CN113449395B - Subcritical boiler barrel down pipe and pipe seat state evaluation method based on off-line inspection - Google Patents
Subcritical boiler barrel down pipe and pipe seat state evaluation method based on off-line inspection Download PDFInfo
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Abstract
A subcritical boiler drum down pipe and tube seat state evaluation method based on off-line inspection comprises the following steps of; 1) Explicitly evaluating the object and the basic information; 2) Defining detailed evaluation points; 3) The specific stage of the full-operation life cycle of the object is clearly evaluated; 4) Calculating a state factor; 5) Calculating a correction factor; 6) An offline inspection scheme is formulated and implemented; 7) Acquiring an offline test result; 8) Evaluating point states; 9) Evaluating the state of an evaluation object; 10 Filing and feeding back the evaluation result. The invention can help technical boilers or metal professionals in thermal power plants to better formulate maintenance strategies.
Description
Technical Field
The invention belongs to the technical field of state evaluation of equipment in a thermal power plant, and particularly relates to a state evaluation method of a subcritical boiler drum down tube and a tube seat based on offline inspection.
Background
The boiler barrel is an important component of a subcritical unit of a thermal power plant. In the face of increasingly severe external environments, subcritical units are subjected to flexibility transformation step by step and participate in deep peak shaving, and are in worse operation working conditions in the operation process. Frequent start-up and shut-down and variable loads can cause frequent alternating thermal and mechanical stresses in the drum, especially stresses at the corner points in the downcomer are usually greatest. In addition, the welding seam area between the boiler barrel down pipe and the cylinder body is a fatigue crack multiple area, and is influenced by factors such as welding level, environment and the like, larger welding seam residual stress can be generated, and the welding seam crack is easily generated due to larger stress after the welding seam residual stress is overlapped with mechanical stress and thermal stress. In addition, since the drum downcomer is located outside the top of the boiler, significant personal safety and economic losses are easily incurred if a leak event occurs, and accurate state assessment of subcritical boiler drum downcomer and tube seat is necessary.
For subcritical boiler drum downcomer and tube seat, only the stress state of the boiler drum downcomer is simulated by adopting finite element software ANSYS, residual stress in different areas of a downcomer weld zone is tested on site by adopting a blind hole method, and total stress is superposed and analyzed, and the comprehensive study of the crack problem of the downcomer weld zone of the boiler drum, electric power and energy, 2018 and 6 are reported in the literature. In addition, state analysis or life assessment of a boiler barrel down pipe and a pipe seat are reported recently.
Whether stress analysis or life loss calculation is performed, the following conditions are required: the personnel to be evaluated have abundant mathematical analysis basic knowledge, metal material basic knowledge, mechanical calculation knowledge, life evaluation knowledge and experience; complete design data and design data need to be collected; complete operation history data needs to be collected; complete and comprehensive offline inspection related data needs to be collected; a stress field and temperature field model is required to be constructed; comprehensive laboratory analysis data of samples of the same material are required as a reference group, etc. These complex conditions determine that the development of stress analysis, life loss calculation, etc. techniques are limited to professional technical institutions and personnel, and that the collection of these basic data and data, complete and comprehensive off-line inspection, and laboratory analysis can lead to increased plant overhaul costs and labor costs.
Therefore, a method with universality is needed to be found, and the state of the subcritical boiler drum down tube and the tube seat can be evaluated by only obtaining the existing offline test data without the need of having abundant mathematical analysis basic knowledge, metal material basic knowledge, mechanical calculation knowledge, service life evaluation knowledge and experience by an evaluator and without bearing additional test expense cost, so that the maintenance strategy is directly assisted by the technicians in the thermal power plant.
Disclosure of Invention
In order to overcome the technical problems, the invention aims to provide a subcritical boiler drum down tube and tube seat state evaluation method based on off-line inspection, which helps technical boilers or metal professionals in thermal power plants to better formulate maintenance strategies.
In order to achieve the above purpose, the technical scheme adopted by the invention and the beneficial effects of the invention are as follows:
a subcritical boiler drum down pipe and tube seat state evaluation method based on off-line inspection comprises the following steps of;
1) Explicitly evaluating the object and the basic information;
2) Defining detailed evaluation points;
3) The specific stage of the full-operation life cycle of the object is clearly evaluated;
4) Calculating a state factor C S ；
5) Calculating correction factor C C ；
6) An offline inspection scheme is formulated and implemented;
7) Acquiring an offline test result;
8) Evaluating point states;
9) Evaluating the state of an evaluation object;
10 Filing and feeding back the evaluation result.
The evaluation object of the step 1) is a subcritical boiler drum downcomer and a tube seat, and the basic information comprises a design drawing, a design diameter, a design wall thickness, a design material and a latest overhaul record file;
the specific operation steps of the step 2) are as follows:
comprehensively considering maintenance plans, time, cost and past maintenance results, determining a plurality of evaluation points in a targeted manner, and classifying the evaluation points into two types: the drop tube and the header are distinguished by subscripts dt and ds, respectively.
The specific operation steps of the step 3) are as follows:
explicitly evaluating which phase of the early, middle and final phases of the full operational life cycle the object is in;
wherein L is c For design life, it is generally defined as the design life of the unit for 30 years.
The specific operation steps for calculating the state factor in the step 4) are as follows:
determining the corresponding state factor C based on the stage of the full operation life cycle of the clear evaluation object in the step 3) S ；
| All phases of the full operational life cycle | State factor C S |
| Early stage | 1+s |
| Mid-stage | 1 |
| End stage | 1+5s |
Wherein the value of s is looked up according to the following table based on the design and manufacturing data collected in step 1).
The specific operation steps for calculating the correction factor in the step 5) are as follows:
searching for feedback of the last evaluation result of the evaluation object based on the last service record file collected from step 1), and determining the correction factor C according to formula (1) C ；
In the formula, the values of the parameters delta and c are searched from the following table.
The specific operation steps of the step 6) are as follows:
comprehensively considering maintenance plan, time, cost and past maintenance results, and selecting proper items from macro inspection, surface flaw detection, nondestructive inspection, metallographic inspection, outer diameter measurement, hardness inspection and wall thickness measurement for the evaluation points determined in the step 2) to formulate an offline inspection scheme and implement.
The specific operation steps of the step 7) are as follows:
according to the offline test items determined in the step 6), obtaining all offline test results of the evaluation points, classifying the state parameters into two main types according to the offline test results, and confirming the state parameters CP and the weights Q corresponding to all the offline test items of all the evaluation points.
The specific operation steps of the step 8) are as follows:
according to step 7)Performing state evaluation on the single evaluation point according to the offline test result, and defining the state of the single evaluation point as C k The evaluation model is shown as a formula (2);
state C of evaluation point k The numerical result of (2) normally falls within [0,5 ]]Within the interval range, when C k The state of the evaluation point becomes worse as the value of (2) changes from 0 to 5.
Weights Q of two types of state parameters in the formula (2) Oi 、Q Ti Giving the rule of formula (3);
the specific operation steps in the step 9) are as follows:
counting all the evaluation points obtained in the step 8) according to the classification of the down pipes and the pipe seats (the subscripts are dt and ds respectively), counting the number m of the evaluation points of the down pipes and the number n of the evaluation points of the pipe seats, and then carrying out overall evaluation on the evaluation objects, wherein an evaluation model of a final state value is shown as a formula (11);
if the state C value of the evaluation object is 0, the state of the evaluation object is considered to be optimal, and when the C value is changed from 0 to 5, the state of the evaluation object gradually becomes worse; when the C value is larger than 3.5, the state of the evaluation object is general, but part of evaluation points are worse, so that the attention of technicians is required, and the maintenance or replacement treatment is timely carried out on part of evaluation points; when the C value is larger than 4.25, the state of the evaluation object is poor, and most evaluation points are poor, particularly, when the evaluation object is in the end stage of the full-operation life cycle, if the evaluation is continuously carried out for multiple times, the state of the evaluation object is also verified to be poor when the C value of the evaluation object is gradually increased, and the enterprise is ready for the whole replacement of the evaluation object.
The specific operation steps in the step 10) are as follows:
and 3) completely recording and archiving the state evaluation result of the evaluation object obtained in the step 9), and feeding back for the next evaluation to calculate the correction factor of the step 5).
The first type of state parameters in the step 8): macroscopic state parameter CP O1-k Results of macroscopic inspection M O1-k : { no defect found, few suspected defects found, invention apparent defect } is defined as shown in formula (4):
the first type of state parameters in the step 8): surface state parameter CP O2-k From the result M of surface inspection O2-k : { no defects found, surface defects found but eliminated after grinding, surface defects found but still present after grinding } are defined as shown in formula (5):
the first type of state parameters in the step 8): lossless state parameter CP O3-k From the result M of non-destructive inspection O3-k : { stage I, stage II, stage III, stage IV } is defined as shown in formula (6):
the first type of state parameters in the step 8): tissue state parameter CP O4-k From the result M of metallographic examination O4-k : { level 1, level 2, level 3, level 4, level 5 } is defined as shown in formula (7):
CP O4-k ＝(M O4-k +1)/5 (7)
the second type of state parameter in the step 8): outer diameter state parameter CP T1-k Knot measured by outer diameterFruit M T1-k Definition, as shown in formula (8):
in the formula (8), D 0 For designing the outer diameter, the unit is mm; e is the limit creep rate, the unit is that for the drum downcomer, the limit creep rate takes the values shown in the following table:
| material of material | Alloy steel | Carbon steel |
| e takes value | 2.5％ | 3.5％ |
The second type of state parameter in the step 8): hardness state parameter CP T2-k From the result M of hardness test T2-k Defined as shown in formula (9):
the hardness in formula (9) is Brinell hardness, HB L And HB H Respectively the minimum and maximum extreme hardness, and HB of common materials for the drum down tube L And HB H The values are summarized in the following table:
| material of material | T22 | T23 | G102 | T91 | 12C1MoV | 15Cr1Mo | … |
| HB L | 120 | 150 | 150 | 180 | 135 | 115 | … |
| HB H | 163 | 220 | 220 | 250 | 179 | 178 | … |
The second type in the step 8)State parameters: wall thickness state parameter CP T3-k From the wall thickness measurement result M T3-k Defined as shown in formula (10):
in the formula (10), d 0 For the design of the wall thickness, the unit is mm.
The invention has the beneficial effects that:
the invention does not need to have abundant metal material basic knowledge, mechanical calculation knowledge, life assessment knowledge and experience by assessment personnel, does not need to bear extra test cost, is based on conventional offline test data such as macro test, surface flaw detection, nondestructive inspection, metallographic inspection, outer diameter measurement and hardness inspection of the subcritical boiler drum downcomer and the tube seat, and carries out state assessment on the subcritical boiler drum downcomer and the tube seat through calibration of state factors and correction factors, thereby directly helping thermal power plant technicians to formulate a next maintenance strategy, and if the state values of the subcritical boiler drum downcomer and the tube seat are gradually increased and the state is poorer and worse by continuous repeated assessment, the enterprise is ready for overall replacement of an assessment object.
Taking the result of repair of a 600MW subcritical boiler drum downcomer and a tube seat in 2020 month A of a certain power plant as an example, the state evaluation is implemented according to the method of the invention, and the evaluation process and the final result are as follows.
Drawings
FIG. 1 is a schematic diagram of a state evaluation flow according to the present invention.
Detailed Description
The invention is further described below with reference to the drawings and examples.
As shown in fig. 1:
1) Explicitly evaluating object and basic information
The object of the first clear evaluation is subcritical boiler drum downcomer and tube seat.
In addition, it is also necessary to collect and explicitly evaluate the design drawings, design diameters, design wall thicknesses, design materials, and most recent overhaul record files of the object.
2) Clear detailed evaluation point
In order to know the actual state of the evaluation object in detail, it is generally recommended to check the drop tube and the tube socket at a plurality of positions, which are also referred to as evaluation points, since the check points ultimately take part in the state evaluation. And the evaluation points are divided into two categories: the drop tube and the header are distinguished by subscripts dt and ds, respectively.
3) Specific stage of full-operation life cycle of object under clear evaluation
The state of the evaluation object has a certain relation with the specific stage of the full-operation life cycle in which the evaluation object is positioned, and the state is not good due to design and manufacturing defects and installation hidden dangers in the early stage of the full-operation life cycle. Along with the stable operation of the unit, the unit enters the middle stage of the full-operation life cycle, and the evaluation object reaches the optimal state and can last for a long time. When the material enters the end stage of the full-operation life cycle, the material is gradually aged at an accelerated speed under the influence of long-term peak regulation operation of the unit, and the state of the evaluation object is gradually deteriorated.
Explicitly evaluating which phase of the early, middle and final phases of the full operational life cycle the object is in;
| all phases of the full operational life cycle | Time ranges for each phase of the full operational life cycle |
| Early stage | (0,0.1L c ] |
| Mid-stage | (0.1L c ,0.8L c ] |
| End stage | (0.8L c ,L c ] |
Wherein L is c For design life, it is generally defined as the design life of the unit for 30 years.
4) Calculating correction factor C S
Determining the corresponding correction factor C based on the stage of 3) definite evaluation object S ；
| All phases of the full operational life cycle | State factor C S |
| Early stage | 1+s |
| Mid-stage | 1 |
| End stage | 1+5s |
Wherein the value of s is looked up according to the following table based on the design and manufacturing data collected in 1).
If all indexes in the design and manufacturing data are normal and no major problem is found, c takes a value of 0.01, otherwise, according to the problem found in the design and manufacturing stage, an evaluator can also adjust according to the actual situation of the component.
5) Calculating correction factor C C
Searching for feedback of the last evaluation result of the evaluation object based on the last service record file collected from step 1), and determining the correction factor C according to formula (1) C ；
In the formula, the values of the parameters delta and c are searched from the following table.
6) Making an offline inspection plan and implementing
Comprehensively considering maintenance plan, time, cost and past maintenance results, and aiming at the evaluation points determined in the step 2), selecting proper items from macro inspection, surface flaw detection, nondestructive inspection, metallographic inspection, outer diameter measurement and hardness inspection to formulate an offline inspection scheme and implementing.
7) Obtaining offline test results
According to the offline test items determined in the step 6), obtaining all offline test results of the evaluation points, classifying the state parameters into two main types according to the offline test results, and confirming the state parameters CP and the weights Q corresponding to all the offline test items of all the evaluation points.
8) Evaluation point state evaluation
Performing state evaluation on the single evaluation point according to the offline test result obtained in the step 7), and defining the state of the single evaluation point as C k The evaluation model is shown in formula (2).
State C of evaluation point k The numerical result of (2) normally falls within [0,5 ]]Within the interval range, when C k The state of the evaluation point becomes worse as the value of (2) changes from 0 to 5.
Comprehensively considering the importance of various offline inspection items, the implementation frequency, the accuracy of results and other factors, and the weights Q of two types of state parameters in the formula (2) Ri 、Q Ni Giving the rule of formula (3);
the following gives an evaluation method of two types of state parameters of a single evaluation point.
8.1 State parameter evaluation of the first class
8.1.1 Macro state parameter evaluation corresponding to macro inspection
Results of macroscopic inspection M O1-k Generally one of the sets { no defects found, out of specification defects found }, corresponding to the macroscopic state parameter CP O1-k The definition of (2) is shown in the formula (4).
8.1.2 Surface state parameter evaluation corresponding to surface flaw detection
Results of surface inspection M O2-k Generally { no defects found, surface defects found but removed after polishing, surface defects found but still present after polishing }, corresponding to the surface state parameter CP O2-k The definition of (2) is shown in the formula (5).
8.1.3 Non-destructive state parameter assessment corresponding to non-destructive inspection
The nondestructive inspection items can be divided into ultrasonic wave, magnetic powder, penetration and ray detection, and the nondestructive inspection result M O3-k Generally defined as { class I, class II, class III, class IV }, if multiple nondestructive inspection items are implemented, selecting the nondestructive inspection item with the highest rating as the nondestructive inspection result, and corresponding nondestructive state parameter CP O3-k The definition of (2) is shown in a formula (6).
8.1.4 Lossless state parameter evaluation corresponding to metallographic examination
Results of metallographic examination M O4-k Is generally defined as { level 1, level 2, level 3, level 4, level 5 }, which corresponds to the organization state parameter CP O4-k The definition of (2) is shown in the formula (7).
CP O4-k ＝(M O4-k +1)/5 (7)
8.2 State parameter evaluation of the second class
8.2.1 Wall thickness state parameter estimation corresponding to outside diameter measurement
The external diameter creep of the evaluation object can gradually occur when the evaluation object operates under high temperature conditions, and the failure is easy to cause when the creep is serious.
Results of outer diameter measurement M T1-k Corresponding outer partDiameter state parameter CP T1-k The definition of (2) is shown in the formula (8).
In the formula (8), D 0 For designing the outer diameter, the unit is mm; e is the limit creep rate, the unit is the limit creep rate for the drum downcomer, and the values of the limit creep rate are shown in the following table.
| Material of material | Alloy steel | Carbon steel |
| e takes value | 2.5％ | 3.5％ |
8.2.2 Hardness check corresponding hardness status parameter assessment
The evaluation object gradually ages under high temperature conditions, so that the hardness gradually decreases and the state becomes worse, and finally, failure may be caused.
Results of hardness inspection M T2-k Corresponding hardness state parameter CP T2-k The definition of (2) is shown in the formula (9).
The hardness in formula (9) is Brinell hardness, HB L And HB H Respectively the minimum and maximum extreme hardness, and HB of common materials for the drum down tube L And HB H The values are summarized in the following table:
| material of material | T22 | T23 | G102 | T91 | 12C1MoV | 15Cr1Mo | … |
| HB L | 120 | 150 | 150 | 180 | 135 | 115 | … |
| HB H | 163 | 220 | 220 | 250 | 179 | 178 | … |
8.2.3 Wall thickness state parameter estimation corresponding to wall thickness measurement
The high-temperature oxidation of the evaluation object can be generated by the erosion and corrosion of steam in the high-temperature operation process, and the process consumes the base metal of the evaluation object, so that the wall thickness of the evaluation object is thinned, larger stress is born, and the evaluation object has a worse state.
Results of wall thickness measurement M T3-k Corresponding wall thickness state parameter CP T3-k The definition of (2) is shown in a formula (10).
In the formula (10), d 0 For the design of the wall thickness, the unit is mm.
9) Evaluation object state evaluation
And (3) counting all the evaluation points obtained in the step 8) according to the classification of the down pipes and the pipe seats (the subscripts are dt and ds respectively), counting the number m of the evaluation points of the down pipes and the number n of the evaluation points of the pipe seats, and then carrying out overall evaluation on the evaluation objects, wherein an evaluation model of the final state value is shown as a formula (10).
If the state C value of the evaluation object is 0, the state of the evaluation object is considered to be optimal, and when the C value is changed from 0 to 5, the state of the evaluation object gradually becomes worse; when the C value is larger than 3.5, the state of the evaluation object is general, but part of evaluation points are worse, so that the attention of technicians is required, and the maintenance or replacement treatment is timely carried out on part of evaluation points; when the C value is larger than 4.25, the state of the evaluation object is poor, and most evaluation points are poor, particularly, when the evaluation object is in the end stage of the full-operation life cycle, if the evaluation is continuously carried out for multiple times, the state of the evaluation object is also verified to be poor when the C value of the evaluation object is gradually increased, and the enterprise is ready for the whole replacement of the evaluation object.
10 Filing and feeding back evaluation results
And 3) completely recording and archiving the state evaluation result of the evaluation object obtained in the step 9), and feeding back for the next evaluation to calculate the correction factor of the step 5).
By adopting the technical scheme to evaluate and obtain the states of the subcritical boiler drum down tube and the tube seat, not only can the technicians in the thermal power plant be helped to know the actual states of equipment, but also the change trend of the states of the technicians in the thermal power plant can be predicted by aiming at the state evaluation results of the same evaluation point for multiple times, and the state results of all the evaluation points can be synthesized to evaluate the states of the whole subcritical boiler drum down tube and the tube seat, so that the method has important significance in making a maintenance plan and a replacement strategy.
Claims (8)
1. The subcritical boiler drum down pipe and tube seat state evaluation method based on offline inspection is characterized by comprising the following steps of;
1) Explicitly evaluating the object and the basic information;
2) Defining detailed evaluation points;
3) The specific stage of the full-operation life cycle of the object is clearly evaluated;
4) Calculating a state factor C S ；
5) Calculating correction factor C C ；
6) An offline inspection scheme is formulated and implemented;
7) Acquiring an offline test result;
8) Evaluating point states;
9) Evaluating the state of an evaluation object;
10 Filing and feeding back an evaluation result;
the specific operation steps of the step 5) are as follows:
searching for feedback of the last evaluation result of the evaluation object based on the last service record file collected from step 1), and determining the correction factor C according to formula (1) C ；
Wherein, the values of the parameters delta and c are searched from the following table;
the specific operation steps of the step 8) are as follows:
performing state evaluation on the single evaluation point according to the offline test result obtained in the step 7), and defining the state of the single evaluation point as C k The evaluation model is shown as a formula (2);
state C of evaluation point k The numerical result of (2) normally falls within [0,5 ]]Within the interval range, when C k As the value of (2) varies from 0 to 5, the state of the evaluation point becomes worse;
weights Q of two types of state parameters in the formula (2) Oi 、Q Ti Giving the rule of formula (3);
the first type of state parameters in the step 8): macroscopic state parameter CP O1-k Results of macroscopic inspection M O1-k : { no defect found, few suspected defects found, invention apparent defect } is defined as shown in formula (4):
the first type of state parameters in the step 8): surface state parameter CP O2-k From the result M of surface inspection O2-k : { no defects found, surface defects found but eliminated after grinding, surface defects found but still present after grinding } are defined as shown in formula (5):
the first type of state parameters in the step 8): lossless state parameter CP O3-k From the result M of non-destructive inspection O3-k : { stage I, stage II, stage III, stage IV } is defined as shown in formula (6):
the first type of state parameters in the step 8): tissue state parameter CP O4-k From the result M of metallographic examination O4-k : { level 1, level 2, level 3, level 4, level 5 } is defined as shown in formula (7):
CP O4-k ＝(M O4-k +1)/5 (7)
the second type of state parameter in the step 8): outer diameter state parameter CP T1-k From the result M of the outer diameter measurement T1-k Definition, as shown in formula (8):
in the formula (8), D 0 For designing the outer diameter, the unit is mm; e is the limit creep rate, and the unit is;
the second type of state parameter in the step 8): hardness state parameter CP T2-k From the result M of hardness test T2-k Defined as shown in formula (9):
in the formula (9), HB L And HB H Respectively is the limitMinimum hardness and maximum extreme hardness;
the second type of state parameter in the step 8): wall thickness state parameter CP T3-k From the result M of the wall thickness inspection T3-k Defined as shown in formula (10):
in the formula (10), d 0 For the design of the wall thickness, the unit is mm.
2. The method for evaluating the states of the down tube and the tube seat of the subcritical boiler drum based on the offline inspection according to claim 1, wherein the evaluation object in the step 1) is the down tube and the tube seat of the subcritical boiler drum, and the basic information comprises a design drawing, a design diameter, a design wall thickness, a design material and a latest overhaul record file.
3. The method for evaluating the state of a subcritical boiler drum downcomer and a tube seat based on offline inspection according to claim 1, wherein the specific operation steps of the step 2) are as follows:
all evaluation points of the evaluation object are explicitly evaluated and are divided into: the drop tube evaluation point and the tube seat evaluation point are respectively distinguished by the subscripts dt and ds.
4. The method for evaluating the state of a subcritical boiler drum downcomer and a tube seat based on offline inspection according to claim 1, wherein the specific operation steps of the step 3) are as follows:
explicitly evaluating which phase of the early, middle and final phases of the full operational life cycle the object is in;
Wherein L is c For design life, it is generally defined as the design life of the unit for 30 years.
5. The method for evaluating the state of a subcritical boiler drum downcomer and tube seat based on offline inspection according to claim 1, wherein the specific operation steps in the step 4) are as follows:
determining the corresponding state factor C based on the stage of the clear evaluation object in the step 3) S ；
Wherein the value of s is looked up according to the design and manufacturing data collected in step 1) and the following table;
6. the method for evaluating the state of a subcritical boiler drum downcomer and tube seat based on offline inspection according to claim 1, wherein the specific operation steps of the step 6) are as follows:
comprehensively considering maintenance plan, time, cost and past maintenance results, and aiming at the evaluation points determined in the step 2), selecting proper items from macro inspection, surface flaw detection, nondestructive inspection, metallographic inspection, outer diameter measurement and hardness inspection to formulate an offline inspection scheme and implementing.
7. The method for evaluating the state of a subcritical boiler drum downcomer and tube seat based on offline inspection according to claim 1, wherein the specific operation steps of the step 7) are as follows:
according to the offline test items determined in the step 6), acquiring all offline test results of the evaluation points, classifying the state parameters into two main types according to the offline test results, and confirming the state parameters CP and the weights Q corresponding to all the offline test items of all the evaluation points;
8. the method for evaluating the state of a subcritical boiler drum downcomer and tube seat based on offline inspection according to claim 1, wherein the specific operation steps in the step 9) are as follows:
counting all the evaluation points obtained in the step 8) according to the classification of the down pipes and the pipe seats, counting the number m of the evaluation points of the down pipes and the number n of the evaluation points of the pipe seats, and then carrying out overall evaluation on the evaluation objects, wherein an evaluation model of a final state value is shown as a formula (11);
if the state C value of the evaluation object is 0, the state of the evaluation object is considered to be optimal, and when the C value is changed from 0 to 5, the state of the evaluation object gradually becomes worse; when the C value is larger than 3.5, the state of the evaluation object is general, but part of evaluation points are worse, so that the attention of technicians is required, and the maintenance or replacement treatment is timely carried out on part of evaluation points; when the C value is larger than 4.25, the state of the evaluation object is poor, and the state of most evaluation points is poor, particularly, when the evaluation object is in the final stage of the full-operation life cycle, if the evaluation is continuously carried out for multiple times, the state C value of the evaluation object is gradually increased, and the state of the evaluation object is also proved to be poor;
the specific operation steps in the step 10) are as follows:
and 3) completely recording and archiving the state evaluation result of the evaluation object obtained in the step 9), and feeding back for the next evaluation to calculate the correction factor of the step 5).
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