Penetrant testing – Based on the properties of capillary action, or the phenomenon of a liquid rising or climbing when confined to a small opening due to surface wetting properties of the liquid, Penetrant testing is used for finding surface breaking discontinuities on relatively smooth, nonporous surfaces. The types of defects that can be found with Penetrant inspection are:
The basic procedure that is followed to perform liquid penetrant testing consist of the following:
- Rolled Products: Penetrant identifies anomalies (cracks, seams or laminations)
- Castings: cold shuts, hot tears, porosity, blow holes or shrinkage
- Forgings: Illuminating cracks, laps or external bursts
- Welds: To identify cracks, porosity, undercut, overlap, lack of fusion or lack of penetration.
There are two main types of Penetrant, Fluorescent or Visible. Within each method there are several methods including water washable, postemulsifiable-lipophilic, solvent removal and postemulsifiable-hyperdrophilic. The type and penetrant method are chosen based on sensitivity levels 1-4 and are based on job site conditions and other variables.
The main advantages of Penetrant testing are:
- Relatively easy to use
- Used on a wide range of material types
- Large areas or large volumes of parts/material can be inspected rapidly and at low cost
- Parts with complex geometries can be inspected easily
- Indications are produced directly on the surface of the part providing a visual image of the anomaly
- Aerosol spray cans can make equipment very portable