October 18, 2014The Gulf Coast Water Authority (GCWA) and the City of League City, Texas, were faced with the need to rehabilitate 6,800 ft of a 39-in. PCCP water transmission main along a relatively narrow section of roadway.
The decision to complete the rehabilitation of this main — which provides an interconnect between the City of Houston and Galveston County — using Swagelining allowed planners to keep the same hydraulic model/capacity, as well as giving the pipe a full structural overhaul that extended the life expectancy to at least 100 years.
According to project officials, the Calder Road project also resulted in a few firsts in North America: 1) it is the largest diameter, high-pressure, full structural pressure pipeline rehabilitation project completed and 2) no other trenchless method has ever completed a project requiring a fully structural solution at an operating pressure of 125 psi.
Pretty impressive results and that is why this project was selected the 2014 Trenchless Technology Project of the Year for Rehabilitation.
“The project certainly represents the largest diameter pipe rehabilitated in North America utilizing the Swagelining technology,” says Tom Hayes, vice president of Murphy Pipeline Contractors (MPC), the contractor for this project and one of the leading contractors in North America that specializes in the Swagelining process. MPC owns the North American licensing rights from U.K.-based Swagelining Ltd.
Swagelining technology uses a high-density polyethylene (HDPE) liner with an outside diameter larger than the inside diameter of the existing pipe to be renewed. The liner is pulled through a single reduction die before entering the host pipe, temporarily reducing the liner’s diameter and allowing insertion. Once insertion is completed, the liner reverts to its original size, expanding until it is stopped by the inside diameter of the pipe and giving it a “tight fit lining” rehabilitation. Due to the tight fit, thin-walled HDPE liners and semi-structural HDPE pipe can be installed.
In the case of the 39-in. PCCP, the existing pipe required a fully structural rehabilitation. The use of Swagelining allowed MPC to install a fully structural HDPE PE4710 DR 17 pipe with a working pressure rating of 125 psi.
What Was Needed
Gulf Coast Water Authority (GCWA) provides water for industry, agriculture and municipalities in Brazoria, Fort Bend, and Galveston counties. This includes more than 185,000 customers in Galveston County alone. Located southeast of Houston, the City of League City is a city on the upswing, with its population nearly doubling since 2000 to more than 83,500, according 2010 census figures.
The 39-in. PCCP water transmission main on Calder Road — owned by GCWA and operated by the City of League City — feeds a water plant supplying water to the western quadrant of the City. The transmission main, originally constructed in 1971 to supply surface water to the City of Galveston, interconnects between GCWA’s Thomas S. Mackey Water Treatment Plant and the City of Houston’s Southeast Water Treatment Plant. The 39-in. main had been experiencing a variety of issues in recent years, including breaks and leaking joints and was in serious need of rehabilitation.
Given the age of the 39-in. PCCP and the operating history of this water transmission main, GCWA and the City knew they needed a fully structural solution to the problem. The main’s capacity also needed to remain the same or be increased to allow for future expanded use.
“Water is becoming scarce [in this area of the country]. The drought in 2011 really opened a lot of people’s eyes,” says James Vanderwater, district engineer with Gulf Coast Water Authority. “We have found that the Brazos River may not be as reliable as we thought it was for a raw water source. This water line provides a critical interconnect between the City of Houston and Galveston County and we believe it was important to maintain as much capacity as possible. The City of League City told us what their future plans were for the water line and there wouldn’t be much left for an interconnect if we sliplined it.”
He further notes that League City needed the capacity at the Calder Road water plant to remain, at minimum, at 25 mgd and any of the proposed options would have to meet that requirement. However, using Swagelining, flow capacity is closer to 38 mgd, leaving 12 to 13 mgd for future added capacity needs, Vanderwater says.
Sounds simple enough but other issues had to be factored into whatever means GCWA and the City elected to use for the project, which also included replacement of twin intake pipes off the 39-in. main, increasing their size from 10 in. to 24 in. in diameter. A bigger concern had nothing to do with the pipes but the location of the work.
In addition to the rehab work to the main, the 6,800-ft section on Calder Road where the work would take place was scheduled for surface improvements and widening; the rehabilitation project needed to be done before that work began. “It was such a small footprint to work in. There was no space to work. [Calder Road] is a two-lane side road that is a feeder road for the community. The road was 22 ft wide and we had an easement area where the pipe laid that was 10 ft wide,” MPC president Andy Mayer explains. “We were only permitted to shut down half of the road.”
The tight space made it challenging to where and how MPC would stage the pipe, weld the pipe, where to dig the insertion pits and where to pull the pipe into place to minimize the disruption to the community.
During the design phase, several trenchless methods were considered and the final bids came down to sliplining vs. a compressive tight-fit HDPE liner installed using Swagelining — both methods that would have solved the rehabilitation issue. But Swagelining proved to be the method that GCWA believed would provide the best overall solution.
“The design criteria required a fully structural rehabilitation solution capable of 125 psi operating pressure,” says Mayer, adding that “Installing the tight compressive fit HDPE liner by Swagelining increased the final ID of the pipe 4.45 in. over the base bid with sliplining.”
MPC would install 39.37-in. DR 17 4710 HDPE pipe (supplied by ISCO) using the Swagelining process. The 2.32-in. wall thickness pipe was pulled through a single reduction die and installed in four installations, ranging from 1,250 to 2,100 ft in length. Each installation also required the liner to be pulled through multiple bends. The long pull lengths aided crews as they allowed for long-fused sections of the HDPE to be installed and eliminating the potential for future leaks. For each pull, 50-ft lengths of pipe were butt-fused using a rolling McElroy 1648 machine. MPC used a HammerHead HB175 static pulling rig for two of the installations and a TT Technologies Grundoburst 1250G pulling rig for the other two. A HammerHead winch was used to pull the pigs and scraping devices to clean the pipe prior to the rehab work.
Hayes notes that the use of the DR 17 HDPE represents a pipe that is not dependent on the host pipe for any structural enhancement. The same pipe was used in making all the end connections installed via direct bury. Any other trenchless process would have needed to transition to either PVC or ductile iron pipe to make the connections and require special end connectors to seal the annulus, he explains.
“The end connections were installed by fusing the lined HDPE pipe directly to the 1,000-mm DR 17 HDPE using a manufactured flange adapter,” Hayes says. “This completely eliminates the need for special end connectors, as well as eliminating mechanical joints that are sources for potential leaks.”
The north end of the project was extended by about 300 ft to an existing 36-in. diameter butterfly valve; the south end required a flanged reducer, butterfly valve and blow off. Thrust restraints were needed at both ends of the project to protect the existing pipe from potentially blowing out from the pressure during construction. During construction, the existing water plant was kept connected to the City of Houston water supply or the GCWA water supply through a 12-in. diameter bypass set up aboveground.
The MPC crews worked closely with the community to minimize the disruption during construction, keeping residents informed each step of the way. “Most people when they are kept informed are understanding,” Mayer says, noting the City “did a great job prior to the project of informing its residents.”
Swagelining is an emerging trenchless technology in North America, already having had success in Europe. The technology lends itself to medium- to large-diameter pressurized mains, both water and sewer force mains.
In an article for Trenchless Technology (November 2012), MPC vice president and educational director Todd Grafenauer wrote about Swagelining and its potential for the trenchless market: Just as the industry has seen various trenchless technologies come to the forefront to rehab smaller diameter pipelines, Swagelining technology is emerging as a leading candidate to renew and replace mid- to large-diameter water transmission and sewer force mains. Developed more than 30 years ago by British Gas and United Utilities (then known as North West Water) to address the problem of failing pipeline systems that were buried and entangled with other utilities throughout urban and rural areas, the principle of Swagelining was developed. It is considered by the pipeline industry as the benchmark in polymer lining technology for its ability to deliver cost-effective lining solutions in every environment. With an extensive list of work across the globe, the technology has been proven in many extreme projects spanning three decades onshore and subsea. Projects have been completed for water, sewer force main, mining, hydrocarbons, chemicals, bulk products and gas distribution.
“The value that client is receiving with Swagelining over [in this case] sliplining is that the client is maximizing their final ID and that is where Swagelining is starting to see a great value to some of these pipeline projects,” Grafenauer says. “The owner has the ability specify a thin walled liner, a semi-structural liner or in this instance a fully structural solution.”
The Calder Road project is an important project for the Swagelining technology, showing just what it can do for municipalities. “We feel we found a solution for aging large diameter infrastructure and each time we successfully deliver a project is testament to the technology and the product we are using,” Mayer says.
Sharon M. Bueno is managing editor for Trenchless Technology.