Abstract: Phased array ultrasonic technology was used to detect weld defects in oil and gas transportation welded pipes. The composition and detection principle of the detection system were introduced, and on-site detection tests were conducted on straight seam submerged arc welded pipes. The experimental results showed that compared with conventional pulse echo ultrasonic technology, the phased array ultrasonic automatic detection system for straight seam submerged arc welded pipes had some advantages such as high detection accuracy, high detection efficiency, high defect detection rate, and intuitive display of detection results. It can quickly and efficiently detect the welds of straight seam submerged arc welded pipes, and had wide development prospects.