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.
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
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 (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 (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.
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!