Magnetic Flux Leakage (MFL) is a nondestructive examination (NDE) technique where electromagnetic energy is applied to equipment in order to detect flaws. Using this method, both top-side and bottom-side corrosion, as well as other damage resulting in material loss can be detected in both lined and unlined ferrous metallic pipelines and storage tank floors. As these pieces of infrastructure effectively form the backbone of our industry, MFL testing is invaluable in keeping them in working condition.
MFL inspection works by applying magnets, which can be either permanent magnets or electromagnets, to a piece of equipment. The electromagnetic energy is adjusted to saturate the material for the given thicjkness. As a result any changes in thickness such as that due to corrosion cause the field to be forced out of the item.. These “leakage fields” may then be detected using Hall effect sensors. The major advantage MFL inspection holds over other nondestructive techniques is that it can detect corrosion and other damages not only on the surface of the pipe or tank floor, but on the iopposite side as well.
That being said, MFL is not a quantitative method, it is strictly a screening tool to indicate areas that require further evaluation. Ultrasonic thickness testing as a follow up is required to "prove-up" the MFL findings and determine the severity and extent of any material loss detected.
MFL is the standard screening tool for examining in-service above ground storage tank floors for corrosion during API 653 inspections. Significant strides have been made in recent years regarding calibration and operator qualification. Equipment functionality and sensitivity has also improved. Contact Hi-Tech Testing today to discuss your tank inspection needs.