Visual Testing

Visual inspection refers to an NDT method which uses eyes, either aided or non-aided to detect, locate and assess discontinuities or defects that appear on the surface of material under test (Fig. 1). It is considered as the oldest and cheapest NDT method. It is also considered as one of the most important NDT method and applicable at all stages of construction or manufacturing sequence. In inspection of any engineering component, if visual inspection alone is found to be sufficient to reveal the required information necessary for decision making, then other NDT methods may no longer considered necessary.

Visual inspection is normally performed by using naked eyes. Its effectiveness may be improved with the aid of special tools. Tools include fiberscopes, borescopes, magnifying glasses and mirrors. In both cases, inspections are limited only to areas that can be directly seen by the eyes.

However, with the availability of more sophisticated equipment known as borescope, visual inspection can be extended to cover remote areas that under normal circumstances cannot be reached by naked eyes. Defects such as corrosion in boiler tube, which cannot be seen with naked eyes can easily be detected and recorded by using such equipment.

Although considered as the simplest method of NDT, such an inspection must be carried out by personnel with an adequate vision. Knowledge and experience related to components are also necessary to allow him to make correct assessment regarding the status of the components.