Abstract: In view of the problems existing in the conventional periodic inspection of pressure pipeline, this paper introduces the principles of the low frequency ultrasonic guided wave and the magnetic flux leakage test for pipeline outer wall. In-site online inspection on pressure pipes was performed and the signal waveform characteristics and defect recognition method were analyzed. The results show that these two pipeline on-line inspection techniques can be well applied to the pressure pipeline detection without the demand for cleaning it beforehand, and can solve two major problems for enterprises:the shut-down of the pipe function and the dismantling the insulation layers for the inspection of the pipe.