Engineers are designing wireless robotic remote sensing agents that manoeuvre around the surface of pipework in nuclear plants and other difficult environments to evaluate structural integrity.
The team from Strathclyde University claims the robotic non-destructive evaluation (NDE) technique will offer plant inspectors an easier and less expensive way to remotely inspect several kilometres of densely-packed pipework for anomalies such as weld defects.
Gordon Dobie, a researcher at Strathclyde’s Centre for Ultrasonic Engineering (CUE), said his group envisions deploying cheap, disposable robots designed to overcome obstacles such as pipe hangers.
The robots would move along pipes using magnetic wheels where appropriate, or vacuum suction. Each robot would inspect an area using methods such as ultrasonic NDE, which sends an ultrasonic wave into a material and determines its integrity by decoding the wave that reflects back.
While most ultrasonic inspection techniques require covering a test specimen’s surface with a special coupling liquid, Dobie said his group has developed prototypes that use a method that does not require such liquid to transfer ultrasonic energy between the transducer and test specimen.
He said: ‘It makes it a lot more suitable for remote inspection because you don’t need to continually pipe coupling fluid onto the surface. You can cut the umbilical and allow the robot to be wireless.’
Each robot is equipped with a pair of piezoelectric composite transducers and a receiver. The transducers are covered with a ‘silicone-based matching layer’ to minimise signal losses created by the large difference in impedance between the transducer face and surrounding air.
The transducers are positioned at an angle specific to the surface the robot will be travelling on. The angle is set to get the optimum amount of signal transfer between the transducer and receiver.
Dobie said if the thickness of a pipe is not as expected, the angle of the transducer will be skewed and the robot will record a loss of signal. Similarly, a crack in the pipe would also show a loss of signal.
The signals would be captured and processed onboard, then sent wirelessly to a PC hub located at the pipework entry hatch. The data could then be sent to a receiver on the other side of the hatch.
Dobie recently received a one- year fellowship from the Royal Society of Edinburgh to investigate the commercialisation of his group’s work. He said the technology is far enough advanced that they may soon be capable of performing one-off inspections.
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Strathclyde’s CUE has also developed robotic pipe crawlers that clamp onto the outside of pipework. Robotic pipe crawlers consist of two rigid, semicircular collar units oriented axially on the pipe and connected by three support shafts. Collar 2 has three linear bearings and slides along the support shafts relative to Collar 1.
Both collars contain a set of retractable grippers mounted on linear bearings to clamp onto the outside of the pipe.
It is anticipated that robotic NDE could be employed in routine testing of aircraft for fatigue cracking and corrosion, the inspection of nuclear processing cells, oil and gas pipelines, rail infrastructure and civil structures.
Siobhan Wagner
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