Researchers at the Fraunhofer Institute for Industrial Mathematics ITWM have developed a mechanised ultrasound process that can be used for the non-destructive testing of complex components such as ships’ propellers.
The scientists received support from Germanischer Lloyd (GL) Group and propeller manufacturer Wärtsilä Propulsion Netherlands.
‘With our mobile ultrasound test system, we can inspect copper-nickel-aluminium bronzes up to 450mm thick and detect fissures down to a few millimetres in length,’ said Dr Martin Spies of ITWM in Kaiserslautern. ‘Because we emit the ultrasound at defined angles, we also find defects positioned at an angle to the surface.’
Currently, propellers are inspected for inner defects with an ultrasound test probe that is passed over the component by hand — a technique that does npt capture the entire volume of the component. The tests are carried out because defects in the component can occur during the casting process.
According to a statement, the new system is capable of recording large volumes of digitised ultrasound test data, taking into account the curvatures of the propeller surface. The device currently scans test grids measuring 700mm by 400mm, achieving a rate of up to 100mm per second.
The mobile scanner can be positioned anywhere on the propeller and, thanks to its suction feet, it can be attached in a horizontal as well as a vertical test position.
‘We obtained the 3D data about the inside of the component by an imaging procedure known as SAFT. It provides a detailed display of inclusions and welding-seam defects. It basically works like computer tomography in medicine,’ said Spies.
With the aid of computational processes and algorithms, the experts are said to have succeeded in reducing interference signals and intensifying error signals — a complicated task, since the various areas of the blade do not have a homogenously coarse grain. This can weaken the echo substantially. The specialists also use simulations to calculate in advance which ultrasound test probe they have to deploy.
The researchers use the mobile scan system for their on-site testing at foundries, at propeller manufacturers, on deck and in dry dock and are currently improving scan times and 3D defect imaging. Recently, they were able to put the efficiency of their procedure to the test at the world‘s largest shipbuilder in Korea.
‘The customer wanted to document the quality of its propellers to gain an edge over the competition,’ said Spies. ‘With our procedure, we can test not only propellers but also other complex components made of materials that are difficult to test, such as offshore components made of duplex steels.’