3. Optical processes

3.1 Visual examination

Visual inspection is the first, simplest and most general inspection procedure, since it is also the end point of most other non-destructive procedures.

As a preliminary examination, visual inspection of an object, a structure or an assembly such as a weld will guide an experienced observer in the definition of another technique: choice of angle for radiography, direction of magnetization, ultrasonic frequency.

Direct visual inspection of parts can be sufficient to detect surface defects and, above all, local and superficial heterogeneities (stains of various kinds), which are a major cause of appearance defects in flat products such as sheet metal, fabrics, glass, etc. However, purely visual inspection has its...