1. Liquid Penetrant Inspection

2. Liquid Penetrant Inspection
Dye Penetrant Inspection(DPI)
Penetrant Flaw Detection (PFD)
Penetrant Testing (PT)
Surface inspection method
Applicable to all non-porous, non-absorbing materials

3. 6 Steps in Penetrant flaw detection
Surface preparation
Penetrant application
Removal of excess penetrant
Application of developer
Inspection
Post cleaning and protection

4. 1. Surface Preparation Scale Oils and Greases Physical Methods
Chemical Methods
Scale
Slag
Corrosion products
Oils and Greases
Paints

5. Chemical Methods Vapour Degreasing Hot Solvent Degreasing
Cold solvent Degreasing
Solvent materials with Emulsifiers
Acid / Alkaline Cleaning
Steam cleaning
Paint Removal

6. 2. Penetrant Application
Penetrating fluid applied to component and drawn into defect by capillary action

7. Penetrant Application Critical factors
Penetration / Dwell time
Component Temperature

8. Principle : Capillary Action
Interaction of adhesive and cohesive forces

9. Principle : Capillary Action
Interaction of adhesive and cohesive forces

10. Penetrant Properties Good Wetting Ability High Surface Tension
Viscosity

11. Wetting Ability
Liquids having good wetting ability have a low contact angle.
Liquids having a contact angle of 90º or less will act as penetrants.
Contact angle is strongly affected by surface cleanliness.

12. Contact Angle
Contact
Angle
Liquid
SOLID

13. Contact Angle
LOW
HIGH

14. Surface Tension
HIGH
LOW

15. Surface Tension
Strongly affected by contamination

16. Viscosity Viscosity is a measure of internal friction
It affects the rate at which a liquid flows
Viscosity has a strong effect on the time taken for capillary action to work
A high viscosity penetrant will require a longer contact time and a longer development time
A low viscosity penetrant may drain too quickly from vertical or overhead surfaces

17. Types of Penetrant Colour Contrast Fluorescent
All other factors being equal, fluorescent penetrants provide the best sensitivity
Each of the above may be water washable, solvent removable or post-emulsifiable (in order of increasing sensitivity)

18. C O N T R A S T
C O N T R A S T
C O N T R A S T
C O N T R A S T

20. 2. Penetrant Application
Preceded by a visual inspection
Spraying
Methods
Brushing
Immersion

21. Penetrant application
Electrostatic spraying
Special Methods
Thixotropic penetrants

22. 3. Removal of Excess Penetrant
Penetrating fluid applied to component and drawn into defect by capillary action
Penetrating fluid removed from component surface (but not from defect)

23. Removal of Excess Penetrant
Water washable
Solvent Removable
Post Emulsifiable
Penetrants are formulated for removal by one or sometimes more than one of the above.

24. Removal of Excess Penetrant
Water Washable Penetrant
Minimise mechanical action
Pressure as low as possible
Spray wash
Temperature less than 50ºC

25. Water Washable Penetrant
ADVANTAGES
Usable on rough surfaces
Suitable for batch testing
Cheaper than other methods
DISADVANTAGES
Susceptible to over washing
Least sensitive method
Requirement for a water source

26. Post Emulsifiable Penetrant
Stages
Immerse component in penetrant
Immerse component in emulsifier
Emulsifier diffuses into the penetrant making it water washable
Water wash removes excess penetrant / emulsifier
Penetrant in defects left unaffected

27. Removal of Excess Penetrant
Hydrophilic
2 Post emulsification systems
Lipophilic
Contact time critical
Determined by experimentation

28. Post emulsifiable ADVANTAGES Maximum penetrating ability
Greater control over penetrant removal
DISADVANTAGES
Not suited to rough surfaces
More expensive
More time consuming

29. Removal of Excess Penetrant
Solvent Removable
Clean off the excess with a lint free cloth.
Wipe with a solvent dampened rag.
Thou shalt not spray the cleaner directly onto the item under test.

30. Solvent Removable ADVANTAGES DISADVANTAGES Portability
No water supply needed
DISADVANTAGES
Not suited to batch testing
Requires hand wiping so time consuming
More expensive than water washable
Potentially hazardous chemicals

31. Hot air recirculating oven (max 80ºC)
Drying
Hot air recirculating oven (max 80ºC)
Forced warm air
Dry clean compressed air
Component temperature shall not exceed 50ºC

32. 4. Development
Penetrating fluid applied to component and drawn into defect by capillary action
Developer applied to surface

33. Developer Properties Absorptive Fine texture
Able to mask out background colour
Evenly and easily applicable
Light and even coat
Non-fluorescing
Easily wetted
Contrasting colour
Easily removed
Non-toxic and Non-irritant

34. Developer action
Penetrating fluid applied to component and drawn into defect by capillary action
Developer applied to surface
Penetrant drawn back out of the defect by reverse capillary action

35. Developer action
Capillary Action - Increases the size of an indication far beyond the actual defect size; increases the “thickness” of an indication, thereby increasing it’s colour brilliance.
Light scattering - Aids the conversion of UVA to visible light when using fluorescent systems; reduces background glare when using visible systems.
Solvent Action - Solvent combines with penetrant, reducing penetrant viscosity, thereby inducing a more rapid, more efficient bleed-out.

36. Light Scattering I0 If If If If

37. No Developer
With Developer

38. No Developer
With Developer

39. Development Dry powder Aqueous liquid Component must be dry
Applied by
Dipping
Blowing
Dust storm cabinet
Aqueous liquid
Dry after application
Applied by
Immersion
Spraying
Brushing
Non-Aqueous liquid
Applied by
Aerosol

40. Dry powder developer ADVANTAGES DISADVANTAGES Easy to handle
No hazardous vapours
Easy to remove
DISADVANTAGES
Difficult to see if properly applied
Fine powders can be hazardous
Does not offer the best degree of colour contrast

41. Aqueous Developer
Solutions

42. Aqueous Developer
Solutions
Suspensions

43. Aqueous Developer ADVANTAGES No vapours or dust
Cheaper than non-aqueous
DISADVANTAGES
Difficult to apply evenly
Requires drying after application

44. Non-Aqueous Developer
ADVANTAGES
Most sensitive
Usable with fluorescent or colour contrast
DISADVANTAGES
Hazardous solvents
Higher cost
Need to be correctly applied

45. Developer Sensitivity
Dry powder %
Aqueous solution %
Aqueous suspension %
Non-Aqueous %

46. System Classification
Type of penetrant
Method of penetrant removal
Type of developer

47. System classification
DEVELOPERS
Dry powder
Aqueous
Non-Aqueous
PENETRANT
Colour contrast
Fluorescent
Dual
REMOVAL
Water washable
Solvent
Post emulsifiable

48. 5. Inspection
Indications viewed as soon as practicable after developer application with final assessment taking place after a minimum development time has elapsed.

49. 30 Seconds
1 Minute
15 Minutes

50. 5. Inspection Lighting levels critical Colour Contrast
White light above 500 lux
Fluorescent
White light below 20 lux
UV-A above 1000µW / cm2

51. 5. Inspection Fluorescent Allow 15 minutes lamp warm-up
Allow 5 minutes dark adaptation
Do not wear photo-chromatic spectacles

52. 6. Post Cleaning DPI residues are required to be removed because
They may be harmful to the component or
They may impair subsequent processing

53. Advantages of DPI Applicable to all non-porous materials
Able to test large parts with a portable kit
Batch testing
Applicable to small parts with complex geometry
Simple,cheap, easy to interpret
Good sensitivity
Training requirements typically less than for other NDT methods.

54. Disadvantages of DPI Will only detect defects open to the surface
Careful surface preparation required
Not applicable to porous materials
Temperature dependent
Cannot retest indefinitely
Compatibility of chemicals

55. Penetrant Systems PENETRANT Colour contrast Fluorescent Dual REMOVAL
Solvent
Water washable
Post emulsifiable
DEVELOPERS
Dry powder
Aqueous
Non-Aqueous

56. Selection of System Nature of discontinuities (size and type)
Geometry and intricacy
Surface condition
Component material and application
Size and position
Equipment and expertise available
Cost
Number of components to be tested

57. Control Checks
Tank levels
Overall system performance

58. Overall System Performance
Chromium plated cracked test panel
Cracked test piece
Quench cracked aluminium alloy block

59. Control Checks Tank levels Overall system performance
Rinse water temperature
Oven temperature
Equipment cleanliness
Airline filters
UV-A filters

60. Control Checks UV-A / visible light levels
Fluorescent / colour intensity
Suppliers check
Hydrophilic remover dilution
Developer
Meter / gauge calibrations

61. Control Checks - Frequency
Tank levels
Overall system performance
Rinse water temperature
Oven temperature
Equipment cleanliness
Airline filters
UV-A filters
UV-A / visible light levels
Daily
Weekly
Monthly

62. Control Checks - Frequency
Fluorescent / colour intensity
Suppliers check
Hydrophilic remover dilution
Developer
Meter / gauge calibrations
Monthly
Annual
when fresh
Daily

63. UV(A)

64. Electromagnetic Spectrum
X-rays & Gamma
Electric Waves
Microwaves
Ultra violet
Infra red TV
Light
cm Wavelength

65. Electromagnetic Spectrum
A Damaged Black Light Emits
UV-C
UV-B
UV-A
ULTRAVIOLET VISIBLE
LIGHT LIGHT

66. Fluorescence UV-A Source : Mercury vapour arc lamp + Filter
Precautions
Avoid looking directly at the lamp
Do not use if filter is cracked, damaged or incorrectly fitted

67. Fluorescence and the Electromagnetic Spectrum
Absorbs
Emits
Dual
ULTRAVIOLET VISIBLE
LIGHT LIGHT

68. Fluorescent v Colour Contrast
Fluorescent more sensitive
Less operator fatigue with fluorescent
More difficulty in monitoring fluorescent penetrant removal
Fluorescence may degrade under UV(A), when exposed to acid and high temperatures