Magnafluxing is an advanced procedure that uses strong magnetic fields to test the structural integrity of metals, especially iron and iron-based alloys. The procedure can determine even microscopic flaws in the surface structure of metals, and so is used to check the quality of a variety of metal parts, pieces and tools.

Magnafluxing consists of submitting the entire structure of the metal to be tested to a strong magnetic field. At the point of imperfections, or the line of seams in the metal, the flaws will cause disturbances in the magnetic field called magnetic flux. The observation of magnetic flux during magnafluxing is the key indication of a problem.

Most magnafluxing procedures use iron oxide to coat the surface of the metal being tested. Disturbances of magnetic flux are visible by the reaction of the iron oxide that coats the surface at the points of the greatest magnetic flux, with the aid of a black light. In effect, the iron oxide gathers to the point of the imperfections, attracted by the magnetic flux.

Magnafluxing can be performed in either wet or dry conditions. In dry conditions, the iron oxide is in the form of a very fine powder, like dust, which is scattered over the part. In wet conditions, a liquid solution of iron oxide is used instead, to coat the entire surface of the metal before subjecting it to a high-energy magnetic field.

Magnafluxing is most commonly used on iron and iron-based alloys, which include steel most prominently. Magnafluxing can also be used on other elements and elemental alloys, including nickel and cobalt. The magnafluxing procedures for different elemental bases and different alloys are not significantly different.

Magnafluxing is extremely useful because it can locate a flaw or potential problem before the worst has happened, when a major malfunction or disaster is still avoidable. They can test steel wheels, pistons and engine casings, and determine if the part might be in danger of exploding or if it is safe for continued use. Many parts are magnafluxed regularly as a part of maintenance.