Selecting a Nondestructive Testing Method, Part II: Visual Inspection

http://ammtiac.alionscience.com The AMMTIAC Quarterly, Volume 1, Number 3 INTRODUCTION Visual inspection is by far the most common nondestructive testing (NDT) technique [1]. When attempting to determine the soundness of any part or specimen for its intended application, visual inspection is normally the first step in the examination process. Generally, almost any specimen can be visually examined to determine the accuracy of its fabrication. For example, visual inspection can be used to determine whether the part was fabricated to the correct size, whether the part is complete, or whether all of the parts have been appropriately incorporated into the device. [2] While direct visual inspection is the most common nondestructive testing technique (Figure 1), many other NDT methods require visual intervention to interpret images obtained while carrying out the examination. For instance, penetrant inspection using visible red or fluorescent dye relies on the inspector’s ability to visually identify surface indications. Magnetic particle inspection falls into the same category of visible and fluorescent inspection techniques, and radiography relies on the interpreter’s visual judgement of the radiographic image, which is either on film or on a video monitor. The remainder of this article provides a summary of the visual testing method, which at the minimum requires visual contact with the portion of the specimen that is being inspected. In arriving at a definition of visual inspection, it has been noted in the literature that experience in visual inspection and discussion with experienced visual inspectors revealed that this NDT method includes more than use of the eye, but also includes other sensory and cognitive processes used by inspectors [3]. Thus, there is now an expanded definition of visual inspection in the literature: “Visual inspection is the process of examination and evaluation of systems and components by use of human sensory systems aided only by mechanical enhancements to sensory input as magnifiers, dental picks, stethoscopes, and the like. The inspection process may be done using such behaviors as looking, listening, feeling, smelling, shaking, and twisting. It included a cognitive component wherein observations are correlated with knowledge of structure and with descriptions and diagrams from service literature.” [3]