What is NDT (Non-Destructive Testing) and its Benefits?

What is NDT?

Non-destructive testing (NDT) is a wide group of analysis techniques used in the science and technology industry to evaluate the properties of a material, component, or system without causing damage. The terms nondestructive examination (NDE), nondestructive inspection (NDI), and nondestructive evaluation (NDE) are also commonly used to describe this technology.


NDT methods rely upon the use of electromagnetic radiation, sound, and other signal conversions to examine a wide variety of articles (metallic and non-metallic, food-product, artifacts, and antiquities, infrastructure) for integrity, composition, or condition with no alteration of the article undergoing examination. Visual inspection (VT), the most commonly applied NDT method, is quite often enhanced by the use of magnification, borescopes, cameras, or other optical arrangements for direct or remote viewing. The internal structure of a sample can be examined for a volumetric inspection with penetrating radiation (RT), such as X-rays, neutrons, or gamma radiation. Sound waves are utilized in the case of ultrasonic testing (UT), another volumetric NDT method – the mechanical signal (sound) being reflected by conditions in the test article and evaluated for amplitude and distance from the search unit (transducer). Another commonly used NDT method used on ferrous materials involves the application of fine iron particles (either suspended in liquid or dry powder – fluorescent or colored) that are applied to a part while it is magnetized, either continually or residually. The particles will be attracted to leakage fields of magnetism on or in the test object, and form indications (particle collection) on the object's surface, which are evaluated visually. Contrast and probability of detection for a visual examination by the unaided eye are often enhanced by using liquids to penetrate the test article surface, allowing for visualization of flaws or other surface conditions. This method (liquid penetrant testing) (PT) involves using dyes, fluorescent or colored (typically red), suspended in fluids and is used for non-magnetic materials, usually metals.

WHY USE NDT?

Here are the top reasons NDT is used by so many companies throughout the world:
 

• Savings. The most obvious answer to this question is that NDT is more appealing than destructive testing because it allows the material or object being examined to survive the examination unharmed, thus saving money and resources.
• Safety. NDT is also appealing because almost all NDT techniques (except radiographic testing) are harmless to people.
• Efficiency. NDT methods allow for the thorough and relatively quick evaluation of assets, which can be crucial for ensuring continued safety and performance on a job site.
• Accuracy. NDT methods have been proven accurate and predictable, both qualities you want when it comes to maintenance procedures meant to ensure the safety of personnel and the longevity of equipment.

"Nondestructive testing is the lifeblood of a well-run facility. NDT techniques and repeatable results depend on highly trained technicians with experience and integrity. Industrial NDT methods and interpretation of results are performed by certified professionals. Not only does the technician need to be certified in a specific NDT method, but they also need to know how to operate the equipment being used to gather data. Understanding equipment capabilities and limitations is the difference between making an accept or reject determination."

The 8 Most Common NDT Methods 

There are several techniques used in NDT for the collection of various types of data, each requiring its own kind of tools, training, and preparation. 

Some of these techniques might allow for a complete volumetric inspection of an object, while others only allow for a surface inspection. In a similar way, some NDT methods will have varying degrees of success depending on the type of material they’re used on, and some techniques—such as Magnetic Particle NDT, for example—will only work on specific materials (i.e., those that can be magnetized).

Here are the eight most commonly used NDT techniques:

1. 1. Visual NDT (VT)
   2. Ultrasonic NDT (UT)
   3. Radiography NDT (RT)
   4. Eddy Current NDT (ET)
   5. Magnetic Particle NDT (MT)
   6. Acoustic Emission NDT (AE) 
   7. Liquid Penetrant NDT (PT)
   8. Leak Testing (LT)