Ultrasonic pig for submarine oil pipeline corrosion inspection

Abstract

This paper introduces the design and development of an ultrasonic pig used for submarine oil pipeline corrosion inspection. Structure and functions of the equipment, as well as ultrasonic data acquisition system and off-line signal processing method are presented. The pig adopts a train-like structure including driver cups, batteries, ultrasonic transducers and data acquisition unit, which can detect and locate the corrosion of inspected pipeline. The data acquisition system is designed based on a digital signal processor and field programmable gate arrays structure to sample, process and compress the ultrasonic data and then store them in a hard disk. The off-line signal analysis method adopts a non-phase delay peak extraction algorithm to accurately calculate the pipe wall thickness. According to the thickness of each detected point, an ultrasonic image is traced by false color image, and then the potential defects are recognized by using a 3 × 3 grids template and classified according to American Petroleum Institute Standard. Both experimental and engineering testing results show that the pig is of perfect performance and could inspect defects greater than 10 × 10 mm2 successfully.