Quantitative evaluation method for fatigue damage of steel gas cylinder based on nonlinear ultrasonic data driving

Abstract

The invention discloses a steel gas cylinder fatigue damage quantitative evaluation method based on nonlinear ultrasonic data driving, which can determine the change of the nonlinear coefficient of a factory or in-service steel gas cylinder made of the same material through nonlinear ultrasonic detection, and fit different inflation and deflation times and relative nonlinear coefficients to obtain the fatigue damage quantitative evaluation result of the steel gas cylinder. And drawing a change curve of the relative nonlinear coefficient along with the inflation and deflation times, wherein the change curve is used for quantitative evaluation of the damage of the seamless steel cylinder in the whole life cycle. The change of the nonlinear ultrasonic coefficient corresponds to the evolution of the internal microstructure, so that the fatigue degree of the steel cylinder is quantified through the nonlinear coefficient, and technical support is provided for safety supervision of the whole life cycle of the gas cylinder.

Description

Technical Field

[0001] The invention relates to the technical field of nondestructive testing of steel gas cylinders, and in particular to a quantitative evaluation method for fatigue damage of steel gas cylinders based on nonlinear ultrasonic technology. Background Art

[0002] Steel gas cylinders are important high-pressure containers and are widely used for gas storage and transportation. However, they are exposed to high pressure and periodic loads for a long time, which makes them susceptible to fatigue damage, gradually forming microcracks or even macrocracks, posing serious safety hazards. Traditional non-destructive testing technologies (such as ultrasonic, X-ray and magnetic particle testing) have limited sensitivity to early fatigue damage, and are particularly difficult to detect microstructural changes or microcracks inside gas cylinders, resulting in problems with gas cylinders being discovered only after they have lost most of their safety reserves.

[0003] In recent years, nonlinear ultrasonic technology has been proven to be an effective method for detecting metal fatigue damage. It is based on the high-order harmonic effect of sound wave propagation, is very sensitive to changes in the microstructure of the material, and can detect phenomena such as dislocations and grain boundary slip earlier, thereby achieving accurate quantification of fatigue damage. Summary of the invention

[0004] In view of the problems existing in the prior art, the present invention provides a quantitative evaluation method for fatigue damage of gas cylinders based on nonlinear ultrasound, so as to improve the ability of early identification and accurate quantification of damage, and provide technical support for the safe management of gas cylinders.

[0005] The present invention is implemented as follows: a method for quantitatively evaluating fatigue damage of steel gas cylinders based on nonlinear ultrasonic data driving, comprising the following steps:

[0006] (1) Select gas cylinders without defects when leaving the factory, and obtain the material parameters and structural parameters related to the gas cylinders;

[0007] (2) Based on the structural parameters and material parameters of the gas cylinder, the dispersion equation of the circumferentially guided wave is established using the elastic wave theory, the dispersion equation is solved, and the dispersion curve of the circumferentially guided wave is plotted;

[0008] (3) Determine the excitation frequency by the point in the dispersion curve where the fundamental frequency and the second harmonic frequency have the same phase velocity;

[0009] (4) Determine the incident angle of the sound wave according to Snell's law and design the sensor wedge;

[0010] (5) Fix the sensor wedge on the gas cylinder, perform nonlinear ultrasonic testing on the gas cylinder leaving the factory as an initial reference, and test the gas cylinders that have been filled and deflated for different times, and calculate the relative nonlinear coefficient;

[0011] (6) The above-mentioned different filling and deflation times and relative nonlinear coefficients are fitted, and a curve of the relative nonlinear coefficient changing with the filling and deflation times is drawn for quantitative evaluation of the damage of seamless steel cylinders throughout their life cycle.

[0012] In step (1), selecting defect-free gas cylinders before leaving the factory means that the gas cylinders to be shipped are subjected to visual inspection, 100% ultrasonic inspection and 100% magnetic particle inspection, and there are no defects inside or outside.

[0013] In step (5), the sensor is fixed on the gas cylinder with an inclined wedge. First, nonlinear ultrasonic testing is performed on the gas cylinders leaving the factory in different areas. Then, the nonlinear ultrasonic testing is performed again after the gas cylinders have been in service for a period of time. Through multiple tests, the nonlinear coefficients of the gas cylinders at different filling and deflation times and different fatigue levels are obtained, and compared with the original nonlinear coefficients to obtain the normalized relative acoustic nonlinear coefficients.

[0014] The advantages and technical effects of the present invention are as follows: the quantitative evaluation of the fatigue degree of steel gas cylinders intuitively reflects the cumulative state of gas cylinder damage through the normalized nonlinear coefficient, provides a clear law of fatigue damage evolution, facilitates the formulation of scientific maintenance plans for gas cylinders, reduces failure risks, and improves the safety and reliability of gas cylinder use. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a flow chart of the present invention;

[0016] Figure 2 is the dispersion curve of the circumferential mode of the gas cylinder of the embodiment of the present invention (a. phase velocity; b. group velocity);

[0017] Figure 3 is a schematic diagram of fixing a sensor according to an embodiment of the present invention;

[0018] Figure 4 is a gas cylinder detection position selection diagram of an embodiment of the present invention;

[0019] Figure 5 is a diagram of an original ultrasonic signal and an ultrasonic signal modulated by a Hanning window according to an embodiment of the present invention;

[0020] Figure 6 is a fast Fourier transform result diagram of an embodiment of the present invention;

[0021] Figure 7 is a variation curve of the nonlinear coefficient (β') before and after fatigue at five positions of the gas cylinder according to an embodiment of the present invention;

[0022] Figure 8 is a normalized nonlinear coefficient histogram of an embodiment of the present invention. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation methods described herein are only used to explain the present invention and are not used to limit the present invention.

[0024] like Figure 1 As shown, the fatigue damage quantitative evaluation method of steel gas cylinders based on nonlinear ultrasonic data driving of the present invention comprises the following steps:

[0025] (1) Select gas cylinders without defects when leaving the factory, and obtain the material parameters and structural parameters related to the gas cylinders;

[0026] (2) Based on the structural parameters and material parameters of the gas cylinder, the dispersion equation of the circumferentially guided wave is established using the elastic wave theory, the dispersion equation is solved, and the dispersion curve of the circumferentially guided wave is plotted;

[0027] (3) Determine the excitation frequency by the point in the dispersion curve where the fundamental frequency and the second harmonic frequency have the same phase velocity;

[0028] (4) Determine the incident angle of the sound wave according to Snell's law and design the sensor wedge;

[0029] (5) Fix the sensor wedge on the gas cylinder, perform nonlinear ultrasonic testing on the gas cylinder leaving the factory as an initial reference, and test the gas cylinders that have been filled and deflated for different times, and calculate the relative nonlinear coefficient;

[0030] (6) The above-mentioned different filling and deflation times and relative nonlinear coefficients are fitted, and a curve of the relative nonlinear coefficient changing with the filling and deflation times is drawn for quantitative evaluation of the damage of seamless steel cylinders throughout their life cycle.

[0031] In step (1), selecting defect-free gas cylinders before leaving the factory means that the gas cylinders to be shipped are subjected to visual inspection, 100% ultrasonic inspection and 100% magnetic particle inspection, and there are no defects inside or outside.

[0032] In step (5), the sensor is fixed on the gas cylinder with an inclined wedge. First, nonlinear ultrasonic testing is performed on the gas cylinders leaving the factory in different areas. Then, the nonlinear ultrasonic testing is performed again after the gas cylinders have been in service for a period of time. Through multiple tests, the nonlinear coefficients of the gas cylinders at different filling and deflation times and different fatigue levels are obtained, and compared with the original nonlinear coefficients to obtain the normalized relative acoustic nonlinear coefficients.

[0033] Specifically, first of all, the gas cylinders to be shipped should be visually inspected, 100% ultrasonically inspected, and 100% magnetic particle inspected. There should be no defects inside and outside. The structural parameters and material parameters of the gas cylinders should be clarified first. As a typical complex structure, the gas cylinder has a cylindrical body and is generally prone to axial cracking in the body. Therefore, ultrasonic circumferential waveguide is used to detect its fatigue damage. After selecting the circumferential waveguide mode, the dispersion curve of the circumferential waveguide is calculated according to the structural parameters and material parameters of the gas cylinder. The excitation condition of nonlinear ultrasonic guided waves must satisfy that the group velocity and phase velocity of the fundamental wave and the second harmonic are equal. Therefore, according to the dispersion curve of the circumferential waveguide mode, the modal parameters of the group velocity and phase velocity of the fundamental wave and the second harmonic are found and applied to the actual detection. Determine the excitation frequency and determine the incident angle of the sound wave according to Snell's law. This step is to optimize the propagation path of the sound wave inside the gas cylinder. By selecting a suitable incident angle, it can be ensured that the sound wave effectively enters the steel gas cylinder and propagates in the material in an appropriate manner, thereby enhancing the sensitivity to damage. The sensor fixture wedge is designed according to the incident angle. This optimized design can maximize the signal-to-noise ratio of the detection, making the characteristics of fatigue damage more obvious, thereby improving the accuracy and reliability of the detection. The sensor wedge is fixed on the gas cylinder. First, the gas cylinder leaving the factory is subjected to nonlinear ultrasonic testing in different areas. Then, it is subjected to nonlinear ultrasonic testing again after being in service for a period of time. Through multiple tests, the nonlinear coefficient of the gas cylinder under different filling and discharging times and different fatigue levels is obtained, and compared with the original nonlinear coefficient, the normalized relative ultrasonic nonlinear coefficient is obtained. The change of the relative nonlinear coefficient is used to characterize the fatigue degree of the cylinder and to quantify fatigue damage.

[0034] The present invention can determine the change of the nonlinear coefficient of steel gas cylinders made of the same material that have left the factory or are in service through nonlinear ultrasonic testing. The change of the nonlinear ultrasonic coefficient also corresponds to the evolution of its internal microstructure. Therefore, the fatigue degree of the steel cylinder can be quantified by the nonlinear coefficient, providing technical support for the safety supervision of the gas cylinder throughout its life cycle.

[0035] Below, taking a seamless steel cylinder with a tensile strength of more than 1100 MPa as an example, a quantitative evaluation method for fatigue damage of steel gas cylinders based on nonlinear ultrasonic data driving is introduced.

[0036] 1. Preparation before testing

[0037] (1) Check the status of the gas cylinder

[0038] For seamless steel gas cylinders that have left the factory or are in service, they are first subjected to visual inspection, 100% ultrasonic inspection, and 100% magnetic particle inspection to ensure that there are no defects inside and outside the gas cylinders. Confirm the structural parameters (such as diameter, wall thickness) and material parameters (such as elastic modulus, density) of the gas cylinder. The material of the experimental gas cylinder is 34CrMo4, the bottle body diameter is 140±1.4mm, the wall thickness is 4mm, the tensile strength is 1100-1220MPa, the Young's modulus is ≥970MPa, and the Poisson's ratio is 0.29-0.30.

[0039] (2) Surface treatment

[0040] Before testing, clean the surface of the gas cylinder to remove impurities such as oil, dust, etc. to ensure the normal transmission of sound waves and reduce the interference of external factors on the ultrasonic signal.

[0041] 2. Preparation for nonlinear ultrasonic testing

[0042] (1) Circumferential waveguide mode selection

[0043] Since the gas cylinder structure is in the shape of a circular tube and is prone to axial cracking, the propagation characteristics of the circumferential guided wave mode are studied for fatigue damage detection. According to the material parameters (density, Young's modulus, Poisson's ratio) and structural dimensions (inner diameter, outer diameter, wall thickness) of the gas cylinder, the dispersion equation of the circumferential guided wave is established using the elastic wave theory. By solving the dispersion equation, the relationship between the phase velocity and group velocity and the frequency is calculated, and the dispersion curve of the guided wave is drawn to further analyze the propagation characteristics of the fundamental wave and the second harmonic, and guide the selection and optimization of damage detection parameters.

[0044] (2) Determination of excitation conditions

[0045] In order to determine the optimal excitation conditions for ultrasonic guided waves, the frequency point at which the group velocity and phase velocity at the fundamental frequency match the group velocity and phase velocity at the second harmonic frequency is selected to maximize the generation efficiency of the second harmonic and ensure its propagation characteristics are optimized. Figure 2 As shown), and adjust the sound wave frequency to determine the appropriate excitation frequency parameters. When the excitation frequency is 0.56MHz, 0.95MHz, 1.13MHz, 1.28MHz, 1.34MHz, 1.41MHz, and 1.7MHz, the phase velocity and group velocity matching conditions of the fundamental wave and the second harmonic are met, so the above frequencies can be used as experimental conditions. In this experiment, 1.13MHz is selected as the excitation frequency for nonlinear ultrasonic testing of gas cylinders.

[0046] (3) Sensor wedge fixture design

[0047] Design and manufacture a suitable sensor fixture based on the determined sound wave propagation path. The sensor fixture is made of organic glass material, and its design must meet the requirements of the sound wave incident angle. The sound wave incident angle is determined according to Snell's law to ensure that the sensor can be stably fixed at the specified position on the outer wall of the gas cylinder. The angle of contact between the sensor and the gas cylinder is optimized by the wedge, so that the sound wave can be effectively coupled into the gas cylinder.

[0048] Snell's law: sinα=ν / ν p , v represents the speed of sound in organic glass, which is measured to be 2732 m / s, v p represents the phase velocity at the excitation frequency. From the dispersion curve, it can be concluded that the phase velocity at 1.13MHz is 4686.55m / s. According to Snell's law, it can be calculated that the acoustic wave incident angle α is 35.68°.

[0049] After determining the incident angle of the sound wave, the sensor fixture wedge is designed. The wedge must ensure that the incident angle of the sensor-excited sound wave is 35.68° and that it can be stably fixed on the outer wall of the gas cylinder. Since the outer wall of the gas cylinder is an arc surface with a diameter of 140 mm, the surface where the wedge contacts the gas cylinder should also be designed to match the outer wall of the gas cylinder and be able to slide along the arc of the outer wall of the gas cylinder to facilitate the adjustment of the specific position of the sensor.

[0050] (4) Sensor fixing

[0051] Install the calibrated ultrasonic sensor at a specific circumferential position of the gas cylinder to ensure the accuracy and repeatability of the installation position so that the data can be compared during multiple tests. The installation position of the sensor should remain constant to avoid affecting the test results due to position changes.

[0052] Figure 3 In the figure, 1 represents the outer surface of the gas cylinder, 2 is the transmitting sensor, 3 is the receiving sensor, 4 and 5 represent the wedges of the organic glass sensor fixture, and the bottom of the wedge is a curved surface, which can be well coupled with the bottle body through the coupling agent.

[0053] 3. Nonlinear ultrasonic testing process

[0054] (1) Detection location selection

[0055] According to the structural dimensions of the gas cylinder, the body of the gas cylinder is divided into five equally spaced detection parts, marked as 1, 2, 3, 4, and 5. Each detection part is divided into three parts according to the circumference and marked as a, b, and c. For example, when the transmitting sensor is placed at position a, the position b or c can be set as the receiving sensor position to receive ultrasonic signals. Nonlinear ultrasonic testing is performed on each part separately to obtain different responses to fatigue damage at different positions of the gas cylinder.

[0056] (2) Excitation fundamental wave

[0057] At any detection position, the transmitting sensor is an Olympus sensor (A102S-RB) with a center frequency of 1MHz. The transmitting sensor excites ultrasonic waves with a frequency of 1.13MHz. The sound waves enter the gas cylinder through the organic glass wedge. When the fundamental wave propagates in the gas cylinder, due to the interaction with the microscopic defects of the material, part of the energy will be converted into high-order harmonics, and finally received by the receiving sensor, which is an Olympus sensor (V104-RB) with a center frequency of 2.25MHz.

[0058] (3) Collecting the second harmonic

[0059] The ultrasonic signal propagated inside the gas cylinder is collected by receiving sensors, and a high-speed data acquisition card and an oscilloscope are used for real-time monitoring to record the time domain waveform data of the ultrasonic signal.

[0060] (4) Nonlinear ultrasonic testing at different locations

[0061] Nonlinear ultrasonic testing is performed on different positions to obtain nonlinear coefficients at different positions.

[0062] 4. Data processing and analysis

[0063] (1) Signal denoising and extraction

[0064] The collected ultrasonic signal time domain waveform data is modulated by Hanning window to reduce spectrum leakage, eliminate waveform edge discontinuity, reduce the impact of wall thickness unevenness, improve the reliability of signal processing and further eliminate interference from other modes. Finally, the waveform is subjected to fast Fourier transform (FFT) to extract its frequency domain characteristics, determine the corresponding relationship between frequency and amplitude, and calculate the nonlinear coefficient of different positions of the cylinder under different conditions. Figure 5 , 6 .

[0065] (2) Calculation of nonlinear coefficients

[0066] The nonlinear coefficient is calculated according to the formula: Among them, A (2w) is the amplitude of the second harmonic, A (w) is the amplitude of the fundamental wave.

[0067] The nonlinear coefficient (β') variation curves of the five positions of the cylinder before and after fatigue are shown in Figure 7 .

[0068] (3) Calculation of normalized nonlinear coefficient

[0069] Compare the nonlinear coefficient β in the initial state and calculate the normalized nonlinear coefficient β' under different usage cycles: The change of β' value can reflect the progress of fatigue damage inside the cylinder.

[0070] The normalized nonlinear coefficient is Figure 8 .

[0071] 5. Quantitative evaluation of fatigue damage driven by nonlinear ultrasonic data

[0072] The normalized nonlinear coefficient obtained by the test is correlated with the number of times the gas cylinder is filled and discharged, and a curve showing the change of the nonlinear coefficient with the use cycle is drawn. The changing trend of the curve can be used to determine the development rate of fatigue damage of the gas cylinder and the remaining service life.

[0073] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A quantitative evaluation method for fatigue damage of steel gas cylinders based on nonlinear ultrasonic data driving, characterized in that: The following steps are involved: (1) Select gas cylinders without defects when leaving the factory, and obtain the material parameters and structural parameters related to the gas cylinders; (2) Based on the structural parameters and material parameters of the gas cylinder, the dispersion equation of the circumferentially guided wave is established using the elastic wave theory, the dispersion equation is solved, and the dispersion curve of the circumferentially guided wave is plotted; (3) Determine the excitation frequency by the point in the dispersion curve where the fundamental frequency and the second harmonic frequency have the same phase velocity; (4) Determine the incident angle of the sound wave according to Snell's law and design the sensor wedge; (5) Fix the sensor wedge on the gas cylinder, perform nonlinear ultrasonic testing on the gas cylinder leaving the factory as an initial reference, and test the gas cylinders that have been filled and deflated for different times, and calculate the relative nonlinear coefficient; (6) The above-mentioned different filling and deflation times and relative nonlinear coefficients are fitted, and a curve of the relative nonlinear coefficient changing with the filling and deflation times is drawn for quantitative evaluation of the damage of seamless steel cylinders throughout their life cycle.

2. The method for quantitatively evaluating fatigue damage of steel gas cylinders based on nonlinear ultrasonic data driving according to claim 1 is characterized in that: In step (1), selecting defect-free gas cylinders before leaving the factory means that the gas cylinders to be shipped are subjected to visual inspection, 100% ultrasonic inspection and 100% magnetic particle inspection, and there are no defects inside or outside.

3. The method for quantitatively evaluating fatigue damage of steel gas cylinders based on nonlinear ultrasonic data driving according to claim 1 is characterized in that: In step (5), the sensor is fixed on the gas cylinder with an inclined wedge. First, nonlinear ultrasonic testing is performed on the gas cylinders leaving the factory in different areas. Then, the nonlinear ultrasonic testing is performed again after the gas cylinders have been in service for a period of time. Through multiple tests, the nonlinear coefficients of the gas cylinders at different filling and deflation times and different fatigue levels are obtained, and compared with the original nonlinear coefficients to obtain the normalized relative acoustic nonlinear coefficients.

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