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The exact cause of the natural gas explosion that killed eight people, injured at least 50, and displaced 100 others when it leveled two buildings in East Harlem in March hasn’t been determined, but it is known the block was serviced by a leaking 127-year-old cast iron main.
A considerable amount of degradation and some corrosion, probably from repair parts for the 1880s-era system, was visible as crews installed a new section of polyethylene pipe under the street in New York City.
PE is the plastic replacement material of choice for modernizing the natural gas distribution system — so much so some are concerned about resin and pipe shortages. However, a spokesman for Performance Pipe expects the plastics industry to keep up with demand.
The number of fatalities from the Harlem incident, sadly, equals the total for 2013, according to statistics kept by the Pipeline & Hazardous Materials Safety Administration (PHMSA), which is part of the U.S. Department of Transportation.
Also sad, the toll keeps climbing.
“Based on my own cases of gas explosions that I am investigating, we have at least 12 deaths half way through the year,” Mark McDonald, owner of NatGas Consulting in Boston said in a telephone interview. “The number of explosions is on the rise in certain parts of the country.”
A 2.1 million-mile system of distribution and service pipelines deliver huge volumes of natural gas to U.S. customers. PMHSA says about 97 percent of the underground network is made up of plastic and steel. The Harlem tragedy renewed public and political outcry to replace the rest — some 30,000 miles of cast and wrought iron pipes mostly in parts of the country with big populations and harsh winters.
“We’re absolutely noticing a new sense of urgency to replace this infrastructure,” said Randy Knapp, engineering director of the energy piping systems division of the Plastics Pipe Institute, which is a 140-member trade association based in Dallas.
About 83 percent of the cast iron pipes lie in 10 states under large cities like New York City, Boston, Philadelphia and Washington, D.C. These parts of the distribution system are susceptible to cracks and leaks due to freeze-thaw cycles, digging, changes in ground water levels and the iron degrading into softer elements.
While some experts like McDonald say coated steel with cathodic protection that fights corrosion would make a strong, long-lasting pipe system, he acknowledges it would be very expensive to install and need costly annual maintenance.
“You don’t have that with plastic,” he said. “Honestly, for the [utility] companies plastic is the best material. It’s easy to install, it’s lightweight and it’s pliable. Clearly that’s what is being put in the ground today.”
The number of miles of iron distribution mains, which supply one or more service lines to homes and businesses, decreased by 17 percent between 2004 and 2013 in the 10 states and by nearly 24 percent nationwide, PHMSA says. The number of iron service lines decreased 73 percent in the same period.
“Right now at least 95 percent of the newly installed pipe in the distribution system is plastic and 99 percent of that is polyethylene pipe,” Knapp said in a telephone interview. “The other 1 percent is a polyamide material, PA 11. There’s not really much else to speak of.”
The use of plastic pipe goes back to the 1950s when PVC was installed but later proved brittle and susceptible to cracking. Demand for next-generation plastics, like PE pipe, started rising in 2009 and really picked up in 2011. That’s when the federal government required natural gas utility operators to have a distribution integrity management plan (DIMP) in place to address the highest risk segments of their systems.
“Since then it has really accelerated,” Knapp said. “There’s still roughly 30,000 miles of cast iron in the ground in distribution, but 10 years ago there were 40,000 miles so it is being replaced over time.”
Step on the gas
Everyone from utility operators to resin producers to politicians is feeling the pressure to replace aging natural gas infrastructure.
New reactors are coming online to boost PE capacity and meet resin demand for gas distribution pipes as well those used for oil and gas gathering.
“Over the past three years just for gas distribution, the market has grown about 35 percent,” Knapp said. “Of course, there are new installations but right now the growth is being driven by replacement efforts. We’re back up, I think, to historically high levels.”
McDonald said he and others have concerns about a PE shortage. However, the industry has kept up so far.
“There have been times where it has been close but the resin manufacturers have recognized this,” Knapp said. “As far as their capacity plans, I know they have some big things coming.”
McDonald said he hopes so.
“Everybody is going to be demanding this material and manufacturers may have to ramp it up,” he said. “Right now it’s not critical but every state is jumping on the bandwagon and as we replace thousands of miles of main across the country it’s going to be with that polyethylene material.”
If PE pipe demand ever does outpace extrusion capability, it shouldn’t be for long, according to Lawyer C. Jolley, general manager of Plano, Texas-based Performance Pipe, which is a division of Chevron Philips Chemical Co.
With estimated sales of $540 million, Performance Pipe is the 7th-ranked PPT extruder in North America. The company makes medium- and high-density density PE pipes for not only natural gas but water, wastewater, energy, mining, landfill, geothermal and trenchless projects.
“Gas distribution standards and customer specifications include certain requirements that are not common to other polyethylene pipe uses, such as water and sewer, and as such, there may be short-term availability challenges, but overall the extrusion capacity is thought to be adequate,” Jolley said in an email.
All pipe materials have pros and cons. Plastic costs less than steel. That’s a major benefit for utility owners and their rate payers, who eventually foot the bill. Plastic also is easier to handle and install. Plastics pipe can be fused by heat for leak-free joints. Plastic doesn’t corrode and it’s more flexible than metal so it can handle freeze-thaw cycles better.
However, plastic is more susceptible to damage from digging, static electricity and it requires the use of tracer wire to locate during excavations. Bar codes are gaining traction.
“As operators develop their systems they have the possibility of scanning the products in, and that goes into the mapping system many of them have,” Knapp said. “They can take that information and know exactly what product is where in their system.”
Still, McDonald foresees problems from third-party persons working near plastic pipes carrying gas — be it a contractor installing a residential sprinkler system or fence or another utility working on nearby water or sewer infrastructure.
“Third-party damage is the No. 1 cause by far of [explosion] incidents across the country,” he said. “It’s someone digging with a bore machine or even [a] shovel. Plastic pipe is the weakest. You can get away with a backhoe touching it but plastic gives way very quickly. With the increase in plastic and without regulators stepping up third-party protection programs, that’s the concern in my opinion.”
Looking further ahead, Bob Ackley, a natural gas consultant who is president of Gas Safety USA, also in Massachusetts, said in a telephone interview that to him the longevity of plastic pipe also is an issue. He isn’t sure what pipe material is best.
“They all have their problems,” Ackley said. “What’s the life expectancy of plastic and will it hold up? What’s the life expectancy of steel and at what cost? I don’t have those answers. The plastics industry is going to say plastic is the best thing since sliced bread and in many ways it is.
“It’s easy to move around. It’s basically a petroleum product and we have plenty of that. There aren’t many leaks with it. It’s performing very well right now. What will it do in 75 years? Are we going to be ripping out this entire system and putting in a new system because the plastic disintegrated in some fashion?”
Knapp said he can say that there is PE pipe in the system that has been performing without problem for 60-plus years.
“PE has a proven track record in natural gas distribution dating back to the 1950s and the newer PE materials are a step-change improvement over the proven vintage PE in service,” he said.
Industry experts from around the world will talk about some of the issues and recent developments when about 500 delegates from 35 countries gather for the XVII Plastics Pipes Conference and Exhibition in Chicago in Sept. 22-24.
One of the first of the 130 sessions is about the environmental footprint of plastic pipe systems in the built environment. Other speakers will address topics, such as the service life predictions for HDPE pipes joined by the butt-fusion process, advanced damage modeling for PE materials, ultrasonic inspections of PE pipelines and fittings, and an evaluation of aged medium density PE.