What is a major limitation of visual testing (VT)?

Visual testing (VT) is primarily an inspection method that focuses on examining the surface of materials and components. One of the key limitations of VT is its inability to detect subsurface defects. Since VT relies on the clarity and visibility of the surface, it requires good lighting and visibility to ensure an accurate assessment. This makes it effective for identifying surface anomalies such as cracks, corrosion, and other external defects, but it cannot provide information about what is happening beneath the surface.

The necessity for optimal lighting also means that if conditions are poor, such as in poorly lit environments or when surfaces are obscured by dirt, coatings, or other materials, the effectiveness of visual testing can be diminished. Therefore, the major limitation is indeed its restriction to assessing surface defects and the dependence on adequate visibility for effective inspection.