| Special pipes are often used in high temperature,high pressure,radiation and other special environment,however,it is inevitable that the gas leakage caused by corrosion,stress cracks and other defects which will lead to security incidents in the service life.Therefore,this kind of in-service pipelines must be regularly checked and maintained.As a new type of nondestructive testing technology,laser ultrasonic becomes the current research focus,which has high spatial resolutions,strong environmental adaptability,non-contact and long-distance etc.In this paper,the laser ultrasonic inspection system design,signal de-noising and pipeline crack detection method are discussed and research.(1)According to the ultrasonic testing hardware system,a set of laser ultrasonic testing software which includes data processing,motion control and data analysis is completed.(2)By analyzing the ultrasonic echoes received when different parameters are set,the factors influencing the ultrasonic propagation characteristics are clearly defined.(3)Different schemes are used to detect the specimens with cracks,and the interaction mechanism between the ultrasonic wave and the crack is analyzed according to the received echo signals.(4)The collected laser ultrasonic signal contains a lot of noise.Firstly,the time domain average method is used to denoise and improve the signal to noise ratio of ultrasonic signal.And then optimized wavelet denoising method is used to denoise the simulated signal and the actual collected signal respectively.In this paper,an optimization algorithm is proposed to find the optimal noise reduction results quickly and compare with the noise reduction results of other schemes to prove the feasibility of the optimization algorithm.(5)The surface crack of pipeline and flat plate was measured by the designed laser ultrasonic platform,and the results show that the platform can realize the quantitative analysis of the location and depth of the defect. |
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