Manufacturing quality grading method for 9-12% cr seamless steel tube for power plant boiler

Abstract

Provided is a manufacturing quality grading method for a 9-12% Cr seamless steel tube for a power plant boiler, comprising the following steps: 1) determining indicators for quality grading of a 9-12% Cr seamless steel tube for a boiler; 2) establishing scoring weights of the indicators for quality grading of said 9-12% Cr seamless steel tube, and establishing scoring mathematical models on the basis of the scoring weights; and 3) acquiring indicator information for quality grading of said 9-12% Cr seamless steel tube, and calculating the quality grading score of said 9-12% Cr seamless steel tube on the basis of the scoring mathematical models, and evaluating the manufacturing quality level of said 9-12% Cr seamless steel tube on the basis of the quality grading score of said 9-12% Cr seamless steel tube. The method can implement grading of the manufacturing quality of a 9-12% Cr seamless steel tube for a power plant boiler.

Description

A manufacturing quality grading method for 9-12% Cr seamless steel pipes for power station boilers Technical Field

[0001] The invention belongs to the technical field of quality grading of metal products for power stations, and relates to a manufacturing quality grading method for 9-12% Cr seamless steel pipes for power station boilers. Background Art

[0002] Over the past two decades, advanced, high-efficiency, low-emission, and environmentally friendly supercritical (ULC) generating units have become the mainstream of thermal power construction. Simultaneously, the thermal parameters of these units have been continuously refined to achieve higher thermal efficiency. With the large-scale construction of ULC thermal power units, China's demand for 9-12% Cr heat-resistant steel pipes has continued to increase. Before 2008, T / P91 and T / P92 steel pipes for power plant boilers primarily came from factories in Japan, the United States, and Germany. After 2008, with the continuous improvement of metallurgical standards and manufacturing capabilities of Chinese steel companies, 9-12% Cr steel pipes for power plant boilers began to be domestically produced and put into engineering applications. Over the past five years, 9-12% Cr steel pipes for ULC units have been fully domestically produced, and numerous domestic steel pipe companies have acquired the ability to supply 9-12% Cr steel pipes.

[0003] There are many steel companies in China, and the technical levels, equipment capabilities and product quality of different manufacturers are uneven. In addition, with the increasingly fierce market competition, some manufacturers have engaged in illegal practices such as cutting corners, saving processes, and passing off inferior products as good ones in order to make illegal profits. This has planted huge quality risks in the final products and seriously threatened the service life and operational safety of power plant equipment.

[0004] The traditional quality certification is a "threshold" level judgment method, which only divides products into two categories: qualified and unqualified. The differences in quality between qualified products are eliminated, causing some companies to blindly pursue "crippling qualified products" to reduce costs. At the same time, it also sacrifices the excellent performance and quality of the products, making it difficult for power station users to obtain steel pipe products with excellent performance and quality.

[0005] Therefore, in response to the above problems, it is urgent to propose a set of effective grading and evaluation methods for the manufacturing quality of 9-12% Cr seamless steel pipes for power station boilers, to provide comprehensive and scientific technical guidance for the selection, procurement, ordering and quality acceptance of 9-12% Cr steel pipes for boilers, and to effectively ensure the manufacturing quality of 9-12% Cr seamless steel pipes for boilers, thereby laying the foundation for the safe operation of ultra-supercritical boilers.

[0006] Summary of the Invention

[0007] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and provide a manufacturing quality grading method for 9-12% Cr seamless steel pipes for power station boilers, which can grade the manufacturing quality of 9-12% Cr seamless steel pipes for power station boilers.

[0008] To achieve the above object, the present invention discloses a method for manufacturing quality grading of 9-12% Cr seamless steel pipes for boilers, comprising the following steps:

[0009] 1) Determine the various indicators for the quality classification of 9-12% Cr seamless steel pipes for boilers;

[0010] 2) Establish the scoring weights of each indicator for the quality grading of 9-12% Cr seamless steel pipes for boilers, and establish a scoring mathematical model based on this;

[0011] 3) obtaining information on various indicators of the quality grading of 9-12% Cr seamless steel pipes for boilers, calculating a quality grading score of 9-12% Cr seamless steel pipes for boilers according to the scoring mathematical model, and evaluating the manufacturing quality level of 9-12% Cr seamless steel pipes for boilers according to the quality grading score of 9-12% Cr seamless steel pipes for boilers.

[0012] In step 1), the quality grading indicators of the 9-12% Cr seamless steel pipe for boiler include but are not limited to: chemical composition index, non-destructive testing index, grain size index, microstructure index, non-metallic inclusion index and mechanical property index.

[0013] In step 3), the process of obtaining the quality grading score of the boiler seamless steel pipe with 9-12% Cr by calculating the quality grading index information of the boiler seamless steel pipe with 9-12% Cr according to the scoring mathematical model is as follows:

[0014] The quality grading score of 9-12% Cr seamless steel pipe for boiler is obtained by weighted summing up the index information of the quality grading of 9-12% Cr seamless steel pipe for boiler and its corresponding grading score weight.

[0015] The chemical composition indicators include but are not limited to: C element index, Si element index, Mn element index, P element index, S element index, Ni element index, Cr element index, Mo element index, Al element index, V element index, Nb element index and N element index.

[0016] The mechanical performance indicators include but are not limited to: tensile strength index, yield strength index, elongation after fracture index, impact absorption energy index and hardness index.

[0017] According to Table 1, the manufacturing quality level of the 9-12% Cr seamless steel pipe for boiler is evaluated according to the quality grading score of the 9-12% Cr seamless steel pipe for boiler.

[0018] Table 1

[0019] Assume that the scoring weight of the chemical composition index of the quality grade of the 9-12% Cr seamless steel pipe for boiler is S1(1), the scoring weight of the non-destructive testing index of the quality grade of the 9-12% Cr seamless steel pipe for boiler is S1(2), the scoring weight of the grain size index of the quality grade of the 9-12% Cr seamless steel pipe for boiler is S1(3), the scoring weight of the microstructure index of the quality grade of the 9-12% Cr seamless steel pipe for boiler is S1(4), the scoring weight of the non-metallic inclusion index of the quality grade of the 9-12% Cr seamless steel pipe for boiler is S1(5), and the scoring weight of the mechanical property index of the quality grade of the 9-12% Cr seamless steel pipe for boiler is S1(6), S1(1)+S1(2)+S1(3)+S1(4)+S1(5)+S1(6)=1.

[0020] Among the chemical composition indicators, the grading scoring weight of the C element indicator is recorded as S11(1), the grading scoring weight of the Si element indicator is recorded as S11(2), the grading scoring weight of the Mn element indicator is recorded as S11(3), the grading scoring weight of the P element indicator is recorded as S11(4), the grading scoring weight of the S element indicator is recorded as S11(5), the grading scoring weight of the Ni element indicator is recorded as S11(6), the grading scoring weight of the Cr element indicator is recorded as S11(7), the grading scoring weight of the Mo element indicator is recorded as S11(8), the grading scoring weight of the Al element indicator is recorded as S11(9), the grading scoring weight of the V element indicator is recorded as S11(10), the grading scoring weight of the Nb element indicator is recorded as S11(11), and the grading scoring weight of the N element indicator is recorded as S11(12).

[0021] The C element index, Si element index, Mn element index, P element index, S element index, Ni element index, Cr element index, Mo element index, Al element index, V element index, Nb element index and N element index and their corresponding graded scoring weights are weighted summed to obtain the score of the chemical composition index.

[0022] Among the mechanical performance indicators, the grading weight of the tensile strength indicator is recorded as S12(1), the grading weight of the yield strength indicator is recorded as S12(2), the grading weight of the elongation after fracture indicator is recorded as S12(3), the grading weight of the impact absorption energy indicator is recorded as S12(4), and the grading weight of the hardness is recorded as S12(5);

[0023] The tensile strength index, yield strength index, elongation after fracture index, impact absorption energy index and hardness index and their corresponding grading weights are weighted and summed to obtain the score of the mechanical performance index.

[0024] In step 3), various index information of quality grading of 100 batches of 9-12% Cr seamless steel pipes produced within one year or recently is collected to obtain various index information of quality grading of 9-12% Cr seamless steel pipes for boilers.

[0025] The present invention has the following beneficial effects:

[0026] The manufacturing quality grading method of 9-12% Cr seamless steel pipe for boilers described in the present invention determines various indicators of quality grading for 9-12% Cr seamless steel pipe for boilers during specific operation, then establishes a scoring mathematical model, and finally collects data on various indicator information of quality grading for 9-12% Cr seamless steel pipe for boilers and inputs the data into the scoring mathematical model to obtain quality grading scores for 9-12% Cr seamless steel pipe for boilers. The quality status level of 9-12% Cr seamless steel pipe for boilers is judged based on the scores. The method is objective and accurate, avoids subjectivity, is more scientific and standardized, can provide strong protection for the operational safety of 9-12% Cr seamless steel pipe for boilers, and at the same time provides scientific guidance for its ordering, procurement and quality acceptance. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG1 is a flow chart of the method of the present invention;

[0028] FIG2 is a schematic diagram of six indicators of the present invention;

[0029] FIG3 is a schematic diagram of a scoring mathematical model of the present invention that is a piecewise function;

[0030] FIG4 is a schematic diagram of a scoring mathematical model of the present invention that is an increasing function;

[0031] FIG5 is a schematic diagram of a scoring mathematical model of the present invention that is a decreasing function;

[0032] FIG6 is a schematic diagram showing a scoring mathematical model of the present invention as a platform function. DETAILED DESCRIPTION

[0033] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only embodiments of a part of the present invention, not all embodiments, and are not intended to limit the scope of the present invention. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion of the concepts disclosed in the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work should fall within the scope of protection of the present invention.

[0034] The accompanying drawings illustrate schematic diagrams of the structures of the disclosed embodiments of the present invention. These figures are not drawn to scale; for the purpose of clarity, some details are exaggerated and some details may be omitted. The shapes of the various regions and layers shown in the figures, as well as their relative sizes and positional relationships, are merely exemplary and may deviate in practice due to manufacturing tolerances or technical limitations. Those skilled in the art may design regions / layers with different shapes, sizes, and relative positions as needed.

[0035] 1 , the manufacturing quality grading method of 9-12% Cr seamless steel pipe for boiler according to the present invention comprises the following steps:

[0036] 1) Determine the quality grading indicators of 9-12% Cr seamless steel pipes for boilers;

[0037] In step 1), the quality grading indicators of the 9-12% Cr seamless steel pipe for boiler include chemical composition indicators, non-destructive testing indicators, grain size indicators, microstructure indicators, non-metallic inclusion indicators and mechanical property indicators.

[0038] The chemical composition indicators include but are not limited to: C element index, Si element index, Mn element index, P element index, S element index, Ni element index, Cr element index, Mo element index, Al element index, V element index, Nb element index and N element index.

[0039] The mechanical performance indicators include but are not limited to: tensile strength index, yield strength index, elongation after fracture index, impact absorption energy index and hardness index.

[0040] 2) Establish the scoring weights for each quality grading index of 9-12% Cr seamless steel pipes for boilers, and establish a scoring mathematical model based on this;

[0041] Among them, the scoring weight of the chemical composition index of the quality grading of the 9-12% Cr seamless steel pipe for boiler is recorded as S1(1), the scoring weight of the non-destructive testing index of the quality grading of the 9-12% Cr seamless steel pipe for boiler is recorded as S1(2), the scoring weight of the grain size index of the quality grading of the 9-12% Cr seamless steel pipe for boiler is recorded as S1(3), the scoring weight of the microstructure index of the quality grading of the 9-12% Cr seamless steel pipe for boiler is recorded as S1(4), the scoring weight of the non-metallic inclusion index of the quality grading of the 9-12% Cr seamless steel pipe for boiler is recorded as S1(5), and the scoring weight of the mechanical property index of the quality grading of the 9-12% Cr seamless steel pipe for boiler is recorded as S1(6), S1(1)+S1(2)+S1(3)+S1(4)+S1(5)+S1(6)=1, as shown in Table 1:

[0042] Table 1

[0043] Among the quality grading indicators of the 9-12% Cr seamless steel pipe for boilers, the scoring mathematical model of the chemical composition indicator includes the grading scoring weights and the scoring piecewise function of each element indicator, and the cumulative sum of the grading scoring weights of each element indicator is 1. The scoring mathematical model of the mechanical property indicator includes the grading scoring weights and the scoring piecewise function of each mechanical property indicator, and the cumulative sum of the grading scoring weights of each mechanical property indicator is 1. The scoring mathematical model of the non-destructive testing, grain size, microstructure and non-metallic inclusion indicators is a piecewise function.

[0044] Among the chemical composition indicators, the grading weight of the C element indicator is recorded as S11(1), the grading weight of the Si element indicator is recorded as S11(2), the grading weight of the Mn element indicator is recorded as S11(3), the grading weight of the P element indicator is recorded as S11(4), the grading weight of the S element indicator is recorded as S11(5), the grading weight of the Ni element indicator is recorded as S11(6), the grading weight of the Cr element indicator is recorded as S11(7), the grading weight of the Mo element indicator is recorded as S11(8), the grading weight of the Al element indicator is recorded as S11(9), the grading weight of the V element indicator is recorded as S11(10), the grading weight of the Nb element indicator is recorded as S11(11), and the grading weight of the N element indicator is recorded as S11(12). The cumulative sum of the grading weights of the above element indicators is 1, as shown in Table 2:

[0045] Table 2

[0046] The scoring piecewise functions of the Ni, P, S, and Al element indicators are decreasing functions, and the scoring piecewise functions of the remaining element indicators are platform functions.

[0047] Among the mechanical performance indicators, the grading scoring weight of tensile strength is recorded as S12(1), the grading scoring weight of yield strength is recorded as S12(2), the grading scoring weight of elongation after fracture is recorded as S12(3), the grading scoring weight of impact absorption energy is recorded as S12(4), and the grading scoring weight of hardness is recorded as S12(5). The cumulative sum of the grading scoring weights of the above mechanical performance indicators is 1, as shown in Table 3:

[0048] Table 3

[0049] The scoring piecewise functions of the tensile strength index, yield strength index and hardness index are platform functions, and the scoring piecewise functions of the elongation after fracture index and impact absorption energy index are increasing functions.

[0050] 3) obtaining information on various indicators of the quality grading of 9-12% Cr seamless steel pipes for boilers, calculating a quality grading score of 9-12% Cr seamless steel pipes for boilers according to the scoring mathematical model, and evaluating the manufacturing quality level of 9-12% Cr seamless steel pipes for boilers according to the quality grading score of 9-12% Cr seamless steel pipes for boilers.

[0051] In step 3), the process of the quality grading information of the 9-12% Cr seamless steel pipe for boilers is as follows: collecting the quality grading index data of the 9-12% Cr seamless steel pipe for boilers produced by the manufacturer in the past year or the most recently produced 100 batches, performing statistical analysis on the data, scoring the analysis results according to the scoring mathematical model, and obtaining the quality grading score of the 9-12% Cr seamless steel pipe for boilers. The steps of judging the quality status level of the 9-12% Cr seamless steel pipe for boilers according to the scoring results include:

[0052] a) Collect the content data of each element of the chemical composition of 9-12% Cr seamless steel pipe for boiler, perform statistical analysis, calculate the 95% confidence interval of each element, score the analysis results according to the scoring mathematical model, and obtain the scoring result x(1).

[0053] b) Collect nondestructive testing data and conduct statistical analysis, score the analysis results according to the scoring mathematical model, and obtain the scoring result x(2).

[0054] c) Collect and statistically analyze the grain size data, score the analysis results according to the scoring mathematical model, and obtain the scoring result x(3).

[0055] d) Collect and statistically analyze microstructural data, score the analysis results according to the scoring mathematical model, and obtain the scoring result x(4).

[0056] e) Collect and statistically analyze the non-metallic inclusion data, score the analysis results according to the scoring mathematical model, and obtain the scoring result x(5).

[0057] f) Collect and statistically analyze the data on tensile properties, impact properties, and hardness, and calculate the 95% confidence intervals of yield strength, tensile strength, elongation after fracture, impact absorption energy, and hardness, respectively. Score the analysis results according to the scoring mathematical model to obtain the scoring result x(6).

[0058] g) Multiplying the scoring weight of each indicator of the quality grading of 9-12% Cr seamless steel pipes for boilers by the corresponding scoring result, and accumulating the sum to obtain the quality grading score X of 9-12% Cr seamless steel pipes for boilers.

[0059] h) The manufacturing quality classification of 9-12% Cr seamless steel pipes for boilers is carried out according to the quality classification scores of 9-12% Cr seamless steel pipes for boilers.

[0060] In step h), the quality status of the 9-12% Cr seamless steel pipe for boiler is divided into grades A to D according to the quality grading scores of the 9-12% Cr seamless steel pipe for boiler, as shown in Table 4.

[0061] Table 4

[0062] Example 1

[0063] As shown in FIG1 to FIG6, the manufacturing quality grading method of 9-12% Cr seamless steel pipe for boilers described in this embodiment includes the following steps:

[0064] 1) Analyze and determine the quality grading indicators of 9-12% Cr seamless steel pipes for boilers, including chemical composition, hardness, non-destructive testing, grain size, microstructure, non-metallic inclusions and mechanical properties;

[0065] The chemical composition indicators include C element index, Si element index, Mn element index, P element index, S element index, Ni element index, Cr element index, Mo element index, Al element index, V element index, Nb element index and N element index.

[0066] Mechanical performance indicators include tensile strength index, yield strength index, elongation after fracture index, impact absorption energy index and hardness index.

[0067] 2) Establish the scoring weight S1(j) and scoring mathematical model for each quality grading index of 9-12% Cr seamless steel pipe for boiler;

[0068] Among them, the scoring weight of the chemical composition index of the quality grading of 9-12% Cr seamless steel pipes for boilers is recorded as S1(1)=0.3, the scoring weight of the non-destructive testing index of the quality grading of 9-12% Cr seamless steel pipes for boilers is recorded as S1(2)=0.05, the scoring weight of the grain size index of the quality grading of 9-12% Cr seamless steel pipes for boilers is recorded as S1(3)=0.05, and the scoring weight of the microstructure index of the quality grading of 9-12% Cr seamless steel pipes for boilers is recorded as S1(5)=0. 05, the scoring weight of the non-metallic inclusion index of the quality grading of 9-12% Cr seamless steel pipes for boilers is recorded as S1(5)=0.05, the scoring weight of the mechanical property index of the quality grading of 9-12% Cr seamless steel pipes for boilers is recorded as S1(6)=0.5, and the cumulative sum of the scoring weights of each index of the quality grading of 9-12% Cr seamless steel pipes for boilers is 1, that is, S1(1)+S1(2)+S1(3)+S1(4)+S1(5)+S1(6)=1, as shown in Table 5.

[0069] Table 5

[0070] Among the quality grading indicators of 9-12% Cr seamless steel pipes for boilers, in addition to chemical composition and mechanical properties, the scoring mathematical models for indicators such as non-destructive testing, grain size, microstructure and non-metallic inclusions are piecewise functions.

[0071] The scoring mathematical model of chemical composition indicators includes: 1) the hierarchical scoring weight S11(j) of each element indicator; 2) the scoring piecewise function.

[0072] The chemical composition indexes include C, Si, Mn, P, S, Ni, Cr, Mo, Al, V, Nb and N element indexes, among which the grading scoring weight of the C index is recorded as S11(1)=0.1, the grading scoring weight of the Si index is recorded as S11(2)=0.05, the grading scoring weight of the Mn index is recorded as S11(3)=0.05, the grading scoring weight of the P index is recorded as S11(4)=0.1, the grading scoring weight of the S index is recorded as S11(5)=0.1, and the grading scoring weight of the Ni index is recorded as S11(6) =0.05, the grading scoring weight of the Cr index is recorded as S11(7)=0.2, the grading scoring weight of the Mo index is recorded as S11(8)=0.15, the grading scoring weight of the Al index is recorded as S11(9)=0.05, the grading scoring weight of the V index is recorded as S11(10)=0.05, the grading scoring weight of the Nb index is recorded as S11(11)=0.05, and the grading scoring weight of the N index is recorded as S11(12)=0.05. The cumulative sum of the grading scoring weights of the above-mentioned element indexes is 1, as shown in Table 6.

[0073] Table 6

[0074] The upper and lower limit requirements for the content of C, Si, Mn, P, S, Ni, Cr, Mo, Al, V, Nb and N elements in 9-12% Cr seamless steel pipes for boilers in GB / T 5310-2017 are shown in Table 7.

[0075] Table 7

[0076] The scoring piecewise function of chemical composition index is as follows:

[0077] The scoring functions for Ni, P, S, and Al are decreasing functions, while those for other elements are plateau functions, reaching optimal values ​​within a certain range and gradually decreasing away from that range. For elements other than Ni, P, S, and Al, the content distribution of other elements is considered optimal within a certain range.

[0078] The scoring piecewise functions for the Ni, P, S, and Al elemental indicators are decreasing functions. When determining the scoring piecewise functions for each of the above elemental indicators, it is necessary to determine the upper and lower limits of the content of each elemental indicator, the corresponding scores for these upper and lower limits, and the turning point content value of each elemental indicator (which can be determined based on experience). The score corresponding to the upper limit of the content can be empirically determined to be 0.6, and the score corresponding to the turning point content value of each elemental indicator is recorded as 1. When the actual tested content value of each elemental indicator is not greater than the turning point content value, the corresponding score value is 1. Otherwise, the score value is calculated using a linear equation. The turning point content values ​​and corresponding scores for the Ni elemental indicator, P elemental indicator, S elemental indicator, and Al elemental indicator are shown in Table 8.

[0079] Table 8

[0080] The scoring piecewise functions of element indicators other than Ni, P, S and Al are platform functions. When determining the scoring piecewise functions of the above element indicators, it is necessary to determine the lower limit and upper limit of the content of each element indicator. The score values ​​corresponding to the lower limit and upper limit of the content are the same and are determined to be 0.6 based on experience. It is also necessary to determine the lower limit and upper limit corresponding to the optimal content range of the element. The score value corresponding to the optimal content range is 1. If the content value obtained by the actual test of each element indicator is within the optimal content range of the element, the score value is 1. Otherwise, the content value obtained by the actual test of each element indicator is not greater than the lower limit corresponding to the optimal content range and not less than the upper limit corresponding to the optimal content range, and the score value is calculated by a linear equation of one variable. The lower limit and upper limit corresponding to the optimal range of the element indicators except Ni, P, S, and Al are shown in Table 9.

[0081] Table 9

[0082] The scoring mathematical model of mechanical performance indicators includes: 1) the hierarchical scoring weight S12(j) of each mechanical performance indicator; 2) the scoring piecewise function.

[0083] Among them, the grading scoring weight of the tensile strength index is recorded as S12(1)=0.25, the grading scoring weight of the yield strength index is recorded as S12(2)=0.25, the grading scoring weight of the elongation index is recorded as S12(3)=0.1, the grading scoring weight of the impact absorption energy index is recorded as S12(4)=0.2, and the grading scoring weight of the hardness index is recorded as S12(5)=0.2. The cumulative sum of the grading scoring weights of the above mechanical properties is 1, as shown in Table 10.

[0084] Table 10

[0085] The requirements for tensile strength, yield strength, elongation after fracture, impact absorption energy and hardness of 9-12% Cr seamless steel pipes for boilers in GB / T 5310-2017 are shown in Table 11.

[0086] Table 11

[0087] The scoring piecewise function of the mechanical performance index is as follows:

[0088] The scoring piecewise functions for tensile strength, yield strength, and hardness are plateau functions. The distribution of tensile strength, yield strength, and hardness is optimal within a certain range, decreasing outside of this range. The scoring piecewise functions for elongation and impact energy absorption are increasing functions.

[0089] The principles for determining the scoring piecewise functions for tensile strength, yield strength, and hardness are similar to those for elemental indices other than Ni, P, S, and Al. Determining the scoring piecewise functions for elongation and impact absorption energy requires determining their lower limits, the corresponding score values ​​(which can be empirically determined as 0.6), and the turning point value (which can also be empirically determined). The score corresponding to the turning point value is 1. The increasing function equation can be a linear equation. Scores not less than the turning point value are 1. Otherwise, scores must be calculated using a linear equation, as shown in Tables 12 and 13.

[0090] Table 12

[0091] Table 13

[0092] 3) The quality grading index data of 9-12% Cr seamless steel pipes for boilers produced by a domestic company were collected and statistically analyzed. The analysis results were scored according to the scoring mathematical model to obtain the quality grading score X of 9-12% Cr seamless steel pipes for boilers. The specific steps are as follows:

[0093] a) The chemical composition element content data of 100 batches of 10Cr9Mo1VNbN seamless steel pipes recently produced by a domestic company were collected, statistically analyzed, and the 95% confidence interval of the content of each element was calculated, as shown in Table 14. The scoring was performed according to the scoring mathematical model, and the scoring result x(1) = 0.995 was obtained.

[0094] Table 14

[0095] b) The non-destructive testing data of the most recently produced 100 batches of 10Cr9Mo1VNbN seamless steel pipes were collected and statistically analyzed. All of the data met the standard requirements. The analysis results were scored according to the scoring mathematical model, and the scoring result x(2)=1 was obtained.

[0096] c) The grain size data of the 100 most recently produced batches of 10Cr9Mo1VNbN seamless steel pipes were collected and statistically analyzed. The average grain size grade was found to be 7.5, with a distribution range of 7-8. The analysis results were scored using a mathematical model, resulting in a scoring result of x(3) = 1.

[0097] d) The microstructure data of 100 batches of 10Cr9Mo1VNbN seamless steel pipes were collected and the metallographic structure was 100% tempered martensite. The standard requirements were met and the scoring was performed according to the scoring mathematical model, and the scoring result was x(4)=1.

[0098] e) The non-metallic inclusion data of the most recently produced 100 batches of 10Cr9Mo1VNbN seamless steel pipes were collected and statistically analyzed. It was found that the total non-metallic inclusions were 2.5 for fine inclusions and 0.95 for coarse inclusions. The non-metallic inclusion content met the standard requirements. The scoring was performed according to the scoring mathematical model, and the scoring result x(5) = 1 was obtained.

[0099] f) The tensile properties, impact properties, and hardness data of the most recently produced 100 batches of 10Cr9Mo1VNbN seamless steel pipes were collected and statistically analyzed to calculate the 95% confidence intervals for tensile strength, yield strength, hardness, elongation after fracture, and impact absorbed energy, as shown in Table 15. Scoring was performed according to the scoring mathematical model, and the scoring result x(6) = 1 was obtained.

[0100] Table 15

[0101] g) Multiply the scoring weight of each indicator of the quality grading of 9-12% Cr seamless steel pipes for boilers by the corresponding score, and add up the cumulative score to obtain the quality grading score of 9-12% Cr seamless steel pipes for boilers As shown in Table 16.

[0102] Table 16

[0103] h) According to the quality grading scores of 9-12% Cr seamless steel pipes for boilers, the quality status of 9-12% Cr seamless steel pipes for boilers is divided into grades A to D, as shown in Table 17. The quality grade of domestically produced P91 seamless steel pipes produced by a domestic company is A+.

[0104] Table 17

[0105] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the claims of the present invention.

Claims

1. A method for grading the manufacturing quality of 9-12% Cr seamless steel pipes for boilers, characterized in that: The following steps are involved: 1) Determine the various indicators for the quality classification of 9-12% Cr seamless steel pipes for boilers; 2) Establish the scoring weights of each indicator for the quality grading of 9-12% Cr seamless steel pipes for boilers, and establish a scoring mathematical model based on this; 3) obtaining information on various indicators of the quality grading of 9-12% Cr seamless steel pipes for boilers, calculating a quality grading score of 9-12% Cr seamless steel pipes for boilers according to the scoring mathematical model, and evaluating the manufacturing quality level of 9-12% Cr seamless steel pipes for boilers according to the quality grading score of 9-12% Cr seamless steel pipes for boilers.

2. The method for grading the manufacturing quality of 9-12% Cr seamless steel pipes for boilers according to claim 1, characterized in that: In step 1), the quality grading indicators of the 9-12% Cr seamless steel pipe for boiler include but are not limited to: chemical composition index, non-destructive testing index, grain size index, microstructure index, non-metallic inclusion index and mechanical property index.

3. The manufacturing quality grading method of 9-12% Cr seamless steel pipe for boiler according to claim 1, characterized in that: In step 3), the process of obtaining the quality grading score of the boiler seamless steel pipe with 9-12% Cr by calculating the quality grading index information of the boiler seamless steel pipe with 9-12% Cr according to the scoring mathematical model is as follows: The quality grading score of 9-12% Cr seamless steel pipe for boiler is obtained by weighted summing up the index information of the quality grading of 9-12% Cr seamless steel pipe for boiler and its corresponding grading score weight.

4. The method for grading the manufacturing quality of 9-12% Cr seamless steel pipes for boilers according to claim 2, characterized in that: The chemical composition indicators include but are not limited to: C element index, Si element index, Mn element index, P element index, S element index, Ni element index, Cr element index, Mo element index, Al element index, V element index, Nb element index and N element index.

5. The manufacturing quality grading method of 9-12% Cr seamless steel pipe for boiler according to claim 2, characterized in that: The mechanical performance indicators include but are not limited to: tensile strength index, yield strength index, elongation after fracture index, impact absorption energy index and hardness index.

6. The method for grading the manufacturing quality of 9-12% Cr seamless steel pipes for boilers according to claim 1, characterized in that: According to Table 1, the manufacturing quality level of the 9-12% Cr seamless steel pipe for boiler is evaluated according to the quality grading score of the 9-12% Cr seamless steel pipe for boiler. Table 1 7. The method for grading the manufacturing quality of 9-12% Cr seamless steel pipes for boilers according to claim 4, characterized in that: Suppose the scoring weight of the chemical composition index of the quality grade of the 9-12% Cr seamless steel pipe for boiler is recorded as S1(1), the scoring weight of the non-destructive testing index of the quality grade of the 9-12% Cr seamless steel pipe for boiler is recorded as S1(2), the scoring weight of the grain size index of the quality grade of the 9-12% Cr seamless steel pipe for boiler is recorded as S1(3), the scoring weight of the microstructure index of the quality grade of the 9-12% Cr seamless steel pipe for boiler is recorded as S1(4), the scoring weight of the non-metallic inclusion index of the quality grade of the 9-12% Cr seamless steel pipe for boiler is recorded as S1(5), and the scoring weight of the mechanical property index of the quality grade of the 9-12% Cr seamless steel pipe for boiler is recorded as S1(6), S1(1)+S1(2)+S1(3)+S1(4)+S1(5)+S1(6)=1.

8. The method for grading the manufacturing quality of 9-12% Cr seamless steel pipes for boilers according to claim 4, characterized in that: Among the chemical composition indicators, the grading scoring weight of the C element indicator is recorded as S11(1), the grading scoring weight of the Si element indicator is recorded as S11(2), the grading scoring weight of the Mn element indicator is recorded as S11(3), the grading scoring weight of the P element indicator is recorded as S11(4), the grading scoring weight of the S element indicator is recorded as S11(5), the grading scoring weight of the Ni element indicator is recorded as S11(6), the grading scoring weight of the Cr element indicator is recorded as S11(7), the grading scoring weight of the Mo element indicator is recorded as S11(8), the grading scoring weight of the Al element indicator is recorded as S11(9), the grading scoring weight of the V element indicator is recorded as S11(10), the grading scoring weight of the Nb element indicator is recorded as S11(11), and the grading scoring weight of the N element indicator is recorded as S11(12). The C element index, Si element index, Mn element index, P element index, S element index, Ni element index, Cr element index, Mo element index, Al element index, V element index, Nb element index and N element index and their corresponding graded scoring weights are weighted summed to obtain the score of the chemical composition index.

9. The method for grading the manufacturing quality of 9-12% Cr seamless steel pipes for boilers according to claim 5, characterized in that: Among the mechanical performance indicators, the grading weight of the tensile strength indicator is recorded as S12(1), the grading weight of the yield strength indicator is recorded as S12(2), the grading weight of the elongation after fracture indicator is recorded as S12(3), the grading weight of the impact absorption energy indicator is recorded as S12(4), and the grading weight of the hardness is recorded as S12(5); The tensile strength index, yield strength index, elongation after fracture index, impact absorption energy index and hardness index and their corresponding grading weights are weighted and summed to obtain the score of the mechanical performance index.

10. The manufacturing quality grading method of 9-12% Cr seamless steel pipe for boiler according to claim 1, characterized in that: In step 3), various index information of quality grading of 100 batches of 9-12% Cr seamless steel pipes produced within one year or recently is collected to obtain various index information of quality grading of 9-12% Cr seamless steel pipes for boilers.

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