Research On Electromagnetic Ultrasonic Detection Technology For Surface Defects Of Tank Bottom Plate

Storage tank plays an important role in the modern petroleum and petrochemical industry.The tank bottom plate,as a key component carrying medium in the tank,is subject to the combined effects of pressure,corrosion and other factors,and its surface has a high risk of damage.And because the storage tank capacity is generally larger,the storage medium is more flammable or toxic and harmful,once the occurrence of safety accidents will cause extremely serious consequences,to the environment,economy and personal safety great harm.Electromagnetic ultrasonic detection technology eliminates the dependence on coupling agent,can adapt to a variety of testing environments,and has a good application prospect in the detection of tank bottom surface defects.Surface defects of tank bottom plate may occur on both upper and lower surfaces of the plate.Therefore,it is of great significance to realize the accurate identification of surface defects for the safe operation of storage tanks and risk prevention.In this paper,based on the application of the electromagnetic ultrasonic detection technology to the surface defect detection of the tank bottom plate,based on the theoretical analysis of the electromagnetic ultrasonic detection principle of the steel plate,the multi-field coupling mechanism is analyzed from the perspective of vectors,and the magnetic vector and displacement vector are used to represent the theoretical model of the equations of magnetic field and field under two-dimensional conditions.A two-dimensional axisymmetric electromagnetic ultrasonic excitation finite element simulation model was established by using the finite element analysis method to simulate the multi-field coupling process of electromagnetic ultrasonic and realize the excitation,transmission and reflection of ultrasonic waves in the steel plate.Based on the simulation model,the electromagnetic ultrasonic excitation system with the same parameters was designed and wound manually.The position of the acoustic sensor is corresponding to that of the finite element model.The accuracy of the theoretical analysis and simulation model is verified by analyzing the propagation law of the collected ultrasonic signal,calculating its wave velocity and comparing it with the theoretical value obtained by the finite element method.Finally based on steel plate surface defects common size and shape,finite element simulation model of optimization analysis of defects of the influence of different factors for ultrasonic excitation by peak,summarizes the different factors influence law for ultrasonic reflection and transmission coefficient,the factors including the defect depth and defect width,surface defect form,defect exists,sheet thickness and coil lift-off values.Based on the reflection and transmission coefficients of ultrasonic signals,a method to determine the surface defect depth of tank bottom plate was obtained.The electromagnetic ultrasonic defect detection experiment was carried out,and the precast defect was fabricated on the steel used for the tank bottom plate.The parameters were consistent with the finite element simulation model.Multiple experiments verify the feasibility of applying electromagnetic ultrasonic technology to the surface defect detection of tank bottom plate.The results are compared with the finite element simulation model to verify the accuracy of the above method.In other words,the surface where the defect is located is judged first and the defect is quantified.