SERVICES >> ADVANCED NDT HEAD E&B TUBES

Magentic Flux Leakage ( MFL )

MFL is a tube testing technique primarily designed for rapid testing of ferromagnetic tubes with non-ferromagnetic fins wrapped around them as in Air Fin Coolers. Two strong magnets generate a static magnetic field that saturates the tube wall. When a flaw (Pit, Wall Loss, etc.,) is located between the two magnets, the magnetic flux in the tube wall is disturbed and a small amount of flux will leak in the inner tube. This leak of flux is detected by the coils placed between the magnets. The variation of the flux leakage induces the current in the coils, thereby causing a signal output. This signal output can be used to provide information on wall thickness reduction, if any in the tube.

Magnetic Flux Leakage (MFL) is mainly applied for the inspection Air Fin Coolers; however it can be used for inspecting bare tubes also.

Advantages

• Not affected by the presence of Aluminum Fins.
• Relatively High Speed Inspection. (up to 1meter/sec).
• Very good sensitivity for both Pitting and Circumferential Grooves.

Limitations

• Presence of residual magnetism hampers tube repulls
• More a detection tool & is not very useful for flaw sizing since the signal represents volumetric change and not the change in depth of the flaw
• Signal sensitivity depends on pull speeds & isolated Pin Hole type of flaws cannot be detected
  

Signal Display