TRUNK MAIN REHABILITATION
One of the largest bulk water suppliers in Germany, Zweckverband Landeswasserversorgung (LW), were battling a major leakage problem on one of their main trunk supply pipelines, which transports water from Geislingen to Langenau. In particular, two sections of this main trunk supply, spanning 6.7km, were experiencing leaks of up to 35ltr per second.
Constructed from 1500mm diameter prestressed concrete spigot and socket pipes in 5m lengths, the joints were sealed using rubber gaskets. Whilst the pipeline fabric was generally structurally sound, the leakage was a result of degradation of the rubber sealing gaskets in many of the joints.
A strategically vital link in the LW network, the pipeline could only be taken out of service for a maximum of three days without significantly impacting supply.
As such, previous repairs using manual installation of internal seals had been limited due to the short amounts of out of service time permitted.
Requiring a more effective and longer term solution, LW engineers undertook a feasibility study to identify potential pipeline rehabilitation options that would be quick to install and maximise the pipline’s capacity.
LW identified the most practical solution as a thin wall polyethylene liner, which would work interactively with the host main to deliver the operating pressure conditions of 8 bar, whilst retaining the pipes diametre and limiting disruption to service.
Following discussions with contractors Pfeiffer (the German licensee for Subterra’s technologies), the Subline PF Close Fit Polyethylene Lining System was selected and a 538 metre section was identified on which to trial the system.
Radius Subterra’s Subline PF Sytem is a well established technique for the installation of large diameter close fit polyethylene liners in any size up to 1200mm diameter.
As much of the preparatory work can be completed prior to the existing main being taken out of service, long lengths of liner pipe can be installed rapidly to provide a continuous barrier between the host pipe and product.
By spanning any open joints or holes and removing the potential for pipe bore internal corrosion, leaching, and any bacteriological issues, the liner works interactively with the pipe to extend its lifetim by a minimum of 50 years.
A pre-project possession and shut of the main to prepare it for liner insertion was carried out in advance. A 1480mm OD SDR 61 PE-100 liner pipe was chosen with a wall thickness of 24.3mm and adaptations to the standard butt fusion welding machine were made to ensure it could both handle and fuse the large pipe.
Whilst the original aim was to butt fuse the entirety of liner pipe into a single string, a lack of space meant that only 510m could be prepared and the remainder was formed into a separate 40m string. These strings were pressure tested and fully chlorinated before being pushed through the Subline machine to fold it ready for insertion.
The main was then drained and the liner was inserted in a single pull of approximately 6.5hrs at 1.4m per minute, before the main was carefully recharged to revert the pipe to its original shape to form a close fit with the host pipe.
The careful preparation of the liner and its rapid insertion allowed service to be returned in less than two days, ensuring that the bulk supply reserves to the receiving communities did not fall below the critical level.
The ongoing leakage losses have been eliminated, and with it, the need for repetitive leakage detection and hazardous man-entry local repair.
It is the largest close-fit PE liner installation to have been carried out in the world to date.Download: