| Petroleum storage tank floors are ageing assets,and there are many defects caused by corrosion and other factors.It’s of great importance to be inspected periodically to avoid leakage to the surroundings,causing catastrophic events and harm to the environment.For many years,traditional NDT techniques,such as electromagnetic technology,radiography technology,and traditional ultrasonic technology,have been widely used to check the health of petroleum storage tanks.However,since the storage tanks must be emptied and cleaned before inspection,the development and application of these techniques are very limited.As a non-invasive and economically viable means of assessing structural degradation,the application of ultrasonic guided waves to assess the structural health of petroleum storage tank floors is an emerging technology.However,Due to the attenuation characteristics of the UGW propagation and multiple reflections and transmissions of Lamb waves caused by welds,the effective UGW will be buried in the noise due to too small energy.Therefore,this thesis carries out work from three aspects: UGW excitation,signal analysis and system construction.The main work is as follows:1.Combined excitation of UGW in "L" type welded structureIn this thesis,we use spatial multi-point combination excitation to enhance the energy of the source signal,so that the received signal energy is higher to increase the guided wave propagation distance and the detection effectiveness.Firstly,different positions in the petroleum storage tank,including the chime edge,the chime upside and the tank wall,are set as single excitation points to analyze the waveform modes and energy characteristics of the receiving signals.Based on the purpose of maximizing the energy of guided waves transmitted to the internal of floors,the characteristics of the Lamb wave mode and energy excited by different spatial position combinations are studied from the characteristics of the frequency and phase of the excitation signal.The results show that when the signal is excited simultaneously to the excitation points of the chime upside and the wall to form a combined excitation,the amplitude of the waveforms obtained by each receiving point is increased by 64% to 100% compared with a single excitation at one point.The excitation method can be used to assess the structural health of the petroleum storage tank floors based on UGW.2.Damage detection technology based on time information extraction inpetroleum storage tank floorsUsing combined excitation,we move the excitation and reception points along the direction of the weld for the whole floor scanning.Using the band-pass filtered signal processing technology and Hilbert transform,the guided-wave-based damage identification is extracted by comparing the captured wave signal from benchmark with that from a damage case,leading to the identification of the defect in the steel plate using hyperbolic algorithm based on TDoA.Experimental results demonstrate that the above method can locate the center of the defect with high precision.3.Guided wave excitation signal generatorCombining our previous experience in damage detection technology of petroleum storage tank floors with the actual working mode of the equipment,for portability and controllable parameters,we use STM32F103 microprocessor as the control unit.With the corresponding DDS signal generation,communication module and the power amplifier circuit,a guided wave excitation signal generator capable of long-term service in the field was developed.Then we develop the PC software of signal generating system based on C# and MATLAB mixed programming to achieve USB communication,waveform parameter control and other functions.Finally,we test the whole system in field to prove that the guided wave excitation signal generator can correctly output the amplified Lamb wave excitation signal,e.g.the Hanning window modulated sinusoid tonebust,set on PC with high reliability and usability. |
PDF Full Text Request