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Visual Testing (VT)

Visual testing (VT) is the most common NDT method. The method is focused on detection and evaluation of the part surface condition (or properties) directly by eyes or by means of the special equipment or aids. VT method is used as classical NDT inspection focused on the detection of cracks, undercuts, and surface porosity, shape irregularities (e.g. linear misalignment, weld root concavity, casting die misalignment), and last, but not least general surface condition. The VT is full-value NDT method comparable with other (PT, RT, ...) and in its extent actually exceeds the scope of abilities of other methods. Visual testing represents one of the NDT methods that shall be performed before another NDT method is applied.

Physical background

The visual testing is performed on a suitably prepared surface of the part (cleaned, degreased and dried). The final testing sensitivity - detectability of the discontinuity is directly affected by the surface conditions. The success of the testing is caused by three basic conditions:

• visual ability of performing worker
• sufficient lightning of the tested surface
• capability - the knowledge and practical abilities of the worker who is performing VT

The testing could be performed without usage of any aid - directly by eyes, than with usage of the basic aids (mirrors, quality indicators, measurement devices, magnifying glasses, etc. eventually with usage of the endoscopes or other special devices). Recently the inspection with usage of the endoscopes (boroscopes, fibroscopes, videoscopes) has been still more commonly asked. The typical applications were recognized mainly in the aerospace sector (during of the maintenance), in the energetic sector (inspection of the pipelines, storage tanks, pressure vessels, ...), but also during the manufacturing process (closed welded frames, profiles, etc.).

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