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Chapter 3 - Liquid Penetrant Inspection (LPI)/Penetrant Testing (PT) [Part…
Chapter 3 - Liquid Penetrant Inspection (LPI)/Penetrant Testing (PT) [Part 1]
How does
PT work?
In penetrant testing, a liquid with high surface wetting characteristics is applied to the surface of a component under test
The penetrant "penetrates" into surface breaking discontinuities via capillary action and other mechanisms
Excess penetrant is removed from the surface and a developer is applied to pull trapped penetrant back the surface
With good inspection technique, visual indications of any discontinuities present become apparent
What makes
PT work?
Every step of the penetrant process is done to promote capillary action
This is the phenomenon of the liquid rising/climbing when confined to small opening due to surface wetting properties of the liquid
Some examples:
Plants and trees draw water up from the ground to their branches and leaves to supply their nourishment
The human body has miles of capillaries that carry life sustaining blood to our entire body
Basic Process
of PT
Remove Excess
Apply Developer
Apply Penetrant
Visual Inspection
Clean & Dry Component
What can be
Inspected via PT
Almost any material that has a relatively smooth, non-porous surface on which discontinuities or defects are suspected
What can NOT be
Inspected via PT
Components with rough surfaces, such as sand castings, that trap & hold penetrant
Porous ceramics
Wood & other fibrous materials
Plastic parts that absorb/react with the penetrant materials
Components with coatings that prevent penetrants from entering defects
What Types of Discontinuities
can be Detected via PT
All defects that are open to the surface
Rolled products
Castings
Forgings
Welds
Choices of
Penetrant Materials
Types of
Penetrants
Dye Penetrants: solution of red dye which reveal red indication on the white developer
Florescent Penetrants: solution containing fluorescence which emits green fluorescence indication when view in dark
Method
Water washable
Solvent Removable
Post emulsifier
Developer
In the
form of:
Dry Powder
Wet, Water Soluble
Wet, Water Suspendable
Wet, Non-Aqueous
What is a penetrant and what
makes a good penetrant?
But, the liquid penetrant must posses certain properties
Basically, any liquid could be considered a penetrant
Properties
(Liquid penetrant posses)
Penetration
Fluidity
Stability
Washability
Drying characteristics
Wetting ability
Sensitivity Levels
Level 3 - High SensitivityLevel
Level 2 - Medium Sensitivity
Level 4 - Ultra-High Sensitivity
As the sensitivity level increases, the number of nonrelevant indications also increases.
Level 1 - Low Sensitivity
Properties that affect
Penetrant Testing
Surface energy
Density/specific gravity
Removability
Color & fluorescence brightness
Viscosity
Dimensional threshold of fluorescence
Ultraviolet & thermal stability