A test method for evaluating the hydrogen embrittlement susceptibility index of welded joints using principal component analysis.

Abstract

This invention discloses a test method for evaluating the hydrogen embrittlement susceptibility index of welded joints using principal component analysis, belonging to the field of material performance evaluation technology. The method includes the following steps: S1, processing the pipe welded joint into a notched round bar slow strain rate tensile specimen and conducting a slow strain rate tensile test; S2, processing the pipe welded joint into a stepped-notch CT specimen for fracture toughness and conducting a fracture toughness test; S3, calculating the specific performance loss rate under hydrogen-doped conditions and performing standardization; S4, calculating the hydrogen embrittlement susceptibility evaluation index I. PC S5. Perform scanning electron microscopy analysis on the slow strain rate tensile fracture surface to determine the risk level of hydrogen-induced cracking in the sample; S6. Determine the I-value that distinguishes different risk levels of hydrogen-induced cracking. PC Scope. This invention employs the aforementioned test method for evaluating the hydrogen embrittlement sensitivity index of welded joints using principal component analysis, which improves the statistical significance of small sample data and yields a more objective and comprehensive evaluation system for hydrogen embrittlement sensitivity.

Description

Technical Field

[0001] This invention relates to the field of material performance evaluation technology, and in particular to a test method for evaluating the hydrogen embrittlement sensitivity index of welded joints using principal component analysis. Background Technology

[0002] Hydrogen energy, as a core clean energy carrier for achieving carbon neutrality, has shown enormous application potential in transportation, energy storage, and industry. The global industrial chain is accelerating the large-scale application of high-pressure hydrogen storage equipment, hydrogen pipelines, and hydrogen fuel cells. However, hydrogen easily induces hydrogen-induced cracking in metallic materials under high-pressure environments, especially in pipeline welded joints. Due to the non-uniformity of the microstructure and properties of welded joints, as well as the influence of residual stress and various welding defects, hydrogen embrittlement failure is a common problem in pipeline steel welded joints in hydrogen environments. The hydrogen embrittlement sensitivity index, as a key parameter for quantifying a material's resistance to hydrogen damage, relies on a single indicator (such as elongation loss rate or reduction of area loss rate) in traditional assessment methods, which has significant limitations. A single indicator cannot characterize the synergistic effect of multi-dimensional performance degradation and is easily affected by fluctuations in test conditions. Summary of the Invention

[0003] The purpose of this invention is to provide a test method for evaluating the hydrogen embrittlement sensitivity index of welded joints using principal component analysis. By employing principal component analysis, this invention innovatively integrates multi-dimensional performance loss rates under hydrogen conditions into a one-dimensional comprehensive index. While retaining key information, it eliminates redundancy and conflicts between indicators and establishes a relationship between the degree of hydrogen-induced cracking risk and performance indicators. This can improve the statistical significance of small sample data and obtain a more objective and comprehensive evaluation system for hydrogen embrittlement sensitivity.

[0004] To achieve the above objectives, this invention provides a test method for evaluating the hydrogen embrittlement susceptibility index of welded joints using principal component analysis, comprising the following steps:

[0005] S1. The pipe weld joint is processed into a notched round bar slow strain rate tensile specimen. Notches are processed in the base material, weld and heat-affected zone respectively, and slow strain rate tensile tests are carried out in hydrogen environment and inert gas environment respectively.

[0006] S2. The welded joint of the pipeline is processed into a fracture toughness stepped notch CT specimen. Notches are processed in the base material, weld and heat-affected zone, and fracture toughness tests are carried out in hydrogen environment and inert gas environment respectively.

[0007] S3. Calculate the specific performance loss rate under hydrogen doping environment based on the data obtained in S1 and S2, and standardize the specific performance loss rate.

[0008] S4. The hydrogen embrittlement sensitivity evaluation index I is calculated based on the standardized specific performance loss rate.PC ;

[0009] S5. Perform scanning electron microscopy analysis on the slow strain rate tensile fracture surface to determine the risk level of hydrogen-induced cracking of the sample.

[0010] S6, Establish I PC The relationship between I and hydrogen-induced cracking risk levels was used to determine the different I levels that differentiate between hydrogen-induced cracking risk levels. PC scope.

[0011] Preferably, in S1, samples of the base material, weld and heat-affected zone machining notches are taken at the 12, 3 and 6 positions of the pipe welding to conduct repeated tests to obtain the notch tensile strength NTS, the maximum displacement l1 of the extensometer and the cross-sectional area A1 at the fracture point.

[0012] The formula for calculating elongation δ is as follows:

[0013]

[0014] Where l0 is the original gauge length and l1 is the maximum displacement of the extensometer during the stretching process;

[0015] The formula for calculating the reduction of area ψ is as follows:

[0016]

[0017] Where A0 is the original cross-sectional area of ​​the test segment, and A1 is the cross-sectional area at the fracture point of the test segment.

[0018] Preferably, S2 obtains the fracture toughness value J of the welded joint.

[0019] Preferably, the specific performance loss rate I in the hydrogen-doped environment of S3 m The calculation formula is as follows:

[0020]

[0021] Where m0 represents the specific performance of the sample in an inert gas environment, m H This refers to the specific properties of the sample under hydrogen-doped conditions; when m is δ, I m For elongation loss rate I δ When m is ψ, I m For the cross-sectional area reduction rate loss rate I ψ When m is NTS, I m Notched tensile strength loss rate I NTS When m is J, I m For fracture toughness loss rate I J ;

[0022] Specific performance loss rate I under hydrogen-doped environmentm The calculation formula for standardization is shown below:

[0023]

[0024] Among them, Z m For the standardized specific performance loss rate, σ is the average specific performance loss rate of the whole. m The standard deviation of the overall specific performance loss rate.

[0025] Preferably, the performance loss rate matrix B in S4 has a dimension of a×b, where a is the number of samples, i.e., the total number of conditions for different combinations of hydrogen doping environments and weld joint regions, and b is the number of performance loss rate types. The covariance matrix Cov(B) is calculated based on the performance loss rate matrix B, and its dimension is b×b. The formula for calculating the covariance matrix Cov(B) is as follows:

[0026]

[0027] Among them, B T Let B be the transpose of the performance loss rate matrix B, and let its dimension be b×a.

[0028] The eigenvalue λ is calculated based on the equation det(Cov(B)-λI)=0. i , i=1,2,...,b, where λ1>λ2>...>λ b `det()` calculates the determinant of a matrix, where I is the identity matrix, and λ... i Substituting into the homogeneous linear equation system (Cov(B)-λ) i I) When v = 0, the eigenvector v is obtained. i and using the formula For the feature vector v i Normalization is performed to obtain the normalized eigenvector u. i ,in

[0029] According to I PCi =Bu i Hydrogen embrittlement sensitivity index I was obtained for different principal component directions. PCi ;

[0030] according to The variance explained rate β was obtained. i Take β i I corresponding to >70% PCi As the final evaluation index for hydrogen embrittlement sensitivity, I PC .

[0031] Preferably, in S5, 10 regions are observed at 1000x magnification for each fracture center. If the number of regions corresponding to the cleavage fracture mode is greater than 5, the hydrogen-induced cracking level of the sample is considered high risk; if the number of regions corresponding to the ductile fracture mode is greater than 5, the hydrogen-induced cracking level of the sample is considered low risk; if the number of regions corresponding to the quasi-cleavage fracture mode is greater than 5, or the number of regions corresponding to the cleavage fracture mode, ductile fracture mode, and quasi-cleavage fracture mode are all less than 5, that is, the fracture surface of the sample is dominated by the quasi-cleavage fracture mode, the hydrogen-induced cracking level of the sample is considered medium risk.

[0032] Preferably, in S6, in I PC When n < n1, the corresponding hydrogen-induced cracking level is low risk; when n2 < I, the level is low risk. PC <n3 corresponds to a medium-risk hydrogen-induced cracking level, and <n4 corresponds to a medium-risk level. PC The corresponding hydrogen-induced cracking level is high risk, where n1≤n2≤n3≤n4, and n1 and n2 represent all I PC After sorting the values ​​from largest to smallest, the values ​​representing the hydrogen-induced cracking risk level are those at the boundary between low and medium risk. Here, n1 corresponds to a low-risk hydrogen-induced cracking risk level for the sample, n2 corresponds to a medium-risk hydrogen-induced cracking risk level for the sample, and n3 and n4 represent all I... PC After sorting the values ​​from largest to smallest, the values ​​that represent the hydrogen-induced cracking risk level at the boundary between medium and high risk are: n3 corresponds to a medium risk level for hydrogen-induced cracking of the sample, and n4 corresponds to a high risk level for hydrogen-induced cracking of the sample.

[0033] Therefore, this invention adopts the above-mentioned test method for evaluating the hydrogen embrittlement sensitivity index of welded joints using principal component analysis. By using principal component analysis, it innovatively integrates the multi-dimensional performance loss rate under hydrogen environment into a one-dimensional comprehensive index. While retaining the main information, it eliminates redundancy and conflict between indicators and establishes the relationship between the degree of hydrogen-induced cracking risk and performance indicators. This can improve the statistical significance of small sample data and obtain a more objective and comprehensive hydrogen embrittlement sensitivity evaluation system.

[0034] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0035] Figure 1 This is a flowchart of the present invention;

[0036] Figure 2 This is a schematic diagram of the sampling for the slow strain rate tensile test of the notched welded joint of X65 pipeline steel according to the present invention.

[0037] Figure 3 This is a schematic diagram of the fracture toughness CT sample collection for the X65 pipeline steel welded joint of the present invention.

[0038] Figure 4 This is the invention IPC Relationship between hydrogen-induced cracking risk level and graph. Detailed Implementation

[0039] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0040] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0041] Example 1

[0042] like Figure 1 As shown, this invention provides a test method for evaluating the hydrogen embrittlement susceptibility index of welded joints using principal component analysis, comprising the following steps:

[0043] S1. The pipe weld joint is processed into a notched round bar slow strain rate tensile specimen. Notches are processed in the base material, weld and heat-affected zone respectively, and slow strain rate tensile tests are carried out in hydrogen environment and inert gas environment respectively.

[0044] The specimen size and test procedure should meet the relevant requirements of GB / T34542.2—2018. Samples of the base material, weld and heat-affected zone machining notches should be taken at the 12, 3 and 6 positions of the pipe weld for repeated tests to obtain the notch tensile strength NTS, the maximum displacement l1 of the extensometer and the cross-sectional area A1 at the fracture point.

[0045] The formula for calculating elongation δ is as follows:

[0046]

[0047] Where l0 is the original gauge length and l1 is the maximum displacement of the extensometer during the stretching process;

[0048] The formula for calculating the reduction of area ψ is as follows:

[0049]

[0050] Where A0 is the original cross-sectional area of ​​the test segment, and A1 is the cross-sectional area at the fracture point of the test segment. The cross-sectional area must be measured at least three times, and the minimum value is taken as the final value of A0 and A1.

[0051] S2. The welded joint of the pipeline is processed into a stepped notch CT specimen for fracture toughness. Notches are processed in the base material, weld and heat-affected zone, and fracture toughness tests are carried out in hydrogen environment and inert gas environment respectively. The specimen size and test procedure shall meet the relevant requirements of GB / T34542.2—2018, and the fracture toughness value J of the welded joint is obtained.

[0052] S3. Calculate the specific performance loss rate under hydrogen doping environment based on the data obtained in S1 and S2, and standardize the specific performance loss rate.

[0053] Specific performance loss rate I under hydrogen-doped environment m The calculation formula is as follows:

[0054]

[0055] Where m0 represents the specific performance of the sample in an inert gas environment, m H This refers to the specific properties of the sample under hydrogen-doped conditions; when m is δ, I m For elongation loss rate I δ When m is ψ, I m For the cross-sectional area reduction rate loss rate I ψ When m is NTS, I m Notched tensile strength loss rate I NTS When m is J, I m For fracture toughness loss rate I J ;

[0056] Specific performance loss rate I under hydrogen-doped environment m The calculation formula for standardization is shown below:

[0057]

[0058] Among them, Z m For the standardized specific performance loss rate, σ is the average specific performance loss rate of the whole. m This represents the standard deviation of the overall specific performance loss rate. The overall specific performance loss rate includes all specific performance loss rates of the base material, weld, and heat-affected zone under nitrogen and different hydrogen doping ratios. Standardization is performed only within the same performance range.

[0059] S4. The hydrogen embrittlement sensitivity evaluation index I is calculated based on the standardized specific performance loss rate. PC ;

[0060] The performance loss rate matrix B has dimensions a×b, where a is the number of samples (i.e., the total number of conditions for different combinations of hydrogen-doped environments and welded joint regions), and b is the number of performance loss rate types. Each row in B represents the performance loss rate of different performance indicators under the same condition, and each column represents the performance loss rate of the same performance indicator under different conditions. The covariance matrix Cov(B), with dimensions b×b, is calculated based on the performance loss rate matrix B. The formula for calculating the covariance matrix Cov(B) is shown below:

[0061]

[0062] Among them, B T Let B be the transpose of the performance loss rate matrix B, and let its dimension be b×a.

[0063] The eigenvalue λ is calculated based on the equation det(Cov(B)-λI)=0. i , i=1,2,...,b, where λ1>λ2>...>λ b `det()` calculates the determinant of a matrix, where I is the identity matrix, and λ... i Substituting into the homogeneous linear equation system (Cov(B)-λ) i I) When v = 0, the eigenvector v is obtained. i and using the formula For the feature vector v i Normalization is performed to obtain the normalized eigenvector u. i ,in

[0064] According to I PCi =Bu i Hydrogen embrittlement sensitivity index I was obtained for different principal component directions. PCi ;

[0065] according to The variance explained rate β was obtained. i Take β i I corresponding to >70% PCi As the final evaluation index for hydrogen embrittlement sensitivity, I PC .

[0066] S5. Perform scanning electron microscopy analysis on the slow strain rate tensile fracture surface to determine the risk level of hydrogen-induced cracking of the sample.

[0067] Cleavage fracture mode: Brittle fracture occurring along a specific crystallographic plane, with fracture surfaces exhibiting tongue-like patterns, river patterns, or cleavage steps, without significant plastic deformation. Ductile fracture mode: Fracture accompanied by significant plastic deformation, characterized by dimples on the fracture surface, formed by micropore aggregation and shear tearing. Quasi-cleavage fracture mode: A hybrid mode exhibiting characteristics of both cleavage and ductile fracture, with fracture surfaces displaying localized facets and tearing ridges, accompanied by a small number of dimples and secondary cracks.

[0068] Ten regions were observed at 1000x magnification at the center of each fracture surface. If the number of regions corresponding to the cleavage fracture mode was greater than 5, the hydrogen-induced cracking level of the sample was considered high risk. If the number of regions corresponding to the ductile fracture mode was greater than 5, the hydrogen-induced cracking level of the sample was considered low risk. If the number of regions corresponding to the quasi-cleavage fracture mode was greater than 5, or the number of regions corresponding to the cleavage fracture mode, ductile fracture mode, and quasi-cleavage fracture mode were all less than 5, that is, the fracture surface of the sample was dominated by the quasi-cleavage fracture mode, the hydrogen-induced cracking level of the sample was considered medium risk.

[0069] S6, Establish I PC The relationship between I and hydrogen-induced cracking risk levels was used to determine the different I levels that differentiate between hydrogen-induced cracking risk levels. PC scope.

[0070] in I PC When n < n1, the corresponding hydrogen-induced cracking level is low risk; when n2 < I, the level is low risk. PC <n3 corresponds to a medium-risk hydrogen-induced cracking level, and <n4 corresponds to a medium-risk level. PC The corresponding hydrogen-induced cracking level is high risk, where n1≤n2≤n3≤n4, and n1 and n2 represent all I PC After sorting the values ​​from largest to smallest, the values ​​representing the hydrogen-induced cracking risk level are those at the boundary between low and medium risk. Here, n1 corresponds to a low-risk hydrogen-induced cracking risk level for the sample, n2 corresponds to a medium-risk hydrogen-induced cracking risk level for the sample, and n3 and n4 represent all I... PC After sorting the values ​​from largest to smallest, the values ​​that represent the hydrogen-induced cracking risk level at the boundary between medium and high risk are: n3 corresponds to a medium risk level for hydrogen-induced cracking of the sample, and n4 corresponds to a high risk level for hydrogen-induced cracking of the sample.

[0071] Example 2

[0072] Using X65 pipeline steel welded joints as the test object, slow strain rate tensile and fracture toughness tests were conducted under five different environments. A sampling diagram is shown below. Figure 1 , Figure 2 As shown in Table 1, BM represents the base metal region, WM represents the weld region, and HAZ represents the heat-affected zone region. The atmosphere is pure nitrogen and a mixed atmosphere of hydrogen and nitrogen with hydrogen doping ratios of 5%, 10%, 15%, and 20%, respectively. The nitrogen environment is used as an inert gas environment. The specific performance loss rate is calculated based on the results of slow strain rate tensile and fracture toughness tests in the five different environments, as shown in Table 1.

[0073] Table 1 Specific performance loss rates

[0074]

[0075] Calculate different eigenvalues ​​λ according to the method of the present invention. i The corresponding feature vector u i And calculate the variance explained rate β i The eigenvalue u1 = 78.7%, which proves that it retains most of the effective information. T Furthermore, β2 = 20.5%, β3 = 0.8%, and β4 is approximately 0. Therefore, the principal component direction corresponding to β1 is chosen to represent the hydrogen embrittlement sensitivity evaluation index I. PC As shown in Table 2.

[0076] Table 2 shows that the principal component direction corresponding to β1 represents the hydrogen embrittlement sensitivity evaluation index I. PC

[0077]

[0078] Where I PC Negative values ​​appear (e.g., when the hydrogen doping ratio of the parent material is 10%). PC The value is -1.78, which essentially reflects that the hydrogen embrittlement sensitivity under this condition is lower than the overall average level. The relative quantification characteristics enable data from different regions and different hydrogen concentrations to be uniformly mapped to the same evaluation system.

[0079] The fracture surfaces of samples under different gas environments and corresponding combinations of welded joint regions were observed according to the method of this invention, and the corresponding hydrogen-induced cracking risk level was determined, establishing a Class I... PC Relationship with hydrogen-induced cracking risk level, such as Figure 3 As shown in the figure, I PC The correlation with the risk level of hydrogen-induced cracking is good, proving that the hydrogen embrittlement sensitivity index obtained by combining multiple performance indicators can truly reflect the actual hydrogen embrittlement sensitivity of the material. Among them, when I PC When the value is <0.92, it is considered a low-risk region for hydrogen-induced cracking; when it is 1.03... PC When I < 4.25, it is a medium-risk area for hydrogen-induced cracking. PC At >6.48, it is a high-risk area for hydrogen-induced cracking.

[0080] Therefore, this invention adopts the above-mentioned test method for evaluating the hydrogen embrittlement sensitivity index of welded joints using principal component analysis. By using principal component analysis, it innovatively integrates the multi-dimensional performance loss rate under hydrogen environment into a one-dimensional comprehensive index. While retaining the main information, it eliminates redundancy and conflict between indicators and establishes the relationship between the degree of hydrogen-induced cracking risk and performance indicators. This can improve the statistical significance of small sample data and obtain a more objective and comprehensive hydrogen embrittlement sensitivity evaluation system.

[0081] 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 them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.​

Claims

1. A test method for evaluating the hydrogen embrittlement susceptibility index of welded joints using principal component analysis, characterized in that: Includes the following steps: S1. The pipe weld joint is processed into a notched round bar slow strain rate tensile specimen. Notches are processed in the base material, weld and heat-affected zone respectively, and slow strain rate tensile tests are carried out in hydrogen environment and inert gas environment respectively. Samples of the base material, weld, and heat-affected zone were taken at the 12 o'clock, 3 o'clock, and 6 o'clock positions of the pipe weld for repeated testing to obtain the notch tensile strength. Maximum displacement of extensometer and cross-sectional area at the fracture ; elongation The calculation formula is as follows: ； in, This is the original gauge length. This represents the maximum displacement of the extensometer during the stretching process; Reduction of area The calculation formula is as follows: ； in, The original cross-sectional area of ​​the test section. The cross-sectional area at the fracture point of the test section; S2. Fabricate the welded joint of the pipeline into a stepped-notch CT specimen for fracture toughness. Notches are fabricated in the base metal, weld, and heat-affected zone, and fracture toughness tests are conducted in hydrogen and inert gas environments, respectively. Obtain the fracture toughness value of the welded joint. ; S3. Calculate the specific performance loss rate under hydrogen doping environment based on the data obtained in S1 and S2, and standardize the specific performance loss rate. Specific performance loss rate under hydrogen-doped environment The calculation formula is as follows: ； in, To determine the specific properties of the sample in an inert gas environment, This refers to the specific properties of the sample under hydrogen-doped conditions; when for hour, For elongation loss rate ;when for hour, For the reduction of area loss rate ;when for hour, Notched tensile strength loss rate ;when for hour, Fracture toughness loss rate ; Specific performance loss rate under hydrogen-doped environment The calculation formula for standardization is shown below: ； in, For the standardized specific performance loss rate, This represents the average specific performance loss rate for the entire system. The standard deviation of the overall specific performance loss rate; the overall specific performance loss rate includes all specific performance loss rates of the base material, weld, and heat-affected zone under nitrogen and different hydrogen doping ratios, and the standardization process is only performed within the same performance range; S4. Calculate the hydrogen embrittlement sensitivity evaluation index based on the standardized specific performance loss rate. ; Performance loss matrix The dimension is ,in, The sample size represents the total number of conditions under different combinations of hydrogen-doped environments and weld joint regions. The number of performance loss rate types is determined by the performance loss rate matrix. Calculate the covariance matrix Its dimensions are covariance matrix The calculation formula is as follows: ； in, Performance loss rate matrix The transpose of the matrix has dimensions of . ; According to the equation Calculate the eigenvalues , ,in , To calculate the determinant of a matrix, For the identity matrix, Substitute into the homogeneous linear equation system Obtain the feature vector and using the formula For eigenvectors Normalization is performed to obtain the normalized eigenvectors. ,in ; according to Hydrogen embrittlement sensitivity index was obtained for different principal component directions. ; according to Obtain the variance explained rate ,Pick Time corresponding As the final indicator for evaluating hydrogen embrittlement sensitivity ; S5. Perform scanning electron microscopy analysis on the slow strain rate tensile fracture surface to determine the risk level of hydrogen-induced cracking of the sample. S6, Establish The relationship between hydrogen-induced cracking risk level and the determination of different hydrogen-induced cracking risk levels. scope.

2. The test method for evaluating the hydrogen embrittlement susceptibility index of welded joints using principal component analysis according to claim 1, characterized in that: In S5, 10 regions were observed at the center of each fracture surface at 1000x magnification. If the number of regions corresponding to the cleavage fracture mode was greater than 5, the hydrogen-induced cracking level of the sample was considered high risk. If the number of regions corresponding to the ductile fracture mode was greater than 5, the hydrogen-induced cracking level of the sample was considered low risk. If the number of regions corresponding to the quasi-cleavage fracture mode was greater than 5, or the number of regions corresponding to the cleavage fracture mode, ductile fracture mode, and quasi-cleavage fracture mode were all less than 5, that is, the fracture surface of the sample was dominated by the quasi-cleavage fracture mode, the hydrogen-induced cracking level of the sample was considered medium risk.

3. The test method for evaluating the hydrogen embrittlement susceptibility index of welded joints using principal component analysis according to claim 2, characterized in that: In S6 The corresponding hydrogen-induced cracking level is low risk. The corresponding hydrogen-induced cracking level is medium risk. The corresponding hydrogen-induced cracking level is high risk, among which , and Representing all After sorting the values ​​from largest to smallest, the values ​​that fall at the boundary between low and medium risk for hydrogen-induced cracking risk are: The corresponding sample has a low risk level for hydrogen-induced cracking. The corresponding sample has a medium risk level for hydrogen-induced cracking. and Representing all After sorting the values ​​from largest to smallest, the values ​​that fall at the boundary between medium and high risk for hydrogen-induced cracking risk are: The corresponding sample has a medium risk level for hydrogen-induced cracking. The corresponding sample has a high risk level for hydrogen-induced cracking.

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