MFLTRATADAThis is a technique of electromagnetics method, which consists of inspection of all the length of tube using a probe built with two strong permanent magnets. These magnets generate a magnetic field  which saturate the tube wall.

An absolute probe measures the time variation of magnetic field caused by thickness losses.

When a failure is found between two magnets, a perturbation in magnetic field takes place resulting in “leaking” of a small quantity of magnetic flow for the internal diameter of the tube.

This flow is detected by a differential bobbin, located between magnets. A bobbin put in  the end of probe detects the residual magnetism and allows the discrimination between internal and external damages.

The main advantages in this technique are:

  • Inspection of finned tubes
  • It allows the inspection of tubes partially embedded
  • It detects pits, circumferential crackings and thickness loss
  • The presence of support plates and tubesheets is not very sensitive.
  • It allows high speed of data acquisition
  • The interpretation of results is relatively simple

The main disadvantages are:

  • Sizing is precarious, it is recommended specially for detection of damages
  • The fill factor required is similar to eddy-current
  • It requires manufacturing of standard tubes to each type of examined tube