There is a “Trenchless” process that can involve no digging at all to replace a sewer line. This involves “shooting” a fiberglass lining into an existing sewer line creating a new pipe within the old deteriorating pipe. The process may be comparable in cost to excavation and may actually be a savings if you look at the cost of repairing the collateral damage to landscaping and the cost of a street opening.
Before a sewer line can be relined it must be cleaned & inspected with a video camera to perform a sewer inspection and determine that it is in fact a viable candidate for relining. The line must have proper pitch maintained without any bellies, or misaligned joints. The liner follows the contour & path of the original line and will not correct these defects. The line may have small breaks where pieces of the pipe have broken or fallen out exposing soil but the pipe must maintain it’s original shape and not be collapsing yet. Very short and shallow belly, or, small misalignment may be of no consequence but that is best determined by the experience of the relining contractor as this is a judgment call.
The lining may be shot through any opening in the pipe that that allows good access for the liner to reach the problem area. The liner may even be shot into the line via a cleanout. Cutting into the pipe may also be done. Best access will be determined again by the relining contractor.
The relining material is essentially a woven fiberglass hose with a thin plastic film on the outside. A calculated amount of fiberglass resin and hardener is mixed then poured inside the liner. the contractor then makes sure that the entire length of the woven fiberglass is fully “wet” with the mixed resin. The liner is then shot into the the sewer line using a gun that inverts the liner so the resin coated weave ends up on the outside where it bonds to the old pipe and the thin plastic film becomes the slick inside surface of the new pipe. The gun uses compressed air to propel the liner into the pipe and the whole process is very similar to turning a sock inside out.
A calibration tube similar to a balloon is also shot inside the liner which is then pressurized with either compressed air or water heated by a portable boiler to accelerate the cure time of the resin. The pressurized calibration tube holds the fiberglass liner out against the existing sewer line until the fiberglass liner cures into a hard new fiberglass one piece pipe within the old pipe. Using the hot water method speeds the curing process but is not required. Once the line has cured the calibration tube is removed.
If there are any tie-ins that need to be reestablished a small device with a cutting burr is inserted into the pipe to cut out openings allowing flows from the other line to flow into the newly relined pipe. At this point the work on the line is done, a quick video inspection to check the line, and the relined sewer is ready for use.
While the relining process sounds very easy in this description I assure you that what I have written is an oversimplification. The sewer line must be cleaned very well prior to relining, and the process requires a careful choreography that even highly experienced crews stop to talk about just before the resin is mixed. The job has a very high pucker factor that comes in as soon as the hardener is added to the resin. At that point the clock is ticking with a count down to the time at which the resin used to impregnate the liner hardens. If the liner hardens before you have completed pressurizing the balloon line you are in trouble.
There are a few different relining processes from different manufacturers used. This article is intended as an overview of the process and is not a full description of every different manufacturers process.
UpDate: Recently Source 1 Environmental introduced PipePatch which is a cured in place fiberglass liner that can be applied in short lengths inside the sewer. The PipePatch is placed on a packer and pushed into place using rods to move it, then once in place the packer is inflated with compressed air until the patch is cured. This new relining technology now allows relining of a specific area of the sewer line without having to reline the entire length of the pipe from an opening to the bad area. The PipePatch may offer significant cost savings to the consumer on sewer line repairs.
I hope this article gives you a good understanding of the sewer line relining process, the steps involved in the relining process, and the limitations of the relining process. The net result is a new one piece pipe within the old pipe that does not leak and is impervious to root intrusion.