Experimental and numerical study of the design and development of a magnetic flux leakage inspection device to detect defects on ferromagnetic plate with the aim of optimizing the effective parameters

Todays, in the oil and gas industry, storage tanks are used to store oil and petroleum products. Industry experience indicates that soil-side corrosion would occur at sever rates at most above ground storage tanks bottom. Since these damages happen at the bottom surface of the tanks and are not visible with visual inspection, a trustable method is needed that can inspect the storage tanks periodically. According to the researches have carried out until now, the most common technology to identify defects in the bottom surface of the storage tanks is the magnetic flux leakage inspection technique (MFL), which can perform the inspection as quickly as possible with proper accuracy. For this purpose, in this article, the aim is to build a magnetic flux leakage inspection device that can perform inspection and identification. There are many various parameters affect the MFL inspection such as environmental conditions, operational parameters and etc. Among the operational parameters the effective variables which have important roles in inspection are: the distance of the sensors to the center of the defect point, the distance between the magnet poles and the distance between the magnets and the tank bottom plate. Also, the reference plates used in this project are steel plates with 6 mm and 10 mm thicknesses include the artificial defects created on the surface according to ASME Section V Article 16. In order to reduce the costs and time of experimental tests Ansys Maxwell simulation program was used and the results obtained from the simulation were used to conduct experimental tests. The results of simulation are compared with the results of experiment. The results showed that by changing the mentioned effective parameters, defects with the depth of 20% to 80% can be detected with trustable accuracy. Also, by changing the parameters in some conditions, the lower depths of 20% can be detectable.