Abstract: The frequently used second-order statistics represented by fast Fourier transform often cause many errors in processing the ultrasonic echo signals of pipeline corrosion． To solve the problem，the formation principle of the pipeline ultrasonic echo signal was studied，and the characteristics of the echo signal were analyzed with the wave theory． A processing method of non-minimum phase system and non-Gaussian signal based on 1. 5-D spectrum esti- mation was proposed． Scanning detection and ultrasonic echo signal analysis were carried out for the normal location of pipe wall，the location of inner wall corrosion and outer wall corrosion respectively． And a special method of echo signal processing for the critical location of corrosion on pipe wall was given． Experimental results of single-point detection and multi-point continuous detection show that 1. 5-D spectrum estimation algorithm can effectively over- come the shortcomings of fast Fourier transform algorithm when analyzing the ultrasonic echo signal of the oil pipe- line corrosion． The relative error of wall thickness obtained is less than 2%． C-scan image can clearly show pipe- line corrosion，which meets the detection requirements of the residual wall thickness of the oil pipeline corrosion．

Key words: pipeline corrosion, ultrasonic echo signal, 1. 5-D spectrum estimation, fast Fourier transform