Stiff brushes drive for inspection and cleaning
Tom Shelley reports on a novel way of moving along pipes and some unexpected spinoffs.
Self propelled pipeline machines use bristle traction to propel themselves, and in some cases, novel joints to navigate particularly tortuous bends.
As well as propelling their way through pipe systems from 50mm diameter upwards, the development process has turned up improvements in brushes and other possibilities for bristle propulsion.
The machines developed by Durham Pipeline Technology, a spin-off of the university, use compressed air to expand longitudinal groups of brushes so they can penetrate grease and general crud to grip on the insides of pipes. Technical Director Professor Ernie Appleton told Eureka that the grip exerted by compressed bristles, when they are oriented to push grip, is normally about three times the friction exerted by them when they are trailing. However, by making the bristles cross plied, so that they tend to support each other raises this ratio to 8:1 and by various other cunning improvements, which the professor declined to identify, it is possible to raise this ratio to 18:1.
For machines that have to negotiate really tight bends, the team has designed a unique quadruple 'S' joint in SolidWorks. Each double 'S' component allows the machine to bend around a point almost adjacent to the pipe wall, regardless of where this is encountered round the pipe circumference.
The use of bristle propulsion allows the machines to traverse changes in pipe diameter and the internals of valves without problem. Machines are also capable of reversing direction and travelling in either direction in the pipe, moving with or against the product flow. The large traction forces available allow them to pull loads in excess of 1 tonne. On the other hand, by relaxing all the brushes, and because the inside diameter of the machines are much less than those of the pipes they travel through, it is quite easy to drive or pull the machines back out of pipe systems, the way they went in. This is in complete contrast to conventional 'pigs', which are liable to get stuck at section changes and sharp bends, and then usually have to be extracted by cutting the pipe open.
Applications include the nuclear and water industries. Going into a nuclear installation to recover a stuck pig is not to be contemplated. In one instance, a DPT machine has been used to inspect nominal 3 1/2 inch bore pipe work in an inaccessible coil, where actual diameters varied from 3 to 3 3/4 inches. In the water industry, the machine avoids the need for "Swabbing", where a foam plug, driven along by differential water pressure, contaminates very large quantities of water. DPT has applied a brush traction system with a specially developed cleaning head that uses only small quantities of cleaning water. The project won the IChemE award for Innovation in the Water Industry 2002.
Other systems too can made using brush traction. A few years ago, Toyota engineers demonstrated that a car could be propelled by moving brushes instead of wheels.
Durham Pipeline Technology
Nick Pearson at Durham Pipeline Technology
* Brushes gripping on the insides of pipes are a very good way of providing traction for inspection and cleaning
* Ordinary brushes exert about three times the friction force in the direction of the bristles than when they are trailing. Careful design can increase this ratio to as much as 18:1.
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