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Visual Inspection is probably the most widely used among all the non-destructive
tests. It is simple, easy to apply, quickly carried out, and usually low in cost.
Even though a component is to be inspected using other NDT methods, a good visual
inspection should be carried out first. A simple visual test can reveal gross surface
defects thus leading to an immediate rejection of the component and consequently
saving much time & money.
BASIC PRINCIPLE -
The basic procedure used in Visual NDT involves illumination of the test
specimen with light usually in the visible region. The specimen is then examined
with eye or by light sensitive devices. The equipment required for visual inspection
is extremely simple, but adequate illumination is absolutely essential. The surface
of the specimen should be adequately cleaned before being inspected.
For visual inspection, adequate lighting i.e.about 800-1000 lux is of prime importance.
The period of time during which an inspector is permitted to work should be limited
to not more than 2 hours on continuous basis to avoid errors due to decrease in
visual reliability and discrimination.
The most valuable NDT tool is the human eye. The eye has excellent visual perception.
The use of optical instruments in visual inspection is beneficial & is recommended
to (a) magnify defects that cannot be detected by the unaided eye and (b) permit
visual checks of areas not accessible to the unaided eye.
Tools include Microscope, Borescope, Endoscope, Flexible Fibre-Optic Borescope,
Telescope etc.
APPLICATIONS -
1. Inspection of plant systems/component for any leakage, abnormal operation
etc.
2. Misalignment of parts in the equipments.
3. Corrosion, erosion, cracks, fracture etc.
4. Defects in the new/repaired weldments such as gross surface cracks, lack of penetration,
tear cracks, excess reinforcements, porosities, mismatch etc.
5. Minute discontinuities with the help of optical aids in pumps, compressors, turbogenerator
parts, instruments etc.
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