Methods of Visual Testing (VT)

This method is not usually listed in the list of NDT methods, the visual inspection method is one of the most popular and most effective in the sense of non-destructive testing. For the visual inspection method, the surface of the test object should have sufficient brightness and the inspector’s field of vision should be adequate. In order to implement the most effective visual inspection method, special attention must be paid to the qualities because in this inspection training is required (knowledge of product and machining processes, predict operating conditions, applicable standards, maintain measurement data) and the testers themselves need to be equipped with a number of devices and instruments. In practice all defects detected by other NDT methods must eventually be verified by visual inspection. Popular NDT methods such as the magnetic particle test (MT) and the liquid penetrant test (PT) are actually also simple scientific methods for highlighting indicators for easier to see. The necessary equipment is simple (Figure 4.1) such as: a portable lamp, a mirror with a handle, a magnifying glass with a 2x or 4x magnification, a light amplifier with a 5x magnification. or 10x. In order to perform internal inspection of materials, a system of light lenses such as a borescope is required, which allows inspection of surfaces from a distance. More sophisticated devices of this type use optical fibers that allow very small holes and slots to be inserted. Most of these systems are fitted with additional cameras that allow the results to be recorded for long-term retention.

Figure 4.1 – Optical aids in visual inspection.
  1. Mirror with handle: can be flat mirror for normal viewing or concave mirror for limited magnification.
  2. Magnifying glass with handle (with magnification usually 2 – 3x).
  3. Light amplification device; field of view is more limited than D (magnification factor 5 – 10x).
  4. Inspection glass, usually fitted with a scale; The front face is placed in contact with the test object (magnification 5-10x).
  5. Endoscope (Borescope or intrascope) with built-in light source (2 – 3x magnification).

Applications of the visual inspection method:

(1) Check the surface condition of the test object.

(2) Check the bonding of the materials on the surface.

(3) Check the shape of the part.

(4) Check for signs of leaks.

(5) Check in inaccessible locations.