Products at Work
A competitive price won the attention of a Texas engineering firm to high density polyethylene (HDPE) pipe. However, good performance won its loyalty.
Seven miles of 20*-diameter HDPE pipe–nearly 37,000 feet–was specified for the El Paso County Water Authority Reverse Osmosis Treatment Project. The pipeline carries drinking water to a reverse osmosis plant from four 250 hp vertical turbine wells that pump 1,000 gallons per minute with 400 feet of total dynamic head. It is the second-largest reverse osmosis system in the state of Texas.
The project’s engineer chose HDPE pipe when the project was being specified two years ago because it was about $5 less per foot than an alternative material. He said that even though the prices have since evened out, his first choice in pipe material is clear.
"After using HDPE pipe for this project, I would use it any time in the future for water projects," said David Goodrum, district manager for ECO Resources, a utility management company. "The wells are always turning on and shutting off, and the high pressure of emergency shutoffs is immense. Other types of pipe can’t handle that pressure. With HDPE, there’s very little water hammer. The pipe absorbs that pressure and you can’t feel it back at the plant.
What the customers of the El Paso Water Authority feel is the extra money in their pockets. The heat-fused joints in the HDPE pipe have zero leakage. No leaks mean no waste, and no waste means customers are only paying for the water that comes out of their faucets, not the water that leaks through a faulty joint. Technicians from a Texas-based company were responsible for heat-fusing all seven miles of the pipe in the field.
"Every municipality allows [budgets] for leaks," said the firm’s district manager for El Paso. "It’s not just the leaks, but the material that’s literally sucked and siphoned into the pipe through the cracks in other kinds of pipe. With HDPE, the pipe won’t come apart."
It took just three months to heat-fuse all seven miles of plastic tubing into one continuous 36,960¢-length of pipe.
"I like this pipe because the maintenance is so low," said the job superintendent Gilbert Zuniga, a contractor for Camino Contracting, Inc. "If the pieces are fused together properly, there’s virtually no maintenance whatsoever. The down time is zero, and the flexibility of the pipe is a huge benefit. When you run into something like an 8* high-pressure gas line, it can be touch-and-go when you’re trying to fit water pipes around that. The flexibility of the HDPE and the ability to perform the in-ground fusion makes the job much easier."
Before the system was installed, the solidity rate in the drinking water was about 1,600 parts per million (ppm). The Environmental Protection Agency (EPA) requires a maximum of 1,000 ppm.
The new reverse osmosis plant removes about 90 percent of the solids in the water supply. That will exceed the EPA requirements. In a reverse osmosis system, the goal is to separate the pure water from the salt and other contaminants. When the natural osmotic flow is reversed, water from the salt solution is forced through a membrane in the opposite direction by application of pressure. Throught this process, pure water can be produced by screening out the solids.