Influencing Factors for the Lamb Wave Detection of Tank Bottom Defects
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摘要: 由于检测条件、储罐内容物等因素的影响,在役油气储罐底板腐蚀检测问题尚未得到有效解决.基于超声兰姆波的多模态及频散特性,利用可变角度探头分别激发出含A0和S0两种模态的兰姆波进行检测试验.通过在储罐底板漏磁检测标准试板上进行检测,研究了波结构对兰姆波检测的影响以及缺陷横截面积与回波信号幅度的关系.针对板厚为6.8 mm的钢板确定了最佳入射角,并从兰姆波振动位移和能流密度分布的角度对试验所得结果进行了分析.结果表明:在工作频率一定的条件下,波结构是影响兰姆波检测的重要因素;缺陷回波信号幅值随缺陷横截面积的增大而增大,不同模态对同一类缺陷的横截面积和缺陷深度变化呈现不同敏感性,同一模态对不同类缺陷横截面积和缺陷深度变化的敏感程度也不同.Abstract: The problem of corrosion inspection of the oil and gas storage tank bottom in service has not been effectively resolved due to the influence of factors such as test conditions and the contents.In this article,the Lamb waves of mainly A0 and S0 modes have been inspired by using the variable angle probe based on ultrasonic Lamb wave mode and dispersion property.The experiment was carried out on the reference plate of tank bottom magnetic flux leakage testing to study the influences of wave structure to the Lamb wave detection and the relationship between the cross-sectional area of defects and the echo signals amplitudes.The optimal angle of excitation is determined for a certain thickness of the steel plate and the experimental results are analyzed from the acoustic vibration displacement distribution and energy density distribution.The study has shown that under certain conditions of the operating frequency,the wave structure is an important factor of affecting Lamb wave detection.Besides,defect echo signal amplitude becomes larger with increasing cross-sectional area .The results show that different modes for the same types of defects have different sensitivity to changes in cross-sectional area and the depth of detects and the degree of sensitivity to changes in cross-sectional area and the depth of detects is different for the same types of defect mode.
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Keywords:
- Ultrasonic lamb wave /
- A0 mode /
- S0 mode /
- Displacement distribution /
- Energy flow density
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