January 2020 Vol. 75 No. 1
Features
Two Cities Add HDPE for Reliable Water Infrastructure
The best predictor of future behavior is past behavior. This is a dependable indicator in psychology, but two cities in Minnesota found this to be especially true when applied to pipe performance.
After successful outcomes with medium-density polyethylene pipe used for decades in their city-owned and operated natural gas systems, both Duluth and Austin standardized HDPE for all of their water mains. In the process, they have found that many of the same qualities that made it great for gas – leak-free joints, easy installation and long life – have made it an environmentally sound choice for water mains, as well.
Duluth, a port city of nearly 86,000, first tried HDPE on the water main side in 2002. Eric Shaffer, chief engineer for utilities at Duluth, was a consultant at the time and was hired to design what would be his first big job for an 8-inch HDPE water main.
“At that time, engineering and the construction crew came together and said, ‘now’s the time to make the switch to PE, it’s worked so well for gas,’” Shaffer said.
Today, Duluth’s water loss rate continues to decline as it replaces more and more of its old pipeline infrastructure with HDPE. Properly fused HDPE joints are largely leak-proof and Duluth has not had a single butt fusion failure since starting to use it. Water losses were 16.5 percent in 2012 and much higher before that. By 2018, water loss had fallen to 11 percent. This dramatic reduction allowed the city to transition to a smaller supply pump, creating further savings in pumping costs.
“We now use HDPE for everything and feel that it is the best product available and the most cost-effective, considering the installation and the long-term maintenance,” Shaffer added.
Austin, a city of 25,000 residents, has been using HDPE for its water mains for the past 21 years, with HDPE representing about 31 percent of the water pipe in the ground. Todd Jorgenson, gas and water operations director for Austin Utilities, said the number of water line breaks is about half of what they were experiencing 20 years ago.
“Our crews do both water and gas, so the transition to water was relatively easy, other than having to buy larger (pipe fusion) equipment,” Jorgenson said. “We’re certainly happy with the results. Our crews – I don’t know if they’d want to change. We have a younger staff now and that’s all they know.”
HDPE replacement cycles
In Duluth, there is still more cast-iron water pipe in the ground in sizes up to 48 inches, followed by ductile iron, HDPE and steel. The HDPE switch has been a gradual process, beginning with larger footage water projects using 8-inch pipe, and on specialty projects using pipe bursting and horizontal directional drilling (HDD) technology.
Currently, Duluth replaces about two miles of water distribution pipeline a year. Within the next five years, it’s looking to replace four miles of pipeline a year – setting an ideal 100-year cycle.
Austin’s replaces two to three miles of water lines every year – for an impressive 46- to 69-year water cycle. Currently, about 31 percent of the water mains are HDPE. And on a positive note for public health, when old service lines to the residence are lead pipe, they’re replaced with 1-inch HDPE service lines.
On the gas side, Austin replaces one to two miles a year with HDPE. Currently there is about a 50/50 mix of steel versus HDPE for gas pipe.
“If we have a new project, it’s always going to be HDPE,” Jorgenson said.
There’s only been one butt fusion failure on gas lines, which was attributed to operator error, and none on the water side.
“I think our guys do a good job; they’re the ones who are going to have to fix it if it fails,” Jorgenson said.
Both Shaffer and Jorgenson serve on the Municipal Advisory Board of the Plastics Pipe Institute (PPI) and share their experiences with other colleagues in the utility industry who are unfamiliar with HDPE and have not developed a comfort level with it yet.
“Once they use it, they’ll see the benefits, especially when you see the HDD option,” Jorgenson said. “It’s just a natural progression.”
Neighborhood infrastructure
For both cities, there is a flurry of HDPE activity during the summer, since Minnesota’s construction window only lasts from April to October. This past July, Austin’s fusion crews were replacing a 1940s cast iron main with 6-inch HDPE. They make it a practice to time their HDPE installations with the street department’s replacement schedule, so that they’re installing pipe while the street is already under construction.
“In most cases, that’s what we look at, so we don’t have to pay to tear up the street and put it back again,” Jorgenson said.
Austin’s 14 crew members form a well-oiled team that operates many types of McElroy fusion equipment. They own manual machines for butt and saddle fusion, as well as rolling and self-contained, self–propelled hydraulic tracked fusion machines for larger-diameter pipe.
Most of the pipe in Duluth’s older Lakeside neighborhood is post World War II era cast iron pipe. It’s caused a lot of problems, because of Duluth’s highly corrosive, clay soil, and the city was spending a lot of time and money cutting open the street and repairing water line breaks.
The city discovered that it’s better and costs less to replace the pipe with HDPE, which does not corrode, and install it using pipe bursting technology instead of open cut. HDPE is ideal for trenchless applications because of its flexibility and strength. Fused joints are as strong or stronger than the pipe itself, which makes it able to hold up to pulling forces.
Duluth’s fusion crew was in full force with this winning combination last summer, bursting a 6-inch cast iron main with 12-inch HDPE using TT Technologies static pipe bursting equipment. Altogether, the crew replaced some 2,600 feet of aged-out cast iron pipe with modern HDPE.
Scott Hegg, engineering technician in Duluth, said that everyone is moving towards trenchless to rehabilitate municipal water infrastructures. In fact, other surrounding towns are in varying stages of following suit, including Superior and Two Harbors.
Duluth also uses McElroy fusion equipment. The TracStar machine allows crews to maneuver down the street on a self-contained track system. They can even use it to perform butt fusions on transition connections by removing the carriage from the vehicle and lowering it directly in the ditch. They simply disconnect the hydraulic hoses and pull a pin. The ability to do a butt fusion reduces costs for electrofusion fittings.
“We like to put the carriage in the ditch,” said Hegg. “We do it every time.”
Downtown revitalization
Over time, Duluth started using HDPE for the underground infrastructure in all its capital projects. The Superior Street “Kick Up the Bricks” reconstruction project underway in the heart of downtown Duluth is probably one of the most spectacular examples.
The three-year, three-phase project is poised to transform one of the city’s oldest commercial streets overlooking the shore of Lake Superior.
As Mayor Emily Larson said at the groundbreaking in 2018, “It’s going to incorporate the entrepreneurial spirit of our downtown, while also honoring the long-term investment of our downtown community that has been here for decades.”
The project calls for replacement of an 1880s 16-inch cast iron water main that lived in the day of mule-drawn cars on rails. Unsurprisingly, this line has suffered multiple breaks in recent years and the city is looking forward to a reliable, modern system. The new main will be 20-inch HDPE pipe with branch mains along perpendicular avenues in 8-, 12- and 20-inch pipe sizes. It’s a total of 11 city blocks, or 5,237 feet, of new HDPE.
It also includes converting an 85-year-old steam heat system to a more energy-efficient, closed-loop hot water system that allows water to circulate to buildings that need it before returning to a plant where the same water is reheated. The new system will reduce water and energy use, and costs.
In efforts to help local businesses during construction, crews kept the sidewalks and pedestrian crossways open during construction, built a temporary water line and offered $1 parking.
For Northland Constructors, the available space for the installation of the water main is severely restricted by other utilities, including sanitary sewer, stormwater, natural gas, central hot water and steam, electric, and numerous telecommunications facilities.
In an intricate design by the LHB/SRF Consulting Group, the pipe weaves through, over and under all these facilities for the entire 11-block stretch.
“The downtown has multi-story buildings constructed right to the edge of the right-of-way. In addition, the sidewalks needed to remain open during construction to access local businesses,” Shaffer said.
It was helpful that workers didn’t have to haul around extra power equipment for the fusion machine when installing the water main. The McElroy TracStar 630 Series 2 is self-contained with an on-board generator to power the heater that is used to melt the pipe ends – a key part of the fusion process for each stick of pipe on the project.
Summer 2020 will be the final construction phase for this rebranding of Duluth’s downtown. City leaders believe the reconstructed street and all its amenities will serve as a catalyst for new growth and development, while also preserving the lifeblood of their downtown core. Their efforts demonstrate, once again, that no matter where you live – what’s underground matters. •
FOR MORE INFO:
McElroy Manufacturing, (918) 836-8611, mcelroy.com
TT Technologies, (800) 533-2078, tttechnologies.com
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