Pitting corrosion evaluation device and pitting corrosion evaluation method

Abstract

To provide a pitting corrosion occurrence evaluation device, etc., capable of executing the prediction of occurrence of pitting corrosion at low cost and effectively.SOLUTION: In a pitting corrosion occurrence evaluation device, based on dry / wet alternation time data, deposit impurity concentration data and pitting corrosion occurrence data relating to pitting corrosion which occurs in each of a plurality of turbine stages when a steam turbine actually performs operation, a pitting corrosion occurrence evaluation section creates and holds a pitting corrosion occurrence evaluation table indicating a relation of a dry / wet alternation time, a deposit impurity concentration and the occurrence of pitting corrosion. The pitting corrosion occurrence evaluation section uses the pitting corrosion occurrence evaluation table to evaluate the pitting corrosion which occurs in each of the plurality of turbine stages in the operation scheduled for the steam turbine.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] Embodiments of the present invention relate to a pitting corrosion occurrence evaluation device and a pitting corrosion occurrence evaluation method.

Background Art

[0002] A steam turbine power generation system is configured such that a steam turbine converts thermal energy of steam into kinetic energy, and a generator converts the converted kinetic energy into electric power.

[0003] In a steam turbine, as the steam supplied as a working medium flows from a high-pressure part to a low-pressure part, a temperature drop and a pressure drop occur, so that the moisture content of the steam increases. For this reason, in a steam turbine, there is a dry-wet alternating region where the steam transitions from dry steam (steam in which saturated liquid phase water does not coexist) to wet steam (steam in which saturated liquid phase water coexists). The dry-wet alternating region may occur, for example, in a turbine stage located on the rear stage side in a low-pressure turbine when the steam turbine is an axial-flow turbine composed of a high-pressure turbine, an intermediate-pressure turbine, and a low-pressure turbine, and a plurality of turbine stages are arranged in the axial direction of the turbine rotor. In addition to this, the dry-wet alternating region may occur, for example, in an intermediate-pressure turbine constituting a geothermal power plant.

[0004] In the dry-wet alternating region, concentration of impurities contained in the steam occurs. The concentration of impurities particularly occurs in a gap intervening between the implanted part of the moving blade and the turbine rotor into which the implanted part of the moving blade is implanted. The impurities are Na, Cl, SO4, etc., and on the surface of turbine constituent members such as the implanted part of the moving blade, deposits that corrode the turbine constituent members are deposited due to the concentration of impurities. As a result, due to the progress of corrosion of the turbine constituent members, pitting corrosion may occur in the turbine constituent members, and it may develop into stress corrosion cracking (SCC) or corrosion fatigue damage.

[0005] When employing a peak load power generation system, steam may be supplied to the steam turbine at a different steam flow rate than that used in rated operation in order to adjust the power output according to the demand for electricity. Therefore, the alternating wet and dry zone may occur at a different location than that used in rated operation.

[0006] Various methods are known as corrosion prevention technologies to prevent corrosion of turbine components. For example, methods such as AVT (All Volatile Treatment) and CWT (Combined Water Treatment) have been proposed to control the amount of dissolved oxygen in the system water and the pH of the system water. In addition, technologies have been proposed to monitor the corrosion environment inside the steam turbine and to control the corrosion environment by injecting a reducing agent into the steam turbine. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Patent No. 3718377 [Patent Document 2] Japanese Patent Application Publication No. 07-54607 [Patent Document 3] Japanese Patent Publication No. 2002-073155 [Patent Document 4] Japanese Patent Publication No. 2004-308522 [Patent Document 5] Japanese Patent Publication No. 2011-202864 [Patent Document 6] Patent No. 5487112 [Patent Document 7] Japanese Patent Application Publication No. 09-287408 [Overview of the project] [Problems that the invention aims to solve]

[0008] However, conventionally, it has not been easy to predict the occurrence of pitting corrosion in a low-cost and effective manner. Therefore, it can sometimes be difficult to adequately suppress the occurrence of stress corrosion cracking and corrosion fatigue damage.

[0009] Therefore, the problem that the present invention aims to solve is to provide a pitting corrosion evaluation device and a pitting corrosion evaluation method that can predict the occurrence of pitting corrosion at low cost and effectively. [Means for solving the problem]

[0010] The pitting corrosion evaluation device of the embodiment is configured to evaluate pitting corrosion occurring in each of a plurality of turbine stages in a steam turbine power generation system. Here, the steam turbine power generation system includes a steam turbine and a generator. The steam turbine is configured such that a plurality of turbine stages are arranged axially along the rotational axis of the turbine rotor, and the turbine rotor rotates as steam supplied from a steam source sequentially expands and performs work in each of the plurality of turbine stages. The generator is configured to output electricity by generating electricity through the rotation of the turbine rotor. The pitting corrosion evaluation device of the embodiment comprises a turbine operation state evaluation unit, a dry / wet alternation time calculation unit, a deposit impurity concentration calculation unit, and a pitting corrosion evaluation unit. The turbine operation state evaluation unit calculates the ratio of the amount of power output output by the generator when the steam turbine is actually operating to the rated power output output that the generator generates when the steam turbine is operating at its rated capacity, and outputs this as turbine operation data. The wet-dry alternation time calculation unit calculates the wet-dry alternation time during which a wet-dry alternation zone occurred in each of the multiple turbine stages when the steam turbine was actually operating, based on the turbine operation data output by the turbine operation state evaluation unit, and outputs this as wet-dry alternation time data. The sediment impurity concentration calculation unit calculates the sediment impurity concentration, which is the impurity concentration of the sediment deposited in each of the multiple turbine stages when the steam turbine was actually operating, based on steam temperature data relating to the temperature of the steam supplied to the steam turbine when the steam turbine was actually operating, steam flow rate data relating to the steam flow rate of the steam supplied to the steam turbine when the steam turbine was actually operating, working medium impurity concentration data relating to the working medium impurity concentration, which is the impurity concentration of the steam supplied to the steam turbine when the steam turbine was actually operating, and the wet-dry alternation time data output by the wet-dry alternation time calculation unit, and outputs this as sediment impurity concentration data.The pitting corrosion evaluation unit creates and maintains a pitting corrosion evaluation table that shows the relationship between the dry-wet alternation time, the sediment impurity concentration, and the occurrence of pitting corrosion, based on the dry-wet alternation time data output by the dry-wet alternation time calculation unit, the sediment impurity concentration data output by the sediment impurity concentration calculation unit, and the pitting corrosion corrosion data related to pitting corrosion that occurred in each of the multiple turbine stages when the steam turbine was actually operated. Furthermore, the pitting corrosion evaluation unit is configured to use the pitting corrosion evaluation table to evaluate the pitting corrosion that occurs in each of the multiple turbine stages during the planned operation of the steam turbine. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a schematic diagram showing an example of a steam turbine power generation system 1 according to an embodiment. [Figure 2] Figure 2 is a schematic diagram showing an example of a low-pressure turbine 3c in the steam turbine power generation system 1 according to the embodiment. [Figure 3] Figure 3 is a schematic block diagram showing the pitting corrosion evaluation device 700 according to the embodiment. [Figure 4] Figure 4 is a schematic diagram showing the data flow when creating the pitting corrosion evaluation table D740 in the pitting corrosion evaluation device 700 according to the embodiment. [Figure 5A] Figure 5A shows an example of power output data D10 in an embodiment. [Figure 5B] Figure 5B shows an example of turbine operation data D711 in an embodiment. [Figure 5C] Figure 5C shows how the dry / wet alternation time t is determined from the turbine operation data D711 in one embodiment. [Figure 5D] Figure 5D shows the relationship between the sediment impurity concentration C, the working medium impurity concentration Cw, and the wet / dry alternation time t in an embodiment. [Figure 5E] Figure 5E shows a pitting corrosion evaluation table D740 in an embodiment. [Figure 6]FIG. 6 is a diagram schematically showing the data flow in the pitting corrosion occurrence evaluation apparatus 700 according to the embodiment when evaluating the occurrence of pitting corrosion using the pitting corrosion occurrence evaluation table D740.

Mode for Carrying Out the Invention

[0012] [A] Configuration of the Steam Turbine Power Generation System 1 FIG. 1 is a diagram schematically showing an example of the steam turbine power generation system 1 according to the embodiment.

[0013] As shown in FIG. 1, the steam turbine power generation system 1 includes a steam source 2 (boiler), a steam turbine 3, a generator 4, a condenser 5, and a feed water pump 6. In this embodiment, the steam turbine 3 includes a high-pressure turbine 3a, an intermediate-pressure turbine 3b, and a low-pressure turbine 3c, and is driven by steam generated by the steam source 2 being supplied as a working medium.

[0014] In the steam turbine power generation system 1 of this embodiment, the steam (main steam) generated by the steam source 2 is introduced as a working fluid into the high-pressure turbine 3a via the main steam pipe P1 provided with the main steam stop valve V11 and the steam control valve V12, and performs work in the high-pressure turbine 3a. Then, the steam discharged from the high-pressure turbine 3a is supplied to the steam source 2 via the low-temperature reheat steam pipe P2 and reheated.

[0015] The steam (reheat steam) reheated by the steam source 2 is introduced as a working fluid into the intermediate-pressure turbine 3b via the high-temperature reheat steam pipe P3 provided with the reheat steam stop valve V21 and the intercept valve V22, and performs work in the intermediate-pressure turbine 3b. Then, the steam discharged from the intermediate-pressure turbine 3b is introduced as a working fluid into the low-pressure turbine 3c via the crossover pipe P4, and performs work in the low-pressure turbine 3c. Then, the steam discharged from the low-pressure turbine 3c is condensed in the condenser 5.

[0016] The water (condensate) condensed in the condenser 5 is pressurized in the feed water pump 6. The water (feed water) pressurized by the feed water pump 6 is returned to the steam source 2.

[0017] In the steam turbine power generation system 1, the steam turbine 3 has a turbine rotor connected between the high-pressure turbine 3a, the intermediate-pressure turbine 3b, and the low-pressure turbine 3c, and the turbine rotor rotates due to the work done by the steam. The rotation of the turbine rotor that makes up the steam turbine 3 drives the generator 4, and electricity is generated.

[0018] [B] Configuration of low-pressure turbine 3c Figure 2 is a schematic diagram showing an example of a low-pressure turbine 3c in a steam turbine power generation system 1 according to an embodiment. Figure 2 shows a vertical cross-section (xz plane), where the vertical direction is the vertical direction z, the horizontal direction is the first horizontal direction x, and the direction perpendicular to the plane of the paper is the second horizontal direction y.

[0019] As shown in Figure 2, the low-pressure turbine 3c is a double-flow type, and the example shown is a downward exhaust system that discharges steam downwards.

[0020] In this embodiment, the low-pressure turbine 3c has an outer casing 10, an inner casing 20, and a turbine rotor 30, wherein the outer casing 10 houses the inner casing 20, and the turbine rotor 30 penetrates both the inner casing 20 and the outer casing 10. The turbine rotor 30 has its rotational axis AX aligned with a first horizontal direction x and is rotatably supported by rotor bearings 301.

[0021] The low-pressure turbine 3c is a multi-stage axial-flow turbine, in which multiple turbine stages 60, including stationary blades 40 and rotor blades 50, are arranged axially along the rotational axis AX inside the internal casing 20.

[0022] There are multiple stationary vanes 40, and the multiple stationary vanes 40 are arranged in the direction of rotation of the turbine rotor 30 between the inner ring 41 and the outer ring 43 of the diaphragm to constitute the nozzle diaphragm 45.

[0023] The rotor blades 50 are multiple in number, and the multiple rotor blades 50 are arranged along the rotational direction of the turbine rotor 30.

[0024] The low-pressure turbine 3c has a steam supply pipe 70 connected to its internal casing 20, and steam is supplied to the steam supply pipe 70 as working fluid. The steam supplied to the steam supply pipe 70 flows sequentially through multiple turbine stages 60 inside the internal casing 20. In other words, the working fluid flows from the first stage turbine stage 60 to the last stage turbine stage 60, expanding and performing work in each turbine stage 60. As a result, the turbine rotor 30 rotates around its central axis AX, and a generator connected to the turbine rotor 30 (not shown in Figure 2; corresponding to generator 4 in Figure 1) generates electricity.

[0025] In the low-pressure turbine 3c, the steam that has passed through the final stage turbine stage 60 is discharged via the cone section 12 from the lower exhaust port 11 located at the lower end of the outer casing 10. The steam discharged from the lower exhaust port 11 is condensed in the condenser (not shown in Figure 2; corresponding to condenser 5 in Figure 1) to produce condensate.

[0026] As explained earlier, in the low-pressure turbine 3c of the steam turbine 3, the humidity of the steam supplied as the working fluid increases, so there may be alternating dry-wet regions where the steam transitions from dry to wet. In these alternating dry-wet regions, impurities contained in the steam become concentrated. This concentration of impurities is particularly likely to occur in the gap between the mounting portion of the rotor blades 50 and the turbine rotor 30 into which the mounting portion of the rotor blades 50 is mounted. As a result, deposits that corrode the turbine components accumulate on the surface of turbine components such as the mounting portion of the rotor blades 50 due to the concentration of impurities. Consequently, the progression of corrosion of the turbine components can lead to pitting corrosion, which may develop into stress corrosion cracking or corrosion fatigue damage.

[0027] [C] Configuration of the pitting corrosion evaluation device 700 Figure 3 is a schematic block diagram showing the pitting corrosion evaluation device 700 according to the embodiment.

[0028] As shown in Figure 3, the pitting corrosion evaluation device 700 includes a turbine operating state evaluation unit 711, a dry / wet alternation time calculation unit 712, a working medium impurity concentration calculation unit 721, a deposit impurity concentration calculation unit 730, and a pitting corrosion evaluation unit 740.

[0029] The pitting corrosion evaluation device 700 is configured to evaluate pitting corrosion occurring in each of the multiple turbine stages 60 (see Figure 2) that make up the steam turbine 3 (for example, the low-pressure turbine 3c shown in Figure 2) in a steam turbine power generation system 1 (see Figure 1) which includes a steam source 2, a steam turbine 3, and a generator 4.

[0030] The pitting corrosion evaluation device 700 includes a computer and a memory device, and the arithmetic unit functions as each component of the pitting corrosion evaluation device 700 using a program stored in the memory device.

[0031] [D] Operation of the pitting corrosion evaluation device 700 [D-1] When creating the pitting corrosion evaluation table D740 In the pitting corrosion evaluation device 700, first, a pitting corrosion evaluation table D740 (see Figure 5E described later) is created for use in evaluating pitting corrosion.

[0032] Figure 4 is a schematic diagram showing the data flow when creating the pitting corrosion evaluation table D740 in the pitting corrosion evaluation device 700 according to the embodiment.

[0033] The operation of each part of the pitting corrosion evaluation device 700 when creating the pitting corrosion evaluation table D740 will be explained with reference to Figure 4.

[0034] [D-1-1] Turbine operating condition evaluation unit 711 As shown in Figure 4, the turbine operation state evaluation unit 711 is configured to receive power generation output data D10 as input and output turbine operation data D711 based on the power generation output data D10.

[0035] Figure 5A shows an example of power output data D10 in an embodiment. Figure 5B shows an example of turbine operation data D711 in an embodiment. Figures 5A and 5B illustrate the operating time, which includes the time from time t0 to time t3 when the steam turbine 3 was operated.

[0036] As shown in Figure 5A, the power output data D10 is data relating to the amount of power output P produced by the generator 4 when the steam turbine 3 was actually in operation. In other words, the power output data D10 is data that associates the operating time (Time) of the steam turbine 3 with the amount of power output P (MW).

[0037] As shown in Figure 5B, the turbine operation data D711 is data relating to the ratio R(%) of the amount of power output P produced by the generator 4 when the steam turbine 3 is actually operating, to the rated power output PR produced by the generator 4 when the steam turbine 3 is operating at its rated capacity (R = 100 * P / PR). In other words, the turbine operation data D711 is data relating to the load conditions of the steam turbine 3, and it is data that associates the above ratio R(%) with the operating time (Time) of the steam turbine 3.

[0038] In this manner, the turbine operation state evaluation unit 711 calculates the ratio R of the amount of power output P (= power output data D10) that the generator 4 outputs when the steam turbine 3 is actually operating, relative to the rated power output PR that the generator 4 generates when the steam turbine 3 is operating at its rated capacity. The turbine operation state evaluation unit 711 then outputs the data related to the calculated ratio R as turbine operation data D711.

[0039] [D-1-2] Dry / wet alternating time calculation unit 712 As shown in Figure 4, the wet-dry alternating time calculation unit 712 is configured to receive turbine operation data D711 as input and output wet-dry alternating time data D712 based on the turbine operation data D711. The wet-dry alternating time data D712 is data relating to the wet-dry alternating time t when a wet-dry alternating zone occurred in each of the multiple turbine stages 60 when the steam turbine 3 was actually in operation.

[0040] Figure 5C shows how the wet / dry alternation time t is determined from the turbine operation data D711 in an embodiment. In Figure 5C, as in Figures 5A and 5B, the operating time is illustrated, including the time from time t0 to time t3 when the steam turbine 3 was operated.

[0041] As shown in Figure 5C, the dry-wet alternation time calculation unit 712 determines the starting point of the dry-wet alternation time t when the increase in the value in the turbine operation data D711 exceeds a predetermined threshold ΔX1 (for example, 50%). Then, after detecting the starting point of the dry-wet alternation time t in the turbine operation data D711, the dry-wet alternation time calculation unit 712 determines the ending point of the dry-wet alternation time t when the decrease in the value in the turbine operation data D711 exceeds a predetermined threshold ΔX2 (for example, 50%). The dry-wet alternation time calculation unit 712 then calculates the dry-wet alternation time t as the period between the starting point and the ending point of the dry-wet alternation time t. Although not shown in the diagram, the dry / wet alternation time t also includes cases where the starting point is when the decrease in value in the turbine operation data D711 exceeds a predetermined threshold ΔX1 (e.g., 50%), and the ending point is when the increase in value in the turbine operation data D711 exceeds a predetermined threshold ΔX2 (e.g., 50%). In other words, the dry / wet alternation time t also includes cases where the starting point is when the change in value (increase or decrease) in the turbine operation data D711 exceeds a predetermined threshold ΔX1 (e.g., 50%), and the ending point is when the change in value (decrease or increase) in the turbine operation data D711 exceeds a predetermined threshold ΔX2 (e.g., 50%).

[0042] The wet / dry alternation time t is calculated for each of the multiple turbine stages 60 that make up the steam turbine 3. The threshold values ​​ΔX1 and ΔX2 are set individually for each of the multiple turbine stages 60. These threshold values ​​ΔX1 and ΔX2 are set to decrease as the turbine blades progress from the first stage to the final stage.

[0043] In this way, the wet-dry alternating time calculation unit 712 calculates the wet-dry alternating time t that occurred in each of the multiple turbine stages 60 when the steam turbine 3 was actually operating, based on the turbine operation data D711. The wet-dry alternating time calculation unit 712 outputs the data related to the calculated wet-dry alternating time t as wet-dry alternating time data D712.

[0044] [D-1-3] Working medium impurity concentration calculation unit 721 As shown in Figure 4, the working medium impurity concentration calculation unit 721 is configured to receive steam temperature data D11 and water quality data D20 as input, and to output working medium impurity concentration data D721 based on the steam temperature data D11 and water quality data D20.

[0045] Steam temperature data D11 is data relating to the temperature T of the steam supplied to the steam turbine 3 when the steam turbine 3 was actually in operation. Water quality data D20 is data relating to the water quality of the feedwater supplied to the steam source 2 when the steam turbine 3 was actually in operation, and includes, for example, data on the acid electrical conductivity κ and pH. Working fluid impurity concentration data D721 is data relating to the working fluid impurity concentration Cw, which is the impurity concentration of the steam supplied to the steam turbine 3 when the steam turbine 3 was actually in operation. Although not shown in the figures, steam temperature data D11, water quality data D20, and working fluid impurity concentration data D721 are data relating to the operating time (see Figures 5A and 5B, etc.), which includes the time from time t0 to time t3 when the steam turbine 3 was operated.

[0046] The impurity concentration (Na, Cl, SO4) Cw that affects pitting corrosion in the working fluid is calculated using a function f1(κ, pH, T) determined by time-dependent data where the acid electrical conductivity κ and pH of the feedwater supplied to the steam source 2 and the temperature T of the steam (main steam) supplied to the steam turbine 3 as the working fluid are variables, as shown in (Equation I) below. Note that the function f1(κ, pH, T) is derived from the results of investigating the relationships between each variable, and A and B are constants determined from pH and temperature T.

[0047] Cw=f1(κ,pH,T)=A·κ B ...(Formula I)

[0048] In this manner, the working medium impurity concentration calculation unit 721 calculates the working medium impurity concentration Cw based on the water quality data D20 and the steam temperature data D11, and outputs the calculated working medium impurity concentration Cw data as working medium impurity concentration data D721.

[0049] [D-1-4] Deposit impurity concentration calculation unit 730 As shown in Figure 4, the sediment impurity concentration calculation unit 730 is configured to receive dry / wet alternation time data D712 (=t), steam temperature data D11, working medium impurity concentration data D721 (=Cw), and steam flow rate data D12 (=v) as input, and to output sediment impurity concentration data D730 (=C).

[0050] Steam flow rate data D12 is data relating to the steam flow rate v of the steam supplied to the steam turbine 3 when the steam turbine 3 was actually in operation. Sediment impurity concentration data D730 is data relating to the sediment impurity concentration C, which is the impurity concentration of the sediment deposited in each of the multiple turbine stages 60 when the steam turbine 3 was actually in operation. Although not shown in the figures, the steam flow rate data D12 and the sediment impurity concentration data D730 are data relating to the operating time (see Figures 5A and 5B, etc.), which includes the time from time t0 to time t3 when the steam turbine 3 was operated.

[0051] The sediment impurity concentration C is an equivalent impurity concentration, representing the proportion (ppm) of the sediment containing impurities present in the vapor as corrosive components (multiple components such as Na, Cl, SO4, etc.) within the sediment itself.

[0052] The sediment impurity concentration C is calculated using a function f2(D(T,v),t,Cw) with the impurity precipitation rate D(T,v), the dry-wet alternation time t, and the working fluid impurity concentration Cw as variables, as shown in (Equation II) below. The impurity precipitation rate D(T,v) is calculated using a function with the steam temperature T and steam flow rate v as variables. Note that the functions f2(D(T,v),t,Cw) and f2(D(T,v)) are derived from the results of an investigation into the relationships between each variable.

[0053] C=f2(D(T,v),t,Cw) (Formula II)

[0054] Figure 5D shows the relationship between the sediment impurity concentration C, the working medium impurity concentration Cw, and the wet / dry alternation time t in an embodiment.

[0055] As shown in Figure 5D, the sediment impurity concentration C increases exponentially as the working medium impurity concentration Cw increases. Furthermore, the sediment impurity concentration C increases with increasing dry-wet alternation time t.

[0056] In this manner, the sediment impurity concentration calculation unit 730 calculates the sediment impurity concentration C based on the steam temperature data D11, steam flow rate data D12, working fluid impurity concentration data D721, and dry / wet alternation time data D712, and outputs the calculated sediment impurity concentration C as sediment impurity concentration data D730.

[0057] [D-1-5] Pitting corrosion evaluation unit 740 As shown in Figure 4, the pitting corrosion evaluation unit 740 receives the dry / wet alternation time data D712 (=t), the sediment impurity concentration data D730 (=C), and the pitting corrosion occurrence data D30 as input.

[0058] The pitting corrosion data D30 is data relating to pitting corrosion that occurred in each of the multiple turbine stages 60 when the steam turbine 3 was actually in operation. The pitting corrosion data D30 is obtained, for example, by inspecting whether or not pitting corrosion occurred on the rotor blades 50 in each of the multiple turbine stages 60. Pitting corrosion is determined to have occurred, for example, when the depth of the hole caused by corrosion exceeds 0.2 mm.

[0059] The pitting corrosion evaluation unit 740 then creates and maintains a pitting corrosion evaluation table D740 based on the dry / wet alternation time data D712 (=t), the sediment impurity concentration data D730 (=C), and the pitting corrosion data D30.

[0060] Figure 5E shows a pitting corrosion evaluation table D740 in an embodiment.

[0061] As shown in Figure 5E, the pitting corrosion evaluation table D740 is a table that associates the relationship between the alternating dry-wet time t, the sediment impurity concentration C, and the presence or absence of pitting corrosion. The pitting corrosion evaluation unit 740 receives multiple datasets as input, which associate the alternating dry-wet time data D712 (=t), the sediment impurity concentration data D730 (=C), and the pitting corrosion data D30. The unit then creates the pitting corrosion evaluation table D740 by, for example, applying interpolation to these datasets.

[0062] As shown in Figure 5E, the pitting corrosion evaluation table D740 is configured to include a boundary that separates the region where pitting corrosion occurs from the region where pitting corrosion does not occur, in a Cartesian coordinate system defined by the coordinate axis of the alternating dry-wet time t and the coordinate axis of the sediment impurity concentration C. As can be seen from the pitting corrosion evaluation table D740, pitting corrosion is more likely to occur as the alternating dry-wet time t increases and as the sediment impurity concentration C increases. The pitting corrosion evaluation table D740 is created for each of the multiple turbine stages 60.

[0063] [D-2] Evaluation of pitting corrosion in the operation plan of steam turbine 3 In the pitting corrosion evaluation device 700, after creating the pitting corrosion evaluation table D740 as described above, the evaluation of pitting corrosion occurring in each of the multiple turbine stages 60 during the planned operation of the steam turbine 3 is performed using the pitting corrosion evaluation table D740. Here, for example, the evaluation of pitting corrosion is performed on the steam turbine 3 after repair of pitting corrosion. Alternatively, the evaluation of pitting corrosion may be performed on other steam turbines 3 of the same type as the steam turbine 3 from which the inspection results for pitting corrosion were obtained.

[0064] Figure 6 is a schematic diagram showing the data flow when evaluating the occurrence of pitting corrosion using the pitting corrosion evaluation table D740 in the pitting corrosion evaluation device 700 according to the embodiment.

[0065] The operation of each part of the pitting corrosion evaluation device 700 when performing pitting corrosion evaluation using the pitting corrosion evaluation table D740 will be explained with reference to Figure 6.

[0066] [D-2-1] Turbine operating condition evaluation unit 711 As shown in Figure 6, the turbine operation state evaluation unit 711 is configured to receive power generation output data D10k as input and output turbine operation data D711k based on the power generation output data D10k.

[0067] Here, the power output data D10k, like the power output data D10 shown in Figure 5A, is data that associates the operating time (Time) of the steam turbine 3 with the power output amount P (MW). However, unlike the power output data D10 shown in Figure 5A, the power output amount P in the power output data D10k is the power output amount P that the generator 4 outputs in the operating plan of the steam turbine 3.

[0068] Furthermore, the turbine operation data D711k, like the turbine operation data D711 shown in Figure 5B, is data that associates a percentage R(%) with the operating time (Time) of the steam turbine 3. However, unlike the turbine operation data D711 shown in Figure 5B, the percentage R(%) of the turbine operation data D711k is the percentage obtained by dividing the amount of power output P that the generator 4 outputs in the operating plan of the steam turbine 3 by the rated power output PR (R=100*P / PR).

[0069] As shown in Figure 6, the turbine operation state evaluation unit 711 calculates the ratio R obtained by dividing the power output amount P (= power output data D10k) that the generator 4 outputs in the operation plan of the steam turbine 3 by the rated power output amount PR, and outputs the data related to the calculated ratio R as turbine operation data D711.

[0070] [D-2-2] Dry / wet alternating time calculation unit 712 As shown in Figure 6, the dry / wet alternating time calculation unit 712 is configured to receive turbine operation data D711k as input and output dry / wet alternating time data D712k based on the turbine operation data D711k.

[0071] Unlike the wet-dry alternating time data D712 shown in Figure 5C, the wet-dry alternating time data D712k is data relating to the wet-dry alternating time t in which a wet-dry alternating zone occurs in each of the multiple turbine stages 60 in the operating plan of the steam turbine 3. The calculation of the wet-dry alternating time t for the wet-dry alternating time data D712k is performed in the same way as for the wet-dry alternating time data D712.

[0072] As shown in Figure 6, the wet-dry alternating time calculation unit 712 calculates the wet-dry alternating time t in which a wet-dry alternating zone occurs in each of the multiple turbine stages 60 in the operation plan of the steam turbine 3, based on the turbine operation data D711k. The wet-dry alternating time calculation unit 712 then outputs the data related to the calculated wet-dry alternating time t as wet-dry alternating time data D712k.

[0073] [D-2-3] Working medium impurity concentration calculation unit 721 As shown in Figure 6, the working medium impurity concentration calculation unit 721 is configured to receive steam temperature data D11k and water quality data D20k as input, and to output working medium impurity concentration data D721k based on the steam temperature data D11k and water quality data D20k.

[0074] Unlike the steam temperature data D11 shown in Figure 4, steam temperature data D11k is data relating to the temperature T of the steam supplied to steam turbine 3 in the operation plan for steam turbine 3. Unlike the water quality data D20 shown in Figure 4, water quality data D20k is data relating to the water quality of the feedwater supplied to steam source 2 in the operation plan for steam turbine 3, and includes, for example, data on acid electrical conductivity κ and pH. In the operation plan corresponding to power output data D10k, steam temperature data D11k and water quality data D20k may be data obtained from past operating history. Unlike the working medium impurity concentration data D721 shown in Figure 4, working medium impurity concentration data D721k is data relating to the working medium impurity concentration Cw of the steam supplied to steam turbine 3 in the operation plan for steam turbine 3.

[0075] The working medium impurity concentration Cw, which is the working medium impurity concentration data D721k, is calculated using the same method as the working medium impurity concentration Cw, which is the working medium impurity concentration data D721 described above.

[0076] As shown in Figure 6, the working medium impurity concentration calculation unit 721 calculates the working medium impurity concentration Cw based on the water quality data D20k and the steam temperature data D11k, and outputs the calculated working medium impurity concentration Cw as working medium impurity concentration data D721k.

[0077] [D-2-4] Deposit impurity concentration calculation unit 730 As shown in Figure 6, the sediment impurity concentration calculation unit 730 is configured to receive dry / wet alternation time data D712k (=t), steam temperature data D11k, working medium impurity concentration data D721k (=Cw), and steam flow rate data D12k (=v) as input, and to output sediment impurity concentration data D730 (=C).

[0078] Unlike the steam flow rate data D12 shown in Figure 4, steam flow rate data D12k is data relating to the steam flow rate v of the steam supplied to steam turbine 3 in the operation plan for steam turbine 3. In the operation plan corresponding to the power output data D10k, steam flow rate data D12k may be data obtained from past operation history, similar to steam temperature data D11k and water quality data D20k. Unlike the sediment impurity concentration data D730 shown in Figure 4, sediment impurity concentration data D730k is data relating to the sediment impurity concentration C of the sediment deposited in each of the multiple turbine stages 60 in the operation plan for steam turbine 3. The calculation of the sediment impurity concentration C for sediment impurity concentration data D730k is performed in the same way as for sediment impurity concentration data D730.

[0079] In this manner, the sediment impurity concentration calculation unit 730 calculates the sediment impurity concentration C based on the steam temperature data D11k, steam flow rate data D12k, working medium impurity concentration data D721k, and dry / wet alternation time data D712k, and outputs the calculated sediment impurity concentration C as sediment impurity concentration data D730k.

[0080] [D-2-5] Pitting corrosion evaluation unit 740 As shown in Figure 6, the pitting corrosion evaluation unit 740 receives the dry / wet alternation time data D712k (=t) and the sediment impurity concentration data D730k (=C) as input. The pitting corrosion evaluation unit 740 then uses the pitting corrosion evaluation table D740 (see Figure 5E), which has already been created and stored, to evaluate the pitting corrosion that occurs in each of the multiple turbine stages 60 in the operation plan of the steam turbine 3.

[0081] Specifically, as shown in Figure 5E, the pitting corrosion evaluation unit 740 outputs the result of pitting corrosion as an evaluation result, corresponding to both the alternating dry-wet time t input as the alternating dry-wet time data D712k and the sediment impurity concentration C input as the sediment impurity concentration data D730k in the pitting corrosion evaluation table D740. In other words, if the coordinate position of the alternating dry-wet time t input as the alternating dry-wet time data D712k and the sediment impurity concentration C input as the sediment impurity concentration data D730k in the pitting corrosion evaluation table D740 is in a region where pitting corrosion occurs, then it is evaluated that pitting corrosion has occurred. Conversely, if the coordinate position of the alternating dry-wet time t input as the alternating dry-wet time data D712k and the sediment impurity concentration C input as the sediment impurity concentration data D730k in the pitting corrosion evaluation table D740 is in a region where pitting corrosion does not occur, then it is evaluated that pitting corrosion has not occurred.

[0082] [E] Summary As described above, in the pitting corrosion evaluation device 700 of this embodiment, a pitting corrosion evaluation table D740 is created using various data acquired when the steam turbine 3 is actually in operation, showing the relationship between the dry / wet alternation time t, the sediment impurity concentration C, and the occurrence of pitting corrosion. Then, in the pitting corrosion evaluation device 700 of this embodiment, the pitting corrosion evaluation table D740 is used to evaluate the pitting corrosion that occurs in each of the multiple turbine stages 60 during the planned operation of the steam turbine 3.

[0083] Therefore, in this embodiment, the occurrence of pitting corrosion can be effectively predicted without installing special sensors or the like on the steam turbine 3. This allows for proper maintenance and management of the steam turbine 3. As a result, in this embodiment, the occurrence of stress corrosion cracking and corrosion fatigue damage can be easily suppressed.

[0084] [F] Variation In the above embodiment, the case in which the pitting corrosion occurrence evaluation device 700 is used to evaluate the occurrence of pitting corrosion in relation to the steam turbine power generation system 1 shown in Figure 1 was described, but the invention is not limited to this. The pitting corrosion occurrence evaluation device 700 can be used as appropriate for steam turbine power generation systems equipped with a steam turbine that generates alternating wet and dry zones. For example, the pitting corrosion occurrence evaluation device 700 may be used to evaluate the occurrence of pitting corrosion in relation to a steam turbine power generation system equipped with a geothermal turbine (intermediate pressure turbine) to which steam generated by geothermal energy is supplied as a working fluid.

[0085] <Other> While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. [Explanation of symbols]

[0086] 1: Steam turbine power generation system, 2: Steam source, 3: Steam turbine, 3a: High-pressure turbine, 3b: Intermediate-pressure turbine, 3c: Low-pressure turbine, 4: Generator, 5: Condenser, 6: Feedwater pump, 10: External casing, 11: Lower exhaust port, 12: Cone section, 20: Internal casing, 30: Turbine rotor, 40: Stationary blades, 41: Diaphragm inner ring, 43: Diaphragm outer ring, 45: Nozzle diaphragm, 50: Rotor blades, 60: Turbine stages, 70: Steam supply pipe, 301: Rotor bearing, 700: Pitting corrosion occurrence evaluation device, 711: Turbine operating state evaluation unit, 712: Dry / wet alternation time calculation unit, 721: Working medium impurity concentration calculation unit, 730: Sediment impurity concentration calculation unit, 740: Pitting corrosion occurrence evaluation unit, AX: Rotational center axis

Claims

1. A steam turbine power generation system includes a steam turbine configured such that a plurality of turbine stages are arranged axially along the rotational axis of the turbine rotor, and steam supplied from a steam source is sequentially expanded and performs work in each of the plurality of turbine stages, thereby causing the turbine rotor to rotate, and a generator configured to output electricity by generating electricity through the rotation of the turbine rotor, wherein a pitting corrosion evaluation device evaluates the pitting corrosion that occurs in each of the plurality of turbine stages, A turbine operation state evaluation unit calculates the ratio of the amount of power output generated by the generator when the steam turbine is actually operating to the rated power output generated by the generator when the steam turbine is operating at its rated capacity, and outputs this as turbine operation data. A dry-wet alternating time calculation unit calculates the dry-wet alternating time during which a dry-wet alternating zone occurred in each of the plurality of turbine stages when the steam turbine actually performed the operation, based on the turbine operation data output by the turbine operation state evaluation unit, and outputs it as dry-wet alternating time data. A sediment impurity concentration calculation unit calculates the sediment impurity concentration, which is the impurity concentration of the sediment deposited on each of the plurality of turbine stages when the steam turbine actually performs the operation, based on steam temperature data relating to the temperature of the steam supplied to the steam turbine when the steam turbine actually performs the operation, steam flow rate data relating to the steam flow rate of the steam supplied to the steam turbine when the steam turbine actually performs the operation, working medium impurity concentration data relating to the working medium impurity concentration, which is the impurity concentration of the steam supplied to the steam turbine when the steam turbine actually performs the operation, and the dry-wet alternation time data output by the dry-wet alternation time calculation unit, and outputs the sediment impurity concentration data. A pitting corrosion evaluation unit creates and maintains a pitting corrosion evaluation table showing the relationship between the dry-wet alternation time, the sediment impurity concentration, and the occurrence of pitting corrosion, based on the dry-wet alternation time data output by the dry-wet alternation time calculation unit, the sediment impurity concentration data output by the sediment impurity concentration calculation unit, and the pitting corrosion occurrence data relating to pitting corrosion that occurred in each of the plurality of turbine stages when the steam turbine actually performed the operation. It has, The pitting corrosion evaluation unit is configured to evaluate the pitting corrosion that occurs in each of the plurality of turbine stages during the planned operation of the steam turbine, using the pitting corrosion evaluation table. Pitting corrosion occurrence evaluation device.

2. The dry-wet alternation time calculation unit calculates the dry-wet alternation time by setting the point in time when the increase or decrease in the value in the turbine operation data exceeds a predetermined threshold as the start point of the dry-wet alternation time, and the point in time when the decrease or increase in the value in the turbine operation data exceeds a predetermined threshold as the end point of the dry-wet alternation time. The pitting corrosion evaluation device according to claim 1.

3. A working medium impurity concentration calculation unit calculates the working medium impurity concentration based on water quality data relating to the water quality of the feedwater supplied to the steam source when the steam turbine actually performed the operation, and the steam temperature data, and outputs the working medium impurity concentration data to the sediment impurity concentration calculation unit. It has, The aforementioned water quality data includes data on acid electrical conductivity and pH data. The pitting corrosion evaluation device according to claim 1.

4. A steam turbine power generation system comprising a steam source that generates steam by heating feedwater, a steam turbine in which a plurality of turbine stages are arranged axially along the rotational axis of the turbine rotor, and the steam supplied from the steam source is configured to rotate the turbine rotor by sequentially expanding and performing work in each of the plurality of turbine stages, and a generator configured to output electricity by generating electricity through the rotation of the turbine rotor, wherein a method for evaluating pitting corrosion occurring in each of the plurality of turbine stages, A turbine operating state evaluation step, which involves calculating the ratio of the amount of power output generated by the generator when the steam turbine is actually operating to the rated power output generated by the generator when the steam turbine is operating at its rated capacity, and outputting this as turbine operating data, A dry-wet alternation time calculation step, which calculates the dry-wet alternation time during which a dry-wet alternation area occurred in each of the plurality of turbine stages when the steam turbine actually performed the operation, based on the turbine operation data output in the turbine operation state evaluation step, and outputs it as dry-wet alternation time data, A deposit impurity concentration calculation step calculates the deposit impurity concentration of the deposits deposited on each of the plurality of turbine stages when the steam turbine actually performs the operation, based on steam temperature data relating to the temperature of the steam supplied to the steam turbine when the steam turbine actually performs the operation, steam flow rate data relating to the steam flow rate of the steam supplied to the steam turbine when the steam turbine actually performs the operation, working medium impurity concentration data relating to the working medium impurity concentration, which is the impurity concentration of the steam supplied to the steam turbine when the steam turbine actually performs the operation, and outputs it as deposit impurity concentration data. A pitting corrosion evaluation step is performed to create and maintain a pitting corrosion evaluation table showing the relationship between the dry-wet alternation time, the sediment impurity concentration, and the occurrence of pitting corrosion, based on the dry-wet alternation time data output in the dry-wet alternation time calculation step, the sediment impurity concentration data output in the sediment impurity concentration calculation step, and pitting corrosion occurrence data relating to pitting corrosion that occurred in each of the plurality of turbine stages when the steam turbine actually performed the operation. It has, The pitting corrosion evaluation step is configured to evaluate the pitting corrosion that occurs in each of the multiple turbine stages during the planned operation of the steam turbine, using the pitting corrosion evaluation table. Method for evaluating the occurrence of pitting.

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