The insertion of an expansion device into a deformed pipe to return it to a circular shape prior to a permanent repair usually with a lining technique.
Re-rounding is not a stand-alone technique but is intended to re-shape a deformed pipe prior to patch repair or relining. An expander unit is used to re-round the pipe and install a metal or plastic clip, which holds the pipe fragments in position until a patch or liner is installed. Deformation of pipes between magnitudes of 10% to 35% is typical for this type of temporary repair.
The expander system is inflated with hydraulic pressure or, alternatively, a hydraulic mole forces steel 'petals' outwards by hydraulic rams. The plastic or metal clip is scrolled around the expander and secured prior to. After positioning under CCTV control, the clip is expanded with sufficient pressure to re-round the pipe.
Care must be taken with severely damaged pipes since the unit will take the path of least resistance when expanding. For example, if there is a void beneath the pipe invert (as a result of exfiltration / infiltration), the clip may be forced down when expanded, rather than re-shaping the soffit of the pipe. It is also important to follow the relining or patch repair as soon as possible after the re-rounding operation, (within 24 hours) since the clip has limited structural strength and may soon become misshapen if left without support.
Photo courtesy of WRc
Last Updated on Thursday, 25 April 2013 16:35