Study on thickness detection of industrial pipe network by high-frequency ultrasound

The inside and outside surfaces of the industrial pipe network could engender the oxidation layer by corrosion because of long-term operation. This could even put industrial production and human safety into a potential threat. So the non-destructive inspection of the metal thickness of pipe networks and the deduction of the erosive distribution of the inference wall is of great significance. However, because the oxidation layer/metal matrix interface reflection signal is low and the resolution is low because of the pulse peak width that is used, the current pipeline thickness measurement instrument is unable to accurately measure the thickness of the pure metal wall and the oxide layer. That is to say, the current instrument measurement of the thickness of the pipe wall is the sum of the metal layer and the oxide, rather than the pure metal layer which contributes to the intensity. Serious errors will occur during the check of the pipeline strength and the calculation of the lifetime. In order to overcome problems that exist in the current ultrasonic measurement of the thickness of the industrial pipe wall, a high-frequency ultrasonic thickness measurement system is proposed in this paper. A high-frequency, narrow-pulse, small chip perforated wedge of longitudinal and transverse sensor is adopted, combined with a broad-spectral-bandwidth oscilloscope, thus composing the metal layer and wall pipe oxide thickness measurement system. The system could greatly improve the testing precision and resolution. Combined with the cross-correlation function method, the distinguished precision of the delay between reflected signals is improved (experiments showed that the thinnest oxide thickness that could be accurately detected is 0.07mm), so the erosive distribution of the steel tube wall could be accurately deduced. A formula for calculating the smallest theoretical resolution of the system is presented, which lays a foundation of the accurate detection of industrial pipe wall stress and other physical quantities.