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We use dye penetrant examination to detect surface flaws in non-ferromagnetic
materials, typically forged, cast or welded products.
The subject to be examined is first of all thoroughly cleaned chemically. Next, a penetrant is applied (a very fine oil usually dyed bright red of ultra
violet fluorescent) and allowed to remain in contact with the surface for a few
minutes. Provided the surface has been cleaned properly, capillary action will then draw
the penetrant into the crack.
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Next, the surplus penetrant on the surface is removed and a thin coating of
powdered chalk is applied.
After a further period the chalk draws the dye out of the crack rather like
blotting paper, forming a visual indication of the flaw – magnified in width – that is in strong contrast to the background.
Dy penetrant testing is a purely mechanical/chemical process. The various substances used may be applied in a number of ways, from aerosol
cans at the simple end to dipping in large tanks on an automatic basis at the
other.
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