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CHAPTER 3: LIQUID (DYE) PENETRANT INSPECTION (LPI) / PENETRANT TESTING…
CHAPTER 3: LIQUID (DYE) PENETRANT INSPECTION (LPI) / PENETRANT TESTING (PT)
Introduction
PT is a
nondestructive testing method
that builds on the
principle of Visual Inspection
PT
increases
the "seeability of
small discontinuities
that the
human eye
might
not be able to detect alone
How does PT work
:question:
in a situation where 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 to the surface
With that, visual indications of any discontinuities present become apparent
What makes PT work
:question:
Key words
: every step of PT process is done to promote
capillary action
Capillary action
: The ability of a liquid to flow in narrow spaces without the assistance of, or even in opposition to, external forces like gravity.
Phenomenon: Liquid rising or climbing when
confined
to
small openings
due to surface wetting properties of the liquid.
Examples: Plants and trees draw water up form the ground to their branches and leaves to supply their nourishment.
What is the basic process of PT
:question:
1) Clean and dry component
2) Apply penetrant
3) Remove excess
4) Apply developer
5) Visual inspection
What can and can NOT be inspected vis PT
:question:
(
YES
)
Almost any material that has a relatively
smooth
,
non-porous surface
on which discontinuities or defects are suspected.
(
NO
)
Components with rough surfaces
(e.g. sand castings, that trap and hold penetrant)
Porous ceramic
Wood and other fibrous materials
Plastic parts that absorb or react with the penetrant materials
Components with coatings
that prevent penetrants from entering defects
What types of Discontinuities can be detected via PT
:question:
All defects that are open to the surface
1) Rolled products
2) Castings
3) Forgings
4) Welds
Choices of Penetrant Materials
Penetrant
Type
1) Dye penetrants
2) Fluorescent penetrants
Method
1) Water washable
2) Solvent removable
3) Post emulsifier
Developer
In the form of
1) Dry powder
2) Wet, Water Soluble
3) Wet, Water Suspendable
4) Wet, Non-Aqueous
What is a penetrant and what makes a good penetrant
:question:
Basically,
any liquid
could be considered a penetrant
BUT
the liquid penetrant must
posses certain properties.
What is the certain properties
:question:
1) Penetration
2) Fluidity
3) Stability (under temperature & humidity)
4) Washability
5) Drying characteristics
6) Wetting abality
Sensitivity Levels
Level 3: High Sensitivity
Level 2 : Medium Sensitivity
Level 4: Ultra High Sensitivity
Level 1: Low Sensitivity
Properties affect PT
1) Surface Energy
2) Density / specific gravity
3) Removability
4) Color & Fluorescence brightness
5) Viscosity
6) dimensional Threshold of Fluorescence
7) Ultraviolet & thermal stability
