What is the difference between dye penetrant and magnetic particle testing?
Answer:
*Dye penetrant testing examines the surface of an item (non destructively) for surface-breaking flaws, such as cracks. A liquid penetrant is applied to the surface and left to soak. The liquid is drawn into any cracks via capillary action. The liquid is typically brightly colored or a fluorescent (under UV light) dye. After the soak time has expired, the excess penetrant is wiped from off and a developer is applied. The developer is usually a dry white powder (for example chalk powder) suspension that is spayed on the component. The developer is drawn out of the crack by reverse capillary action, resulting in a colored indication on the surface that is broader than the actual flaw, and therefore, much more visible. This technique can be used to detect surface flaws on essentially any non-porous material. Typical applications include:
Grinding cracks
Heat zone cracks
Poor weld penetrations
Heat treatment cracks
Fatigue cracks
Inclusions
Laminations
Micro shrinkage
Hot tears
cold shuts
Stress corrosion cracks
Intergranular corrosion.
http://www.contech.com/dye_penetrant.htm...
*Magnetic particle testing is accomplished by inducing a magnetic field in a ferromagnetic material and then dusting the surface with iron particles (either dry or suspended in liquid). Surface and near-surface imperfections distort the magnetic field and concentrate iron particles near imperfections, previewing a visual indication of the flaw. The method is used to inspect a variety of product forms such as castings, forgings, and weldments. Many different industries use magnetic particle inspection for determining a component's fitness-for-use. Some examples of industries that use magnetic particle inspection are the structural steel, automotive, petrochemical, power generation, and aerospace industries. Underwater inspection is another area where magnetic particle inspection may be used to test such things as offshore structures and underwater pipelines.
http://www.contech.com/magnetic_particle...
[This inspection can be applied to raw material in a steel mill (billets or slabs), in the early stages of manufacturing (forgings, castings), or most commonly to machined parts before they are put into service. It is also very commonly used for inspecting structural parts (e.g. landing gear) that have been in-service for some time to find fatigue cracks.]
http://en.wikipedia.org/wiki/magnetic-pa...
Not really a whole lot as far as its use. But dye pen test uses capillary action of the dye to find its way into the cracks and pores. The magnetic particle test uses fine magnetic powders or slurry of poweders to outline cracks and imperfactions. They both indicate similar things, just the difference is in the procedure.
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