Visual examination or testing (VT) is a method of nondestructive testing that has been neglected for much of its industrial application life.
Often overlooked in listings of NDT methods, visual inspection is one of the most common and powerful means of non-destructive testing (NDT).
VT was the first nondestructive test (NDT) method used in the nondestructive testing industry, but was last method to be formally acknowledged.
Although a visual test is a test in itself, it also forms an integral part of many of the other non-destructive testing methods.
Magnetic particle and penetrant inspection requires visual observation and assessment of the detected indication;
Radiographs require visual inspection for the interpretation of results;
Ultrasonic inspection often requires the visual assessment of the trace on a CRT.
Visual Testing (VT) is the observation of a test object, either directly with the eyes or indirectly using optical instruments, by an inspector to evaluate the presence of surface anomalies and the object's conformance to specification. Visual testing should be the first nondestructive test method applied to an item.
Visual Testing (VT) is the monitoring of specific parameters by visual and optical assessments of test objects and surfaces using the visible portion of the electromagnetic spectrum.
Brief overview of the procedure:
The test procedure is to clear obstructions from the surface, provide adequate illumination and observe.
Visual testing requires adequate illumination of the test surface and proper eye-sight of the tester.
A prerequisite necessary for competent visual testing of an object is knowledge of the manufacturing processes by which it was made, of its service history and of its potential failure modes, as well as related industry experience.
Visual testing is widely used on a variety of objects to detect surface discontinuities associated with various structural failure mechanisms.
It is also a fact that all defects found by other NDT methods ultimately must be substantiated by visual testing.
Even when other non-destructive tests are performed, visual tests often provide a useful supplement. When the eddy current testing of process tubing is performed, for example, visual testing is often performed to verify and more closely examine the surface condition.
Some of the discontinuities that may be detected by a simple visual test are surface discontinuities, cracks, weld undercut, weld overlap, misalignment, incorrect dimensions, incorrect profile, warping, corrosion, wear and physical damage.
Some of the applications of visual testing include Checking of the surface condition of the component, checking of alignment of mating surfaces, checking of shape of the component, checking for evidence of leaking.