An AC Magnetic Flux Leakage (MFL) survey is a non-destructive pipeline inspection method used to detect corrosion, metal loss, and wall thinning in buried or aboveground pipelines.

An AC Magnetic Flux Leakage (MFL) survey is a non-destructive pipeline inspection method used to detect corrosion, metal loss, and wall thinning in buried or aboveground pipelines. The technique works by applying an alternating current to the pipeline, generating a magnetic field within the pipe wall. Magnetic field sensors positioned around the pipeline detect localized flux leakage — anomalies caused by material defects such as pitting corrosion, general wall loss, or coating-related damage.

AC MFL surveys are especially valuable because they can be performed externally, without requiring internal access or pipeline shutdowns. This makes them suitable for in-service inspection of both piggable and unpiggable pipelines. Results are used for pipeline integrity assessment, corrosion growth monitoring, and maintenance planning.

While AC MFL is effective for detecting external and near-surface defects, it may be complemented by other techniques — such as Current Magnetometry Inspection (CMI) or ultrasonic testing — for a comprehensive pipeline condition assessment.