Erosion estimation method

Abstract

This erosion estimation method is for estimating the degree of progress of erosion of a last-stage rotor blade of a steam turbine, the method including: a step for sampling supplied water containing a substance to be detected, which is included in the material constituting the last-stage rotor blade, from a water supply line that is connected to the steam turbine; a step for measuring the concentration of the substance to be detected in the sampled supplied water; and a step for estimating the degree of progress of erosion on the basis of the concentration thereof.　

Description

[Technical field]

[0001] The present disclosure relates to an erosion estimation method. This application claims priority to Patent Application No. 2021-109140, filed in Japan on June 30, 2021, the contents of which are incorporated herein by reference. [Background technology]

[0002] In steam turbines, water droplets that condense on the surface of stationary blades are carried away by the steam flow and collide with the surface of downstream moving blades, causing erosion. It is known that erosion is particularly likely to occur in the last stage moving blades. If such erosion progresses, it may affect the strength of the blades.

[0003] Conventionally, the turbine casing was opened during regular inspection of the steam turbine to expose the blades and to actually measure and evaluate the progress of erosion. However, because opening the turbine casing requires a lot of time and cost, there has been a demand in recent years to reduce the frequency of such inspections.

[0004] On the other hand, as shown in Patent Document 1 below, a method of testing the quality of feed water has also been proposed in order to detect corrosion in various parts of a steam turbine system. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2019-178824 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, there was no established method for estimating the progress of erosion from the water quality of the supply water.

[0007] The present disclosure has been made to solve the above-mentioned problems, and has an object to provide an erosion estimation method capable of estimating the progress of erosion simply and at low cost. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems, an erosion estimation method according to the present disclosure is an erosion estimation method for estimating a progress of erosion of a last stage moving blade of a steam turbine, the method including the steps of: sampling feedwater containing a detection target substance contained in a material constituting the last stage moving blade from a feedwater line connected to the steam turbine; measuring a concentration of the detection target substance in the sampled feedwater; and estimating a progress of erosion based on the concentration. In the step of estimating the degree of progress of erosion, it is estimated from the amount of change over time of the detection target substance whether the degree of progress of erosion corresponds to an initial period during which almost no erosion occurs after the start of operation, a transitional period after the initial period in which erosion progresses rapidly compared to the initial period, or a stable period after the transitional period in which the slope of the degree of progress of erosion becomes gentler compared to the transitional period. . In addition, an erosion estimation method according to the present disclosure is an erosion estimation method for estimating the progress of erosion of a final stage blade of a steam turbine, and includes the steps of sampling feedwater containing a detection target substance contained in a material constituting the final stage blade from a feedwater line connected to the steam turbine, measuring the concentration of the detection target substance in the sampled feedwater, and estimating the progress of erosion based on the concentration, wherein the final stage blade has a blade main body and the detection target substance embedded in the blade main body. In addition, an erosion estimation method according to the present disclosure is an erosion estimation method for estimating the progress of erosion of a final stage blade of a steam turbine, and includes the steps of sampling feedwater containing a detection target substance contained in a material constituting the final stage blade from a feedwater line connected to the steam turbine, measuring the concentration of the detection target substance in the sampled feedwater, and estimating the progress of erosion based on the concentration, wherein the detection target substance is a radioactive element that has been impregnated in advance into the final stage blade. Effect of the Invention

[0009] According to the present disclosure, it is possible to provide an erosion estimation method that is capable of estimating the progress of erosion simply and at low cost. [Brief description of the drawings]

[0010] [Figure 1] 1 is a system diagram showing a configuration of a steam turbine system according to an embodiment of the present disclosure. [Diagram 2] FIG. 1 is a schematic diagram illustrating a configuration of a steam turbine according to an embodiment of the present disclosure. [Diagram 3] FIG. 2 is a schematic diagram illustrating a configuration of a final stage blade according to an embodiment of the present disclosure. [Figure 4] 1 is a flowchart illustrating steps of an erosion estimation method according to an embodiment of the present disclosure. [Diagram 5] 4 is a graph showing an example of the progress of erosion in a final stage rotor blade. [Figure 6] FIG. 2 is a system diagram illustrating a modified example of a steam turbine system according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, a steam turbine system 100, a final stage rotor blade 90, and an erosion estimation method according to an embodiment of the present disclosure will be described with reference to FIGS. 1 to 4. FIG.

[0012] (Configuration of Steam Turbine System) As shown in FIG. 1, the steam turbine system 100 includes a steam turbine 1, a condenser 2, a condensate pump 3, a low-pressure economizer 41, an intermediate-pressure economizer 43, a high-pressure economizer 42, a feedwater pump 5, a high-pressure evaporator 61, an intermediate-pressure evaporator 62, a low-pressure evaporator 63, a high-pressure drum 71, an intermediate-pressure drum 72, a low-pressure drum 73, a high-pressure superheater 81, an intermediate-pressure superheater 82, a low-pressure superheater 83, a reheater 9, a collection line 10, a feedwater line 30, a high-pressure steam line 51, an intermediate-pressure steam line 52, a low-pressure steam line 53, an extraction line 54, and a reheat steam line 55.

[0013] (Steam turbine configuration) As shown in Fig. 2, the steam turbine 1 has a rotating shaft 11, a casing 12, a row of rotor blades 16, and a row of stator blades 18. The rotating shaft 11 extends along an axis O and is rotatable about the axis O. A pair of journal bearings 14 and one thrust bearing 15 are provided at the shaft end of the rotating shaft 11. The journal bearing 14 supports a radial load on the rotating shaft 11. The thrust bearing 15 supports a load on the rotating shaft 11 in the direction of the axis O.

[0014] A plurality of rotor blade rows 16 are provided on the outer circumferential surface of the rotating shaft 11 and are arranged at intervals in the direction of the axis O. Each rotor blade row 16 has a plurality of rotor blades 17 arranged at intervals in the circumferential direction about the axis O. Of the plurality of rotor blade rows 16, the rotor blade 17 included in the rotor blade row 16 located furthest to one side in the direction of the axis O is designated as a final stage rotor blade 90.

[0015] The casing 12 covers the rotating shaft 11 and the row of moving blades 16 from the outer periphery. The casing 12 has a cylindrical shape centered on the axis O. A steam supply port 12a for guiding steam from the outside is formed on the other side of the casing 12 in the direction of the axis O. A steam exhaust port 12b for guiding steam to the outside is formed on one side of the casing 12 in the direction of the axis O. A steam flow path is formed between the steam supply port 12a and the steam exhaust port 12b. In the following description, the side where the steam supply port 12a is located from the steam exhaust port 12b is referred to as the upstream side, and the opposite side is referred to as the downstream side.

[0016] A plurality of stator blade rows 18 arranged at intervals in the direction of the axis O are provided on the inner circumferential surface of the casing 12. Each stator blade row 18 has a plurality of stator blades 19 arranged at intervals in the circumferential direction about the axis O. The stator blade rows 18 and the rotor blade rows 16 are arranged alternately in the direction of the axis O. In other words, one rotor blade row 16 is arranged downstream of one stator blade row 18.

[0017] (Configuration of final stage rotor blade) As shown in FIG. 3, the final stage rotor blade 90 has a blade body 91 and an erosion shield 92. The blade body 91 extends from the outer circumferential surface of the rotating shaft 11 toward the radially outward direction. When viewed from the radial direction, the cross-sectional shape of the blade body 91 is an airfoil shape with the upstream side as the leading edge. An erosion shield 92 is provided on the leading edge side of the tip portion (i.e., the portion including the radially outer end portion) of the blade body 91. The erosion shield 92 is provided to prevent erosion from occurring on the surface of the final stage rotor blade 90 due to droplets scattered from the upstream stator blade row 18. The erosion shield 92 is integrally formed of Stellite. Stellite is a metal material mainly composed of cobalt element. Although details will be described later, in this embodiment, the cobalt element contained in this Stellite is called the detection target substance.

[0018] (Other components of the steam turbine system) 1, a feedwater line 30 is connected to the downstream side (i.e., steam exhaust port 12b) of the steam turbine 1. A condenser 2, a condensate pump 3, a collection line 10, a low-pressure economizer 41, and a feedwater pump 5 are provided on the feedwater line 30 in this order from the steam turbine 1 side.

[0019] The condenser 2 is a device for cooling the low-pressure steam discharged from the steam turbine 1 and returning it to liquid water. The condensate pump 3 pumps this liquid water downstream on the feedwater line. The collection line 10 is a pipe for extracting a portion of the feedwater flowing in the feedwater line 30 to the outside. The low-pressure economizer 41 is provided for preheating the feedwater. The feedwater pump 5 further pumps the feedwater in the feedwater line 30.

[0020] A downstream end of the water supply line 30 is connected to the high-pressure economizer 42. A first branch line 31 is connected to the water supply line 30 between the low-pressure economizer 41 and the feed water pump 5. A downstream end of the first branch line 31 is connected to a low-pressure evaporator 63 described below. Furthermore, a second branch line 32 is connected to the water supply line 30 on the downstream side of the feed water pump 5. A downstream end of the second branch line 32 is connected to the medium-pressure economizer 43.

[0021] Similar to the low pressure economizer 41, the medium pressure economizer 43 and the high pressure economizer 42 are devices for preheating feedwater. The feedwater preheated by the low pressure economizer 41 is sent to the low pressure evaporator 63. The low pressure evaporator 63 further heats the feedwater to generate low pressure steam. The feedwater preheated by the medium pressure economizer 43 is sent to the medium pressure evaporator 62. The medium pressure evaporator 62 further heats the feedwater to generate medium pressure steam. Similarly, the feedwater preheated by the high pressure economizer 42 is sent to the high pressure evaporator 61. The high pressure evaporator 61 further heats the feedwater to generate high pressure steam.

[0022] The high-pressure drum 71 is provided to separate the high-pressure steam generated in the high-pressure evaporator 61 into gas and liquid. The gas phase component of the separated gas and liquid is sent to the high-pressure superheater 81 via the high-pressure steam line 51. The high-pressure superheater 81 superheats the high-pressure steam to generate high-pressure superheated steam. The high-pressure superheated steam is sent to the steam turbine 1 via the high-pressure steam line 51.

[0023] The intermediate-pressure drum 72 is provided to separate the medium-pressure steam generated in the intermediate-pressure evaporator 62 into gas and liquid. The gas phase component of the gas-liquid separated steam is sent to the intermediate-pressure superheater 82 through the intermediate-pressure steam line 52. The intermediate-pressure superheater 82 superheats the medium-pressure steam to generate medium-pressure superheated steam. The medium-pressure superheated steam is sent to the reheater 9 through the intermediate-pressure steam line 52. The reheater 9 further heats the medium-pressure superheated steam. The superheated steam heated in the reheater 9 is sent to the steam turbine 1 through the reheat steam line 55. Furthermore, a portion of the steam extracted from the steam turbine 1 flows into the reheater 9 through the extraction line 54. This extracted steam is also heated in the reheater 9 and then supplied to the steam turbine 1 through the reheat steam line 55.

[0024] The low-pressure drum 73 is provided to separate the low-pressure steam generated in the low-pressure evaporator 63 into gas and liquid. The gas phase component of the separated gas and liquid is sent to the low-pressure superheater 83 through the low-pressure steam line 53. The low-pressure superheater 83 superheats the low-pressure steam to generate low-pressure superheated steam. The low-pressure superheated steam is sent to the steam turbine 1 through the low-pressure steam line 53.

[0025] (Method of estimating erosion) Next, a method for estimating erosion according to this embodiment will be described. When the above-mentioned steam turbine 1 is operated, the steam temperature increases toward the upstream side of the steam flow passage, and decreases toward the downstream side. For this reason, steam is likely to condense in the downstream region, generating water droplets (liquid droplets). Such water droplets may ride the steam flow and flow further downstream, and collide with the rotating rotor blade row 16. In this case, the surface of the rotor blade row 16 is eroded by the energy of the collision (causing erosion). It is known that erosion is particularly likely to occur in the final stage rotor blade 90. If such erosion progresses, it may affect the strength of the blade. Therefore, in this embodiment, the progress of erosion is estimated by the following method.

[0026] As shown in FIG. 4, the method for estimating erosion according to this embodiment includes step S1 of sampling feedwater, step S2 of measuring the concentration of the substance to be detected in the feedwater, step S3 of estimating the degree of progress of erosion from the concentration, step S4 of determining whether the degree of progress is equal to or greater than a predetermined threshold value, and step S5 of repairing or replacing final stage blade 90 when it is determined that the degree of progress is equal to or greater than the threshold value.

[0027] In step S1, a portion of the feed water is sampled through the sampling line 10 described above. In the process of erosion, a portion of the erosion shield 92 described above is eroded, and some of its components become contained in the feed water. Therefore, in this embodiment, the cobalt element contained in the stellite that forms the erosion shield 92 is set as the detection target substance. In step S2, the concentration of the cobalt element contained in the sampled feed water is measured. A plasma emission mass spectrometer is preferably used to measure the concentration.

[0028] In the subsequent step S3, the progress of erosion is estimated based on the concentration of the cobalt element measured in step S2. It is known that erosion follows a time change as shown in the graph in FIG. 5. The horizontal axis of the graph in FIG. 5 is not real time, but an equivalent time expressed as a function of the steam wetness, steam turbine output, and steam flow rate as variables. The vertical axis of the graph represents the progress of erosion. As shown by the curve in the figure, erosion hardly occurs or is very small until a certain period (initial period t1) has passed since the start of operation. On the other hand, in the period after the initial period t1 (transitional period t2), erosion progresses rapidly. After that, when the stable period t3 is entered, the slope of the progress of erosion becomes gentle and takes an approximately constant value. In step S3, the progress of erosion is estimated by comparing the graph in FIG. 5 based on the amount of change in the cobalt element over time. In other words, the amount of change in the cobalt element over time is used to estimate which stage in the graph in Figure 5 the current progress of erosion corresponds to.

[0029] In step S4, it is determined whether the progress of erosion is equal to or greater than a threshold value. If it is determined that the progress is equal to or greater than the threshold value (step S4: Yes), the final stage rotor blade 90 is replaced or repaired in the subsequent step S5. If it is determined that the progress is less than the threshold value (step S4: No), steps S1 to S4 are repeated again. This completes all the steps of the erosion estimation method according to this embodiment.

[0030] (Action and effect)

[0031] As described above, according to the above method, the progress of erosion of the last stage rotor blades 90 can be estimated without opening the casing 12 of the steam turbine 1, simply by measuring the concentration of the detection target substance in the feedwater. In particular, inspection work involving opening the casing 12 incurs costs for the work itself, and also incurs large costs for the user since operation is not possible during the inspection period. By employing the above method, it is possible to reduce the frequency of opening, thereby reducing costs due to maintenance and lost opportunities to operate.

[0032] According to the above method, the erosion shield 92, which is most likely to concentrate erosion, contains a detection target substance that is not used in other parts of the steam turbine. This makes it possible to estimate the progress of erosion based on the concentration of the detection target substance. Degree can be estimated with high accuracy. Furthermore, according to the above method, the cobalt element is used as the detection target substance. The cobalt element is not used in other parts, and since it has properties similar to iron (Fe), it is possible to easily repurpose existing monitoring equipment that was installed for the purpose of detecting iron content for estimating erosion. In other words, in many steam turbine systems 100, equipment similar to the above-mentioned sampling line 10 is already installed, and it is possible to repurpose this equipment to sample feedwater.

[0033] Furthermore, according to the above method, the progress of erosion can be estimated by sampling the relatively low-temperature feedwater flowing between the condensate pump 3 and the economizer (low-pressure economizer 41). This reduces the burden on workers, since there is no need for them to come into contact with high-temperature steam or feedwater, for example.

[0034] (Other embodiments) Although the embodiments of the present disclosure have been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and design changes and the like that do not depart from the gist of the present disclosure are also included.

[0035] For example, in the above embodiment, the cobalt element contained in the stellite forming the erosion shield is used as the detection target substance. However, it is also possible to embed the detection target substance itself in the blade main body 91 with a different degree of penetration. With this configuration, since the detection target substance is embedded in the blade main body 91, erosion can be detected with high accuracy no matter where erosion progresses in the blade main body 91.

[0036] Furthermore, instead of the cobalt element, a radioactive element that has been impregnated in the final stage rotor blade 90 in advance can be used as the detection target substance.

[0037] According to the above configuration, a radioactive element is used as the detection target substance. The radioactive element is not used in other parts of the steam turbine. Therefore, by using a radioactive element as the detection target substance, it is possible to clearly and accurately estimate the progress of erosion.

[0038] In the above embodiment, an example has been described in which the erosion estimation method is applied to the steam turbine 1 in the steam turbine system 100. However, the method can also be applied to a thermal power generation system 200 as shown in FIG.

[0039] In the thermal power generation system 200, a condenser 2, a condensate pump 3, a collection line 10, a desalination device 4b, a condensate boost pump 3b, a plurality of low-pressure heaters 5b, a deaerator 6b, a feedwater pump 7b, a plurality of high-pressure heaters 8b, a coal economizer 9b, a furnace 10b, and a superheater 11b are provided on a feedwater line 30b in this order from the steam turbine 1 toward the downstream side. Superheated steam generated in the superheater 11b is sent to the steam turbine 1 through a high-pressure steam line 51b. Also, a part of the steam in the steam turbine 1 is sent to the reheater 13b through an extraction line 52b. Steam heated in the reheater 13b is sent to the steam turbine 1 through a reheat steam line 53b.

[0040] Of these elements, the collection line 10 may be provided anywhere in the section of the feedwater line 30b from the condenser 2 to the low-pressure heater 5b.

[0041] <Additional Notes> The erosion estimation method described in each embodiment can be understood, for example, as follows.

[0042] (1) The erosion estimation method of the first aspect is an erosion estimation method for estimating the degree of erosion of a final stage moving blade 90 of a steam turbine 1, and includes a step S1 of sampling feedwater containing a detection target substance contained in a material constituting the final stage moving blade 90 from a feedwater line 30, 30b connected to the steam turbine 1, a step S2 of measuring the concentration of the detection target substance in the sampled feedwater, and a step S3 of estimating the degree of erosion based on the concentration.

[0043] According to the above method, the progress of erosion of the last stage rotor blade 90 can be estimated without opening the casing 12 of the steam turbine 1, simply by measuring the concentration of the detection target substance in the feed water.

[0044] (2) In the erosion estimation method of the second aspect, the final stage rotor blade 90 may have a blade main body 91 and an erosion shield 92 provided on the leading edge side of the tip of the blade main body 91 and formed of a material containing the substance to be detected.

[0045] According to the above method, the detection target substance is contained in the erosion shield 92 where erosion is most likely to concentrate. Degree can be detected with greater accuracy.

[0046] (3) In the erosion estimation method according to the third aspect, the final stage rotor blade 90 may have a blade main body 91 and the detection target substance embedded in the blade main body 91.

[0047] According to the above method, since the detection target substance is embedded in the blade main body 91, no matter where erosion progresses in the blade main body 91, it can be detected with high accuracy.

[0048] (4) In the erosion estimation method according to the fourth aspect, the detection target substance may be elemental cobalt.

[0049] According to the above method, the cobalt element is used as the detection target substance. Since the cobalt element exhibits properties similar to those of iron (Fe), it is possible to easily convert existing monitoring equipment installed for the purpose of detecting iron to the estimation of erosion.

[0050] (5) In the erosion estimation method according to the fifth aspect, the detection target substance may be a radioactive element that has been impregnated into the final stage rotor blade 90 in advance.

[0051] According to the above method, a radioactive element is used as the detection target substance. The radioactive element is not used in other parts of the steam turbine 1. Therefore, by using a radioactive element as the detection target substance, the progress of erosion can be estimated clearly and with high accuracy.

[0052] (6) In an erosion estimation method according to a sixth aspect, in a steam turbine system 100 having a condenser 2 that cools steam discharged from the steam turbine 1 and returns it to water, a condensate pump 3 provided downstream of the condenser 2, a coal economizer (low-pressure economizer 41) provided downstream of the condensate pump 3 that preheats the water, evaporators (high-pressure evaporator 61, medium-pressure evaporator 62, low-pressure evaporator 63) that heat the water preheated in the economizer to generate steam, and superheaters (high-pressure superheater 81, medium-pressure superheater 82, low-pressure superheater 83) that superheat the steam generated in the evaporators, in step S1 of sampling the feedwater, the feedwater may be sampled from between the condensate pump 3 and the coal economizer.

[0053] According to the above method, the progress of erosion can be estimated by sampling the relatively low-temperature feedwater flowing between the condensate pump 3 and the low-pressure economizer 41. This reduces the burden on workers, for example, because there is no need for them to come into contact with high-temperature steam or feedwater. [Industrial Applicability]

[0054] According to the present disclosure, it is possible to provide an erosion estimation method that is capable of estimating the progress of erosion simply and at low cost. [Explanation of symbols]

[0055] 100 Steam Turbine System 1. Steam turbine 2 Condenser 3 Condensate pump 3b Condensate booster pump 4b Desalination equipment 5. Water Pump 5b Low pressure heater 6b Deaerator 7b Water pump 8b High pressure heater 9 Reheater 9b Economizer 10b Furnace 10 Harvesting Line 11 Rotation axis 11b Superheater 12 Casing 12a Steam supply port 12b Steam exhaust port 13b Reheater 14 Journal bearings 15 Thrust bearing 16 Moving blade row 17 Moving blade 18 Stator blade row 19 Stator blade 30,30b Water supply line 31 First Branch Line 32 Second Branch Line 41 Low-pressure economizer 42 High-pressure economizer 43 Medium pressure economizer 51,51b High pressure steam line 52 Medium pressure steam line 53 Low Pressure Steam Line 54,52b Bleed line 55,53b Reheat steam line 61 High-pressure evaporator 62 Medium pressure evaporator 63 Low Pressure Evaporator 71 High Pressure Drum 72 Medium Pressure Drum 73 Low Pressure Drum 81 High Pressure Superheater 82 Medium pressure superheater 83 Low Pressure Superheater 90 Last stage rotor blade 91 Wing body 92 Erosion Shield 200 Thermal Power Generation System O axis

Claims

1. An erosion estimation method for estimating a progress of erosion of a last stage rotor blade of a steam turbine, comprising: A step of collecting feed water containing a detection target substance contained in a material constituting the final stage rotor blade from a feed water line connected to the steam turbine; measuring a concentration of the detection target substance in the collected feed water; estimating a degree of erosion based on the concentration; Including, In the step of estimating the degree of erosion, an erosion estimation method is used to estimate, from the amount of change over time in the substance to be detected, whether the degree of erosion corresponds to an initial period during which almost no erosion occurs after the start of operation, a transitional period after the initial period in which erosion progresses rapidly compared to the initial period, or a stable period after the transitional period in which the slope of the rate of erosion progression becomes gentler compared to the transitional period.

2. The final stage rotor blade is The wing body and 2. The erosion estimation method according to claim 1, further comprising: an erosion shield provided on a leading edge side of a tip portion of the blade main body and made of a material containing the detection target substance.

3. The final stage rotor blade is The wing body and The detection target substance embedded in the blade body; The erosion estimation method according to claim 1 , comprising:

4. 4. The erosion estimation method according to claim 1, wherein the detection target substance is a cobalt element.

5. 4. The erosion estimation method according to claim 1, wherein the detection target substance is a radioactive element that has been impregnated in advance into the last stage rotor blade.

6. An erosion estimation method for estimating a progress of erosion of a last stage moving blade of a steam turbine, comprising: A step of collecting feed water containing a detection target substance contained in a material constituting the final stage rotor blade from a feed water line connected to the steam turbine; measuring a concentration of the detection target substance in the collected feed water; estimating a degree of erosion based on the concentration; Including, The final stage rotor blade is The wing body and The detection target substance embedded in the blade body; The erosion estimation method has the following structure:

7. An erosion estimation method for estimating a progress of erosion of a last stage moving blade of a steam turbine, comprising: A step of collecting feed water containing a detection target substance contained in a material constituting the final stage rotor blade from a feed water line connected to the steam turbine; measuring a concentration of the detection target substance in the collected feed water; estimating a degree of erosion based on the concentration; Including, The detection target substance is a radioactive element that has been impregnated in advance into the last stage rotor blade.

8. a condenser that cools the steam discharged from the steam turbine and converts it back into water; a condensate pump provided downstream of the condenser; a fuel economizer provided downstream of the condensate pump for preheating the water; an evaporator that heats the water preheated by the economizer to generate steam; a superheater that superheats the steam generated in the evaporator; In a steam turbine system having The erosion estimation method according to claim 1 , wherein in the step of sampling the feedwater, the feedwater is sampled from between the condensate pump and the economizer.

Images