Study On Acoustic Source Characteristics And Severity Analysis Of Tank Bottom Corrosion

Atmospheric vertical storage tank is important storage devices of raw materials for petrochemical industry such as crude oil, refined petroleum and intermediate products. Tank bottom corrosion state is a main factor of tank safe operation, its severity is the leading indicator which guides tank maintenance decision-making, and tank bottom corrosion state testing is the main method to ensure the tank running well in the next cycle. Acoustic emission(AE) testing technology has been the main method of tank bottom corrosion condition monitoring and evaluation internationally for its advantage of online testing without opening tank. However, there are some key problems to be solved at this stage in order to apply AE method to test and evaluate the tank bottom corrosion, such as weak corrosion signal strength, complex corrosion acoustic emission sources and difficulty in acquiring corrosion signals from the centre zone of large storage tank bottom. In order to solve these problems, theoretical study, numerical simulation and experimental research were used to study the AE source characteristics and corrosion severity of the tank bottom.The following research contents and results are acquired:AE source mechanism during tank bottom corrosion process is studied. Point stress pulse theory was applied to calculate the source signal amplitude of bubble breakage in cathodic hydrogen process. Fluent was used to simulate the bubble breakage away from and near tank bottom, through which the stress and displacement curve were obtained. It is found that bubble breakage in cathodic process will release stress wave and metal dissolution in anode process is the acoustic emission source. Meanwhile, the energy released from the anode process is also calculated in corrosion kinetic analysis, thermodynamic energy analysis and atomic primary simulation.Experimental study of AE source during tank bottom corrosion process was conducted in the paper. Cathodic process and anode process are divided by different polarization curve testing to verify the acoustic emission source mechanism of cathode bubbles breakage and obtain the energy value of the anode metal dissolution.AE signal characteristics of bubble breakage, metal dissolution and mixture were extracted respectively by the K-means clustering method. The results show that acoustic emission can identify not only the hydrogen evolution corrosion source with bubbles but also oxygen corrosion source without bubbles.AE characteristics of tank bottom corrosion process were studied in the self-corrosion, polarization curve and electrochemical impedance spectroscopy test process. Comparing with the electrochemical test results, count rate can be used to describe the tank bottom corrosion process accurately. AE parameter formula is established to characterize the tank bottom corrosion. At the same time characteristic parameters of tank bottom corrosion severity was got.Weak acoustic signal extraction method in tank bottom corrosion process was established. AE all-region monitoring method is put forward based on the AE characteristics of tank bottom corrosion. There are two kinds of AE sensor layouts in the tank bottom which are immersion and embedded layouts respectively. The paper studied the acoustic wave propagation process of two layouts by the parameter analysis and waveform feature extraction of AE signals. The results show that the layouts can be used to monitor the tank bottom corrosion which can be chosen according to the actual situation and transformation factor R.Study of multi-source signals identification method was conducted in the tank bottom corrosion process. The homogenous signals were clustered in the correlation analysis. And then, short baseline plane grid identification method of AE source in tank bottom based on all-region monitoring and acoustic phase array principle was established to determine the source distribution in tank bottom. Which rid the acoustic emission source belongs to can be determined according to the method.Corrosion severity analysis method was studied based on the all-region monitoring. Sensor amplitude weight analysis method was established based on the MAS theory and AE source identification method. And then, according to information entropy severity comprehensive index analysis method, tank bottom corrosion severity evaluation method were obtained, with which corrosion acoustic emission level can be evaluated based on the rid identifications of the hydrogen evolution corrosion and oxygen corrosion source to give some guidance on the future maintenance of tank bottom.Multi-source weak acoustic signal extraction, identification and severity evaluation of tank bottom corrosion are studied on the basis of theoretical research in the paper. The conclusions can be used to evaluate the tank bottom corrosion state more accurately. The results provide the theoretical and experimental basis for the application and development of AE all-region monitoring in tank bottom corrosion.