Study on Magnetic Memory Testing Signal Characteristics of Pipeline Defects Based on Wavelet Packet Analysis

At present, the judging principle of Magnetic Memory Testing technology (MMT) can only indicate the stress concentration zone, but can not get information from the stress concentration further. In the paper, to get information from the stress concentration zone, a MMT signal analysis method based on wavelet packet energy spectrum is proposed. The specimen tension load experiment shows that when the tension load is 200MPa, the signal wavelet packet energy spectrum distributes uniformly, the percentage of separate energy to total energy is lower than 15%. When the tension load is 410MPa, the maximum wavelet packet energy locate in 1, 3 and 4 spectrum, the percentage of 1 similar to 4 energy to total energy is 73.8%, and the main wavelet packet energy locates in the low frequency area. After the specimen yields, the maximum wavelet packet energy locates in 1 and 2 spectrum; the percentage of 1 similar to 3 energy to total energy is 87.3%. The distribution of wavelet packet energy spectrum is very separate, and the main wavelet packet energy locates in 1 and 2 spectrum. If the stress concentration degree is low, then the wavelet packet energy spectrum distribution is equal; if the stress concentration degree is high, then the wavelet packet energy spectrum distribution is concentrated, and the main energy is concentrated in low frequency area.