Application Research Of Low Frequency Electromagnetic Technology In Defect Detection Of Tank Bottom

Storage tank is important storage devices of oil, gas and other chemical raw materials in Petrochemical industry. With the constant improvement of national economic system, the state for crude oil reserve system is also more and more attention, and the number of tanks is increasing. The specific environment of tanks bottom led to that it is the most prone to corrosion of the storage tank area. If the damage of storage tank causing leaks, which will cause huge losses for the ecological environment and people’s lives and property. Therefore, in order to ensure operation of the tanks safe and stable, it is necessary that attend a full range of monitoring and protection on the quality of the tank. The detection of defects in the storage tank bottom has an important significance for the safe operation of the storage tank.This paper mainly aim at the current situation of domestic and foreign of tank bottom detection, study detection methods of low frequency electromagnetic technology, design structure of the exciting coil,and induction type magnetic sensor detecting coil array is used as the magnetic field signal detection sensor, magnetic core size and the size of the coil are calculated and demonstrated detailedly. Embed FATFS file operating system to manage storage media SD card, storage real time detection data, call and deal with later. The application effect of the four parameter sine curve fitting algorithm in obtaining the amplitude and phase of the detection signal is analyzed. On the basis of this, low frequency electromagnetic testing system for tank bottom is developed,which comprised mainly by main control circuit, signal conditioning circuit,storage system, exciting coil array, induction type magnetic sensor coil array, liquid crystal display positioning module and so on.Tank bottom low frequency electromagnetic detection system mainly uses the extremely low frequency AC unsaturated magnetization way, through the main control circuit loads sinusoidal signal to the exciting coil, generates an alternating electromagnetic field through the tank bottom and induction type magnetic sensor on the surface of it. The output signal of the sensor coil is analyzed and calculated by using the four parameter sine curve least square fitting algorithm, the amplitude and phase of detection signal of the defect position is extracted, the purpose of identifying the defect size and position of the tank bottom is reached. In this paper, the effect of the exciting frequency and the lift off value of the low frequency electromagnetic testing system to tank bottom is analyzed in detail. The results show that the system can detect the corrosion defects of 20 mm length, 2mm width and wall thickness of steel plate 20%, penetrate the thickness of the 8mm standard coating to detect cracks, realize the comprehensive detection of tank bottom without coupling agent and magnet, the precision is high, the equipment is light, and the use is convenient.