A Practical Study of the Behaviour of Magnetic Particles in Magnetic Leakage Fields

Abstract

Magnetic Particle Inspection is one of the oldest methods of non-destructive testing and remains very important today. Throughout the years during which the method has been used many practical studies of its application have been published as have reports concerning the basic physics of the process, the levels of applied magnetic field needed for generating leakage fields at magnetic discontinuities. During the last twenty-five years there have been several publications on the nature of the fields within discontinuities and the relationships between these fields and the leakage fields in the vicinity. In contrast to this the amount of published work concerning the magnetic particles themselves is very small and reports of the behaviour of magnetic particles in magnetic fields are even rarer. This study was designed to observe the general behaviour of magnetic particle inspection inks in the presence of leakage fields. Both black and fluorescent particles suspended in oil and water based carrier fluids were studied.