November 2017 Vol. 72 No. 11
Rehabilitation
CIPP Lateral Sewer Rehabilitation: Does It Perform As Expected?
By Larry Kiest, Jr.
A major challenge faced by nearly every utility is how to address its aging underground infrastructure. Sewer pipes are failing from coast to coast as America finds itself on a fast track to replace or renew sewer collection systems. A major driving force is the mandate set forth by state and federal regulators that require utility owners to renew their systems so they are watertight.
Today, if a utility uses State Revolving Loan Funds (SRF) to pay for its sewer rehabilitation project, the design must be justified based on life-cycle cost analysis. This requirement is imposed by legislation passed by the U.S. Congress in 2014 known as the Water Resource Reform and Development ACT (WRRDA). Even without the requirement for such an analysis, a responsible utility should perform one to ensure the best value for the rate payer’s investment. The days of ground water infiltrating and overloading pipes, pumps and wastewater treatment plants at public expense is now a priority to correct.
Today, more and more engineers have experienced the limitations and capabilities of cured-in-place pipe (CIPP) and understand the need for water tightness, as well as the need for long-lasting performance. CIPP is the most sought-after trenchless technology. However, case studies have shown that CIPP rehabilitation of sewer mains allows continued leakage, as groundwater tracks behind the liner and reenters the sewer at service connections.
Likewise, service lateral pipes have deteriorated and must be renewed and sealed. Studies have shown that up to 70 percent of extraneous water can be derived from defective lateral pipes. In order for a rehabilitated system to be watertight, a holistic approach must be used, which includes addressing the main pipe, manholes and similar structures, service lateral pipes and cleanouts.
When materials and methods designed to rehabilitate and seal up a system by adherence to established engineering industry standards are commissioned, many utility owners are experiencing “good as new results” on their projects. In other words, they are receiving performance comparable to new pipe construction.
The most difficult challenge utility owners must overcome is the sales pitch for low-cost, short-lived solutions by many providers and contractors alike. The notion of CIPP bonding to fats, oils and grease (FOG) in a wet sewer pipe for 50 years has led to millions of dollars going down the drain. The industry has responded by developing more appropriate and stringent specifications and industry standards for CIPP requiring high-quality construction materials, including CIPP gasket seals, to achieve “as good as new” results.
Industry standards
The primary objectives for renewing a sewer collection system should include both renewed structural integrity and to provide a long-term watertight seal. To be effective and meet those objectives, one must first understand the technology and apply the correct industry standards. Those who have been involved with pipeline rehabilitation are familiar with the ASTM F1216 standard, the granddaddy of standards for the CIPP industry. But being familiar with a standard doesn’t necessarily mean one truly understands what the standard entails.
ASTM F1216-16, “Standard Practice for Rehabilitation of Existing Pipelines and Conduits by the Inversion and Curing of a Resin-Impregnated Tube,” has guided the CIPP industry since it was published in 1989. The F1216 standard is a practice for installing CIPP in mainline pipes that have easy access from manholes located at each end of the sewer pipe. The F1216 standard makes no mention of robotically positioning a lateral connection liner from within the main pipe, and makes no mention of providing a long-term seal utilizing a pipe gasket.
Too often, there is confusion as technology providers and contractors alike make the statement “my lateral liner meets F1216.” What people really should be saying is, “My lateral liner meets the non-mandatory design of F1216 found in appendix X1.”
Did you know that F1216 section 8.2 actually includes an allowable leakage rate? The F1216 standard allows for 400 gallons of leakage per day, per mile for an 8-inch pipe. That equates to 146,000 gallons of leakage per year, per mile while maintaining compliance to the standard. There is so much in-depth information relating to CIPP that to really understand the limitations and capabilities of the technology, one must get back to the basics and adhere to practical engineering principles.
Everyone understands that butter in a frying pan is used for two reasons: it makes food taste good and it prevents the egg from sticking to the pan. FOG is prevalent in all sewer pipes and the cleaning method described in F1216 simply references the NASSCO-recommended specifications, which call for removing any debris in the pipe. There is no mention of using hot water or detergents, and the presence of FOG ensures no chemical bonding can occur, just as the butter in the frying pan.
In fact, let’s take another look at the F1216 standard and dial in on section 7.5 Lubricant. In this section, lubricant is described as an oil-based product applied to the coated surface of the liner tube for purposes of reducing friction during inversion installation. You may see municipal specifications that call for a lateral connection liner to form a long-term watertight seal based on bonding the connection liner to the mainline liner. The concept of bonding a connection liner to a mainline liner that has the coating purposely greased up, as prescribed in F1216, is just not practical and does not adhere to engineering principles.
Another misconception of bonding a connection liner to a mainline liner is the use of incompatible substrate material. The coated surface of a CIPP mainline, per F1216, is made from polyethylene (PE), polypropylene (PP), or thermal plastic urethane (TPU). The PP and PE coatings are olefin-based plastics that are well-known to be non-stick materials. For the reasons explained so far, bonding CIPP in an active sewer is not realistic and cannot provide long-term results.
There is more to understanding how CIPP can perform to the point where it can truly be comparable to that of new pipe. As described in F1216 section 7.2 Resin Impregnation, the standard calls for 5 to 10 percent excess resin to be inserted into the lining tube. Most of this resin is consumed by pipe defects such as open joints and fractures in the host pipe.
However, there is no scientific method or exact calculation for determining just how much resin will be consumed in the pipe defects. In the case of CIPP for mainline rehabilitation, excess resin is not a concern because the resin is expelled at the receiving manhole, captured and removed. However, when a lateral connection liner is inverted from the main pipe to the property line, a slug of excess resin can accumulate at the end of the liner and, if left to harden, an obstruction leading to potential blockage can occur. It’s for this reason that a cleanout is necessary to remove a resin slug. Cleanouts are essential for a successful installation and ensuring longevity of the new CIPP.
It is not best practice to install a CIPP lateral connection liner without a cleanout. Installation of a resin shy liner can be used to try to prevent a resin slug, but that results in a structurally deficient CIPP that can buckle under a hydraulic load. The good news is there are products available for installing a clean-out by creating a small-diameter hole using vacuum excavation. This method is described in ASTM 3097-15, “Standard Practice for Installation of an Outside Sewer Service Cleanout Through A Minimally Invasive Small Bore Vacuum Excavation.”
Although ASTM 1216 provides a 50-year design life, it does not provide a solution for watertightness. The design life needs to match the service life, but if the intent is watertightness and the liner leaks in the first five years, at that point the service life has expired. This results in rate payers continuing to pay for transportation and treatment of extraneous water.
It is for all the reasons explained above that the ASTM F2561 standard practice was created and has been specified by municipal agencies and their engineers since 2006. The ASTM F2561 “Standard Practice For Rehabilitation of a Sewer Service Lateral and Its Connection to the Main Using a One-Piece Main and Lateral Cured-In-Place Liner” covers requirements and test methods for the reconstruction of a sewer service lateral pipe. This standard is specific to materials and installation practices for renewing a CIPP lateral connection liner including pre-molded gasket seals, which provide a watertight CIPP so the design life matches the service life.
Gasket sealing
In order for CIPP rehabilitation to be comparable to new pipe, pre-molded engineered gaskets must be utilized, just as they are used to seal pipe joints in PVC, ductile iron, concrete and most all other pipes. The use of an expanding flange-shaped gasket located at the main-to-lateral pipe juncture, prevents water tracking behind the mainline CIPP and provides a watertight seal between the main and lateral CIPP liner.
Does lateral rehabilitation really work? Just about anything could work; the question is for how long? Actually, bubble gum attached to a liner might initially perform a seal for a short period, but 50 years is a long time and taxpayers cannot afford bubble gum, paste, caulking, or the notion of bonding to a wet, greasy sewer pipe to form a long-term seal. Trenchless lateral rehabilitation does work when the design adheres to sound science and practical engineering principles.
About The Author: Larry Kiest, Jr. is an innovator, entrepreneur, writer and speaker who has shaped the global conversation about the best ways of using the trenchless technology of CIPP to rehabilitate underground infrastructure. As founder and president of LMK Technologies, Larry has developed multiple trenchless systems that have resulted in over 90 patents issued throughout North America, Europe and Australia.
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