Method for detecting cracks in carbon steel in any direction based on magnetic resistance disturbance

Abstract

The invention belongs to the technical field of nondestructive defect detection, and particularly relates to a method for detecting cracks in any direction in carbon steel based on magnetic resistance disturbance. The crack detection method comprises the following steps: applying a static magnetic field to magnetically conduct a carbon steel structure to a high-sensitivity stage; and then exciting an alternating-current magnetic field in an excitation range defined on the surface of the carbon steel structure to be detected, and counting the change condition of the magnetic conductivity of the carbon steel structure, so that effective identification and detection of internal cracks in any direction are realized. The crack detection method comprises the following steps of: magnetizing a carbon steel structure to be detected to the left side of a peak value of a magnetic conductivity curve by using a static magnetic field B0; defining an excitation range on the surface of the carbon steel structure to be detected, and exciting an alternating current magnetic field B1 in the excitation range; collecting an alternating current magnetic field B1 and a secondary alternating current magnetic field B2 in the excitation range, and converting to obtain a signal Bx; obtaining an alternating current component JBx and a direct current component ZBx; and moving the alternating-current magnetic field B1 in the excitation range, and counting the change trend of the alternating-current component JBx.

Description

Technical Field

[0001] The present invention belongs to the technical field of non-destructive defect detection, and in particular relates to a method for detecting cracks in arbitrary directions inside carbon steel based on magnetoresistance disturbance. Background Art

[0002] Due to their high strength and hardness, carbon steel structures are widely used in industrial facilities and social infrastructure construction. However, during field use, carbon steel structures are susceptible to internal or surface cracks due to complex factors such as alternating loads, environmental and media corrosion. Once these cracks propagate and lead to structural failure, they are bound to cause safety accidents and, in severe cases, threaten people's production safety and property.

[0003] Further research revealed that among the existing non-destructive testing technologies for carbon steel structures, the detection technology for surface cracks is relatively mature, while the detection of internal cracks in carbon steel structures still faces many challenges; especially for the detection of cracks distributed in any direction inside carbon steel, the detection difficulty is even more prominent.

[0004] It should be pointed out that, due to the complexity of the geometric characteristics of the crack itself and its magnetic response behavior, for example, when the crack opening is narrow or the crack direction is consistent with the direction of the excitation magnetic field, the leakage magnetic signal generated is often extremely weak and even difficult to be effectively identified and captured. In addition, since carbon steel structural cracks may be distributed at any depth and position inside the material and have uncertain directionality, the existing detection method based on single-direction excitation is difficult to fully stimulate the abnormal magnetic response of the crack, which can easily lead to missed detection or misjudgment. Therefore, how to achieve high-sensitivity and high-reliability detection of cracks in any direction inside carbon steel has become a technical problem that needs to be solved urgently by those skilled in the art. Summary of the Invention

[0005] The present invention provides a method for detecting cracks in arbitrary directions inside carbon steel based on magnetic reluctance disturbance. The crack detection method applies a static magnetic field to magnetically conduct the carbon steel structure to a high-sensitivity stage; then an AC magnetic field is excited within an excitation range defined on the surface of the carbon steel structure to be inspected, and the change in the magnetic permeability of the carbon steel structure is statistically analyzed; based on the magnetic reluctance disturbance on the carbon steel surface, effective identification and detection of internal cracks in arbitrary directions is achieved, which significantly improves the detection efficiency while greatly reducing the risk of missed detection.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions: A method for detecting cracks in any direction inside carbon steel based on magnetic reluctance disturbance includes the following steps: Step S1: Use a static magnetic field B0 to magnetize the carbon steel structure to its magnetic permeability The rising phase to the left of the curve peak; Step S2: defining an excitation range on the surface of the carbon steel structure to be inspected, and exciting an AC magnetic field B1 within the excitation range; wherein the AC magnetic field B1 induces a secondary AC magnetic field B2 above the surface of the carbon steel structure to be inspected; Step S3: Calculate the overall magnetic resistance response of the carbon steel structure to be inspected within the excitation range; collect the AC magnetic field B1 and the secondary AC magnetic field B2 within the excitation range, and convert them into a signal Bx; Step S4: Calculate the signal Bx to obtain the AC component JBx and the DC component ZBx; Step S5: Moving the AC magnetic field B1 within the excitation range and calculating the variation trend of the AC component JBx; wherein the direction of the AC magnetic field B1 within the moving excitation range is determined by the inspection task of the carbon steel structure to be inspected; The statistically obtained variation trend of the AC component JBx can be used to determine the magnetic reluctance disturbance on the carbon steel surface, thereby realizing the detection and evaluation of cracks in any direction inside the carbon steel.

[0007] Preferably, the static magnetic field B0 in step S1 is excited by a plurality of DC coils or permanent magnets matched with the carbon steel structure to be inspected, and the magnetic field strength is 0.1T to 0.5T.

[0008] Preferably, the AC magnetic field B1 excited within the excitation range in step S2 satisfies: Formula (1); In formula (1), N is the number of turns of the AC magnetic field excitation coil, and I1 is the amplitude of the AC magnetic field excitation current.

[0009] Preferably, the overall magnetic resistance of the carbon steel structure to be inspected within the excitation range in step S3 satisfies: Formula (2); In formula (2), is the surface magnetic permeability of the carbon steel structure to be inspected; L is the length of the excitation range, and W is the width of the excitation range.

[0010] Preferably, the magnetic field direction of the static magnetic field B0 is in the same direction as the arrangement direction of the magnetic core for generating the alternating magnetic field B1.

[0011] The present invention provides a method for detecting cracks in any direction inside carbon steel based on magnetic resistance disturbance, which specifically includes the following steps: using a static magnetic field B0 to magnetize the carbon steel structure to be inspected to its magnetic permeability The rising phase on the left side of the curve peak; defining an excitation range on the surface of the carbon steel structure to be inspected, and exciting an AC magnetic field B1 within the excitation range; wherein, the AC magnetic field B1 induces a secondary AC magnetic field B2 above the surface of the carbon steel structure to be inspected; calculating the overall magnetic reluctance response of the carbon steel structure to be inspected within the excitation range; collecting the AC magnetic field B1 and the secondary AC magnetic field B2 within the excitation range and converting them into a signal Bx; calculating the signal Bx to obtain the AC component JBx and the DC component ZBx; moving the AC magnetic field B1 within the excitation range and calculating the variation trend of the AC component JBx. The variation trend of the AC component JBx can be used to determine the magnetic reluctance disturbance of the carbon steel surface, thereby realizing the detection and evaluation of cracks in any direction within the carbon steel.

[0012] The method for detecting cracks in arbitrary directions inside carbon steel based on magnetic resistance disturbance, which has the above-mentioned steps and features, has at least the following technical advantages over the existing technology: (1) The present invention provides a method for detecting cracks in any direction in carbon steel based on magnetic resistance disturbance. The method uses a static magnetic field B0 to magnetize the carbon steel structure to be inspected to its magnetic permeability. The rising stage on the left side of the curve peak; during this process, the static magnetic field B0 will bypass the area above the crack inside the carbon steel structure to be inspected, making the surface magnetic permeability of the carbon steel structure to be inspected Along The curve gets bigger.

[0013] (2) The method for detecting cracks in any direction inside carbon steel based on magnetic resistance disturbance provided by the present invention excites an AC magnetic field B1 within an excitation range, and further induces a secondary AC magnetic field B2 above the surface of the carbon steel structure to be inspected; by statistically analyzing the changing trend of the AC component JBx in the signal Bx (obtained by converting the AC magnetic field B1 within the excitation range and the secondary AC magnetic field B2), the detection and evaluation of cracks in any direction inside carbon steel can be achieved.

[0014] (3) The method for detecting cracks in any direction in carbon steel based on magnetoresistance disturbance provided by the present invention generates magnetoresistance disturbance of the same order of magnitude for cracks in any direction, which makes up for the deficiency of the existing detection method that it is difficult to fully stimulate the magnetic abnormal response of cracks, effectively reduces the missed detection rate of cracks in any direction in carbon steel, and has the characteristics of fast detection speed and high effective recognition rate of cracks in any direction in carbon steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the following drawings: Figure 1 A schematic flow chart of a method for detecting cracks in arbitrary directions inside carbon steel based on magnetic reluctance disturbance provided by the present invention; Figure 2 Schematic diagram of the magnetization curve of the carbon steel structure to be inspected using a static magnetic field B0; Figure 3 Schematic diagram of the magnetic permeability disturbance distribution above the internal crack after the carbon steel structure to be inspected is magnetized using a static magnetic field B0; Figure 4 This is a schematic diagram of the detection signal result (after normalization) finally obtained by the method for detecting cracks in arbitrary directions inside carbon steel based on magnetoresistive perturbation provided by the present invention; Figure 5 This is a schematic diagram of the detection signal result (after normalization) finally obtained by the existing detection method based on single-direction excitation; Figure 6 A schematic diagram of the structure of a detection device for verifying the method for detecting cracks in arbitrary directions inside carbon steel based on magnetic reluctance disturbance provided by the present invention; Reference numerals: 10. AC signal generator; 20. DC signal generator; 30. DC excitation coil assembly; 301. First winding; 302. Second winding; 40. Carbon steel structure to be inspected; 50. Signal Bx; 60. U-shaped magnetic core; 70. AC excitation coil; 80. Amplification and filtering circuit; 90. Array magnetic field sensor. DETAILED DESCRIPTION

[0016] The present invention provides a method for detecting cracks in arbitrary directions inside carbon steel based on magnetic reluctance disturbance. The crack detection method applies a static magnetic field to magnetically conduct the carbon steel structure to a high-sensitivity stage; then an AC magnetic field is excited within an excitation range defined on the surface of the carbon steel structure to be inspected, and the change in the magnetic permeability of the carbon steel structure is statistically analyzed; based on the magnetic reluctance disturbance on the carbon steel surface, effective identification and detection of internal cracks in arbitrary directions is achieved, which significantly improves the detection efficiency while greatly reducing the risk of missed detection.

[0017] The present invention provides a method for detecting cracks in any direction inside carbon steel based on magnetic resistance disturbance, such as Figure 1 As shown, the following steps are included: Step S1: Use a static magnetic field B0 to magnetize the carbon steel structure to its magnetic permeability The rising phase to the left of the peak of the curve.

[0018] Specifically, as a more preferred embodiment of the present invention, the static magnetic field B0 can be formed by multiple DC coils or permanent magnets adapted to the carbon steel structure to be inspected, and its magnetic field strength is 0.1T to 0.5T, which is specifically used to magnetize the carbon steel structure to be inspected to its magnetic permeability. The rising phase on the left side of the curve peak, refer to Figure 2 shown.

[0019] The static magnetic field B0 will bypass the area above the crack inside the carbon steel structure to be inspected and cause disturbance. This disturbance behavior will cause the surface magnetic permeability of the carbon steel structure to be inspected to Along The curve becomes larger, please refer to Figure 3 shown.

[0020] After completing step S1, step S2 is further implemented. Specifically, step S2: an excitation range is defined on the surface of the carbon steel structure to be inspected, and an AC magnetic field B1 is excited within the excitation range; wherein the AC magnetic field B1 induces a secondary AC magnetic field B2 above the surface of the carbon steel structure to be inspected.

[0021] It is worth noting that the AC magnetic field B1 (whose frequency does not exceed 10 kHz) excited within the static magnetization range in step S2 specifically satisfies: Formula (1). In formula (1), N is the number of turns of the AC magnetic field excitation coil, and I1 is the amplitude of the AC magnetic field excitation current.

[0022] In addition, it is also preferred that the magnetic core generating the alternating magnetic field B1 is arranged in the same direction as the magnetic field direction of the static magnetic field B0.

[0023] Step S3: Calculate the overall magnetic resistance response of the carbon steel structure to be inspected within the excitation range; collect the AC magnetic field B1 and the secondary AC magnetic field B2 within the excitation range, and convert them into a signal Bx.

[0024] After completing step S2, step S3 is further implemented. In the process of implementing step S3, the excitation range of the excitation AC magnetic field B1 is first determined. The length of the excitation range is set to L, and the width of the excitation range is set to W. Further deduction shows that the surface magnetic resistance of the carbon steel structure to be inspected within the excitation range satisfies: Formula (2).

[0025] In formula (2), is the surface magnetic permeability of the carbon steel structure to be inspected; L is the length of the excitation range, and W is the width of the excitation range. It is worth noting that since L and W are both fixed values; therefore, the surface magnetic resistance of the carbon steel structure to be inspected within the excitation range is actually determined by the surface magnetic permeability of the carbon steel structure to be inspected. (Change) is determined by the magnetic permeability of the carbon steel structure to be inspected. When it increases, the surface magnetic resistance R of the carbon steel structure to be inspected within the excitation range will decrease.

[0026] Step S4: Calculate the signal Bx to obtain the AC component JBx and the DC component ZBx.

[0027] After completing step S3, step S4 is further implemented. Specifically, by filtering and amplifying the signal Bx, the AC component JBx and the DC component ZBx can be obtained.

[0028] Step S5: Move the AC magnetic field B1 within the excitation range and collect statistics on the change trend of the AC component JBx.

[0029] On the basis of completing step S4, step S5 is further implemented. Among them, the direction of the AC magnetic field B1 within the moving excitation range is specifically determined by the inspection task of the carbon steel structure to be inspected. For example, if the inspection task is the fillet weld of the carbon steel structure to be inspected, the AC magnetic field B1 within the excitation range is usually set in the same direction as the fillet weld; at this time, the AC magnetic field B1 within the excitation range is moved along the extension direction of the fillet weld, that is, the moving direction of the AC magnetic field B1 within the excitation range is in the same direction as the setting direction of the AC magnetic field B1. If the inspection task is the girth weld of the carbon steel structure to be inspected, the static magnetic field B0 is usually set perpendicular to the girth weld; the setting direction of the AC magnetic field B1 within the excitation range is also perpendicular to the girth weld; at this time, the AC magnetic field B1 within the excitation range is moved along the extension direction of the girth weld, that is, the moving direction of the AC magnetic field B1 within the excitation range is perpendicular to the setting direction of the AC magnetic field B1.

[0030] Then the changing trend of AC component JBx is calculated to detect cracks in the carbon steel structure to be inspected. Figure 4 As shown, Figure 4 This diagram illustrates the (normalized) detection signal obtained using the magnetic reluctance perturbation-based method for detecting arbitrary-direction cracks in carbon steel. When there are no defects, the background value of JBx is 0. However, when JBx shows a distinct trough, it indicates the presence of a crack in that area.

[0031] After further analysis, it can be found that the above test results show good sensitive response to cracks parallel to and perpendicular to the static magnetic field B0. Figure 5 A schematic diagram of the detection signal result obtained by the existing detection method based on single direction excitation is provided. Figure 4 It can be found that Figure 5 The detection result of the prior art shown can only respond well to cracks perpendicular to the magnetic field direction, but has difficulty responding to cracks parallel to the magnetic field direction.

[0032] On the other hand, in order to facilitate those skilled in the art to understand the present invention, a detection device is further provided for use in verifying the effect. Figure 6As shown, the detection device mainly includes an AC signal generator 10, a DC signal generator 20, a DC excitation coil group 30, a carbon steel structure to be detected 40, a signal Bx50, a U-shaped magnetic core 60, an AC excitation coil 70, an amplifying and filtering circuit 80, and an array magnetic field sensor 90.

[0033] During the testing process, the constant current source output by the DC signal generator 20 is first loaded into the DC excitation coil group 30 to generate a static magnetic field B0 of 0.2 T. Then, the carbon steel structure 40 to be tested is placed in the static magnetic field B0 generated by the DC excitation coil group 30, so that it is magnetized to The rising phase to the left of the curve peak. The DC excitation coil assembly 30 includes two first windings 301 and second windings 302 of the same specification and direction at a certain interval. These windings can be used to direct the uniform static magnetic field B0 generated in the space between the first windings 301 and the second windings 302 into the interior of the carbon steel structure 40 to be inspected.

[0034] Furthermore, a U-shaped magnetic core 60 is placed on the surface of the carbon steel structure 40 to be inspected, at the center of the static magnetic field B0. The distance between the two legs of the U-shaped magnetic core 60 is 20 mm, and the width is 10 mm. An AC excitation coil 70 is wound around the crossbeam of the U-shaped magnetic core 60. An AC signal generator 10 generates a sinusoidal signal with a frequency of 1 kHz and applies it to the AC excitation coil 70, thereby generating an AC magnetic field B1 parallel to the direction of the static magnetic field B0 within a range of L = 20 mm and W = 10 mm on the surface of the carbon steel structure 40 to be inspected. This AC magnetic field B1 induces a secondary AC magnetic field B2 above the surface of the carbon steel structure 40 to be inspected. Finally, a 3×2 uniformly distributed array of magnetic field sensors 90 is arranged within a range of L = 20 mm and W = 10 mm. This array of magnetic field sensors 90 is specifically used to collect the AC magnetic field B1 and the secondary AC magnetic field B2 within the excitation range, thereby generating multiple electrical signals (which, after superposition and conversion, can generate signal Bx).

[0035] The method for detecting cracks in arbitrary directions inside carbon steel based on magnetic resistance disturbance provided by the present invention is continued to be implemented. It is worth noting that the AC magnetic field B1 and the secondary AC magnetic field B2 will have a disturbing effect on the magnetic permeability within the excitation range. At this time, the array magnetic field sensor 90 directly below the AC excitation coil 70 picks up the multiple electrical signals obtained by the AC magnetic field B1 and the secondary AC magnetic field B2 and superimposes them to obtain a signal Bx50. Subsequently, the signal Bx50 is filtered and amplified by the amplifying and filtering circuit 80 located above the AC excitation coil 70, and the AC component JBx and the DC component ZBx can be further obtained.

[0036] Furthermore, the AC magnetic field B1 within the excitation range is moved (for example, by adjusting the position of the DC excitation coil assembly 30 and the AC excitation coil 70 along the length of the carbon steel structure 40 to be inspected). The trend of the signal Bx50 and the AC component JBx output by the array magnetic field sensor 90 is statistically analyzed. By analyzing the trend of the AC component JBx, the magnetic reluctance disturbance of the carbon steel structure 40 to be inspected can be determined, thereby enabling the detection and assessment of internal cracks. A crack is detected when the AC component JBx exhibits a trough characteristic.

[0037] The present invention provides a method for detecting arbitrary-direction cracks in carbon steel based on reluctance perturbation. This method utilizes a static magnetic field B0 to generate an AC magnetic field B1 within an excitation range. The method then analyzes the variation trend of the signal Bx to detect and assess arbitrary-direction cracks within the carbon steel. In this process, the signal Bx, derived from the AC magnetic field B1 and the secondary AC magnetic field B2 within the excitation range, produces reluctance perturbations of the same magnitude for cracks in arbitrary directions. This method overcomes the technical shortcoming of existing detection methods, which struggle to fully excite the magnetic anomaly response to cracks in arbitrary directions.

[0038] The present invention provides a method for detecting cracks in any direction inside carbon steel based on magnetic resistance disturbance, which specifically includes the following steps: using a static magnetic field B0 to magnetize the carbon steel structure to be inspected to its magnetic permeability The rising phase on the left side of the curve peak; defining an excitation range on the surface of the carbon steel structure to be inspected, and exciting an AC magnetic field B1 within the excitation range; wherein, the AC magnetic field B1 induces a secondary AC magnetic field B2 above the surface of the carbon steel structure to be inspected; calculating the overall magnetic reluctance response of the carbon steel structure to be inspected within the excitation range; collecting the AC magnetic field B1 and the secondary AC magnetic field B2 within the excitation range and converting them into a signal Bx; calculating the signal Bx to obtain the AC component JBx and the DC component ZBx; moving the AC magnetic field B1 within the excitation range and calculating the variation trend of the AC component JBx. The variation trend of the AC component JBx can be used to determine the magnetic reluctance disturbance of the carbon steel surface, thereby realizing the detection and evaluation of cracks in any direction within the carbon steel.

[0039] The method for detecting cracks in arbitrary directions inside carbon steel based on magnetoresistive perturbation, which has the above-mentioned steps and features, has at least the following technical advantages over the existing technology: (1) The present invention provides a method for detecting cracks in any direction in carbon steel based on magnetic resistance disturbance. The method uses a static magnetic field B0 to magnetize the carbon steel structure to be inspected to its magnetic permeability. The rising stage on the left side of the curve peak; during this process, the static magnetic field B0 will bypass the area above the crack inside the carbon steel structure to be inspected, making the surface magnetic permeability of the carbon steel structure to be inspected Along The curve gets bigger.

[0040] (2) The method for detecting cracks in any direction inside carbon steel based on magnetic resistance disturbance provided by the present invention excites an AC magnetic field B1 within an excitation range, and further induces a secondary AC magnetic field B2 above the surface of the carbon steel structure to be inspected; by statistically analyzing the changing trend of the AC component JBx in the signal Bx (obtained by converting the AC magnetic field B1 within the excitation range and the secondary AC magnetic field B2), the detection and evaluation of cracks in any direction inside carbon steel can be achieved.

[0041] (3) The method for detecting cracks in any direction in carbon steel based on magnetoresistance disturbance provided by the present invention generates magnetoresistance disturbance of the same order of magnitude for cracks in any direction, which makes up for the deficiency of the existing detection method that it is difficult to fully stimulate the magnetic abnormal response of cracks, effectively reduces the missed detection rate of cracks in any direction in carbon steel, and has the characteristics of fast detection speed and high effective recognition rate of cracks in any direction in carbon steel.

[0042] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for detecting cracks in any direction inside carbon steel based on magnetic reluctance disturbance, characterized in that: The following steps are included: Step S1: Use a static magnetic field B0 to magnetize the carbon steel structure to its magnetic permeability The rising phase to the left of the curve peak; Step S2: defining an excitation range on the surface of the carbon steel structure to be inspected, and exciting an AC magnetic field B1 within the excitation range; wherein the AC magnetic field B1 induces a secondary AC magnetic field B2 above the surface of the carbon steel structure to be inspected; Step S3: Calculate the overall magnetic resistance response of the carbon steel structure to be inspected within the excitation range; collect the AC magnetic field B1 and the secondary AC magnetic field B2 within the excitation range, and convert them into a signal Bx; Step S4: Calculate the signal Bx to obtain the AC component JBx and the DC component ZBx; Step S5: Moving the AC magnetic field B1 within the excitation range and calculating the variation trend of the AC component JBx; wherein the direction of the AC magnetic field B1 within the moving excitation range is determined by the inspection task of the carbon steel structure to be inspected; The statistically obtained variation trend of the AC component JBx can be used to determine the magnetic reluctance disturbance on the carbon steel surface, thereby realizing the detection and evaluation of cracks in any direction inside the carbon steel.

2. The method for detecting cracks in any direction in carbon steel based on magnetic reluctance disturbance according to claim 1, characterized in that: In step S1 , the static magnetic field B0 is excited by a plurality of DC coils or permanent magnets matched with the carbon steel structure to be inspected, and the magnetic field strength is 0.1T to 0.5T.

3. The method for detecting cracks in any direction in carbon steel based on magnetoresistive disturbance according to claim 1, characterized in that: The AC magnetic field B1 excited within the excitation range in step S2 satisfies: Formula (1); In formula (1), N is the number of turns of the AC magnetic field excitation coil, and I1 is the amplitude of the AC magnetic field excitation current.

4. The method for detecting cracks in any direction in carbon steel based on magnetoresistive perturbation according to claim 1, characterized in that: The overall magnetic resistance of the carbon steel structure to be inspected within the excitation range in step S3 satisfies: Formula (2); In formula (2), is the surface magnetic permeability of the carbon steel structure to be inspected; L is the length of the excitation range, and W is the width of the excitation range.

5. The method for detecting cracks in any direction in carbon steel based on magnetoresistive disturbance according to claim 1, characterized in that: The magnetic field direction of the static magnetic field B0 is the same as the setting direction of the magnetic core used to generate the AC magnetic field B1.

Images