An introduction to NDT
Non destructive test methods are often crucial in all three phases of a product lifecycle – prototyping, production and deployment. Without them, designing and delivering products with the right balance of qualities can be difficult if not impossible. In service, testing often becomes critical for maintenance – ensuring maximum value and avoiding catastrophic failures. Imagine operating airliners or a nuclear plant without non destructive testing.
Destructive tests are often simpler (hit one until it breaks) but rarely cheaper and certainly not safer. NDT methods not only leave the item unharmed but often provide far more precise and detailed information about structural characteristics. For example, you might need to know how electrical insulation or conductivity or corrosion resistance hold up across a broad range of conditions. This is much easier to chart with an NDT approach.
Coatings and surface treatments
Using NDT and surface treatments together can help you achieve the characteristics and standards required with minimum overheads.
Coatings can be highly complex. For example, anodising provides metallic surfaces such as aluminium or titanium with columnar structures of oxide, but how deep should the process penetrate and what are the effects of anomalies, impurities or variations? How well will chemical after-treatments penetrate this relatively porous surface and are they achieving the required properties?
The range of substrates, treatments and coatings available today is highly diverse (see https://www.poeton.co.uk/treatments) and the qualities that need to be tested equally so (ductility, conductivity, corrosion resistance, tensile strength and so on). Consequently, an NDT toolbox is diverse and sophisticated.
Given its often critical importance, several national and international standards and accredited training schemes have been established (see https://www.astm.org/Standards/nondestructive-testing-standards.html).
Common NDT methodologies
In radiographic testing (RT), electromagnetic radiation is passed through the item like an X-Ray, although for thicker and denser materials, gamma radiation is often used.
Ultrasonic testing (UT) is a little like sonar and ultrasound scans. Density variations cause reflections and acoustic velocity changes that can be presented visually on a screen.
Electromagnetic Testing (ET) is a broad term, but a common variety induces eddy currents using the flux of an alternating current electromagnetic coil. The induced currents can be charted to reveal discontinuities in the test material.
Other popular methods use liquid penetrants, borroscopes, microscopes, magnetism, neutrons, infra-red, radar, lasers, microwaves and physical vibration.
Manufactures can benefit considerably by consulting with test specialists early in their design process.
