Dye Penetrant Testing

Primarly oil and lime mixture was used to find defect in casting and welded parts. Today advances in chemical industry modern penetrant liquids are used in nondestructive testing applications.

Liquid penetrant inspection is a method that is used to reveal surface breaking flaws by bleedout of a colored or fluorescent dye from the flaw. The technique is based on the ability of a liquid to be drawn into a "clean" surface breaking flaw by capillary action. After a period of time called the "dwell," excess surface penetrant is removed and a developer applied. This acts as a blotter. It draws the penetrant from the flaw to reveal its presence. Colored (contrast) penetrants require good white light while fluorescent penetrants need to be used in darkened conditions with an ultraviolet "black light".

Liquid penetrant inspection offers flexibility in performing inspections because it can be applied in a large variety of applications ranging from automotive spark plugs to critical aircraft components. Penetrant materials can be applied with a spray can or a cotton swab to inspect for flaws known to occur in a specific area or it can be applied by dipping or spraying to quickly inspect large areas.

Advantages

• Cheap and practical
• Mobile
• Sensitive to detect thin surface discontiniuty
• Applicable for range of materials
• iscontinuities all directions can be detected