A defect detection method for carbon fiber wound type III hydrogen storage cylinder

Abstract

The present invention relates to a method for detecting defects in a carbon fiber-wound type III hydrogen storage cylinder, and belongs to the field of nondestructive testing. The present invention comprises the following steps: Step 1: Using a microwave detection device to measure the characteristic frequency band of a standard cylinder by frequency sweeping and obtain the reflection coefficient S 11 ‑Frequency reference curve; Step 2: Transmit microwave signals to the gas cylinder to be inspected at a frequency within the characteristic frequency band to obtain the reflection coefficient S 11 ‑Frequency detection curve; Step 3: Compare reflection coefficient S 11 ‑Frequency reference curve and reflection coefficient S 11 ‑Frequency detection curve, based on the reflection coefficient S 11 The reflection coefficient S corresponding to the trough of the frequency detection curve 11 and reflection coefficient S 11 ‑The reflection coefficient S corresponding to the trough of the frequency reference curve 11 The present invention uses a microwave detection method to detect defects in carbon fiber-wound type III hydrogen storage cylinders, which is simple and effective, and has the advantages of non-contact, non-destructive, high sensitivity, and no need for electrical quantity conversion.

Description

Technical Field

[0001] The invention relates to a method for detecting defects of a carbon fiber wound type III 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 inner 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, high detection cost, and low efficiency. Acoustic emission testing 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 type III 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 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;

[0008] Specifically, a defect-free carbon fiber-wrapped type III hydrogen storage cylinder of the same model as the cylinder to be inspected is taken as the standard cylinder, and the microwave probe is placed 0-2 cm away from the outer surface of the standard cylinder. A microwave signal with a continuously changing frequency is emitted to any position of the standard cylinder within the frequency range of 3-40 GHz, and the change of the reflected signal is collected and observed. Within this frequency range, the difference between the maximum and minimum values ​​of the reflected signal amplitude is taken as the extreme difference, and the frequency band corresponding to the difference between the reflected signal amplitude and the minimum value reaching 80% of the extreme difference is selected as the characteristic frequency band. According to the reflection coefficient S of the standard cylinder, the reflected signal amplitude is measured by the frequency band. 11 The change curve in the characteristic frequency band gives the reflection coefficient S 11 -Frequency reference curve;

[0009] Step 2: Collect the reflection signal of the gas cylinder to be inspected and obtain the reflection coefficient S 11 -Frequency detection curve;

[0010] Specifically, the microwave probe is placed 0-2 cm away from the outer surface of the gas cylinder to be inspected, and transmits microwave signals to the gas cylinder to be inspected at a continuously changing frequency within the characteristic frequency band selected in step 1, and collects the reflected signals 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;

[0011] 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;

[0012] Specifically, 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 and calculate the reflection coefficient S at 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 3dB, it is determined that there is a defect in the carbon fiber winding layer at that position of the gas cylinder to be inspected.

[0013] Preferably, the reflection coefficient S 11 The resolution is set to 0.01dB.

[0014] Preferably, in step three, according to the corresponding relationship between the defect and the difference, when the difference is greater than 3dB and less than 5.5dB, it is judged that there is a defect in the carbon fiber winding layer at that position and the defect is a crack; when the difference is greater than 5.5dB, it is judged that there is a defect in the carbon fiber winding layer at that position 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, and if they encounter defects, the reflection will be significantly enhanced, and the reflection coefficient S 11 The value of will change significantly. 11 The formula for calculation is as follows:

[0017] Reflection coefficient S 11 =20Lg(V R / V I )

[0018] Among them, V R is the incident microwave signal voltage, V I is the reflected microwave signal voltage.

[0019] When the microwave detection equipment is used to scan the gas cylinder to be inspected, the reflection coefficient S at a certain point on the surface of the cylinder is 11 -Reflection coefficient S corresponding to the trough of the frequency detection curve 11 Reflection coefficient S of standard gas cylinder 11 -Reflection coefficient S corresponding to the trough of the frequency reference curve 11 If there is a significant change in the comparison, it can be determined that there is a defect in the carbon fiber winding layer at that position of the gas cylinder to be inspected.

[0020] The first detection step of the present invention is to use a microwave probe to measure 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 difference in the reflected signals between 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 the premise of the subsequent detection steps. At the same time, the reflection coefficient S of the standard gas cylinder is observed. 11 The change within the characteristic frequency band, with the frequency of the characteristic frequency band as the horizontal axis and the reflection coefficient S as the horizontal axis. 11 As the vertical axis, the reflection coefficient S is obtained 11 The change curve in the characteristic frequency band is used as the reflection coefficient S 11 -Frequency reference curve.

[0021] For a standard sample bottle without defects, the reflection coefficient S 11-The frequency reference curve is displayed as a concave curve with a trough, and the reflection coefficient S 11 The trough values ​​of are shown as smaller negative values ​​(larger absolute values).

[0022] In the second detection step of the present invention, within the characteristic frequency range determined in step 1, the microwave probe is used to move and scan the outer surface of the gas bottle to be inspected at a continuously changing frequency to obtain the reflection coefficient S of each position point on the bottle surface. 11 -Frequency detection curve; when the reflection coefficient S corresponding to the trough on the detection curve at a certain position 11 The reflection coefficient S corresponding to the trough on the reference curve of the standard gas cylinder 11 If the difference is greater than 3dB, it is determined that the gas cylinder to be inspected has a defect at that position.

[0023] Furthermore, in the detection step, the reflection coefficient S 11 The resolution is set to 0.01dB, which is convenient for observing and distinguishing the reflection coefficient S 11 The amplitude of change can be increased to improve the efficiency of frequency scanning and detection.

[0024] Furthermore, according to the reflection coefficient S 11 The difference in the trough values ​​and the corresponding relationship between the difference and the defect (crack / void) are used to determine that the defect 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 non-destructive testing of high-pressure hydrogen storage containers and provides a method for defect detection of carbon fiber-wound type III hydrogen storage cylinders. Compared with other non-destructive 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] Figure 1 It is a block diagram of the detection step in the present invention;

[0027] Figure 2 is the reflection coefficient S of a certain position point on the gas cylinder to be inspected in a preferred embodiment of the present invention 11 -Frequency detection curve;

[0028] Figure 3 is the reflection coefficient S of another position point on the gas cylinder to be inspected in a preferred embodiment of the present invention 11 -Frequency detection curve;

[0029] Figure 4 is the reflection coefficient S of the standard gas cylinder in a preferred embodiment of the present invention 11 - Frequency reference graph. 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] Example 1: Figure 1 , Figure 2 , 3 , Figure 4 As shown, the present invention adopts a vector network analyzer for detection, the reflection coefficient resolution is set to 0.01dB, and includes the following steps:

[0032] Step 1:

[0033] Take a carbon fiber-wound type III hydrogen storage gas cylinder of the same model as the gas cylinder to be inspected and without defects as the standard gas cylinder. The microwave probe of the vector network analyzer is 0-2 cm away from the surface of the standard gas cylinder body. A microwave signal with a continuously changing frequency is transmitted to any position point of the standard gas cylinder body. The change of the reflected signal is collected and observed. In the frequency range of 3-40 GHz, the difference between the maximum and minimum values ​​of the reflected signal amplitude is taken as the range. The frequency band corresponding to when the difference between the reflected signal amplitude and the minimum value reaches 80% of the range is selected as the characteristic frequency band. The characteristic frequency band is determined to be 13.4-14.5 GHz. A microwave signal with a frequency continuously changing within 13.4-14.5 GHz is transmitted to any position point of the standard gas cylinder body.

[0034] The reflection coefficient S of the standard gas cylinder 11 The variation curve within 13.4-14.5GHz is taken as the reflection coefficient S 11 -Frequency reference curve (such as Figure 4 As shown), the curve shows the reflection coefficient S 11 The trough value is -13.42dB;

[0035] Step 2: The microwave probe of the vector network analyzer is 0-2 cm away from the surface of the gas cylinder to be tested. The various positions of the gas cylinder to be tested are scanned at a continuously changing frequency within the characteristic frequency range of 13.4-14.5 GHz determined in step 1, and the reflected signal of the gas cylinder to be tested is collected to obtain the reflection coefficient S of each position of the gas cylinder to be tested. 11 -Frequency detection curve;

[0036] Among them, the reflection coefficient S of a certain position point of the gas cylinder to be inspected is 11 -Frequency detection curve such as Figure 2 As shown, the curve shows the reflection coefficient S 11 The trough value is -6.93dB; the reflection coefficient S at another position of the gas cylinder to be inspected 11 -Frequency detection curve such as Figure 3 As shown, the curve shows the reflection coefficient S 11The trough value is -9.39dB;

[0037] Step 3: Compare the reflection coefficient S at different points on the gas cylinder to be inspected 11 -Frequency detection curve and reflection coefficient S of standard gas cylinder 11 -Compare with the frequency reference curve to calculate the reflection coefficient S at each 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 The difference is used to determine whether there is a defect at the corresponding position of the gas cylinder to be inspected;

[0038] Figure 2 The reflection coefficient S shown 11 -Frequency detection curve and reflection coefficient S of standard gas cylinder 11 - Compared with the frequency reference curve, the reflection coefficient S 11 The difference of the trough value is 6.49dB, which is greater than 3dB, so it is judged that there is a defect at this position. Since the difference is greater than 5.5dB, it is further judged that the defect at this position of the gas cylinder to be inspected is a gap;

[0039] Figure 3 The reflection coefficient S shown 11 -Frequency detection curve and reflection coefficient S of standard gas cylinder 11 - Compared with the frequency reference curve, the reflection coefficient S 11 The difference in trough values ​​is 4.03dB, which is greater than 3dB, so it is judged that there is a defect at this position. Since the difference is greater than 3dB but less than 5.5dB, it is judged that the defect at this position of the gas cylinder to be inspected is a crack.

[0040] 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 III 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-wound type III hydrogen storage gas cylinder of the same model as the gas cylinder to be inspected and without defects as the standard gas cylinder, place a microwave probe at a distance of 0-2 cm from the outer surface of the body of the standard gas cylinder, and transmit a microwave signal with a continuously changing frequency to any position point of the body of the standard gas 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 80% of the extreme difference as the characteristic frequency band, and select the characteristic frequency band according to the reflection coefficient S of the standard gas cylinder. 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 at a distance of 0-2 cm 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 3dB, it is determined that there is a defect in the carbon fiber winding layer at the position of the gas cylinder to be inspected; In the step three, according to the corresponding relationship between the defect and the difference, when the difference is greater than 3 and less than 5.5 dB, it is judged that there is a defect in the carbon fiber winding layer at the position point and the defect is a crack; when the difference is greater than 5.5 dB, it is judged that there is a defect in the carbon fiber winding layer at the position point and the defect is a gap.

2. According to claim 1, a method for detecting defects in a carbon fiber wound type III hydrogen storage cylinder is characterized in that: Reflection coefficient S 11 The resolution is set to 0.01dB.

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