Magnetic testing method and apparatus for storage tank floor

One of the critical areas of integrity testing is that of storage tank floor in the petrochemical industry. Examination of tank floor traditionally depended mainly upon ultrasonic and magnetic particle test methods. The two methods required slow and painstaking application. Therefore, they have been limited to spot testing only. Based on the principle of the magnetic testing, the magnetic testing method and apparatus for storage tank floor are proposed. The whole magnetic testing apparatus includes detector, photoelectric pulse encoder, scanner unit, computer aided signal processing unit, alarm, and so on. The detector contains permanent magnets and Hall sensors. As the detector moves by the scanner, it magnetizes the tank floor Any damages cause distortion in the magnetic field and this distortion can then be detected by the Hall elements. The Hall elements send the information to the computer for analysis. At the same time, the photoelectric pulse encoder recorder the distance from the start point to locate the discontinuity in space domain. Any damages are detected, the alarm unit can send out different light according to the extent of the damage. Two different types of scanner have been developed. One type of scanner is driven by motor and it can pull the larger detector that can inspect 300mm wide in one time. Another is driven by manpower and it can pull the smaller detector that can inspect 150mm wide only. But the smaller scanner can detect the area that the larger scanner difficult to arrive. Sensing system are non-contacted and not affected by scale, oil, mud, paraffin and water It can detect most of test coverage of the tank floor within a reasonable test time. Experimental and field testing have show that as low as 10 percents tank floor wall thickness loss can be located using the magnetic testing system.