Liquid Penetrant Testing

About liquid penetrant testing

Liquid Penetrant (LP) testing is a non-destructive examination method typically utilized on non-ferrous materials or ferrous materials when magnetic particle examination is difficult to use (Wikipedia, 2005, September 7). During Liquid Penetrant testing, an examiner will use red dye to determine where the equipment flaw exists.

The images here indicate a crack as highlighted with the red dye. 

The lP Testing Process

Before work can begin, the area needs to be thoroughly cleaned. A red dye is placed on the machinery and within 10 to 30 minutes any excess fluid is removed with a cloth doused with solvent remover. Then a white developer is sprayed on the surface that draws the dye into defects to the surface. If one sees a colored dye appear, that indicates the position of the flaw (Wikipedia, 2005, September 7). Once the area has been inspected, the surface area is cleaned. 

Oftentimes, the leaking oil from the machinery also acts as a Liquid Penetrant to an experienced examiner.