A method for studying weak magnetic signal characteristics of ferromagnetic materials

Abstract

The application discloses a kind of weak magnetic signal characteristic research methods for ferromagnetic material, comprising: according to the magnetomechanics model in the step of establishing magnetomechanics model, the verification of magnetomechanics model is carried out by pipeline weld model, pipeline weld crack model and pipeline base material crack model in the step of initial pressure simulation calculation, then according to the magnetomechanics model after verification, the step of pressurization simulation calculation is carried out, the stress damage degree of magnetomechanics model of pipeline weld model, pipeline weld crack model and pipeline base material crack model is obtained, based on the step of pressurization simulation calculation, by gradient energy factor calculation step and introduction same rate growth rate step, the stress damage degree of pipeline weld model, pipeline weld crack model and pipeline base material crack model is realized quantitative reflection.This application establishes magnetomechanics model, and introduces gradient energy factor, better reflects the stress damage of pipeline weld model, pipeline weld crack model and pipeline base material crack model.

Description

Technical Field

[0001] This invention belongs to the field of weak magnetic signal detection technology for ferromagnetic materials, and particularly relates to a method for studying the characteristics of weak magnetic signals in ferromagnetic materials. Background Technology

[0002] With the development of modern industry, ferromagnetic materials play a significant role in daily life. Taking long-distance oil and gas pipelines as an example, pipeline transportation has become one of the main modes of international oil and gas transportation due to its low transportation costs and its resistance to the influence of the surrounding environment and temperature. The integrity of oil and gas pipelines is directly related to the safety of oil and gas energy transportation. Pipeline leaks not only cause economic losses but also serious environmental pollution and even casualties.

[0003] Therefore, the study of the weak magnetic signal characteristics of ferromagnetic materials is receiving increasing attention. Currently, research on the weak magnetic signal characteristics of ferromagnetic materials is still in the basic research stage. For example, the axial and radial peak values ​​of the weak magnetic signal, and the gradient and maximum values ​​of the characteristic parameters of the weak magnetic signal, are studied. However, due to the small order of magnitude of these characteristic values, the changes in the weak magnetic signal characteristics under the influence of internal pressure in the pipe are relatively small. If the crack size is small, it is impossible to accurately determine the changes in the weak magnetic signal characteristics.

[0004] Therefore, in order to address the above shortcomings, it is necessary to study a method for researching the weak magnetic signal characteristics of ferromagnetic materials. Summary of the Invention

[0005] The purpose of this invention is to provide a method for studying the characteristics of weak magnetic signals in ferromagnetic materials. Based on the magnetic model established by this invention and the introduced gradient energy factor, the stress damage of the pipeline weld model, the pipeline weld crack model, and the pipeline base material crack model is better reflected. This avoids the technical problem that the change amplitude of the weak magnetic signal characteristic parameters is small under the pressure inside the pipeline, making it impossible to accurately determine the change of weak magnetic signal characteristics.

[0006] This invention provides a method for studying the weak magnetic signal characteristics of ferromagnetic materials, comprising: firstly, in the initial pressure simulation calculation step, verifying the magnetic model using a pipe weld model, a pipe weld crack model, and a pipe base material crack model based on the established magnetic model; secondly, performing a pressure simulation calculation step based on the verified magnetic model to obtain the stress damage degree of the pipe weld model, pipe weld crack model, and pipe base material crack model; and thirdly, through the gradient energy factor calculation step and the introduction of a year-on-year growth rate step, quantitatively reflecting the stress damage degree of the pipe weld model, pipe weld crack model, and pipe base material crack model based on the pressure simulation calculation step.

[0007] Preferably, in the step of establishing the magnetomechanical model, based on the ferromagnetization theory, a force-magnetic coupling model is derived, and then, according to the relationship between magnetization intensity and relative permeability, the relationship between stress and relative permeability is obtained:

[0008]

[0009] In formula (1), α is the coupling parameter; H is the external magnetic field, μT; σ is the stress, MPa; E is Young's modulus, GPa; M is the magnetization, A / m; M s M is the saturation magnetization, A / m; an The hysteresis-free magnetization; H e The effective magnetic field is μ0; μ0 is the free permeability, N·A. -2 ξ is the energy per unit volume, Pa; α is the material planning constant, A / m; c is the reversibility coefficient; γ1, γ2 and A is a parameter related to the magnetostriction coefficient. -4 ·m 4 ·Pa -1 ;

[0010] Preferably, in the initial pressure simulation calculation step, the stress values ​​of the three models of the pipeline weld model, pipeline weld crack model and pipeline base material crack model are calculated using the stress simulation calculation model. The three stress values ​​of the three models are substituted into the formula (1) to obtain the corresponding three relative permeabilities. The three relative permeabilities are then substituted into the magnetic simulation calculation model to obtain the initial pressure distribution of the axial and radial weak magnetic signals of the pipeline weld model, pipeline weld crack model and pipeline base material crack model, so as to verify the magnetic model.

[0011] Preferably, in the pressure simulation calculation step, under the action of internal pressure in the pipeline, the magnetic model is used to simulate and calculate the pressure distribution of axial and radial weak magnetic signals of the pipeline weld model, pipeline weld crack model, and pipeline base material crack model, respectively. The initial pressure characteristic parameters and pressure characteristic parameters of the axial and radial weak magnetic signals of the pipeline weld model, pipeline weld crack model, and pipeline base material crack model are also simulated and calculated to reflect the stress damage degree of the pipeline weld model, pipeline weld crack model, and pipeline base material crack model.

[0012] Preferably, in the pressurization simulation calculation step, the initial pressure characteristic parameters of the axial and radial magnetic weakening signals are the axial peak value and radial peak value, magnetic field strength gradient and magnetic field strength gradient maximum value under the initial pressure condition, and the pressurization characteristic parameters of the axial and radial magnetic weakening signals are the axial peak value and radial peak value, magnetic field strength gradient and magnetic field strength gradient maximum value under the pressurization condition.

[0013] Preferably, in the gradient energy factor calculation step, in the Cartesian coordinate system, the gradient energy factor is the area enclosed by the magnetic field intensity gradient curve and the horizontal axis, and then the stress damage degree of the pipeline weld model, the pipeline weld crack model and the pipeline base material crack model is reflected according to the gradient energy factor.

[0014] Preferably, in the step of introducing the year-on-year growth rate, the year-on-year growth rate of the gradient energy factor is introduced and calculated in the gradient energy factor, and then the year-on-year growth rate of the gradient energy factor of the axial and radial weak magnetic signals of the pipeline weld model, the pipeline weld crack model and the pipeline base material crack model is quantitatively analyzed, so as to further quantitatively reflect the stress damage degree of the pipeline weld model, the pipeline weld crack model and the pipeline base material crack model.

[0015] The expression for the year-on-year growth rate is:

[0016]

[0017] In formula (2), ν is the year-on-year growth rate; A2 is the current period number, which is the gradient energy factor under maximum pressure when pressurized; A1 is the same period number, which is the gradient energy factor under minimum pressure when initially pressurized; ΔA is the increment, which refers to the increment of the gradient energy factor between the gradient energy factor under maximum pressure and the gradient energy factor under minimum pressure when initially pressurized.

[0018] Preferably, in the initial pressure simulation calculation step and the pressurization simulation calculation step, the pipe material of the pipe weld model is X70, the pipe length is set to 1000mm, the outer diameter is 1219mm, the thickness is 16mm, the weld width is 20mm, the welding line speed V is 1mm / s, the welding voltage U is 36V, the welding current I is 32A, the welding thermal efficiency η is 0.75, and the internal pressure applied to the pipe weld model is 0.5-3MPa with an interval of 0.5MPa.

[0019] Preferably, in the initial pressure simulation calculation step and the pressurization simulation calculation step, the pipe material of the weld crack model is X70, the pipe length is set to 1000mm, the outer diameter to 1219mm, the thickness to 16mm, the weld width to 20mm, and microcracks are created. The dimensions of the microcracks (length * width * depth) are 2mm * 0.95mm * 1mm. The welding line speed V is 1mm / s, the welding voltage U is 36V, the welding current I is 32A, and the welding thermal efficiency η is 0.75. The internal pressure applied to the weld crack model is 0.5-3MPa, with an interval of 0.5MPa.

[0020] Preferably, in the initial pressure simulation calculation step and the pressurization simulation calculation step, the pipe material of the pipe base material crack model is X70, the pipe length is set to 1000mm, the outer diameter is 1219mm, and the thickness is 16mm. Microcracks are created, and the length * width * depth of the microcracks is 2mm * 0.95mm * 1mm. The internal pressure applied to the pipe base material crack zone model is 0.5-3MPa, with an interval of 0.5MPa.

[0021] Compared to existing technologies, this invention obtains the gradient energy factor in the Cartesian coordinate system by utilizing the area enclosed by the magnetic field intensity gradient curve and the horizontal axis. Furthermore, it introduces a year-on-year growth rate into the gradient energy factor, facilitating quantitative analysis of the weak magnetic signal. This quantitatively reflects the degree of stress damage to the pipeline, effectively avoiding the technical problem that the small magnitude of traditional characteristic values ​​leads to small changes in the weak magnetic signal characteristics under pressure within the pipeline, making it impossible to accurately determine the changes in the characteristic parameters of the weak magnetic signal. Attached Figure Description

[0022] The above and other objects, features, and advantages of exemplary embodiments of the present invention will become readily apparent upon reading the following detailed description with reference to the accompanying drawings. In the drawings, several embodiments of the invention are illustrated by way of example and not limitation, with the same or corresponding reference numerals denoteing the same or corresponding parts, wherein:

[0023] Figure 1 This is a schematic diagram of the stress magnetic curve of the present invention;

[0024] Figure 2 This is a schematic diagram of the simulation results of the pipeline welding stress field according to the present invention;

[0025] Figure 3 This is a schematic diagram of the magnetic signals of the pipeline weld under different internal pressures as simulated in this invention.

[0026] Figure 4 This is a schematic diagram showing the variation of the axial peak value and radial peak value of the simulated pipeline weld magnetic signal with internal pressure according to the present invention.

[0027] Figure 5 This is a schematic diagram showing the change of magnetic field intensity gradient with internal pressure in the simulated weld magnetic signal of the present invention.

[0028] Figure 6 This is a schematic diagram showing the variation of the maximum magnetic field strength gradient of the simulated pipeline weld magnetic signal with internal pressure according to the present invention.

[0029] Figure 7 This is a schematic diagram illustrating the variation of the gradient energy factor of the simulated pipeline weld magnetic signal with internal pressure according to the present invention.

[0030] Figure 8This is a schematic diagram of the magnetic signals of the simulated pipe weld crack of the present invention;

[0031] Figure 9 This is a schematic diagram of the magnetic signals of pipe weld cracks under different internal pressures as simulated in this invention.

[0032] Figure 10 This is a schematic diagram showing the variation of the axial and radial peak values ​​of the simulated magnetic signal of pipe weld cracks with internal pressure according to the present invention.

[0033] Figure 11 This is a schematic diagram showing the change of magnetic field intensity gradient with internal pressure in the simulated weld crack magnetic signal of the present invention.

[0034] Figure 12 This is a schematic diagram showing the variation of the maximum magnetic field strength gradient of the simulated weld crack magnetic signal with internal pressure according to the present invention.

[0035] Figure 13 This is a schematic diagram illustrating the variation of the gradient energy factor of the simulated weld crack magnetic signal with internal pressure according to the present invention.

[0036] Figure 14 This is a schematic diagram of the magnetic signals of the simulated pipe base material crack in this invention;

[0037] Figure 15 This is a schematic diagram of the magnetic signals of the pipe base material crack under different internal pressures as described in this invention.

[0038] Figure 16 This is a schematic diagram showing the variation of the axial and radial peak values ​​of the simulated magnetic signal of pipe weld cracks with internal pressure according to the present invention.

[0039] Figure 17 This is a schematic diagram showing the change of magnetic field intensity gradient with internal pressure in the simulated weld crack magnetic signal of the present invention.

[0040] Figure 18 This is a schematic diagram showing the variation of the maximum magnetic field strength gradient of the simulated weld crack magnetic signal with internal pressure according to the present invention.

[0041] Figure 19 This is a schematic diagram illustrating the variation of the gradient energy factor of the simulated weld crack magnetic signal with internal pressure according to the present invention.

[0042] Figure 20 This is a schematic diagram of the magnetic signals of the pipe weld under different internal pressures in the experiment of this invention;

[0043] Figure 21 This is a schematic diagram showing the variation of the axial and radial peak values ​​of the magnetic signal of the experimental pipeline weld as a function of internal pressure.

[0044] Figure 22 This is a schematic diagram showing the change of magnetic field intensity gradient of the experimental weld magnetic signal as a function of internal pressure.

[0045] Figure 23 This is a schematic diagram showing the variation of the maximum magnetic field strength gradient of the experimental weld magnetic signal with internal pressure according to the present invention.

[0046] Figure 24 This is a schematic diagram showing the variation of the gradient energy factor of the experimental weld magnetic signal with internal pressure according to the present invention.

[0047] Figure 25 This is a schematic diagram of the magnetic signals of pipe weld cracks under different internal pressures in the present invention.

[0048] Figure 26 This is a schematic diagram showing the variation of the axial and radial peak values ​​of the magnetic signal of the experimental pipeline weld crack with internal pressure according to the present invention.

[0049] Figure 27 This is a schematic diagram showing the change of magnetic field intensity gradient with internal pressure in the experimental weld crack magnetic signal of the present invention.

[0050] Figure 28 This is a schematic diagram showing the variation of the maximum magnetic field intensity gradient of the experimental weld crack magnetic signal with internal pressure according to the present invention.

[0051] Figure 29 This is a schematic diagram illustrating the variation of the gradient energy factor of the magnetic signal of the experimental weld crack as a function of internal pressure.

[0052] Figure 30 This is a schematic diagram of the magnetic signals of cracks in the pipe base material under different internal pressures as described in this invention.

[0053] Figure 31 This is a schematic diagram showing the variation of axial and radial peak values ​​of the magnetic signal of the experimental pipe material crack in this invention with internal pressure.

[0054] Figure 32 This is a schematic diagram showing the change of magnetic field intensity gradient with internal pressure in the magnetic signal of the experimental parent material crack in this invention.

[0055] Figure 33 This is a schematic diagram showing the variation of the maximum magnetic field intensity gradient of the experimental parent material crack magnetic signal with internal pressure in this invention.

[0056] Figure 34 This is a schematic diagram showing the gradient energy factor of the magnetic signal of the experimental parent material crack as a function of internal pressure. Detailed Implementation

[0057] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Unless otherwise specified, the techniques used in the embodiments are conventional means well known to those skilled in the art.

[0058] It should be noted that, unless otherwise stated, the technical or scientific terms used in this invention should be understood in their ordinary sense by those skilled in the art. The terms "comprising," "including," or any other variations thereof are intended to cover a 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 a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0059] This embodiment provides a method for studying the weak magnetic signal characteristics of ferromagnetic materials. Based on the magnetic model established in the magnetic model establishment step, the magnetic model is first verified in the initial pressure simulation calculation step using a pipe weld model, a pipe weld crack model, and a pipe base material crack model. Then, based on the verified magnetic model, a pressure simulation calculation step is performed to obtain the stress damage degree of the pipe weld model, pipe weld crack model, and pipe base material crack model. Based on the pressure simulation calculation step, through the gradient energy factor calculation step and the introduction of the year-on-year growth rate step, the stress damage degree of the pipe weld model, pipe weld crack model, and pipe base material crack model is quantitatively reflected.

[0060] In the step of establishing the magnetic model, this embodiment, based on the ferromagnetism theory proposed by Jiles and Atherton, derives a force-magnetic coupling model, and obtains the following relationship between stress σ and magnetization M:

[0061]

[0062] Where α is the coupling parameter; H is the external magnetic field, μT; σ is the stress, MPa; E is Young's modulus, GPa; M is the magnetization, A / m; M s M is the saturation magnetization, A / m; an The hysteresis-free magnetization; H e The effective magnetic field is μ0; μ0 is the free permeability, N·A. -2ξ is the energy per unit volume, Pa; α is the material planning constant, A / m; c is the reversibility coefficient; γ1, γ2 and A is a parameter related to the magnetostriction coefficient. -4 ·m 4 ·Pa -1 ;

[0063] According to formula (1), the material parameters are taken as c = 0.25 and μ0 = 4π × 10 -7 NA -2 γ1=7×10 -18 A -2 ·m 2 , γ2=-3.3×10 -30 A -4 ·m 4 , Saturation magnetization Ms = 1.585 × 10 6 A / m, calculate the force-magnetic curve, such as Figure 1 As shown, there is a one-to-one correspondence between stress and magnetization, and the magnetization increases with increasing stress.

[0064] Based on magnetization M and relative permeability μ r Relationship:

[0065] M=(μ r -1)·H (2)

[0066] Substituting equation (2) into equation (1), we obtain the relationship between stress and relative permeability as follows:

[0067]

[0068] Where α is the coupling parameter; H is the external magnetic field, μT; σ is the stress, MPa; E is Young's modulus, GPa; M is the magnetization, A / m; M s M is the saturation magnetization, A / m; an The hysteresis-free magnetization; H e The effective magnetic field is μ0; μ0 is the free permeability, N·A. -2 ξ is the energy per unit volume, Pa; α is the material planning constant, A / m; c is the reversibility coefficient; γ1, γ2 and A is a parameter related to the magnetostriction coefficient. -4 ·m 4 ·Pa -1 ;

[0069] In one possible embodiment, in the gradient energy factor calculation step, the gradient energy factor is represented by , which is the area enclosed by the magnetic field intensity gradient curve and the horizontal axis of the curve in the Cartesian coordinate system, which more intuitively reflects the stress damage degree of the pipeline weld model, the pipeline weld crack model, and the pipeline base material crack model.

[0070] In one possible embodiment, in the step of introducing the year-on-year growth rate, the year-on-year growth rate of the gradient energy factor is introduced and calculated in the gradient energy factor, and then the year-on-year growth rate of the gradient energy factor of the axial and radial weak magnetic signals of the pipeline weld model, the pipeline weld crack model and the pipeline base material crack model is quantitatively analyzed, and the stress damage degree of the pipeline weld model, the pipeline weld crack model and the pipeline base material crack model is further quantitatively reflected.

[0071] The expression for introducing the year-on-year growth rate is as follows:

[0072]

[0073] In formula (4), ν is the year-on-year growth rate; A2 is the current period number, which is the gradient energy factor under maximum pressure when pressurized; A1 is the same period number, which is the gradient energy factor under minimum pressure when initially pressurized; ΔA is the increment, which refers to the increment of the gradient energy factor between the gradient energy factor under maximum pressure and the gradient energy factor under minimum pressure when initially pressurized.

[0074] In this embodiment, the software used for both the initial pressure simulation calculation step and the pressurization simulation calculation step is ANSYS software.

[0075] In this embodiment, the gradient energy factor is represented by S(K), the magnetic field strength gradient curve is represented by K, and the maximum value of the magnetic field strength gradient curve is represented by K. max The axial gradient is represented by K. x The radial gradient is represented by K. y The axial year-on-year growth rate is expressed in ν. x The radial year-on-year growth rate is expressed in ν. y express.

[0076] In one possible embodiment, the method further includes simulation calculation of the characteristic parameters of the weak magnetic signal of the pipe weld under the action of internal pipe pressure, and the specific steps are as follows:

[0077] The initial pressure simulation calculation steps, taking X70 pipeline steel in actual engineering applications as the research object, establish a magnetic model. The specific steps are as follows: A mechanical analysis model of the weld is established in a rectangular coordinate system (x, y, z). The pipeline material used in this paper is X70 pipeline steel, which is widely used in engineering. The pipeline length is set to 1000mm, the outer diameter to be 1219mm, the thickness to be 16mm, the weld width to be 20mm, the welding line speed V to be 1mm / s, the welding voltage U to be 36V, the welding current I to be 32A, and the welding thermal efficiency η to be 0.75. Figure 2 As shown, the stress distribution at the pipe weld is uneven, with stress concentration, and gradually weakens towards both sides.

[0078] In the pressure simulation calculation step, internal pressures of 0–3 MPa were applied to the pipeline, and simulations were performed every 0.5 MPa to obtain the changes in the weak magnetic signal at the weld, as shown below. Figure 3 As shown, the characteristic parameters of the weak magnetic signal will be analyzed below.

[0079] The variations in axial peak value and radial peak value are as follows: Figure 4 :from Figure 4 As can be seen, both the axial and radial peak values ​​increase linearly with increasing internal pressure. Furthermore, for every 0.5 MPa, the average change in axial peak value is 20, and the radial peak value... max The average change was 13.33.

[0080] Axial gradient K x and radial gradient K y like Figure 5 :from Figure 5 As can be seen from this, the axial gradient K x and radial gradient K y All of these gradually increase with increasing internal pressure.

[0081] Axial and radial K max like Figure 6 :from Figure 6 As can be seen from this, axial and radial K max Both increase linearly with increasing internal pressure. Furthermore, for every 0.5 MPa, the axial K... max The average change is 2.83, and the radial K... max The average change was 1.95.

[0082] The steps for calculating the gradient energy factor are as follows: the variation curves of the gradient energy factor S(K) for the axial magnetic signal and the gradient energy factor S(K) for the radial magnetic signal as a function of internal pressure are shown below. Figure 7 As can be seen from the figure, the gradient energy factor S(K) also gradually increases with the increase of internal pressure. Furthermore, for every 0.5 MPa, the average axial change of the gradient energy factor S(K) is 77.5, and the average radial change is 36.7.

[0083] Introducing the year-on-year growth rate step, the gradient energy factor S(K) axial year-on-year growth rate ν x The radial year-on-year growth rate of the gradient energy factor S(K) is 106.67%. y The radial year-on-year growth rate ν of the gradient energy factor S(K) is 109.43%. y Year-on-year growth rate ν of axial direction x The 3.24% increase indicates that the radial magnetic signal at the weld of ferromagnetic materials is more sensitive to stress changes. In comparison, the change in energy factor S(K) is greater than that of K and K0 in terms of both magnitude and average variation. max The changes are large and obvious, and can more intuitively reflect the changes in magnetic signals. Therefore, the gradient energy factor S(K) can be used as a new characteristic parameter of weak magnetic signal that comprehensively reflects the damage state at the weld.

[0084] In one possible embodiment, the simulation calculation of the characteristic values ​​of the weak magnetic signal of the pipe weld crack under internal pressure is also included, and the specific steps are as follows:

[0085] The initial pressure simulation calculation steps involve creating a crack on the above weld mechanical simulation model, with dimensions of 2mm * 0.95mm * 1mm (length * width * depth), and then performing magnetic simulation calculations. The results are as follows: Figure 8 As shown, the weak magnetic signal of the weld crack exhibits a maximum value in the axial direction and two sinusoidal fluctuations in the radial direction. By comparing the magnetic signal characteristics with the weld magnetic signal, the presence of a crack in the weld can be clearly identified.

[0086] The pressure simulation calculation steps involve applying internal pressures of 0–3 MPa to the pipeline, with simulations performed every 0.5 MPa. The influence of internal pressure on the weak magnetic field at the weld crack is analyzed, and the results of the weak magnetic field changes at the weld crack are as follows: Figure 9 Next, we will analyze the characteristic parameters of the weak magnetic signal.

[0087] The variations in axial peak value and radial peak value are as follows: Figure 10 :from Figure 10 As can be seen, both the axial peak value and the radial peak value increase linearly with increasing internal pressure. Furthermore, for every 0.5 MPa, the average change in axial peak value is 83.33, and the average change in radial peak value is 137.5.

[0088] Axial gradient K x and radial gradient K y like Figure 11 ,from Figure 11 As can be seen, both the axial and radial gradients K gradually increase with the increase of internal pressure.

[0089] Axial and radial K max like Figure 12 :from Figure 12 As can be seen from this, K max The axial K gradually increases with the increase of internal pressure in the pipeline. Furthermore, for every 0.5 MPa, the axial K... max The average change is 12.5, and the radial K... max The average change was 23.3.

[0090] The steps for calculating the gradient energy factor are as follows: the variation curves of the gradient energy factor S(K) for the axial magnetic signal and the gradient energy factor S(K) for the radial magnetic signal as a function of internal pressure are shown below. Figure 13 ,from Figure 13 As can be seen, both the axial and radial gradient energy factors S(K) gradually increase with the increase of internal pressure. Furthermore, for every 0.5 MPa, the average axial change in gradient energy factor S(K) is 125, and the average radial change is 340.

[0091] Introducing the year-on-year growth rate step, the variation curves of S(K) for the axial magnetic signal and the gradient energy factor S(K) for the radial magnetic signal as a function of internal pressure are as follows: Figure 11 : Gradient energy factor S(K) axial year-on-year growth rate ν x The radial year-on-year growth rate of the gradient energy factor S(K) was 59.57%; y The rate was 61.54%. The axial growth rate was 1.97% higher than the radial growth rate, indicating that the radial magnetic signal at the weld crack of ferromagnetic materials is more sensitive to stress changes.

[0092] The comparison revealed that the change in gradient energy factor S(K) was greater than that of K and K'. max The variation range is more significant, meaning that the gradient energy factor S(K) can replace the gradient to analyze the stress state at the weld.

[0093] In one possible embodiment, the simulation calculation of the characteristic values ​​of the weak magnetic signal of the crack in the pipeline base material under pressure is also included, and the specific steps are as follows:

[0094] The initial pressure simulation calculation steps involve creating a crack with dimensions of 2mm x 0.95mm x 1mm (length x width x depth) on the pipe base material (with parameters consistent with the weld base material). The weak magnetic simulation results are as follows: Figure 14 As shown, the axial weak magnetic signal at the crack in the pipe base material has a maximum value, and the radial signal has sinusoidal fluctuation characteristics, which are typical characteristics of stress concentration areas, confirming the feasibility of using the weak magnetic internal detection method to detect cracks in the pipe base material.

[0095] The pressure simulation calculation steps involve applying internal pressures of 0–3 MPa to the pipeline, with simulations performed every 0.5 MPa. The influence of internal pressure on the weak magnetic field at the weld crack is analyzed, and the results of the weak magnetic field changes at the weld crack are as follows: Figure 15 Next, we will analyze the characteristic parameters of the weak magnetic signal.

[0096] The variations in axial peak value and radial peak value are as follows: Figure 16 ,from Figure 16 As can be seen, both the axial peak value and the radial peak value increase linearly with increasing internal pressure. Furthermore, for every 0.5 MPa, the average change in axial peak value is 17.67, and the average change in radial peak value is 52.17.

[0097] Axial gradient K x and radial gradient K y like Figure 17 ,from Figure 17 As can be seen from this, the axial gradient K x and radial gradient K y All of these gradually increase with increasing internal pressure.

[0098] K max Axial and radial, such as Figure 18 ,from Figure 18 As can be seen from this, K max The axial and radial forces gradually increase with increasing internal pressure in the pipe. Furthermore, for every 0.5 MPa, K... max The average axial variation is 5.83, K max The radial mean variation is 3.5.

[0099] The steps for calculating the gradient energy factor are as follows: the variation curves of the gradient energy factor S(K) for the axial magnetic signal and the gradient energy factor S(K) for the radial magnetic signal as a function of internal pressure are shown below. Figure 19 :from Figure 19 As can be seen, both the axial and radial gradient energy factors S(K) increase linearly with the increase of internal pressure. Furthermore, for every 0.5 MPa, the average axial change in gradient energy factor S(K) is 6.5, and the average radial change is 10.33.

[0100] Introducing the year-on-year growth rate step, the gradient energy factor S(K) axial year-on-year growth rate ν x It is 64.15%; gradient energy factor S(K) radial ν y The year-on-year growth rate was 77.5%. The axial year-on-year growth rate was 13.35% higher than the radial year-on-year growth rate, indicating that the radial magnetic signal at the crack in the ferromagnetic material matrix is ​​more sensitive to stress changes. In terms of both order of magnitude and average change, the change in the gradient energy factor S(K) was greater than that of K and K0. max The changes will be significant, and the degree of change will be more pronounced.

[0101] The parameter analysis of the weld, weld crack, and base metal crack above shows that the proposed gradient energy factor S(K) has a better order of magnitude and average variation than K and K. maxTherefore, the gradient energy factor S(K) can be used as a new parameter to comprehensively reflect the stress damage state of the pipeline.

[0102] In one possible embodiment, the calculation of the characteristic value of the weak magnetic signal of the pipeline weld under internal pressure is further verified experimentally. The specific steps are as follows:

[0103] In this embodiment, the two ends of the pipe are first sealed, and a [missing information] is welded to each end of the pipe. The water tap has one end as the inlet and the other end as the outlet. During the experiment, a pressure pump is first used to inject water into the inlet, while a water pressure sensor is used to monitor the changes in water pressure in the pipe in real time to prevent pipe rupture and to prevent safety and leakage accidents.

[0104] The pressure simulation calculation steps involve applying internal pressures of 0.5–3 MPa to the pipeline during pressure testing, maintaining this pressure for 30 minutes for each 0.5 MPa increase. After the stress distribution stabilizes, the weak magnetic signal at the weld is measured. Figure 20 The trends of the axial and radial magnetic weakening signals are consistent with the simulation, verifying the correctness of the simulation results.

[0105] The variations in axial peak value and radial peak value are as follows: Figure 21 :from Figure 21 As can be seen, both the axial and radial peak values ​​increase linearly with increasing internal pressure. Axial gradient K x and radial gradient K y like Figure 22 ,from Figure 22 As can be seen from this, the axial gradient K x and radial gradient K y Both K and K increase with increasing internal pressure, verifying the correctness of the simulation results. max Axial and radial, such as Figure 23 It can be seen that as the internal pressure increases, K max The result is larger, consistent with the simulation results.

[0106] The steps for calculating the gradient energy factor are as follows: the variation curves of the gradient energy factor S(K) for the axial magnetic signal and the gradient energy factor S(K) for the radial magnetic signal as a function of internal pressure are shown below. Figure 24 The fitted curves show that the gradient energy factor S(K) increases with increasing internal pressure, which is consistent with the simulation results.

[0107] Introducing the year-on-year growth rate step, the gradient energy factor S(K) axial year-on-year growth rate ν x It is 26.39%; the radial year-on-year growth rate of the gradient energy factor S(K) is ν. y The rate was 30.77%. The radial growth rate was larger than the axial growth rate, indicating that the radial magnetic signal at the weld crack was more sensitive to stress changes, thus verifying the accuracy of the simulation results.

[0108] In terms of magnitude, the gradient energy factor S(K) is greater than K and K'. max The magnitude of the gradient energy factor S(K) is larger, and the degree of change is more obvious. The experimental results are consistent with the simulation results, verifying that the proposed gradient energy factor S(K) can more intuitively and comprehensively reflect the degree of damage at the pipeline weld.

[0109] In one possible embodiment, the calculation of the characteristic values ​​of the weak magnetic signal of the pipe weld crack under internal pressurization is also included in the experiment. The specific steps are as follows:

[0110] In this embodiment, both ends of the pipe are first sealed, and a φ50mm water nozzle is welded to each end, one end serving as the inlet and the other as the outlet. During the experiment, water is first injected into the inlet using a pressure pump, while a water pressure sensor monitors the changes in water pressure inside the pipe to prevent pipe rupture. Strain gauges are attached to the crack tip, and a stress-strain measurement device is used to detect the stress at the crack tip. Once the strain at the crack tip exceeds a preset threshold, an alarm is triggered, and the pressure pump stops injecting water into the pipe to reduce the internal pressure and ensure the safety of the measurement personnel.

[0111] The pressure simulation calculation steps involve applying internal pressures of 0.5–3 MPa to the pipeline during pressure testing, maintaining the pressure for 30 minutes for each 0.5 MPa increase. After the stress distribution stabilizes, the weak magnetic signal at the weld crack is measured. Figure 25 The trends of the axial and radial magnetic weakening signals are consistent with the simulation, verifying the correctness of the simulation results.

[0112] The variations in axial peak value and radial peak value are as follows: Figure 26 :from Figure 26 As can be seen, both the axial and radial peak values ​​increase linearly with increasing internal pressure. Axial gradient K x and radial gradient K y like Figure 27 ,from Figure 27 As can be seen from this, the axial gradient K x and radial gradient K y Both values ​​increase with increasing internal pressure, verifying the correctness of the simulation results.

[0113] K max Axial and radial, such as Figure 28 It can be seen that as the pressure inside the pipeline increases, K max The increase is consistent with the simulation results.

[0114] The simulation calculation steps under pressure, the variation curves of the gradient energy factor S(K) of the axial magnetic signal and the gradient energy factor S(K) of the radial magnetic signal with internal pressure are as follows: Figure 29 .from Figure 29 It can be seen that as the pressure inside the pipeline increases, the gradient energy factor S(K) value increases, which is consistent with the simulation calculation results.

[0115] Introducing the year-on-year growth rate step, the gradient energy factor S(K) axial year-on-year growth rate ν x It is 29.63%; the radial year-on-year growth rate of the gradient energy factor S(K) is ν. y The rate was 30.88%. The radial growth rate was larger than the axial growth rate, indicating that the radial magnetic signal at the weld crack was more sensitive to stress changes, thus verifying the accuracy of the simulation results.

[0116] In one possible embodiment, the calculation of the characteristic values ​​of the weak magnetic signal of the pipe base material crack under internal pressure is further verified experimentally. The specific steps are as follows:

[0117] In this embodiment, the two ends of the pipe are first sealed, and a [missing information] is welded to each end of the pipe. The water tap has one end as the inlet and the other as the outlet. During the experiment, a pressure pump is first used to inject water into the inlet, while a water pressure sensor monitors the water pressure changes within the pipe in real time to prevent pipe rupture and accidents. Strain gauges are attached to the crack tip, and a stress-strain measurement device is used to detect the stress at the crack tip. Once the strain at the crack tip exceeds a preset threshold, an alarm is triggered, and the pressure pump stops injecting water into the pipe to reduce the internal pressure and ensure the safety of the measurement personnel.

[0118] The pressure simulation calculation steps involve holding the pressure for 30 minutes for every 0.5 MPa increase during pipeline pressurization, until the stress distribution stabilizes. Then, the weak magnetic signal at the crack in the pipeline base material is measured. Figure 30 The trends of the axial and radial magnetic weakening signals are consistent with the simulation, verifying the correctness of the simulation results.

[0119] The variations in axial peak value and radial peak value are as follows: Figure 31 :from Figure 31 As can be seen, both the axial and radial peak values ​​increase linearly with increasing internal pressure. Axial gradient K x and radial gradient K y like Figure 32 ,from Figure 32 As can be seen from this, the axial gradient K x and radial gradient K y Both values ​​increase with increasing internal pressure, verifying the correctness of the simulation results.

[0120] Axial and radial K max like Figure 33 It can be seen that as the internal pressure increases, K max The result is larger, consistent with the simulation results.

[0121] The steps for calculating the gradient energy factor, and the variation curves of S(K) for the axial weak magnetic signal and the gradient energy factor S(K) for the radial magnetic signal with internal pressure are as follows: Figure 34 It can be seen that as the pressure inside the pipe increases, the gradient energy factor S(K) increases, which is consistent with the simulation results. Furthermore, in terms of magnitude, the gradient energy factor S(K) is significantly larger than K and K0. max The magnitudes are all large, and the degree of change will be more obvious. The experimental results are consistent with the simulation results.

[0122] Introducing the year-on-year growth rate step, the gradient energy factor S(K) axial year-on-year growth rate ν x The radial year-on-year growth rate of the gradient energy factor S(K) was 18.09%; y The rate is 50%. The radial growth rate is larger than the axial growth rate, indicating that the radial magnetic signal at the base metal crack is more sensitive to stress changes, thus verifying the accuracy of the simulation results. Through the parameter analysis of the weld, weld crack, and base metal crack, it can be seen that the proposed gradient energy factor S(K) has a larger order of magnitude and average variation than K and K0. max Since the gradient energy factor S(K) is large, it can be used as a new parameter to comprehensively reflect the stress damage state.

[0123] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for studying the weak magnetic signal characteristics of ferromagnetic materials, characterized in that: Based on the magnetic model established in the magnetic model establishment step, the magnetic model is first verified in the initial pressure simulation calculation step using the pipe weld model, pipe weld crack model, and pipe base material crack model. Then, based on the verified magnetic model, the pressure simulation calculation step is performed to obtain the stress damage degree of the pipe weld model, the pipe weld crack model, and the pipe base material crack model. Based on the pressure simulation calculation step, through the gradient energy factor calculation step and the introduction of the year-on-year growth rate step, the stress damage degree of the pipe weld model, the pipe weld crack model, and the pipe base material crack model is quantitatively reflected. In the step of establishing the magnetic model, based on the ferromagnetization theory, a force-magnetic coupling model is derived. Then, according to the relationship between magnetization intensity and relative permeability, the relationship between stress and relative permeability is obtained: （1） In formula (1), α is the coupling parameter; H is the external magnetic field; σ is the stress; E is Young's modulus; M is the magnetization; M s M is the saturation magnetization. an The hysteresis-free magnetization; H e ξ is the effective magnetic field; µ0 is the free magnetic permeability; ξ is the energy per unit volume factor; α is the material planning constant; c is the reversibility coefficient. These are parameters related to the magnetostriction coefficient; In the initial pressure simulation calculation step, the stress values ​​of the three models—the pipe weld model, the pipe weld crack model, and the pipe base material crack model—are calculated using the stress simulation calculation model. The three stress values ​​of the three models are substituted into the formula (1) to obtain the corresponding three relative permeabilities. The three relative permeabilities are then substituted into the magnetic simulation calculation model to obtain the initial pressure distribution of the axial and radial weak magnetic signals of the pipe weld model, the pipe weld crack model, and the crack region of the pipe base material, so as to verify the magnetic model. In the pressurization simulation calculation step, under the action of internal pressure in the pipeline, the magnetic model is used to simulate and calculate the pressurization distribution of axial and radial weak magnetic signals of the pipeline weld model, the pipeline weld crack model, and the pipeline base material crack model, respectively. The initial pressure characteristic parameters and pressurization characteristic parameters of the axial and radial weak magnetic signals of the pipeline weld model, the pipeline weld crack model, and the pipeline base material crack model are also simulated and calculated to reflect the stress damage degree of the pipeline weld model, the pipeline weld crack model, and the pipeline base material crack model. In the pressurization simulation calculation step, the initial pressure characteristic parameters of the axial and radial magnetic weakening signals are the axial peak value and radial peak value, magnetic field strength gradient and magnetic field strength gradient maximum value under the initial pressure condition, and the pressurization characteristic parameters of the axial and radial magnetic weakening signals are the axial peak value and radial peak value, magnetic field strength gradient and magnetic field strength gradient maximum value under the pressurization condition. In the gradient energy factor calculation step, in the Cartesian coordinate system, the gradient energy factor is the area enclosed by the magnetic field intensity gradient curve and the horizontal axis. Therefore, the gradient energy factor reflects the stress damage degree of the pipeline weld model, the pipeline weld crack model, and the pipeline base material crack model. In the step of introducing the year-on-year growth rate, the year-on-year growth rate is introduced into the gradient energy factor, the year-on-year growth rate of the gradient energy factor is calculated, and then the year-on-year growth rate of the gradient energy factor of the axial and radial weak magnetic signals of the pipeline weld model, the pipeline weld crack model and the pipeline base material crack model is quantitatively analyzed, further quantitatively reflecting the stress damage degree of the pipeline weld model, the pipeline weld crack model and the pipeline base material crack model. The expression for the year-on-year growth rate is as follows: （2） In formula (2), ν is the year-on-year growth rate; A2 is the current period number, which is the gradient energy factor under maximum pressure when pressurized; A1 is the same period number, which is the gradient energy factor under minimum pressure when initially pressurized; ΔA is the increment, which refers to the increment of the gradient energy factor between the gradient energy factor under maximum pressure and the gradient energy factor under minimum pressure when initially pressurized.

2. The method for studying the weak magnetic signal characteristics of ferromagnetic materials according to claim 1, characterized in that, In the initial pressure simulation calculation step and the pressurization simulation calculation step, the pipe material of the pipe weld model is X70, the pipe length is set to 1000 mm, the outer diameter to 1219 mm, the thickness to 16 mm, the weld width to 20 mm, the welding line speed to 1 mm / s, the welding voltage to 36 V, the welding current to 32 A, the welding thermal efficiency to 0.75, and the internal pressure applied to the pipe weld model to 0.5-3 MPa, with an interval of 0.5 MPa.

3. The method for studying the weak magnetic signal characteristics of ferromagnetic materials according to claim 1, characterized in that, In the initial pressure simulation calculation step and the pressurization simulation calculation step, the pipe material of the pipe weld crack model is X70, the pipe length is set to 1000 mm, the outer diameter is 1219 mm, the thickness is 16 mm, the weld width is 20 mm, a microcrack is created, the length*width*depth dimensions of the microcrack are 2mm*0.95mm*1mm, the welding line speed is 1mm / s, the welding voltage is 36V, the welding current is 32A, the welding thermal efficiency is 0.75, and the internal pressure applied to the pipe weld crack model is 0.5-3MPa, with an interval of 0.5MPa.

4. The method for studying the weak magnetic signal characteristics of ferromagnetic materials according to claim 1, characterized in that, In the initial pressure simulation calculation step and the pressurization simulation calculation step, the pipe material of the pipe base material crack model is X70, the pipe length is set to 1000 mm, the outer diameter is 1219 mm, and the thickness is 16 mm. Microcracks are created, and the dimensions of the microcracks are 2 mm * 0.95 mm * 1 mm (length * width * depth). The internal pressure applied to the pipe base material crack model is 0.5-3 MPa, with an interval of 0.5 MPa.

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