A method for defect detection of carbon fiber wound IV type hydrogen storage cylinder
Through the comparison method of microwave detection equipment and reflection coefficient S11, the technical defects of the carbon fiber winding layer defect detection in high-pressure hydrogen storage container are solved, efficient and low-cost defect identification is achieved, and an effective non-destructive detection solution is provided.
Patent Information
- Application Number
- CN202210579069.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2022-05-26
- Publication Date
- 2024-12-13
- Estimated Expiration
- 2042-05-26
AI Technical Summary
There is a lack of effective microwave detection methods in the prior art for non-destructive detection of high-pressure hydrogen storage containers, especially in the detection of defects of carbon fiber winding layer. Other detection methods have problems such as low accuracy, high cost and low efficiency.
Using microwave detection equipment, the reflected signals of standard gas cylinders are collected, the characteristic frequency segment is measured, and the reflected signals of the gas cylinders to be detected are compared. The carbon fiber winding layer is determined by the change curve of the reflection coefficient S11. The difference in the reflection coefficient in the characteristic frequency range determines the type of defect, such as cracks or gaps.
It realizes efficient detection of defects in carbon fiber winding layer, and has the advantages of low detection cost, high efficiency, non-contact, non-destructive and high sensitivity, and can effectively identify defects on gas cylinders.
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Figure CN114813789B_ABST
Abstract
Description
Technical Field
[0001] The invention relates to a defect detection method for a carbon fiber-wound IV-type hydrogen storage cylinder, belonging to the technical field of nondestructive testing. Background Art
[0002] In the entire hydrogen energy industry chain, the storage and transportation of hydrogen is an important link in the development of the hydrogen energy and fuel cell industries. Gaseous high-pressure transportation is currently the most widely used method of hydrogen storage and transportation, and high-pressure hydrogen storage cylinders are the key to ensuring the safe and efficient use of compressed hydrogen. Aluminum alloy liner type cylinders (Type III cylinders) and polymer liner type cylinders (Type IV cylinders) are the mainstream cylinders currently manufactured by fiber composite winding, which are mainly composed of liner and high-performance fiber composite winding layer. The production process of carbon fiber composite hydrogen storage cylinders is relatively complex and has many influencing factors. In order to meet the design pressure and the safety and reliability requirements of subsequent use, each cylinder needs to be non-destructively tested during the manufacturing process, and the cylinders also need to be non-destructively tested regularly during subsequent use.
[0003] The main non-destructive testing methods for high-pressure hydrogen storage containers at home and abroad include visual inspection, X-ray inspection, computer tomography (industrial CT) inspection, ultrasonic inspection, acoustic emission inspection, etc. Visual inspection can only detect the fiber winding condition of the outer wall of the container. X-ray inspection, industrial CT inspection, and ultrasonic inspection are mainly used to detect defects inside the fiber winding layer and its bonding layer with the liner. Among them, the ultrasonic pulse echo method has high accuracy, but can only produce discontinuous two-dimensional plane views within a given depth range; the X-ray inspection method mainly detects volume defects such as inclusions and pores, and cannot effectively detect crack defects; the industrial CT technology has high detection accuracy, but the detection cost is high and the efficiency is low. Acoustic emission detection is only suitable for the detection of dynamic defects such as delamination and resin cracking that can emit acoustic signals. It is ineffective for static defects and has low detection accuracy for single defects.
[0004] Compared with the above-mentioned non-destructive testing technologies, microwave testing has the advantages of non-contact, non-destructive, high sensitivity, and no need for electrical power conversion. However, it has not yet been used in the field of non-destructive testing of high-pressure hydrogen storage containers and lacks specific testing methods. Summary of the invention
[0005] The present invention mainly solves the technical defect of the prior art that there is a lack of microwave detection method for defects of high-pressure hydrogen storage containers, and provides a method for detecting defects of carbon fiber wound IV type hydrogen storage cylinders.
[0006] The present invention solves the above technical problems mainly through the following technical solutions: The present invention uses a microwave detection device and includes the following steps:
[0007] Step 1: Collect the reflection signal of the standard gas cylinder, measure the characteristic frequency band of the standard gas cylinder and obtain the reflection coefficient S11-frequency reference curve;
[0008] Take a carbon fiber-wrapped IV-type hydrogen storage cylinder with the same model as the cylinder to be inspected and without defects as the standard cylinder, place the microwave probe at a distance of 0-2 cm from the outer surface of the standard cylinder, and transmit a microwave signal with a continuously changing frequency to any position point on the standard cylinder within the frequency range of 3-40 GHz, collect and observe the change of the reflected signal, and within this frequency range, take the difference between the maximum and minimum values of the reflected signal amplitude as the extreme difference, select the frequency band corresponding to when the difference between the reflected signal amplitude and the minimum value reaches 90% of the extreme difference as the characteristic frequency band, and obtain the reflection coefficient S11-frequency reference curve according to the change curve of the reflection coefficient S11 of the standard cylinder within the characteristic frequency band;
[0009] Step 2: Collect the reflection signal of the gas cylinder to be inspected and obtain the reflection coefficient S11-frequency detection curve;
[0010] The microwave probe emits microwave signals to the gas cylinder to be inspected at a distance of 0-2 cm from the outer surface of the gas cylinder to be inspected at a frequency that continuously changes within the characteristic frequency band selected in step 1, and collects the reflected signals of the gas cylinder to be inspected. According to the change curve of the reflection coefficient S11 within the characteristic frequency band, the reflection coefficient S11-frequency detection curve of each position point of the gas cylinder to be inspected is obtained;
[0011] Step 3: Compare the reflection coefficient S11-frequency reference curve with the reflection coefficient S11-frequency detection curve to determine whether the carbon fiber winding layer of the gas cylinder to be inspected has defects;
[0012] The reflection coefficient S11-frequency detection curve of each position point of the gas cylinder to be inspected is compared with the reflection coefficient S11-frequency reference curve of the standard gas cylinder, and the difference between the reflection coefficient S11 corresponding to the trough of the reflection coefficient S11-frequency detection curve at a certain position point of the gas cylinder to be inspected and the reflection coefficient S11 corresponding to the trough of the reflection coefficient S11-frequency reference curve of the standard gas cylinder is calculated. When the difference is greater than 3.5dB, it is judged that there is a defect in the carbon fiber winding layer at this position point of the gas cylinder to be inspected.
[0013] Preferably, the resolution of the reflection coefficient S11 is set to 0.01 dB.
[0014] Preferably, in step three, according to the corresponding relationship between the defect and the difference, if the difference is greater than 3.5dB and less than 5dB, it is judged that there is a defect in the carbon fiber winding layer at the position point and the defect is a crack; if the difference is greater than 5.5dB, it is judged that there is a defect in the carbon fiber winding layer at the position point and the defect is a gap.
[0015] The detection method of the present invention is simple and effective, and has the following advantages:
[0016] In the present invention, the defects in the carbon fiber winding layer are regarded as media with different dielectric properties. When microwaves penetrate the carbon fiber winding layer, a certain amount of reflection will occur. If a defect is encountered, the reflection will be significantly enhanced, and the value of the reflection coefficient S11 will change significantly. The formula for calculating the reflection coefficient S11 is as follows:
[0017] Reflection coefficient S11 = 20Lg (VR / VI)
[0018] Among them, VR is the incident microwave signal voltage, and VI is the reflected microwave signal voltage.
[0019] The gas cylinder to be inspected is scanned by microwave detection equipment. When the reflection coefficient S11 corresponding to the trough of the reflection coefficient S11-frequency detection curve at a certain position on the surface of the gas cylinder to be inspected shows a significant change compared with the reflection coefficient S11 corresponding to the trough of the reflection coefficient S11-frequency reference curve of the standard gas cylinder, it can be determined that the carbon fiber winding layer at that position on the gas cylinder to be inspected has defects.
[0020] The first detection step of the present invention is to use a microwave probe to determine the characteristic frequency band of the standard gas cylinder by frequency scanning. The reflection of microwaves is closely related to the dielectric properties of the composite winding layer. In order to facilitate the observation and comparison of the reflection signals of the standard gas cylinder and the gas cylinder to be inspected, the characteristic frequency band of the defect-free standard gas cylinder is determined, which is a prerequisite for the subsequent detection steps; at the same time, the change of the reflection coefficient S11 of the standard gas cylinder in the characteristic frequency band is observed, and the frequency of the characteristic frequency band is used as the horizontal axis, and the reflection coefficient S11 is used as the vertical axis to obtain the change curve of the reflection coefficient S11 in the characteristic frequency band. The change curve is used as the reflection coefficient S11-frequency reference curve for comparison when judging defects later.
[0021] For a standard sample bottle without defects, the reflection coefficient S11-frequency reference curve is displayed as a concave curve with a trough, and the trough value of the reflection coefficient S11 is displayed as a smaller negative value (larger absolute value).
[0022] In detection steps 2 and 3 of the present invention, within the characteristic frequency band determined in step 1, the outer surface of the gas cylinder to be inspected is scanned by a microwave probe at a continuously changing frequency to obtain a reflection coefficient S11-frequency detection curve at each position point on the surface of the bottle body; when the difference between the reflection coefficient S11 corresponding to the trough of the reflection coefficient S11-frequency detection curve at a certain position point and the reflection coefficient S11 corresponding to the trough of the reflection coefficient S11-frequency reference curve of the standard gas cylinder is greater than 3.5dB, it is judged that the gas cylinder to be inspected has a defect at this position point.
[0023] Furthermore, in the above detection steps, the resolution of the reflection coefficient S11 is set to 0.01 dB, which can facilitate the observation and resolution of the change of the reflection coefficient S11, thereby improving the detection efficiency.
[0024] Furthermore, according to the difference between the trough values of the reflection coefficient S11 and the corresponding relationship between the difference and the defect (crack / void), it is determined that the defect existing in the carbon fiber winding layer of the gas cylinder to be inspected is a crack or a void.
[0025] Therefore, the present invention solves the application problem of microwave detection in the field of nondestructive testing of high-pressure hydrogen storage containers and provides a method for defect detection of carbon fiber-wound type IV hydrogen storage cylinders. Compared with other nondestructive testing technologies, the present invention is based on microwave technology and has the advantages of low detection cost, high efficiency, wide detection range, non-contact, non-destructive, high sensitivity, and no need for power conversion. BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG1 is a block diagram of the detection step in the present invention;
[0027] FIG2 is a reflection coefficient S11-frequency detection curve of a certain position point on the gas cylinder to be inspected in a preferred embodiment of the present invention;
[0028] FIG3 is a reflection coefficient S11-frequency detection curve of another position point on the gas cylinder to be inspected in a preferred embodiment of the present invention;
[0029] FIG. 4 is a reflection coefficient S11-frequency reference curve of a standard gas cylinder in a preferred embodiment of the present invention. DETAILED DESCRIPTION
[0030] The technical solution of the present invention is further specifically described below through embodiments and in conjunction with the accompanying drawings.
[0031] Embodiment 1: As shown in FIG. 1 , FIG. 2 , FIG. 3 , and FIG. 4 , the present invention uses a vector network analyzer for detection, the resolution of the reflection coefficient S11 is set to 0.01 dB, and includes the following steps:
[0032] Step 1: Take a carbon fiber-wrapped IV-type hydrogen storage cylinder with the same model as the cylinder to be inspected and without defects as the standard cylinder. The microwave probe of the vector network analyzer is 0-2 cm away from the surface of the standard cylinder. A microwave signal with a continuously changing frequency is emitted to any position point on the standard cylinder. The change of the reflected signal is collected and observed. In the frequency range of 3-40GHz, the difference between the maximum and minimum values of the reflected signal amplitude is taken as the extreme difference. The frequency band corresponding to when the difference between the amplitude of the reflected signal and the minimum value reaches 90% of the extreme difference is selected as the characteristic frequency band, and the characteristic frequency band is determined to be 9.2-10.2GHz; The change curve of the reflection coefficient S11 of the standard cylinder body in the frequency range of 9.2-10.2GHz is taken as the reflection coefficient S11-frequency reference curve (as shown in Figure 4). The curve shows that the trough value of the reflection coefficient S11 is -18.88dB;
[0033] Step 2: The microwave probe of the vector network analyzer is 0-2 cm away from the surface of the gas cylinder to be inspected, and the frequency of the continuously changing characteristic frequency range of 9.2-10.2GHz determined in step 1 is used to scan various positions of the gas cylinder to be inspected, and the reflection signal of the gas cylinder to be inspected is collected to obtain the reflection coefficient S11-frequency detection curve of each position of the gas cylinder to be inspected; wherein, the reflection coefficient S11-frequency detection curve of a certain position of the gas cylinder to be inspected is shown in FIG2, and the curve shows that the trough value of the reflection coefficient S11 is -9.79dB; the reflection coefficient S11-frequency detection curve of another position of the gas cylinder to be inspected is shown in FIG3, and the curve shows that the trough value of the reflection coefficient S11 is -15.03dB;
[0034] Step 3: Compare the reflection coefficient S11-frequency detection curve of each position point on the gas cylinder to be inspected with the reflection coefficient S11-frequency reference curve of the standard gas cylinder, calculate the difference between the reflection coefficient S11 corresponding to the trough of the reflection coefficient S11-frequency detection curve of a certain position point of the gas cylinder to be inspected and the reflection coefficient S11 corresponding to the trough of the reflection coefficient S11-frequency reference curve of the standard gas cylinder, and judge whether there is a defect at the corresponding position point of the gas cylinder to be inspected and the type of defect according to the difference;
[0035] Compared with the reflection coefficient S11-frequency detection curve shown in Figure 2 and the reflection coefficient S11-frequency reference curve of the standard gas cylinder, the difference in the reflection coefficient S11 trough value between the two is 9.09 dB, which is greater than 3.5 dB, and it is judged that there is a defect at this position. Since the difference is greater than 5.5 dB, it is further judged that the defect at this position of the gas cylinder to be inspected is a gap;
[0036] The reflection coefficient S11-frequency detection curve shown in Figure 3 is compared with the reflection coefficient S11-frequency reference curve of the standard gas cylinder. The difference in the reflection coefficient S11 trough value between the two is 3.85dB. The difference is greater than 3.5dB, so it is judged that there is a defect at this position. Since the difference is greater than 3.5dB but less than 5dB, it is judged that the defect at this position of the gas cylinder to be inspected is a crack.
[0037] Of course, the above-mentioned drawings and embodiments are only used to explain and illustrate the present invention, and cannot be used as improper limitations of the present invention. Any technical solutions obtained by those skilled in the art making equivalent adjustments and changes based on the present invention fall within the protection scope of the present invention.
Claims
1. A method for detecting defects in carbon fiber-wound type IV hydrogen storage cylinders, characterized in that: Using microwave testing equipment and including the following steps: Step 1: Collect the reflected signal of the standard gas cylinder, measure the characteristic frequency band of the standard gas cylinder and obtain the reflection coefficient S 11 -Frequency reference curve; Take a carbon fiber-wrapped IV type hydrogen storage cylinder with the same model as the cylinder to be inspected and without defects as the standard cylinder, place a microwave probe at a distance of 0-2 cm from the outer surface of the standard cylinder, and transmit a microwave signal with a continuously changing frequency to any position point on the standard cylinder within a frequency range of 3-40 GHz. Collect and observe the change of the reflected signal. Within this frequency range, the difference between the maximum and minimum values of the reflected signal amplitude is taken as the extreme difference. The frequency segment corresponding to the difference between the reflected signal amplitude and the minimum value reaching 90% of the extreme difference is selected as the characteristic frequency segment. According to the reflection coefficient S of the standard cylinder, the characteristic frequency segment is selected as the characteristic frequency segment. 11 The change curve in the characteristic frequency band is used to obtain the reflection coefficient S 11 -Frequency reference curve; Step 2: Collect the reflection signal of the gas cylinder to be inspected and obtain the reflection coefficient S 11 -Frequency detection curve; The microwave probe is located 0-2 cm away from the outer surface of the gas cylinder to be inspected, and transmits a microwave signal to the gas cylinder to be inspected at a frequency that continuously changes within the characteristic frequency band selected in step 1, and collects the reflected signal of the gas cylinder to be inspected. 11 The change curve within the characteristic frequency range is used to obtain the reflection coefficient S of each position point on the gas cylinder to be inspected. 11 -Frequency detection curve; Step 3: Compare the reflection coefficient S 11 -Frequency reference curve vs. the reflection coefficient S 11 - Frequency detection curve, to determine whether there are defects in the carbon fiber winding layer of the gas cylinder to be inspected; The reflection coefficient S of each position point of the gas cylinder to be inspected is 11 - Frequency detection curve and reflection coefficient S of the standard gas cylinder 11 - Compare with the frequency reference curve to calculate the reflection coefficient S of a certain position of the gas cylinder to be inspected 11 -The reflection coefficient S corresponding to the trough of the frequency detection curve 11 The reflection coefficient S of the standard gas cylinder 11 -Reflection coefficient S corresponding to the trough of the frequency reference curve 11 When the difference is greater than 3.5 dB, it is determined that there is a defect in the carbon fiber winding layer at that position of the gas cylinder to be inspected.
2. According to claim 1, a carbon fiber wound IV type hydrogen storage cylinder defect detection method is characterized in that: Reflection coefficient S 11 The resolution is set to 0.01dB.