Nondestructive testing - Canadian Nuclear Association

Nondestructive testing

Nondestructive testing, or NDT, is a quality-assurance practice conducted on machines and materials to verify their structural integrity without having to cause damage, thereby reducing the time and expense required. NDT can be performed through a variety of techniques, depending on the material being tested. Two of the most common and effective methods to perform NDT rely on radiation and nuclear substances: industrial radiography and neutron radiography.

Industrial radiography

Industrial radiography is a common portable method for verifying welds during the construction and inspection of pipelines, pressurized vessels, and important structural supports, and for locating materials embedded inside others, such as a water or electrical conduit running through concrete.

This is performed through the use of a radiographic camera – a heavily shielded device that encloses a radioactive source material. When the device is prompted, it opens, and radiation passes through the material being analyzed, to a detector that picks up an image of the radiation. The image can be analyzed by trained personnel to assess the quality of the weld and decide whether the object is safe for use.

Industrial radiography

Picture taken using a radiographic camera. Source: Diamond Technical Services.

Industrial radiography is most commonly performed using gamma-emitting sources such as cobalt-60 or iridium-192. Industrial radiographers are highly trained and certified to practice. Although they do receive among the highest occupational exposures among Canadian professionals, annual doses are usually no more than annual background-radiation levels.

Neutron radiography

Neutron radiography is another method of non-destructive testing that uses a source of neutron radiation instead of the gamma sources used in conventional industrial radiography. While portable sources for neutrons exist, neutron radiography is very often performed using direct ports at nuclear research reactors, such as the National Research Universal reactor or the McMaster Nuclear Reactor.

Neutrons interact better with organic material and water than gamma rays do; whereas gamma rays better image denser materials such as metals. Because of this, neutron radiography is very effective at detecting corrosion and moisture-based damage, and is used very successfully to verify the integrity of aircraft components.

The capacity for neutron radiography is demonstrated by this image taken of a Buddha statue. An x-ray of the object is very fuzzy by comparison.

tron radiography - 2 Buddhas

Left: X-ray does not show content. Right: Neutrons can provide information about the embedded organic material. Source: Paul Scherrer Institut.