ELECTROMAGNETIC DETECTION METHOD FOR DETECTING DEFECTS IN WELD BEADS ON STAINLESS STEEL TUBES AND ELECTROMAGNETIC DETECTION SYSTEM FOR USE WITH SAID METHOD

Abstract

This disclosure provides an electromagnetic detection method for detecting weld bead defects in a stainless steel tube. The electromagnetic detection method comprises: acquiring a system noise value a in a gradient signal from a region of the weld bead without defects from a reference block, a maximum value b of background noise in the gradient signal of the region of the weld bead without defects, and a maximum value c of a gradient signal from a location of the defective weld bead from the reference block; setting an alarm signal value d = the maximum value b of the background noise * a preset interval, and setting the alarm signal value d < the maximum value c of the gradient signal from the location of the defective weld bead;The system detects the weld bead to be evaluated on the stainless steel tube in sections, and when a gradient signal during detection appears greater than the alarm signal value d, a region of the weld bead to be evaluated is determined to be possibly defective; the region determined to be possibly defective is polished and then detected N times, and when all the gradient signals from the N detections are greater than the alarm signal value d, the region is confirmed to be defective. This disclosure also provides an electromagnetic detection system for detecting weld defects on a stainless steel tube.

Description

Electromagnetic detection method for detecting defects in weld seams in stainless steel pipes and electromagnetic detection system for use with said method Requested by: 1) CHINA NUCLEAR POWER ENGINEERING CO., LTD. 2) CHINA NUCLEAR INDUSTRY 23 CONSTRUCTION CO, LTD. 3) CHINA UNIVERSITY OF PETROLEUM (EAST CHINA) Addressed at: 1) N° 117 WEST THIRD RING ROAD, BEIJING, CHINA 2) NO. 58 SHUNKANG ROAD, BEIJING, CHINA 3) NO.66 CHANGJIANGXI ROAD, HUANGDAO, SHANDONG, CHINA Priority: CN 202111458048.3 of December 2, 2021 2050863 of 2 20272175471 Palace - 20272175471 Digitally signed by PORTALTRAMITES - INPI Date: 2022.11.29 13:22:42 -03:00 Reason: Digitally signed by the INPI Location: Buenos Aires, Argentina 2050863 of 2 Electromagnetic detection method for detecting defects in weld seams in stainless steel pipes and electromagnetic detection system for use with said method Technical field The present disclosure belongs to a field of electromagnetic detection technology, and in particular relates to an electromagnetic detection method and an electromagnetic detection system for detecting defects of welding beads in a stainless steel pipe. Background Thin-walled stainless steel pipe, being an important means of transporting materials, plays a substantial role in the nuclear industry due to its wide use. However, weld seam defects such as voids, slag, and cracks may occur in thin-walled stainless steel pipe, and these defects may cause leakage of nuclear materials and thus endanger the safe operation of nuclear industrial facilities. Therefore, for the purpose of nuclear engineering, it is necessary to detect weld seam defects in stainless steel pipe. 2050863 of 40 thin wall in order to completely eliminate potential safety hazards. Currently, commonly used weld seam defect detection methods include penetration testing and radiographic testing. However, penetration testing can only detect surface defects and cannot effectively detect internal defects such as voids, slag, and cracks. Radiographic testing poses risks in terms of radiation safety and requires separate operation in a dedicated time window and operating location. Therefore, weld construction and defect detection cannot be performed in parallel (simultaneously). There are disadvantages such as large differences in penetrated thickness, defect image distortion, and the like in weld seam detection for thin-walled stainless steel pipes. Therefore, a detection medium is required that can detect an internal defect in a stainless steel pipe weld bead and that can improve the reliability and accuracy of detection without producing harmful radiation. Summary In view of the above-mentioned disadvantages in the state of the 2050863 of 40 technique, the present disclosure is directed to solving a technical solution of providing an electromagnetic detection method and an electromagnetic detection system for detecting weld seam defects in a stainless steel pipe. Compared with penetration tests, the electromagnetic detection method and the electromagnetic detection system can detect an internal defect in a weld seam of the stainless steel pipe; and compared with radiographic tests, the electromagnetic detection method and the electromagnetic detection system do not produce harmful radiation, do not require a separate dedicated time window, and improve the reliability and accuracy of the detection. According to one aspect of the present disclosure, the present disclosure provides an electromagnetic detection method for detecting welding defects in a stainless steel pipe, the electromagnetic detection method comprising: detecting a reference block with prefabricated defects to acquire a system noise value a in a gradient signal of a defect-free weld bead region of the reference block, a maximum value b of a background noise in the gradient signal of the defect-free weld bead region, and a maximum value c of a gradient signal of a defective weld seam location of the reference block, wherein the reference block has the same specifications, welding method, and welding process as a weld seam a. 2050863 of 40 detect the stainless steel tube; set an alarm signal value d = the maximum value b of the background noise * a preset interval, and set the alarm signal value d <que el valor máximo c de la señal de gradiente de la ubicación del cordón de soldadura defectuoso;detecting the weld seam to be evaluated of the stainless steel pipe in pieces, and when a gradient signal during the detection appears to be greater than the alarm signal value d, it is determined that a region of the weld seam to be evaluated is possibly defective and polishing the region determined to be possibly defective and then detecting the region for N times, when all of the gradient signals of the N times detections are greater than the alarm signal value d, it is confirmed that the region is defective and when a gradient signal of the detection of at least one time is less than or equal to the alarm signal value d, it is confirmed that the region is not defective, N being a positive integer greater than or equal to 2;wherein the electromagnetic detection method further comprises acquiring a gradient signal corresponding to a magnetic field signal based on the magnetic field signal detected by an electromagnetic detection probe before acquiring the system noise value a in the gradient signal of the defect-free weld bead region of the reference block, the maximum value b of the background noise in the gradient signal of the defect-free weld bead region, and the maximum value c of the gradient signal of the weld bead location; 2050863 of 40 of defective welding of the reference block, where the electromagnetic detection probe is configured to detect the weld seam to be detected of the reference block or the stainless steel tube; where the acquisition of the gradient signal corresponding to the magnetic field signal based on the magnetic field signal detected by the electromagnetic detection probe comprises applying an alternating current magnetic field to the electromagnetic detection probe; acquiring a tangential magnetic field signal B along a circumferential direction of the stainless steel tube in a region of the weld seam to be evaluated of the reference block or the stainless steel tube by the electromagnetic detection probe; differentiating the tangential magnetic field signal B to obtain a signal B0;taking as 0 the values ​​of the signal B0 greater than or equal to 0, and taking the absolute values ​​of the values ​​of the signal B0 less than 0 to obtain a signal B1; Fourier transforming the signal B1 to obtain a frequency at which a maximum value of a noise amplitude is concentrated, and setting the frequency at which the maximum value of the noise amplitude is concentrated as a cut-off frequency of a low-pass filter; low-pass filtering the Fourier transformed signal B1 to obtain a gradient signal B2 corresponding to the magnetic field signal B in the region of the weld bead; where the acquisition of the noise value of the system a in the gradient signal of the defect-free weld bead region of the block of; 2050863 of 40 reference, the maximum value b of the background noise in the gradient signal of the defect-free weld bead region, and the maximum value c of the gradient signal of the defective weld bead location of the reference block comprises arranging the electromagnetic detection probe in the defect-free weld bead region of the reference block stationarily, reading a maximum value in the gradient signal of the defect-free weld bead region, repeating the reading for M times to calculate an average value as the system noise value a, where M is a positive integer greater than or equal to 2;and sweeping the electromagnetic detection probe along a direction of the weld bead of the reference block at a uniform speed, taking as 0 the gradient signal values ​​less than or equal to a, reading the maximum value b of the background noise in the gradient signal of the region of the weld bead without defects, and reading the maximum value c of the gradient signal of the location of the defective weld bead.; In an embodiment of the present disclosure, the electromagnetic detection method further comprises: before detecting the weld bead to be evaluated of the piece stainless steel pipe, cleaning and polishing the weld bead to be evaluated of the stainless steel pipe in a range including a surface of the weld bead to be evaluated and heat affected zones on both sides of the weld bead to be evaluated, so that a surface unevenness of the weld bead to be evaluated is less than ±1 mm. 2050863 of 40 In one embodiment of the present disclosure, the preset interval is [2, 3], and N=M=3. In an embodiment of the present disclosure, the electromagnetic detection method further comprises: providing P prefabricated holes uniformly along a circumferential direction of the weld bead of the reference block before evaluating the reference block, wherein a size of each of the prefabricated holes does not exceed 80% of an allowable circular display defect, and P is a positive integer greater than 2. In an embodiment of the present disclosure, the electromagnetic detection method is further adapted to detect weld bead defects in a stainless steel plate, and wherein the stainless steel tube is replaced by the stainless steel plate. According to another aspect of the present disclosure, the present disclosure provides an electromagnetic detection system for detecting weld seam defects in a stainless steel pipe, the electromagnetic detection system comprising an upper computer and an electromagnetic detection probe, the electromagnetic detection probe being configured to detect a weld seam to be evaluated from a reference block or the stainless steel pipe, the upper computer including an acquisition module, an adjustment module, and a determination module, the acquisition module being electrically connected to the electromagnetic detection probe. 2050863 of 40 and is configured to acquire a gradient signal corresponding to a magnetic field signal based on the magnetic field signal detected by the electromagnetic detection probe, acquiring the gradient signal corresponding to the magnetic field signal based on the magnetic field signal detected by the electromagnetic detection probe comprising applying an alternating current magnetic field to the electromagnetic detection probe; acquiring a tangential magnetic field signal B along a circumferential direction of the stainless steel tube in a region of the weld bead to be evaluated from the reference block or the stainless steel tube by the electromagnetic detection probe; differentiating the tangential magnetic field signal B to obtain a signal B0; taking values ​​of the signal B0 greater than or equal to 0 as 0, and taking absolute values ​​of values ​​of the signal B0 less than 0 to obtain a signal B1;transforming the signal B1 into a Fourier to obtain a frequency at which a maximum value of a noise amplitude is concentrated, and setting the frequency at which the maximum value of the noise amplitude is concentrated as a cutoff frequency of a low-pass filter; low-pass filtering the Fourier-transformed signal B1 to obtain a gradient signal B2 corresponding to the magnetic field signal B in the weld bead region; where the acquisition module is further configured to acquire a system noise value a in a gradient signal of a defect-free weld bead region of the reference block, a maximum value b of a background noise in the gradient signal of the; 2050863 of 40 region of the weld seam without defects, and a maximum value c of a gradient signal of a defective weld seam location from the reference block after acquiring a gradient signal corresponding to a magnetic field signal based on the magnetic field signal detected by the electromagnetic detection probe, where the reference block has the same specifications, welding method and welding process as the weld seam to be detected of the stainless steel pipe;wherein acquiring the system noise value a at the gradient signal of the defect-free weld bead region of the reference block, the maximum value b of the background noise at the gradient signal of the defect-free weld bead region, and the maximum value c of the gradient signal of the defective weld bead location of the reference block comprises arranging the electromagnetic detection probe in the defect-free weld bead region of the reference block in a stationary manner, reading a maximum value in the gradient signal of the defect-free weld bead region, repeating the reading for M times to calculate an average value as the system noise value a, where M is a positive integer greater than or equal to 2;and sweeping the electromagnetic detection probe along a direction of the weld bead of the reference block at a uniform speed, taking as 0 the gradient signal values ​​less than or equal to a, reading the maximum value b of the background noise in the gradient signal of the region of the weld bead without defects, and reading the maximum value c of the signal of; 2050863 of 40 gradient of the location of the defective weld bead; where the adjustment module is configured to set an alarm signal value d = the maximum value b of the background noise * a preset interval and set the alarm signal value d < the maximum value c of the gradient signal of the location of the defective weld bead; and where the determination module is electrically connected to the electromagnetic detection probe and is configured to: determine that a region of the weld bead to be evaluated is possibly defective and display a determination result when a gradient signal while the electromagnetic detection probe is detecting the weld bead to be evaluated of the piece stainless steel pipe appears to be greater than the alarm signal value d;confirming that the region is defective and displaying a confirmation result when all gradient signals from the N detections after polishing the region determined to be possibly defective are greater than the alarm signal value d; and confirming that the region is not defective and displaying a confirmation result when a gradient signal from the at least one detection is less than or equal to the alarm signal value d, where N is a positive integer greater than or equal to 2.; In one embodiment of the present disclosure, the electromagnetic detection probe comprises a contact assembly, a probe assembly and a connection assembly, the probe assembly comprises a probe housing and detection elements, the contact assembly is located at the bottom of the 2050863 of 40 probe housing, and the contact assembly includes a semicircular arc structure, wherein the semicircular arc structure is used to position the stainless steel tube, a first slot is provided at a center of the semicircular arc structure along a circumferential direction of the stainless steel tube, and the first slot is used to accommodate the weld seam of the stainless steel tube, sensing elements are provided in the probe housing, and the sensing elements include magnetic field sensors, a magnetic core, an excitation coil and a signal processing circuit, a row of second slots are provided at a center of a bottom surface inside the probe housing along an axial direction of the stainless steel tube, the second slots are equally spaced, the second slots are used to hold the magnetic field sensors,and the number of the second slots is the same as the number of the magnetic field sensors, a third slot is provided on each of the two opposite inner side surfaces of the probe housing along the axial direction of the stainless steel tube, and each third slot is used to hold the magnetic core, the excitation coil is wound around a cross bar of the magnetic core to generate the alternating current magnetic field when an alternating current power supply is turned on, and the signal processing circuit is provided in a space between the excitation coil and an upper surface of the probe housing to process the collected magnetic field signals, 2050863 of 40 by the magnetic field sensors, a plurality of threaded ports are provided in an upper opening of the probe housing, the connection assembly includes a probe cover and a connector, and the probe cover includes a base plate and a cover body, a plurality of threaded holes 5 matching the threaded ports in the upper opening of the probe housing are provided on the base plate, the probe cover is fixed to the probe housing by the base plate, a connector hole is provided in the center of the cover body, the connector is fixed to the probe cover by the connector hole, and the connector is used to be connected to the upper computer. The electromagnetic detection method and electromagnetic detection system for detecting welding defects in a stainless steel pipe provided by the present disclosure can eliminate an influence of an intrinsic noise of the electromagnetic detection system on the detection results by acquiring a noise amplitude of the electromagnetic detection system itself and replacing a signal less than or equal to the noise amplitude of the electromagnetic detection system with 0 in subsequent detection signals; further, by acquiring a maximum value of a background noise of the electromagnetic detection system during sweeping and setting an alarm signal value based on the maximum value of the background noise, 2050863 of 40 electromagnetic detection method and electromagnetic detection system exclude the influences of a variety of interference factors, such as unevenness of a weld seam surface, take-off motion of the electromagnetic detection probe, fluctuation of a detection speed and the like on the detection results, improve the reliability and accuracy of detection, and can completely eliminate potential safety hazards. Brief description of the drawings Fig. 1 is a flowchart of an electromagnetic detection method for detecting welding defects in a stainless steel pipe according to Embodiment 1 of the present disclosure; Fig. 2 is a schematic diagram of a reference block used in the electromagnetic detection method according to Embodiment 1 of the present disclosure; Fig. 3 is a cross-sectional view of the reference block of Fig. 2; Fig. 4 is a schematic diagram of operation of an electromagnetic detection probe used in the electromagnetic detection method according to Embodiment 1 of the present disclosure; 2050863 of 40 Fig. 5 is a graph of the detection signal of an original magnetic field signal B in the electromagnetic detection method according to Embodiment 1 of the present disclosure; Fig. 6 is a detection signal graph of a magnetic field differential signal B0 in the electromagnetic detection method according to Embodiment 1 of the present disclosure; Fig. 7 is a graph of the detection signal of a B1 signal in the electromagnetic detection method according to Embodiment 1 of the present disclosure; Fig. 8 is a graph of the detection signal of a filtered signal B2 in the electromagnetic detection method according to Embodiment 1 of the present disclosure; Fig. 9 is a graph of the detection signal of a possibly defective region before being polished in the electromagnetic detection method according to Embodiment 1 of the present disclosure; Fig. 10 is a graph of the detection signal of the possibly defective region after being polished in the electromagnetic detection method according to Embodiment 1 of the present disclosure; Fig. 11 is a structural schematic diagram of an electromagnetic detection system for detecting welding defects in a stainless steel pipe according to Embodiment 2 of the present disclosure; 2050863 of 40 Fig. 12 is an exploded view of an electromagnetic detection probe according to Embodiment 2 of the present disclosure; Fig. 13 is a structural diagram of the cover of the electromagnetic detection probe according to Embodiment 2 of the present disclosure; Fig. 14 is a bottom structural diagram of a probe housing of the electromagnetic detection probe according to Embodiment 2 of the present disclosure; Fig. 15 is an internal structural diagram of the housing of the electromagnetic detection probe according to Embodiment 2 of the present disclosure; Fig. 16 is a graph of the detection signal of a first stationary detection of a region of the defect-free weld bead of the reference block according to Embodiment 3 of the present disclosure; Fig. 17 is a graph of the detection signal of a second stationary detection of the defect-free weld bead region of the reference block according to Embodiment 3 of the present disclosure; Fig. 18 is a detection signal graph of a third stationary detection of the defect-free weld bead region of the reference block according to Embodiment 3 of the present disclosure; Fig. 19 is a graph of the sweep detection signal over a defect-free location along the weld bead direction. 2050863 of 40 of the reference block at a uniform speed according to embodiment 3 of the present disclosure; Fig. 20 is a graph of the detection signal of sweeping over a defective location along the weld bead direction of the reference block 5 at a uniform speed according to Embodiment 3 of the present disclosure; Fig. 21 is a detection signal graph of a first detection of a possibly defective region after being polished according to Embodiment 3 of the present disclosure; Fig. 22 is a detection signal graph of a second detection of the possibly defective region after being polished according to Embodiment 3 of the present disclosure; Fig. 23 is a detection signal graph of a third detection of the possibly defective region after being polished according to embodiment 15 3 of the present disclosure; Fig. 24 is a detection signal graph of a region confirmed as non-defective after a uniform velocity sweep according to Embodiment 3 of the present disclosure; and Fig. 25 is a schematic diagram of the operation of the application 20 of the electromagnetic detection method for detecting defects of the 2050863 of 40 weld bead on the stainless steel tube to a stainless steel plate according to a modification of the present disclosure. Detailed description of the achievements In order that those skilled in the art may better understand the technical solutions of the present disclosure, implementations of the present disclosure will be described in more detail below in connection with the drawings and embodiments. Realization 1: As shown in Fig. 1, the present embodiment provides an electromagnetic detection method for detecting weld defects in stainless steel pipes, and the electromagnetic detection method is especially applicable to detecting weld defects in a thin-walled stainless steel pipe used in nuclear engineering. The electromagnetic detection method according to the present embodiment comprises the following steps: Step 101, detecting a reference block with prefabricated defects to acquire a system noise value a in a gradient signal of a weld bead region without defects of the reference block, a maximum value b of a background noise in the gradient signal of the weld bead region 2050863 of 40 without defects, and a maximum value c of a gradient signal of a defective weld seam location of the reference block, wherein the reference block has the same specifications, welding method and welding process as a weld seam to be detected of the stainless steel pipe; Step 102, setting an alarm signal value d = the maximum value b of the background noise * a preset interval, and setting the alarm signal value d < the maximum value c of the gradient signal of the location of the defective weld bead; Step 103, detecting the weld seam to be evaluated of the piecewise stainless steel pipe 10, and when a gradient signal during detection appears to be greater than the alarm signal value d, it is determined that a region of the weld seam to be evaluated is possibly defective; and Step 104, polish the region determined as possibly defective, and then detect the region for N times, when all the gradient signals of the N detections are greater than the alarm signal value d, the region is confirmed to be defective; and when a gradient signal of the detection at least once is less than or equal to the alarm signal value d, the region is confirmed to be non-defective, where N is a positive integer greater than or equal to 2. 2050863 of 40 In the present embodiment, the reference block has the same specifications, welding method, and welding process (e.g., automation level) as the weld seam to be evaluated of the thin-walled stainless steel tube used in nuclear engineering. For example, 5 uniformly formed P prefabricated holes are provided to simulate voids along a circumferential direction of the weld seam of the reference block, wherein a size of each of the prefabricated holes does not exceed 80% of an allowable circular display defect, and P is a positive integer greater than 2 (as shown in Figs. 2 and 3, three 10 prefabricated holes are provided). Since the detection results of slag and cracks are more obvious and noticeable compared with the detection results of voids, the reference block in the present embodiment is used to simulate voids.A specific region of the defect-free weld bead and a specific location of the defective weld bead and the like of the reference block 15 are known in advance because the reference block is formed with prefabricated defects. In the present embodiment, acquiring the system noise value a in the gradient signal of the defect-free weld bead region of the reference block and the maximum value b of the background noise in the gradient signal of the defect-free weld bead region by detecting the defect-free weld bead region 20 of the reference block, and acquiring the maximum value c of the gradient signal of the defective weld bead region of the block. 2050863 of 40 reference by detecting the defective weld bead region of the reference block are equivalent to acquiring the system noise value a, the maximum value b of the background noise and the maximum value c of the gradient signal of the weld bead to be detected of the stainless steel pipe. Alternatively, in step 101, the electromagnetic detection method of the present embodiment further comprises acquiring a gradient signal corresponding to a magnetic field signal based on the magnetic field signal detected by an electromagnetic detection probe 2 (to be described later) before acquiring the system noise value a in the gradient signal 10 of the defect-free weld bead region of the reference block, the maximum value b of the background noise in the gradient signal of the defect-free weld bead region, and the maximum value c of the gradient signal of the defective weld bead location of the reference block, wherein the electromagnetic detection probe 2 is configured to detect the to-be-detected weld seam 15 of the reference block or the stainless steel pipe. In the present embodiment, when detecting defects in the weld seam of the reference block or the stainless steel pipe, the magnetic field sensors 20 of the electromagnetic detection probe 2 detect a magnetic field signal. However, the magnetic field signal is a time-domain signal 20 that is susceptible to environmental disturbances and is inconvenient for identifying and extracting a defect signal. Consequently, 2050863 of 40 detected magnetic field signal is converted into a gradient signal corresponding to the magnetic field signal in the present embodiment. Alternatively, the acquisition of the gradient signal corresponding to the magnetic field signal based on the magnetic field signal detected by the electromagnetic detection probe 2 specifically comprises steps S1-S6. In step S1, an alternating current magnetic field is applied to the electromagnetic detection probe 2. In the present embodiment, since the stainless steel pipe is made of a non-ferromagnetic material and an earth's magnetic field or the like cannot be used to perform electromagnetic detection, an additional alternating current magnetic field is applied. Specifically, the electromagnetic detection probe 2 has a magnetic core 30 and an excitation coil 40, the excitation coil 40 is connected to an alternating current power supply, and then an alternating current magnetic field is generated in the electromagnetic detection probe 2, so that the electromagnetic detection probe 2 can be used to detect the weld seam to be detected from the reference block or the stainless steel pipe (as shown in Fig. 4). In step S2, the electromagnetic detection probe 2 acquires a tangential magnetic field signal B along a circumferential direction of the magnetic field tube. 2050863 of 40 stainless steel in a region of the weld bead to be evaluated of the reference block or the stainless steel tube, as shown in Fig. 5. In the present embodiment, since a tangential magnetic field as the main magnetic field has a large magnetic field signal strength and is sensitive to volume defects such as voids, slag, and the like, using the magnetic field signal B along a tangential direction of a circumferential weld seam of the stainless steel pipe as the original detection signal (original magnetic field signal) is useful for discovering defects such as voids, slag in the weld seam of the thin-walled stainless steel pipe. As shown in Fig. 5, the voltage signal corresponding to the magnetic field strength output by the magnetic field sensors 20 is indicated by a vertical coordinate in a unit of mV, for example, and the number of sampling points during detection is indicated by a horizontal coordinate. In step S3, the tangential magnetic field signal B is differentiated to obtain a signal B0, as shown in Fig. 6. In the present embodiment, a rate of change of the original magnetic field signal is obtained by differentiating the tangential magnetic field signal B. 2050863 of 40 In step S4, the values ​​of signal B0 greater than or equal to 0 are taken as 0, and the absolute values ​​of signal B0 values ​​less than 0 are taken to obtain a signal B1, as shown in Fig. 7. In the present embodiment, since the signal B0 has an upper peak and a lower peak (two peaks in total), which does not conform to the original magnetic field signal B having a single peak, the intuitive judgment of a peak signal from a noise or a defect will be affected. Furthermore, it can be concluded from the test results that acquiring the lower peak of the signal B0 is more advantageous for effectively identifying an abrupt change in the signal, so numerical transformation processing is performed on the signal B0 to obtain the signal B1. In step S5, signal B1 is Fourier transformed to obtain a frequency at which the maximum value of a noise amplitude is concentrated, and the frequency at which the maximum value of the noise amplitude is concentrated is set as the cutoff frequency of a low-pass filter. In step S6, the Fourier transformed signal B1 is low-pass filtered to obtain a gradient signal B2 corresponding to the magnetic field signal B in the weld bead region, as shown in Fig. 8. In the present embodiment, the time domain signal B1 on which numerical transformation processing has been performed is converted into a frequency domain signal 20 by steps S5-S6 to facilitate identification. 2050863 of 40 of a signal with an abrupt change. So far, the original magnetic field signal B that has been detected is converted into the gradient signal B2 corresponding to the magnetic field signal B to intuitively visualize the abrupt change signal and favorably improve the accuracy of the detection results. Alternatively, in step 101, acquiring the system noise value a at the gradient signal of the defect-free weld bead region of the reference block, the maximum value b of the background noise at the gradient signal of the defect-free weld bead region, and the maximum value c of the gradient signal of the defective weld bead location of the reference block comprises arranging the electromagnetic detection probe 2 at the defect-free weld bead region of the reference block in a stationary manner, reading a maximum value in the gradient signal of the defect-free weld bead region, repeating the reading for M times to calculate an average value as the system noise value a, where M is a positive integer greater than or equal to 2;and sweeping the electromagnetic detection probe 2 along the weld bead direction of the reference block at a uniform speed, taking gradient signal values ​​less than or equal to a as 0, reading out the maximum value b of the background noise in the gradient signal of the defect-free weld bead region, and reading out the maximum value c of the gradient signal of the defective weld bead location.; 2050863 of 40 In the present embodiment, the system noise value a (as intrinsic noise) of the electromagnetic detection system is acquired by stationary detection of the defect-free weld bead region, and in order to avoid the influence of the intrinsic noise of the electromagnetic detection system on the detection results of the defective weld bead location, data processing is performed on the gradient signal data less than or equal to a in subsequent detection. For example, when detecting the defect-free weld bead region, the gradient signal data less than or equal to a is replaced by 0 to facilitate effective identification and extraction of the maximum background noise value b and eliminate the influence of the system noise on the detection results.In addition, the mean of the peak values ​​in the gradient signals from M tests is calculated to reduce test error and facilitate improved detection accuracy. For example, M can be 3. In step 102, an alarm signal value d = the maximum value b 15 of the background noise * a preset interval is set, and the alarm signal value d <que el valor máximo c de la señal de gradiente de la ubicación del cordón de soldadura defectuoso. In the present embodiment, it is shown by testing that an appropriate preset interval may be [2, 3], and the alarm signal value d is set to be equal to the maximum value b of the background noise multiplied by the preset interval to effectively identify a defective signal and eliminate 2050863 of 40 effectively the influence of background noise on detection results, where the maximum value b of the background noise includes noises caused by a variety of interference factors, such as unevenness of a weld bead surface, take-off shock of the electromagnetic detection probe, fluctuation of a detection speed and the like. In step 103, the weld bead to be evaluated of the stainless steel pipe is detected in parts, and when a gradient signal during detection appears to be greater than the alarm signal value d, it is determined that a region of the weld bead to be evaluated is possibly defective (as shown in Fig. 9). In the present embodiment, the electromagnetic detection probe 2 is used to detect the weld seam on the thin-walled stainless steel pipe used in nuclear engineering in pieces, and it is ensured that the detections of all pieces overlap each other and no omitted region occurs during the detection. When the gradient signal during the detection appears to be greater than the alarm signal value d, it is determined that a region of the weld seam to be evaluated is possibly defective. It should be noted that gradient signal data less than or equal to in step 103 are also replaced by 0 to facilitate effective identification and extraction of the defect signal. 2050863 of 40 Alternatively, to further improve the detection accuracy, in Step 103, the electromagnetic detection method further comprises: before detecting the weld bead to be evaluated of the piece stainless steel pipe, cleaning and polishing the weld bead to be evaluated of the stainless steel pipe in a range that includes a surface of the weld bead to be evaluated and heat affected zones on both sides of the weld bead to be evaluated, such that an unevenness of the surface of the weld bead to be evaluated is less than ±1 mm and a detected region is free of welding spatter, iron chips, oil dirt and other impurities. In step 104, the region determined to be possibly defective is polished and detected for N times; when all of the gradient signals from the N detections are greater than the alarm signal value d, the region is confirmed to be defective; and when a gradient signal from the detection of at least one time is less than or equal to the alarm signal value d, the region is confirmed to be non-defective, where N is a positive integer greater than or equal to 2. In the present embodiment, in order to further reduce the judgment error rate, the region determined as possibly defective is polished and then detected for N times, where N may be 3 for example. When the gradient signal of the at least one detection time is not greater than the alarm signal value d, it is confirmed that the region is not defective, but only contains a 2050863 of 40 noise caused by unevenness of a weld seam structure or shaking of the electromagnetic detection probe (as shown in Fig. 10). Compared with conventional penetration tests, the electromagnetic detection method for detecting weld seam defects in a stainless steel pipe of the present embodiment can detect an internal defect in a weld seam of the stainless steel pipe; and compared with conventional radiographic tests, the electromagnetic detection method of the present embodiment does not produce any harmful radiation, does not require a separate dedicated time window, and has a high detection efficiency. In the electromagnetic detection method of the present embodiment, the electromagnetic detection probe is stationary placed in the defect-free weld bead region of the reference block, a maximum value in the gradient signal of the defect-free weld bead region is read, the reading is repeated for three times in the above-mentioned manner to calculate an average value as the system noise value a, and the acquired gradient signal data less than or equal to a are replaced by 0 in subsequent detection to eliminate the influence of intrinsic noise on the detection results;and the electromagnetic detection probe is swept along a direction of the weld bead of the reference block at a uniform speed, the maximum value b of the background noise in the gradient signal of the region of the defect-free weld bead, the maximum value c of the gradient signal of the location of the; 2050863 of 40 defective weld seam and the alarm signal value d is reasonably set based on the maximum value b of the background noise, wherein the maximum value b of the background noise includes noise signals caused by a variety of interference factors, such as unevenness of a surface of a weld seam 5, shaking of the electromagnetic detection probe, fluctuation of a detection speed and the like. By setting the alarm signal value to 2-3 times the maximum b value of the background noise, the influence of these interference factors can be completely excluded and the reliability and accuracy of detection is improved. In the electromagnetic detection method, the magnetic field signal B along the tangential direction of the circumferential weld seam of the stainless steel pipe is used as the original detection signal. As for the electromagnetic detection method, since the tangential magnetic field as the main magnetic field has a large magnetic field signal strength and is sensitive to volume defects such as voids, slag and the like, it facilitates the detection of defects such as voids, slag in the weld seam of the thin-walled stainless steel pipe, and further improves the reliability and accuracy of the detection. Realization 2: 2050863 of 40 The present embodiment provides an electromagnetic detection system for detecting weld defects in a stainless steel pipe. As shown in Fig. 11, the electromagnetic detection system according to the present embodiment comprises an upper computer 1 and an electromagnetic detection probe 2. The electromagnetic detection probe 2 is configured to detect a weld bead to be evaluated on a reference block or stainless steel tube. As shown in Fig. 11, the upper computer 1 includes an acquisition module 11, a setting module 12, and a determination module 13. The acquisition module 11 is electrically connected to the electromagnetic detection probe 2 and is configured to acquire a gradient signal corresponding to a magnetic field signal based on the magnetic field signal detected by the electromagnetic detection probe 2, acquiring the gradient signal corresponding to the magnetic field signal based on the magnetic field signal detected by the electromagnetic detection probe 2 comprising: applying an alternating current magnetic field to the electromagnetic detection probe 2; acquiring a tangential magnetic field signal B along a circumferential direction of the stainless steel pipe in a region 20 of the weld seam to be evaluated from the reference block or the stainless steel pipe by the electromagnetic detection probe 2; differentiating the gradient signal B from the reference block or the stainless steel pipe to be evaluated; 2050863 of 40 tangential magnetic field B to obtain a signal B0; taking values ​​of signal B0 greater than or equal to 0 as 0, and taking absolute values ​​of signal B0 values ​​less than 0 to obtain a signal B1; Fourier-transforming signal B1 to obtain a frequency at which a maximum value of a noise amplitude is concentrated, and setting the frequency at which the maximum value of the noise amplitude is concentrated as a cut-off frequency of a low-pass filter; low-pass-filtering the Fourier-transformed signal B1 to obtain a gradient signal B2 corresponding to the magnetic field signal B in the weld bead region. The acquisition module 11 is further configured to acquire a system noise value a in a gradient signal of a defect-free weld bead region of the reference block, a maximum value b of a background noise in the gradient signal of the defect-free weld bead region, and a maximum value c of a gradient signal of a defective weld bead location of the reference block after acquiring a gradient signal corresponding to a magnetic field signal based on the magnetic field signal detected by the electromagnetic detection probe 2, wherein the reference block has the same specifications, welding method, and welding process as the to-be-detected weld seam of the stainless steel pipe. 2050863 of 40 The acquisition of the system noise value a in the gradient signal of the defect-free weld bead region of the reference block, the maximum value b of the background noise in the gradient signal of the defect-free weld bead region, and the maximum value c of the gradient signal of the defective weld bead location of the reference block comprises: arranging the electromagnetic detection probe 2 in the defect-free weld bead region of the reference block stationarily, reading a maximum value in the gradient signal of the defect-free weld bead region, repeating the reading for M times to calculate an average value as the system noise value a, where M is a positive integer greater than or equal to 2;and sweeping the electromagnetic detection probe 2 along the weld bead direction of the reference block at a uniform speed, taking gradient signal values ​​less than or equal to a as 0, reading out the maximum value b of the background noise in the gradient signal of the defect-free weld bead region, and reading out the maximum value c of the gradient signal of the defective weld bead location.; The adjustment module 12 is configured to set an alarm signal value d = the maximum value b of the background noise * a preset interval and set the alarm signal value d< the maximum value c of the gradient signal 20 of the location of the defective weld bead. 2050863 of 40 The determination module 13 is electrically connected to the electromagnetic detection probe 2 and is configured to: determine that a region of the weld seam to be evaluated is possibly defective and display a determination result when a gradient signal while the electromagnetic detection probe 2 is detecting the weld seam to be evaluated of the piecewise stainless steel pipe appears to be greater than the alarm signal value d; confirm that the region is defective and display a confirmation result when all of the gradient signals from the N detections after polishing the region determined to be possibly defective are greater than the alarm signal value d; and confirm that the region is not defective and display a confirmation result when a gradient signal from the at least one detection is less than or equal to the alarm signal value d, where N is a positive integer greater than or equal to 2. Alternatively, as shown in Figures 12 to 15, the electromagnetic detection probe 2 comprises a contact assembly, a probe assembly and a connection assembly, and the probe assembly comprises a probe housing 10 and detection elements. The contact assembly is located at the bottom of the probe housing 10, and the contact assembly includes a semicircular arc structure 101, wherein the semicircular arc structure 101 is used to position the stainless steel tube, a first groove 102 is provided in the center of the structure of 2050863 of 40 semicircular arc 101 along a circumferential direction of the stainless steel pipe, and the first groove 102 is used to position the weld bead of the stainless steel pipe. The sensing elements are provided in the probe housing 10, and the 5 sensing elements include magnetic field sensors 20, a magnetic core 30, an excitation coil 40, and a signal processing circuit 50. A row of second grooves 104 is arranged at the center of a bottom surface of the inside of the probe housing 10 along an axial direction of the stainless steel tube 10, the second grooves 104 are equally spaced, the second grooves 104 are used to hold the magnetic field sensors 20, and the number of the second grooves 104 is the same as the number of the magnetic field sensors 20. On each of the two opposite inner side surfaces of the probe housing 10 along the axial direction of the stainless steel tube is a third groove 105, and each third groove 105 is used to hold the magnetic core 30. The excitation coil 40 is wound around a cross bar of the magnetic core 30 to generate the alternating current magnetic field when an alternating current power supply is turned on, and the signal processing circuit 50 is provided in a space between the excitation coil 40 and the magnetic core 30. 2050863 of 40 excitation 40 and an upper surface of the probe housing 10 for processing the magnetic field signals collected by the magnetic field sensors 20. A plurality of threaded ports 103 are provided in an upper opening of the probe housing 10. The connection assembly includes a probe cover 60 and a connector 70. The probe cover 60 includes a base plate and a cover body, a plurality of threaded holes 601 matching the threaded ports 103 in the upper opening of the probe housing 10 are provided on the base plate, the probe cover 60 is fixed to the probe housing 10 by the base plate, a connector hole 602 is provided in the middle of the cover body, the connector 70 is fixed to the probe cover 60 by the connector hole 602, and the connector 70 is used to be connected to the upper computer 1. Realization 3: Taking a thin-walled stainless steel tube used in nuclear engineering (an allowable defect with a minimum size is a circular hole having a diameter of 0.4 mm) having a tube diameter of 17. The electromagnetic detection system for detecting welding defects in a thin-walled stainless steel tube for nuclear engineering according to Embodiment 2 is adopted in the present embodiment to perform specific steps of the detection method. 2050863 of 40 electromagnetic for detecting welding defects in the thin-walled stainless steel pipe according to the requirements of electromagnetic detection for welding defects in the thin-walled stainless steel pipe. A reference block with a pipe diameter of 17.1 mm is designed, and a circumferential weld bead with a width of 6 mm and an excess weld metal of 1 mm is provided in the center of the reference block. Three air holes, each of which has a diameter of 0.32 mm and a depth of 0.32 mm, are provided at a constant distance on an inner surface of the circumferential weld bead along a circumferential direction of the circumferential weld bead of the reference block. The electromagnetic detection method according to the present embodiment includes the following specific steps. In step 301, the electromagnetic detection probe 2 is stationary positioned in the defect-free weld bead region of the reference block 15, a maximum value of the gradient signal of the defect-free weld bead region is read out, and the reading is repeated three times in the above-mentioned manner; as shown in Figs. 16 to 18, the maximum values ​​of the gradient signal that have been read out are 15.46, 21.59, and 20.84 respectively, an average value of these maximum values ​​is calculated as the system noise value 19.3, and the gradient signal data less than or equal to 19.3 are replaced by 0 in the subsequent detection, so that the system noise of the detection probe 2050863 of 40 electromagnetic 2 or the electromagnetic detection system itself can be significantly suppressed. Step 302, the electromagnetic detection probe 2 is swept along the weld bead direction of the reference block at a uniform speed, 5 the peak value 37.74 of the background noise in the gradient signal of the defect-free weld bead region is acquired (as shown in Fig. 19, the gradient signal data less than or equal to 19.3 is replaced by 0), the peak value 147. 1 of the gradient signal of the defective weld bead region is acquired (as shown in Fig. 20, the gradient signal data 10 less than or equal to 19.3 is replaced by 0), and the alarm signal value is set to 100, so that noises caused by interferences such as peeling off of the electromagnetic detection probe and excess metal of the weld bead and the like during sweeping are reduced, and the judgment error rate is reduced. Step 303, the weld bead to be tested of the thin-walled stainless steel pipe for nuclear engineering is cleaned and polished in a range including the surface of the weld bead to be tested and the heat affected zones on both sides of the weld bead to be tested, so that an unevenness of the surface of the weld bead to be tested is less than ±1 mm and a detected region is free of weld spatter, iron chips, oil dirt and other impurities. 2050863 of 40 In Step 304, the electromagnetic detection probe 2 is used to detect the weld seam on the thin-walled stainless steel pipe for nuclear engineering in pieces, ensuring that the detections of all pieces overlap each other and that no missed regions occur during detection. When the gradient signal during detection appears greater than the alarm signal value 100, it is determined that a region of the weld seam to be detected is possibly defective. Step 305, the region determined as possibly defective is polished and detected three times, when all the gradient signals of the three detections are greater than the alarm signal value 100 (as shown in Figs. 21 to 23), the region is confirmed to be defective; and when a gradient signal of the detection at least once is not greater than the alarm signal value 100 (as shown in Fig. 24), the region is confirmed to be non-defective, so that the judgment error rate is further reduced. Modification In the foregoing, the electromagnetic detection method and the electromagnetic detection system for detecting weld seam defects in the stainless steel pipe are involved in Embodiments 1-3. However, the disclosure is not limited thereto. The electromagnetic detection method and the system 2050863 of the aforementioned 40 electromagnetic detection probes are also applicable to detecting weld defects in a stainless steel plate. As shown in Fig. 25, when detecting weld seam defects in the stainless steel plate, the semicircular arc structure 101 shown in Fig. 14 is not provided, and the electromagnetic detection probe 2 translates but does not rotate relative to a surface of the stainless steel plate, which is different from the detection of the stainless steel tube. It can be understood that the above implementations are merely exemplary embodiments adopted to explain a principle of the present disclosure, and this disclosure is not restricted thereto. Various modifications and improvements may be made by those skilled in the art without departing from the spirit or essence of this disclosure, and such modifications and improvements should be considered to be included within the scope of this disclosure. 2050863 of 40 20272175471 Palace - 20272175471 Digitally signed by PORTALTRAMITES - INPI Date: 2022.11.29 13:22:43 -03:00 Reason: Digitally signed by the INPI Location: Buenos Aires, Argentina 2050863

Claims

1. An electromagnetic detection method for detecting defects in weld beads on stainless steel tubes, characterized in that it comprises the steps of: detecting a reference block with prefabricated defects to acquire a system noise value a in a gradient signal from a region of weld bead without defects of the reference block, a maximum value b of a background noise in the gradient signal of the region of weld bead without defects, and a maximum value c of a gradient signal from a location of defective weld bead of the reference block, wherein the reference block has the same specifications, welding method and welding process as a weld bead to be evaluated from the stainless steel tube;set an alarm signal value d = the maximum value b of the background noise * a preset interval, and set the alarm signal value d < the maximum value c of the gradient signal of the location of the defective weld bead; detect the weld bead to be evaluated of the stainless steel tube in parts, and when a gradient signal during detection appears as greater than the alarm signal value d, a region of the weld bead to be evaluated is determined to be possibly defective; and polish the region determined to be possibly defective and then detect the region for N times, when all the gradient signals of the detections of N times are greater than the alarm signal value d, the region is confirmed to be defective;and when a gradient signal from the detection at least once is less than or equal to the alarm signal value d, it is confirmed that the region is not defective, N being a positive integer greater than or equal to 2; wherein the electromagnetic detection method further comprises acquiring a gradient signal corresponding to a magnetic field signal based on the magnetic field signal detected by an electromagnetic detection probe before acquiring the system noise value a in the gradient signal of the region of the weld bead without defects of the reference block, the maximum value b of the background noise in the gradient signal of the region of the weld without defects, and the maximum value c of the gradient signal of the location of the defective weld bead of the reference block, wherein the electromagnetic detection probe is configured to detect the weld seam to be detected of the reference block or stainless steel tube;Where the acquisition of the gradient signal corresponding to the magnetic field signal based on the magnetic field signal detected by the electromagnetic detection probe comprises applying an alternating current magnetic field to the electromagnetic detection probe; acquiring a tangential magnetic field signal B along a circumferential direction of the stainless steel tube in a region of the weld bead to be evaluated from the reference block or the stainless steel tube by the electromagnetic detection probe; differentiating the tangential magnetic field signal B to obtain a signal B0; taking the values ​​of the signal B0 greater than or equal to 0 as 0, and taking the absolute values ​​of the values ​​of the signal B0 less than 0 to obtain a signal B1;transform the signal B1 into Fourier to obtain a frequency at which a maximum value of a noise amplitude is concentrated, and establish the frequency at which the maximum value of the noise amplitude is concentrated as the cutoff frequency of a low-pass filter; low-pass filter the Fourier-transformed signal B1 to obtain a gradient signal B2 corresponding to the magnetic field signal B in the weld bead region;and wherein the acquisition of the system noise value a in the gradient signal of the region of the weld bead without defects of the reference block, the maximum value b of the background noise in the gradient signal of the region of the weld bead without defects, and the maximum value c of the gradient signal of the location of the defective weld bead of the reference block comprises: placing the electromagnetic detection probe in the region of the weld bead without defects of the reference block in a stationary manner, reading a maximum value of the gradient signal of the region of the weld bead without defects, repeating the reading for M times to calculate an average value as the system noise value a, M being a positive integer greater than or equal to 2;and sweeping the electromagnetic detection probe along the direction of the weld bead of the reference block at a uniform speed, taking as 0 the gradient signal values ​​less than or equal to aa, reading the maximum value b of the background noise in the gradient signal of the region of the weld bead without defects, and reading the maximum value c of the gradient signal of the location of the defective weld bead. Six claims follow;