Dye penetrant (liquid penetrant) is a defect inspection on the use of the principle of capillarity on liquids. Its working principle is to penetrate the open defects on the surface of the object. Non Destructive Testing using penetrant fluids can be used in ferrous and non ferrous objects, conductors and non-conductors, magnetic and non-magnetic, and all alloy and plastic. Weakness nondestructive testing with this method is the detection of defects can only be done on the surface of the specimen.
Common procedures performed on this test include:
a. Cleaning early (pre-cleaning)
The surface of the test material must be cleaned in advance of dirt that will prevent the entry of liquid penetrating into the defect. Surfaces must be free of paint, dirt, crust, varnishes, oils, fillings, lubricants, oxide, wax, rust, machining fluids, and the rest of the previous penetrant inspection.
A good cleaning procedure will remove all contaminants from the test object and not leave remnants that can interfere with the inspection process. The means used to pre-dry, among others:
- Detergents (detergent)
- Steam grease remover (vapor degreasing)
- Steam cleaners (steam cleaning)
- Substances cleaning solvent (dry solvent)
- Cleaning with ultrasonic (ultrasonic cleaning)
- In the etching (etching)
b. The use of liquid penetrant
Once the surface has been cleaned and dried thoroughly, penetrant materials used by spraying, rubbing, or dipping the specimen into a tub of penetrant.
After use penetrant, it takes some time for the liquid penetrant really seep into the defect. The time it takes liquid penetrant that can seep into the so-called penetrant flaw time / penetrant dwell time. The time needed usually ranges between 5-60 minutes.
c. Eliminating residual penetrant
Excess residual penetrant on the surface of the specimen, must be removed as small as possible. Cleaning is done in different ways depending on the type of penetrant used.
Types use liquid penetrant can be categorized based on the type of cleaner is used, which can be cleaned with a solvent and which can be cleaned with water. Penetrant cleaner types including Water-washable, Solvent-removable, post-emulsifiable lipophilic and hydrophilic post-emulsifiable.
After the process of removing the liquid penetrant done, the drying process should be carried out with hot air is blown with a blower where the temperature should not exceed 225º F.
e. The use of substances developers (developers)
To draw the liquid penetrant testing that surfaced used liquid developers. Type of developers there are two types of liquid and dry type. Developer liquid type made of powder dissolved in water and volatile solvent. Developer substances must be white in order to provide color contrast to liquid penetrant, so defects will be obvious.
Dry type developer substances commonly used for liquid penetrant fluorescent types while the liquid developer used in liquid penetrant contrasting color. The use of liquid developer is shown in the figure below:
f. Interpretation of disability
Interpretation of defects that arise should be done as soon as possible after the visible indications of the developer substance. To get the good interpretation on liquid penetrant inspection method must be done on the type of fluorescent dark room with the aid of ultraviolet light (black light).