Visual inspection is the mostwidely used among all Non Destructive Tests. It is simple, easy to apply,quickly carried out, and usually low in cost. Even though a component is to beinspected using other NDT methods, a good visual inspection should be carriedout first. A simple visual test can reveal gross surface defects thus leadingto an immediate rejection of the component and consequently saving much timeand money, which would otherwise be spent on more complicated means of testing.It is often necessary to examine for the presence of finer defects. For thispurpose, visual methods have been developed to a very high degree of precision.With the advent of microprocessor and computers, visual examination can becarried out very reliably and with minimum cost. Image processing patternsrecognition and automatic accept/reject choices are used when large numbers ofcomponents are to be assessed.
The basicprocedure used in visual NDT involves illumination of the test specimen withlight, usually in visible region. The specimen is then examined with eye or bylight sensitive devices such as photocells. The equipment required for visualinspection is extremely simple, but adequate illumination is absolutelyessential. The surface of the specimen should be adequately cleaned beforebeing inspected.