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What is dye penetration test? Why it is done? & how it is done?

Used to detect cracks in components on board ship. Penetrant is same penetrating oil used to loose a rusted nut & bolt except it contains a dye which will find its way in to the smallest of cracks, even those invisible to the naked eye. Some of them are fluorescent dye, which is then used in conjunction with an ultraviolet light, which makes the cracks glow green when ordinary lighting is reduced.Some of them are developer which makes the dye stand out as a red line. This type usually comes in three aerosols.
• First is cleaner, which is sprayed on it.
• Then the component is allowed to dry.
• Then the penetrating dye is sprayed on & after 5 minutes the excess coating on surface is wiped off.
• The developer is sprayed on which will highlight any crack present.

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