Eddy current nondestructive testing method for quantitative penetration of liquid rocket engine injector welds

Abstract

The present invention relates to an eddy current nondestructive testing method for quantitatively measuring the penetration depth of liquid rocket engine injector welds. The principle is that when a probe coil carrying an alternating current approaches the weld surface, the primary excitation magnetic field induced by the probe coil generates an induced current in the conductor being tested, referred to as an eddy current. The eddy current then generates a secondary induced magnetic field in the opposite direction of the primary magnetic field, affecting the coil impedance signal. By analyzing the change in this impedance, defect information and quantitative analysis of the conductor being tested can be obtained. The present invention utilizes a spring-shaped, self-excited, self-testing probe coil concentrically arranged on the injector weld ring, as well as an eddy current testing experimental system, assisted by a four-axis mechanical scanning device. The method of the present invention can effectively evaluate welds with complex surface shapes and internal surface defects, has better detection capabilities and sensitivity, and has the advantages of high detection rate, fast detection speed, and high efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of eddy current testing, and in particular to an eddy current non-destructive testing method for quantitatively measuring the penetration depth of a liquid rocket engine injector weld. Background Art

[0002] Liquid rocket engine injectors consist of an injector disc welded to multiple injector rings of varying sizes, typically made of stainless steel. Each nozzle ring is connected to the injector disc by two electron beam welds, one on the inner and one on the outer sides. The center-to-center spacing between adjacent welds is approximately 2 mm, and there is a residual height on the welded surface. The quality of electron beam welding determines the structural integrity and reliability of the injector, and is crucial for the safe and stable operation of liquid rocket engines. Therefore, high-precision testing of the injector weld penetration is crucial.

[0003] At present, the main methods used to detect weld penetration include eddy current testing, radiographic testing, and ultrasonic testing. 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 testing. In addition, the spacing between electron beam welds is narrow, and there are injection holes of different diameters around them, which is not conducive to the use of oblique incidence ultrasonic testing technology. At the same time, the diameter and thickness of the injection disk are large, and it is made of stainless steel. It is difficult for the microfocus 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 testing method. The detection probe is small in size and has a diverse and flexible configuration. It can realize non-destructive testing in a small 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 a test coil carrying an alternating current is brought close to a conductive test piece, eddy currents are induced in the test piece. These eddy currents, in turn, affect the original magnetic field, causing changes in the impedance of the test coil and the induced voltage. By analyzing these changes in impedance or induced voltage, information about defects in the conductor can be obtained and quantitatively analyzed. 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 liquid rocket engine injector welds. 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, and the data acquisition device 4 is connected to the phase-locked amplifier 3. A sinusoidal signal is applied to the probe coil 6-4-4 through the signal generator 1 and the power amplifier 2. Since the electromagnetic induction 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 causes 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 process of generating 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 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 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 is used as the signal characteristic of the penetration depth. A penetration depth-signal characteristic curve is established. The phase corresponding to the test point, i.e., the signal characteristic, is obtained through experiments. The corresponding penetration depth value is extracted from the penetration depth-signal characteristic calibration curve, which is the penetration 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, the Z-axis is first lifted and then radially moved at a constant speed from the inside to the outside to insert into welds of different curvatures for mechanical scanning to achieve a comprehensive scanning of the test piece 6-6 to be tested; taking into account both detection accuracy and scanning efficiency.

[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 results; 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 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.

[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 principle of conventional electromagnetic eddy current testing to the non-destructive testing of injector welds. The eddy current probe has a small coil size and a variety of flexible configurations, which solves the difficulty of testing in the narrow space environment of the injector.

[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, greatly improving 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 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 will be further described in detail below with reference to the accompanying drawings and embodiments.

[0023] Combine 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 to the primary excitation magnetic field, affecting the impedance signal of the probe coil. During the eddy current flow in the injector specimen under test, the eddy current flow is disturbed and abnormalities occur due to the inconsistent depth of the injector electron beam weld; the impedance change of the probe coil as the detection coil is then 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 A Lissajous diagram is formed with resistance R as the horizontal axis and inductive reactance X as the vertical axis. Different penetration depths correspond to different resistance R and inductive reactance X, resulting in impedance points corresponding to different penetration depths on the Lissajous diagram. Each impedance point has a corresponding phase θ, which can be used as a characteristic of penetration depth to construct a penetration-signal characteristic curve. Experimental analysis reveals the phase, or signal characteristic, corresponding to the test point. The corresponding penetration value, extracted from the penetration-signal characteristic calibration curve, represents the penetration depth at the test point. Furthermore, the probe auxiliary spring ensures the same spring deformation during each test. According to Hooke's law, the pressure on the probe coil remains the same each time, ensuring the same lift-off distance for each test. This, in principle, eliminates the adverse effects of lift-off distance on test results. Simultaneously, four-axis mechanical scanning is used to assist in comprehensive and rapid weld penetration testing.

[0024] The following combination Figure 1 、 Figure 2 、 Figure 3 、 Figure 4 The present invention is further described in detail with reference to specific examples.

[0025] like Figure 1As shown, the experimental system for the eddy current nondestructive testing method of this embodiment includes a signal generator 1, a power amplifier 2, a lock-in amplifier 3, a data acquisition device 4, a differential amplifier 5, and a scanning device 6. The signal generator 1 is connected to the power amplifier 2 and the lock-in 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 lock-in amplifier 3. The data acquisition device 4 is connected to the lock-in amplifier 3. The signal generator 1 first generates a 100 kHz sinusoidal signal as a driving signal input to the power amplifier 2, providing sufficient current to drive the probe coil. The probe coil generates an alternating magnetic field. When it approaches the object being tested, it generates an induced current through the eddy current effect. The eddy current changes in the object being tested are fed back to the probe coil, generating a weak response signal. This signal is transmitted to the lock-in amplifier 3, which compares the phase with the reference signal to extract the response signal at the target frequency, thereby improving the signal-to-noise ratio. The extracted signal is then fed into a differential amplifier 5, which amplifies the difference signal between the probe coils and suppresses common-mode noise, further enhancing signal contrast. Finally, a 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 includes 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 rotary table is turned on to rotate the rotary table 5 with the injector to be tested to achieve rapid circumferential scanning; on the basis of the said rapid circumferential scanning, the Z-axis is first lifted off and then radially moved at a constant speed from the inside to the outside 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, spring probe 6-4 comprises a spring coil housing 6-4-5, a rotating head 6-4-1, a spring 6-4-2, a coil bobbin 6-4-3, and a coil 6-4-4. Probe coil 6-4-4 is secured to the lower portion of coil bobbin 6-4-3 and connected to rotating head 6-4-1 via spring 6-4-2. Together, the probe coil 6-4-4 is rotated into spring coil housing 6-4-5. The electronic wire is connected to probe coil 6-4-4 and then passes through the central hole of rotating head 6-4-1 to connect to the experimental system. The upper hole of spring coil housing 6-4-5 is aligned and secured with the hole on probe mounting plate 6-3 in scanning device 6 using screws and nuts. The bottom plane of the probe coil is parallel to the weld cross-section of test piece 6-6. The probe coil 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, providing the highest sensitivity to penetration signal results. The probe's auxiliary spring ensures that the spring 6-4-2 experiences the same deformation during each test. According to Hooke's law, the coil is subjected to the same pressure each time, thus ensuring the same lift-off distance for each test. This fundamentally eliminates the adverse effect of lift-off distance on test results. Simultaneously, four-axis mechanical scanning enables comprehensive and rapid testing of weld penetration.

[0028] like Figure 4 As shown in the figure, 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 groove.

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

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

[0031] 2) At the same time, the scanning platform path is set according to the different curvatures of the injector weld. The probe coil is fixed to the innermost weld by moving the scanning platform along the X, Y, and Z axes, so that the probe coil fits the weld surface.

[0032] 3) A 100 kHz excitation voltage is applied to the probe coil via the signal generator 1, and then the rotating table 6-5 is turned on, causing the rotating table 6-5 to rotate with the test piece 6-6 to achieve circumferential scanning;

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

[0034] 5) After completing the above detection process, the real resistance R and imaginary reactance X of the detection signal of different welds are intercepted, and a rectangular coordinate system (impedance plane diagram / Lissajous figure) is formed with resistance R as the horizontal coordinate and reactance 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 manifested on the impedance plane diagram: due to various factors causing the change in the eddy current signal component - resistance R or reactance X value, the eddy current detection signal vector point on the impedance plane diagram will shift accordingly. The amplitude of the eddy current signal after the point shifts and phase The weld penetration is determined by analyzing the changes in amplitude and phase to calibrate the curve. Figure 6 .

[0035] In this embodiment of the present invention, the workpiece to be electron beam welded is the injector of a certain type of aerospace engine. The workpiece is made of stainless steel and has a disc-shaped structure. It is formed by electron beam welding the injector disc and several injector rings. The welds are butt welds. To ensure safety, each weld must have a penetration depth of at least 1.1 mm. As a preferred embodiment of the present invention, the rotating head 6-4-1, coil bobbin 6-4-3, and spring coil cover 6-4-5 are all made of non-conductive, non-magnetic plastic or rubber, so they do not affect the magnetic field generated by the probe coil.

Claims

1. A method for quantitative eddy current nondestructive testing of liquid rocket engine injector weld penetration, characterized by: 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 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 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 electromagnetic induction alternating current is generated in the The probe coil of the excitation coil induces a changing magnetic field around it, 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 being measured, 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 a phase-locked amplifier (3). During the eddy current flow in the injector specimen being measured, 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. 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 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 is used as the signal characteristic of the penetration depth. A penetration depth-signal characteristic curve is established. The phase corresponding to the test point, i.e., the signal characteristic, is obtained through experiments. The corresponding penetration depth value is extracted from the penetration depth-signal characteristic calibration curve, which is the penetration 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 with 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 relying on the movement of the scanning table X-axis (6-2), Y-axis (6-7) and 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 (6-5) with the injector to be tested, so as to realize circumferential rapid scanning; on the basis of the circumferential rapid scanning, the Z-axis is first lifted and then radially moved at a constant speed from the inside to the outside to insert into welds with different curvatures for mechanical scanning to realize comprehensive scanning of the test piece (6-6) to be tested, and 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 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 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 realizing comprehensive and rapid detection of 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 eddy current nondestructive testing method for quantitative penetration of liquid rocket engine injector welds according to claim 4, characterized in that: 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.

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