A method for evaluating the condition of a high-pressure steam pipe of a steam turbine

Abstract

A method for evaluating the status of a high-pressure steam pipe of a steam turbine comprises the following steps: 1) clarifying the evaluation object steam turbine high-pressure steam pipe and confirming basic information; 2) clarifying the stage of the full operation life cycle of the evaluation object; 3) selecting evaluation points from straight pipes, elbows and welds; 4) calculating basic status factors according to the stage of the full operation life cycle and the defects found in the design, manufacturing and installation stages; 5) calculating correction factors according to the feedback of the evaluation results of the evaluation object; 6) selecting executable projects for the selected evaluation points to formulate and implement offline detection plans; 7) obtaining offline detection state parameter results; 8) performing status evaluation on the selected straight pipes, elbows and welds evaluation points; 9) performing status evaluation on the evaluation object based on the status evaluation results of the comprehensive evaluation points; 10) providing feedback for the next evaluation to calculate correction factors. The present invention can help steam turbine or metal professional and technical personnel in thermal power plants to better formulate maintenance strategies.

Description

Technical Field

[0001] The invention belongs to the technical field of equipment status assessment in thermal power plants, and in particular relates to a method for assessing the status of a high-pressure steam conduit of a steam turbine. Background Art

[0002] The high-pressure steam pipe of the steam turbine is an important component of the steam turbine system of a thermal power plant. In recent years, thermal power units have frequently participated in the peak load regulation of the power grid, which makes the high-pressure steam pipe of the steam turbine in a relatively harsh working condition during operation. It is easily affected by the thermal alternating load. In addition, long-term high-temperature and high-pressure operation makes it easy for creep voids in local areas to form microcracks. In particular, under the influence of high-temperature and high-pressure variable loads, the weld tissue state of the high-pressure steam pipe and the high-pressure outer cylinder of the steam turbine deteriorates and the tissue embrittlement increases the risk of failure. In addition, since the high-pressure steam pipe of the steam turbine is located outside the high-pressure cylinder of the steam turbine platform, if it fails, it will cause a major safety accident. Therefore, it is necessary to accurately evaluate the state of the high-pressure steam pipe of the steam turbine.

[0003] Regarding the high-pressure steam pipe of a steam turbine, there are literature reports on the use of non-destructive testing methods to evaluate the material status and estimate the creep residual life of the boiler steam pipe of a power plant, such as the literature "Material Status and Creep Remaining Life Evaluation of Boiler Steam Pipes, Thermal Power Generation, 2011 (8)". There are literature reports on the determination of the high-temperature impact energy and high-temperature endurance strength of the steam pipe based on laboratory material performance tests, and the calculation of the maximum stress of the steam pipe under working conditions and the prediction of the remaining life of the steam pipe based on the finite element method, such as the literature "Availability Assessment and Remaining Life Analysis of Power Plant Boiler Steam Pipes, East China University of Science and Technology, 2002". There are also literature reports on the calculation of the residual life of the high-pressure steam pipe based on the comprehensive strength analysis method based on material aging factors and the creep damage method, such as the literature "Usage Status Evaluation and Life Assessment of the High-Pressure Steam Pipe of Huainan Tianjia'an Power Plant, Proceedings of the Sixth National Conference on Failure Analysis and Life Management of Metal Components in Power Plants, 2000". However, no reports on the status evaluation of the high-pressure steam pipe of a steam turbine were found.

[0004] Therefore, it is necessary to find a universal method that does not require the evaluator to have rich basic knowledge of mathematical analysis, basic knowledge of metal materials, knowledge of mechanical calculation, knowledge and experience of life assessment, and does not require the evaluator to bear additional testing costs. Only by obtaining existing offline detection data, the condition of the turbine high-pressure steam pipe can be evaluated, thereby directly helping thermal power plant technicians to formulate maintenance strategies. Summary of the invention

[0005] In order to overcome the above technical problems, the purpose of the present invention is to provide a method for evaluating the status of a high-pressure steam duct of a steam turbine, so as to help steam turbine professionals or metal professionals in thermal power plants to better formulate maintenance strategies.

[0006] In order to achieve the above object, the technical solution adopted by the present invention and the beneficial effects of the present invention are:

[0007] A method for evaluating the status of a high-pressure steam duct of a steam turbine comprises the following steps:

[0008] 1) Clarify the assessment object and its basic information. The assessment object is the high-pressure steam pipe of the steam turbine, such as the high-pressure steam pipe on the left side of the steam turbine and the high-pressure steam pipe on the right side of the steam turbine. The basic information includes design drawings, design diameter, design wall thickness, design material, design and manufacturing data, and previous maintenance records;

[0009] 2) Clarify the four stages of the entire operational life cycle of the assessment object: early, mid, late and final stages;

[0010] 3) Based on the principles of key parts of equipment, easy inspection and operation, lowest maintenance cost, and controllable maintenance plan, detailed evaluation points are selected from straight pipes, elbows and welds;

[0011] 4) Calculate the basic condition factor based on the full operational life cycle stage and defects found during the design, manufacturing and installation stages;

[0012] 5) Calculate the correction factor based on the feedback of the last three evaluation results of the evaluation object;

[0013] 6) For the selected evaluation points, select appropriate items from macro inspection, surface flaw detection, non-destructive testing, metallographic inspection, pipe diameter inspection, ovality measurement, hardness inspection, and wall thickness measurement to formulate and implement offline inspection plans;

[0014] 7) Obtain offline detection status parameter results;

[0015] 8) Conduct condition assessment on selected straight pipes, elbows and weld assessment points;

[0016] 9) Comprehensively evaluate the status of all evaluation points and conduct status evaluation on the evaluation object;

[0017] 10) The status of the evaluation object is used as feedback for the next evaluation and to calculate the correction factor.

[0018] The specific operation steps of step 2) are:

[0019] It is clear that the assessment object is in a specific stage of the entire operational life cycle. The early stage is (0,0.1L c ], the middle stage is (0.1L c ,0.8L c ], the final stage is (0.8L c ,0.9L c ], the terminal stage is (0.9L c ,Lc ], L c is the design life, L c Generally, it is 30 years.

[0020] The specific operation steps of step 3) are:

[0021] Based on comprehensive consideration of the principles of key parts of equipment, easy detection, lowest maintenance cost, and controllable maintenance plan, the evaluation points are determined in a targeted manner and divided into three categories: straight pipes, elbows, and welds, which are distinguished by the following subscripts st, et, and wb respectively.

[0022] The specific operation steps for calculating the basic state factor in step 4) are:

[0023] Based on the full operational life cycle stage of the evaluation object identified in step 2), and combined with the defects found in the design, manufacturing and installation stages, the basic state factor C is determined according to formula (1): S ;

[0024] C S =α·S (1)

[0025] In the formula, the values ​​of parameters α and S are found in the following table according to the basic information collected in step 1);

[0026]

[0027] The specific operation steps for calculating the correction factor in step 5) are:

[0028] Based on the feedback of the last three evaluation results of the evaluation object, the correction factor C is determined according to formula (2): C ;

[0029]

[0030] In the formula, parameter δ is the operating time of the evaluation object (unit: year);

[0031] C1, C2, and C3 are the correction coefficients corresponding to the three most recent evaluation results, and their values ​​are shown in the following table.

[0032]

[0033]

[0034] The specific operation steps of step 6) are:

[0035] For the evaluation points determined in step 3), select executable items from macro inspection, surface flaw detection, non-destructive testing, metallographic inspection, pipe diameter inspection, ovality measurement, hardness inspection, and wall thickness measurement to develop and implement an offline inspection plan.

[0036] The specific operation steps of step 7) are:

[0037] According to the offline detection items determined in step 6), the offline detection status parameter results of the evaluation points are obtained and divided into two categories: rating category and measurement category.

[0038] The state parameters corresponding to the four offline inspection items of macro inspection, surface flaw detection, nondestructive testing, and metallographic inspection are collectively referred to as rating state parameters. The state parameters and weights are denoted by CP G1 , CP G2 , CP G3 , CP G4 and W G1 , W G2 , W G3 , W G4 express.

[0039] The state parameters corresponding to the four offline inspection items of pipe diameter inspection, ovality measurement, hardness inspection, and wall thickness measurement are collectively referred to as rating state parameters. The state parameters and weights are denoted by CP M1 , CP M2 , CP M3 , CP M4 and W M1 , W M2 , W M3 , W M4 express.

[0040] The specific operation steps of step 8) are:

[0041] According to the offline detection state parameter results obtained in step 7), a state evaluation is performed on a single evaluation point, and the state of a single evaluation point is defined as C j , the evaluation model is shown in formula (3);

[0042]

[0043] Status C of the evaluation point j The numerical result of C normally falls within the range of [0,1]. j When the value of changes from 0 to 1, the status of the evaluation point becomes worse and worse;

[0044] The weights W of the two types of state parameters in formula (3) are Gi , W Mi The value of gives the rule of formula (4);

[0045]

[0046] The specific operation steps in step 9) are:

[0047] For all the evaluation points obtained in step 8), statistics are performed according to the classification of straight pipes, elbows and welds (the subscripts are st, et and wb respectively), and the number of straight pipe evaluation points x, elbow evaluation points y and weld evaluation points z are counted. Then, the evaluation object is evaluated as a whole, and the evaluation model of the final state value is shown in formula (13).

[0048]

[0049] If the status C value of the evaluation object is 0, the status of the evaluation object is considered to be the best. When the C value changes from 0 to 1, the status of the evaluation object gradually deteriorates. When the C value is greater than 0.8, the status of the evaluation object is poor, and there are many evaluation points in poor condition, especially at the end and terminal stages of the full operating life cycle. If the status C value of the evaluation object is greater than 0.8 for three consecutive evaluations, it also confirms that the status of the evaluation object is poor, and the enterprise should be prepared to replace the overall evaluation object.

[0050] The specific operation steps in step 10) are:

[0051] The state evaluation result of the evaluation object obtained in step 9) is fed back for the next evaluation and used to calculate the correction factor in step 5).

[0052] Rating state parameter in step 7): macro state parameter CP G1-j , OS by macroscopic inspection results G1-j : {no defects found, a small number of suspected defects found, obvious defects found} is defined as shown in formula (5):

[0053]

[0054] In step 7), the rating state parameter: surface state parameter CP G2-j , according to the results of surface flaw detection OS G2-j : {no defects found, surface defects found but eliminated after polishing, surface defects found but still exist after polishing} is defined as shown in formula (6):

[0055]

[0056] Rating class status parameter in step 7): lossless status parameter CP G3-j , based on the results of nondestructive testing OS G3-j :{Level I, Level II, Level III, Level IV} definition, as shown in formula (7):

[0057]

[0058] Rating status parameter in step 7): Organization status parameter CP G4-j, the results of metallographic examination OS G4-j : {level 1, level 2, level 3, level 4, level 5} is defined as shown in formula (8):

[0059]

[0060] The measurement state parameter in step 7): pipe diameter state parameter CP M1-j , the result of the pipe diameter inspection OS M1-j The definition is as shown in formula (9):

[0061]

[0062] In formula (9), D0 is the design pipe diameter, in mm; e is the limit creep rate, in %. For the high-pressure steam guide pipe of the steam turbine, the limit creep rate is as shown in the following table:

[0063] Material alloy steel Carbon Steel e value 2.5％ 3.5％

[0064] The measurement state parameter in step 7): ellipticity state parameter CP M2-j , the result of the ellipticity check OS M2-j The definition is as shown in formula (10):

[0065]

[0066] In formula (10), D max To measure the maximum outer diameter, the unit is mm; D min is the minimum outer diameter to be measured, in mm; β is the ovality limit value, in %, for the high-pressure steam guide pipe of the steam turbine, the ovality limit value is shown in the following table:

[0067] Material <![CDATA[R / D0≥4]]> <![CDATA[2.5≥R / D0>4]]> <![CDATA[R / D0<2.5]]> β value 10％ 12％ 14％

[0068] Wherein, R is the bending radius, in mm; D0 is the designed pipe diameter, in mm.

[0069] The state parameter measured in step 7): hardness state parameter CP M3-j , according to the hardness test results OS M3-j The definition is as shown in formula (11):

[0070]

[0071] The hardness in formula (11) is the Brinell hardness, HB L and HB H They are the minimum and maximum limit hardness respectively. For the high-pressure steam pipe of the steam turbine, the HB of common materials L and HB H The values ​​are summarized in the following table:

[0072] Material P91 P92 P122 … <![CDATA[HB L ]]> 185 185 185 … <![CDATA[HB H ]]> 270 270 270 …

[0073] The state parameter measured in step 7): wall thickness state parameter CP M4-j , the result of the wall thickness inspection OS M4-j Definition, as shown in formula (12):

[0074]

[0075] In formula (12), d0 is the designed wall thickness, in mm.

[0076] Beneficial effects of the present invention:

[0077] The present invention does not require the assessor to have rich basic knowledge of metal materials, mechanical calculation knowledge, life assessment knowledge and experience, nor does it need to bear additional testing costs. Based on conventional metal inspection data of the steam turbine high-pressure steam pipe, the steam turbine high-pressure steam pipe is assessed for its condition through correction of basic condition factors and correction factors, thereby directly helping thermal power plant technicians to formulate the next maintenance strategy. If the condition value of the steam turbine high-pressure steam pipe gradually increases and the condition becomes worse and worse after three consecutive assessments, the company should be prepared to replace the entire assessment object.

[0078] The above technical scheme is used to evaluate the status of the steam turbine high-pressure steam pipe, which can not only help the technical personnel of the thermal power plant understand the actual status of the steam turbine high-pressure steam pipe, but also predict the changing trend of its status through multiple status evaluation results at the same evaluation point. It can also comprehensively evaluate the overall status of the steam turbine high-pressure steam pipe based on the status results of all evaluation points, which is of great significance for formulating maintenance plans and replacement strategies. BRIEF DESCRIPTION OF THE DRAWINGS

[0079] Figure 1 It is a schematic diagram of the state evaluation process of the present invention. DETAILED DESCRIPTION

[0080] The present invention is further described below in conjunction with the accompanying drawings and two specific implementation examples.

[0081] Implementation case 1:

[0082] Taking the results of the A-level overhaul of the high-pressure cylinder steam guide pipe of a 300MW subcritical unit steam turbine in December 2019 as an example, the status assessment was implemented according to the method of this invention:

[0083] 1) The evaluation object is clearly defined as: steam turbine high-pressure cylinder steam guide pipe. Basic information: Design diameter and wall thickness: Φ413.8×69.6mm, design material P22, bending radius 1050mm.

[0084] There were no abnormalities in the turbine high-pressure cylinder steam guide pipe during the design and manufacturing stages, and there was no record of replacement and maintenance during operation. The results of the last three status assessments were: good, general, and general, respectively.

[0085] 2) The steam pipe of the high-pressure cylinder of the steam turbine has been in operation for 27.5 years and is at the end of its full operating life cycle.

[0086] 3) Considering the three recent maintenance situations, 4 straight pipe evaluation points, 2 elbow evaluation points, and 4 weld evaluation points were selected.

[0087] 4) The steam pipe of the high-pressure cylinder of the steam turbine is at the end stage of its full operating life cycle. The parameter α is 5. There are a few abnormalities during design, manufacturing and installation, but they do not affect normal use. S is 0.01, and the calculated basic state factor value is 0.05.

[0088] 5) The results of the last three status assessments of the steam turbine high-pressure cylinder steam guide pipe are: good, fair, and poor, and the calculated correction factor value is 0.117;

[0089] 6) For the selected evaluation points of the steam turbine high-pressure cylinder steam guide pipe, select macro inspection, surface flaw detection, non-destructive testing, metallographic inspection, pipe diameter inspection, hardness inspection and wall thickness measurement items, formulate and implement offline inspection plans;

[0090] 7) Obtain the offline detection status parameter results of the high-pressure cylinder steam guide pipe of the steam turbine, as shown below;

[0091]

[0092] 8) Perform condition assessment on 4 straight pipe assessment points, 2 elbow assessment points, and 4 weld assessment points selected for the high-pressure steam pipe of the steam turbine, as shown below:

[0093]

[0094] 9) Based on the status assessment results of all assessment points, a status assessment is conducted on the assessment object. The assessed status value of the high-pressure steam pipe is 0.72. Compared with the most recent status assessment value of 0.69, its status has a trend of deterioration. Real-time status monitoring of the high-pressure steam pipe should be carried out.

[0095]

[0096] 10) Finally, the status assessment results of the high-pressure steam pipe are archived and used as feedback for the next assessment and to calculate the correction factor.

[0097] Implementation case 2:

[0098] Taking the results of the A-repair of the left and right high-pressure upper cylinder steam guide pipes of a 600MW supercritical unit steam turbine in October 2020 as an example, the status assessment is implemented according to the method of this invention:

[0099] 1) The evaluation objects are clearly defined as: the high-pressure steam pipe on the left side of the steam turbine and the high-pressure steam pipe on the right side of the steam turbine.

[0100] The high-pressure steam pipe on the left side of the turbine and the high-pressure steam pipe on the right side of the turbine are symmetrically distributed, and the basic information is basically the same. The design diameter and wall thickness are: 392.2mm×65.9mm, the design material is P122, and the bending radius is 1450mm.

[0101] There were no abnormalities with the high-pressure steam pipe on the left side and the high-pressure steam pipe on the right side of the turbine during the design and manufacturing stages. There was no record of replacement and maintenance during operation. The results of the last three status assessments were: general, poor, and poor, respectively.

[0102] 2) The high-pressure steam duct on the left side of the turbine and the high-pressure steam duct on the right side of the turbine have been in operation for 25 years and are at the end of their full operating life cycle.

[0103] 3) Taking into account the three recent maintenance situations, for each steam pipe, three straight pipe evaluation points were selected at the upper, middle and lower parts of the straight pipe, one elbow evaluation point was selected at the upper elbow, and two weld evaluation points were selected at the weld between the elbow and the straight pipe.

[0104] 4) The high-pressure steam pipe on the left side of the steam turbine and the high-pressure steam pipe on the right side of the steam turbine are at the end stage of their full operating life cycle. The parameter α is 2. No abnormality is found during design, manufacturing and installation. S is 0, and the calculated basic state factor values ​​are all 0.

[0105] 5) The results of the latest three status assessments of the left and right high-pressure steam pipes of the steam turbine are: fair, poor, and poor, and the calculated correction factor values ​​are all 0.21;

[0106] 6) For the selected evaluation points of the high-pressure steam pipe on the left side of the steam turbine and the high-pressure steam pipe on the right side of the steam turbine, select the items of macro inspection, surface flaw detection, non-destructive flaw detection, metallographic inspection, pipe diameter inspection, ovality measurement, hardness inspection, and wall thickness measurement, formulate and implement the offline inspection plan;

[0107] 7) Obtain offline detection status parameter results of the left high-pressure steam pipe and the right high-pressure steam pipe of the steam turbine, as shown below;

[0108]

[0109] 8) Perform condition assessment on the selected straight pipes, elbows and weld assessment points of the high-pressure steam pipe on the left side of the steam turbine and the high-pressure steam pipe on the right side of the steam turbine, as shown below:

[0110]

[0111] 9) Comprehensively consider the status assessment results of all assessment points and conduct status assessment on the assessment object.

[0112] The status assessment value of the left high-pressure upper cylinder steam pipe has reached the critical limit of 1.00, and it is recommended to replace it directly.

[0113] Although the right-side high-pressure upper cylinder steam pipe has not reached the critical limit, the evaluation points of the elbow and straight pipe welds are in poor condition and should be dealt with in a timely manner.

[0114]

[0115] 10) Finally, the status assessment results of the right high-pressure upper cylinder steam pipe are archived as feedback for the next assessment and used to calculate the correction factor. As the left high-pressure upper cylinder steam pipe is replaced with a new pipe, the calculation will be restarted at the next assessment without correction.

Claims

1. A method for evaluating the status of a high-pressure steam duct of a steam turbine, characterized in that: The steps include: 1) Clarify the assessment object and its basic information. The assessment object is the high-pressure steam pipe on the left side of the steam turbine and the high-pressure steam pipe on the right side of the steam turbine. The basic information includes design drawings, design diameter, design wall thickness, design material, design and manufacturing data, and all previous maintenance records; 2) Clarify the four stages of the evaluation object's entire life cycle: early, mid, late, and final stages 3) Based on the principles of key parts of equipment, easy inspection and operation, lowest maintenance cost, and controllable maintenance plan, detailed evaluation points are selected from straight pipes, elbows and welds; 4) Calculate the basic condition factor based on the full operational life cycle stage and defects found during the design, manufacturing and installation stages; 5) Calculate the correction factor based on the feedback of the last three evaluation results of the evaluation object; 6) For the selected evaluation points, select appropriate items from macro inspection, surface flaw detection, non-destructive testing, metallographic inspection, pipe diameter inspection, ovality measurement, hardness inspection, and wall thickness measurement to formulate and implement offline inspection plans; 7) Obtain offline detection status parameter results; 8) Conduct condition assessment on selected straight pipes, elbows and weld assessment points; 9) Comprehensively evaluate the status of all evaluation points and conduct status evaluation on the evaluation object; 10) The status of the evaluation object is used as feedback for the next evaluation and to calculate the correction factor; The specific operation steps in step 4) are: Based on the full operational life cycle stage of the assessment object identified in step 2), the basic state factor C is determined according to formula (1): S ; C S =α·S (1) In the formula, the values ​​of parameters α and S are found in the following table according to the basic information collected in step 1); The specific operation steps of step 5) are: Based on the feedback of the last three evaluation results of the evaluation object, the correction factor C is determined according to formula (2): C ; In the formula, parameter δ is the operating time of the evaluation object, in years; C1, C2, and C3 are the correction coefficients corresponding to the results of the three most recent evaluations, and their values ​​are shown in the following table. The specific operation steps of step 8) are: According to the offline detection state parameter results obtained in step 7), a state evaluation is performed on a single evaluation point, and the state of a single evaluation point is defined as C j , the evaluation model is shown in formula (3); CP Gi-j , CP Mi-j Represent the state parameters of rating and measurement categories respectively; W Gi , W Mi are the measurement weights for rating and measurement categories, respectively; Status C of the evaluation point j The numerical result of C normally falls within the range of [0,1]. j When the value of changes from 0 to 1, the status of the evaluation point becomes worse and worse; The weights W of the two types of state parameters in formula (3) are Gi , W Mi The value of gives the rule of formula (4); Rating state parameter in step 7): macro state parameter CP G1-j , OS by macroscopic inspection results G1-j : {no defects found, a small number of suspected defects found, obvious defects found} is defined as shown in formula (5): In step 7), the rating state parameter: surface state parameter CP G2-j , according to the results of surface flaw detection OS G2-j : {no defects found, surface defects found but eliminated after polishing, surface defects found but still exist after polishing} is defined as shown in formula (6): Rating class status parameter in step 7): lossless status parameter CP G3-j , based on the results of nondestructive testing OS G3-j :{Level I, Level II, Level III, Level IV} definition, as shown in formula (7): Rating status parameter in step 7): Organization status parameter CP G4-j , the results of metallographic examination OS G4-j : {level 1, level 2, level 3, level 4, level 5} is defined as shown in formula (8): The measurement state parameter in step 7): pipe diameter state parameter CP M1-j , the result of the pipe diameter inspection OS M1-j The definition is as shown in formula (9): In formula (9), D0 is the design pipe diameter, in mm; e is the limit creep rate, in %; The measurement state parameter in step 7): ellipticity state parameter CP M2-j , the result of the ellipticity check OS M2-j The definition is as shown in formula (10): In formula (10), D max To measure the maximum outer diameter, the unit is mm; D min is the minimum outer diameter measured in mm; β is the ovality limit in %; The state parameter measured in step 7): hardness state parameter CP M3-j , according to the hardness test results OS M3-j The definition is as shown in formula (11): In formula (11), HB L and HB H are the minimum and maximum limit hardness, respectively; The measurement state parameter in step 7): wall thickness state parameter CP M4-j , the result of the wall thickness inspection OS M4-j Definition, as shown in formula (12): Formula (12), d0 is the designed wall thickness, in mm; The specific operation steps in step 9) are: For all the evaluation points obtained in step 8), statistics are performed according to the classification of straight pipes, elbows and welds. Straight pipes, elbows and welds are distinguished by subscripts st, et and wb respectively. The number of straight pipe evaluation points x, elbow evaluation points y and weld evaluation points z are counted, and then the evaluation object is evaluated as a whole. The evaluation model of the final state value is shown in formula (12); If the status C value of the evaluation object is 0, the status of the evaluation object is considered to be the best. When the C value changes from 0 to 1, the status of the evaluation object gradually deteriorates. When the C value is greater than 0.8, the status of the evaluation object is poor, and there are many evaluation points in poor condition, especially at the end and terminal stages of the full operating life cycle. If the status C value of the evaluation object is greater than 0.8 for three consecutive evaluations, it also confirms that the status of the evaluation object is poor, and the enterprise should be prepared to replace the overall evaluation object.

2. A method for evaluating the status of a high-pressure steam duct of a steam turbine according to claim 1, characterized in that: The specific operation steps of step 2) are: It is clear that the assessment object is in a specific stage of the entire operational life cycle. The early stage is (0,0.1L c ), the middle stage is (0.1L c ,0.8L c ), the final stage is (0.8L c ,0.9L c ), the terminal stage is (0.9L c ,L c ), L c is the design life, L c For 30 years.

3. A method for evaluating the status of a high-pressure steam duct of a steam turbine according to claim 1, characterized in that: The specific operation steps of step 3) are: Based on the comprehensive consideration of the key parts of the equipment, easy detection, lowest maintenance cost and controllable maintenance plan, the evaluation points are determined in a targeted manner and divided into three categories: straight pipes, elbows and welds, which are distinguished by the following subscripts st, et and wb respectively.

4. A method for evaluating the status of a high-pressure steam duct of a steam turbine according to claim 1, characterized in that: The specific operation steps of step 6) are: For the evaluation points determined in step 3), select executable items from macro inspection, surface flaw detection, non-destructive testing, metallographic inspection, pipe diameter inspection, ovality measurement, hardness inspection, and wall thickness measurement to develop and implement an offline inspection plan.

5. The method for evaluating the status of a high-pressure steam duct of a steam turbine according to claim 1, characterized in that: The specific operation steps of step 7) are: According to the offline detection items determined in step 6), the offline detection status parameter results of the evaluation points are obtained and divided into two categories: rating category and measurement category; The state parameters corresponding to the four offline inspection items of macro inspection, surface flaw detection, nondestructive testing, and metallographic inspection are collectively referred to as rating state parameters. The state parameters and weights are denoted by CP G1 , CP G2 , CP G3 , CP G4 and W G1 , W G2 , W G3 , W G4 express; The state parameters corresponding to the four offline inspection items of pipe diameter inspection, ovality measurement, hardness inspection, and wall thickness measurement are collectively referred to as measurement state parameters. The state parameters and weights are denoted by CP M1 , CP M2 , CP M3 , CP M4 and W M1 , W M2 , W M3 , W M4 express.

6. A method for evaluating the status of a high-pressure steam duct of a steam turbine according to claim 1, characterized in that: The specific operation steps in step 10) are: The state of the evaluation object obtained in step 9) is fed back for the next evaluation and used to calculate the correction factor in step 5).

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