Non-contact Thickness Detection Technology By Laser Ultrasound On High-temperature Metal

Corrosion is one of the main failure modes of chemical,petrochemical,refining and other process equipment,of which the inspection is mainly conducted through the thickness measurement.Conventional ultrasonic testing technology is affected by the shape and temperature of the measured object,and it has certain limitations.Due to the limitation of current testing methods,most of the equipment needs to be shut down and maintained.For high-temperature material and complex measurement environment,laser ultrasonic detection technology can realize non-contact excitation and reception of ultrasonic,which has a certain application value.This paper mainly introduces a non-contact thickness detection technology by laser ultrasound on high-temperature metal,which is studied by theoretical analysis,finite element simulation and experimental analysis.In theoretical analysis,the mechanism of laser excitation and the propagation of longitudinal wave are introduced.Moreover,the influence of temperature variation on the longitudinal wave velocity is analyzed,and the optical detection method of longitudinal wave is briefly described.In finite element simulation,the basic principle of finite element simulation is introduced,and the influence of material parameters,laser parameters and meshing on the simulation results is analyzed.Finite element simulations are carried out on the metal of different thicknesses at different temperature.The propagation time of longitudinal wave along the vertical direction of the model is obtained by plotting the upper and lower envelopes of the simulated waveform.According to the theoretical analysis of longitudinal wave velocity at different temperatures,the simulated thickness of model is calculated.The simulated thickness is basically consistent with the actual thickness,which provides a basis for experimental analysis.In experimental analysis,the experiments are carried out on metal specimens of different thicknesses at different temperatures,and the original signals containing longitudinal wave information are obtained.Aiming at the problem that the original signals have low signal-to-noise ratio,the wavelet threshold de-nosing is adopted to achieve noise suppression.The cubic spline function is used to interpolate the de-nosing signal,shortening the distance between adjacent data points,and obtaining more time-domain information of the longitudinal wave.By calculating the cross-correlation function between different echoes in the longitudinal wave,the position with the highest correlation between the echoes is obtained,and the propagation time of the longitudinal wave in metal specimens is obtained indirectly.Quantitative detection of the thickness is realized according to the longitudinal wave velocity at different temperatures.In summary,the measurement of thickness on high-temperature metal is realized by laser ultrasonic testing technology,and the propagation properties of longitudinal wave at different temperatures are analyzed.The propagation law of longitudinal wave is verified by simulation and experiment.The results of this study provide a good theoretical and experimental basis for applications in the petrochemical industry.