Rising to the Challenge
By Brian Sandalow, Associate Editor
Click here to see this story as it appears in Modern Casting
What comes to mind when you think of ductile iron pipe?
Maybe it’s toughness and how it can withstand the most challenging conditions and thrive. Maybe it’s the durability and how it can last generations. Or maybe it’s innovation, with new and interesting additions coming frequently to improve the value of the product.
In fact, all of those would be true.
“It is tough in any service condition,” said Maury Gaston, manager, marketing services, AMERICAN Ductile Iron Pipe (Birmingham, Alabama). “It can withstand all installation environments, rocky trenches, soft trenches, aggressive handling. While we may not recommend aggressive handling, underground utility construction is a demanding environment and ductile iron has the toughness to withstand that.”
Manufactured via centrifugal casting, ductile iron pipe was introduced to the marketplace in the 1950s as a replacement and improvement of older gray iron. Ductile iron contains a magnesium additive that makes it stronger and more flexible, which enables it to withstand even greater stresses and loads. In addition, modern ductile iron pipe is cement lined, which eliminates tuberculation, a process that might restrict the flow in older, unlined pipe.
“The older gray cast iron pipe that ductile iron replaced was first installed in the early 1800s, and thousands of miles of gray iron pipe continues to serve reliably after more than 100 years of service,” said Jeff Otterstedt, executive vice president, McWane Ductile. “Modern, cement-lined ductile iron can be expected to last even longer, even in corrosive soils when protected by polywrap. That’s a proven track record that no other material can match.”
In 1958, LaFourche Parrish (Louisiana) was the first municipality to install ductile iron pipe with a polyethylene encasement. It’s an 8-mm loose polyethylene fill that’s wrapped around the pipe.
And it’s thriving 58 years later.
“We looked at it last in 2013 after 55 years of service. We go back at that location every five years and expose a length of the pipe and peel back the polyethylene encasement, examine the pipe for corrosion, and test the fill to see what its physicals are. So far so good,” said Gregg Horn, executive vice president, Ductile Iron Pipe Research Association (DIPRA). “We’ve looked at it about half a dozen times now over the years and haven’t seen any evidence of corrosion under the wrap. The film is a good strong film that is protecting that pipeline.”
More recently, the industry has built on the polyethylene encasement with the introduction of the V-Bio polyethylene encasement for corrosion control of underground pipes. It builds on the polyethylene encasement and adds corrosion inhibition and even a biocide, coming in three layers.
The product has been in test sites for 14 years using corrosion probes to measure the corrosion rate underneath the V-Bio. So far, they’re getting readings that show no corrosion is occurring.
“We’re taking advantage of a relatively new extrusion process and we’re enhancing the film by adding an anti-microbial component and a corrosion inhibitor,” Horn said. “So it provides an active aspect to the protection that traditional polyethylene encasement provides for iron pipe. Our industry bought the patent in December 2012 and introduced it to the marketplace in 2013 and it’s been doing pretty well.”
In general, ductile iron pipe can do well in the toughest of conditions.
Many times, ductile iron pipe will be used in an underground environment that’s going to be aggressive to iron pipe. Some soils can promote corrosion, which is the single thing that can have a negative impact on the service life of ductile iron. That then is why it’s important to protect pipes from corrosion.
“Ductile iron’s a tremendously strong product and takes advantage of the strength to employ some very conservative design assumptions when you go to decide what class of pipe to use for a given installation,” Horn said. “Taking advantage of that strength, you can get a tremendous service life with proper design and installation practices, including protection in certain aggressive soils.
“We do have a model that we use as a risk-based model that evaluates the likelihood that a soil would cause corrosion and balances that against the consequences of the corrosion related problem to come up with a series of recommendations for corrosion control that make it pretty easy for a utility engineer to know what to do.”
As a whole, the industry is looking to improve the service that the product provides.
Gaston has been at AMERICAN for many years and in his time there he’s seen his company move from making ductile iron pipe in sand-lined molds with one sand line application for each pipe to a process using permanent molds and repeated castings with the same mold.
“Manufacturing and metallurgical advances like the introduction of ductile iron have been made, and restrained joints that were introduced in the 1960s are now used by virtually every pipe material. Corrosion control research that’s been performed has also led to advancements in durability,” Gaston said. “Even more recently, a zinc coating and topcoat has been made available and many utilities are adopting it and using 100-year service life planning.”
Corrosion control research has also led to advancements in durability and production.
“We’ve embraced an environmental stewardship which our industry has pursued for quite a while now. Today we’ve gone through a pretty rigorous certification with the market for transformation to sustainability and achieving a smart certification for ductile iron pipe,” Horn said. “It included the development of a life cycle analysis which we did in the early 2000s and which we’re doing again right now. And that analysis allows the companies to see which aspects of their manufacturing impacts various parts of the environment, including human health, climate and the consumption of natural resources.
“It lets them see which parts of their manufacturing process have the largest impact on those various criteria so that they can find ways to improve, which is an important thing,” Horn added. “It’s a commitment that the industry has to improving on those lines.”
And that leads into another area where the ductile iron pipe industry prides itself.
Since it’s made from recycled iron and steel products, it doesn’t have a costly environmental footprint. Life expectancy is extremely long, and that means less construction and less environmental disruption.
“Unlike cheaper pipe materials such as PVC, ductile iron pipe is 100% recyclable,” Otterstedt said. “If a utility digs up a ductile iron pipe and returns it to the (metalcaster), or any scrap dealer, it can be made into new pipe. You can’t do that with PVC. Ductile iron pipe is simply the smart, strong, sustainable choice.”
It’s also efficient and saves money.
A lesser-known fact is pipe materials and pieces have the same outside diameters so they can fit together. The standards are uniform, so they can mate with fittings and with other types of pipe, with valves and with various types of equipment. Having the same outside diameter and having different wall thicknesses (because plastic pipe is not as strong as iron pipe) means the inside diameter of iron pipe is bigger than the inside diameter of the same nominally sized plastic pipe.
That means less energy is required to pump the same volume of water or waste water through the ductile iron pipe.
“Think about it this way. Try drinking through a regular straw compared to a coffee stirrer,” Otterstedt said. “It takes a lot more energy to drink through the smaller diameter coffee stirrer. The same goes for pumping water through ductile iron pipe compared to PVC.”
Gaston echoed that.
“When you add up those energy savings, day after day, year after year, over the life of a pipeline project, the electric pumping cost savings associated with ductile iron pipe are staggering,” Gaston said. “The (reduced) greenhouse gas emissions (due to) requiring less electricity to operate a ductile iron pipeline is staggering. The financial savings available through a present worth calculation due to those lower operating costs is absolutely staggering.
“We’ve got all these energy efficiency stickers on our cars and on our appliances. We ought to put them on our pipe materials because the energy savings associated with ductile iron pipe compared to plastic pipe, high density polyethylene pipe and other types of pipe is just absolutely remarkable.”