1. Visual Inspection
โข Visual inspection also known as visual testing(VT) is one of the most common techniques which
involves the operator looking at the test piece and finding defects that are visible to the naked eye.
This can be aided by the use of optical instruments such as magnifying glasses or computer-assisted
systems (known as 'Remote Viewing'). visual testing remains the most popular NDT method across
all industries..
โข It is a quick and feasible method of tracking product quality at every stage of the manufacturing
process as well as for those products that are in service.
โข With visual inspections, we can detect corrosion, cracks, damage, misalignment, welding defects,
deformation, etc. All we need are simple instruments such as rulers, gauges or a camera.
โข When inspectors are not able to reach hard-to-access places or dangerous environments, drones can
often be the solution.
โข Many industries are in fact using AI and machine learning to improve visual inspection results. For
instance, such technology is becoming common in the maintenance of conveyor belts, rollers and
pulleys in conveyor systems.
โข Visual testing is inherent in most other types of NDT as they will generally require an operator to
look for defects.
โข Ultrasonic and radiographic inspections typically require visual inspections prior to performing the
method. Liquid penetrant and magnetic particle inspections become a visual inspection once the
penetrant or magnetic particles have been applied. A film or digital image that has been taken of a
part will be evaluated using visual inspection.
2. VT Techniques
Direct Visual Testing
โข When addressing VT as a standalone inspection method rather than supporting other methods it is performed
in one of two techniques. First, VT may by performed by direct viewing, normally at a distance no more than
24 in. at an angle less than 30ยฐ from the part using line-of-sight vision. Items evaluated may be weld, surface
coatings, and dimensional measurements. Testing may be enhanced with the use of optical instruments such as
magnifying glasses, optical comparators, mirrors, scales, and supplementary lighting at the inspection
surface.
Remote Visual Testing
โข The second technique in VT is remote visual testing, which addresses visual inspection with the use of
borescopes, fiberscopes and cameras, as well as computer-assisted viewing systems allowing remote viewing.
Remote visual testing is used to identify corrosion, misalignment of parts, internal physical damage, and
cracks. The use of drones is becoming more widely used in petrochemical and structural inspections. Some
specialized drones are designed to be submersed in large tanks to evaluate product, valves, and corrosion.
Visual inspectors in the field today may one day performing visual inspection of welds and the next
controlling a drone evaluating an area that in the past was not assessable to visual inspection without special
access.
3. Advantages of visual testing:
โข Safe
โข Portable
โข Effective
โข Inexpensive
โข Easy to train
โข Minimal or no downtime
โข Minimum or no part preparation needed
Disadvantages of visual testing
โข Only works with surface defects
โข Possible misinterpretation of flaws
โข Cannot detect minute defects without additional optical instruments
