Visual inspection is the monitoring of specific parameters by visual and optical assessments of test objects and surfaces using the visible portion of the electromagnetic spectrum.
Visual Inspection may be by the use of the eye alone or can enhance using optical systems such as magnifiers and microscopes. A variety of equipment is available to the visual inspector including mirrors and gauges, which can be used for profile assessment, borescopes, and endoscopes, which are used on parts with limited access, and video or computer enhancement systems.
Although a Visual Inspection test is a test in itself, it also forms an integral part of many other non-destructive testing methods, For example, magnetic and penetrant inspection requires visual observation and assessment of the detected indication; radiographs require visual inspection for the interpretation of results; ultrasonic inspection requires the visual assessment of the trace on a CRT.
Visual inspection is a vital part of an in-service inspection, which may or may not be backed up by other NDT methods. The examinations made are for fatigue cracks creep failure, corrosion, erosion, abrasion, mechanical damage, wear and tear, distortion, and poor workmanship.
The ability to differentiate between different damage mechanisms, which may to an untrained, experienced visual inspector have similar appearances, often results in an incorrect diagnosis. The trained, experienced visual inspector can elicit a great deal of information, and could use this information to decide which other tests to perform in order to confirm a diagnosis of the problem.
Visual inspection must take place in a clean, comfortable environment with adequate lighting. There should be reasonable access to the parts to be inspected and attention should be paid to safety, working position, and atmospheric conditions. The test piece should be clean and free from protective coatings. Any equipment to be used would be checked for accuracy and its operation understood by the inspector.