It is important to understand the purpose and the long-term goals for sealing a collection system. In any given collection system, inflow and infiltration (I&I) can cause havoc for valid reasons. However, there are circumstances where installing a new cured-in-place pipe (CIPP) alone is not enough to prevent I&I – this is particularly the case for greasy sewers and in sewers where hydrostatic loading is present. The standard industry practice for cleaning a sewer pipe in preparation for CIPP lining often involves nothing more than hydraulic jetting to remove any debris in the pipe. The residual fats, oils, and grease (FOG) present on the walls of a host pipe are in no way diminished due to high pressure hydro cleaning.
Sealed with a gasket
These problems have not gone unnoticed, and over the years there have been numerous attempts to correct these issues without notable success. The attempted remedies range from methods of injecting a chemical grout post-lining, to packing of cementitious material at the liner/manhole interface, to the insertion of expanding end seals positioned in the pipe prior to lining.
The concept of a compression gasket to form an engineered seal is an accepted industry practice used for years in the installation and joining of sewer pipes. Even though the engineering society understands that the best long-term solution is an engineered gasket seal, one must select the proper gasket, which is designed for CIPP applications.Article continues below…
The use of a hydrophilic rope or belt shaped material commonly used in a cold-concrete-joint is not suitable for CIPP renewal works. Those who have attempted to use this type of seal will appreciate the challenges of effectively securing a penannular or non-monolithic gasket to the inside of a pipe. Some of the problems that occur with this method are that gluing anything into a wet and greasy sewer pipe is a challenge in itself. If the gasket falls over during insertion of the liner, the result is a large bump at the invert of the pipe; or the contractor simply doesn’t install the problematic gasket as required. Even if one were to assume the gasket could remain in-place as the liner is inserted, the ends of the gasket would have to abut or overlap.
The belt type gasket creates a significant opportunity for separation or a gap in the gasket resulting in continued leakage where hydraulic loading is present. Furthermore, these belt shaped gaskets are fairly narrow, producing an insignificant sealing surface. They are also quite bulky in thickness, reducing the cross section of the pipe which may hinder the insertion of robotic cutters, maintenance and lateral connection lining equipment.
In order to correct these deficiencies, a considerable amount of research and development has been initiated to produce a truly engineered mechanical end seal which is simple to install, is effectively secured to the inside of the pipe, and has a significant sealing surface and a low profile that maximises the cross section of the pipe opening.
A total system seal
Those who invested in the research and development of LMK’s Insignia™ Hydrophilic Sealing System could not stop supporting the research project until it proved to conclude a total system seal that is compatible with all mainline CIPP systems – regardless if the mainline liner is pulled into place or inverted into place. To achieve the objective of a total sealed system, the team had to first identify additional locations for continued leakage post mainline CIPP rehabilitation. Identifying this source was quite simple, as the trenchless industry has widely accepted that a vast majority of infiltration is derived from service lateral pipes.
Infiltration found at a service connection may have more than one source; where one source is water that infiltrates through lateral pipe defects and another is water that tracks behind mainline linings and re-enters the collection system at service connections.
The renewal of lateral pipes and the main/lateral connection is typically performed by pressing a resin saturated mainline member against the interior of a mainline CIPP as a resin saturated liner tube is inverted into the lateral pipe. Most commonly, the lateral pipe is renewed to the property line. The challenge is how to form a long-lasting seal between the lateral CIPP and the mainline CIPP. Long-term bonding to the interior surface of a mainline CIPP is problematic for a few practical reasons:
- CIPP includes inner coatings made of materials that are incompatible for long-term thermoset bonding
- CIPP liners are lubricated with mineral oil, vegetable oil, cooking grease and similar lubricants to reduce friction during inversion – these materials are well-known release agents that actually prevent bonding
- Thermal expansion/contraction of plastic CIPP
- If water is present, it is a relentless force working against any bonded connection.
The solution for obtaining a long-term seal starts by applying common engineering principles. The science of a compression gasket seal is where two structural materials are joined and during the joining process, the gasket is compressed resulting in a flexible seal that has been proven to be extremely effective in sealing pipes for many years in the pipeline industry.
In the case of CIPP applications, the design team applied these same engineering principles. The research project concluded with a final solution for a mainline and service lateral collection system seal consisting of a high-strength, low-profile, short, full-hoop CIPP outfitted with a flange or hat-shaped, hydrophilic neoprene rubber gasket and a single-piece lateral liner tube assembly.
The full-hoop mainline member provides a structural bridge as an opposing force from the swelling gasket occurs forming a compression seal that is comparable to that of new pipe. An added benefit of this sealing method is compatibility with all mainline CIPP lining systems and the peace of mind that an engineered structural mainline member combined with an engineered seal can be designed and stamped by professional engineers providing a true service life, and not simply relying on ‘let’s hope it sticks.’