Liquid penetrant testing (LPT) is a non-destructive test that uses a liquid dye to detect surface defects in materials. The dye is drawn into surface cracks by capillary action, and then a developer is applied to make the defects visible. LPT can be used to find surface cracks, porosity, poor fusion, and inter-granular corrosion.
Here are the steps for LPT:
- Clean the surface: The surface must be free of oil, grease, water, or other contaminants.
- Apply the penetrant: The penetrant is usually a colored fluid that is applied by spraying or brushing.
- Allow the penetrant to soak in: The penetrant needs time to soak into any flaws, which is usually 5 to 30 minutes. The dwell time depends on the penetrant, the material, and the size of the flaws.
- Remove excess penetrant: Remove any excess penetrant and apply a remover.
- Apply developer: Apply a developer, such as a dry powder, to draw out the penetrant in the crack.
- Inspect: Inspect the surface for defects.
- Clean the surface: Clean the surface again.
LPT can be used on both parent materials and welds.
APPLICATIONS
Weld inspection – Structural / Piping
Casting / Forgings / Valves
