Visual and Optical Testing

Visual inspection is probably the most widely used among all the non – destructive tests. It is easy to apply, quickly carried out, and usually low in cost. A simple visual test can reveal gross surface defects thus leading to an immediate rejection of the component and consequently saving much time and money, which would otherwise be spent on more complicated means of testing. Visual methods have been developed to a very high degree of precision. Visual inspection involves using an inspector's eyes to look for defects. The inspector may also use special tools such as magnifying glasses, mirrors, or borescopes to gain access and more closely inspect the subject area. Visual examiners follow procedures that range from simple to very complex.

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 such as photocells. The equipment required for visual inspection is extremely simple, but adequate illumination is absolutely essential. The surface of the specimen shoud be adequately cleaned before being inspected.

Optical aids used for visual inspection

  • The Eye
  • Microscope
  • Borescope
  • Endoscope
  • Flexible Fibre-Optic Borescope
  • Telescope

Applications of Visual and Optical Testing

  • Inspection of plant systems for any leakage
  • Misalignment of parts in the equipment
  • Corrosion, erosion, cracks, fractures etc
  • Minute discontinuities
  • Defects in weldments