Liquid Penetrant Testing
Liquid penetrant testing is used to detect surface breaking flaws, which is not restricted to just ferromagnetic materials but all non-porous materials. The method is based on a liquid penetrant being applied to the test area by using the capillary effect to draw the liquid in any surface breaking flaws.
Once excess penetrant has been removed from the test piece a coat of developer is applied causing the penetrant in any surface breaking flaws to ‘bleed’ out to the surface allowing for the flaw to be easily identified.
Discontinuities can be best detected when the direction of magnetic field is perpendicular. The chance of detection reduces as the angle between the magnetic field and the plane of defect decreases. When the angle between the magnetic field and the plane of defect is zero, i.e. the magnetic field is parallel with the plane of defect then the chance of detection becomes zero.
