MAGNETIC FLUX EXCLUSION (MFE)

MFE is typically used on above ground storage tank floors as a rapid way to inspect the large floor area for wall loss. It is also sometimes used on heat exchanger tubing, and process piping as a screening technique for wall loss. MFE can be performed on all carbon steel materials.

For tank bottoms, a magnetic scanner is used to identify soil and product side floor metal losses. Between the scanner bridge magnetic poles, a near-saturation magnetic flux is induced in the material examined. The scanner sensor detects flux leakage changes when the plate thickness changes. This may indicate discontinuities such as pitting and corrosion are present on the process and/or soil side. The scanner is moved over the entire tank bottom surface to provide the required inspection coverage.

MFE is a fast and sensitive metal loss assessment tool. MFE inspections provide a rapid, reliable, and economic qualitative tank floor assessment with minimal set-up time. Typically, acceptable sensitivity can be obtained through up to 0.500" of combined steel and coating thickness. MFE is a non-hazardous inspection method.

Most tanks get 95% or more of their floor surface inspected with MFE. Multiple scanner configurations are available for specific field applications. MFE can be used in conjunction with other NDT methods to facilitate inspections. MFE requires access to only one side of the material.

MFE is not a quantitative technique for identifying remaining wall thickness, and thus requires ultrasonic follow up when indications are found. MFE cannot differentiate between the response from process side and soil side indications. Poor surface conditions, such as scale, debris and roughness, as well as the presence of certain coatings, may limit the integrity of the inspection. Internal tank components that are close to the floor will limit the access to a particular area.

All thickness losses detected by ultrasound are reported and mapped in a CAD rendering of the floor. If no indications are found, a report stating that a scan was performed will be issued. Standard reports are computer generated and may be completed on-site.