Dye penetrant inspection (DP), also called Penetrant Testing(PT), is a widely applied and low cost inspection method used to check surface-breaking defects in ferrous materials including our bolt products. 

For ferrous components magnetic-particle inspection is often used instead for its subsurface detaction capability. Liquid penetrate inspection is often used to detect casting, forging and welding surface defects such as hairline cracks, surface porosity, leaks in new products.

Inspection steps:

1. Pre-cleaning 

The test surface is cleaned to remove any dirt, paint, oil, grease or any loose scale that could either keep penetrant out of a defect or cause irrelevant or false indications.

2. Application of penetrant

The penetrant is then applied to the surface of the item being tested. The penetrant is usually a brilliant coloured mobile fluid with high wetting capability.

3. Excess penetrant removal 

The excess penetrant is then removed from the surface.

4. Application of developer

After excess penetrant has been removed, a white developer is applied to the sample. 

5. Inspection

The inspector will use visible light with adequate intensity for visible dye penetrant. 

6. Post cleaning

The test surface is often cleaned after inspection and recording of defects, especially if post-inspection coating processes are scheduled.