Introduction to non destructive testing (NDT):
Non destructive testing (NDT) for welding is a term used for the examination of welded joints in a way that allows them to be examined without changing or destroying them.
NDT plays an important role in everyday life and is necessary to assure safety and reliability. Examples are found in aircraft, motor vehicles, pipelines, bridges, trains, power stations; refineries and oil platforms which are all inspected using NDT.
NDT is a Quality Assurance management tool which can give impressive results when used correctly. It requires an understanding of the various methods available, their capabilities and limitations, knowledge of the standards and specifications for performing the tests.
Welded joints which fail to achieve their design requirements or projected life because of undetected defects may require expensive repair or early replacement, Such defects may also be the cause of unsafe conditions or terrible failure, as well as loss of profits because of unplanned plant shutdown.
Non destructive testing can be applied to each stage of an items construction. The materials and welds can be examined using NDT and either accepted, rejected or repaired. NDT techniques can then be used to monitor the integrity of the item or structure throughout its design life.
The method that can be used for non-destructive testing depends on the physical properties of the material. A thorough knowledge of each NDT method is required to ensure the correct selection of the appropriate method for each application.
NDT is used for the following reasons:
1- Accident prevention.
2- To reduce costs.
3- To improve product reliability.
4- To determine acceptance to a given requirement.
5- To give information on repair criteria.
NDT can be used to find, size and locate surface as well as subsurface defects.
The NDT methods...