ENGINEERS used a device more often employed for drainage pipes when builders feared a blocked gas main could delay completion of a new school.
A team from specialist company Lanes for Drains used ‘poly-pigs’ to root out the problem, as the company’s Chris Norbury explained: “The pipe had been laid but not capped. When it rained, silt and debris was washed into the pipes and caused a blockage. Because the pipe was undulating up and down, within the ground, it wasn’t possible to use a jet vac to clean it out so we turned to older technology, poly-pigging, to get the job done.”
Lanes has a sophisticated jet vac tanker. Engineers guide the tanker’s high pressure hose into the pipe, which is then powered along the drain line using a powerful jet of water, forcing debris out of the pipe, either forwards or backwards, depending on what type of jetting head is attached to the hose. The jet vac can also be used to suck debris from a pipe.
However, the technique used for the gas mains job involved inserting a poly-pig, a cylinder made of flexible plastic or foam that is often shaped like a bullet, into the pipe and forcing it along the run with compressed air.
The poly-pig is highly effective at clearing blockages and pushing material out of a pipe – and, because it is flexible, it can get round kinks and curves in pipes that jet vac hoses can’t.
Norbury added: “Pipeline pigging, as it is called, is a very useful technique. In this case, 180 metres of pipe were pigged. Because the diameter of the gas main ranged from 180mm to 50mm, several different sizes of poly-pig were used.
“We were able to clear the blockage and the contractors could test the boiler in the new school. To their relief, it fired up first time, so the poly-pigs had done their job very well.”
Image – Poly pigs from Girard Industries Europe.