Abstract: Described in the paper is the process of on-line automatic ultrasonic flaw detection of SAW spiral welded pipe, focusing on analysis of the different elements responsible for the detection precision which involves eight major aspects, namely, the function configuration of the detector and the probes, the design of the probe support mechanism, response/running of the actuator, control of water coupling, suitability of the detection process, professional qualification of the inspectors, interferences with the UT auto-inspection operation caused by different electrical actuating parts and the pipe-formation quality. Based on the said analysis, relevant countermeasures are proposed.