The next generation MEC (Magnetic Eddy Current) technique has demonstrated superior defect detection capability in a successful test performed for a petroleum and petrochemical Operator.
The analysis focused on the simulated inspection of a tank floor plate installed on top of an existing floor with varying distances in between. The ability of the MEC technique to inspect reliably the ’New’ plate on top of the ’Old’ plate with varying distances to each other - no gap, 3mm and 5mm gap underneath as well as the reliability of defect detection on either side of the top layer plate is tested.
The target was to analyse the influence of the ’Old’ bottom plate below the ’New’ bottom plate on the inspection results as well as the capability of the MEC technique to detect flaws in a distanced second steel layer.
Results showed that the defect indications and magnetic field in the top layer plate are not affected by the direct contact or increased gap distance of the bottom plate. Defects on the upper and underside of the top plate layer can be confidently detected and analysed without the influence from the defects in the bottom plate unless they are of significant size.
This is possible because the MEC technique operates its magnetic field strength of at the retentivity point of the hysteresis curve which requires lesser field strength. This is a major difference to the MFL technique operating at the saturation level of the hysteresis curve where the close or in contact neighbouring plate layer will affect the field strength absorption.