Dye Penetration Testing

Dye Penetration Testing

Any liquid with good wetting properties will act as a penetrant, which is attracted into surface-breaking discontinuities by capillary forces. Penetrant which has entered a tight discontinuity will remain even when the excess is removed.

Application of a suitable developer will encourage the penetrant within discontinuities to bleed out. If there is a suitable contrast between the penetrant and the developer an indication visible to the eye will be formed. Provided by either visible or fluorescent dyes.

Use of fluorescent dyes considerably increases the sensitivity of the technique. The technique is not applicable at extremes of temperature as at below 5°C the penetrant vehicle, normally oil, will become excessively viscous causing an increase in the penetration time with a consequent decrease in sensitivity.


Above 60°C the penetrant will dry out and the technique will not work.

Advantages

• All non porous materials
• Portable
• Applicable to small parts with complex geometry
• Simple
• Inexpensive
• Sensitive
• Relatively low skill level (easy to interpret)

Limitation

• Will only detect defects open to the surface
• Requires careful space preparation
• Not applicable to porous surfaces
• Temperature dependent
• Cannot retest indefinitely
• Potentially hazardous chemicals
• No permanent record
• Time lapse between application and results
• Messy

Normal Dye Penetrant Testing

Fluorescence Dye Penetrant  Testing

Source :
CSWIP 3.1 - Welding Inspector WIS5, TWI Ltd, 2017.