on the sample damage time.

Description

Technical Field

[0001] The present disclosure relates to a method for evaluating stress corrosion cracking of a steam turbine. Background Art

[0002] In equipment such as steam turbines, it is known that stress corrosion cracking (SCC) occurs when structural components are exposed to wet steam in a high-temperature environment for a long time. If such stress corrosion cracking develops, it will cause equipment failure, so it is required to quantitatively evaluate the degree of corrosion development to predict the remaining life of the equipment and the appropriate maintenance implementation period.

[0003] For example, Patent Document 1 proposes making a sample (test piece) using the same material as the part where stress corrosion cracking is a concern, and quantitatively evaluating stress corrosion cracking in the evaluation object part based on the crack propagation rate of the sample under the same environment as the evaluation object part.

[0004] Prior Art Literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2001-305043 Summary of the invention

[0007] Problems to be solved by the invention

[0008] In the above-mentioned Patent Document 1, a sample is housed in a constant environment assumed according to the operating environment of the evaluation object part, and the stress corrosion cracking of the evaluation object part is evaluated based on its corrosion state. However, there are great differences in temperature and humidity between the test environment of the sample and the operating environment of the evaluation object part as an actual machine. Therefore, in such a method, it may not be possible to accurately evaluate the stress corrosion cracking in the evaluation object part as an actual machine.

[0009] In addition, in Patent Document 1, a test piece is made of the same material as the evaluation target part. Therefore, in order to evaluate stress corrosion cracking using such a test piece, a test period equivalent to the period required until stress corrosion cracking actually occurs in the evaluation target part as a real machine is required.

[0010] At least one aspect of the present disclosure has been made in view of the above-described circumstances, and an object of the present disclosure is to provide a stress corrosion cracking evaluation method for a steam turbine that can rapidly and accurately perform reliable quantitative evaluation of stress corrosion cracking.

[0011] Solutions to Solve Problems

[0012] In order to solve the above-mentioned problems, a method for evaluating stress corrosion cracking of a steam turbine according to one aspect of the present disclosure includes:

[0013] a sample failure time acquisition step of acquiring a sample failure time of a sample contained in a sample box of a steam turbine and configured to have a higher sensitivity to stress corrosion cracking than an evaluation target material of the steam turbine; and

[0014] The damage time estimating step estimates a damage time of the steam turbine based on the sample damage time.

[0015] Effects of the Invention

[0016] According to at least one aspect of the present disclosure, it is possible to provide a stress corrosion cracking evaluation method for a steam turbine that can rapidly and accurately perform reliable quantitative evaluation of stress corrosion cracking. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a schematic cross-sectional view of a steam turbine.

[0018] Figure 2A It means to be contained in Figure 1 Schematic diagram of an example of a sample in a sample box.

[0019] Figure 2B It means to be contained in Figure 1 Schematic diagram of another example of a sample in a sample box.

[0020] Figure 2C It means to be contained in Figure 1 Schematic diagram of another example of a sample in a sample box.

[0021] Figure 2D It means to be contained in Figure 1 Schematic diagram of another example of a sample in a sample box.

[0022] Figure 2E It means to be contained in Figure 1 Schematic diagram of another example of a sample in a sample box.

[0023] Figure 3 Yes means Figure 1 FIG. 1 is a block diagram of a steam turbine evaluation device 100 .

[0024] Figure 4 It is represented by each process Figure 3 Flow chart of the stress corrosion cracking evaluation method implemented by the evaluation device.

[0025] Figure 5 is an example of a principal curve.

[0026] Figure 6 yes Figure 4 Sub-flow chart of step S106.

[0027] Figure 7 This is a graph that compares the master curve with the calibration master curve.

[0028] Figure 8 This is a graph showing a master curve when there are a plurality of measurement points by comparison with a calibration master curve.

[0029] Fig. 9 This is a graph showing a characteristic function of the correlation between the normalized damage degree value and humidity. DETAILED DESCRIPTION

[0030] Hereinafter, several embodiments of the present invention will be described with reference to the 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.

[0031] Figure 1 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 accommodates the rotor 2 so as to cover the rotor 2 from the outer peripheral side.

[0032] The rotor 2 includes a rotor body 6 and turbine blades 8. The turbine blades 8 are rows of blades including a plurality of blade bodies 10 and blade tip shrouds 12, and a plurality of rows are arranged at certain intervals in the direction of the axis O. The plurality of blade bodies 10 are installed to extend radially from the rotor body 6 that rotates around the axis O in the casing 4, and are arranged at intervals in the circumferential direction of the rotor body 6. The plurality of blade bodies 10 are components that have a blade-shaped cross-section when viewed from the radial direction. The blade tip shroud 12 is an annular blade tip shroud that connects the front end portions (radially outer ends) of each of the plurality of blade bodies 10.

[0033] The casing 4 is a roughly cylindrical member provided in a manner covering the rotor 2 from the outer peripheral side. A plurality of stationary blades 16 are provided on the 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 the direction of the axis O. Furthermore, the turbine blades 8 are arranged in a manner entering the region between the plurality of adjacent stationary blades 16.

[0034] In addition, the casing 4 is connected to a steam supply pipe 18 for supplying steam S as a working fluid from a steam supply source (not shown) to the steam turbine 1, and a steam discharge pipe 20 connected to the downstream side of the steam turbine 1 and discharging the steam. Inside the casing 4, the region where the stationary blades 16 and the turbine blades 8 are arranged forms a main flow path 22 for the steam S supplied from the steam supply pipe 18 to flow. The steam S flowing in the main flow path 22 is received by the turbine blades 8, thereby driving the rotor 2 to rotate (see arrow R). The 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 supported by a bearing 26 so as to be rotatable relative to the casing 4.

[0035] In addition, a sample box 28 is provided in the housing 4. The sample box 28 has a space 30 for accommodating a sample 50 used in the evaluation method described later, and an opening and closing portion 32 (such as a manhole or a hand hole) for taking the sample 50 into and out of the space 30. The sample box 28 can be arranged at any position of the housing 4, but for example, it can also be arranged at a position that is in the same or close environment as the evaluation object part of the steam turbine 1 when the steam turbine 1 is in operation. For example, the space 30 that accommodates the sample 50 is arranged at a position where the temperature and humidity are the same or close to each other by being connected to the evaluation object part. Figure 1 In the example, the sample box 28 is arranged at a position adjacent to the main flow path 22 for the high-temperature steam S to flow, thereby configuring the sample 50 contained in the sample box 28 to be placed in an environment that is the same as or close to the components (turbine moving blades 8, stationary blades 16) exposed to the steam S flowing in the main flow path 22.

[0036] In addition, the sample box 28 may be provided at a position in the housing 4 that is easily accessible from the outside, so as to facilitate the operation of taking out and placing the sample 50 described later. In this case, the opening and closing portion 32 is configured to be adjacent to a passage (for example, a manhole or a hand hole provided on the flow path of the steam exhaust pipe 20) through which an operator in the steam turbine 1 can enter and exit, thereby making it easy to take out and place the sample 50 into the space 30 through the opening and closing portion 32.

[0037] Here, the sample 50 accommodated in the sample box 28 is described (hereinafter, as examples of the sample 50, the samples 50A to 50E are described, but they are collectively referred to as the sample 50). By using the sample 50 having such a structure, the constituent members of the steam turbine 1 that may cause stress corrosion cracking can be effectively simulated.

[0038] Figure 2A It means to be contained in Figure 1Schematic diagram of an example of a sample 50A of a sample box 28. The sample 50A includes two sample materials 52A and 52B that are in contact with each other and to which stress is applied. The sample 50A is a so-called double U-shaped bending test piece, which is configured such that two sample materials 52A and 52B as plate-like members are fixed by bolts 54 in a bent state, thereby being able to apply stress of the yield strength level to the two sample materials 52A and 52B. In the sample 50A, the two sample materials 52A and 52B are in close contact with each other so that there is no gap between them.

[0039] The two sample materials 52A and 52B constituting the sample 50A include materials constituting the evaluation target materials (e.g., the rotor 2, the turbine blades 8, etc.) included in the steam turbine 1. The two sample materials 52A and 52B may be composed of the same material as each other. For example, when the rotor 2 in the steam turbine 1 is the evaluation target, the two sample materials 52A and 52B are formed of the same material as the rotor 2.

[0040] In addition, the two sample materials 52A and 52B may be made of different materials. For example, when the rotor body 6 and the turbine blades 8 constituting the rotor 2 are made of different materials and come into contact with each other when the rotor body 6 and the turbine blades 8 are combined, contact corrosion (galvanic corrosion) of different materials may occur, which causes corrosion to progress faster, due to the contact of different materials. When such a part is used as an evaluation object, by forming the two sample materials 52A and 52B from the materials constituting the rotor body 6 and the turbine blades 8, respectively, it is possible to form a sample 50 that simulates the state in which different materials come into contact with each other in the rotor 2.

[0041] Figure 2B It means to be contained in Figure 1 Schematic diagram of another example of a sample 50 in the sample box 28. Sample 50B and Figure 2A The sample 50A shown is similarly configured as a double U-bend test piece, but is different in that a gap 56 is partially provided between two sample materials 52A and 52B. By using such a sample 50B, evaluation can be performed in consideration of crevice corrosion that may occur in the steam turbine 1.

[0042] Figure 2C to Figure 2E It means to be contained in Figure 1 FIG. 2 is a schematic diagram of another example of a sample 50 in a sample box 28 . Figure 2C The sample 50C shown is a wedge-shaped DCB (Double-Cantilever Beam) test piece, and the crack progress can be evaluated while changing the applied stress by the thickness of the wedge. In particular, the wedge-shaped DCB test piece has the characteristic that the stress amplification factor hardly changes even if the crack length changes. Figure 2DThe sample 50D shown is a branch notch CT test piece, and crack generation can be evaluated by applying a predetermined applied stress by changing the thickness of the wedge. Figure 2E The sample 50E shown is a pre-crack CT test piece, which can evaluate the crack progress while changing the applied stress by the thickness of the wedge. In this test piece, the stress amplification factor decreases as the crack length increases.

[0043] In addition, the sample 50 contained in the sample box 28 may include a plurality of samples having different sensitivities. Generally, the sensitivity of the sample 50 depends on the yield strength, and can be adjusted by, for example, high-strength processing, heat treatment, etc. when manufacturing the sample 50.

[0044] Figure 3 Yes means Figure 1 The block diagram of the evaluation device 100 of the steam turbine 1 is shown. The evaluation device 100 is, for example, an analysis unit for implementing the evaluation of the steam turbine 1. The evaluation device 100 is, for example, composed of a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), and a computer-readable storage medium. Moreover, as for a series of processes for realizing various functions, as an example, they are stored in a storage medium in the form of a program, and the CPU reads the program into the RAM, etc., and executes information processing / calculation processing, thereby realizing various functions. It should be noted that the program can also be applied in a manner of being pre-installed in a ROM or other storage medium, provided in a state of being stored in a computer-readable storage medium, distributed via a wired or wireless communication mechanism, etc. The computer-readable storage medium refers to a magnetic disk, a magnetic optical disk, a CD-ROM, a DVD-ROM, a semiconductor memory, etc.

[0045] The evaluation device 100 includes a sample damage time acquisition unit 102 for acquiring a sample damage time, a storage unit 104 for storing the master curve 60, a correction master curve creation unit 106 for correcting the master curve 60, a damage time estimation unit 108 for estimating the damage time of the steam turbine 1, and an evaluation unit 110 for evaluating the steam turbine 1 based on the damage time.

[0046] It should be noted that the composition Figure 3Each module of the evaluation device 100 shown is a module recorded corresponding to the function played when implementing the evaluation method described later, and can be combined with each other as needed, or can be further subdivided. In addition, at least a part of the structure of the evaluation device 100 can be configured to communicate via a network, so as to be arranged at a location far away from the steam turbine 1 as the evaluation object. For example, the evaluation device 100 can be arranged at a base station located at a remote location that can communicate with the steam turbine 1 through a network, or can be configured as a cloud server.

[0047] Figure 4 It is expressed by each process. Figure 3 Flow chart of the stress corrosion cracking evaluation method performed by the evaluation device 100. It should be noted that the stress corrosion cracking evaluation method described below is described for the case where it is performed using the aforementioned evaluation device 100, but it can also be performed by an operator without using the evaluation device 100.

[0048] First, a master curve 60 is prepared to define the correlation between the sensitivity to stress corrosion cracking and the standard failure time (step S100: master curve preparation step). The master curve 60 is prepared by a fracture test using a plurality of test pieces. The plurality of test pieces used in the fracture test are test pieces containing the same material as the rotor material as an example of the evaluation object material of the steam turbine 1 and having different sensitivities from each other. In the present embodiment, a plurality of test pieces are prepared to be compared with the reference material. Figure 2A to Figure 2E The above-mentioned sample 50 is prepared as test pieces of the same shape so that the sensitivities of the test pieces are different. Since the sensitivity is generally related to the yield strength, the method of making the sensitivities of the plurality of test pieces different is performed by, for example, performing strong working or heat treatment.

[0049] Then, by performing a fracture test on a plurality of test pieces having different sensitivities, the fracture time of each test piece is obtained (hereinafter, the fracture time obtained in the fracture test for preparing the master curve 60 is referred to as the reference fracture time). The master curve 60 is prepared by associating the sensitivity thus obtained with the reference fracture time.

[0050] Figure 5 This is an example of the master curve 60. The master curve 60 is expressed as a function f(t, y) with sensitivity y and damage time t as variables, and shows that the standard damage time t tends to decrease as the sensitivity y increases. The master curve 60 thus created is readable and stored in the storage unit 104. For example, Figure 5 The sensitivity of the vertical axis refers to the load stress of the test performed by applying a stress equivalent to the yield strength to the test piece 50 using the test piece 50 that changes the yield strength. Figure 5 The indicator of the vertical axis.

[0051] Next, the sample 50 is stored in the sample box 28 (step S101). The sample 50 stored in the sample box 28 is configured to have a higher sensitivity to stress corrosion cracking than the steam turbine 1 to be evaluated. Specifically, Figure 2A to Figure 2E The sample 50 of the above-mentioned shape is subjected to strong processing or heat treatment to adjust the sensitivity of the sample 50. By using the sample 50 having a higher sensitivity to stress corrosion cracking than the steam turbine 1, stress corrosion cracking can be generated in the sample 50 accommodated in the sample box 28 before the steam turbine 1.

[0052] It should be noted that the sample box 28 may contain a plurality of samples 50. In this case, the plurality of samples 50 may also be subjected to high-strength processing, heat treatment, etc. to adjust the yield strength of each sample 50, so that the samples 50 have different sensitivities. Figure 2A to Figure 2E By using a plurality of samples 50 as described above, the influence of differences in sensitivity and sample shapes on the sample breakage time can be considered, thereby enabling a more detailed evaluation.

[0053] Next, the operation of the steam turbine 1 is started with the sample 50 stored in the sample box 28 (step S102). During the operation of the steam turbine 1, the steam S passing through the main flow path 22 causes corrosion of the steam turbine 1. After the operation of the steam turbine 1 is started, the sample 50 is monitored for damage (step S103). The monitoring in step S103 may be performed by an operator checking the sample 50 in the sample box 28 during maintenance, for example, when the maintenance of the steam turbine 1 can be performed at intervals that are sufficiently shorter than the expected sample damage time. Alternatively, a damage state detection sensor may be pre-installed on the sample 50 stored in the sample box 28, and the presence of damage may be monitored by acquiring a detection signal of the damage state sensor. In this case, by configuring the damage state sensor to be able to communicate with the evaluation device 100 in a wired or wireless manner, the damage state of the sample 50 can be monitored without actually removing 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.

[0054] When it is determined that the sample 50 is damaged (step S104: Yes), the sample damage time acquisition unit 102 acquires the sample damage time (step S105: sample damage time acquisition process). The sample damage time is the time elapsed from the start of operation of the steam turbine 1 in step S102 until damage is found in the sample 50. For example, when the operator checks the condition of the sample 50 in the sample box 28 during maintenance and finds that the sample 50 is damaged, the time elapsed from the start of operation of the steam turbine 1 to the time of inspection can also be regarded as the sample damage time. As described above, the sample 50 is configured to be more sensitive than the steam turbine 1, so stress corrosion cracking progresses at a timing sufficiently earlier than that of the steam turbine 1, and the sample damage time required for evaluation can be acquired.

[0055] Furthermore, when a plurality of samples 50 are stored in the sample box 28 and the plurality of samples 50 are damaged, the sample damage time acquisition unit 102 may acquire the sample damage time for each damaged sample 50 .

[0056] Next, the damage time estimating unit 108 estimates the damage time of the steam turbine 1 based on the sample damage time acquired by the sample damage time acquiring unit 102 (step S106: damage time estimating process). The specific method performed by the damage time estimating unit 108 will be described later. Since the sample damage time is acquired from the sample 50 stored in the sample box 28 of the actual machine, that is, the steam turbine 1 to be evaluated, the influence of the operating state including the temperature and humidity of the actual steam turbine is reflected. Therefore, by estimating the damage time of the steam turbine 1 based on such a sample damage time, it is possible to evaluate the steam turbine with good accuracy.

[0057] Next, the evaluation unit 110 evaluates the remaining life or maintenance period of the steam turbine 1 based on the damage time estimated in step S106 (step S107: evaluation process). 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 to date and the damage time estimated in step S106. In addition, the evaluation unit 110 obtains the remaining life for each component of the steam turbine 1, and obtains the implementation period of maintenance work such as repair and replacement of each component based on the remaining life. Such an evaluation result is effective for formulating a maintenance plan for preventing stress corrosion cracking in the steam turbine 1.

[0058] Next, a method of estimating the damage time of the steam turbine 1 in the damage time estimating step of step S106 will be described in detail. Figure 6 yes Figure 4 Sub-flow chart of step S106.

[0059] First, the damage time estimation unit 108 obtains the master curve 60 stored in the storage unit 104 (step S200). The master curve 60 refers to Figure 5 As described above, a function representing the correlation between the predetermined sensitivity and the standard failure time is stored in advance in the storage unit 104 .

[0060] Next, the damage time estimation unit 108 corrects the master curve 60 obtained in step S200 based on the sample damage time obtained by the sample damage time acquisition unit 102 and the sensitivity of the sample 50 corresponding to the sample damage time, thereby creating a corrected master curve 70 (step S201). Figure 7 60 and the corrected master curve 70 are compared. Figure 7 In FIG. 1 , the horizontal axis represents the damage time t, the vertical axis represents the sensitivity y (yield strength), and the master curve 60 before correction obtained from the storage unit 104 is represented as a function f(t, y). Figure 7 , the sample damage time obtained by the sample damage time acquisition unit 102 and the measurement point A (t1, y1) determined by the sensitivity of the sample 50 corresponding to the sample damage time are shown. If the damage time corresponding to the sensitivity y1 on the master curve 60 is t2, the correction master curve 70 is obtained by the following formula.

[0061] f'(t,y)=f(t×t2 / t1,y)

[0062] That is, the correction in step S201 is performed by adjusting the magnification of the horizontal axis direction of the master curve 60 so that the master curve 60 passes through the measurement point A (t1, y1). There is a great difference between the environment (reference environment) in which the master curve 60 is prepared and the actual operating environment of the steam turbine 1, but by correcting the master curve 60 based on the actual measurement point (t1, y1) in this way, it is possible to create a corrected master curve 70 that takes into account the influence of the difference between the two.

[0063] It should be noted that when the sample box 28 contains a plurality of samples 50 having different sensitivities and there are a plurality of measurement points corresponding to each sample 50, the master curve 60 can be corrected based on the sensitivity and sample failure time corresponding to the sample 50 in which stress corrosion cracking develops the fastest. Figure 8 This is a diagram showing a master curve 60 and a correction master curve 70 when there are a plurality of measurement points A1 (t1-1, y1-1), A2 (t1-2, y1-2), ... by comparison. Figure 8In the example, the sample 50 in which the stress corrosion crack develops fastest, for example, is determined to be the measurement point A2(t1-2, y1-2) located at the bottom leftmost among a plurality of measurement points A1(t1-1, y1-1), A2(t1-2, y1-2), ···. By using the determined measurement point A2(t1-2, y1-2) as a reference and making a corrected master curve 70 in the same manner as in the case of Figure 7 , the break time of the steam turbine 1 can be estimated with a large allowable error (Japanese: margin), so that the steam turbine 1 can be evaluated with higher reliability.

[0064] Next, the break time estimation unit 108 obtains the sensitivity of the steam turbine 1 to be evaluated (step S202). Since the sensitivity generally corresponds to the strength, the sensitivity can also be calculated by obtaining the strength of the steam turbine 1 in step S202.

[0065] Next, the break time estimation unit 108 uses the corrected master curve 70 produced in step S201 to find the break time corresponding to the sensitivity of the steam turbine 1 obtained in step S202 (step S203). When referring to Figure 7 for explanation, if the sensitivity of the steam turbine 1 is set to y0, then based on the corrected master curve 70, the break time t0 of the steam turbine 1 is found.

[0066] Next, the break time estimation unit 108 performs a first correction on the break time t0 obtained in step S203 based on the reference temperature corresponding to the master curve 60 and the temperature during the operation of the steam turbine 1 (step S204: first correction process). The first correction is performed by first calculating a time evaluation base value Δt based on the break time t0 obtained in step S203. As Figure 7 shown, the time evaluation base value Δt is calculated as the difference between the break time t0 obtained in step S203 and the sample break time at the current time (since this step is the time when the sample break time is obtained, the sample break time becomes the current time).

[0067] 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 temperature during the operation of the steam turbine 1. For example, the following Clark formula (coefficients A, B, C) is used to find the parameters X1, X2 corresponding to the test environment temperature T1 when making the master curve 60 and the temperature T2 of the actual steam turbine 1, respectively (a is the crack length, σ0.2 is the 0.2% yield strength (or ultimate stress (Japanese: yield push)), and the coefficients A, B, C are constants defined based on conditions such as materials).

[0068] X1 = ln(da / dt) = -A - B / T1 + Cσ0.2

[0069] X2=ln(da / dt)=-AB / T2+Cσ0.2

[0070] 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 (X2 / X1) of X. 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 steam turbine 1 as an actual machine, and can perform a more accurate evaluation of the steam turbine.

[0071] 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 humidity corresponding to the master curve 60 and the humidity during operation of the steam turbine 1 (step S205: second correction process). In the second correction, a characteristic function f(s, D) is prepared in advance to define the correlation of the damage degree normalized value D with respect to the humidity s. Fig. 9 It is a graph of a characteristic function f(s, D) representing the correlation of a specified damage degree normalized value D with respect to humidity s. Here, the damage degree D1 of the test environment when the master curve 60 was prepared and the assumed damage degree D2 of the steam turbine 1 as an actual machine are used to evaluate the ratio of the two. In the case of D2>D1, the second correction value T” is obtained by dividing the first correction value Δt' of the time evaluation base value by the ratio of D (D2 / D1). By obtaining the second correction value T” in this way, the influence of the difference between the reference humidity of the master curve 60 and the humidity during operation of the actual machine, i.e., the steam turbine 1, can be taken into account, and a more accurate evaluation of the steam turbine can be performed.

[0072] It should be noted that, in the embodiment, the case where the second calibration is performed in step S205 after the first calibration is performed in step S204 is illustrated, but the first calibration may be performed after the second calibration, or only the first calibration or the second calibration may be performed. In addition, in step S106, the first calibration and the second calibration may not be performed, and the damage time t0 calculated in step S3 itself may be output as the estimation result.

[0073] As described above, according to the above-mentioned embodiment, by using the sample 50 having a higher sensitivity to stress corrosion cracking than the steam turbine 1, stress corrosion cracking occurs in the sample 50 accommodated in the sample box 28 before the steam turbine 1. Therefore, by using the sample 50 accommodated in the sample box 28 provided in the steam turbine 1, it is possible to obtain the sample failure time at a sufficiently early timing before stress corrosion cracking actually occurs in the steam turbine 1, and estimate the failure time of the steam turbine 1 based on the sample failure time. In addition, the sample failure time is obtained from the sample 50 accommodated in the sample box 28 of the steam turbine 1, which is the actual machine to be evaluated. Since the influence related to the operating state including the temperature and humidity of the actual steam turbine 1 is reflected in such a sample failure time, it is possible to evaluate the steam turbine 1 with good accuracy.

[0074] Furthermore, the components in the above-described embodiments may be appropriately replaced with well-known components without departing from the gist of the present disclosure, and the above-described embodiments may be appropriately combined.

[0075] The contents described in the above-mentioned embodiments can be understood as follows, for example.

[0076] (1) A method for evaluating stress corrosion cracking of a steam turbine according to one embodiment, wherein:

[0077] The stress corrosion cracking evaluation method of the steam turbine comprises:

[0078] a sample failure time acquisition step (e.g., step S105 of the above embodiment), in which a sample failure time of a sample (e.g., the sample 50 of the above embodiment) is acquired, the sample being contained in a sample box (e.g., the sample box 28 of the above embodiment) of a steam turbine (e.g., the steam turbine 1 of the above embodiment) and being configured to have a higher sensitivity to stress corrosion cracking than an evaluation target material of the steam turbine; and

[0079] A damage time estimating step (for example, step S106 in the above embodiment) is performed in which a damage time of the steam turbine is estimated based on the sample damage time.

[0080] According to the scheme of (1) above, by using a sample that is more sensitive to stress corrosion cracking than the evaluation target material of the steam turbine (e.g., rotor material, moving blade material, etc.), stress corrosion cracking occurs in the sample contained in the sample box before the steam turbine. Therefore, by using the sample contained in the sample box provided in the steam turbine, it is possible to obtain the sample failure time at a sufficiently early timing when stress corrosion cracking actually occurs in the steam turbine, and estimate the failure time of the steam turbine based on the sample failure time. In addition, the sample failure time is obtained from the sample contained in the sample box of the actual machine, i.e., the steam turbine, which is the evaluation target. Since the influence related to the operating state including the temperature and humidity of the actual steam turbine is reflected in such a sample failure time, it is possible to evaluate the steam turbine with good accuracy.

[0081] (2) In another embodiment, in the embodiment of (1) above,

[0082] The sample has higher strength than the evaluation object material.

[0083] According to the above-mentioned aspect (2), 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.

[0084] (3) In another embodiment, in the embodiment of (1) or (2) above,

[0085] The damage time estimation process comprises:

[0086] a calibration master curve preparation step (e.g., step S201 of the above embodiment), in which a master curve (e.g., master curve 60 of the above embodiment) that specifies the correlation between the sensitivity and the standard breakage time is calibrated using the sensitivity of the sample and the breakage time of the sample used in the first step, thereby preparing a calibration master curve (e.g., calibration master curve 70 of the above embodiment); and

[0087] A damage time determining step (for example, step S203 of the above embodiment) is performed in which the damage time corresponding to the design yield strength of the steam turbine is determined based on the correction master curve.

[0088] According to the above-mentioned solution (3), a master curve is prepared in advance to define the correlation between the sensitivity and the standard failure time under the reference environment for the materials constituting the steam turbine. Since there is a great difference between the reference environment of the master curve and the actual operating environment of the steam turbine, the master curve is corrected by the sensitivity and the sample failure time of the samples contained in the sample box of the steam turbine. By finding the failure time of the steam turbine based on the master curve after correction, it is possible to evaluate the steam turbine with good accuracy.

[0089] (4) In another embodiment, in the embodiment of (3) above,

[0090] In the sample damage time acquisition step, the sample damage time is acquired for the plurality of samples having different sensitivities.

[0091] In the corrected master curve creating step, the master curve is corrected based on the sensitivity corresponding to the sample in which the stress corrosion cracking develops fastest and based on the sample breakage time, thereby creating the corrected master curve.

[0092] According to the scheme (4) above, the sample failure time is obtained for each of the plurality of samples contained in the sample box. Then, the sample with the fastest growth rate of stress corrosion cracking calculated based on the sensitivity and the sample failure time is selected from the samples, and the master curve is corrected using the sensitivity and the sample failure time corresponding to the sample. As a result, the failure time of the steam turbine can be estimated with a larger allowable error, so that the steam turbine can be evaluated with higher reliability.

[0093] (5) In another embodiment, in the embodiment of (3) or (4) above,

[0094] The method further includes a master curve preparation step (eg, step S100 of the above embodiment), in which the master curve is prepared by performing a fracture test using a plurality of test pieces made of the same type of material of the steam turbine and having different sensitivities.

[0095] According to the above aspect (5), a master curve of the correlation between the predetermined sensitivity and the standard failure time can be prepared by using a plurality of test pieces having different sensitivities with respect to the same type of material as the steam turbine to be evaluated.

[0096] (6) In another embodiment, in any one of the above embodiments (1) to (5),

[0097] The method further includes a first correction step (for example, step S204 of the above embodiment) in which the damage time is corrected based on a reference temperature corresponding to the master curve and a temperature during operation of the steam turbine.

[0098] According to the above-mentioned configuration (6), the damage time of the steam turbine estimated based on the sample damage time is corrected based on the reference temperature of the master curve and the temperature of the actual machine, that is, the steam turbine during operation. As a result, the influence of the difference between the reference temperature of the master curve and the temperature of the actual machine, that is, the steam turbine during operation can be considered, and the steam turbine can be evaluated with higher accuracy.

[0099] (7) In another embodiment, in any one of the above embodiments (1) to (6),

[0100] The method further includes a second correction step (for example, step S205 of the above embodiment) in which the damage time is corrected based on a reference humidity corresponding to the master curve and humidity during operation of the steam turbine.

[0101] According to the above-mentioned configuration (7), the failure time of the steam turbine estimated based on the sample failure time is corrected based on the reference humidity of the master curve and the humidity of the actual machine, i.e., the steam turbine, during operation. Thus, the influence of the difference between the reference humidity of the master curve and the humidity of the actual machine, i.e., the steam turbine, during operation can be considered, and the steam turbine can be evaluated with higher accuracy.

[0102] (8) In another embodiment, in any one of the above embodiments (1) to (7),

[0103] The sample includes two sample materials (for example, the sample materials 52A and 52B of the above-described embodiment) that are at least partially in contact with each other and subjected to stress.

[0104] According to the above-mentioned aspect (8), by using a sample having such a structure, it is possible to effectively simulate a component member of a steam turbine in which stress corrosion cracking occurs.

[0105] (9) In another embodiment, in the embodiment of (8) above,

[0106] The two sample materials each include different materials contained in the steam turbine.

[0107] According to the above aspect (9), by configuring the two sample materials constituting the sample to include different materials included in the steam turbine, evaluation can be performed taking into account the dissimilar material contact corrosion (galvanic corrosion) that may occur in the steam turbine.

[0108] (10) In another embodiment, in the embodiment of (8) or (9),

[0109] A gap (such as the gap 56 in the above embodiment) is provided between the two sample materials.

[0110] According to the above-mentioned aspect (10), by providing a gap between two sample materials constituting the sample, it is possible to perform evaluation taking into account the crevice corrosion that may occur in the steam turbine.

[0111] (11) In another embodiment, in any one of the above embodiments (1) to (10),

[0112] The samples are double U-shaped bending test pieces (such as samples 50A and 50B of the above embodiment), wedge-shaped DCB test pieces (such as sample 50C of the above embodiment), branch notch CT test pieces (such as sample 50D of the above embodiment), and pre-crack CT test pieces (such as sample 50E of the above embodiment).

[0113] According to the above-mentioned aspect (11), by using these test pieces as samples, the steam turbine can be appropriately evaluated by the methods of the above-mentioned aspects.

[0114] (12) In another embodiment, in any one of the above embodiments (1) to (11),

[0115] In the sample damage time acquisition step, the sample damage time is acquired based on a detection signal of a damage state detection sensor provided on the sample.

[0116] According to the above-mentioned aspect (12), the presence or absence of stress corrosion cracking in the sample can be confirmed based on the detection signal of the damage state detection sensor, so the sample damage time can be obtained without removing the sample from the sample box.

[0117] (13) In another embodiment, in any one of the above embodiments (1) to (12),

[0118] The method further includes an evaluation step (for example, step S107 of the above embodiment) in which a remaining life or a maintenance period of the steam turbine is evaluated based on the damage time.

[0119] According to the above-mentioned aspect (13), by evaluating the remaining life or maintenance period of the steam turbine based on the damage time of the steam turbine estimated by the methods of the above-mentioned aspects, stress corrosion cracking can be effectively prevented in the steam turbine.

[0120] Description of Reference Numerals

[0121] 1 Steam turbine

[0122] 2 Rotors

[0123] 4. Housing

[0124] 6 Rotor body

[0125] 8 Turbine blades

[0126] 10 Blade body

[0127] 12 Blade tip guard

[0128] 14 Inner Surface

[0129] 16 Stationary blades

[0130] 18 Steam supply pipe

[0131] 20 Steam exhaust pipe

[0132] 22 Main Road

[0133] 24 Rotation axis

[0134] 26 Bearing

[0135] 28 Sample Box

[0136] 30 Space

[0137] 32 Opening and closing part

[0138] 50 samples

[0139] 52A, 52B Sample Materials

[0140] 54 Bolt

[0141] 56 Gap

[0142] 60 Main Curve

[0143] 70 Calibration master curve

[0144] 100 Evaluation Devices

[0145] 102 Sample damage time acquisition unit

[0146] 104 Storage

[0147] 106 Calibration Master Curve Production Department

[0148] 108 Damage Time Estimation Department

[0149] 110 Evaluation Department

[0150] S Steam.

Claims

1. A method for evaluating stress corrosion cracking of a steam turbine, wherein: The stress corrosion cracking evaluation method of the steam turbine comprises: a sensitivity adjustment step of adjusting the sensitivity of the sample by subjecting the sample to strong processing or heat treatment so that the sensitivity to stress corrosion cracking becomes higher than that of an evaluation target material of a steam turbine; a sample damage time acquisition step, in which the sample is stored in a sample box of the steam turbine and a sample damage time of the sample is acquired; and A damage time estimating step of estimating a damage time of the steam turbine based on the sample damage time.

2. The method for evaluating stress corrosion cracking of a steam turbine according to claim 1, wherein: The sample has higher strength than the evaluation object material.

3. The method for evaluating stress corrosion cracking of a steam turbine according to claim 1, wherein: The damage time estimation process comprises: a calibration master curve creating step of creating a calibration master curve by using the sensitivity of the sample and the sample damage time used in the sample damage time acquisition step to calibrate a master curve that defines a correlation between the sensitivity and a standard damage time, thereby creating a calibration master curve; and and a damage time determining step of determining the damage time corresponding to the design yield strength of the steam turbine based on the correction master curve.

4. The method for evaluating stress corrosion cracking of a steam turbine according to claim 3, wherein: In the sample damage time acquisition step, the sample damage time is acquired for the plurality of samples having different sensitivities. In the correction master curve preparation step, the master curve is corrected based on the sensitivity corresponding to the sample in which the stress corrosion cracking develops fastest and the sample failure time, thereby preparing the correction master curve.

5. The method for evaluating stress corrosion cracking of a steam turbine according to claim 3, wherein: The stress corrosion cracking evaluation method for a steam turbine further includes a master curve creating step of creating the master curve by performing a fracture test using a plurality of test pieces made of the same type of material of the steam turbine and having different sensitivities.

6. The method for evaluating stress corrosion cracking of a steam turbine according to claim 3, wherein: The stress corrosion cracking evaluation method for a steam turbine further includes a first correction step of correcting the damage time based on a reference temperature corresponding to the master curve and a temperature during operation of the steam turbine.

7. The method for evaluating stress corrosion cracking of a steam turbine according to claim 3, wherein: The stress corrosion cracking evaluation method for a steam turbine further includes a second correction step of correcting the damage time based on a reference humidity corresponding to the master curve and humidity during operation of the steam turbine.

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 subjected to stress.

9. The method for evaluating stress corrosion cracking of a steam turbine according to claim 8, wherein: The two sample materials each include different materials contained in the steam turbine.

10. The method for evaluating stress corrosion cracking of a steam turbine according to claim 8, wherein: A gap is arranged between the two sample materials.

11. The method for evaluating stress corrosion cracking of a steam turbine according to any one of claims 1 to 7, wherein: The samples are double U-bend test pieces, wedge-shaped DCB test pieces, branch notch CT test pieces, and pre-crack CT test pieces.

12. The method for evaluating stress corrosion cracking of a steam turbine according to any one of claims 1 to 7, wherein: In the sample damage time acquisition step, the sample damage time is acquired based on a detection signal of a damage state detection sensor provided on the sample.

13. The method for evaluating stress corrosion cracking of a steam turbine according to any one of claims 1 to 7, wherein: The stress corrosion cracking evaluation method for a steam turbine further includes an evaluation step of evaluating a remaining life or a maintenance period of the steam turbine based on the damage time.

14. A method for evaluating stress corrosion cracking of a steam turbine, wherein: The stress corrosion cracking evaluation method of the steam turbine comprises: a sample failure time acquisition step of acquiring a sample failure time of a sample contained in a sample box of a steam turbine and configured to have a higher sensitivity to stress corrosion cracking than an evaluation target material of the steam turbine; and a damage time estimating step of estimating a damage time of the steam turbine based on the sample damage time, The damage time estimation process comprises: a calibration master curve creating step of creating a calibration master curve by using the sensitivity of the sample and the sample damage time used in the sample damage time acquisition step to calibrate a master curve that defines a correlation between the sensitivity and a standard damage time, thereby creating a calibration master curve; and and a damage time determining step of determining the damage time corresponding to the design yield strength of the steam turbine based on the correction master curve.

15. A method for evaluating stress corrosion cracking of a steam turbine, wherein: The stress corrosion cracking evaluation method of the steam turbine comprises: a sample failure time acquisition step of acquiring a sample failure time of a sample contained in a sample box of a steam turbine and configured to have a higher sensitivity to stress corrosion cracking than an evaluation target material of the steam turbine; and a damage time estimating step of estimating a damage time of the steam turbine based on the sample damage time, The sample includes two sample materials that are at least partially in contact with each other and are subjected to stress, The two sample materials each include different materials contained in the steam turbine.

16. A method for evaluating stress corrosion cracking of a steam turbine, wherein: The stress corrosion cracking evaluation method of the steam turbine comprises: a sample failure time acquisition step of acquiring a sample failure time of a sample contained in a sample box of a steam turbine and configured to have a higher sensitivity to stress corrosion cracking than an evaluation target material of the steam turbine; and a damage time estimating step of estimating a damage time of the steam turbine based on the sample damage time, The sample includes two sample materials that are at least partially in contact with each other and are subjected to stress, A gap is arranged between the two sample materials.

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