A method for evaluating the condition of steam turbine medium-pressure steam pipe based on field inspection parameters

Abstract

A method for evaluating the status of a steam turbine medium-pressure steam pipe based on field inspection parameters comprises the following steps: 1) clarifying the evaluation object and its basic information; 2) clarifying the specific stage of the evaluation object in the full operating life cycle; 3) calculating the status correction factor; 4) clarifying the detailed evaluation points; 5) formulating and implementing a field inspection plan; 6) obtaining field inspection results; 7) evaluating the status of the evaluation point; 8) evaluating the status of the evaluation object; 9) archiving and feedback of the evaluation results. The present invention can help steam turbine or metal professionals 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 medium-pressure steam pipe of a steam turbine based on on-site inspection parameters. Background Art

[0002] The medium-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-shaving operation of the power grid, which makes the medium-pressure steam pipe of the steam turbine in a relatively harsh operating condition during operation and is easily affected by the effects of thermal alternating loads. In particular, the weld at the connection between the medium-pressure steam pipe and the medium-pressure outer cylinder of the steam turbine is affected by high temperature and variable loads, and the weld microstructure deteriorates and the microstructure becomes brittle, which increases the risk of failure. In addition, since the medium-pressure steam pipe of the steam turbine is located on the steam turbine platform, if it fails, it will cause a major safety accident. Therefore, it is necessary to more accurately evaluate the status of the medium-pressure steam pipe of the steam turbine.

[0003] Regarding the medium-pressure steam pipe of the steam turbine, some literatures have reported the use of hardness testing, microstructure analysis, welding process analysis and other testing methods to analyze the cracking phenomenon of the dissimilar steel pipe welding joints of the medium-pressure steam pipe, such as the literature "Analysis of cracking failure of dissimilar steel welding of high and medium-pressure steam pipes in power plants, Welding Technology, 2017 (10)". Some literatures have reported the analysis of the causes of cracks in the medium-pressure steam pipe from the aspects of metallographic structure, stress analysis, crack location, unit operation status, etc., such as the literature "Preliminary analysis of the causes of cracks in high and medium-pressure steam short pipes of steam turbines in Yunfu Power Plant and rectification measures, Proceedings of the Sixth National Academic Conference on Failure Analysis and Life Management of Metal Components in Power Plants, 2000". However, no reports on the condition assessment of the medium-pressure steam pipe of the steam turbine were found.

[0004] To this end, it is planned to find a method to conduct condition assessment of the turbine medium-pressure steam duct by simply obtaining on-site inspection data, which does not require the assessors to have extensive mathematical and material expertise, nor does it require additional laboratory analysis costs. Summary of the invention

[0005] The purpose of the present invention is to provide a method for evaluating the status of a medium-pressure steam pipe of a steam turbine based on field inspection parameters, 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 medium-pressure steam duct of a steam turbine based on field inspection parameters comprises the following steps;

[0008] 1) Clarify the assessment object and its basic information. The assessment object is the medium-pressure steam pipe of the steam turbine. The basic information includes design drawings, design diameter, design wall thickness, design material, design and manufacturing data, and the two most recent status assessment files;

[0009] 2) Clarify the operating time of the assessment object and the specific stage of its entire operating life cycle;

[0010] 3) Calculate the state correction factor;

[0011] 4) Clarify the detailed evaluation points;

[0012] 5) Formulate and implement on-site inspection plans;

[0013] 6) Obtain on-site inspection results;

[0014] 7) Assessment point status assessment;

[0015] 8) Assessment of the status of the assessment object;

[0016] 9) Archive and provide feedback on evaluation results.

[0017] The specific operation steps of step 2) are:

[0018] The entire operational life cycle of the evaluation object is divided into three stages: in the early stage, the evaluation object is not in good condition due to design and manufacturing defects as well as hidden dangers left over from installation; in the mid-term stage, the unit operates stably and the evaluation object reaches its best condition; in the final stage, due to long-term high temperature and high pressure service, the materials gradually age and their condition deteriorates.

[0019] Specify the operating time δ of the evaluation object and determine which stage of the three stages of the full operating life cycle it is in. The specific stages and their corresponding time ranges are shown in the table below;

[0020] Full operational life cycle phase Time frame of the full operational life cycle phase Early stage <![CDATA[(0,0.1L c ]]]> Mid-term <![CDATA[(0.1L c ,0.8L c ]]> Late Stage <![CDATA[(0.8L c ,L c ]]]>

[0021] Among them, L c The design life is generally defined as the design life of the unit is 30 years.

[0022] The specific operation steps of calculating the state correction factor in step 3) are:

[0023] Determine the state correction factor CF according to formula (1);

[0024]

[0025] Wherein, L is the actual operating time of the evaluation object, unit: year.

[0026] Based on the data collected in step 1), during the design, manufacturing and installation phases, for the four situations where no defects were found, there were a few anomalies that did not affect normal use, there were many anomalies but the system was normal after repair, and there were many anomalies that were not completely resolved after repair but the system was still operating with defects, the values ​​of s were 0, 0.02, 0.05, and 0.1 respectively.

[0027] Based on the stage of the entire operational life cycle of the assessment object specified in step 2), the values ​​of μ are 2, 1 and 5 in the early, middle and final stages respectively.

[0028] Based on the results of the two most recent status assessments in step 1), the values ​​of Cf1 and Cf2 are found in the table below.

[0029] The results of the second recent assessment The results of the first recent assessment <![CDATA[Cf2 value]]> <![CDATA[Cf1 value]]> better better 0 0 better generally 0 0.5 generally generally 0.5 0.5 generally Poor 0.5 1 Poor Poor 1 1

[0030] The specific operation steps of step 4) are:

[0031] The evaluation points are divided into two categories: welds and mother pipes, which are distinguished by the subscripts wb and mp respectively. Based on the maintenance plan and cost, as well as the results of previous maintenance, the evaluation points are selected for the evaluation objects in a targeted manner.

[0032] The specific operation steps of step 5) are:

[0033] For the evaluation points determined in step 4), select appropriate items from macro inspection, surface flaw detection, non-destructive testing, metallographic inspection, outer diameter inspection, wall thickness measurement, and hardness testing to develop and implement on-site inspection plans.

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

[0035] Divide the on-site inspection items determined in step 5) into two categories, and confirm the state parameters ES and weights ESQ corresponding to the on-site inspection items at each assessment point according to the on-site inspection results of each assessment point;

[0036]

[0037] The specific operation steps of step 7) are:

[0038] Based on the on-site inspection results obtained in step 6), for a single assessment point, whether it is a weld assessment point or a mother pipe assessment point, its status is defined as C k , and use the evaluation model as formula (2) to perform single state evaluation;

[0039]

[0040] Status C of the evaluation point k The numerical result of C normally falls within the range of [0,1]. kWhen the value of changes from 0 to 1, the status of the evaluation point becomes worse and worse.

[0041] The specific operation steps in step 8) are:

[0042] Based on the weld and mother pipe evaluation points obtained in step 7), the overall state of the evaluation object is evaluated as shown in formula (10);

[0043]

[0044] Wherein, the subscripts wb and mp identify the weld and mother pipe respectively, and the number of evaluation points is represented by m and n respectively.

[0045] The numerical result of the state C of the evaluation object normally falls within the range of [0,1]. When the C value changes from 0 to 1, the state of the evaluation object gradually deteriorates. When the C value is greater than 0.85, the state of the evaluation object is poor, and there are many evaluation points in poor condition. Especially at the end of the full operational life cycle, if the state C value of the evaluation object is greater than 0.85 for two consecutive evaluations, it is recommended that the enterprise replace the evaluation object as a whole.

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

[0047] The status evaluation results of the evaluation object obtained in step 8) are fully recorded and archived, and are used as feedback for the next evaluation to calculate the status correction factor in step 3).

[0048] In step 7), the status parameter of the A-type field inspection item: macro inspection status ES A1-k , the results of macroscopic inspection ER A1-k Define, as shown in formula (3), and define the macro inspection state weight ESQ A1-k 10% of the total:

[0049]

[0050] In step 7), the status parameters of the A-type on-site inspection items: surface flaw detection status ES A2-k , according to the surface flaw detection results ER A2-k Definition, as shown in formula (4), and define the surface flaw detection state weight ESQ A2-k 15% of the total:

[0051]

[0052] In step 7), the status parameter of the A-type field inspection item: non-destructive testing status ES A3-k , according to the results of nondestructive testing ER A3-k Definition, as shown in formula (5), and define the non-destructive testing state weight ESQ A3-k30% of the total:

[0053]

[0054] In step 7), the status parameters of the A-type on-site inspection items: metallographic inspection status ES A4-k , the results of metallographic examination ER A4-k Define, as shown in formula (6), and define the metallographic inspection state weight ESQ A4-k 20% of the total:

[0055]

[0056] In step 7), the status parameter of the B-type on-site inspection item: outer diameter inspection status ES B1-k , the result of the outer diameter inspection ER B1-k Define, as shown in formula (7), and define the outer diameter inspection state weight ESQ B1-k 5% of the total:

[0057]

[0058] In formula (7), D0 is the design pipe diameter, in mm; e is the limit creep rate, in %. For the medium-pressure steam guide pipe of the steam turbine, the limit creep rate is as shown in the following table:

[0059] Material alloy steel Carbon Steel e value 2.5％ 3.5％

[0060] In step 7), the status parameters of the B-type on-site inspection items: wall thickness measurement status ES B2-k , the wall thickness inspection result ER B2-k Define, as shown in formula (8), and define the wall thickness measurement state weight ESQ B2-k 10% of the total:

[0061]

[0062] In formula (8), d0 is the designed wall thickness, in mm.

[0063] In step 7), the status parameter of the B-type on-site inspection item: hardness test status ES B3-k , according to the hardness test results ER B3-k Define, as shown in formula (9), and define the wall thickness measurement state weight ESQ B3-k 10% of the total:

[0064]

[0065] The hardness in formula (9) is the Brinell hardness, HB L and HBH They are the minimum and maximum limit hardness respectively. For the medium-pressure steam pipe of the steam turbine, the HB of common materials L and HB H The values ​​are summarized in the following table:

[0066]

[0067]

[0068] Beneficial effects of the present invention:

[0069] The present invention does not require the assessor to have rich basic knowledge of materials, mechanical calculation knowledge, life assessment knowledge and experience, nor does it need to bear additional test costs. Based on conventional on-site inspection items and results, the state correction factor is corrected to assess the state of the steam turbine medium-pressure steam pipe, thereby helping thermal power plant technicians to formulate the next maintenance strategy. At the end of the full operating life cycle, if the state C value of the assessment object is greater than 0.85 for two consecutive assessments, it is recommended that the enterprise replace the assessment object as a whole. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] Figure 1 It is a schematic diagram of the state evaluation process of the present invention. DETAILED DESCRIPTION

[0071] The present invention is further described below in conjunction with two specific implementation cases.

[0072] Implementation case 1:

[0073] Taking the results of the B+ level overhaul of the medium-pressure steam pipe of the steam turbine of a 330MW subcritical unit in a power plant in May 2020 as an example, the status assessment is implemented according to the method of this invention:

[0074] 1) The evaluation object is clearly defined as: medium-pressure steam pipe of steam turbine. Basic information: Design diameter and wall thickness: Φ564.9×27.7mm, design material 12Cr1MoV, bending radius 842mm.

[0075] There were no abnormalities in the turbine's medium-pressure steam guide pipe during the design and manufacturing stages, and there was no record of its replacement during operation. The only condition assessment was conducted in 2014, and the results of the condition assessment were average.

[0076] 2) The turbine medium-pressure steam pipe has been in operation for a total of 22.5 years and is in the middle stage of its full operating life cycle.

[0077] 3) If the turbine medium-pressure steam pipe has no abnormality during the design and manufacturing stage, s takes the value of 0; if it is in the middle stage of the full operating life cycle, μ takes the value of 1;

[0078] Calculating the state correction factor

[0079] 4) Considering the low cost and short time of this overhaul, combined with the only condition assessment result, 2 weld assessment points and 4 mother pipe assessment points were selected.

[0080] 5) Based on the evaluation points selected for the medium-pressure steam pipe of the steam turbine, select appropriate items to formulate and implement on-site inspection plans.

[0081] 6) Obtain the on-site inspection results of the steam turbine medium-pressure steam pipe and calculate the state parameter results as shown below;

[0082]

[0083] 7) Perform condition assessment on the two welds and four main pipe assessment points selected for the medium-pressure steam guide pipe of the steam turbine, as shown below:

[0084]

[0085] 8) Based on the status evaluation results of all evaluation points, the status of the medium-pressure steam pipe under evaluation was evaluated. The final evaluation status value was 0.69, which showed a trend of deterioration compared with the evaluation results in 2014. In addition, one weld evaluation point and one main pipe evaluation point were in poor condition and should be eliminated in time.

[0086]

[0087] 9) The final status assessment result of the medium-pressure steam pipe is fed back to the next assessment and used to calculate the status correction factor.

[0088] Implementation case 2:

[0089] Taking the results of the A-level maintenance of the medium-pressure steam pipe of the steam turbine of a 1000MW subcritical unit in a power plant in January 2021 as an example, the status assessment is implemented according to the method of this invention:

[0090] 1) The evaluation objects are clearly defined as: medium-pressure steam pipe of steam turbine on side A and medium-pressure steam pipe of steam turbine on side B. Basic information: Design diameter and wall thickness: Φ610×45mm, design material A335P92, bending radius 1067mm.

[0091] The intermediate pressure steam pipe of the steam turbine on the A side was found to be abnormal during the design and manufacturing stage, but it was normal after being returned to the factory for treatment. The intermediate pressure steam pipe of the steam turbine on the B side was not found to be abnormal during the design and manufacturing stage. There was no replacement record during operation, and only a simple status assessment was conducted in 2015, with good results.

[0092] 2) The intermediate-pressure steam pipe of the turbine on the A side and the intermediate-pressure steam pipe of the turbine on the B side have been in operation for a total of 12 years and are in the middle stage of their full operating life cycle.

[0093] 3) The intermediate pressure steam pipe of the turbine on side A is found to be abnormal during the design and manufacturing stage but is normal after being returned to the factory for treatment, and the value of s is 0.05; in the middle stage of the full operating life cycle, the value of μ is 1;

[0094] Calculate the status correction factor of the medium-pressure steam pipe of the turbine on side A:

[0095]

[0096] If no abnormality is found in the design and manufacturing stage during the operation of the medium-pressure steam guide pipe of the turbine on the B side, s takes the value of 0; if it is in the middle stage of the full operation life cycle, μ takes the value of 1;

[0097] Calculate the status correction factor of the medium-pressure steam pipe of the B-side steam turbine:

[0098]

[0099] 4) Considering that this overhaul will take a long time and the cost is controllable, combined with the results of the previous status assessment, 3 weld assessment points and 3 mother pipe assessment points are selected for the medium-pressure steam pipe of the turbine on the A side; 2 weld assessment points and 4 mother pipe assessment points are selected for the medium-pressure steam pipe of the turbine on the B side.

[0100] 5) Based on the assessment points selected for the intermediate-pressure steam pipe of the turbine on side A and the intermediate-pressure steam pipe of the turbine on side B, select appropriate items to formulate and implement an on-site inspection plan.

[0101] 6) Obtain the on-site inspection results of the medium-pressure steam pipe of the steam turbine on the A side and the medium-pressure steam pipe of the steam turbine on the B side, and calculate the state parameter results, as shown below;

[0102]

[0103] 7) Perform status assessment on the assessment points of the intermediate pressure steam pipe of the steam turbine on the A side and the intermediate pressure steam pipe of the steam turbine on the B side as shown below:

[0104]

[0105] 8) Based on the status evaluation results of all evaluation points, the status of the evaluation objects was evaluated separately. The final evaluation status value of the intermediate pressure steam pipe of the steam turbine on the A side was 0.462, and the final evaluation status value of the intermediate pressure steam pipe of the steam turbine on the B side was 0.457. Compared with the evaluation results in 2015, there is no trend of worsening status of the two steam pipes. However, in comparison, the status of the intermediate pressure cylinder steam pipe on the A side is slightly worse than that on the B side, which may be related to the slightly higher operating temperature of the reheat steam on the A side, which should be paid attention to.

[0106]

[0107] 9) The final status evaluation result of the intermediate pressure cylinder steam pipe on the A side is compared with the status evaluation result of the intermediate pressure cylinder steam pipe on the B side, which is fed back for the next evaluation and used to calculate the status correction factor.

Claims

1. A method for evaluating the status of a steam turbine medium-pressure steam pipe based on field inspection parameters, characterized in that: The steps include: 1) Clarify the assessment object and its basic information. The assessment object is the medium-pressure steam pipe of the steam turbine. The basic information includes design drawings, design diameter, design wall thickness, design material, design and manufacturing data, and the two most recent status assessment files; 2) Identify the specific stage of the entire operational life cycle of the assessment object; 3) Calculate the state correction factor; 4) Clarify the detailed evaluation points; 5) Formulate and implement on-site inspection plans; 6) Obtain on-site inspection results; 7) Assessment point status assessment; 8) Assessment of the status of the assessment object; 9) Archiving and feedback of evaluation results; The specific operation steps for calculating the state correction factor in step 3) are: Determine the state correction factor CF according to formula (1); Where, L is the actual operating time of the evaluation object, unit: year; L c Design life; Based on the data collected in step 1), during the design, manufacturing and installation phase, for the four situations where no defects were found, there were a few abnormalities but they did not affect normal use, there were many abnormalities but they were normal after repair, and there were many abnormalities that were not completely resolved after repair but still operated with defects, the values ​​of s were 0, 0.02, 0.05, and 0.1 respectively; Based on the full operational life cycle stage of the evaluation object identified in step 2), the values ​​of μ are 2, 1 and 5 for the early, middle and final stages respectively; Based on the results of the last two status assessments in step 1), the values ​​of Cf1 and Cf2 are found in the following table; ； The specific operation steps of step 7) are: Based on the on-site inspection results obtained in step 6), for a single assessment point, whether it is a weld assessment point or a mother pipe assessment point, its status is defined as C k , and use the evaluation model as formula (2) to perform single state evaluation; Status C of the evaluation point k The numerical result of C normally falls within the range of [0,1]. k When the value of changes from 0 to 1, the status of the evaluation point becomes worse and worse; The specific operation steps in step 8) are: Based on the weld and mother pipe evaluation points obtained in step 7), the overall state of the evaluation object is evaluated as shown in formula (10); In the formula, the subscripts wb and mp indicate the weld and the mother pipe respectively, and the number of evaluation points is represented by m and n respectively; The numerical result of the status C of the evaluation object normally falls in the range of [0,1]. When the C value changes from 0 to 1, the status of the evaluation object gradually deteriorates. When the C value is greater than 0.85, the status of the evaluation object is poor. There are many evaluation points in poor status, especially at the end of the full operating life cycle. If the status C value of the evaluation object is greater than 0.85 for two consecutive evaluations, it is recommended that the enterprise replace the evaluation object as a whole. In step 7), the status parameter of the A-type field inspection item: macro inspection status ES Α1-k , the results of macroscopic inspection ER Α1-k Definition, as shown in formula (3), and define the macro inspection state weight ESQ Α1-k 10% of the total: In step 7), the status parameters of the A-type on-site inspection items: surface flaw detection status ES Α2-k , according to the surface flaw detection results ER Α2-k Definition, as shown in formula (4), and define the surface flaw detection state weight ESQ Α2-k 15% of the total: In step 7), the status parameter of the A-type field inspection item: non-destructive testing status ES Α3-k , according to the results of nondestructive testing ER Α3-k Definition, as shown in formula (5), and define the non-destructive testing state weight ESQ Α3-k 30% of the total: In step 7), the status parameters of the A-type on-site inspection items: metallographic inspection status ES Α4-k , the results of metallographic examination ER Α4-k Define, as shown in formula (6), and define the metallographic inspection state weight ESQ Α4-k 20% of the total: In step 7), the status parameter of the B-type on-site inspection item: outer diameter inspection status ES Β1-k , the result of the outer diameter inspection ER B1-k Define, as shown in formula (7), and define the outer diameter inspection state weight ESQ B1-k 5% of the total: In formula (7), D0 is the design pipe diameter, in mm; e is the limit creep rate, in %; In step 7), the status parameters of the B-type on-site inspection items: wall thickness measurement status ES Β2-k , the wall thickness inspection result ER B2-k Define, as shown in formula (8), and define the wall thickness measurement state weight ESQ B2-k 10% of the total: In formula (8), d0 is the designed wall thickness, in mm; In step 7), the status parameter of the B-type on-site inspection item: hardness test status ES Β3-k , according to the hardness test results ER B3-k Define, as shown in formula (9), and define the wall thickness measurement state weight ESQ B3-k 10% of the total: The hardness in formula (9) is the Brinell hardness, HB L and HB H are the minimum and maximum limit hardness respectively.

2. A method for evaluating the status of a steam turbine medium-pressure steam pipe based on field inspection parameters according to claim 1, characterized in that: The specific operation steps of step 2) are: The entire operational life cycle of the evaluation object is divided into three stages: the early stage, due to design and manufacturing defects and installation hidden dangers, the evaluation object is not in good condition; the mid-term stage, the unit is running stably, and the evaluation object has reached the best condition; the final stage, long-term high temperature and high pressure service, the material gradually accelerates aging and the condition deteriorates; Specify the operating time δ of the evaluation object and determine which stage of the three stages of the full operating life cycle it is in. The specific stages and their corresponding time ranges are shown in the table below; Among them, L c The design life is generally defined as the design life of the unit is 30 years.

3. The method for evaluating the status of a steam turbine medium-pressure steam pipe based on field inspection parameters according to claim 1, characterized in that: The specific operation steps of step 4) are: The evaluation points are divided into two categories: welds and mother pipes, which are distinguished by the subscripts wb and mp respectively. Based on the maintenance plan and cost, as well as the results of previous maintenance, the evaluation points are selected for the evaluation objects in a targeted manner.

4. The method for evaluating the status of a steam turbine medium-pressure steam pipe based on field inspection parameters according to claim 1, characterized in that: The specific operation steps of step 5) are: For the evaluation points determined in step 4), select appropriate items from macro inspection, surface flaw detection, non-destructive testing, metallographic inspection, outer diameter inspection, wall thickness measurement, and hardness testing to develop and implement on-site inspection plans.

5. The method for evaluating the status of a steam turbine medium-pressure steam pipe based on field inspection parameters according to claim 1, characterized in that: The specific operation steps of step 6) are: Divide the on-site inspection items determined in step 5) into two categories, and confirm the state parameters ES and weights ESQ corresponding to the on-site inspection items at each assessment point according to the on-site inspection results of each assessment point; 6. The method for evaluating the status of a steam turbine medium-pressure steam pipe based on field inspection parameters according to claim 1, characterized in that: The specific operation steps in step 9) are: The status evaluation results of the evaluation object obtained in step 8) are completely recorded and filed, and used as feedback for the next evaluation to calculate the status correction factor of step 3).

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