Non-Destructive Evaluation (NDE) or Non Destructive Testing (NDT) is the technique of applying physical principles to determine the characteristics of materials, components, or systems. It is also used for detecting and assessing inhomogeneity and harmful defects without impairing the usefulness of such materials, components, or systems. NDT enables defects in the products to be examined without affecting the performance of the item being testing.
NDT plays an important role not only in the control of quality of products but also during various stages of manufacturing. NDT is also used in condition monitoring of various items during operation to predict and assess the remaining life of the component while at the same time retaining its structural integrity. It enables optimum utilization of components without sacrificing safety. Operator dependency for routine inspection is reduced thereby allowing personnel to concentrate more on technological aspects. The end result is savings in time, cost and improvement in precision and reliability of the output.
The three stages where NDT is applied are (1) pre-manufacturing stage for inspection of raw materials (2) during manufacturing to check if the product meets its specifications and (3) during the service life of a product to check fitness for purpose and make life prediction. NDT offers the following advantages:
- Tests are made directly on the object. 100% testing on actual components is possible
- Many NDT methods can be applied on the same part, hence many properties of interest can be measured
- In-service testing of components is possible
- Repeated checks over a period of time are possible
- Very little preparation is sufficient to conduct NDT
- Most NDT methods are rapid
NDT methods range from simple to intricate. Visual inspection is the simplest of all NDT methods. The choice of a specific NDT method depends on factors such as availability, cost and suitability based on analysis and past experience. Another important factor to be considered is the type and origin of the defect in the product to be tested. The use of one NDT method is sometimes necessary to confirm the findings of another. Capabilities of one test method may overlap with those of another. No single method, for example, is capable of revealing all surface and subsurface discontinuities in all types of materials. For these reasons it is necessary to use a combination of tests to obtain complementary information helpful in evaluating the quality of the component.