MAGNETIC FLUX TUBE INSPECTION
Magnets are used on an inspection probe to generate a static magnetic field that saturates the tube wall. The magnetic flux in the tube wall is disturbed when a flaw is located and a small amount of flux leaks into the tube.
The flux leakage is detected by coils placed in the magnetic field.This type of inspection is suitable for ferromagnetic tubes such as those found in air coolers and heat exchangers.
It has very good sensitivity to pitting, baffle wear, circumferential cracking and wall loss.
It is suitable for ferromagnetic tubes such as those found in air coolers and heat exchangers.
In Magnetic Flux Leakage the signal output is sensitive to speed variation. There is no phase component to the signal and differentiation between OD and ID is made by comparing the signals from the lead and trial coils. As such defect sizing is only semi-quantitive. Generalised wall loss is measured using a Hall sensor. It is similar to eddy-current, in that the inspection requires a reasonable fill factor to achieve good sensitivity.