Application of Zero-Phase Digital Filter in Magnetic Flux Leakage Testing for Tank Floor Inspection

Abstract

Magnetic flux leakage (MFL) testing, as a modern nondestructive testing technology, has significant application in tank floor corrosion defect inspection. In view of signal characteristics in the MFL testing of tank floor, an improved signal progressing method combining software and hardware was presented. Especially, in order to avoid phase distortion caused by applying common digital filter, zero-phase digital filter which could effectively eliminate the phase distortion was proposed to improve the location accuracy of defect. Experiment results showed that the signal progressing method could improve signal-to-noise ratio, and the peak-peak value of defect signal had a good linear relationship with the depth of defect which showed that the proposed method could meet the requirement of the MFL testing. Comparing results showed that, the maximal location error of zero-phase filter was 2 mm and that of common digital filter was 24 mm, which showed that zero-phase filter had better defect location accuracy.