A steel bifurcated pipe welding residual stress detection system and method based on water pressure loading

Abstract

The application provides a steel bifurcated pipe welding residual stress detection system and method based on water pressure loading, relates to the technical field of residual stress detection, and obtains stress and strain information on all detection mark points; determines stress correction coefficients on the detection mark points in the pressure maintaining stage, determines the spatial displacement amount of the detection mark points under the corresponding pressure according to all stress correction coefficients and stress distribution coordinates, determines the strain detection value under each pressure according to the spatial displacement amount under the corresponding pressure; judges the strain response relationship when all the spatial displacement amounts change with the water pressure, determines the residual compensation value after complete pressure relief based on the corresponding deformation difference characteristics; and evaluates the residual stress distribution grade of the steel bifurcated pipe welding area according to the strain detection value under each pressure and the residual compensation value after complete pressure relief. The application can accurately detect the residual stress of the steel bifurcated pipe welding area under the step-by-step water pressure loading cycle, so as to improve the accuracy of the residual stress distribution grade evaluation.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of residual stress detection, and more particularly to a steel bifurcated pipe welding residual stress detection system and method based on water pressure loading. BACKGROUND

[0002] Residual stress detection is widely used in the manufacturing quality acceptance and service safety evaluation of welding components such as steel bifurcated pipes, pressure vessels and bridge steel structures. As a key pressure-bearing component of a water conservancy hub, the steel bifurcated pipe has a complex welding process, and residual stress is easily generated in the weld and heat-affected zone. The distribution state directly affects the fatigue resistance and crack resistance of the component, and has the characteristics of strong concealment, uneven distribution and high correlation with the geometric shape of the structure. The accuracy of the residual stress detection results directly determines the reliability of the structure safety evaluation and life prediction. Relying on residual stress detection to realize the quantitative characterization and distribution analysis of the stress in the welding area is the key foundation to ensure the manufacturing quality, service safety and long-term stable operation of the pressure-bearing components of water conservancy projects.

[0003] However, the existing steel bifurcated pipe welding residual stress detection based on water pressure loading does not arrange precise optical detection marker points, lacks stress correction mechanisms during the pressure maintaining stage, precise spatial displacement calculation methods, strain response relationship echelon comparison systems and scientific determination paths for residual compensation values, resulting in insufficient stress and strain information collection accuracy, large spatial displacement calculation deviation, limited accuracy of strain detection values, insufficient extraction of deformation difference characteristics, and lack of reliable basis for determining residual compensation values, so that the accuracy of the residual stress distribution grade evaluation results of the steel bifurcated pipe welding area is difficult to guarantee. Therefore, how to accurately detect the residual stress of the steel bifurcated pipe welding area under the condition of step-by-step water pressure loading cycles to improve the accuracy of the residual stress distribution grade evaluation is a problem faced by the industry. SUMMARY

[0004] The present application provides a steel bifurcated pipe welding residual stress detection system and method based on water pressure loading, which can accurately detect the residual stress of the steel bifurcated pipe welding area under the condition of step-by-step water pressure loading cycles to improve the accuracy of the residual stress distribution grade evaluation.

[0005] In a first aspect, the present application provides a steel bifurcated pipe welding residual stress detection method based on water pressure loading, which comprises the following steps:

[0006] A plurality of optical detection marker points are arranged on the surface of the shell of the steel bifurcated pipe to be detected, and stress and strain information on all detection marker points is obtained during step-by-step water pressure loading cycles;

[0007] The stress correction coefficients of the detection mark points in the pressure maintaining stage of each loading cycle are determined through all stress and strain information, the spatial displacement amounts of the detection mark points under corresponding pressures are determined according to all stress correction coefficients and stress distribution coordinates of the detection mark points in the pressure maintaining stage, and then the strain detection values under each pressure are determined from the spatial displacement amounts under the corresponding pressures;

[0008] The strain response relationships of all spatial displacement amounts when the spatial displacement amounts change with water pressure are determined, all strain response relationships are compared in echelon, the deformation difference characteristics of the detection mark points in corresponding pressure increasing processes and pressure releasing processes are obtained, and then the residual compensation values after complete pressure releasing are determined based on the corresponding deformation difference characteristics;

[0009] The residual stress distribution grades of the steel bifurcated pipe welding areas are evaluated according to the strain detection values under each pressure and the residual compensation values after complete pressure releasing.

[0010] In the embodiment, the detection mark point refers to a high-reflective circular aluminum foil mark used for reflecting optical measurement signals, for identifying and positioning and calculating spatial displacement.

[0011] In the embodiment, the stress correction coefficients of the detection mark points in the pressure maintaining stage of each loading cycle are determined through all stress and strain information specifically include:

[0012] Stress and strain characteristics of the detection mark points in the pressure maintaining stage of each loading cycle are extracted from all stress and strain information;

[0013] All stress and strain characteristics are synchronized based on a material constitutive relationship to obtain stress correction factors;

[0014] The stress correction coefficients of the detection mark points in the pressure maintaining stage of each loading cycle are generated from the stress correction factors.

[0015] In the embodiment, the spatial displacement amount refers to an index for quantifying deformation of a steel bifurcated pipe shell.

[0016] In the embodiment, the strain detection values under each pressure are determined from the spatial displacement amounts under the corresponding pressures specifically include:

[0017] Displacement vector differences between each detection mark point and its adjacent points are extracted from the spatial displacement amounts under the corresponding pressures;

[0018] Preliminary strain tensors under each pressure are determined according to the displacement vector differences and initial relative coordinates of the detection mark points;

[0019] All preliminary strain tensors are aligned to obtain the strain detection values under each pressure.

[0020] In the embodiment, the strain response relationships of all spatial displacement amounts when the spatial displacement amounts change with water pressure specifically include:

[0021] constructing a water pressure-displacement sequence of all spatial displacement amounts varying with water pressure;

[0022] screening the water pressure-displacement sequence to obtain a plurality of strain response indexes of displacement varying with water pressure;

[0023] comparing all strain response indexes with a preset strain response threshold to obtain a strain response relationship of all spatial displacement amounts varying with water pressure.

[0024] In this embodiment, the step-by-step comparison of all strain response relationships obtains the deformation difference features of the detection marker points in the corresponding pressure increasing process and pressure releasing process, which specifically include:

[0025] determining strain response data segments of the pressure increasing process and the pressure releasing process;

[0026] gradually embedding all strain response data segments into all strain response relationships to obtain strain response deviations of the detection marker points in the corresponding pressure increasing process and pressure releasing process;

[0027] determining the deformation difference features of the detection marker points in the corresponding pressure increasing process and pressure releasing process according to the strain response deviations.

[0028] In this embodiment, the complete pressure release refers to a state that the water pressure in the steel bifurcated pipe is reduced to 0 MPa and stabilized after all loading cycles.

[0029] In this embodiment, the residual stress distribution grade of the steel bifurcated pipe welding area is evaluated according to the strain detection value under each pressure and the residual compensation value after complete pressure release, which specifically includes:

[0030] determining the residual stress influence amount of each detection marker point under each pressure according to the strain detection value under each pressure;

[0031] determining a residual stress grade interval through the residual compensation value after complete pressure release;

[0032] grading all residual stress influence amounts according to the residual stress grade interval to obtain the residual stress distribution grade of the steel bifurcated pipe welding area.

[0033] In a second aspect, the present application provides a steel bifurcated pipe welding residual stress detection system based on water pressure loading, which is used to execute a steel bifurcated pipe welding residual stress detection method based on water pressure loading, and the detection system includes:

[0034] a water pressure loading module, configured to arrange a plurality of optical detection marker points on the surface of the shell of the steel bifurcated pipe to be detected, and acquire stress and strain information on all detection marker points in a step-by-step water pressure loading cycle;

[0035] a deformation detection module configured to determine stress correction coefficients of the detection marker points in a pressure maintaining stage of each loading cycle based on all the stress strain information, determine spatial displacement amounts of the detection marker points under corresponding pressures based on the stress correction coefficients and stress distribution coordinates of the detection marker points in the pressure maintaining stage, and further determine strain detection values under each pressure based on the spatial displacement amounts under the corresponding pressures;

[0036] a difference judgment module configured to judge strain response relationships of all the spatial displacement amounts with respect to water pressure changes, compare all the strain response relationships in echelon, obtain deformation difference characteristics of the detection marker points in corresponding pressure increasing processes and pressure releasing processes, and further determine residual compensation values after complete pressure release based on the corresponding deformation difference characteristics;

[0037] a stress evaluation module configured to evaluate residual stress distribution levels of the steel bifurcated pipe welding area according to the strain detection values under each pressure and the residual compensation values after complete pressure release.

[0038] The technical scheme provided by the embodiments disclosed in the application has the following beneficial effects:

[0039] A plurality of optical detection marker points are arranged on a shell surface of a steel bifurcated pipe to be detected, and stress strain information of all the detection marker points is obtained in a step-by-step water pressure loading cycle. Stress correction coefficients of the detection marker points in a pressure maintaining stage of each loading cycle are determined based on all the stress strain information, spatial displacement amounts of the detection marker points under corresponding pressures are determined based on the stress correction coefficients and stress distribution coordinates of the detection marker points in the pressure maintaining stage, and further strain detection values under each pressure are determined based on the spatial displacement amounts under the corresponding pressures. Strain response relationships of all the spatial displacement amounts with respect to water pressure changes are judged, all the strain response relationships are compared in echelon, deformation difference characteristics of the detection marker points in corresponding pressure increasing processes and pressure releasing processes are obtained, and further residual compensation values after complete pressure release are determined based on the corresponding deformation difference characteristics. Residual stress distribution levels of the steel bifurcated pipe welding area are evaluated according to the strain detection values under each pressure and the residual compensation values after complete pressure release.

[0040] It can be seen that in the present application, the accuracy of the detection process can be improved when the detection accuracy of the steel bifurcated pipe welding residual stress based on water pressure loading is insufficient. By arranging multiple optical detection markers on the surface of the steel bifurcated pipe shell to be detected, the spatial correlation of the stress and strain information and the pertinence of the collection process can be ensured when the water pressure is loaded in stages. By determining the stress correction coefficient based on all the stress and strain information, and determining the spatial displacement amount based on the stress distribution coordinates, the strain detection value can be determined. Relying on the material constitutive relation and the geometric deformation law, the measured stress can be accurately corrected and the spatial displacement amount can be accurately calculated, which can make up for the defects of the traditional detection lacking stress correction mechanism and large displacement calculation deviation, and ensure the quantitative accuracy of the strain detection value. By judging the strain response relationship, the deformation difference characteristics are obtained by hierarchical comparison, and then the residual compensation value is determined, which can accurately distinguish different deformation characteristics such as elastic hysteresis and plastic accumulation, and solve the problems that the traditional detection is difficult to capture the deformation difference of pressure increase and pressure decrease, and there is no reliable basis for residual compensation. By evaluating the residual stress distribution level of the steel bifurcated pipe welding area, the quantitative and level interval calibration of the residual stress influence can be combined to improve the accuracy and reliability of the evaluation results, and meet the needs of steel bifurcated pipe manufacturing quality acceptance and service safety evaluation.

[0041] In summary, the technical scheme adopted by the present application can accurately detect the residual stress of the steel bifurcated pipe welding area under the condition of step-by-step water pressure loading cycle, so as to improve the accuracy of the residual stress distribution level evaluation. BRIEF DESCRIPTION OF DRAWINGS

[0042] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiment or prior art description will be briefly introduced below. Obviously, the drawings in the following description are only the embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0043] Figure 1 is an exemplary flowchart of a steel bifurcated pipe welding residual stress detection method based on water pressure loading provided by the present application;

[0044] Figure 2 is a flowchart of determining the spatial displacement amount provided by the present application;

[0045] Figure 3 is a flowchart of determining the residual compensation value provided by the present application;

[0046] Figure 4 is a module structure diagram of a steel bifurcated pipe welding residual stress detection system based on water pressure loading provided by the present application. DETAILED DESCRIPTION

[0047] The technical solutions in the embodiments of the present application will be described clearly and completely in the following with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of the present application.

[0048] The embodiments of the present application provide a steel bifurcated pipe welding residual stress detection system and method based on water pressure loading. The core is to arrange multiple optical detection mark points on the surface of the shell of the steel bifurcated pipe to be detected, and to obtain stress and strain information on all detection mark points in a water pressure loading cycle.

[0049] Embodiment one, in order to better understand the above technical solutions, the above technical solutions will be described in detail in the following with reference to the drawings and specific embodiments of the specification. Referring to Figure 1 The figure is an exemplary flow chart of a steel bifurcated pipe welding residual stress detection method based on water pressure loading according to the embodiments of the present application. The detection method includes the following steps:

[0050] In step S1, multiple optical detection mark points are arranged on the surface of the shell of the steel bifurcated pipe to be detected, and stress and strain information on all detection mark points is obtained in a water pressure loading cycle.

[0051] In a specific implementation, the following method can be used to arrange multiple optical detection mark points on the surface of the shell of the steel bifurcated pipe to be detected: The welding area and a 50-mm range around the periphery of the surface of the shell of the steel bifurcated pipe to be detected are cleaned, and the oil stains, rust and dust are removed by wiping with anhydrous ethanol. After the surface is completely dried, a circular high-reflectivity aluminum foil sheet with a diameter of 8 mm and a reflectivity of not less than 95% is used as an optical detection mark point, and a 0.5-mm-thick epoxy structural adhesive is evenly applied to the back of the aluminum foil sheet. The aluminum foil sheet is sequentially attached to the center of the welding seam, the two sides of the welding seam each at a distance of 50 mm, and the branch angle of the steel bifurcated pipe. All the mark points are uniformly distributed, and the linear distance between adjacent mark points is 40 mm. After the attachment, a clean block is used to press for 5 minutes, and the structural adhesive is completely cured after 24 hours of standing. After curing, the detection mark points are checked one by one to ensure that there is no lifting, falling off or surface scratch. In other embodiments, other methods can be used to set the optical detection mark points, which are not limited herein.

[0052] It should be noted that in this application, the detection mark point refers to a high-reflectivity circular aluminum foil mark used for reflecting an optical measurement signal, for identifying and positioning and calculating a spatial displacement.

[0053] In this embodiment, the following method can be used to obtain the stress and strain information of all the detection mark points during the step-by-step water pressure loading cycle: An electro-hydraulic servo water pressure loading system can be used to perform a step-by-step water pressure loading cycle on the steel bifurcated pipe, and a VIC-3D digital image correlation method measurement system is started at the same time. The system and the water pressure loading system are synchronously triggered through data connection lines, the system is adjusted to be 3 meters away from the steel bifurcated pipe, 4 industrial cameras with a 12-million-pixel resolution are used to ensure that all the optical detection mark points are clearly imaged without obstruction, and the sampling frequency is set to 15 Hz. Starting from 0 MPa at the beginning of loading, the image data of all the detection mark points are continuously collected during the whole process of pressure increase, pressure maintenance and pressure release at each pressure level. The image information and the corresponding real-time water pressure value are synchronously recorded once every 0.1 second, the dynamic change data of the mark points at each pressure level are completely captured, and a data set containing the stress and strain information of all the detection mark points is formed, that is, the stress and strain information of all the detection mark points is obtained.

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

[0055] In step S2, the stress correction coefficients of the detection mark points in the pressure maintenance phase of each loading cycle are determined based on all the stress and strain information. The spatial displacement of the detection mark points at the corresponding pressure is determined based on all the stress correction coefficients and the stress distribution coordinates of the detection mark points in the pressure maintenance phase, and then the strain detection value at each pressure is determined based on the spatial displacement at the corresponding pressure.

[0056] In the embodiment, the stress correction factor on the detection mark point in the pressure maintaining stage of each loading cycle is determined by all stress and strain information, which can be achieved by the following steps:

[0057] Extracting stress and strain characteristics of the detection mark point in the pressure maintaining stage of each loading cycle from all stress and strain information;

[0058] Synchronizing all stress and strain characteristics based on the material constitutive relation to obtain a stress correction factor;

[0059] Generating the stress correction coefficient of the detection mark point in the pressure maintaining stage of each loading cycle from the stress correction factor.

[0060] In specific implementation, first, all data of the pressure maintaining stage in each loading cycle are screened from the stress and strain information (the pressure maintaining stage is a time period of stable pressure maintaining). The screened data are processed by using the moving average method, 10 groups of continuous data are divided into a window in time sequence, the arithmetic average of stress and strain values in each window is calculated, and abnormal data exceeding ±3 times of the standard deviation of all window average values are removed. Then, the stress peak value, stress average value, strain peak value, strain average value and stress and strain stable duration of each detection mark point in the pressure maintaining stage are extracted to form the stress and strain characteristics of the detection mark point in the pressure maintaining stage of each loading cycle. Then, the elastic constitutive relation σ=Eε (σ is stress, E is elastic modulus, and ε is strain) corresponding to the material of the steel bifurcated pipe to be detected is obtained, and the elastic modulus E is determined by the unidirectional tensile experiment of the standard test block of the same material as the steel bifurcated pipe (the experiment is performed according to the metal material tensile test standard). The stress and strain characteristics of each detection mark point are substituted into the constitutive relation to calculate the theoretical stress characteristic value. The deviation rate of the measured stress characteristic value of each mark point from the theoretical stress characteristic value is calculated, the deviation rate = (measured value-theoretical value) / theoretical value, and the arithmetic average of all deviation rates is taken as the stress correction factor of the pressure maintaining stage. Finally, an association model k=1+f (k is the stress correction coefficient, and f is the stress correction factor) is established, and the association model is verified by a plurality of experiments of the standard test block of the same material (the deviation between the measured stress of the standard test block after correction and the true stress is ≤3%). The stress correction factor is substituted into the association model to calculate the initial stress correction coefficient of each detection mark point. Then, the arithmetic average of the initial correction coefficients is calculated by combining the data of the same pressure maintaining stage of three repeated loading cycles to obtain the stress correction coefficient of the detection mark point in the pressure maintaining stage of each loading cycle.

[0061] It should be noted that in the present application, the stress-strain characteristics refer to a parameter set of the stress-strain stable state of the detection marker point in the pressure maintaining stage; the material constitutive relation refers to a mechanical model describing the stress-strain fixed correlation law of the material; the stress correction factor refers to an intermediate parameter for coordinating the differences in stress-strain characteristics of different detection marker points and establishing the correlation between the measured value and the true value; and the stress correction coefficient refers to a coefficient for correcting the measured stress value of the detection marker point in the pressure maintaining stage.

[0062] Preferably, in the present embodiment, the spatial displacement amount of the detection marker point under the corresponding pressure is determined according to all the stress correction coefficients and the stress distribution coordinates of the detection marker point in the pressure maintaining stage, and the spatial displacement amount is determined according to the stress correction coefficient and the stress distribution coordinates of the detection marker point in the pressure maintaining stage. Figure 2 As shown in the figure, the figure is a flowchart for determining the spatial displacement amount in some embodiments of the present application, and the spatial displacement amount in the present embodiment can be realized by the following steps:

[0063] In step S21, the corrected stress distribution field in the pressure maintaining stage is constructed based on all the stress correction coefficients and the stress distribution coordinates of the detection marker point in the pressure maintaining stage;

[0064] In step S22, the strain components of the detection marker point in the direction of each coordinate axis are determined according to the corrected stress distribution field and the elastic modulus of the material;

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

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

[0067] In a specific implementation, first, the stress correction coefficient of each detection marker point and the stress distribution coordinates in the pressure maintaining stage are obtained, the measured stress value of each marker point is multiplied by the corresponding stress correction coefficient to obtain the corrected stress value. The linear interpolation method is used, the three-dimensional coordinates of the detection marker points are taken as the nodes, the stress blank area between adjacent marker points is filled based on the corrected stress value, the interpolation operation is realized through the griddata function of MATLAB software, the three-dimensional stress distribution model is generated by dividing the coordinates grid, and the corrected stress distribution field in the pressure maintaining stage is output through the three-dimensional stress distribution model. The three-dimensional stress distribution model is based on stress and strain information and coordinate data measured by the laser tracker. It is verified that the interpolated stress distribution conforms to the shell stress transmission law in material mechanics and has no mutation or abnormality. Then, based on the corrected stress distribution field, the normal stress and the plane shear stress in the X, Y and Z axis directions of each detection marker point are extracted. The strain components are calculated using Hooke's law (linear elastic constitutive relation extension), the normal strain components are derived according to σ=Eε (σ is stress, E is elastic modulus, and ε is strain), the X-axis normal strain component is X-axis corrected normal stress / elastic modulus, and the Y and Z axes are the same; the shear strain component is derived according to τ=Gγ (τ is shear stress, G is shear modulus, and γ is shear strain component), the shear modulus G=E / (2(1+μ)), μ is the Poisson's ratio of the steel bifurcated pipe material, which is determined by the uniaxial tensile test of the standard test block of the same material (the ratio of transverse and longitudinal strain is measured in the experiment to obtain μ). The stress data in each direction are substituted into the formula to obtain six strain components (three normal strains and three shear strains) of each marker point. Then, the initial spatial coordinates (coordinates measured by the laser tracker at 0MPa) of each detection marker point are obtained, and the strain components are extracted. Based on the strain-displacement geometric relationship, the offset amount corresponding to the normal strain is equal to the normal strain component multiplied by the initial characteristic length of the marker point along the coordinate axis (the initial coordinate difference of adjacent marker points in the axis), and the offset amount corresponding to the shear strain is equal to the shear strain component multiplied by the initial characteristic length. The linear offset amount of each marker point along the X, Y and Z axes and the angular offset amount in each shear direction are calculated, and the offset data are collected to form a spatial offset feature set containing the directional offset value and the offset direction. The spatial offset feature set is taken as the spatial offset feature under the corresponding pressure. Finally, the directional offset amount in the spatial offset feature of each detection marker point is extracted, and the total displacement amount can be calculated by using the spatial vector synthesis method. The linear offset amount of the X, Y and Z axes is taken as the three components of the vector, the total displacement size is calculated according to the vector length formula, the displacement direction is determined by the direction cosine formula, and the calculated result is taken as the spatial displacement amount of the detection marker point under the corresponding pressure.

[0068] It should be noted that in the present application, the stress distribution coordinates refer to the three-dimensional coordinates of the spatial positions of the detection mark points; the corrected stress distribution field refers to the global stress distribution model of the steel bifurcated pipe shell surface; the material elastic modulus refers to the mechanical parameter of the material linear elastic stage resisting positive deformation; the strain component refers to the positive strain along the X, Y, Z axes and the shear strain in each plane obtained by decomposing the three-dimensional strain according to the coordinate axes; the initial spatial coordinates refer to the three-dimensional coordinates of the detection mark points under the initial pressure of 0 MPa; the spatial displacement characteristic refers to the displacement change trend of the detection mark points along the X, Y, Z axes and each shear direction; and the spatial displacement amount refers to an index for quantifying the deformation of the steel bifurcated pipe shell.

[0069] In the present embodiment, the determination of the strain detection value under each pressure by the spatial displacement amount under the corresponding pressure can be realized by the following steps:

[0070] extracting the displacement vector difference between each detection mark point and its adjacent point from the spatial displacement amount under the corresponding pressure;

[0071] determining the preliminary strain tensor under each pressure according to each displacement vector difference and the initial relative coordinates of the detection mark point;

[0072] aligning all the preliminary strain tensors to obtain the strain detection value under each pressure.

[0073] In a specific implementation, first, the spatial displacement of each detection marker point and 3-4 detection marker points directly adjacent thereto under a corresponding pressure is obtained, and each spatial displacement includes three directional components of X, Y and Z axes. Taking the displacement vector of the target detection marker point as a reference, the displacement vector of each adjacent point is subtracted from the reference vector to obtain the displacement vector difference between each detection marker point and the adjacent point, and the three components of the displacement vector difference correspond to the displacement difference values of X, Y and Z axes, respectively. Then, the initial relative coordinates (the distances between two points in X, Y and Z axes measured by the laser tracker under 0 MPa) of the detection marker point and each adjacent point are obtained, and the displacement vector difference is combined. According to the geometric calculation principle of the strain tensor, the normal strain component is obtained by dividing the module of the corresponding axial displacement vector difference by the initial relative distance of the axis, and the shear strain component is obtained by dividing the module of the shearing direction displacement vector difference by the initial relative distance perpendicular to the shearing plane, and the normal strain of the target marker point in X, Y and Z axes and the shear strain in each plane are sequentially calculated, a 3x3 symmetric strain tensor is constructed, and the preliminary strain tensor under each pressure is obtained. Finally, the rigid body transformation alignment method is adopted, the preliminary strain tensor of the center intersection point (fixed reference point) of the steel bifurcated pipe branch is taken as a reference reference, the rotation matrix and the translation vector of the preliminary strain tensor of each detection marker point relative to the reference reference are calculated, and the coordinate system deviation of each tensor is corrected through matrix operation. Subsequently, all the aligned preliminary strain tensors are counted, the abnormal tensors exceeding 3 times of the standard deviation (regarded as local measurement interference) are removed, and the arithmetic mean of each component of the remaining effective tensors is taken to obtain the strain detection value of each detection marker point under the corresponding pressure.

[0074] It should be noted that in the present application, the displacement vector difference refers to the displacement difference of the detection marker point and the adjacent point in the three-dimensional space, the initial relative coordinates refer to the relative position of the detection marker point and the adjacent point under the initial pressure of 0 MPa, the preliminary strain tensor refers to the parameter set quantifying the local three-dimensional deformation state of the detection marker point in the form of a 3x3 matrix, and the strain detection value refers to the benchmark quantization result of the real deformation state of the detection marker point.

[0075] In step S3, the strain response relationship of all the spatial displacement amounts when the water pressure changes is judged, all the strain response relationships are compared in echelon, the deformation difference characteristics of the detection marker point in the corresponding pressure increasing process and pressure releasing process are obtained, and then the residual compensation value after complete pressure release is determined based on the corresponding deformation difference characteristics.

[0076] In the present embodiment, the strain response relationship of all the spatial displacement amounts when the water pressure changes can be realized by the following steps:

[0077] A water pressure-displacement sequence of all the spatial displacement amounts when the water pressure changes is constructed.

[0078] The water pressure-displacement sequence is screened to obtain a plurality of strain response indexes of displacement varying with water pressure.

[0079] All strain response indicators are compared with the preset strain response threshold to obtain the strain response relationship of all spatial displacement amounts with water pressure changes.

[0080] In the specific implementation, first, the spatial displacement amounts (including X, Y, and Z axis components and total displacement amounts) of all detection marker points at each pressure level in the pressure maintaining stage are extracted, and the water pressure values corresponding to the pressure levels are synchronously called. In the order from 0 MPa to 1.0 P0, data sequences are individually constructed for each detection marker point, and each element in the sequence contains a water pressure value, a total displacement amount, and three-axis displacement components, that is, the water pressure-displacement sequence of the spatial displacement amount with the water pressure change is obtained. Then, the linear regression analysis method can be used to fit the water pressure-displacement sequence of each detection marker point, and the water pressure value is used as the horizontal coordinate and the total displacement amount is used as the vertical coordinate. The linear correlation coefficient and the fitting straight line slope of the sequence are calculated by Origin software. At the same time, the maximum displacement residual (the maximum difference between the measured value and the fitted value) of the sequence is extracted, and the three parameters are used as the strain response indicators of the displacement with the water pressure change. Finally, the strain response threshold is calibrated by the uniaxial tensile test of the standard test block of the same material, and the linear correlation coefficient threshold is 0.99, the slope threshold is the theoretical slope range of the material in the elastic stage, and the maximum residual threshold is 0.02 mm. The three strain response indicators of each detection marker point are compared with the corresponding threshold, and if the correlation coefficient is greater than or equal to 0.99 and the residual is less than or equal to the threshold, it is determined that the linear strain response relationship exists; otherwise, it is determined that the nonlinear strain response relationship exists.

[0081] It should be noted that in the present application, the water pressure-displacement sequence refers to an ordered data set integrating each pressure level and the corresponding spatial displacement amount; the strain response indicator refers to a parameter quantifying the change rule of the water pressure-displacement sequence; the strain response threshold refers to a standard parameter for comparing with the strain response indicator to distinguish different response characteristics; and the strain response relationship refers to the deformation response characteristics of the spatial displacement amount with the water pressure.

[0082] In the present embodiment, the deformation difference characteristics of the detection marker points in the corresponding pressure increasing process and pressure releasing process are obtained by performing step-by-step comparison on all strain response relationships.

[0083] Determine the strain response data segments of the pressure increasing process and the pressure releasing process;

[0084] Embed all strain response data segments into all strain response relationships step by step to obtain the strain response deviation of the detection marker points in the corresponding pressure increasing process and pressure releasing process;

[0085] According to the strain response deviation, the deformation difference characteristics of the detection marker points in the corresponding pressure increasing process and pressure releasing process are determined.

[0086] In a specific implementation, first, complete data of each loading cycle is extracted from all constructed detection marker point water pressure-displacement sequences, and phases are divided according to water pressure variation trends: the pressure increasing process is a time period in which water pressure increases from the lower limit of the current level to the target pressure maintaining pressure, and the pressure decreasing process is a time period in which water pressure decreases from the target pressure maintaining pressure to the lower limit of the current level. The displacement and water pressure data at each pressure level are screened according to the division, and the pressure increasing and pressure decreasing strain response data segments of each detection marker point are generated respectively. Then, the pressure increasing and pressure decreasing strain response data segments of each detection marker point are embedded into the overall strain response relationship (linear or nonlinear fitting model) corresponding to the marker point in order from low to high water pressure level. 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 pressure increasing response deviation and the pressure decreasing response deviation at the level. The deviation data of all pressure levels are summarized to form the strain response deviation of the detection marker point in the corresponding pressure increasing process and pressure decreasing process. Finally, the strain response deviation sequence of each detection marker point is extracted, and the mean value, maximum value and change rate with respect to the water pressure level of the deviation in the sequence are calculated. In combination with the strain response relationship type of the detection marker point, the deformation difference characteristics are determined: if the mean value of the deviation is small and the change rate is low, it is the elastic hysteresis type; if the deviation continuously increases with the increase of the water pressure, it is the plastic accumulation type; if the deviation is irregular and fluctuates greatly, it is the stress concentration type, and the determined strain response relationship type is taken as the deformation difference characteristic of the detection marker point in the corresponding pressure increasing process and pressure decreasing process.

[0087] It should be noted that, in the present application, the pressure increasing process refers to the stage in which the water pressure increases from the lower limit of the current level to the target pressure maintaining pressure; the pressure decreasing process refers to the stage in which the water pressure decreases from the target pressure maintaining pressure to the lower limit of the current level; the strain response data segment refers to the strain response data set divided from the pressure increasing or pressure decreasing stage; the strain response deviation refers to a parameter quantifying the deviation of the measured pressure increasing / decreasing response from the predicted value of the overall response; and the deformation difference characteristic refers to the characteristic of the inconsistency of deformation in the pressure increasing and pressure decreasing processes.

[0088] Preferably, in the present embodiment, the residual compensation value after complete pressure decreasing is determined based on the corresponding deformation difference characteristic, and the residual compensation value is determined according to the following formula: Figure 3 As shown in the figure, the figure is a flowchart for determining the residual compensation value in some embodiments of the present application, and the residual compensation value in the present embodiment can be realized by the following steps:

[0089] In step S31, residual strain data of different detection marker points is determined according to the corresponding deformation difference characteristic;

[0090] In step S32, a stress prediction value after complete pressure decreasing is determined according to all residual strain data;

[0091] In step S33, the stress prediction value is compensated and corrected to obtain a residual stress segment after complete pressure decreasing;

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

[0093] In a specific implementation, first, three types of classification of deformation difference characteristics are calculated: the steady-state residual value of the deviation of the strain response of the elastic hysteresis type to the pressure increase and pressure relief; the residual proportion of the maximum deviation value of the plastic accumulation type; and the stress concentration type is corrected by combining the deviation value with the finite element simulation model of the same material. The strain response deviation sequence of all detection markers is obtained by substituting the corresponding type into the calculation formula to obtain the residual strain data. Then, the elastic modulus E is calculated by using the linear elastic constitutive relation formula σ=Eε, and the value of the elastic modulus E is obtained from the uniaxial tensile test of the standard test block of the same material as the steel bifurcated pipe (the value is 200-210 GPa). The residual strain data of each detection marker is substituted into the formula, the plastic correction coefficient is introduced for the plastic accumulation type data, and the calculation result is taken as the stress prediction value after complete pressure relief. Then, the correction coefficient of the stress prediction value of each detection marker is calculated by using the multi-source data fusion correction method in combination with the residual displacement data of the optical measurement system and the measured residual strain data of the strain gauge (correction coefficient = measured residual stress / predicted stress). The stress prediction value is corrected by using the correction coefficient, and the corrected data is segmented and summarized according to the welding area to form the residual stress segment after complete pressure relief. Finally, statistical analysis is performed on each residual stress segment, the stress mean and standard deviation in the segment are calculated, the stress sensitivity coefficient of the welding area (which can be calibrated by engineering experiments and the value is 1.0-1.2) is introduced, and the stress mean is multiplied by the sensitivity coefficient to obtain the residual compensation value after complete pressure relief.

[0094] It should be noted that in the present application, complete pressure relief refers to the state that the internal water pressure of the steel bifurcated pipe is reduced to 0 MPa and stabilized after all loading cycles are completed; the residual strain data refers to the quantitative parameter of the residual deformation of the detection marker after complete pressure relief; the stress prediction value refers to the residual stress value predicted based on the residual strain data after complete pressure relief; the residual stress segment refers to the local residual stress data set after compensation and correction; and the residual compensation value refers to the data used to compensate the residual stress influence in the strain detection value.

[0095] In step S4, the residual stress distribution level of the welding area of the steel bifurcated pipe is evaluated according to the strain detection value under each pressure and the residual compensation value after complete pressure relief.

[0096] In the present embodiment, the residual stress distribution level of the welding area of the steel bifurcated pipe can be evaluated according to the strain detection value under each pressure and the residual compensation value after complete pressure relief by using the following steps:

[0097] The residual stress influence of each detection marker under each pressure is determined according to the strain detection value under each pressure;

[0098] The residual stress level interval is determined by the residual compensation value after complete pressure relief;

[0099] According to the residual stress level interval, the residual stress distribution level of the steel bifurcated pipe welding area is obtained.

[0100] In the implementation, first, the linear elastic constitutive relation σ=Eε is adopted, and the elastic modulus E is obtained from the unidirectional tensile test results of the standard test block of the same material as the steel bifurcated pipe. The strain detection value of each detection mark point under each pressure is substituted into the formula, and the initial stress influence quantity under the corresponding pressure is calculated. The pressure level weight coefficient (increasing from low to high, and the weight range can be calibrated to 0.8-1.2) is introduced, and the initial stress influence quantity is multiplied by the corresponding weight coefficient to obtain the residual stress influence quantity of each detection mark point under each pressure. Then, the residual compensation values of all detection mark points are collected, and the arithmetic mean and standard deviation are calculated. Combined with the steel bifurcated pipe welding engineering acceptance standard, the interval threshold is calibrated through multiple residual stress experiments of the standard test block of the same material: the upper limit of the excellent level is the mean value minus 1.5 times the standard deviation, the upper limit of the qualified level is the mean value plus 0.5 times the standard deviation, and the unqualified level is above the qualified upper limit, that is, the residual stress level interval is obtained. Finally, the residual stress influence quantity of each detection mark point under each pressure is compared with the residual stress level interval one by one, and the level (excellent, qualified, and unqualified) to which each influence quantity belongs is judged. The number of influence quantities corresponding to each level is counted, and the proportion of the influence quantity is also checked, and the mark points of the key positions such as the welding seam center and the branch angle are also checked. If the key positions have no unqualified level and the excellent level accounts for ≥80%, it is determined that the distribution level is excellent; if the key positions have no unqualified level and the qualified and above account for ≥90%, it is determined that the distribution level is qualified; otherwise, it is unqualified, which is not described here.

[0101] It should be noted that in the present application, the residual stress influence quantity refers to the contribution degree of the strain detection value under each pressure to the residual stress; the residual stress level interval refers to the reference range for dividing the qualified degree of the residual stress; and the residual stress distribution level refers to the classification standard of the overall distribution qualified state of the residual stress of the steel bifurcated pipe welding area.

[0102] It can be seen that in the present application, the accuracy of the detection process can be improved when the detection accuracy of the steel bifurcated pipe welding residual stress based on water pressure loading is insufficient. By arranging multiple optical detection markers on the surface of the steel bifurcated pipe shell to be detected, the spatial correlation of the stress and strain information and the pertinence of the collection process can be ensured when the stress and strain information on all detection markers is obtained during the step-by-step water pressure loading cycle. By determining the stress correction coefficient based on all stress and strain information, and determining the spatial displacement amount based on the stress distribution coordinates, the strain detection value can be determined. By relying on the material constitutive relationship and the geometric deformation law, the accuracy of the measured stress correction and the accurate calculation of the spatial displacement amount can be realized, which can compensate for the defects of the traditional detection lacking stress correction mechanism and large displacement calculation deviation, and ensure the quantitative accuracy of the strain detection value. By judging the strain response relationship, the deformation difference characteristics are obtained by hierarchical comparison, and then the residual compensation value is determined, which can accurately distinguish different deformation characteristics such as elastic hysteresis and plastic accumulation, and solve the problem that the traditional detection is difficult to capture the deformation difference of pressure increase and pressure decrease, and there is no reliable basis for residual compensation. By evaluating the residual stress distribution level of the steel bifurcated pipe welding area, the accuracy and reliability of the evaluation results can be improved by combining the residual stress influence quantity quantization and grade interval calibration, which meets the needs of steel bifurcated pipe manufacturing quality acceptance and service safety evaluation.

[0103] In summary, the technical scheme adopted by the present application can accurately detect the residual stress of the steel bifurcated pipe welding area under the step-by-step water pressure loading cycle, so as to improve the accuracy of the residual stress distribution level evaluation.

[0104] In embodiment two, the present application provides a steel bifurcated pipe welding residual stress detection system based on water pressure loading, as shown in Figure 4 The detection system includes:

[0105] The water pressure loading module 100 is used to arrange multiple optical detection markers on the surface of the shell of the steel bifurcated pipe to be detected, and obtain the 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 of the detection marker in each loading cycle by all stress and strain information, determine the spatial displacement amount of the detection marker under the corresponding pressure based on all stress correction coefficients and stress distribution coordinates of the detection marker in the pressure maintaining stage, and then determine the strain detection value under each pressure based on the spatial displacement amount under the corresponding pressure.

[0107] The difference judgment module 300 is configured to judge strain response relationships of all spatial displacement amounts with respect to water pressure changes, perform echelon comparison on all the strain response relationships, obtain deformation difference characteristics of the detection marker points in corresponding pressure increasing processes and pressure releasing processes, and then determine residual compensation values after complete pressure release based on the corresponding deformation difference characteristics.

[0108] The stress evaluation module 400 is configured to evaluate residual stress distribution levels of the steel bifurcated pipe welding area according to the strain detection values under each pressure and the residual compensation values after complete pressure release.

[0109] The present application is described with reference to flowcharts and / or block diagrams of the methods, devices (systems) and computer program products according to embodiments of the present application. It should be understood that each flow in the flowchart, each function block in the block diagram, and any combination of the contents corresponding to the flows and function blocks can be implemented by computer program instructions. The computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device produce a device that implements the functions specified in the flowchart Figure 1 The device that implements the functions specified in one flow or multiple flows and / or one block or multiple blocks. Figure 1 The device that implements the functions specified in one flow or multiple flows and / or one block or multiple blocks.

[0110] Those skilled in the art can understand that all or part of the steps in the above-mentioned embodiments can be completed by programs instructing related hardware, and the programs can be stored in a computer readable storage medium, including a read-only memory (ROM), a random access memory (RAM), a programmable read-only memory (PROM), an erasable programmable read-only memory (EPROM), a one-time programmable read-only memory (OTPROM), an electrically erasable programmable read-only memory (EEPROM), a compact disc read-only memory (CD-ROM) or other optical disk memories, magnetic disk memories, magnetic tape memories, or any other computer readable medium capable of carrying or storing data.

[0111] It is also to be noted that the terms "comprising", "including", and any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can also include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by "comprises a... " does not, without further restriction, exclude the existence of additional elements of the process, method, article, or apparatus that comprises the element.

Claims

1. A method for detecting welding residual stress of a steel bifurcated pipe based on water pressure loading, characterized in that, The detection method comprises the following steps: A plurality of optical detection mark points are arranged on the shell surface of the steel bifurcated pipe to be detected, and stress and strain information on all the detection mark points is acquired during the step-by-step water pressure loading cycle; Stress correction coefficients of the detection mark points in the pressure maintaining stage of each loading cycle are determined through all the stress and strain information, the spatial displacement of the detection mark points under the corresponding pressure is determined according to all the stress correction coefficients and the stress distribution coordinates of the detection mark points in the pressure maintaining stage, and then the strain detection value under each pressure is determined according to the spatial displacement under the corresponding pressure; The strain response relationship of all the spatial displacements with the change of water pressure is judged, the strain response relationships are compared in echelon, the deformation difference characteristics of the detection mark points in the corresponding pressure increasing process and pressure releasing process are obtained, and then the residual compensation value after complete pressure releasing is determined based on the corresponding deformation difference characteristics; The residual stress distribution level of the welding area of the steel bifurcated pipe is evaluated according to the strain detection value under each pressure and the residual compensation value after complete pressure releasing; The stress correction coefficients of the detection mark points in the pressure maintaining stage of each loading cycle are determined through all the stress and strain information, which specifically comprises: extracting stress and strain characteristics of the detection mark points in the pressure maintaining stage of each loading cycle from all the stress and strain information; synchronizing all the stress and strain characteristics based on the material constitutive relation to obtain a stress correction factor; and generating the stress correction coefficients of the detection mark points in the pressure maintaining stage of each loading cycle from the stress correction factor. The strain detection value under each pressure is determined according to the spatial displacement under the corresponding pressure, which specifically comprises: extracting the displacement vector difference between each detection mark point and its adjacent point from the spatial displacement under the corresponding pressure; determining the preliminary strain tensor under each pressure according to each displacement vector difference and the initial relative coordinates of the detection mark point; and aligning all the preliminary strain tensors to obtain the strain detection value under each pressure.

2. The method for detecting the welding residual stress of the steel bifurcated pipe based on the water pressure loading according to claim 1, characterized in that, The detection mark point refers to a high-reflective circular aluminum foil mark used for reflecting optical measurement signals, for identifying and positioning and calculating spatial displacement.

3. The method for detecting the welding residual stress of the steel bifurcated pipe based on the water pressure loading according to claim 1, characterized in that, The spatial displacement refers to an index for quantifying the deformation of the shell of the steel bifurcated pipe.

4. The method for detecting the welding residual stress of the steel bifurcated pipe based on the water pressure loading according to claim 1, characterized in that, The strain response relationship of all the spatial displacements with the change of water pressure specifically comprises: A water pressure-displacement sequence of all the spatial displacements with the change of water pressure is constructed; A plurality of strain response indexes of displacement with the change of water pressure are obtained by screening the water pressure-displacement sequence; All the strain response indexes are compared with a preset strain response threshold to obtain the strain response relationship of all the spatial displacements with the change of water pressure.

5. The method for detecting the welding residual stress of the steel bifurcated pipe based on the water pressure loading according to claim 1, characterized in that, The strain response relationship of all the spatial displacements with the change of water pressure specifically comprises: Strain response data segments of the pressure increasing process and the pressure releasing process are determined; All the strain response data segments are embedded in all the strain response relationships in stages to obtain the strain response deviation of the detection mark points in the corresponding pressure increasing process and pressure releasing process; The deformation difference characteristics of the detection mark points in the corresponding pressure increasing process and pressure releasing process are determined according to the strain response deviation.

6. The method for detecting the welding residual stress of the steel bifurcated pipe based on the water pressure loading according to claim 1, characterized in that, The complete pressure relief refers to a state that the water pressure in the steel bifurcated pipe is reduced to 0 MPa and is stable after all loading cycles are completed.

7. The method for detecting the welding residual stress of the steel bifurcated pipe based on the water pressure loading according to claim 1, characterized in that, The residual stress distribution grade of the steel bifurcated pipe welding area is evaluated according to the strain detection value under each pressure and the residual compensation value after complete pressure relief, and specifically includes: The residual stress influence amount of each detection mark point under each pressure is determined according to the strain detection value under each pressure; The residual stress grade interval is determined through the residual compensation value after complete pressure relief; The residual stress influence amount of all detection mark points is graded according to the residual stress grade interval, so as to obtain the residual stress distribution grade of the steel bifurcated pipe welding area.

8. A water pressure loading based steel bifurcated pipe welding residual stress detection system for performing a water pressure loading based steel bifurcated pipe welding residual stress detection method according to any one of claims 1 to 7, characterized by, The detection system includes: A water pressure loading module is configured to arrange a plurality of optical detection mark points on the surface of the shell of the steel bifurcated pipe to be detected, and to obtain stress and strain information on all detection mark points during a step-by-step water pressure loading cycle; A deformation detection module is configured to determine stress correction coefficients of the detection mark points in a pressure maintaining stage of each loading cycle through all stress and strain information, to determine spatial displacement amounts of the detection mark points under corresponding pressures according to all stress correction coefficients and stress distribution coordinates of the detection mark points in the pressure maintaining stage, and to further determine strain detection values under each pressure from the spatial displacement amounts under the corresponding pressures; A difference judgment module is configured to judge strain response relationships of all spatial displacement amounts when the spatial displacement amounts change with water pressure, to perform gradient comparison on all strain response relationships, to obtain deformation difference characteristics of the detection mark points in corresponding pressure increasing processes and pressure relief processes, and to further determine residual compensation values after complete pressure relief based on the corresponding deformation difference characteristics; A stress evaluation module is configured to evaluate the residual stress distribution grade of the steel bifurcated pipe welding area according to the strain detection value under each pressure and the residual compensation value after complete pressure relief.

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