Which of the following is a typical surface discontinuity detectable by VT?

• A. Cracks.
• B. Internal voids beneath surface.
• C. Subsurface delamination.
• D. Through-holes

Answer: (A)

Visual testing looks for flaws that break the surface and can be seen with light and shadow. A crack is a surface-breaking flaw that interrupts the continuity of the material, so it readily shows up as a visible line or opening along the surface when properly illuminated. This makes cracks the classic example of a defect detectable by VT.

Internal voids beneath the surface and subsurface delamination are hidden from direct sight and typically require other NDT methods, such as radiography or ultrasound, to reveal them. Through-holes may be visible if they reach the surface, but in the context of surface discontinuities that VT is used to detect, the most reliably detectable type is a crack because it directly alters the surface itself.