Although plastic pipe has been actively used in the natural gas industry since the late 1950s, it is still considered by some to be the “the new kid on the block.” Perhaps one of the key reasons for this reputation is the fact that the plastics industry continues to push the envelope in creating higher performance materials that inspire new compositions and installation techniques. And the main benefactors are gas utilities, exploration and production companies and ultimately their customers.
The first high-density polyethylene (HDPE) gas line was installed in Caney, KS, in 1959. At that time, HDPE truly was a new material, having just been invented in 1951. A few years later, scientists at Phillips Petroleum developed a commercially and economically manufacturing process. By licensing this new technology to other petrochemical companies, HDPE became readily available nationwide.
Even though it was in its infancy, the unique properties of this new plastic provided a pipe system that would not rust or leak – perhaps the two best reasons for its warm embrace by gas utilities around the world. In just North America alone, there are now over 3 billion feet of polyethylene pipe (PE) used in gas distribution and over 40 million PE gas services for residential and commercial applications. Most recently, the American Gas Foundation released a report entitled Gas Distribution Infrastructure: Pipeline Replacement and Upgrades, which clearly indicated that plastic pipe is the preferred material of the gas distribution pipeline industry.
While those materials used in Caney, KS, were a vast improvement over cast iron and steel pipe, the plastics industry continued its quest to produce even better solutions to meet the needs of the gas industry. During the next three generations, advancements in catalyst technologies would provide higher performing resins that improved the long-term life and capabilities in gas pipelines.
Today, two specific grades of PE resins demonstrate these characteristics. The first, PE 4710, is the ASTM material designation for the latest high-performance grade of HDPE. This grade of resin has demonstrated remarkable benefits, namely in the form of higher pressure ratings, less raw material needed, increased resistance to environmental stress crack and longer life. The other, PE 2708, is a medium-density polyethylene (MDPE) that many gas utilities prefer for their distribution systems.
While improved performance during the lifetime of the pipeline is critical, economic factors should be considered as well. As a comparison, the cost for direct burial installations of pipe 2 inches up to 6 inches range from $4/ft. to $32/ft. for PE, while similar sizes of protected steel pipe range from $12/ft. to $75/ft. It has also been shown that 12-inch PE mains are cost-effective compared to steel and as a result are considered standard products.
One doesn’t have to look far to read articles calling out the dismal shape of our country’s underground infrastructure. While not in nearly as bad shape as the water and sewer industry (which the American Society of Civil Engineers grades as “D+”), older cast-iron and steel pipelines are succumbing to corrosion and reaching the end of their service life. According to industry and government statistics, there are still more than 30,000 miles of cast-iron pipe and more than 50,000 miles of bare steel pipe moving gas in the United States. Because of the aging cast-iron and steel pipelines, soil movement and construction, the number of leaks and the potential for serious incidents will increase. The need to replace these lines is critical and urgent.
Recognizing this need, the Pipeline and Hazardous Materials Safety Administration (PHMSA) called out the need to replace deteriorating gas lines in the Pipeline Safety, Regulatory Certainty, and Job Creation Act of 2011. Most recently, PHMSA has issued a “Call to Action” to accelerate the rehabilitation, repair and replacement of high-risk pipeline infrastructure.
With the need to meet specific deadlines, the demand for plastic pipe has significantly increased. As mentioned, HDPE and MDPE pipe is the most widely used material in distribution systems. However, with the high demand for pipeline replacement, other polymers are being employed as well.
Polyamides (PA), or more commonly known as “nylons,” have been used in gas systems going back to the 1990s. PA11 and PA12 are the most common of these grades of materials used for pipe. They bring the same corrosion-resistant and leak-free characteristics as PE pipe systems with a higher hydrostatic design basis (HDB), allowing use at higher pressures and higher temperatures.
Perhaps the biggest difference between these two grades is how they are made. PA11’s monomer is derived from the oil of the castor plant, which is grown in large quantities in India, Brazil and other countries. PA12 is entirely petroleum based with the monomer synthesized starting with butadiene. Yet they are often specified for the same types of applications, sometimes interchangeably. On the horizon is pipe being made from PA6.6 with a similar focus on pressure and temperature.
With today’s attention on energy independence, plastic pipe, not surprisingly, is in high demand in the oil and gas exploration industry. Affectionately known as the “oil patch,” HDPE pipe was first used in gas gathering in 1957. Today, it is the largest market served by pressure-rated PE pipe. Chemical resistance, abrasion resistance and a fused joining system are just some of the reasons HDPE pipe is so widely accepted in this industry.
Hydrofracturing, or “fracking,” uses HDPE pipe for not only the collection and transportation of hydrocarbons, but also for the transportation and collection of water used in this process. Once again, the durability and leak-free characteristics of the system make it the number one choice when pressures allow its use.
With the great acceptance of plastic pipe in the Oil Patch, design engineers began looking for more opportunities to use it. However, many of the applications exceeded the pressure design limitations of conventional HDPE. As a result, a whole new category of plastic pipe has been developed incorporating layers of HDPE and metallic and non-metallic (glass and carbon fiber) substrates, creating a composite structure.
Ranging in size from 2-inch up to 8-inch in diameter, these pipes can handle pressures from 300 psi up to 3,000 psi and in some of the most difficult terrains across the country. As an example, a composite structured pipe operating at 1,500 psi was used to create a 3-mile water transfer line in the Marcellus formation in rural north-central Pennsylvania. Because the pipe could be put on spools, the 16,000 feet of pipe was installed in just three weeks with minimal joints.
Even though plastic resins and structures continue to be improved and created, one key property still finds exceptional demand: flexibility. It has been documented many times that gas distribution systems are more apt to survive severe ground shifts, especially from earthquakes, when they are made from fused PE pipe. But that flexibility also makes PE pipe the material of choice in the growing use of trenchless installation, including horizontal directional drilling (HDD), pipe bursting and slip lining. In a 2013 survey, HDPE pipe was the number one product used for HDD more than a 3-to-1 margin compared to steel and ductile iron.
Trenchless applications avoid the need for long, wide trenches to be dug, which is significantly more expensive, and would create a negative impact on the local citizenry by damaging existing pavement and landscaping, as well as causing traffic congestion from construction.
As just one example of employing trenchless technologies, Chicago’s Peoples Gas is on a continuing program of upgrading its system that serves some 850,000 customers. The utility uses 18-inch diameter HDPE pipe to slipline existing 20-inch, 24-inch, and 30-inch cast-iron lines. By using the smaller diameter HDPE pipe and being able to also increase the operating pressure, Peoples Gas can maintain the same flow rate while providing a new leak-free, long-life replacement system with minimal impact on the public.
For more than 60 years, the plastic pipe industry has continued to bring new and innovative materials, structures and installation techniques to the energy market. Higher performance and lower costs are the hallmarks in an ever-dynamic industry. And yet, it’s not just limited to pipe and installations.
Industry support is also growing for improved tracking and traceability. Progress in this area includes a tracking and traceability system that provides a standardized approach to marking all gas distribution system components, including barcode markings. It was developed so manufacturers could easily provide product traceability information that gas utilities can use in the implementation of their own distribution integrity management program (DIMP), a program that has been mandated by the U.S. Department of Transportation’s Pipeline and Hazardous Materials Safety Administration (PHMSA). The Plastic Pipe Institute (PPI) has agreed to operate and maintain this registry at www.ComponentID.org
Since 1951, the PPI has been engaged in the mission to make plastics the material of choice for pipe applications. Whether through research, testing, product development or industry advocacy, our members continue to search for more avenues to support the energy marketplace. More recently we have developed various software tools to assist in the design and installation of PE pipe:
• The PPI-BoreAid™ software simplifies the design process of complex calculations for trenchless applications of PE. Project and pipe details can be entered into the PPI-BoreAid tool to assess deflection, critical collapse, pull back force and allowable pullback force.
• The PPI Design and Engineering Calculator assists the design engineer in performing multiple computations relating to internal and external pressure ratings, low-pressure and high-pressure gas flow, and automates other assessments.
As one can now easily see, the plastic pipe industry has, and continues to be a force of innovation. More than a half-century of continuous development has provided gas utilities and exploration companies with state-of-the-art systems with improvements in safety and economics. If the past is any indication, the next 50 years can be summed up in one word: Exciting!
For more information, I encourage you to visit our website at www.plasticpipe.org.
Author: Tony Radoszewski is president of Irving, TX-based Plastics Pipe Institute, a North American trade association rep¬resenting all segments of the plastic pipe industry. He is a veteran of the plastics industry with nearly 35 years of experience. He spent 15 years at Phillips 66 Company/Phillips Driscopipe (now part of the Performance Pipe Division of Chevron Phillips) in various leadership positions in sales, marketing and business development. He also served as director of marketing and business development for Advanced Drainage Systems. Radoszewski earned a bach¬elor’s degree in chemistry in 1980 from St. Mary’s University in San Antonio, TX.