Sliplining is one of the oldest trenchless methods of rehabilitating existing underground pipelines. This technique involves inserting and installing a marginally smaller diameter carrier pipe into a larger host pipe between two predefined points. Sliplining is considered to be a type of structural renovation since the structural properties of the host pipe (flexural strength, tensile strength, ring stiffness, etc.) are replaced by the properties of the carrier pipe.
Sliplining is typically a seven-step process. Though the actual number of steps may vary depending on several factors, including field conditions, pipe materials, piping network configuration, and host pipe condition, the basic principles of installation remain the same.
The 7 Steps to Sliplining an Existing Pipe
Inspect the existing pipe
The first and most crucial step to sliplining involves inspecting and assessing the condition of the existing pipe. Inspection is essential to determine the level of pipe deterioration and the feasibility of the sliplining procedure. This can be carried out using several methods including manual inspection and remote controlled CCTV equipment. (Read Using CCTV to Inspect Pipes.)
Clean and clear the existing pipeline
Once inspection is completed, the host pipe must then be thoroughly cleaned in preparation for the lining installation. Cleaning operations can be performed using a variety of tools and equipment including kites or plugs, cleaning buckets, water jetting, or pigging. (Learn more about pigging with How Pigging Works in Trenchless Repair and Rehabilitation.)
Join the carrier pipes
The liner or carrier pipe is usually transported to the site in sections and subsequently joined together to the desired installation length. Liner sections are usually welded using either extrusion or butt fusion technologies. (Read Butt Fusion & Polyethylene Pipe: How to Effectively Use This Trenchless Method.)
Some pipe sections may also consist of gasketed bell and spigot joints, whereby the pipe ends may be joined via insertion.
Gain access to the existing host pipe
In order to proceed with the liner installation, the host pipe must first be accessed via two relatively small excavations known as the entry and exit pits. The location of these excavated areas represents the extent of the liner installation.
Install the liner (carrier pipe)
Once the entry and exit pits are complete, the liner is ready to be installed at the specific location. Installation can be accomplished by either pushing or pulling the carrier pipe through the host pipe. Butt or extrusion welded HDPE pipes are typically pulled into place (though they may be driven as well).
Bell and spigot joined pipes, on the other hand, must be pushed from the entry to the exit pit; this keeps the pipe joints from separating and help maintain a watertight seal.
Restore the lateral connections
After the recommended 24-hour relaxing period following liner installation, each lateral connection must now be reinstated. One of the most common methods of restoring the laterals involves placing a wrap-around saddle over openings that have been cut into the liner at the location of the intended lateral connection.
Restore terminal connections and stabilize the annular space
This final step involves restoring the connections at the terminal ends of the liner. Connections to various system appurtenances are usually completed using a variety of pressure-rated fittings, flanges or fusion technologies. The annular space between the carrier pipe and the host pipe is also grouted to help stabilize the installed liner.