May 2011, Vol. 66 No. 5
Features
Defining, Understanding Lateral Rehab Options
Members of the NASSCO Lateral Committee continue to refine a document to provide a comprehensive overview of lateral and main-lateral connection repair and sealing technologies.
NASSCO (the National Association of Sewer Service Companies) is a national organization dedicated to establishing and implementing standards for rehabilitation of underground utilities and is comprised of several hundred members representing rehabilitation industry manufacturers and suppliers, municipalities and utility districts, engineers and contracting firms.
A draft of the report was completed in January 2011 and is undergoing peer review by committee members, said Larry Kiest, chairperson of the committee. The draft’s contents covering types of resin systems and lining tubes for lateral rehabilitation appeared in the March issue of Underground Construction magazine. This report covers methods of installation, curing and sealing connections.
Cured-in-place pipe (CIPP) liners are available with various resin systems, including polyester, epoxy, vinyl ester and silicate. Depending on job conditions and pipeline effluent, one resin may be preferable over another.
Lining tubes typically are constructed from a needle punched felt or a knitted tube. Liner tubes vary in density and flexibility in order to negotiate small diameter pipe and bends and to reduce pressures for inverting the liner so the tube is not overstressed. Correct installation practices combined with the right material are keys to successful lateral lining rehabilitation.
Manufacturer installation procedures must be strictly followed to reduce risk and increase the chances of a successful installation. It is easier to renew a lateral from an excavated pit, and the risk is much less than renewing a lateral from a clean out or remotely from the main pipe. However, there is no digging required when a lateral is renewed through a clean-out or from the main pipe and when a lateral is renewed from the main, the connection is also sealed.
Basically, there are risks and rewards for all lateral repair/renewal methods, and the positive and negative attributes of these technologies are a major part of the NASSCO lateral committee’s report. The key is to know which technology to use and when.
For the lining process, laterals may be accessed from a clean out located either outside or inside a building, from a manhole connecting to a lateral, an access point made by an excavation, or remotely from the sewer main. Accessing the lateral where no excavation is required is typically preferred.
Sectional lateral CIPP lining
When inspection and evaluation reveals that only an isolated section needs repair, sectional CIPP repairs can be made by pull in place, push in place, or inversion methods.
Pull-In-Place Method — A resin-saturated liner is positioned on a pneumatic plug, inserted through a clean out and pulled to the point of repair. The plug is inflated until the resin is cured, then the plug is deflated and removed, leaving behind the finished cured-in-place sectional liner.
Push-In-Place Method — This method involves positioning a resin-saturated liner on a pneumatic plug, inserting it through a clean out and pushing it to the point of repair. The plug is inflated until the resin is cured and then deflated and removed leaving behind the finished cured-in-place sectional liner.
Inversion Method — A resin saturated liner is moved into position by attaching it with a frangible connection to an inversion bladder. Swelling compression gaskets or other approved seals can be attached to each end of the liner in cases where severe leaks are present. The inverting bladder carries the liner through a clean out and positions the liner at the exact location of repair. Prior to curing, an inspection camera can be inserted into the bladder while pressure is maintained to determine proper placement.
Lateral renewal by CIPP Lining
Lateral lining is defined as rehabilitation of the lateral from the lateral access point continuously to a specified point, typically the sewer main. CIPP lining is also used to renew a portion of the lateral from an access point to a point near a building foundation. Technology providers have developed four distinct installation methods to accomplish the lateral lining objective.
Double Inversion Method — An excavation is made, and a section of lateral pipe is removed. A predetermined length of resin-saturated liner is inverted into the lateral pipe using air pressure. When the liner is fully inverted, the end is open allowing the inflation pressure to release. A bladder then is inverted inside the liner causing the liner to be repressed tightly against the pipe until the resin is cured.
Single Inversion Method — An excavation is made and a section of the lateral pipe is removed. A liner tube is positioned inside of a bladder, and the liner assembly is resin saturated. The liner/bladder assembly is simultaneously inverted into the lateral pipe using air pressure. Prior to curing, an inspection camera can be inserted into the bladder while pressure is maintained to determine proper placement. The liner remains pressed tightly against the wall from the initial inversion until fully cured when pressure is released and the bladder is removed.
Pull-In-Place Method — This method allows the liner to be installed from an excavated pit or a clean out. Preferably, a pull cable is strung from the clean-out through the lateral and main sewer pipe to a receiving manhole. A resin-saturated liner with a secondary non-stick skin is positioned on a pneumatic plug. The liner/plug assembly then is pulled through the clean out by the pull cable, far enough to get past the clean-out opening. A closed-circuit television (CCTV) camera in the sewer main is used to ensure that the liner is correctly positioned at the lateral terminus and not protruding into the main sewer. The plug is inflated pushing the liner tightly against the lateral pipe until cured. Then the plug is deflated and removed along with the secondary skin from the liner.
Clean-Out Inversion Method — A resin-saturated liner is frangibly attached to a bladder by simultaneously inverting them through a clean-out. Swelling compression gaskets or other approved seals can be attached to each end of the liner ensuring water can’t track behind the liner. The liner is positioned along the bladder at a point just past the clean out. Inversion pressure keeps the liner pressed tightly against the lateral pipe. Prior to curing, a CCTV inspection camera is inserted into the bladder to insure correct positioning of the liner. The pressure is maintained until the liner is fully cured. Then pressure is released and the bladder removed.
Connection Sealing
Brim-Style Main/Lateral Connection Lining — Brim-style liners typically are installed after the sewer main pipe has had a cured-in-place liner installed. The cured-in-place mainline liner inner’s surface, around the lateral, needs to be properly prepared immediately prior to a brim installation. A resin saturated liner in the shape of a brim or a top hat is positioned on a bladder within the sewer main at the lateral connection allowing the lateral liner to extend into a portion of the lateral pipe. The bladder is inflated pressing the brim against the main and around the lateral opening and the lateral liner is placed tightly against the inside of the lateral pipe. Once the liner is cured the bladder is deflated and removed.
Full-Circle Style Main/Lateral Connection Lining — This repair is the same as the brim style where a section of the lateral pipe is renewed and the seal is made at the main connection. The full-circle connection liner is structural and can be designed by an engineer to withstand hydrostatic loading.
Installation methods for main/lateral connection lining
The main/lateral lining process rehabilitates both the lateral and the main/lateral connection and always is done from within the main pipe. Lateral and main/lateral connection lining involves one of three installation methods.
Pull-In-Place Method — A liner assembly of lateral liner tube and either a main brim liner or a full-circle liner is positioned on an inflatable tee-shaped plug which is positioned at the lateral connection from within the main sewer. Then the lateral liner is pulled through the main pipe and up into the lateral via a pull cable that has been previously strung from a clean out to the insertion manhole.
Inversion Method — Initial steps are similar to the pull-in method with insertion of a liner assembly comprised of a lateral liner tube and a structural or non-structural main connection liner. The main/lateral liner is loaded into a robotic launcher and when positioned at the main/lateral opening, the main liner is inflated against the main pipe and the lateral liner tube is inverted up the lateral pipe. The distance the liner inverts up the lateral is predetermined and can be as little as 6 inches or can be as long as 200 feet. This distance is typically consistent to the length of lateral that is the responsibility of the sewer authority.
Curing methods
Resin systems can be cured in ambient conditions or by heat either as hot water, steam or ultraviolet light.
Ambient curing under air pressure is a common curing method because it requires less equipment. Ambient cure time typically ranges from 1 to 12 hours, depending on the resin system and length of the liner.
Steam curing proves to be the most productive since the contractor has plenty of work-time which is especially important when long liners are installed and curing is complete in as little as 30 minutes once the liner has been inverted in place. Also resin that is steam cured achieves a high level of cross-linking resulting in higher physical properties.
Ultraviolet light curing is used with some technologies and offers the shortest cure-times, as fast as 10-minutes for short liners that extend about eight inches into the lateral pipe.
Hot water curing is used to line a lateral from an access point toward the main, but is not typically used to make main/lateral connection repairs due to the lateral liner inverting from within the main pipe
Educational benefits cited
The report includes detailed positive and negative attributes of each method. “There is an enormous amount of information that needs to be discussed and put into booklet form that is easy to understand and will provide significant education on the benefits of trenchless lateral repairs,” said Committee Chairperson Kiest. “The document will assist NASSCO in working with local and state governing health and plumbing boards through education to encourage these agencies to accept these technologies into the code books.”
After the document is finalized, NASSCO will make it available to association members and the public.
Kiest is president and chief executive officer of LMK Enterprises, Ottawa, IL.
NASSCO is a national organization comprised of several hundred members representing rehabilitation industry manufacturers and suppliers, municipalities and utility districts, engineers and contracting firms. Ted DeBoda is executive director.
FOR MORE INFORMATION:
NASSCO, (410) 486-3500, www.nassco.org
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