Magnetic Leakage Flux Density
Stray flux density is the portion of magnetic flux that leaks out through material discontinuities such as cracks or weld areas. It indicates how much a magnetic field is disturbed by these locations.
Physical-Chemical Mechanism of Action
The magnetic field of a magnet is influenced by materials. Ferromagnetic materials like steel strengthen the field, while others can weaken or block it. At discontinuities such as cracks or weld areas, a magnetic resistance arises that disturbs the flow of the magnetic field and diverts it at these points.
Metallurgical Relevance & Welding Risks
A high leakage flux density indicates strong material discontinuities that significantly affect the magnetic field. This can lead to errors when testing workpieces because the ferromagnetic test particles are not attracted correctly and possible defects can be overlooked. In the weld, a high leakage flux density can indicate incomplete welding operations or cracks that have penetrated the material.
Shop Practice & Action Instructions
To ensure accurate testing, the leakage flux density should be as low as possible during magnetic inspection. This can be achieved by carefully preparing the workpiece before testing and removing any cracks or weld defects. When selecting the magnetic field, make sure it is strong enough to attract the test particles but not so strong that it is disturbed by discontinuities.