The Experimental Research Of Acoustic Emission Detection Of Tank Bottom Defects

As oil and petrochemical products are being used more and more widely in industry areas,the degree of dependence on oil of the world increases,because of being easy to manage and inexpensive,etc,vertical metal atmospheric tanks on the ground have been the main container of reserve base and developing towards integration and large capacity.Because of the influence of the tank material and the external environment,the pit and crack defects of the tanks inevitably occur,this has reduced the security of the tanks greatly and increased the accident rate of storage medium leakage and caused environmental pollution and financial loss.The position of the defects in tank bottom plate are secluded and the accident rate increases as the tank service years grow,so the condition of the defects of tank bottom plate should be detected regularly.Conventional detection methods need to stop tank operation,drain tank products,clean up the rest of the warp of the tank and detect the defects of tank bottom plate by magnetic flux leakage testing or ultrasonic testing,so conventional detection methods can easily cause waste of human power,material and financial resources.The acoustic emission detection method which doesn't need to stop operation uses the way of “passive listening” to acquire acoustic emission signal of defects in tank bottom plate,determining the position and the acoustic emission signal time of the defects and evaluating the seriousness of the defects.Through reviewing the literature,there have been certain achievements in acoustic emission detection of defects in tank bottom plate until now,but qualitative judgment and quantitative analysis of defects in tank bottom plate haven't been achieved yet.Focusing on these problems,this paper has carried out the indoor experimental research,the detailed research contents and results are as follows.(1)Establishing the indoor vertical metal atmospheric tank model and making cylindrical pit and crack defects of typical sizes in tank bottom plates.(2)Making the second development and configuring the waveform acquisition card and waveform analysis software packages for the acoustic emission instrument,developing the multi filtering function,optimizing filtering parameters and improving the effect of noise reduction.(3)Preparing the experimental plan and carrying out it,acquiring the acoustic emission signal data of pit and crack defects in tank bottom plates.(4)Through the ways of multi filtering and normalized processing,the correspondence between characteristic parameters and the development degree of pit and crack defects has been found out.The quantitative mathematical models and the database of defects' acoustic emission characteristic parameters have been set up,so the quantitative analysis of pit and crack defects has been achieved.(5)Through the ways of spectral and wavelet analysis,the correspondence between acoustic emission spectrum signature and pit and crack defects,the qualitative analysis of typical defects has been achieved.(6)Using the quantitative mathematical models of pit and crack defects to analysis and calculate the acoustic emission detection data of atmospheric tank bottom plate in the field,then comparing the calculation result with the detection result after opening the tank,the comparation result shows that the accuracy rate of the quantitative mathematical models of the pit can be up to 76% and the crack 75%.