What Does Non-Destructive Testing (NDT) Mean?
Non-destructive testing (NDT) is a material testing method that does not damage the material or component being tested. The test evaluates a material's properties and structure and identifies defects or discontinuities.
Castings, forgings, pipes, and rolled and welded products are most frequently tested using NDT.
Non-destructive testing is also known as non-destructive evaluation, non-destructive examination (NDE), or non-destructive inspection (NDI).
Safeopedia Explains Non-Destructive Testing (NDT)
Non-destructive testing can involve a number of specialized tools and a variety of technical approaches. What they all have in common is that the tested components remain usable after being tested.
Non-Destructive Testing Methods
There are several types of modern NDT methods available and their names indicate what type of penetrating medium or equipment is used to perform the test. Here are a few:
- Ground Penetrating Radar (GPR) - Radar pulses are sent down through a material’s surface. When these pulses encounter an object or boundary with different electromagnetic properties, the waves are reflected or refracted.
- Acoustic Emission Testing (AE) - Sensors are dispersed over the surface of a structure to detect short bursts of ultrasound emitted by active cracks under a load. This method can locate leaks and active corrosion.
- Laser Testing Methods (LM) - There are three types of laser testing methods:
- Holographic testing detects changes in the surface of a material, which has been subjected to stress from pressure, vibration, or heat (results are compared with a reference sample)
- Laser profilometry detects corrosion, pitting, and cracks using a high-speed rotating laser light source and miniature optics
- Laser shearography creates an image of the surface using laser light before it is stressed - images are then compared to identify defects
- Magnetic Particle Testing (MT) - An electromagnet or permanent magnet creates a magnetic field that highlights discontinuities, such as corrosion or leakage.
- Liquid Penetration Testing (PT) - A penetrant liquid is applied to a testing surface and penetrates any fissures or holes. Once excess liquid is removed, the penetrant will flow back to the surface, indicating the location of cracks and other issues.
- Neutron Radiographic Testing (NR) - An intense beam of low-energy neutrons penetrates through a metal component and creates an image of its internal structure.
Organizations That Set NDT Codes and Standards
The following are some of the organizations that set NDT standards and codes:
- The American Society for Non-Destructive Testing (ASNT)
- The American Society for Testing and Materials (ASTM)
- The American Petroleum Institute (API)
- The American Society for Mechanical Engineers (ASME)
- The Canadian Standards Association (CSA Group)
- The Canadian General Standards Board (CGSB)
- The French Committee for Non-Destructive Testing Studies (COFREND)
NDT is very important when it comes to the inspection and maintenance of high-risk assets such as boilers and pressure vessels. Defects and damages in these vessels can lead to catastrophic consequences if undetected.