Non destructive testing
The field of Non destructive Testing (NDT) is a very broad, interdisciplinary field that plays a critical role in assuring that structural components and systems perform their function in a reliable and cost effective fashion.
NDT technicians and engineers define and implement tests that locate and characterize material conditions and flaws that might otherwise cause planes to crash, reactors to fail, trains to derail, pipelines to burst, and a variety of less visible, but equally troubling events.
These tests are performed in a manner that does not affect the future usefulness of the object or material. In other words, NDT allows parts and materials to be inspected and measured without damaging them.
Because it allows inspection without interfering with a product`s final use, NDT provides an excellent balance between quality control and cost-effectiveness.
Generally speaking, NDT applies to industrial inspections. While technologiesare used in NDT that are similar to those used in the medical industry, typically non living objects are the subjects of the inspections.
Non Destructive Evaluation
Nondestructive Evaluation (NDE) is a term that is often used interchangeably with NDT. However, technically, NDE is used to describe measurements that are more quantitative in nature.
For example, a NDE method would not only locate a defect, but it would also be used to measure something about that defect such as its size, shape, and orientation.
NDE may be used to determine material properties such as fracture toughness, formability, and other physical characteristics.
The number of NDT methods that can be used to inspect components and make measurements is large and continues to grow.
Researchers continue to find new ways of applying physics and other scientific disciplines to develop better NDT methods.
However, there are six NDT methods that are used most often. These methods are visual inspection, penetrant testing, magnetic particle testing, electromagnetic or eddy current testing, radiography, and ultrasonic testing. These methods and a few others are briefly described below.
Visual and Optical Inspection (VI)
Visual inspection involves using an inspector`s eyes to look for defects. The inspector may also use special tools such as magnifying glasses, mirrors, or borescopes to gain access and more closely inspect the subject area. Visual examiners follow procedures that range from simple to very complex.
Dye Penetrant Inspection (DPI)
Test objects are coated with visible or fluorescent dye solution. Excess dye is then removed from the surface, and a developer is applied. The developer acts as blotter, drawing trapped penetrant out of imperfections open to the surface. With visible dyes, vivid color contrasts between the penetrant and developer make "bleedout" easy to see. With fluorescent dyes, ultraviolet light is used to make the bleedout fluoresce brightly, thus allowing imperfections to be readily seen.