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Sliplining is one of the oldest methods for trenchless rehabilitation of existing pipelines. Sliplining is used to repair leaks or restore structural stability to an existing pipeline. Sliplining is completed by installing a smaller, "carrier pipe" into a larger "host pipe", grouting the annular space between the two pipes, and sealing the ends. Sliplining has been used since the 1940s. The most common material used to slipline an existing pipe is high density polyethylene (HDPE), but fiberglass reinforced pipe (FRP) and PVC are also common. Sliplining can be used to stop infiltration and restore structural integrity to an existing pipe. The most common size is 0.20m - 1.5m (8"-60"), but sliplining can occur in any size given appropriate access and a new pipe small or large enough to install.
There are two methods used to install a slipline: continuous and segmental.
Continuous sliplining uses a long continuous pipe, such as HDPE or fusible PVC, that can be welded into continuous pieces of any length. The continuous carrier pipe is pulled through the existing host pipe starting at an insertion pit and continuing to a receiving pit. Either the insertion pit, the receiving pit, or both can be manholes or other existing access points if the size and material of the new carrier pipe can maneuver the existing facilities.
Segmental sliplining is very similar to continuous sliplining. The difference is primarily based on the pipe material used as the new carrier pipe. When using any bell and spigot pipe such as FRP, PVC, or HDPE the individual pieces of pipe are lowered into place, pushed together, and pushed along the existing pipe corridor.
Using either method the annular space between the two pipes must be grouted. In the case of sanitary sewerlines, the service laterals must be reconnected via excavation.
Sliplining is generally a very cost effective rehabilitation method. It is also very easy to install and requires tools and equipment widely available to any pipeline contractor. Segmental sliplining may not require bypassing of the existing flow.
The new pipe will generally have a significantly reduced cross sectional area because of the size difference between the inside diameter of the existing pipe and the outside diameter of the new pipe, as well as the wall thickness of the new pipe. Sewer laterals must be reconnected via excavation. Installation usually requires excavation at the insertion and receiving pits. Continuous sliplining generally requires bypassing the existing flow.