Ductile iron was first used in water supply networks in 1955. It replaced cast iron pipe, which dominated water conveyance for decades. Although the switch reduced catastrophic circular breaks and corrosion found with cast iron pipe, it did not eliminate these issues, as ductile iron still corrodes and breaks.
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Many utilities have since begun opting for lighter, more durable, and noncorrosive materials like PVC and high-density polyethylene (HDPE), which were commercialized in the 1960s. PVC remains the more popular pipe, given its pre-COVID-19 abundance and relative cost advantage.
Tradition and marketing also have a lot to do with PVC’s success today. In the mid-1960s, the American Water Works Association published a set of material standards. PVC met them in 1965, and HDPE met the same criteria two years later. While PVC chased the water market, HDPE held the natural gas and oil market. Thus, PVC became the more commonly used pipe for water and HDPE for oil and natural gas.
Industries have a habit of adopting and standardizing a particular material, and manufacturers market to the industries that demand their materials. While HDPE has proven itself a superior material for water applications, the industry has been slow to adapt.
With that in mind, let’s look at the differences between ductile iron, PVC, and HDPE.
The Big Three: Ductile Iron, PVC, and HDPE
There are 55,000 municipalities across the country, that use a wide variety of piping materials to move natural gas and water. We’re covering three of the primary material options:
Ductile Iron Pipe
Ductile iron pipe (DIP) is a pressure pipe commonly used for potable water and sewage. Ductile iron is strong, but corrosion and tuberculation cause it to deteriorate over time. Worse, the remaining service life cannot be determined from the outside, and the level of tuberculation that may be present on the interior of the pipe cannot be assessed without special equipment. In other words, you might have a problem and not even know it—until the pipe fails.
Other issues with DIP include joint separation as a result of ground movement, a need for open-cut construction that can be disruptive to communities, and cost. DIP is two to four times more expensive than its competitors.
Polyvinyl Chloride
Polyvinyl chloride (PVC) is a commonly used polymer for potable water systems that can withstand significant water pressure. Some manufacturers, claim PVC pipe has a service life of more than 100 years, but there is consensus that a 100-year lifespan is greatly exaggerated. Typically PVC lasts between 25 and 50 years. The list of negatives is headlined with disruption of the supply chain for PVC, as lead times have been long throughout 2022 due to supply shortages.
PVC is rigid and brittle and therefore prone to cracking. UV exposure, cold temperatures, age, overbending, and chemical exposure can all lead to failure. In addition, fatigue caused by water surge or water hammer can also damage PVC pipe and fittings.
High-Density Polyethylene
High-density polyethylene (HDPE) pipe has quickly grown in popularity and gained approval in municipalities for its many advantages over legacy pipe material. The solid waste management, natural gas, geothermal, mining, and oil patch markets have relied on its leak-free, corrosion-resistant, and flexible benefits for years.
The combination of flexibility and leak-free joints allows for unique and cost-effective installation methods. HDPE allows for minimum surface and environmental disruptions using trenchless installation techniques. It is maintenance-free and adopters of HDPE enjoy, low water loss rates, and reduced repair costs.
HDPE is a polyethylene thermoplastic made from ethylene, a petroleum byproduct. It’s one of the most versatile types of plastic on the market and has a lifespan of 50 to 100 years when installed correctly.
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Additional benefits of HDPE include: surge tolerance, and resistance to corrosion, ultraviolet rays, and chlorine, as well as bacteriological and chemical buildup.
Join us for future blog post, where we will go into greater depth regarding the benefits of HDPE, design considerations, installation methods, and more!
Sewer systems have been around in one form or another for thousands of years. As technology advanced, pipeline materials have changed, improving durability and functionality. With all these developments over time, most utilities have to contend with multiple pipeline materials, each of which have different maintenance concerns and a different lifespan.
Early Sewer Systems
The first sewer pipes were constructed of brick and mortar in the Indus Valley in 2500 BC. Some of these systems, constructed by the Persians, Macedonians and Minoans, contained brick-lined pits similar to modern septic systems. Eventually, the Romans and Greeks built extensive, open sewer systems of brick and stone which carried effluent and trash to cesspools constructed of stone or concrete. Solids would then settle to the bottom and liquid would flow to nearby bodies of water. After the fall of the Roman Empire, Europe entered the Middle Ages and many of these sewer systems fell into disrepair as sanitation and cleanliness became less important.
Materials in the 1800s
It wasn’t until the beginning of the nineteenth century when urbanization created a larger disease issue that sanitation efforts picked up again. Sewer technology progressed rapidly over the next few decades with new pipe materials entering the market and new technologies changing the industry. Each of these new materials found popularity and success in different regions. The first waterworks in the United States was installed in Philadelphia in 1802. Many of these early systems were still built with brick and mortar. Lines had to be much larger to account for the rough interior and required more structural support. Over time, corrosive materials in the sewer also wore away mortar, leading cities to invest in other, newer materials.
One of the new pipe materials to find popular use was wooden pipe. These pipes came in two styles: stave style, made by pressing beveled boards together with steel banding, or log style, made by hollowing out the middle of a log. These types of pipes were installed across the United States, from Philadelphia to Portland, Oregon. As recently as July of 2018, crews unearthed a wooden log pipe in downtown Spokane, Washington on the Idaho border.
New Materials for a Modern Age
By the 1900s, vitrified clay was the piping material of choice for most cities. First discovered in Babylonia in 4000 BC, vitrified clay is made by firing clay pipes and throwing salt into the kiln to produce vapor. Clay pipes are very heavy and required water or rail transport, meaning many cities could only install them if they had a local supply of clay. Though popular, vitrified clay requires care during installation.
Another popular material during this time was fiber conduit, more commonly known as Orangeburg pipe, named for one of its manufacturers, Orangeburg Manufacturing Company. Fiber conduit was created by impregnating wood fibers with coal-tar pitch. This pipe material became popular for a number of uses: water transmission, sanitary sewers, electrical lines and more. It grew in popularity throughout the 1800s and the early 1900s. Its popularity declined beginning in the late 1960s as PVC entered the market. Orangeburg pipe is not currently used for new piping due to its shorter lifespan.
Cast iron was also a popular material at this time. The first cast iron pipes were installed at Versailles in 1664. In the United States, the first cast iron pipes were installed in Philadelphia in the 1810s to replace deteriorated spruce log pipes. Eventually, Philadelphia was entirely piped with cast iron due to its longevity and ability to withstand higher water pressure. Many of the sewer lines in use today are piped with cast iron. However, cast iron has a high risk of corrosion, so different coatings were developed to help slow down the corrosion process. One of the most popular coatings was cement-lined cast iron.
Improved Durability
In the 1950s, ductile iron pipe was introduced as an improvement on cast iron. It has higher strength and similar corrosion resistance, making it an attractive material for water and wastewater uses. Similar to cast iron, there were also many types of linings developed to prevent corrosion in line interiors.
Concrete pipe was also rising in popularity during this time, though it was significantly heavier and more expensive. Prestressed concrete cylinder pipe was first manufactured in 1942 and consists of a thin steel ring encased in concrete. This type of pipe material is still being installed today and is commonly used for larger pipe diameters, storm sewer lines and water mains.
Finally, plastic pipes including PVC, ABS and PEX pipe came into popular use. Although PVC was first developed in the 1860s, it didn’t take off until the 1950s and ‘60s when more precise extrusion techniques allowed for more reliable manufacturing. Today, plastic pipe is an increasingly popular pipe material, used for everything from sewer laterals and residential plumbing to gas distribution and chemical processing. It has some of the highest corrosion resistance and claims a long-projected service life, although to date it’s only been in the ground approximately 60 years—as yet well short of materials like clay, which have a demonstrated service life that can exceed 125 years.
Today, almost all of these pipe materials can be found in use somewhere in the United States, though many are reaching the end of their expected lifespans. Each material type has its advantages and disadvantages; each works better in certain applications or under certain conditions. And maintaining them—cleaning, repairing and improving—requires specialized knowledge. As investment in our national infrastructure increases, the durability of these materials will continue to remain a key consideration.
Want to learn more about sewer line maintenance? Check out our free training guide, Sewer Maintenance 101:
Brick Sewer Photo Courtesy of Les Chatfield via Flickr (CC BY 2.0). Wooden Water Pipe Photo Courtesy of Caitriana Nicholson via Flickr (CC BY-SA 2.0). Concrete Stormwater Pipe Courtesy of Aaron Volkening via Flickr (CC BY 2.0).
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