NDT Method : Visual Inspection

Often overlooked in any listing of NDT methods, visual inspection is one of the most common and most powerful means of non-destructive testing. Visual testing requires adequate illumination of the test surface and proper eye-sight of the tester. To be most effective visual inspection does however, merit special attention because it requires training (knowledge of product and process, anticipated service conditions, acceptance criteria, record keeping, for example) and it has its own range of equipment and instrumentation. It is also a fact that all defects found by other NDT methods ultimately must be substantiated by visual inspection.

Visual testing can be classified as direct visual testing, remote visual testing and translucent visual testing. The most common NDT methods MT and PT are indeed simply scientific ways of enhancing the indication to make it more visible. Often the equipment needed is simple Figure 1.1 a portable light, a mirror on stem, a 2´ or 4´ hand lens, one illuminated magnifier with magnification 5x or 10´. For internal inspection, light lens systems such as borescopes allow remote surfaces to be examined . More sophisticated devices of this nature using fibre optics permit the introduction of the device into very small access holes and channels. Most of these systems provide for the attachment of a camera to permit permanent recording.

(a) Mirror on stem: may be flat for normal view or concave for limited magnification.
(b) Hand magnifying glass (magnification usually 2–3´).
(c) Illuminated magnifier; field of view more restricted than D (magnification 5–10´).
(d) Inspection glass, usually fitted with a scale for measurement; the front surface is placed in contact with the work (magnification 5–10´).
(e) Borescope or intrascope with built-in illumination (magnification 2–3´).

The applications of visual testing include:
(1) Checking of the surface condition of the test specimen.
(2) Checking of alignment of mating surfaces.
(3) Checking of shape of the component.
(4) Checking for evidence of leaking.
(5) Checking for internal side defects.

source : International Atomic Energy Agency; TRAINING COURSE SERIES No. 11

1 Response to "NDT Method : Visual Inspection"

  1. Visual Inspection is one of the most widely used Non-Destructive Testing methods for the detection of discontinuities before they cause major problems, e.g. poor welding, surface defects, corrosion pits, general condition, degradation, blockages and foreign materials.

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