1. PDT 154 MATERIALS TESTING LIQUID PENETRANT TESTING
MRS NOORINA HIDAYU JAMIL
FACULTY OF ENGINEERING TECHNOLOGY
UNIVERSITI MALAYSIA PERLIS

2. Introduction Also known as Penetrant Testing / Inspection (PT/I),
Dye Penetrant Testing/Inspection (DPT/I),
Liquid Penetrant Testing (LPT).
Penetrant Flaw Detection (PFD).

3. Intrduction Liquid (or dye) penetrant testing is:
surface testing method.
used for detecting surface-breaking defects.
applicable to all materials - except for high porous (absorbing) materials.

4. Penetrant Testing: SurfaceTesting
Cannot be detected by Penetrant Testing
OPEN TO SURFACE/ SURFACE BREAKING
SUBSURFACE
INTERNAL
Penetrant Testing can only detect surface breaking defects
Penetrant must be able to enter the defect to form indication

5. Materials
LPT can be used to inspect almost any material provided that its surface is not extremely rough or porous. Materials that are commonly inspected using PT include the following:
Metals (aluminum, copper, steel, titanium, etc.)
Glass
Many ceramic materials
Rubber
Plastics

6. Not suitable for porous or very absorbent materials
Examples:
Wood
Cloth/fabric
Unglazed ceramic /pottery

7. LPT Detection
Liquid penetrant inspection is used to inspect of flaws that break the surface of the sample. Some of these flaws are listed below:
Fatigue cracks
Quench cracks
Grinding cracks
Overload and impact fractures
Porosity
Laps
Seams
Surface defect in welds

8. Fatigue Crack

9. Quench Crack

10. A gear with a fractured tooth showing adjacent teeth with incipient cracks. There are also surface cracks due to heavy grinding which line up with the fatigue cracks and might have acted as stress raisers.

11. Basic Principle of PT Liquid Penetrant & Developer
Penetrant testing is a process in which the liquid penetrant is drawn into small openings by capillary action when it is applied to a surface.

12. After a specified time, excess penetrant is removed from the surface.

14. Then developer is applied to the surface
Then developer is applied to the surface. The developer absorbs residual penetrant drawn from the flaw (reserve capillary action) leaving a bright-colored penetrant “bleeding” through the developer’s white background giving a clear visual indication of cracks, porosity, and other flaws.

17. Penetrant which pulled out from the defect by the developer and forms indication of the defect
Indications

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

20. Capillarity The formula = 2S Cos  W = Capillary pressure
The ability of a material to enter opening examples: tube or defects
The formula
= 2S Cos  W
= Capillary pressure
S = Surface tension
 = Contact angle
W = Width of opening

21. Penetrant Properties Good Wetting Ability High Surface Tension
Viscosity

22. 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.

23. Contact angle
Less than 90º High
90º Moderate
More than 90º Low

24. Meniscus The contact angle determines the wetting ability
The smaller the contact angle the higher the wetting ability

25. A good penetrant should have concave meniscus
Mitre
Convex
A good penetrant should have concave meniscus

26. Surface Tension High Surface Tension Low Surface Tension
Example: Water
Example: Oil

27. Surface Tension From the formula Capillary pressure = 2S Cos O W
The higher the surface tension the higher the capillary pressure

28. Surface Tension
Strongly affected by contamination
HIGH
LOW

29. 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

30. Advantages & Disadvantages of LPT

31. Advantages of LPT
The method has high sensitive to small surface discontinuities/defects.
The method has few material limitations, i.e. metallic and nonmetallic, magnetic and nonmagnetic, and conductive and nonconductive materials may can be inspected.
Large areas and large volumes of parts/materials can be inspected rapidly and at low cost.

32. Advantages
Parts with complex geometric shapes can be routinely inspected.
Indications are produced directly on the surface of the part.
Aerosol spray cans make penetrant materials very portable.
Penetrant materials and associated equipment are relatively inexpensive.

33. Disadvantages of LPT Only surface breaking defects can be detected.
Only materials with a relative nonporous surface can be inspected.
Precleaning is critical as contaminants can mask defects.

34. Disadvantages
Metal smearing from machining, grinding, and grit or vapor blasting must be removed before LPT.
Defect
Peened or Closed

35. Disadvantages
The inspector 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 or materials is required.
Chemical handling and proper disposal is required.

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

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

38. PENETRANT
Colour Contrast
Dual sensitivity
Fluorescent

39. Colour Contrast Also known as Visible Dye Penetrant
Uses white light : Daylight or artificial white light
Bright coloured dye : usually RED

40. Fluorescent Penetrant
Fluorescent :Material with the ability to convert one wavelength to another.
570nm
365nm
UV Light
Visible Light
Fluorescent Dye

41. Ultraviolet light

42. UV-A Source : Mercury vapour arc lamp
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

43. Fluorescent vs Colour Contrast
Fluorescent more sensitive
More difficulty in monitoring fluorescent penetrant removal

44. Basic Processing Steps of a Liquid Penetrant Testing

45. Procedure
Standards specify test methods, eg ASTM E165, ASME Section V, ISO 3879, AS 2062, BS EN571, Mil-L-25135, Mil-L-6866 etc.
All materials (penetrant, remover and developer) should be from one supplier as a kit
Follow the supplier's directions
Parts must be clean and dry and at the correct temperature (~50oC)
Precleaning requires removal of all oil, grease, dirt, paint, slag, spatter.

46. 6 Basic Steps Pre-cleaning Penetrant application
Removal of excess penetrant
Application of Developer
Inspection
Post-cleaning

47. Preclean/Surface Preparation
Penetrant Application
Dwell
Penetrant Removal
Dry
Developer
Dry
Inspect
Post Cleaning/Surface clean

48. 1. Surface Preparation
One of the most critical steps of a liquid penetrant inspection is the surface preparation.
The surface must be free of oil, grease, water, or other contaminants that may prevent penetrant from entering flaws/defects.
The sample may also require etching if mechanical operations such as machining, sanding, grinding or grit blasting have been performed.
These and other mechanical operations can smear the surface of the sample, thus closing the defects.

49. Pre-Cleaning: The most important step
Contaminants:
Restrict penetrant from entering defects
Produce false indications

50. Surface Preparation Scale Oils and Greases Physical Methods
Chemical Methods
Capable of removing contaminants on the surface but not in the defects
Chemical reactions to remove
Scale
Slag
Corrosion products
Carbon
Oils and Greases

51. Methods of Cleaning
Physical methods
Brushing
Blasting
Chemical methods
Hot solving degreasing
Vapour degreasing
Cold solvent degreasing
Solvent material with emulsifiers
Alkaline cleaning
Acid pickling
Steam cleaning
Paint removal

52. After abrasive cleaning
Physical Cleaning
Grinding
Abrasive Blasting
Wire brushing
Defect
Peened or Closed
Before Cleaning
After abrasive cleaning

53. Light Acid Etching Light Acid applied
Thin layer of the surface dissolved

54. Light Acid Etching The defect opened again to the surface
After Acid Etching

55. Chemical Methods Solvent Components Heating Element
Hot Solvent Degreasing
Heating Element
Solvent
Components

56. Vapour Degreasing The most effective method for degreasing Condensor
Components
vapour
vapour
Solvent
Drip Tray
Heating Element
The most effective method for degreasing

57. Steam Cleaning
For large objects

58. Chemical Methods Other methods Cold solvent Degreasing
Solvent materials with Emulsifiers
Acid / Alkaline Cleaning
Paint Removal
Ultrasonic Cleaning

59. Ultrasonic Cleaning
Solvent/ water
Components
Ultrasonic Crystal
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60. 2. Penetrant Application
Once the surface has been thoroughly cleaned and dried, the penetrant material is applied by spraying, brushing, or immersing the parts in a penetrant bath.
Type 1: Fluorescent Penetrants
Type 2: Visible Penetrants
Type 3: Dual

61. Penetrant Application
Spraying
Methods
Brushing
Immersion

62. Penetrant application
Electrostatic spraying
Special Methods
Thixotropic penetrants

63. Electrostatic Spray Extrator Fan Component +ve charged
Penetrant -ve charged

64. Thixotrophic Penetrant
Two stages of viscosity penetrant
Penetrant stirred
Shear action convert it into liquid
Penetrant in Gel Form
Simillar to NO DRIP Paint
Ideal for overhead works
Higher viscosity means longer contact time required
Applicable to higher temperature component upto 200OC

65. Penetrant Application Critical factors
Penetration / Dwell time/ Contact time
The time allowed for the penetrant to be on the surface of component
Component Temperature
Low temperature: Penetrant more viscous and sluggish, precipitation occurs. Requires longer Contact time.
High Temperature: Penetrant may evaporate, dries up, or flash.
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66. 3. Penetrant Dwell
The penetrant is left on the surface for a sufficient time to allow as much penetrant as possible to be drawn from or to seep into a defect.
Dwell times are usually recommended by the penetrant producers or required by the specification being followed.
The times vary depending on the application, penetrant materials used, the material, the form of the material being inspected, and the type of defect being inspected.
Minimum dwell times typically range from 5 to 60 minutes. Generally, there is no harm in using a longer penetrant dwell time as long as the penetrant is not allowed to dry.
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67. 4. Excess Penetrant Removal
This is a most delicate part of the inspection procedure because the excess penetrant must be removed from the surface of the sample while removing as little penetrant as possible from defects.
Depending on the penetrant system used, this step may involve cleaning with a solvent, direct rinsing with water, or first treated with an emulsifier and then rinsing with water .

68. Removing excess penetrant
Penetrant are then classified by the method used to remove the excess penetrant form the part.
Method A : Water washable.
Method C : Solvent removable.
Post Emulsifiable
Method B : Lipophilic (Oil-based emulsifier)
Method D : Hydrophilic(water soluble detergent emulsifier)

69. Removal of Excess Penetrant
Solvent Removable
Water washable
Post Emulsifiable
The method of removal influences the make-up penetrant.

70. Removal of Excess Penetrant
Solvent Removable
Clean of the excess with a lint free cloth.
Wipe with a solvent dampened rag.
Solvent not be sprayed directly onto the item under test.

71. Solvent Removable DISADVANTAGES ADVANTAGES Not suited to batch testing
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

72. Water Washable Penetrant
Also known as SELF-EMULSIFIED PENETRANT
Pre-mixed penetrant and emulsifier
Easily washed by water rinse
Oily Penetrant
Emulsifier
Water Washable Penetrant + =

73. WATER SPRAY
PENETRANT

74. Penetrant been washed off
Shallow wide defects
Deep or gross defects shows

75. Removal of Excess Penetrant
Water Washable Penetrant
Water shall free from contaminants example: oil
Pressure usually below 2 bar
Water spray
Temperature max 50ºC as BS EN 571

76. Water WashablePenetrant

77. Water Washable Penetrant
ADVANTAGES
Ideal for rough surfaces
Suitable for batch testing
Cheaper than other methods
DISADVANTAGES
Susceptible to over washing
Least sensitive method
Requirement for a water source
Corrosion problems

78. Removal of Excess Penetrant
Post Emulsifiable
Hydrophilic (Method D)
2 Post emulsification systems
Lipophilic (Method B)
Emulsification time critical:
Too short- too much background
Too long-penetrant in shallow/ wide defect removed
Determined by experimentation

79. 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 mixed with emulsifier
Penetrant in defects left unaffected

80. Post emulsifiable Now the surface penetrant is water washable
Post Emulsifiable Penetrant
Emulsifier

81. Post emulsifiable Water Spray Penetrant mixed with emulsifier

82. Penetrant in defect not mixed with emulsifier : NOT REMOVED

83. Emulsifier Lipophilic Oil based
Difficult to control emulsification time:
too quick (diffusion of oil and oil)
Rarely used nowadays
Hydrophilic
Water based
Similar to domestic detergent
Easier to control emulsification time
Offers OPTIONAL FIRST STAGE RINSE

84. Lipophilic Remover * The emulsification time is critical
A. Apply the penetrant
B. Apply emulsifier
C. Diffusion Begins
E. Rinsing
D. Diffusion complete
* The emulsification time is critical
* Usually not more than 3 minutes

85. Hydrophilic Remover (Detergent)
B. Pre-rinse
Clear water
Detergent molecules
C. Detergent Action
Begins
A. Apply the penetrant
E. Rinsing
D. Detergent + Agitation
F. Clean Surface

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

87. Drying It is an intermediate stage after penetrant removal
Purpose of this stage to remove any droplets and
puddles of water from the part.
Methods of drying are :-
a) wiping with clean, dry, lint - free cloth
b) evaporation at ambient temperature
c) evaporation at elevated temperature
d) forced air circulation
e) combination of the methods listed under a) to
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* The surface temperature shall not exceed 50° C during drying

88. 5. Developers Application
The role of the developer is to pull the trapped penetrant material out of defects and to spread the developer out on the surface of the part so it can be seen by an inspector.
Another function that some developers performs is to create a white background so there is a greater degree of contrast between the indication and the surrounding background.

89. Developer Application
A thin layer of developer is then applied to the sample to draw penetrant trapped in flaws/defects back to the surface where it will be visible.
Developers come in a variety of forms that may be applied by dusting (dry powdered), dipping, or spraying (wet developers).
Developer

90. Developer
Functions:
Bleed the penetrant back to the surface by the reverse capillary action
Spread the penetrant into larger area : easier to be seen
Improve background contrast

91. Developer Properties Easily wetted Contrasting colour Easily removed
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

92. Developers classify into six standard forms:
The developer can be applied as a dry powder, or dissolved or suspended in a liquid carrier.
Developers classify into six standard forms:
Dry Powder
Aqueous - Water Soluble
- Water Suspendible
Nonaqueous Type 1 Fluorescent (Solvent Based)
Nonaqueous Type 2 Visible Dye (Solvent Based)
Special Applications

93. Dry powder developer
puffer
dust cabinet

94. electrostatic powder spray guns

95. Dry powder developer DISADVANTAGES ADVANTAGES
Difficult to ensure if it has been properly applied
Fine powders can be hazardous
Do not offer a high degree of colour contrast
ADVANTAGES
Easy to handle
No hazardous vapours
Easy to remove

96. The particles settled down if not agitated
Aqueous Developer
TWO TYPES
WATER SUSPENDIBLE
WATER SOLUBLE
The particles settled down if not agitated

97. Form b - Water Soluble The developer can be applied by:
Water soluble developers consist of a group of chemicals that are dissolved in water and form a developer layer when the water is evaporated away.
The developer can be applied by:
Spraying (the best method)
Dipping, pouring, or brushing the solution on to the surface is sometimes used but these methods are less desirable.
Parts coated with a water soluble developer must be forced dried.

98. Water Suspendible
This developers consist of insoluble developer particles suspended in water.
Water suspendible developers are applied to parts in the same manner as water soluble developers.
Parts coated with a water suspendible developer must be forced dried.

99. Aqueous Developer
ADVANTAGES
No vapours or dust
Cheaper than non-aqueous
DISADVANTAGES
Difficult to apply evenly
Requires drying after application
Proper mixing required
Too little developer particle : Very weak indications
Too much : Developer layer will crack when dry

100. Non-aqueous Developer
Nonaqueous developers are generally recognized as the most sensitive when properly applied.
Nonaqueous developers suspend the developer particle in a volatile solvent and are typically applied with a spray gun or aerosol spray cans.
Since the solvent is highly volatile, forced drying is not required.

101. Non-Aqueous Developer
ADVANTAGES
Most sensitive
Dry Powder
GAP: Penetrant unable to be developed

102. Non-Aqueous Developer
Solvent can bridge the gap,
dilute the penetrant
Solvent
And develop the penetrant to surface

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

104. Solvent Based developer
Dry powder developer
Solvent Based developer
Solvent
Developer particle
Gap
The solvent mix with the penetrant resulting -larger volume
The solvent is pull in the defect by capillary force
The Penetrant unable to be developed due to the gap
Non-Aqueous (Solvent-Based) developer is the MOST SENSITIVE developer
Reason: The ability to bridge the gap - solvent action

105. Form f - Special Applications
Special developers that are primarily used when a permanent record of the inspection is required.
Plastic or lacquer based developers are commonly used as special developer.

106. Penetrant Testing
Penetrant which pulled out from the defect by the developer forms indication of the defect
Indications

107. Developer action
Capillarity
Light scattering
Solvent action

108. Penetrant Testing Developer applied to surface
Penetrant drawn back out of the defect by reverse capillary action

109. Light Scattering I0 If

110. Light Scattering The light scattered by the developer :
spread the light to wider angle
Improve seeability

111. Light Scattering If =  I0 ( 1 - e-kcx )
If = Intensity of fluorescence
I0 = Intensity of UV light
k = Ability of penetrant to absorb UV light
c = Concentration of dye
x = Thickness of penetrant film
= Amount visible light dye will produce

112. Developer action
Capillarity
Light scattering
Solvent action

113. Non-Aqueous Developer
Solvent can bridge the gap,
dilute the penetrant
And develop the penetrant to surface
Solvent

114. Developers: Considerations
Solvent Based (Non-Aqueous) is the most sensitive developer
Problem: Tendency to apply too much-will bury the indication
Dry powder developer mainly used with fluorescent penetrant
Dry powder restrict bleed out- only stick to wet area where most likely the area of defect
Aqueous developer mixture
Too low – will produce weak indication
Too strong- will crack when dry

115. Development Aqueous liquid Non-aqueous liquid Dry Powder (Suspendible)
(Soluble)
- Component must be
dry
- Applied by :-
* Dipping
* Blowing
* Dust storm cabinet
-Dry after application
-Applied by
*Aerosol
-Applied by :-
*Immersion
*Spraying
*Brushing
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116. 6. Dry/Indication Development
The developer is allowed to stand on the part surface for a period of time sufficient to permit the extraction of the trapped penetrant out of any surface flaws/defects.
This development time is usually a minimum of 10 minutes and significantly longer times may be necessary for tight cracks.

117. Inspection
Inspection is then performed under appropriate lighting to detect indications from any flaws which may be present.
Indications

119. Inspection Colour Contrast White light above 500 Lux Fluorescent
Indications viewed during and after the development time
Lighting levels critical
Colour Contrast
White light above 500 Lux
Fluorescent
White light below 10 Lux or 20 Lux
UV-A above 1mW / cm2 or 1000µW / cm2

120. Viewing Conditions COLOUR CONTRAST PENETRANT Minimum 500 LUX
Day light or artificial White Light
ILLUMINATION:
Minimum 500 LUX

121. Viewing Conditions FLUORESCENT PENETRANT
Ambient Background Lighting Maximum 20 lux
5 minutes minimum for operator’s eyes become dark-adapted
UV-A IRRADIANCE
1 mW / cm² or
1000µW / cm² Minimum
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122. Clean Surface
The final step in the process is to throughly clean the part surface to remove the developer from the parts that were found to be acceptable.