Dye Penetrant NDT (PT)

Liquid penetrant testing is another popular non-destructive testing method used to identify surface-level defects.

In this method, a low-viscosity liquid (penetrant) enters the surface defects such as cracks, fissures and voids. The excess liquid is then wiped off and the specimen is left alone for some time (penetrant dwell time).

The inspector then applies a developer that allows the penetrant to move towards the surface. The specimen is again left alone for a prescribed amount of time (developer dwell time).

Now, the inspector performs the surface inspection. If the dye is visible, it can be inspected with the naked eye. In the case of fluorescent dyes, black light is needed for inspection.

We can detect surface discontinuities such as cracks, porosity, seams, laps and leaks using this method.

Advantages of liquid penetrant tests:

• Works with many materials. Material properties such as magnetism, conductivity and metallic/non-metallic do not matter
• Can spot tiny defects such as hairline cracks
• Suitable for complex part geometries
• Low cost
• Can test large areas
• Portable
• Easy to use

Disadvantages of liquid penetrant tests:

• The depth of defects is not known
• Risk of exposure to toxic fumes
• Cannot identify subsurface defects
• Does not work with porous materials
• Time-consuming, generally needs more than 30 minutes
• Messy operation, pre- and post-cleaning are necessary
• Involves handling of chemicals and therefore not it’s not as safe as other methods. Chemical disposal may also become an issue