When a ferromagnetic material is magnetised the flux lines flow inside the component
When there is a discontinuity in the material there is flux leakage
The leaking flux attracts a magnetic medium resulting in an indication.
What is magnetic particle testing?
This method is used for the detection of surface and near-surface flaws in ferromagnetic materials and is primarily used for crack detection. The specimen is magnetised either locally or overall, and if the material is sound the magnetic flux is predominantly inside the material. If, however, there is a surface-breaking flaw, the magnetic field is distorted, causing local magnetic flux leakage around the flaw. This leakage flux is displayed by covering the surface with very fine iron particles applied either dry or suspended in a liquid. The particles accumulate at the regions of flux leakage, producing a build-up which can be seen visually even when the crack opening is very narrow. Thus, a crack is indicated as a line of iron powder particles on the surface.
post emulsifiable liquid penetration testing: It is divided in to two category:
- Method B: Post-Emulsifiable, Lipophilic
- Method D: Post-Emulsifiable, Hydrophilic
General formulas used in Ultrasonic flaw detection.
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Penetrant Classification System
Type 1 Fluorescent Dye
Type 2 Visible (Red) Dye
Method A Water Washable
Method B Post Emulsifiable, lipophilic (oil base)
Method C Solvent
Method D Post Emulsifiable, hydrophilic (water base)
Class 1 Halogenated (non-flammable)
Class 2 Nonhalogenated (flammable)
Class 3 Special Application
Form a Dry Powder
Form b Water Soluble
Form c Water Suspendable
Form d Nonaqueous Type 1 Fluorescent (solvent based)
Form e Nonaqueous Type 2 Visible (solvent based)
Form f Special Application
Level 1/2 Ultra Low
Level 1 Low
Level 2 Medium
Level 3 High
Level 4 Ultra High