Damage detection on invisible reverse side of planar steel using disturbance measurement of magnetic flux
T. Nakagawa, H. Mikada and J. Takekawa
Event name: The 22nd International Symposium on Recent Advances in Exploration Geophysics (RAEG 2018)
Publication date: 24 May 2018
Info: Extended abstract, PDF ( 364.02Kb )
Many steel pipes are made with planar steel plates and are used at oil and gas plants. Steels could easily corrode due to anode and cathode reactions causing electrochemical redox. Defects or corrosions are formed on both surfaces of a planar steel but it is difficult to perceive them formed on the other invisible side of plate from one surface with conventional non-destructive testing methods such as eddy current inspection, multi-finger caliper measurement, electromagnetic/acoustic casing thickness measurement, etc. Because of very high conductivity of steel materials, the penetration of electric current for measurement from the surface would be limited to a thin range. In this research we propose a new non-destructive testing method using magnetic field to detect defects on the invisible side, i.e., the reverse side from the measurement, of steel materials. We conducted numerical analysis using an FDTD method for showing that we could find the defects on the rear side of steel material. It is confirmed that the spatial variation of the amplitude of magnetic flux gives a change at the location of a defect on the other side when applying magnetic field to the material. We verified that the change comes from the magnetic flux leakage caused by the circumvention of magnetic flux around the defect. The phase of magnetic component normal to the surface showed an amplitude reversal at the center of a defect on the other side of the plate. We conclude that detects on the other side of a plate could be detected in the measurement on one side.