Non-destructive Testing is one part of the function of Quality Control and is complementary to other long established methods. By definition non-destructive testing is the testing of materials, for surface or internal flaws or metallurgical condition, without interfering in any way with the integrity of the material or its suitability for service. The technique can be applied on a sampling basis for individual investigation or may be used for 100% checking of material in a production quality control system.
Non-destructive Testing is not just a method for rejecting substandard material; it is also an assurance that the supposedly good is good. The technique uses a variety of principles; there is no single method around which a black box may be built to satisfy all requirements in all circumstances.
What follows is a brief description of the methods most commonly used in industry, together with details of typical applications, functions and advantages.
COMMON NDT METHODS
While there are many different methods of NDT only the more common NDT methods used for the evaluation of materials and welds will be outlined here. These methods are the following:
(1) Visual inspection
(2) Liquid penetrant inspection
(3) Magnetic particle testing
(4) Radiographic inspection
(5) Ultrasonic testing
(6) Eddy current testing
Non-Destructive Testing (NDT) training is provided for people working in many industries. It is generally necessary that the candidate successfully completes a theoretical and practical training program, as well as have performed several hundred hours of practical application of the particular method they wish to be trained in. At this point, they may pass a certification examination. While online training has become more popular, many certifying bodies will require additional practical training.
Levels of certification
Most NDT personnel certification schemes listed above specify three "levels" of qualification and/or certification, usually designated as Level 1, Level 2 and Level 3 . The roles and responsibilities of personnel in each level are generally as follows (there are slight differences or variations between different codes and standards.
- Level 1 are technicians qualified to perform only specific calibrations and tests under close supervision and direction by higher level personnel. They can only report test results. Normally they work following specific work instructions for testing procedures and rejection criteria.
- Level 2 are engineers or experienced technicians who are able to set up and calibrate testing equipment, conduct the inspection according to codes and standards (instead of following work instructions) and compile work instructions for Level 1 technicians. They are also authorized to report, interpret, evaluate and document testing results. They can also supervise and train Level 1 technicians. In addition to testing methods, they must be familiar with applicable codes and standards and have some knowledge of the manufacture and service of tested products.
- Level 3 are usually specialized engineers or very experienced technicians. They can establish NDT techniques and procedures and interpret codes and standards. They also direct NDT laboratories and have central role in personnel certification. They are expected to have wider knowledge covering materials, fabrication and product technology.