The importance of NDT and CM
What are NDT and CM?
Non-destructive testing (NDT) is the application of four areas of science – physics, chemistry, biology and maths – to create methods of testing that leave the item under test totally undamaged. This means that the component – the casting, weld or forging, for example – can continue to be used and that the non-destructive testing method has done no harm.
Items can be tested before they are finally shaped or whilst they are in service. This means that the continuing quality of components can be assured, such as checking railway lines, aero engine turbine blades and the welds on a high-speed theme park ride.
Condition monitoring (CM) aims to ensure plant efficiency, productivity and reliability by monitoring and analysing the wear of operating machinery and components to provide an early warning of impending failure, thereby reducing costly plant shutdown.
|The high-speed theme-park ride – safety depends on reliable NDT, in this case the alternating current field measurement (ACFM) technique|
Why is NDT important?
NDT is necessary whenever we need to assure ourselves of the integrity of our infrastructure. Aircraft, trains, pipelines, oil rigs, bridges and pressure vessels are examples of everyday things that are regularly examined.
In addition to the need to ensure safety, non-destructive testing can be used to improve output and profitability. Furthermore, a component or an entire structure or machine can be tested many times using several types of tests through the complete life cycle to ensure its continued integrity.
Non-destructive testing in the offshore industry – the pipes and welds in the platform structure are examined regularly
Consider an offshore oil platform standing on the seabed and projecting upwards above sea level. The supporting structure consists of a complex array of tubular steel fabrications.
The starting point will be steel plate made to the correct specification in a steel mill. It will be formed then welded to produce a pipe. Many pipe sections will be welded together onshore and the finished structure towed out to sea and placed in position.
Non-destructive tests will be used to examine the original steel plate, the pipes and the welds in the finished structure. The important point is that non-destructive testing can be applied at each stage of construction, from the initial plate to the finished structure, and materials and welds can either be accepted or, if unsatisfactory, rejected and repaired.
Finally, non-destructive methods can be employed to monitor the integrity of the structure through its useful life. They supplement other techniques, which can be applied without interruption to normal operation of a structure or a machine. These techniques are known as condition monitoring.
There is continuous progress in the development and application of NDT methods that are often used in conjunction with CAD and computer-based modelling to match the advances in new materials, component design and new products.
R&D in this field is yielding healthy dividends.