The liquid penetrant testing method is defined as a Physical chemical nondestructive testing procedure designed to detect and expose surface discontinuities in nonporous materials. The method also reveals void typo subsurface discontinuities that are open to the surface.The objective of liquid penetrant testing is to locate cracks, porosity, laps, seams and other surface discontinuities rapidly and economically.
Classification of penetrant Materials
From 1955, Classification or designation of penetrant materials has followed the military specification, MIL-I-25135. At that time, penetrant materials were listed as six family groups. In 1964, a seventh group, Group VII, consisting of aerosol packaged group VI penetrants. Was added. In 1982, another change in designation occurred high sensitivity penetrant. By 1980, it became apparent that additional designations were necessary to include:
- Types of penetrant dye
- Methods of removal
- Penetrant sensitivities
- Forms of developers
- Classes of solvent removers
The MIL-I-25135 D revision, released in June 1985, incorporated these designations. A subsequent revision, MIL-I-25135E, was released in June 1989. A consensus document (SAE/AMS) superseded MIL-I-25135 E in August 1996, However, the designations are identical. The revisions also eliminate the family group (Penetrant, emulsifier and developer) and substitute the system concept is based on the fact that manufacturers formulate their penetrants and emulsifiers/removers to be used. The use of one manufacturer`s penetrant with another manufacturer`s lipophilic emulsifier or hydrophilic remover may not produce optimal results. Therefore, a manufacturer`s penetrant and emulsifier/remover are considered to be a system and the components are not interchangeable from manufacturer to manufacturer. Developers and solvent removers are not part of the system and, therefore, any qualified material may be used. However, because each manufacturer has its own proprietary formula., the specification prohibits the mixing or combining of developers or solvent removers of different manufacturers.