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CHAPTER 2 - Visual Inspection - Coggle Diagram
CHAPTER 2 - Visual Inspection
Visual Inspection is probably the first and most widely used method of NDT. Simplest and easiest method to apply
It involves inspecting and
evaluating components for
Surface condition
Presence of defects
Surface roughness
Dimensional changes
Application of Visual Inspection
Weld Inspection
Metrology
Monitoring in Service
Etch Inspection
In visual inspection, access to the surface is required and its capability relies on good illumination (lighting) & the eyesight of the inspector
Visual inspection can be
enhanced by using various aids
Magnifying glasses
Borescopes
TV camera systems
Surface replication
LIQUID (DYE) PENETRANT
INSPECTION (LPI)
Liquid penetrant inspection (LPI) or Penetrant Testing (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
LPI method is used to reveal surface breaking flaws by bleed out of a colored or fluorescent dye from the flaw
Based on the ability of a liquid to be drawn into a "clean" surface discontinuity or flaw by capillary action
Capillary action is the ability of a liquid to flow in a narrow spaces without the existence of or in even the opposition to external forces like gravity
The tendency such as a liquid to penetrate/migrate into a small opening such as cracks is due to the capillary action
When a liquid wets a surface, the angle of contact / the wetting angle (defined as the angle between the contact surface and the tangent at the point of contact) is less than 90˚. Therefore, wettability reduces as the contact angle increase