Steel branch pipe welding residual stress detection system and method based on water pressure loading

Abstract

The invention provides a steel bifurcated pipe welding residual stress detection system and method based on water pressure loading, and relates to the technical field of residual stress detection. Determining a stress correction coefficient on the detection mark point in the pressure maintaining stage, determining a spatial displacement of the detection mark point under the corresponding pressure according to all the stress correction coefficients and the stress distribution coordinates, and determining a strain detection value under each pressure according to the spatial displacement under the corresponding pressure; judging a strain response relationship when all the spatial displacements change along with the water pressure, and determining a residual compensation value after complete pressure relief based on corresponding deformation difference characteristics; and evaluating the residual stress distribution grade of the steel branch pipe welding area according to the strain detection value under each pressure and the residual compensation value after complete pressure relief. According to the method, the residual stress of the welding area of the steel branch pipe can be accurately detected under step-by-step water pressure loading circulation, so that the accuracy of residual stress distribution grade evaluation is improved.

Description

Technical Field

[0001] This application relates to the field of residual stress detection technology, and more specifically, to a system and method for detecting residual stress in steel branch pipe welding based on water pressure loading. Background Technology

[0002] Residual stress testing is widely used in the manufacturing quality acceptance and service safety assessment of welded components such as steel branch pipes, pressure vessels, and bridge steel structures. Steel branch pipes, as key pressure-bearing components in hydraulic engineering projects, involve complex welding processes, and residual stress is easily generated in the weld seams and heat-affected zones. The distribution of residual stress directly affects the fatigue resistance and crack resistance of the components, and it is characterized by its high degree of concealment, uneven distribution, and strong correlation with the structural geometry. Furthermore, the accuracy of residual stress testing results directly determines the reliability of structural safety assessments and service life predictions. Quantitative characterization and distribution analysis of stress in welded areas based on residual stress testing, adapting to the stress testing needs of complex steel branch pipe structures, is a crucial foundation for ensuring the manufacturing quality, service safety, and long-term stable operation of pressure-bearing components in hydraulic engineering projects.

[0003] However, existing methods for detecting residual stress in welded steel branch pipes based on hydraulic loading lack precise optical detection markers, a stress correction mechanism during the pressure holding stage, accurate spatial displacement calculation methods, a hierarchical comparison system for strain response relationships, and a scientific path for determining residual compensation values. This results in insufficient accuracy in stress-strain information acquisition, significant deviations in spatial displacement calculations, limited accuracy in strain detection values, and inadequate extraction of deformation difference characteristics. Consequently, the determination of residual compensation values ​​lacks a reliable basis, and the accuracy of the residual stress distribution level assessment results in the welded area of ​​the steel branch pipe is difficult to guarantee. Therefore, how to accurately detect residual stress in the welded area of ​​steel branch pipes under progressive hydraulic loading cycles to improve the accuracy of residual stress distribution level assessment is a problem facing the industry. Summary of the Invention

[0004] This application provides a system and method for detecting residual stress in steel branch pipe welding based on water pressure loading. It can accurately detect residual stress in the welding area of ​​steel branch pipe under progressive water pressure loading cycles, thereby improving the accuracy of residual stress distribution level assessment.

[0005] In a first aspect, this application provides a method for detecting residual stress in welded steel branch pipes based on hydraulic loading, the method comprising the following steps:

[0006] Multiple optical detection markers are set on the shell surface of the steel branch pipe to be tested, and stress and strain information on all detection markers is obtained during the stepwise water pressure loading cycle.

[0007] The stress correction factor on the detection marker point in the holding stage of each loading cycle is determined by all stress and strain information. Based on all stress correction factors and the stress distribution coordinates of the detection marker point in the holding stage, the spatial displacement of the detection marker point under the corresponding pressure is determined. Then, the strain detection value under each pressure is determined by the spatial displacement under the corresponding pressure.

[0008] The strain response relationship of all spatial displacements with water pressure is determined, and all strain response relationships are compared in a stepwise manner to obtain the deformation difference characteristics of the detection markers in the corresponding pressurization and depressurization processes. Then, the residual compensation value after complete depressurization is determined based on the corresponding deformation difference characteristics.

[0009] The residual stress distribution level of the welded area of ​​the steel branch pipe is evaluated based on the strain test value under each pressure and the residual compensation value after complete depressurization.

[0010] In this embodiment, the detection marker point refers to a highly reflective circular aluminum foil marker used to reflect optical measurement signals for identification, positioning, and calculation of spatial displacement.

[0011] In this embodiment, determining the stress correction factor at the detection marker point during the holding phase of each loading cycle using all stress-strain information specifically includes:

[0012] Extract the stress-strain characteristics of the detection markers during the holding phase of each loading cycle from all stress-strain information;

[0013] Based on the material constitutive relation, all stress-strain characteristics are synchronized to obtain the stress correction factor;

[0014] The stress correction factor is used to generate the stress correction coefficient at the detection marker point during each loading cycle holding pressure phase.

[0015] In this embodiment, the spatial displacement refers to an index that quantifies the deformation of the steel branch pipe shell.

[0016] In this embodiment, determining the strain detection value under each pressure based on the spatial displacement under the corresponding pressure specifically includes:

[0017] The displacement vector difference between each detection marker point and its adjacent points is extracted from the spatial displacement under the corresponding pressure.

[0018] The initial strain tensor under each pressure is determined based on the initial relative coordinates of each displacement vector difference and the detection marker point.

[0019] All the initial strain tensors are aligned to obtain the strain readings for each pressure.

[0020] In this embodiment, determining the strain response relationship of all spatial displacements as water pressure changes specifically includes:

[0021] Construct water pressure-displacement sequences for all spatial displacements as water pressure changes;

[0022] The water pressure-displacement sequence was filtered to obtain multiple strain response indices for displacement as water pressure changes.

[0023] By comparing all strain response indicators with preset strain response thresholds, the strain response relationships of all spatial displacements with changes in water pressure are obtained.

[0024] In this embodiment, a stepwise comparison is performed on all strain response relationships to obtain the deformation difference characteristics of the detection marker points during the corresponding pressurization and depressurization processes. Specifically, this includes:

[0025] Determine the strain response data segments for the pressurization and depressurization processes;

[0026] All strain response data segments are embedded into all strain response relationships step by step to obtain the strain response deviation of the detection marker points in the corresponding pressurization and depressurization processes;

[0027] The deformation difference characteristics of the detection marker points during the corresponding pressurization and depressurization processes are determined based on the strain response deviation.

[0028] In this embodiment, complete depressurization refers to the state where the water pressure inside the steel branch pipe drops to 0 MPa and stabilizes after all loading cycles have ended.

[0029] In this embodiment, the assessment of the residual stress distribution level in the welded area of ​​the steel branch pipe based on the strain detection value under each pressure and the residual compensation value after complete depressurization specifically includes:

[0030] The residual stress influence of each detection marker point under each pressure is determined based on the strain detection value under each pressure.

[0031] The residual stress level range is determined by the residual compensation value after complete depressurization;

[0032] Based on the residual stress level range, all residual stress influence quantities are classified into levels to obtain the residual stress distribution level of the steel branch pipe welding area.

[0033] Secondly, this application provides a system for detecting residual stress in steel branch pipe welding based on hydraulic loading, used to perform a method for detecting residual stress in steel branch pipe welding based on hydraulic loading, the detection system comprising:

[0034] The water pressure loading module is used to set up multiple optical detection markers on the shell surface of the steel branch pipe to be tested, and to acquire stress and strain information on all detection markers during the step-by-step water pressure loading cycle.

[0035] The deformation detection module is used to determine the stress correction coefficient on the detection marker point in the holding stage of each loading cycle through all stress and strain information. Based on all stress correction coefficients and the stress distribution coordinates of the detection marker point in the holding stage, the spatial displacement of the detection marker point under the corresponding pressure is determined, and then the strain detection value under each pressure is determined by the spatial displacement under the corresponding pressure.

[0036] The difference judgment module is used to judge the strain response relationship of all spatial displacements as water pressure changes, perform a stepwise comparison of all strain response relationships, obtain the deformation difference characteristics of the detection mark points in the corresponding pressurization process and depressurization process, and then determine the residual compensation value after complete depressurization based on the corresponding deformation difference characteristics.

[0037] The stress assessment module is used to assess the residual stress distribution level of the welded area of ​​the steel branch pipe based on the strain detection value under each pressure and the residual compensation value after complete depressurization.

[0038] The technical solutions provided by the embodiments disclosed in this application have the following beneficial effects:

[0039] Multiple optical detection markers are deployed on the shell surface of the steel branch pipe to be tested. Stress and strain information on all detection markers is acquired during progressive water pressure loading cycles. The stress correction coefficient on the detection markers during the pressure holding phase of each loading cycle is determined using all stress and strain information. Based on all stress correction coefficients and the stress distribution coordinates of the detection markers during the pressure holding phase, the spatial displacement of the detection markers under the corresponding pressure is determined. The strain detection value under each pressure is then determined based on the spatial displacement. The strain response relationship of all spatial displacements with water pressure changes is judged, and a stepwise comparison of all strain response relationships is performed to obtain the deformation difference characteristics of the detection markers during the corresponding pressurization and depressurization processes. The residual compensation value after complete depressurization is then determined based on the corresponding deformation difference characteristics. The residual stress distribution level of the welded area of ​​the steel branch pipe is evaluated based on the strain detection value under each pressure and the residual compensation value after complete depressurization.

[0040] Therefore, this application demonstrates that when the accuracy of residual stress detection in steel branch pipe welding based on water pressure loading is insufficient, it can improve the accuracy of the entire inspection process. Specifically, by deploying multiple optical detection markers on the surface of the steel branch pipe shell under inspection, and acquiring stress and strain information at all detection markers during progressive water pressure loading cycles, the spatial correlation and targeted nature of the stress and strain information can be ensured. By determining the stress correction coefficient using all stress and strain information, and combining it with the stress distribution coordinates to determine the spatial displacement, the strain detection value can be determined. Based on the material constitutive relationship and geometric deformation laws, accurate correction of the measured stress and accurate calculation of the spatial displacement can be achieved, overcoming the shortcomings of traditional inspection methods that lack stress correction mechanisms and have large displacement calculation deviations, thus ensuring the quantitative accuracy of the strain detection value. By judging the strain response relationship and performing a stepwise comparison to obtain deformation difference characteristics, and then determining the residual compensation value, different deformation characteristics such as elastic hysteresis and plastic accumulation can be accurately distinguished, solving the problems of traditional inspection methods that struggle to capture pressure increase and decrease deformation differences and lack reliable basis for residual compensation. By assessing the residual stress distribution level in the welded area of ​​the steel branch pipe, the accuracy and reliability of the assessment results can be improved by combining the quantification of the residual stress influence and the calibration of the level range, thus meeting the needs of steel branch pipe manufacturing quality acceptance and service safety assessment.

[0041] In summary, the technical solution adopted in this application can accurately detect the residual stress in the welded area of ​​the steel branch pipe under progressively increasing water pressure, thereby improving the accuracy of residual stress distribution level assessment. Attached Figure Description

[0042] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only for this embodiment of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0043] Figure 1 This is an exemplary flowchart of a method for detecting residual stress in steel branch pipe welding based on water pressure loading, provided in this application.

[0044] Figure 2 This is a flowchart illustrating the determination of spatial displacement provided in this application;

[0045] Figure 3 This is a flowchart illustrating the process for determining the residual compensation value provided in this application;

[0046] Figure 4 This is a module structure diagram of a steel branch pipe welding residual stress detection system based on water pressure loading, provided in this application. Detailed Implementation

[0047] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0048] This application provides a system and method for detecting residual stress in steel branch pipe welding based on water pressure loading. The core of this system involves deploying multiple optical detection markers on the shell surface of the steel branch pipe to be tested. Stress and strain information is acquired at all detection markers during a series of water pressure loading cycles. The stress correction coefficient for each detection marker during the pressure holding phase of each loading cycle is determined using all stress and strain information. Based on all stress correction coefficients and the stress distribution coordinates of the detection markers during the pressure holding phase, the spatial displacement of the detection markers under the corresponding pressure is determined. The strain detection value under each pressure is then determined from the spatial displacement. The strain response relationship of all spatial displacements with water pressure changes is judged, and a stepwise comparison of all strain response relationships is performed to obtain the deformation difference characteristics of the detection markers during the corresponding pressurization and depressurization processes. Based on the corresponding deformation difference characteristics, the residual compensation value after complete depressurization is determined. The residual stress distribution level of the welded area of ​​the steel branch pipe is evaluated based on the strain detection value under each pressure and the residual compensation value after complete depressurization.

[0049] Example 1: To better understand the above technical solution, the following will provide a detailed description of the technical solution in conjunction with the accompanying drawings and specific implementation methods. (Refer to...) Figure 1 As shown in the figure, this is an exemplary flowchart of a method for detecting residual stress in steel branch pipe welding based on water pressure loading according to this embodiment of the present application. The detection method includes the following steps:

[0050] In step S1, multiple optical detection markers are set on the shell surface of the steel branch pipe to be tested, and stress and strain information on all detection markers is obtained during the stepwise water pressure loading cycle.

[0051] In specific implementation, multiple optical detection markers can be deployed on the shell surface of the steel branch pipe to be inspected in the following way: Clean the welding area and the surrounding 50 mm range of the shell surface of the steel branch pipe to be inspected. First, wipe away oil, rust and dust with anhydrous ethanol. After the surface is completely dry, take a circular high-reflectivity aluminum foil with a diameter of 8 mm and a reflectivity of not less than 95% as the optical detection marker. Apply a 0.5 mm thick epoxy structural adhesive evenly to the back of the foil. Then, attach the aluminum foil to the center of the weld, 50 mm on each side of the weld, and the angle of the branch of the steel branch pipe. All markers are evenly distributed, and the straight-line distance between adjacent markers is 40 mm. After pasting, press with a clean pressure block for 5 minutes and let stand for 24 hours to allow the structural adhesive to fully cure. After curing, check each detection marker to ensure that there is no lifting, falling off or surface scratches. In other embodiments, other methods can also be used to set the optical detection markers, which are not limited here.

[0052] It should be noted that, in this application, the detection marker point refers to a highly reflective circular aluminum foil mark used to reflect optical measurement signals for identification, positioning, and calculation of spatial displacement.

[0053] In this embodiment, the stress and strain information of all detection markers during the progressive water pressure loading cycle can be obtained in the following way: an electro-hydraulic servo water pressure loading system can be used to perform progressive water pressure loading cycles on the steel branch pipe, while the VIC-3D digital image correlation measurement system is activated. This system and the water pressure loading system are synchronously triggered through a data connection line. Four 12-megapixel industrial cameras of the system are positioned 3 meters around the steel branch pipe to ensure that all optical detection markers are clearly imaged without obstruction. The sampling frequency is set to 15 Hz. Starting from 0 MPa at the beginning of the loading, image data of all detection markers are continuously collected throughout the entire process of pressurization, holding, and depressurization at each pressure level. Image information and corresponding real-time water pressure values ​​are recorded synchronously every 0.1 seconds to fully capture the dynamic change data of the markers at each pressure level, forming a dataset containing stress and strain information of all detection markers, thus obtaining the stress and strain information of all detection markers.

[0054] It should be noted that, in this application, stress-strain information refers to the original measurement data reflecting the deformation state of the shell at the detection marker point.

[0055] In step S2, the stress correction coefficient on the detection marker point in the holding stage of each loading cycle is determined by all stress and strain information. Based on all stress correction coefficients and the stress distribution coordinates of the detection marker point in the holding stage, the spatial displacement of the detection marker point under the corresponding pressure is determined. Then, the strain detection value under each pressure is determined by the spatial displacement under the corresponding pressure.

[0056] In this embodiment, the stress correction factor at the detection marker point during the holding phase of each loading cycle can be determined using the following steps based on all stress and strain information:

[0057] Extract the stress-strain characteristics of the detection markers during the holding phase of each loading cycle from all stress-strain information;

[0058] Based on the material constitutive relation, all stress-strain characteristics are synchronized to obtain the stress correction factor;

[0059] The stress correction factor is used to generate the stress correction coefficient at the detection marker point during each loading cycle holding pressure phase.

[0060] In practice, firstly, all data from the holding pressure phase of each loading cycle (the holding pressure phase being the period during which pressure is maintained) are selected from the stress-strain information. The selected data is processed using a moving average method, dividing 10 consecutive data sets into a window in chronological order. The arithmetic mean of stress and strain values ​​within each window is calculated, and outliers exceeding ±3 standard deviations of the average value of all windows are removed. Then, the peak stress, mean stress, peak strain, mean strain, and duration of stress-strain stability for each detection marker point during the holding pressure phase are extracted, forming the stress-strain characteristics at the detection marker points during the holding pressure phase of each loading cycle. Next, the elastic constitutive relation σ=Eε (σ is stress, E is the elastic modulus, and ε is strain) corresponding to the material of the steel branch pipe under test is obtained. The elastic modulus E is determined through a uniaxial tensile test on a standard specimen of the same material as the steel branch pipe (the experiment is performed according to the standard for tensile testing of metallic materials). The stress-strain characteristics of each detection marker point are substituted into the constitutive relation to calculate the theoretical stress characteristic value. The deviation rate between the measured stress characteristic value and the theoretical stress characteristic value at each marker point is calculated as follows: Deviation rate = (Measured value - Theoretical value) / Theoretical value. The arithmetic mean of all deviation rates is taken as the stress correction factor for this pressure holding stage. Finally, a correlation model between the stress correction coefficient and the stress correction factor is established: k = 1 + f (where k is the stress correction coefficient and f is the stress correction factor). This correlation model is verified through multiple sets of experimental calibrations using standard test blocks of the same material (the deviation between the measured stress and the true stress of the standard test blocks after correction is ≤3%). The stress correction factor is substituted into this correlation model to calculate the initial stress correction coefficient for each test marker point. Then, combined with the data from the same pressure holding stage in three repeated loading cycles, the arithmetic mean of the initial correction coefficients is calculated to obtain the stress correction coefficient at the test marker points in each loading cycle's pressure holding stage.

[0061] It should be noted that, in this application, stress-strain characteristics refer to the set of parameters of the stable stress-strain state at the test marker point during the pressure holding stage; the material constitutive relation is a mechanical model that describes the inherent correlation between stress and strain in a material; the stress correction factor refers to an intermediate parameter that coordinates the differences in stress-strain characteristics at different test marker points and establishes a correlation between the measured value and the true value; and the stress correction coefficient refers to a coefficient used to correct the measured stress value at the test marker point during the pressure holding stage.

[0062] Preferably, in this embodiment, the spatial displacement of the detection marker under the corresponding pressure is determined based on all stress correction factors and the stress distribution coordinates of the detection marker during the pressure holding stage, with reference to... Figure 2 As shown in the figure, this is a schematic flowchart of determining the spatial displacement in some embodiments of this application. In this embodiment, the spatial displacement can be determined by the following steps:

[0063] In step S21, based on all stress correction coefficients and the stress distribution coordinates of the detection markers during the pressure holding stage, a corrected stress distribution field is constructed under the pressure holding stage;

[0064] In step S22, the strain components of the detection marker points in each coordinate axis direction are determined based on the corrected stress distribution field and the material elastic modulus.

[0065] In step S23, the spatial offset characteristics under the corresponding pressure are determined based on all strain components and the initial spatial coordinates of the detection marker points;

[0066] In step S24, the spatial displacement of the detection marker point under the corresponding pressure is determined based on all spatial offset characteristics.

[0067] In practice, firstly, the stress correction coefficient and stress distribution coordinates during the pressure holding stage are obtained for each detection marker point. The measured stress value of each marker point is multiplied by the corresponding stress correction coefficient to obtain the corrected stress value. Using linear interpolation, with the three-dimensional coordinates of the detection marker points as nodes, the stress gaps between adjacent marker points are filled based on the corrected stress values. The interpolation operation is performed using the `griddata` function in MATLAB software, generating a three-dimensional stress distribution model based on the coordinate grid. This three-dimensional stress distribution model outputs the corrected stress distribution field during the pressure holding stage. This three-dimensional stress distribution model is based on stress-strain information and coordinate data measured by a laser tracker. Verification shows that the interpolated stress distribution conforms to the stress transmission law of shells in mechanics of materials, without any abrupt changes. Next, based on the corrected stress distribution field, the normal stress in the X, Y, and Z axes and the shear stress in each plane are extracted for each detection marker point. Strain components were calculated using Hooke's Law (an extension of the linear elastic constitutive relation). The normal strain components were derived using σ=Eε (σ is stress, E is the elastic modulus, and ε is strain). The X-axis normal strain component = X-axis corrected normal stress / elastic modulus; the Y and Z axes were calculated similarly. The shear strain components were derived using τ=Gγ (τ is shear stress, G is shear modulus, and γ is the shear strain component). The shear modulus G = E / (2(1+μ)), where μ is the Poisson's ratio of the steel branch pipe material, determined through a uniaxial tensile test on a standard specimen of the same material (μ was obtained by measuring the ratio of transverse to longitudinal strain in the experiment). Substituting the stress data in each direction into the formula yielded six strain components (three normal strains and three shear strains) for each marker point. Then, the initial spatial coordinates of each detection marker point (coordinates at 0 MPa measured by the laser tracker) were obtained, and each strain component was extracted. Based on the strain-displacement geometry, the offset corresponding to normal strain = normal strain component × initial characteristic length of the marker point along the coordinate axis (initial coordinate difference between adjacent marker points on the axis), and the offset corresponding to shear strain = shear strain component × initial characteristic length. The linear offset along the X, Y, and Z axes and the angular offset in each shear direction are calculated for each marker point. These offset data are then summarized to form a spatial offset feature set containing the numerical values ​​and directions of the offsets in each direction. This spatial offset feature set is used as the spatial offset feature under the corresponding pressure. Finally, the offsets in each direction are extracted from the spatial offset features of each detection marker point, and the total displacement can be calculated using a spatial vector synthesis method. The linear offsets along the X, Y, and Z axes are used as the three components of the vector, and the total displacement is calculated using the vector magnitude formula. The displacement direction is determined using the direction cosine formula, and the calculated result is used as the spatial displacement of the detection marker point under the corresponding pressure.

[0068] It should be noted that, in this application, stress distribution coordinates refer to the three-dimensional coordinates of the spatial position of the detection marker; the corrected stress distribution field refers to the global stress distribution model on the surface of the steel branch pipe shell; the material elastic modulus refers to the mechanical parameter that the material's ability to resist normal deformation in the linear elastic stage; strain components refer to the normal strain along the X, Y, and Z axes and the shear strain in each plane obtained by decomposing the three-dimensional strain according to the coordinate axes; initial spatial coordinates refer to the three-dimensional coordinates of the detection marker under an initial pressure of 0 MPa; spatial offset characteristics refer to the quantitative trend of displacement change of the detection marker along the X, Y, and Z axes and in each shear direction; and spatial displacement refers to the index that quantifies the deformation of the steel branch pipe shell.

[0069] In this embodiment, determining the strain detection value under each pressure based on the spatial displacement under the corresponding pressure can be achieved through the following steps:

[0070] The displacement vector difference between each detection marker point and its adjacent points is extracted from the spatial displacement under the corresponding pressure.

[0071] The initial strain tensor under each pressure is determined based on the initial relative coordinates of each displacement vector difference and the detection marker point.

[0072] All the initial strain tensors are aligned to obtain the strain readings for each pressure.

[0073] In practice, firstly, the spatial displacement of each detection marker point and its 3-4 directly adjacent detection marker points under the corresponding pressure is obtained. Each spatial displacement includes components in the X, Y, and Z axes. Using the displacement vector of the target detection marker point as a reference, the displacement vector of each adjacent point is subtracted from this reference vector to obtain the displacement vector difference between each detection marker point and its adjacent points. The three components of the displacement vector difference correspond to the displacement difference values ​​in the X, Y, and Z axes, respectively. Then, the initial relative coordinates between the detection marker point and each adjacent point (the distance between two points in the X, Y, and Z axes measured by the laser tracker at 0 MPa) are obtained and combined with the displacement vector difference. Based on the geometric calculation principle of the strain tensor, the normal strain component is obtained by dividing the magnitude of the displacement vector difference in the corresponding axis direction by the initial relative distance of that axis, and the shear strain component is obtained by dividing the magnitude of the displacement vector difference in the shear direction by the initial relative distance perpendicular to the shear plane. The normal strain of the target marker point in the X, Y, and Z axes and the shear strain in each plane are calculated sequentially to construct a 3x3 symmetric strain tensor, thus obtaining the preliminary strain tensor under each pressure. Finally, a rigid body transformation alignment method was adopted. Using the initial strain tensor at the intersection of the steel branch center points (fixed reference point) as the reference, the rotation matrix and translation vector of the initial strain tensor of each detection marker point relative to the reference were calculated. Matrix operations were then used to correct the coordinate system deviation of each tensor. Subsequently, all aligned initial strain tensors were statistically analyzed, and outlier tensors exceeding three times the standard deviation (considered as local measurement interference) were removed. The arithmetic mean of each component of the remaining effective tensors was taken to obtain the strain detection value of each detection marker point under the corresponding pressure.

[0074] It should be noted that in this application, displacement vector difference refers to the displacement difference between the detection marker point and its adjacent points in three-dimensional space; initial relative coordinates refer to the relative positions of the detection marker point and its adjacent points under an initial pressure of 0 MPa; preliminary strain tensor refers to the set of parameters that quantify the local three-dimensional deformation state of the detection marker point in the form of a 3x3 matrix; and strain detection value refers to the benchmark quantification result of the actual deformation state of the detection marker point.

[0075] In step S3, the strain response relationship of all spatial displacements with water pressure changes is determined, and all strain response relationships are compared in a stepwise manner to obtain the deformation difference characteristics of the detection markers in the corresponding pressurization and depressurization processes. Then, the residual compensation value after complete depressurization is determined based on the corresponding deformation difference characteristics.

[0076] In this embodiment, the strain response relationship of all spatial displacements as water pressure changes can be determined by the following steps:

[0077] Construct water pressure-displacement sequences for all spatial displacements as water pressure changes;

[0078] The water pressure-displacement sequence was filtered to obtain multiple strain response indices for displacement as water pressure changes.

[0079] By comparing all strain response indicators with preset strain response thresholds, the strain response relationships of all spatial displacements with changes in water pressure are obtained.

[0080] In practice, firstly, the spatial displacement (including X, Y, and Z axis components and total displacement) of all detection markers during the pressure holding stage at each pressure level is extracted, and the water pressure value of the corresponding pressure level is retrieved simultaneously. A data sequence is constructed separately for each detection marker, arranged in ascending order of water pressure from 0 MPa to 1.0 MPa. Each element in the sequence includes the water pressure value, total displacement, and triaxial displacement components, thus obtaining the water pressure-displacement sequence as the spatial displacement changes with water pressure. Then, linear regression analysis is used to fit the water pressure-displacement sequence of each detection marker. With the water pressure value on the x-axis and the total displacement on the y-axis, the linear correlation coefficient and the slope of the fitted line are calculated using Origin software. Simultaneously, the maximum displacement residual (the maximum difference between the measured value and the fitted value) is extracted, and these three parameters are used as strain response indicators for displacement changing with water pressure. Finally, the strain response threshold is calibrated through uniaxial tensile tests on standard specimens of the same material, determining the linear correlation coefficient threshold to be 0.99, the slope threshold to be within the theoretical slope range of the material's elastic stage, and the maximum residual threshold to be 0.02 mm. The three strain response indices of each detection marker are compared with the corresponding thresholds. If the correlation coefficient is ≥0.99 and the residual is ≤threshold, it is determined to be a linear strain response relationship; otherwise, it is determined to be a nonlinear strain response relationship.

[0081] It should be noted that, in this application, the water pressure-displacement sequence refers to an ordered set of data that integrates various pressure levels with their corresponding spatial displacements; the strain response index refers to a parameter that quantifies the variation law of the water pressure-displacement sequence; the strain response threshold refers to a standard parameter that is compared with the strain response index to distinguish different response characteristics; and the strain response relationship refers to the deformation response characteristics of spatial displacement with water pressure.

[0082] In this embodiment, the deformation difference characteristics of the detection marker points during the corresponding pressurization and depressurization processes can be obtained by performing a stepwise comparison of all strain response relationships using the following steps:

[0083] Determine the strain response data segments for the pressurization and depressurization processes;

[0084] All strain response data segments are embedded into all strain response relationships step by step to obtain the strain response deviation of the detection marker points in the corresponding pressurization and depressurization processes;

[0085] The deformation difference characteristics of the detection marker points during the corresponding pressurization and depressurization processes are determined based on the strain response deviation.

[0086] In practice, firstly, complete data for each loading cycle is extracted from the constructed water pressure-displacement sequences of all detection markers. The process is divided into stages based on the water pressure change trend: the pressurization process is the time interval from the current level's lower limit to the target holding pressure, and the depressurization process is the time interval from the target holding pressure to the current level's lower limit. Displacement and water pressure data for each pressure level are then filtered according to this division, generating pressurization and depressurization strain response data segments for each detection marker. Next, in ascending order of water pressure level, the pressurization and depressurization strain response data segments for each detection marker are progressively embedded into the corresponding overall strain response relationship (linear or nonlinear fitting model). At each water pressure level, the difference between the measured displacement value and the model-predicted displacement value in the data segment is calculated to obtain the pressurization response deviation and depressurization response deviation for that level. The deviation data for all pressure levels are summarized to form the strain response deviation of the detection marker during the corresponding pressurization and depressurization processes. Finally, the strain response deviation sequence for each detection marker is extracted, and the mean, maximum, and rate of change of the deviation with respect to the water pressure level are calculated. Based on the strain response relationship type of the detection marker, the deformation difference characteristics are determined: if the mean deviation is small and the rate of change is low, it is an elastic hysteresis type; if the deviation continues to increase with the increase of water pressure, it is a plastic accumulation type; if the deviation is irregular and fluctuates greatly, it is a stress concentration type. The determined strain response relationship type is used as the deformation difference characteristics of the detection marker in the corresponding pressurization and depressurization processes.

[0087] It should be noted that, in this application, the pressurization process refers to the stage in which the water pressure rises from the current lower limit to the target holding pressure; the depressurization process refers to the stage in which the water pressure drops from the target holding pressure to the current lower limit; the strain response data segment refers to the set of strain response data divided into the pressurization or depressurization stages; the strain response deviation refers to the parameter that quantifies the deviation between the measured pressurization / depressurization response and the overall response prediction value; and the deformation difference characteristics refer to the characteristics of inconsistency in deformation during the pressurization and depressurization processes.

[0088] Preferably, in this embodiment, the residual compensation value after complete depressurization is determined based on the corresponding deformation difference characteristics, with reference to... Figure 3 As shown in the figure, this is a schematic flowchart of determining the residual compensation value in some embodiments of this application. In this embodiment, the residual compensation value can be determined by the following steps:

[0089] In step S31, the residual strain data of different detection marker points are determined based on the corresponding deformation difference characteristics;

[0090] In step S32, the predicted stress value after complete decompression is determined based on all residual strain data;

[0091] In step S33, the predicted stress value is compensated and corrected to obtain the residual stress segment after complete decompression.

[0092] In step S34, the residual compensation value after complete depressurization is determined by the residual stress segment.

[0093] In practice, the process begins with three classifications based on deformation difference characteristics: for elastic hysteresis, the steady-state residual value of the strain response deviation between pressure increase and depressurization is used; for plastic accumulation, the residual ratio of the maximum deviation value is used; and for stress concentration, the deviation value is corrected using a finite element simulation model of the same material. The strain response deviation sequences of all detection markers are extracted and substituted into the calculation formula according to their corresponding types to obtain residual strain data. Next, the linear elastic constitutive relation formula σ=Eε is used for calculation, with the elastic modulus E taken from a uniaxial tensile test of a standard specimen of the same material as the steel branch pipe (value 200~210 GPa). The residual strain data of each detection marker is substituted into the formula, and a plastic correction coefficient is introduced for the plastic accumulation data. The calculation result is used as the predicted stress value after complete depressurization. Then, a multi-source data fusion correction method is used, combining the residual displacement data from the optical measurement system and the measured residual strain data from the strain gauges, to calculate the correction coefficient for the predicted stress value of each detection marker (correction coefficient = measured residual stress / predicted stress). The predicted stress value is corrected using the correction coefficient, and the corrected data is summarized in segments according to the welded area to form a residual stress segment after complete depressurization. Finally, statistical analysis is performed on each residual stress segment to calculate the mean and standard deviation of stress within the segment. A stress sensitivity coefficient for the welding area (which can be calibrated by engineering experiments and taken as 1.0~1.2) is introduced. The mean stress is multiplied by the sensitivity coefficient to obtain the residual compensation value after complete decompression.

[0094] It should be noted that, in this application, complete depressurization refers to the state in which the water pressure inside the steel branch pipe drops to 0 MPa and stabilizes after all loading cycles are completed; residual strain data refers to the quantitative parameters of residual deformation after complete depressurization of the detection marker point; stress prediction value refers to the residual stress value predicted based on the residual strain data after complete depressurization; residual stress segment refers to the set of local residual stress data after compensation and correction; residual compensation value refers to the data used to compensate for the influence of residual stress in the strain detection value.

[0095] In step S4, the residual stress distribution level of the welded area of ​​the steel branch pipe is evaluated based on the strain detection value under each pressure and the residual compensation value after complete depressurization.

[0096] In this embodiment, the residual stress distribution level of the welded area of ​​the steel branch pipe can be assessed based on the strain detection value under each pressure and the residual compensation value after complete depressurization using the following steps:

[0097] The residual stress influence of each detection marker point under each pressure is determined based on the strain detection value under each pressure.

[0098] The residual stress level range is determined by the residual compensation value after complete depressurization;

[0099] Based on the residual stress level range, all residual stress influence quantities are classified into levels to obtain the residual stress distribution level of the steel branch pipe welding area.

[0100] In practice, firstly, the linear elastic constitutive relation σ=Eε is adopted, and the elastic modulus E is taken from the uniaxial tensile test results of a standard test block of the same material as the steel branch pipe. The strain test values ​​of each test marker point under various pressures are substituted into the formula to calculate the initial stress influence at the corresponding pressure. A pressure level weighting coefficient is introduced (increasing sequentially from low to high pressure, with a calibrated weighting range of 0.8~1.2), and the initial stress influence is multiplied by the corresponding weighting coefficient to obtain the residual stress influence at each test marker point under various pressures. Then, the residual compensation values ​​of all test marker points are collected, and their arithmetic mean and standard deviation are calculated. Combining the steel branch pipe welding engineering acceptance standards, the interval threshold is calibrated through multiple sets of residual stress tests on standard test blocks of the same material: the upper limit of the excellent grade is the mean minus 1.5 times the standard deviation, the upper limit of the qualified grade is the mean plus 0.5 times the standard deviation, and exceeding the qualified upper limit is the unqualified grade, thus obtaining the residual stress level interval. Finally, the residual stress influence and residual stress level range of each detection marker point under various pressures are compared to determine the level (excellent, qualified, unqualified) of each influence quantity. The percentage of influence quantities corresponding to each level is statistically analyzed, with particular attention paid to the marker point levels at key locations such as the weld center and branch angles. If there are no unqualified levels at key locations and the percentage of excellent levels is ≥80%, it is classified as an excellent distribution level; if there are no unqualified levels at key locations and the percentage of qualified or above is ≥90%, it is classified as a qualified distribution level; otherwise, it is classified as an unqualified distribution level, which will not be elaborated further here.

[0101] It should be noted that, in this application, the residual stress influence refers to the degree of contribution of each strain test value under pressure to the residual stress; the residual stress level range refers to the benchmark range for classifying the degree of acceptance of residual stress; and the residual stress distribution level refers to the grading standard for the overall acceptance status of residual stress in the welded area of ​​the steel branch pipe.

[0102] Therefore, this application demonstrates that when the accuracy of residual stress detection in steel branch pipe welding based on water pressure loading is insufficient, it can improve the accuracy of the entire inspection process. Specifically, by deploying multiple optical detection markers on the surface of the steel branch pipe shell under inspection, and acquiring stress and strain information at all detection markers during progressive water pressure loading cycles, the spatial correlation and targeted nature of the stress and strain information can be ensured. By determining the stress correction coefficient using all stress and strain information, and combining it with the stress distribution coordinates to determine the spatial displacement, the strain detection value can be determined. Based on the material constitutive relationship and geometric deformation laws, accurate correction of the measured stress and accurate calculation of the spatial displacement can be achieved, overcoming the shortcomings of traditional inspection methods that lack stress correction mechanisms and have large displacement calculation deviations, thus ensuring the quantitative accuracy of the strain detection value. By judging the strain response relationship and performing a stepwise comparison to obtain deformation difference characteristics, and then determining the residual compensation value, different deformation characteristics such as elastic hysteresis and plastic accumulation can be accurately distinguished, solving the problems of traditional inspection methods that struggle to capture pressure increase and decrease deformation differences and lack reliable basis for residual compensation. By assessing the residual stress distribution level in the welded area of ​​the steel branch pipe, the accuracy and reliability of the assessment results can be improved by combining the quantification of the residual stress influence and the calibration of the level range, thus meeting the needs of steel branch pipe manufacturing quality acceptance and service safety assessment.

[0103] In summary, the technical solution adopted in this application can accurately detect the residual stress in the welded area of ​​the steel branch pipe under progressively increasing water pressure, thereby improving the accuracy of residual stress distribution level assessment.

[0104] Example 2: This application provides a residual stress detection system for welded steel branch pipes based on water pressure loading, referencing... Figure 4 As shown in the figure, this is a modular structure diagram of a steel branch pipe welding residual stress detection system based on water pressure loading according to this embodiment of the present application. The detection system includes:

[0105] The water pressure loading module 100 is used to set up multiple optical detection markers on the shell surface of the steel branch pipe to be tested, and to acquire stress and strain information on all detection markers during the step-by-step water pressure loading cycle.

[0106] The deformation detection module 200 is used to determine the stress correction coefficient on the detection marker point in the holding stage of each loading cycle through all stress and strain information, determine the spatial displacement of the detection marker point under the corresponding pressure based on all stress correction coefficients and the stress distribution coordinates of the detection marker point in the holding stage, and then determine the strain detection value under each pressure based on the spatial displacement under the corresponding pressure.

[0107] The difference judgment module 300 is used to judge the strain response relationship of all spatial displacements when the water pressure changes, perform a stepwise comparison of all strain response relationships, obtain the deformation difference characteristics of the detection mark point in the corresponding pressurization process and depressurization process, and then determine the residual compensation value after complete depressurization based on the corresponding deformation difference characteristics.

[0108] The stress assessment module 400 is used to assess the residual stress distribution level of the welded area of ​​the steel branch pipe based on the strain detection value under each pressure and the residual compensation value after complete depressurization.

[0109] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It should be understood that the technical content corresponding to each process in the flowchart, each functional block in the block diagram, and any combination of these processes and corresponding functional blocks can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to create a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the processes... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0110] Those skilled in the art will understand that all or part of the steps in the various methods of the above embodiments can be implemented by a program instructing related hardware. The program can be stored in a computer-readable storage medium, including read-only memory (ROM), random access memory (RAM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), one-time programmable read-only memory (OTPROM), electrically-Erasable Programmable Read-Only Memory (EEPROM), compactdisc read-only memory (CD-ROM) or other optical disc storage, disk storage, magnetic tape storage, or any other computer-readable medium capable of carrying or storing data.

[0111] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

Claims

1. A method for detecting residual stress in welded steel branch pipes based on water pressure loading, characterized in that, The detection method includes the following steps: Multiple optical detection markers are set on the shell surface of the steel branch pipe to be tested, and stress and strain information on all detection markers is obtained during the stepwise water pressure loading cycle. The stress correction factor on the detection marker point in the holding stage of each loading cycle is determined by all stress and strain information. Based on all stress correction factors and the stress distribution coordinates of the detection marker point in the holding stage, the spatial displacement of the detection marker point under the corresponding pressure is determined. Then, the strain detection value under each pressure is determined by the spatial displacement under the corresponding pressure. The strain response relationship of all spatial displacements with water pressure is determined, and all strain response relationships are compared in a stepwise manner to obtain the deformation difference characteristics of the detection markers in the corresponding pressurization and depressurization processes. Then, the residual compensation value after complete depressurization is determined based on the corresponding deformation difference characteristics. The residual stress distribution level of the welded area of ​​the steel branch pipe is evaluated based on the strain test value under each pressure and the residual compensation value after complete depressurization.

2. The method for detecting residual stress in steel branch pipe welding based on water pressure loading as described in claim 1, characterized in that, The aforementioned detection markers are highly reflective circular aluminum foil markers used to reflect optical measurement signals for identification, positioning, and calculation of spatial displacement.

3. The method for detecting residual stress in steel branch pipe welding based on water pressure loading as described in claim 1, characterized in that, The stress correction factor at the detection marker point during the holding phase of each loading cycle is determined using all stress and strain information. Specifically, this includes: Extract the stress-strain characteristics of the detection markers during the holding phase of each loading cycle from all stress-strain information; Based on the material constitutive relation, all stress-strain characteristics are synchronized to obtain the stress correction factor; The stress correction factor is used to generate the stress correction coefficient at the detection marker point during each loading cycle holding pressure phase.

4. The method for detecting residual stress in steel branch pipe welding based on water pressure loading as described in claim 1, characterized in that, The spatial displacement refers to an index that quantifies the deformation of the steel branch pipe shell.

5. The method for detecting residual stress in steel branch pipe welding based on water pressure loading as described in claim 1, characterized in that, The strain measurement value under each pressure is determined by the spatial displacement under the corresponding pressure, specifically including: The displacement vector difference between each detection marker point and its adjacent points is extracted from the spatial displacement under the corresponding pressure. The initial strain tensor under each pressure is determined based on the initial relative coordinates of each displacement vector difference and the detection marker point. All the initial strain tensors are aligned to obtain the strain readings for each pressure.

6. The method for detecting residual stress in steel branch pipe welding based on water pressure loading as described in claim 1, characterized in that, Determining the strain response relationship of all spatial displacements as a function of water pressure specifically includes: Construct water pressure-displacement sequences for all spatial displacements as water pressure changes; The water pressure-displacement sequence was filtered to obtain multiple strain response indices for displacement as water pressure changes. By comparing all strain response indicators with preset strain response thresholds, the strain response relationships of all spatial displacements with changes in water pressure are obtained.

7. The method for detecting residual stress in steel branch pipe welding based on water pressure loading as described in claim 1, characterized in that, A stepwise comparison of all strain-response relationships was performed to obtain the deformation differences of the detection markers during the corresponding pressurization and depressurization processes. Specifically, these differences included: Determine the strain response data segments for the pressurization and depressurization processes; All strain response data segments are embedded into all strain response relationships step by step to obtain the strain response deviation of the detection marker points in the corresponding pressurization and depressurization processes; The deformation difference characteristics of the detection marker points during the corresponding pressurization and depressurization processes are determined based on the strain response deviation.

8. The method for detecting residual stress in steel branch pipe welding based on water pressure loading as described in claim 1, characterized in that, The term "complete depressurization" refers to the state where the water pressure inside the steel branch pipe drops to 0 MPa and stabilizes after all loading cycles have been completed.

9. The method for detecting residual stress in steel branch pipe welding based on water pressure loading as described in claim 1, characterized in that, The residual stress distribution level of the welded area of ​​the steel branch pipe is evaluated based on the strain test values ​​under each pressure and the residual compensation values ​​after complete depressurization. Specifically, this includes: The residual stress influence of each detection marker point under each pressure is determined based on the strain detection value under each pressure. The residual stress level range is determined by the residual compensation value after complete depressurization; Based on the residual stress level range, all residual stress influence quantities are classified into levels to obtain the residual stress distribution level of the steel branch pipe welding area.

10. A system for detecting residual stress in steel branch pipe welding based on hydraulic loading, used to perform the method for detecting residual stress in steel branch pipe welding based on hydraulic loading as described in any one of claims 1 to 9, characterized in that, The detection system includes: The water pressure loading module is used to set up multiple optical detection markers on the shell surface of the steel branch pipe to be tested, and to acquire stress and strain information on all detection markers during the step-by-step water pressure loading cycle. The deformation detection module is used to determine the stress correction coefficient on the detection marker point in the holding stage of each loading cycle through all stress and strain information. Based on all stress correction coefficients and the stress distribution coordinates of the detection marker point in the holding stage, the spatial displacement of the detection marker point under the corresponding pressure is determined, and then the strain detection value under each pressure is determined by the spatial displacement under the corresponding pressure. The difference judgment module is used to judge the strain response relationship of all spatial displacements as water pressure changes, perform a stepwise comparison of all strain response relationships, obtain the deformation difference characteristics of the detection mark points in the corresponding pressurization process and depressurization process, and then determine the residual compensation value after complete depressurization based on the corresponding deformation difference characteristics. The stress assessment module is used to assess the residual stress distribution level of the welded area of ​​the steel branch pipe based on the strain detection value under each pressure and the residual compensation value after complete depressurization.

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