Nonlinear Ultrasonic Lamb Wave Detection Technology For The Corrosion Depth Of Tank Bottom

Large-scale oil storage tanks,as a major basic key equipment to protect my country's oil and gas resources,are widely used in petroleum refineries and other bases.The petroleum storage tank is a storage container for crude oil,etc.,and its bottom plate is welded by a plate-like structure.During the service life of the storage tank,the environment is humid and the stored liquid is corrosive,which makes the bottom of the tank prone to pitting corrosion and area-shaped corrosion.Therefore,the tank bottom is the most severely corroded area of the tank body.The existence of corrosion defects will cause the loss of the thickness of the bottom plate,thereby reducing the structural strength of the bottom plate.In severe cases,it will also cause fires,explosions and other accidents,endangering personal and property safety.The monitoring and evaluation of the corrosion status of the storage tank bottom plate provides a strong guarantee for preventing the occurrence of dangerous accidents,provides support for predicting the service life of the storage tank bottom plate,and provides a basis for scientific management and decision-making.Most of the traditional non-destructive testing techniques are offline(can opening)testing,which requires a series of steps such as stopping the can,clearing the can,and testing in the can with human equipment,which is not only low in detection efficiency but also consuming manpower and material resources.Ultrasonic guided waves have the advantages of long propagation distance,high detection efficiency and little environmental impact.They are the most potential type of structural health monitoring technology for detecting corrosion defects on the bottom of storage tanks.However,the complexity of the bottom plate structure and the attenuation characteristics of the guided wave make the guided wave signal received by the sensor weak.The existing guided wave technology is difficult to evaluate the corrosion status of the bottom plate of a large tank;at the same time,most of the existing corrosion damage evaluation methods A defect-free signal is required as a reference signal,and it is difficult to obtain a defect-free signal in actual inspection.Therefore,this thesis is supported by the national key research and development plan of "Storage facility monitoring technology based on the integration of sound and light"(2016YFC0801202),with the purpose of evaluating the corrosion state of the bottom plate of large storage tanks,from the mechanism of defects and guided waves,the classification technology of corrosion defects and the construction of inspection platform are studied in three aspects.The specific research contents are as follows:(1)Research on the propagation mechanism of ultrasonic guided waves in plate-like structures with corrosion defects.The excitation and signal receiving mechanism of ultrasonic guided waves for typical corrosion defects at different depths,as well as the characteristics of guided wave signals after corrosion defects and guided waves are studied.(2)Research on the classification of corrosion depth of tank bottom plate based on non-referenced nonlinear ultrasonic Lamb wave detection technology.The effects of stress amplitude ratio,wave field propagation distance and corrosion defect depth on guided wave signals are studied;the principle of detecting defects with the nonlinear characteristics of ultrasonic guided waves is used to extract the time-domain damage factor in the difference signal containing defect information Establish a classification model for the evaluation of typical corrosion depth.(3)The construction of the experimental platform for non-linear ultrasonic guided wave corrosion depth detection.According to defect detection principles and on-site inspection requirements,typical corrosion defects are simulated through electrochemical corrosion experiments,and the depth and shape of defects are changed by controlling the corrosion time and the shape of the corroded vessels;and on-site inspection of oil storage tanks at a Sinopec base The results show that the above method can better evaluate the depth of corrosion defects and the corrosion status of the tank floor.