liquid penetrant testing

1. Liquid Penetrant
Testing (PT)
Satyakiran School of NDT
BU-3, SFS, Outer Ring Road, pitampura, Delhi-110088, India
Ph: 91-11-27345252, 27342948; satyakiran@vsnl.com

2. www.satyakir
an.com
Introduction
PT is one of the oldest NDT techniques. Earliest forms
of penetrant inspection was the use of carbon black
on glazed pottery.
This method can be used to detect defects in a wide
range of components provided that the defect break
the surface of the material.
However liquid penetrant testing can be done only on
non-porous materials such as all metals amd alloys,
non metals (plastic, polymers, glassware)

3. www.satyakir
an.com
There are five essential steps
in PT
1. Cleaning and Surface preparation
2. Application of Penetrant
3. Removal of excess penetrant
4. Development
5. Observation and Inspection

4. www.satyakir
an.com
Characteristics of a Penetrant
• Penetration ability – to enter into extremely fine
defects or openings.
• Surface tension & Wettability - to maintain a
continuous film over the part
• Fluidity – ability to drain away through the opening.
• Solubility – capability to dissolve in contaminants
possible in defects.
• Washability – capability to removing penetrant from
the part without dragging out penetrant
trapped in defects.

5. www.satyakir
an.com
Characteristics of a Penetrant
contd...
• Stability – composition should not change over a
wide range of temperature and humidity.
• Resistance to drying during the test
• Viscosity – To control fluidity and washability
• Ignition point – higher to be inflammable
• Chemical composition – to resist corrosion and
reaction with the part

6. www.satyakir
an.com
Visibility of a penetrant
1. Colour contrast method – Deep red
colour against white contrasting
background of developer.
2. Fluorescent method – Glowing green-
yellow or orange colour under ‘black
light’ (near UV)

7. www.satyakir
an.com
Characterization of
penetrant systems
1. Water-washable system – lower sensitivity,
low cost, used for bulk goods in field inspection
2. Solvent-removable system – medium
sensitivity, general purpose
3. Post emulsification system – high sensitivity
and expensive, used in critical inspections
(Based on penetrant removal method)

8. www.satyakir
an.com
Developer should posses
following properties:
• Absorption – developer must be easily wetted by the penetrant
in the flaw and absorptive to suck back.,
• Application – must be easy to apply and capable of forming thin
and uniform surface coating
• Background masking – interference from background colours
should be masked and provide contrasting
background for indications
• Physical characteristics – It must have grain size and shape
to easily disperse the penetrant in the flaw, so that
clearly defined indication is attained. Must neither be
hygroscopic nor excessively dusty.
• Chemical characteristics – must not contain ingredients
harmful to the parts.

9. www.satyakir
an.com
Limitations
• Only surface breaking flaws can be
detected
• Part material should be non porous
• Affected by part temperature
Advantages
• Low cost, no instrumentation
• No need higher operator competence and
experience

10. Process of
Liquid Penetrant
Inspection

11. www.satyakir
an.com
Removal of oxide, rust, weld
spattrer etc:
Wire brushing, or
abrasive blasting
followed by
chemical cleaning
When a number of small
parts involved:
Ultrasonic cleaning
To clean all narrow
openings:
Vapour degreasing

12. www.satyakir
an.com
Penetration dwell time:
5 to 30 minutes

13. www.satyakir
an.com
• Water spray:
Less than 50 psi
• Solvent:
Wipe with a moist
cloth or absorbent
paper
• Post-Emulsifying:
Emulsifier shall be applied by spraying or dipping.
Emulsification time is critical and determined
experimentally (never exceed 5 min.)

14. www.satyakir
an.com

15. www.satyakir
an.com

16. www.satyakir
an.com

17. www.satyakir
an.com

18. www.satyakir
an.com