Large-Diameter Plastic Pipe Mains Are Helping Gas Distribution

Ever since Union Gas in Caney, KS successfully inserted a 4-inch polyethylene pipeline into a corroded 6-inch steel pipeline in 1959, polyethylene pipes have steadily become the material of choice for the North American gas distribution market.

Polyethylene alone represents more than 39 million services and 3 billion feet of the pipes in service (1), and more than 97% of all new gas distribution piping installed each year.

Throughout the 50 years of service, polyethylene pipe resins and pipes have improved in both toughness and durability from the original pipelines that have served our industry well.

Figure 1.

Despite the success of polyethylene pipe in the gas distribution industry, only 10% (by length) of new polyethylene gas distribution mains are larger in diameter than six inches IPS (Figure 1). This occurs even though polyethylene pipe is generally found to be less expensive to install than protected steel mains as reported in Pipeline & Gas Journal’s 43rd Annual Pipe Report based on a survey of utilities (Table 1).

Several large utility companies today are using or evaluating polyethylene pipes up through 12-inch diameter due to both the performance of polyethylene pipe and the cost savings through operations and installation. Twelve-inch diameter polyethylene pipes are now considered standard products for both trenchless and open-cut installations. Pipelines larger than 12-inch have also been installed and are operating successfully. One of the earliest installations larger than 12-inch diameter occurred in 1989 with a 20-inch diameter pipe sliplined into existing cast iron mains in Colorado.(2)

Table 1. Source: Tubb, Rita, “43rd Annual Pipe Report -- Gas Demand, Maintenance Projected to Drive Distribution Spending,” Pipeline & Gas Journal, Dec. 2008.

With lower installation costs and a proven long-term service life, the question remains as to why the use of larger diameter polyethylene pipe mains has lagged the use of larger diameter pipelines in other industries such as water, wastewater, mining, firewater and many other industrial applications where polyethylene pipes are routinely installed up through 65-inch diameter.

While the confidence in polyethylene pipe is high, there can be a perception of logistical and operational obstacles to integrating large-diameter polyethylene mains into gas distribution. Two case studies are offered as evidence of the suitability and ease of installation of large-diameter polyethylene pipes for gas distribution.

Chicago, IL (see image, "18-inch pipe installation in Chicago, IL"). With a customer base of 830,000, Peoples Gas, a subsidiary of Integrys Energy Group, serves the city of Chicago. The utility uses polyethylene pipe extensively because of the pipe’s corrosion resistance, cost effectiveness and ease of installation. For Peoples Gas, the driving force to move to larger diameters was the need for a cost-effective rehabilitation of older cast-iron pipelines.