Research on Ultrasonic Testing and Image Preprocessing Method of Remanufactured Oil Pipe Inner Wall

摘要

Discarded steel oil pipes can be remanufactured by Centrifugal Self-propagating High temperature Synthesis (SHS) method. A ceramic layer can be attached onto the inner wall of the steel pipe. The ceramic-lined steel composite pipes possess better wear and corrosion resisting properties as well as longer life-span, which creates huge economic benefits. However, due to electric insulation, nonferromagnetism, anisotropy, high noise and acoustic attenuation, it is difficult to detect long and narrow ceramic inner wall, which can damage service security. In this work, ultrasonic A- and C-scan was implemented on a ceramic-lined steel composite pipe. The C-scan RGB image of a test block with precast flat bottom holes was transformed into a grey-scale map. Then a contour plot was drawn for flaw edge detection. Finally, visualized images of defect locations on the test block were captured. The experiment results indicate that ultrasonic technology is adaptive for detecting ceramic-lined steel composite material from outside the pipe. The results of A-scan reflect the bonding state of ceramic and metal layers. Grey-scale map method can do effective preprocessing on C-scan images so that defects can be visualized.