Non-destructive testing, NDT, is a very broad group of structural or material inspections and as the name implies, these inspections do not destroy the material/structure being examined. NDT plays a critical role in assuring that structural components and systems perform their function in a reliable and cost effective fashion. Because NDT does not permanently alter the article being inspected, it is a highly valuable technique that can save both money and time in product evaluation, troubleshooting, and research. NDT technicians and engineers define and implement tests that locate and characterize material conditions and flaws that might otherwise cause serious accidents such as, planes to crash, reactors to fail, trains to derail, pipelines to burst, and a variety of troubling events.
This concept is extended, and known as Non-Destructive Evaluation (NDE), when combined with an assessment of the significance of any defects found. However, they are both terms often used interchangeably. Some testing methods must be conducted in a laboratory setting, others may be adapted for use in the field. Several commonly employed NDT techniques and their characteristics are described below.
Visual and Optical Testing
Visual inspection involves using an inspector’s eyes to look for defects, such as scratches, presence of debris, corrosion or oxidation. The inspector may also use special tools such as magnifying glasses, mirrors, or borescopes to gain access and more closely inspect the subject area. In nuclear power plants, an extensive fuel inspection programme (including e.g., visual inspections, oxide layer measurements, eddy-current tests of control rods), is carried out under water and supervised by the regulatory body. So that visual testing are usually a part of the Post Irradiation Examination. Visual examinations are also very common in aircraft industry, where over 80 percent of the inspections done to an aircraft are visual inspections, being often used as an initial screening method to detect gross defects and target subsequent testing by other methods.
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