Study Of Tank Bottom Corrosion Propagation Simulation Of Acoustic Emission

With the development of economy, the safety of oil storage tanks is becoming more and more important.It is very easy to happen that the corrosion of tank bottom plate and lead to security risks, because of the particularity of the storage medium, Acoustic emission testing is an effective method for testing tank bottom corrosion. The characteristics of acoustic emission signal were characterized by decomposition of acoustic emission signals obtained by simulation into stress and all directions of displacement components.In this paper, the nature of acoustic emission and wave theory are summarized, and the use of wave theory to solve the problem of acoustic emission is established. The finite element method is used to simulate the fluctuation in the complex structure like the tank bottom plate,and the COMSOL finite element software is used for simulation. The excitation signal of acoustic emission is summarized. The parameter selection of tank bottom plate model in simulation was analyzed.The structure mechanics-solid mechanics module is used in simulation and it’s solved by the transient analysis method.Finite element simulation software is used to simulate the Lamb wave, for establish the simulation object and the research focus. Then the tank bottom plate is respectively carried out two dimensional, three dimensional with no weld model, three dimensional simulation with the weld model. The stress and displacement components of different sampling points were selected。The filter using on the signal obtained from the simulation, obtain the frequency spectrum. Wavelet analysis is carried out to obtain the time-frequency for further extract the signal characteristics.Through the theoretical and simulation studies,in the frequency spectrum, the low frequency signal has the large signal strength, but it contains less information.In 100 khz signal,the intermediate frequency signal form 20-80 khz is the most abundant with large amount of information. Energy is higher than the 100 khz frequency. In the waveform and wavelet time frequency diagram, the intermediate frequency signal is also the most consistent with the actual acquisition of the acoustic emission signal. It shows that the main acquisition signal of acoustic emission is the 50 khz frequency signal. On the excitation signal,the step signal is used to generate multi-channel pulse in two dimensional simulation, similar with Lamb experiment.The pulse signal is used in three dimensional simulation and the signal decays withtime. The signal in normal direction(X direction) with small attenuation and the large signal strength is the main transmission mode, also the best way to accept.The signal in tangent direction(Y direction) is the weakest, but it’s spectrum is the same, the signal intensity decreases only with the distance increasing.The signal in tangent direction can be used as an auxiliary signal to determine the distance of the acoustic emission source in conditional.