Data collected during select insertions of a cured-in-place pipe (CIPP) project in Collierville, Tenn., may lay the foundation for increased use of steam-cure in future CIPP projects.
The practical evaluation of steam-cure was the result of a team effort that involved the Town of Collierville, consulting engineering firm Jordan, Jones & Goulding Inc. (JJG), CIPP specialist Insituform Technologies Inc. (ITI) and leading resin supplier AOC.
East of Memphis, Collierville has a quaint downtown district with a classic gazebo town square listed on the National Register of Historic Places. Residents, businesses and local government work together to maintain the town’s genteel ambianc that spreads out from the downtown into neighboring streets.
When engineers concluded that underground sewer lines needed rehabilitation, the idea of tearing up streets to replace the pipe had the makings of a civic nightmare.
“This was a major infrastructure management undertaking,” said Murray Beard, project manager for the Collierville Public Service Department. “There were a variety of issues in different areas. In some places, soil settlement was causing depressions in the roadway. There were leaking joints. Heavy root intrusions in some segments were causing backup. And we had inflow and infiltration of storm waters during heavy rains.”
To solve these problems with minimal disruption, the Town of Collierville decided to use CIPP. “Our decision was based on extensive research and previous good experience with CIPP,” said Beard.
“Collierville Public Services contracted out our first sewer rehabilitation by CIPP in 2004 with 1,500 lf of badly deteriorated 8-in. concrete gravity sewer. This was after we had evaluated sliplining, pipe bursting, and open-cut excavation and replacement methods.”
Beard says Insituform won bids for the 2004 CIPP project and a larger one in 2006 and both projects were a success. Then in 2007, Collierville hired Jordan, Jones & Goulding to rewrite the town’s CIPP technical specification and provide onsite consult during project execution.
Senior pipelines rehabilitation specialist Steve Lindsey helped design a CIPP trenchless solution that was installed by ITI crews using a felt tube saturated with Vipel corrosion-resistant resin from AOC.
To speed installation and eliminate digging, access to the pipe was made through existing manholes. Insituform operations manager Randy Hansbrough, who oversaw the installation, observed: “If this project had been standard open-cut construction, it would have taken six months, instead of four-and-a-half weeks. By not having to dig trenches, businesses did not have to face shutdowns and roads stayed open to traffic.”
About the Project
Underground liner insertions were manhole-to-manhole. Some 40 pipe segments were rehabilitated using this method with shots ranging in length from 104 to 523 ft. The project rehabilitated a total 12,550 lf of aged 8-in. pipe, which was installed in various stages in the 1960s. Most of the host pipe was concrete. The remainder involved sections of vitrified clay pipe in which video inspection revealed heavy root intrusion.
“In preparing the pipe for the new cured-in-place pipe, 589 ft of the host pipe required heavy cleaning,” Beard stated. “We also removed 29 protruding service connections, or taps and reinstated 146 active live taps. And we needed to perform one point repair to replace a badly disconnected and misaligned joint.”
After the pipe was prepared, Insituform crews inserted a non-woven polyester fiber felt tube. Each section of tube was custom-made for the host pipe and supplied in a predetermined length for the insertion. Prior to being shipped to the jobsite, the tube was impregnated with wet resin at Insituform’s special facility in Jacksonville, Fla. The tube was shipped to insertion sites in Insituform-owned vehicles.
The vehicles stored the tubes under controlled, refrigerated conditions that prevented pre-mature resin cure.
Insituform Processing and Quality
The majority of the pipe was rehabilitated using hot water-cure. As the wet-out tube was inserted through the manhole and pipe, water was injected into the liner to create waterhead pressure inside the tube. Under pressure, the tube was sequentially inverted (turned inside out) and lined against the pipe’s inner wall.
Upon completion of a tube insertion, the water was heated to bring the temperature of the resin to its curing point. The temperature was held for a specified time to ensure a complete cure. When fully cured, the liquid resin became a cross-linked solid to form a new seamless liner inside the old pipe.
The high-quality and consistency of CIPP gives the work crews the repeatable and predictable handling characteristics that keep a job on schedule and within specs. Insituform controls the quality of its product by vertically integrating design, manufacturing, installation and service.
“Having Insituform handle every step of the process in-house gives the onsite crew quite an advantage in ensuring the quality of the finished product,” said Hansbrough. “Every aspect of our process is under a Total Quality Management program that is ISO 9001:2000 certified. ISO certification confirms that there are management systems in place to focus on customer quality requirements, regulatory compliance, customer satisfaction and continual improvement.”
Importance of Resin Quality
With more than 22 years of experience, Lindsey is a published author and leading authority in the CIPP field.
He pointed out that the resin specification is a crucial link in a CIPP project’s value chain. The resin for the Collierville job was a high molecular weight Vipel isophthalic polyester engineered specifically for CIPP and proven in applications throughout North America.
Gary Tullis, AOC director of quality systems, underscored AOC’s attention to detail in pursuit of quality. “AOC has an extensive list of active resin formulations and each one has its own customized quality profile,” he said. “Our manufacturing uses a proprietary adaptation of specialized process control software designed to produce the same exact material time and time again.
“The quality management system of each AOC manufacturing facility is certified as meeting ISO 9001:2000 standards. Our quality control is extensively documented, very comprehensive and very rigorous.”
Supplier quality was a contributing factor in the decision to allow two insertions of the Collierville job to be used to generate data on steam cure. “I have a reputation for being one of the most difficult specifiers in the country,” stated Lindsey. “Sometimes I have to convince a municipality that certain jobs are better served by a higher quality resource who may not be the lowest bidder. Nobody wins when an installer has to go back in with a second pass because physical properties or the wall thickness of the first insertion is under-spec.
“The CIPP business has become very competitive over the years, and installers have to innovate to continue to deliver value to their customers,” said Lindsey. “They are looking for ways to be more competitive. Steam-cure is attractive because it is faster, which not only helps the installer. It helps the customer by getting street traffic back to normal sooner.”
Steam-Cure & Enhanced Resin
Lindsey worked with other team members to use two Collierville insertions to learn more about steam-cure. In addition, the tubes for these insertions used an enhanced resin system that is designed to increase the flexural properties of the end-product.
The total installation cycle for steam-cure was significantly lower because the steam-cured/enhanced resin system reached it exotherm temperature in about half as much time. Exotherm is the peak temperature released during the resin’s chemical reaction.
For steam-cured insertions, the tube continued to be inverted into a PVC pipe that was placed in the manhole at the end of the insertion path. The extensions of the steam-cure insertions were cut off to create test specimens that were formed under “real world” conditions. Similar specimens were obtained from hot water-cured sections, and both sets of CIPP sections were sent to the independent testing labs of HTS Consultants Inc., Houston. Lindsey said test results showed the physical properties of steam-cured liners surpassed specifications.Ben R. Bogner, P.E., C.Eng., is a corrosion and infrastructure market development specialist for AOC, which is based in Collierville, Tenn.