Vortex nondestructive testing method for quantitative weld penetration depth of injector of liquid rocket engine

Abstract

The invention relates to an eddy current nondestructive testing method for quantitative weld penetration depth of an injector of a liquid rocket engine, which adopts the principle that when a probe coil with alternating current is close to the surface of a weld seam, a primary excitation magnetic field induced by the probe coil enables an induced current to be generated in a detected conductor, namely eddy current; the eddy current then generates a secondary induced magnetic field which is opposite to the primary magnetic field in direction to influence a coil impedance signal, and defect information and quantitative analysis in the detected conductor can be obtained by analyzing the impedance change. According to the invention, a spring-shaped self-excitation and self-detection probe coil concentrically arranged on a weld joint ring of an injector and an eddy current detection experiment system are adopted, and a four-axis mechanical scanning device is used for assistance; the method provided by the invention can realize effective evaluation of the weld joint with complex surface shape and inner surface defects, has better detection capability and sensitivity, and has the advantages of high detection rate, high detection speed, high efficiency and the like.

Description

Technical Field

[0001] The invention relates to the technical field of eddy current testing, and in particular to an eddy current nondestructive testing method for quantitative penetration of a weld of an injector of a liquid rocket engine. Background Art

[0002] The injector of a liquid rocket engine is welded from an injector disc and multiple injector rings of different sizes, and the material is usually stainless steel. Each nozzle ring is connected to the injector disc by two electron beam welds on the inner and outer sides. The center spacing between adjacent welds is about 2mm, and there is excess height on the surface after welding. The quality of electron beam welding determines the integrity and reliability of the injector structure, which is related to the safe and stable operation of the liquid rocket engine. Therefore, high-precision detection of the weld penetration of the injector is very important.

[0003] At present, the main detection methods for weld penetration are eddy current detection, X-ray detection, ultrasonic detection, etc. Since the electron beam weld of the injector is a concave structure, the weld penetration is equivalent to a crack defect perpendicular to the upper surface, which is not suitable for vertical incidence ultrasonic detection. In addition, the electron beam weld is narrowly spaced and surrounded by injection holes of different diameters, which is not conducive to the use of oblique incidence ultrasonic detection technology. At the same time, the diameter and thickness of the injection disk are large and made of stainless steel. It is difficult for the micro-focus industrial CT system to penetrate the injection disk for effective imaging detection. In principle, the X-ray transmission method cannot reflect the depth information of the weld penetration. Eddy current detection technology has high sensitivity in detecting surface and near-surface defects of metal welds. It is a non-contact non-destructive detection method. The detection probe is small in size and has a variety of flexible configurations. It can realize non-destructive detection in a narrow space environment and is expected to be used for weld penetration evaluation.

[0004] Eddy current testing technology is based on the principle of electromagnetic induction. When the detection coil with alternating current is close to the conductive test piece, eddy current is induced in the test piece, which in turn affects the original magnetic field, causing the impedance and induced voltage of the detection coil to change. By analyzing the change of this impedance or induced voltage, the defect information and quantitative analysis of the conductor under test can be obtained. Summary of the invention

[0005] In order to solve the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide an eddy current non-destructive testing method for quantitative penetration of liquid rocket engine injector welds. The method of the present invention has the advantages of high detection rate, fast detection speed and high efficiency, and can be widely used in non-destructive testing of welds with complex surface shapes and internal surface defects.

[0006] In order to achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] An eddy current nondestructive testing method for quantitative penetration of a liquid rocket engine injector weld is disclosed. The experimental system for implementing the eddy current nondestructive testing method includes a signal generator 1, a power amplifier 2, a phase-locked amplifier 3, a data acquisition device 4, a differential amplifier 5 and a scanning system 6; wherein the signal generator 1 is connected to the power amplifier 2 and the phase-locked amplifier 3, the probe coil 6-4-4 in the scanning device 6 is connected to the power amplifier 2, the probe coil 6-4-4 in the scanning device 6 is connected to the phase-locked amplifier 3, the data acquisition device 4 is connected to the phase-locked amplifier 3, and a sinusoidal signal excitation is applied to the probe coil 6-4-4 through the signal generator 1 and the power amplifier 2. Since the electromagnetically induced alternating current will be in the excitation coil The changing magnetic field induced around the probe coil is called the primary excitation magnetic field. When the probe coil is close to the weld surface, the primary excitation magnetic field induced by the probe coil generates an induced current in the conductor under test, which is called eddy current. The eddy current then generates a secondary induced magnetic field in the opposite direction of the primary excitation magnetic field, affecting the impedance signal of the probe coil. The impedance signal of the probe coil 6-4-4 is then collected by the phase-locked amplifier 3. During the eddy current flow in the injector specimen under test, the eddy current flow is disturbed and abnormal due to the inconsistent depth of the injector electron beam weld. The impedance change of the probe coil as the detection coil reflects the result of the combined effect of the two magnetic fields. The impedance includes resistance R and inductive reactance X. The impedance amplitude and impedance phase A Lissajous diagram is formed with resistance R as the horizontal coordinate and inductive reactance X as the vertical coordinate. When the melting depth is different, the corresponding resistance R and inductive reactance X are also different. Impedance points corresponding to different melting depths will appear on the Lissajous diagram. Each impedance point has a corresponding different phase θ. The phase is used as the signal characteristic of the melting depth. A melting depth-signal characteristic curve is established. The phase corresponding to the test point, that is, the signal characteristic, is obtained through experiments, and the corresponding melting depth value is extracted from the melting depth-signal characteristic calibration curve, which is the melting depth at the detection point.

[0008] Preferably, the scanning device 6 includes an X-axis 6-2, a Y-axis 6-7, a Z-axis 6-1, a rotating table 6-5, a probe mounting plate 6-3, a spring probe 6-4 and a test piece 6-6 of a four-axis scanning table; the spring probe 6-4 is fixed to the probe mounting plate 6-3 of the scanning table with screws and nuts, and the scanning table path is set according to the different curvatures of the injector weld. The probe coil is fixed to the innermost weld by relying on the movement of the X-axis 6-2, the Y-axis 6-7 and the Z-axis 6-1 of the scanning table, so that the probe coil fits the weld surface, and then the rotating table is turned on to rotate the rotating table 5 with the injector to be tested to achieve circumferential rapid scanning; on the basis of the circumferential rapid scanning, a comprehensive scanning of the test piece 6-6 is achieved by first lifting the Z-axis and then moving radially from the inside to the outside at a constant speed to insert into welds of different curvatures for mechanical scanning; both detection accuracy and scanning efficiency are taken into account.

[0009] Preferably, the circumferential rapid scanning speed is selected in the range of 1° / s to 10° / s.

[0010] Preferably, the spring probe 6-4 includes a spring coil cover 6-4-5, a rotating head 6-4-1, a spring 6-4-2, a coil skeleton 6-4-3 and a probe coil 6-4-4. The probe coil 6-4-4 is fixed on the coil skeleton 6-4-3. The bottom plane of the probe coil is parallel to the weld cross-section of the test piece 6-6. The probe auxiliary spring ensures that the spring 6-4-2 produces the same deformation in each test. According to Hooke's law, the pressure applied to the probe coil 6-4-4 is the same each time, thereby controlling the lifting distance of the probe coil 6-4-4 to be the same in each test, that is, in principle eliminating the adverse effect of the lifting distance on the test result; at the same time, it is assisted by four-axis mechanical scanning to achieve comprehensive and rapid detection of weld penetration.

[0011] Preferably, the probe coil 6-4-4 has 1 detection coil, an outer diameter of 3.2 mm, an inner diameter of 1.2 mm, a thickness of 0.8 mm, and 140 turns.

[0012] Preferably, the rotating head 6-4-1, the coil skeleton 6-4-3, and the spring coil cover 6-4-5 are all made of non-conductive, non-magnetic plastic or rubber products.

[0013] Compared with the prior art, the advantages of the present invention are as follows:

[0014] 1) The present invention applies the conventional electromagnetic eddy current detection principle to the non-destructive detection of injector welds. The eddy current probe has a small coil size and a variety of flexible configurations, which solves the difficulty of injector detection in a small space environment.

[0015] 2) The present invention adopts a four-axis scanning table tooling system, combined with a spring probe frame structure, which can realize full-circle rapid eddy current detection of the injector and greatly improve the detection efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a schematic diagram of the connections of the components of the eddy current detection experimental system used in the method of the present invention.

[0017] Figure 2 Schematic diagram of the scanning system of the injector nondestructive testing system based on the electromagnetic eddy current testing principle according to the method of the present invention.

[0018] Figure 3 It is a schematic diagram of the electromagnetic eddy current spring probe used in the present invention.

[0019] Figure 4 Schematic diagram of the injector specimen used in the present invention.

[0020] Figure 5Schematic diagram of eddy current detection principle.

[0021] Figure 6 This is a calibration curve of penetration depth-signal characteristic quantity established in an embodiment of the present invention. DETAILED DESCRIPTION

[0022] The present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0023] Combination Figure 5 , Figure 6 The detection principle of the method of the present invention is further described in detail: according to the eddy current detection principle, an alternating current is passed through the probe coil through the eddy current detection method experimental system. Due to electromagnetic induction, the alternating current will induce a changing magnetic field around the probe coil as an excitation coil, which is called the primary excitation magnetic field. When the probe coil is close to the weld surface, the primary magnetic field induced by the probe coil causes an induced current to be generated in the conductor under test, which is called eddy current. The eddy current then generates a secondary magnetic field in the opposite direction of the primary excitation magnetic field, affecting the impedance signal of the probe coil. In the process of generating eddy current flow in the injector specimen under test, due to the inconsistent depth of the injector electron beam weld, the eddy current flow is disturbed and abnormalities occur; then the impedance change of the probe coil as the detection coil is used to reflect the result of the combined effect of the two magnetic fields. The impedance includes electrical impedance and inductive reactance X; the impedance amplitude and impedance phase The Lissajous diagram is formed with resistance R as the horizontal coordinate and inductive reactance X as the vertical coordinate. When the penetration depth is different, the corresponding resistance R and inductive reactance X are also different. Impedance points corresponding to different penetration depths will appear on the Lissajous diagram. Each impedance point has a corresponding different phase θ. The phase can be used as the characteristic quantity of penetration depth. The penetration depth-signal characteristic quantity curve is established. The phase corresponding to the test point, that is, the signal characteristic quantity, can be obtained through experiments, and the corresponding penetration depth value can be extracted from the penetration depth-signal characteristic quantity calibration curve, which is the penetration depth at the detection point. In addition, the probe auxiliary spring can ensure that the spring produces the same deformation in each detection. According to Hooke's law, the pressure on the probe coil is the same each time, so that the lifting distance of the probe coil in each detection can be controlled to be the same, that is, in principle, the adverse effect of the lifting distance on the detection result is eliminated. At the same time, it is assisted by four-axis mechanical scanning to achieve comprehensive and rapid detection of weld penetration.

[0024] Combine the following Figure 1 , Figure 2 , Figure 3 , Figure 4 The present invention is further described in detail with reference to the accompanying drawings and specific embodiments.

[0025] like Figure 1As shown, the experimental system of the eddy current nondestructive testing method of this embodiment comprises a signal generator 1, a power amplifier 2, a phase-locked amplifier 3, a data acquisition device 4, a differential amplifier 5 and a scanning device 6, wherein the signal generator 1 is connected to the power amplifier 2 and the phase-locked amplifier 3, the probe coil 6-4-4 in the scanning system device 6 is connected to the power amplifier 2, the probe coil 6-4-4 in the scanning device 6 is connected to the phase-locked amplifier 3, and the data acquisition device 4 is connected to the phase-locked amplifier 3. The signal generator 1 first generates a 100kHZ sinusoidal signal, which is input into the power amplifier 2 as a driving signal to provide sufficient current to drive the probe coil. The probe coil generates an alternating magnetic field. When it is close to the object to be measured, an induced current is generated through the eddy current effect. The eddy current changes in the object to be measured will be fed back to the probe coil to generate a weak response signal. The signal is transmitted to the phase-locked amplifier 3, which compares the phase with the reference signal to extract the response signal of the target frequency, thereby improving the signal-to-noise ratio. Afterwards, the extracted signal is sent to the differential amplifier 5 to amplify the difference signal between the probe coils and suppress the common mode noise, further enhancing the contrast of the signal. Finally, the data acquisition device 4 records and stores the signal output by the differential amplifier 5 for subsequent data analysis and processing.

[0026] like Figure 2 As shown, the scanning device 6 comprises components such as the X-axis 6-2, Y-axis 6-7, Z-axis 6-1, and rotating table 6-5 of the four-axis scanning table, a probe mounting plate 6-3, a spring probe 6-4, and a test piece 6-6; the spring probe 6-4 is fixed to the probe mounting plate 6-3 of the scanning table with screws and nuts, and the scanning table path is set according to the different curvatures of the injector weld. The probe coil is fixed to the innermost weld by moving the X-axis 6-2, Y-axis 6-7, and Z-axis 6-1 of the scanning table, so that the probe The head coil is fitted with the weld surface, and then the rotating table is turned on to rotate the rotating table 5 with the injector to be tested to achieve rapid circumferential scanning; on the basis of the rapid circumferential scanning, the Z-axis is first lifted and then radially moved from the inside to the outside at a constant speed to insert welds of different curvatures for mechanical scanning to achieve a comprehensive scan of the test piece 6-6 to be tested; taking into account both detection accuracy and scanning efficiency, the circumferential scanning speed is selected in the range of 1° / s to 10° / s, which more effectively ensures that the scanning results are stable and comprehensive.

[0027] like Figure 3As shown, the spring probe 6-4 includes a spring coil cover 6-4-5, a rotating head 6-4-1, a spring 6-4-2, a coil frame 6-4-3 and a coil 6-4-4. The probe coil 6-4-4 is fixed to the lower part of the coil frame 6-4-3, and is connected to the rotating head 6-4-1 through the spring 6-4-2, and is rotated into the spring coil cover 6-4-5 together, so that the electronic wire is connected to the probe coil 6-4-4 and then passes through the middle hole of the rotating head 6-4-1 to connect to the experimental system. The hole in the upper part of the spring coil cover 6-4-5 is aligned and fixed with the hole on the probe mounting plate 6-3 in the scanning device 6 by screws and nuts. The bottom plane of the probe coil is parallel to the weld section of the test piece 6-6. The number of detection coils is 1, the outer diameter is 3.2mm, the inner diameter is 1.2mm, the thickness is 0.8mm, the number of turns is 140, and it is most sensitive to the result of the penetration signal. The probe auxiliary spring can ensure that the spring 6-4-2 produces the same deformation in each test. According to Hooke's law, the coil is subjected to the same pressure each time, so the probe coil can be controlled to have the same lifting distance in each test, that is, the adverse effect of the lifting distance on the test result can be eliminated in principle. At the same time, it is assisted by four-axis mechanical scanning to achieve comprehensive and rapid detection of weld penetration.

[0028] like Figure 4 As shown, there are weld grooves with different curvatures in the injector specimen, and there are two welds with similar distances and almost identical penetration depths in the grooves.

[0029] The eddy current nondestructive testing method for quantitative penetration of a liquid rocket engine injector weld according to the present invention is carried out by the following steps:

[0030] 1) Build an array eddy current detection experimental system, and fix the spring probe 6-4 on the probe mounting plate 6-3 of the scanning device 6 with screws and nuts;

[0031] 2) At the same time, the scanning table path is set according to the different curvatures of the injector weld, and the probe coil is fixed to the innermost weld by moving the scanning table XYZ axis so that the probe coil fits the weld surface;

[0032] 3) A 100 kHz excitation voltage is introduced into the probe coil through the signal generator 1, and then the rotating table 6-5 is turned on, so that the rotating table 6-5 rotates with the test piece 6-6 to achieve circumferential scanning;

[0033] 4) On the basis of the rapid scanning in step 3 in the circumferential direction, the Z-axis 6-1 is first lifted off and then moved radially from the inside to the outside at a constant speed to insert into weld grooves of different curvatures for mechanical scanning, thereby achieving a comprehensive scanning of the test piece 6-6 to be inspected;

[0034] 5) After completing the above detection process, intercept the real resistance R and imaginary reactance X of the detection signal of different welds, and form a rectangular coordinate system (impedance plane diagram / Lissajous figure) with resistance R as the horizontal coordinate and inductance X as the vertical coordinate. The change in the electrical impedance of the detection coil is measured by the eddy current instrument, and a point can be marked in the above coordinate system. This point is a vector point with a certain amplitude Z and phase θ. The impedance change is shown on the impedance plane diagram: due to various factors causing the change in the eddy current signal component - resistance R or inductance X value, the eddy current detection signal vector point on the impedance plane diagram will be displaced accordingly, and the amplitude of the eddy current signal after the point is displaced and Phase The change of amplitude and phase is also changed accordingly; the weld penetration is judged by analyzing the change of amplitude and phase to calibrate the curve such as Figure 6 .

[0035] In the embodiment of the present invention, the electron beam welding workpiece is selected as: the injector of a certain type of aerospace engine. Its material is stainless steel, and the overall structure is disc-shaped. It is welded by the injector disc and a plurality of injection rings by electron beam welding. The weld is a butt weld. To ensure its safety performance, the penetration depth of each weld is required to be not less than 1.1mm. As a preferred embodiment of the present invention, the rotating head 6-4-1, the coil skeleton 6-4-3, and the spring coil cover 6-4-5 are all made of non-conductive, non-magnetic plastic or rubber products, which have no effect on the magnetic field generated by the probe coil.

Claims

1. An eddy current nondestructive testing method for quantitative penetration of liquid rocket engine injector welds, characterized in that: The experimental system for realizing the eddy current nondestructive testing method comprises a signal generator (1), a power amplifier (2), a phase-locked amplifier (3), a data acquisition device (4), a differential amplifier (5) and a scanning system (6); wherein the signal generator (1) is connected to the power amplifier (2) and the phase-locked amplifier (3), the probe coil (6-4-4) in the scanning device (6) is connected to the power amplifier (2), the probe coil (6-4-4) in the scanning device (6) is connected to the phase-locked amplifier (3), and the data acquisition device (4) is connected to the phase-locked amplifier (3). A sinusoidal signal excitation is applied to the probe coil (6-4-4) through the signal generator (1) and the power amplifier (2). Since the electromagnetically induced alternating current will be used as the excitation A changing magnetic field is induced around the probe coil of the coil, which is called the primary excitation magnetic field. When the probe coil is close to the weld surface, the primary excitation magnetic field induced by the probe coil generates an induced current in the conductor under test, which is called eddy current. The eddy current then generates a secondary induced magnetic field in the opposite direction to the primary excitation magnetic field, which affects the impedance signal of the probe coil. The impedance signal of the probe coil (6-4-4) is then collected by a phase-locked amplifier (3). During the eddy current flow in the injector specimen under test, the eddy current flow is disturbed and abnormal due to the inconsistent depth of the injector electron beam weld. The impedance change of the probe coil as a detection coil reflects the result of the combined effect of the two magnetic fields. The impedance includes resistance R and inductive reactance X. The impedance amplitude is and impedance phase A Lissajous diagram is formed with resistance R as the horizontal coordinate and inductive reactance X as the vertical coordinate. When the melting depth is different, the corresponding resistance R and inductive reactance X are also different. Impedance points corresponding to different melting depths will appear on the Lissajous diagram. Each impedance point has a corresponding different phase θ. The phase is used as the signal characteristic of the melting depth. A melting depth-signal characteristic curve is established. The phase corresponding to the test point, that is, the signal characteristic, is obtained through experiments, and the corresponding melting depth value is extracted from the melting depth-signal characteristic calibration curve, which is the melting depth at the detection point.

2. The eddy current nondestructive testing method for quantitative penetration of liquid rocket engine injector welds according to claim 1, characterized in that: The scanning device (6) comprises an X-axis (6-2), a Y-axis (6-7), a Z-axis (6-1), a rotating table (6-5), a probe mounting plate (6-3), a spring probe (6-4) and a test piece (6-6) of a four-axis scanning table; the spring probe (6-4) is fixed to the probe mounting plate (6-3) of the scanning table by means of screws and nuts, the scanning table path is set according to the different curvatures of the injector weld, the probe coil is fixed to the innermost weld by means of the movement of the scanning table X-axis (6-2), the Y-axis (6-7) and the Z-axis (6-1), so that the probe coil fits the weld surface, and then the rotating table is turned on to rotate the rotating table (5) with the injector to be tested, so as to realize circumferential rapid scanning; on the basis of the circumferential rapid scanning, the test piece (6-6) is fully scanned by first lifting the Z-axis and then moving radially from the inside to the outside at a constant speed to insert into welds with different curvatures for mechanical scanning; both detection accuracy and scanning efficiency are taken into consideration.

3. The eddy current nondestructive testing method for quantitative penetration of liquid rocket engine injector welds according to claim 2, characterized in that: The circumferential rapid scanning speed is selected in the range of 1° / s to 10° / s.

4. The eddy current nondestructive testing method for quantitative penetration of liquid rocket engine injector welds according to claim 2, characterized in that: The spring probe (6-4) comprises a spring coil cover (6-4-5), a rotating head (6-4-1), a spring (6-4-2), a coil frame (6-4-3) and a probe coil (6-4-4). The probe coil (6-4-4) is fixed on the coil frame (6-4-3). The bottom plane of the probe coil is parallel to the weld cross section of the tested piece (6-6). The probe auxiliary spring ensures that the spring (6-4-2) produces the same deformation in each test. According to Hooke's law, the pressure applied to the probe coil (6-4-4) is the same each time, thereby controlling the lifting distance of the probe coil (6-4-4) to be the same in each test, that is, in principle, eliminating the adverse effect of the lifting distance on the test result. At the same time, four-axis mechanical scanning is used to assist in the comprehensive and rapid detection of the weld penetration.

5. The eddy current nondestructive testing method for quantitative penetration of liquid rocket engine injector welds according to claim 4, characterized in that: The probe coil (6-4-4) has one detection coil, an outer diameter of 3.2 mm, an inner diameter of 1.2 mm, a thickness of 0.8 mm, and 140 turns.

6. The method for nondestructive testing of injectors based on the electromagnetic eddy current testing principle according to claim 4 is characterized in that: The rotating head (6-4-1), the coil frame (6-4-3) and the spring coil cover (6-4-5) are all made of non-conductive, non-magnetic plastic or rubber products.

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