July 12, 2013
Robots a tool for safer infrastructure
Wild and weird weather events are getting a lot of attention lately, especially the stresses they impose upon people who have to survive during floods or fires, and then rebuild afterwards.
Less attention is given to the infrastructure that surrounds us. That we repair or replace infrastructure that is damaged during a storm is a given. But we are also faced with the need for better infrastructure management, so that our built environment is better able to withstand the rigours imposed by wild weather.
Part of that infrastructure management is regular inspection and timely repair, and advances in robotic inspection are both more necessary and more common. Now researchers at the Fraunhofer Institute for Non-destructive Testing, in Germany, have come up with a crawling robot that is capable of testing load-bearing cables and tethers of bridges, elevators and cable cars.
Fraunhofer-Gesellschaft is a huge research organization, made of up many specialized institutes. It does research and development on its own, and is frequently involved in co-operative research projects with other organizations in other countries.
FluxCrawler is one such project, carried out in collaboration with the French Carnot Institute. FluxCrawler is a small robot that climbs a wire cable, spiralling upward as it monitors the quality of stay cables and wire ropes which, until now, have been difficult and expensive to test adequately
These cables are exposed to tension-induced strain and wear. And often, especially in the salty air of seaside structures, corrosion is an important factor.
The robot conducts magnetic flux leakage tests as it goes, identifying tiny fissures in the cable surface. It also recognizes deeper cracks.
The theory behind it is well-known. Basically, a powerful magnet is used to magnetize the steel. Where there is corrosion or missing metal, the magnetic field “leaks” from the steel. This leakage field is detected and a chart of it is created so engineers can identify the damaged area and estimate the amount of metal loss.
Magnetic flux leakage testing is common in pipelines and storage tanks. What the Fraunhofer researchers have done is adapt the technique for cable testing, and then mount the detector on a small crawler robot.
Until now, magnetic flux leakage testing wasn’t commonly used on cables because limitations on the size of the testing machine meant a limitation on the size of cables that could be tested. It couldn’t be used on large cables.
FluxCrawler, on the other hand, can be used regardless of a cable’s diameter. It’s only about 70 centimetres long and just a few centimetres wide, and it works its way around the cable, worm-like, scanning as it goes, identifying the precise location and orientation of any defects it finds.
The battery-operated robot is controlled by a computer with a wireless connection. An image of the magnetic field on the cable’s entire surface appears on the computer screen, and each damaged area is shown as a high-resolution image.
Where FluxCrawler can’t function — in areas where the cable is covered, for example — another non-destructive test is used. It involves a device that allows researchers to create a guided ultrasound wave that penetrates the material. When a wave hits a flaw, it’s reflected back to a computer, which shows the flaw in a high-resolution image.
This whole system has already been used successfully on a bridge in Germany that is presently being renovated. Patents have been granted, and more tests are scheduled at a cable-testing facility.
Fraunhofer has already received inquiries from industry, and it is expected that the system will be used in everyday practice within a year or two.
When it arrives, it will give managers an important new tool in their quest for safer, longer-lasting infrastructure in an uncertain world.
Korky Koroluk is an Ottawa-based freelance writer. Send comments to firstname.lastname@example.org
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