Non-Destructive Testing - Dye Penetration Inspection (DPI)

Question 1

What are the steps of PDI

Answer 1

1. A liquid with high surface wetting characteristic is applied to the surface of the part and allowed time to seep into the surface breaking defects (liquids are coloured so that they provide good contrast against the developer, usually red liquid against white developer)
2. The excess liquid is removed from the surface of the part (using water or other method)
3. A developer (powder) is applied to the part. This pulls the trapped penetrant out of the defect and spread onto the surface
4. Visual inspection is the final step in the process

Question 2

List 3 advantages of DPI

Answer 2

Any 3 of:

• The method has a high sensitivity to small surface discontinuities
• The method can be used on a variety of materials
• Large areas and large volumes can be inspected rapidly at low costs
• Parts with complex geometric shapes can be routinely inspected
• Indications are produced directly on the surface of the part and constitute a visual representation of the flaw
• Aerosol spray cans make penetrant materials very portable

Question 3

List 3 disadvantages of DPI

Answer 3

Any 3 of:

• Only surface breaking defects can be detected
• Only materials with relative nonporous surfaces can be inspected
• Pre-cleaning is critical as contaminants can mask defects
• Must have direct access to the surface being inspected
• Surface finish and roughness can affect inspection sensitivity
• Multiple process operations must be performed and controlled
• Post cleaning of acceptable parts is required
• Chemical handling and proper disposal is required

Question 4

What are the two main factors for using Liquid penetrant inspection (LPI)

Answer 4

relative ease

flexibility

Question 5

For what surfaces can LPI NOT be used on?

Answer 5

Extremely rough or porous surfaces