Non-Destructive Testing

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Non-Destructive Testing

Nondestructive testing (NDT) is the process of inspecting materials for discontinuities, or differences in characteristics without destroying their serviceability.

In contrast to NDT, other tests are destructive in nature and are therefore done on a limited number of samples (“lot sampling”), rather than on the materials, components or assemblies actually being put into service.

These destructive tests are often used to determine the physical properties of materials such as impact resistance, ductility, yield and ultimate tensile strength, fracture toughness and fatigue strength, but discontinuities and differences in material characteristics are more effectively found by NDT.

There are a number of distinct advantages to non-destructive testing.

The most obvious of which is that the pieces being tested are left undamaged by the process, allowing for an item to be repaired rather than replaced should any problems be found.

It is also a very safe testing method for operators, with most techniques being harmless to humans, although some types of test – such as radiographic testing – still need to be conducted under strict conditions. This testing technique can also help prevent injury or fatalities by ensuring structures, components and machinery is safe.

Non-destructive testing is also a very accurate way of inspection since the tests are repeatable and a number of tests can be used together to correlate results.

Non-Destructive Testing Methods

Acoustic Emission (AE) Testing

This is a passive NDT technique, which relies on detecting the short bursts of ultrasound emitted by active cracks under a load. Sensors dispersed over the surface the structure detect the AE. It is even possible to detect AE from plasticisation in highly stressed areas before a crack forms. Frequently a method for use during proof tests of a pressure vessel, AE testing is also a continuous Structural Health Monitoring (SHM) method, for example on bridges. Leaks and active corrosion are detectable AE sources too.

Electromagnetic Testing

This testing method uses an electric current or magnetic field which is passed through a conductive part. There are three types of electromagnetic testing, including eddy current testing, alternating current field measurement (ACFM) and remote field testing (RFT).

Eddy current testing uses an alternating current coil to induce an electromagnetic field into the test piece, alternating current field measurement and remote field testing both use a probe to introduce a magnetic field, with RFT generally used to test pipes.

Ground Penetrating Radar

This geophysical NDT method sends radar pulses through the surface of a material or subsurface structure, such as rock, ice, water or soil. The waves are reflected or refracted when they encounter a buried object or material boundary with different electromagnetic properties.

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Kabbani Construction Group