The acoustic emission signals were measured during plastic deformation and crack propagation in Q235-B and 0Cr18Ni9 stainless steel.Wavelet transform was applied to analyze inspection signal for investigating the acoustic emission characteristics of material. The results show that the acoustic emission signal of carbon steel is analyzed by six-layer db5 wavelet transform, the most energy is concentrated in d5 level.Peak frequency is located in the range of 166~176 kHz.Energy ratio in d5 level is higher during crack propagation than palstic transform.While the acoustic emission signal of stainless steel through the same wavelet transform, the most energy is concentrated in d6 level.Peak frequency is located in the range of 88～112 kHz. Energy ratio in d6 level is higher during crack propagation than palstic transform.

The characteristics of acoustic signal for pipe leakage and general wavelet primary function were analyzed. It concludes that the suitable primary functions for acoustic signal of pipe leakage are Daubechies wavelet and Symlet wavelet. The experiments of the acoustic inspection were conducted in water leakage of the carbon steel pipe and the wavelet transform of the leakage signal was done by db5 and sym5 wavelet. It shows that the most energy is a6 level signal energy and the peak frequency of the signal focus on 2.90~3.81 kHz. The maximum relative error of two different wavelet transforms is 0.77% in the energy analysis and 5.17% in frequency analysis.