Question – What is the difference between Ductile Iron (DI) and Polyvinyl Chloride (PVC)?
Answer – Many things, but some groups may attempt to “muddy the waters” with inaccurate information regarding the two materials.
Goto MIDAS to know more.
With the information that follows, we will take a closer look at what really separates Ductile iron pipe (DI pipe) from PVC pipe and why it matters.
Click the red play button in the image below to view a helpful video on the advantages of DI over PVC.
Ductile iron pipe is a flexible conduit - Ductile means flexible! Because DI pipe is flexible, this means it is less likely to shear under stress from normal soil pressure or ground shifts that occur throughout the life cycle of your water system.
Ductile iron is primarily made from recycled iron and steel scrap. DI pipe is recyclable and has no end of life.
PVC is made from chlorine (derived from salt) and carbon (predominantly derived from oil and gas via ethylene). PVC pipe is weak or fragile when compared to the strength of DI pipe. The recycled content of PVC is nearly zero and PVC can only be down-cycled. In addition, PVC is derived from vinyl chloride monomer which is a Group A Human Carcinogen.
It is made rigid by the addition of a stabilizer, and at one time, the PVC industry used lead as a stabilizer. Today, PVC manufacturers use organotins that may pose health risks, but some foreign manufacturers continue to use lead.
A recent water pipe project at a major university involved installing dual 36-inch DI pipelines underneath a critical building on campus. The lines were installed to transport water to a chiller system to cool other buildings.
The piping material selected for this project was Ductile iron because of its ability to withstand ground shift and heavy pressures from the structure that rests above it. PVC, being weak in nature, tends to burst into small pieces due to heavy pressures versus stronger materials such as DI that will not obliterate.
PVC failures also have a history of being catastrophic. That is, not just a loss of some water or water pressure but a TOTAL LOSS of water. This instability is a severe issue for seismic prone areas. Not only is there a threat of damage from earthquakes, but also vulnerability to destruction from fires that typically follow the earthquakes. If there’s no water, there’s no fire protection.
PVC pipe can also be adversely affected in areas prone to wildfires. For example, the City of Santa Rosa, California estimates the repair of the contaminated Fountain Grove water system could take up to two years. Test results conducted on PVC pipelines indicated they absorbed benzene and other chemicals, resulting in an advisory to residents to not drink or bathe in the water. Replacement costs are estimated at more than $43 million dollars.
Permeation
DI pipe is impermeable and protects the water supply from toxic infiltration. The C909-16 Molecularly Oriented Polyvinyl Chloride Standard states that polyvinyl chloride may be subject to permeation by low molecular weight organic solvents or petroleum products. Why take a chance with a permeable material?
Would you trust plastic on a bridge? Didn't think so. DI pipe is an excellent choice for high-profile projects such as bridge installations. DI pipe possesses expansion and contraction capabilities required for such constructions. There is no trench support on a bridge to handle PVC pipe versus DI pipe, which does not require trench support. There are many above-ground installations on bridges and piers where DI pipe excels.
Penstocks are installations involving the redirection of streams down a mountain to a power plant. These lines are often subject to extremely high internal pressures due to the elevation changes and head pressure. The physical properties of DI pipe shine again versus the weaker PVC pipe for high-profile installations.
Fire hydrants give us a sense of security, knowing brave firefighters have the equipment available to protect us. Have you ever seen a fire hydrant made of PVC? I didn't think so.
Fire hydrants are made of Ductile iron. The hydrant standpipe is made of Ductile iron as well. There are times when a section of pipe between the DI is installed with PVC with the presumption of “saving money.” However, PVC is typically not connected directly to the hydrant section due to potential thrust forces in that area.
DI pipe is non-combustible and can withstand the stress caused by fires. In an emergency, it can be counted on to provide a safe and reliable supply of water for firefighting.
On the other hand, PVC pipe is combustible. Polyvinyl Chloride, of all the plastic polymers, has been implicated primarily in causing the most severe problem in firefighting today because PVC releases hydrogen chloride gas when as it melts in a fire. Many plastics produce large volumes of pulmonary irritant gases when burned. The firefighter is at fatal risk if he does not know that plastic covered cable is involved in a fire. (U.S. EPA)
I wish I had a nickel for every time a Municipal Operator has mentioned how many PVC leaks must be repaired the same month the hydrants are exercised. Just a coincidence? No, it’s not.
Municipal Operators are trained to slowly open and close valves on the hydrants to reduce the potential for a surge. Firefighters – on the other hand – are clearly focused on THE FIRE. What are the odds that firefighters are going to carefully and gently open or close the valve on a fire hose during the fire? The same surges are present when opening or closing the hydrant valve and are detrimental to products that cannot handle a surge.
The maximum allowable surge pressure for PVC is based on an operating temperature of 73 degrees Fahrenheit. We all know waterlines will not always operate at 73 degrees Fahrenheit. The PVC material is more susceptible to surge as temperature varies. Allowance is also based on a minor velocity change of 1.0 feet/second. PVC also has a "Time to Failure Rate." That's correct, the clock is ticking as soon as PVC is placed into service. See our down-loadable comparison sheet for more details on this.
Ductile iron pipelines are the only material to be included in the International Seismic Design Standards. DI pipe, being a flexible conduit with high tensile strength, provides a product with the ability to flex during seismic activity versus brittle materials that are subject to shear during the same seismic event.
Expansion joints may also be installed to provide expansion and contraction of axial movements. Restraint systems available with DI pipe provide a system that is independently strong and does not rely on ground surfaces for stability.
Another potential installation in areas susceptible to ground shifts is the Horizontal Directional Drilling (HDD) method. This process involves boring a path underground and installing DI pipe below an area that has been reclaimed or is subject to slipping.
For an efficient and easy way to check horizontal drilling calculations, download the McWane Pocket Engineer. We developed this handy app to allow engineers and contractors to do their job by quickly providing critical calculations in the field that would otherwise take valuable time to compute. It's FREE and designed to work on any mobile device.
Water systems achieve maximum flow by using Ductile iron pipe. The strength of DI pipe provides an opportunity for larger Inside Diameters (ID) that result in additional flow. Because it is a weaker material, a 30-inch PVC pipe is needed to match the same ID as a 24-inch DI pipe. Therefore, additional costs must be included for a larger trench and the up-sizing of valves and fittings.
The C Factor is a value used to indicate the smoothness of the interior of a pipe. The PVC industry contends that the C Factor is an issue for DI pipe. However, that is simply not the case with modern, cement-mortar lined DI pipe. Laminar Flow is the real key to flow, not the C factor. Essentially, Laminar Flow is when the fluid flows through the middle of the pipe, reducing the significance of the C Factor as a contributing factor.
For more information, please visit Di Pipe Manufacturer.
The Type I or Type II trench is used for Ductile iron pipe installation versus a Type IV or V trench required for PVC pipe. Type IV or V trench is required for PVC pipe due to the compaction that must be achieved to support the weaker material. Compacting the soil takes extra time and additional equipment.
The soil must be compacted to 80 to 90 percent of initial soil density for a Type IV or V trench. It is very challenging to compact to 90 percent with optimal conditions. The same size trench must be excavated for an 8-inch pipe regardless of the pipe materials used.
Check out this helpful blog by my colleague Gary Gula, McWane Ductile Sales Representative, that discusses the various trench types for DI pipeline installation.
Ductile iron pipe reduces installation costs due to the ability to direct tap. Tapping saddles or sleeves are required to tap PVC, which adds more costs. A popular event at water industry conventions is the tapping contest. Operators race against the clock and compete to determine who has the best crew. It is an exciting event, and operators are proud to be victors.
What kind of pipe do you think is used for these tapping contests? That's right: DI pipe. To see this contest in action, hop on over to our ACE’18 Pipe Tapping Contest post where you can watch the AWWA’s teams compete for the fastest time.
Jerry Regula, "JR" is a product engineer with McWane Ductile. Jerry’s responsibility is to provide technical support for water professionals at all levels including engineers, private water companies, contractors, municipalities, and water districts. JR has been with McWane Ductile for more than 30 years, starting on the ground floor. Jerry has been involved in nearly all facets of the foundry, providing him with extensive experience in manufacturing, installation, and design of ductile iron water products. JR is a NACE Certified Corrosion Technician, Envision Specialist, and member of the American Society of Civil Engineers. He enjoys spending time with his church where he is a speaker and treasurer, as well as spending time with his wife Susan and their two daughters, Katelyn and Shannon on their farm in Ohio. “Many people do not realize how their water gets to them or how blessed we are to have clean drinking water,” says Regula. “I am honored as a water professional to do my part in ‘Building Iron Strong Utilities for Generations.’" Jerry’s favorite quote: "I can do all things through Christ who strengthens me.” ://www.linkedin.com/in/jerry-regula-6a87b/
Water and wastewater professionals have developed methodologies and testing requirements that are outlined in AWWA/ANSI standards for DI pipe regarding its manufacture, required capability, testing, design, and ultimate use. Additionally, the American facilities that produce DI pipe must comply with standards such as those provided by the U.S. Environmental Protection Agency. All these factors can be found only with domestically produced DI pipe. This article details key attributes found only with installing domestically manufactured DI pipe.
Additionally, mill certs are used to track each pipe through the manufacturing process and certify that it meets or exceeds all required quality standards. This rigorous quality assurance has allowed DI pipe to serve many communities across our country for decades. Learn more about this by viewing another Iron Strong vlog, "What Are Mill Certs and Why Are They Needed?" by my colleague Ken Rickvalsky.
Conversely, DI pipe manufactured in other countries does not guarantee material quality with these standards, as factories are regulated by other governments that may not have the same quality measures in place, causing ambiguity regarding material quality and production. The DI pipe industry encourages clients to tour manufacturing facilities to see quality control and testing measures firsthand.
Transporting non-domestic DI pipe across thousands of miles, likely in a saltwater environment, can be detrimental to pipe. In addition to corrosion, which can cause many application problems, high salt content in Portland cement with relatively hard water could cause degradation and failure of cement linings.
During the design, construction, testing, and operation of a pipeline project, having access to professionals to provide expertise is critical. McWane Ductile is a partner that provides:
Our team members have varied and lengthy backgrounds in utility operation, consulting services, plant operations, and field services. This personal service is not readily available with non-domestic entities. Having support services when and where pipelines are being installed is vital to successful pipeline installation.
In addition, domestic DI pipe manufacturers have testing facilities to evaluate quality aspects of the product, which are also frequently used to conduct forensic exams of material. Choosing a domestic manufacturer provides an efficient and economic resource with a transparent operation, which is not the case with facilities located outside our country. To learn more about the research and testing performed on domestically manufactured DI pipe, see this informative Iron Strong vlog, by my colleague, Jerry Regula.
Domestic DI pipe is made by recycling steel scrap, preventing several thousand tons of scrap per week from being dumped in landfills and diverting one million tons of waste from landfills each year. Foreign DI pipe is most likely produced in a blast furnace operation from iron ore, which requires the mining, transportation, extraction, and processing of virgin minerals at a significantly greater cost to the environment. For more information on the recycled content of DI pipe, see this Iron Strong Blog by my colleague, Stuart Liddell.
All American DI pipe manufacturing facilities comply with stringent EPA and Occupational Safety and Health Administration (OSHA) standards, which protect both the environment and worker safety. Foreign DI pipe manufacturers do not have these same standards. Studies have shown that domestic DI pipe producers are more energy-efficient, and produce significantly less air pollution, carbon emissions, and greenhouse gases than foreign manufacturers. In addition, local, domestic production further reduces carbon emissions by eliminating the need to transport the pipe over thousands of miles of ocean.
Domestic DI pipe manufacturers employ thousands of people in numerous communities throughout the U.S. and Canada. Employees are provided healthy, good quality jobs, but ultimately these wages benefit respective economies both locally and nationwide. According to the Economic Policy Institute, for every 100 iron and steel mill manufacturing jobs, 923.7 indirect jobs are created. An example of this small business support is the scrap recycling business, where an average of 50 people are employed at each facility. This domestic DI pipe manufacturing component enhances the environment by using recycled goods and adds to our country's economic prosperity.
Additionally, the immediate availability of technical assistance and support allows for efficiently designed and constructed projects that benefit the utility's and, ultimately, the customer's bottom line. The purchase of non-domestic products cannot replicate these intrinsic advantages of domestic DI pipe.
When constructing water and wastewater pipelines, time is money. When a contractor must cease or slow work, added compensation for delay is usually in the conversation. Often, unknown conditions in the field require adjustments that can only be made by the efficient supply of materials suited for that scenario.
Also, materials will, from time to time, have defects. When this occurs, an immediate forensic determination needs to occur, and the product's replacement needs to be expeditious to get the contractor back to work. Trying to access replacement or specialty products from thousands of miles away can create delays and expenses.
What happens when a domestic DI pipe manufacturing plant ceases production because of natural disasters, a pandemic, work stoppage, or other factors? Logistics are in place to guarantee a seamless supply chain of domestically produced DI pipe. This network of resources does not exist when looking at the use of foreign DI pipe.
Domestically produced DI pipe offers total pipeline solutions, including restrained joints, river crossing pipe, and applicable appurtenances. These offerings eliminate non-compatibility issues with manufacturing facilities and technical assistance close by to resolve field-related issues quickly without inordinate delays.
Leaders in our country have recognized the value of purchasing domestically- made iron and steel, as demonstrated by the American Iron and Steel Act. Domestic production promotes economic growth in our country while taking advantage of high-quality products and the environmental benefits of American-made iron and steel products. Specifications that allow foreign pipe can result in the use of inferior quality foreign products, with little or no service support, that cause significantly greater harm to the environment.
As we've discussed, there are compelling reasons to utilize American-made Ductile iron pipe. I encourage you to check out our Iron Strong Insights Magazine's upcoming issues and our Iron Strong Blog as we will delve deeper into this topic over the next several months.
If you have any questions or need further assistance with anything DI pipe related, please contact your local McWane Ductile sales representative. We have team members who have managed small and large water utility systems, served in engineering consulting firms, and bring decades of experience in solving field issues involving pipeline construction and operation. From design to submittal to installation, we strive to provide education and assistance to water professionals throughout the water and wastewater industry.
Roy Mundy, P.E., ENV SP, Assoc. DBIA, currently serves as Senior Regional Engineer for McWane Ductile, assisting utilities and engineering firms with value engineering of pipeline projects, education in pipeline material selection, and providing assistance with specification development and updating. Roy has a BS in Civil Engineering from West Virginia Institute of Technology; MS in Engineering Management West Virginia University College of Graduate Studies; and is a Registered Professional Engineer in six states; ENVISION Sustainability Professional. Prior to McWane Ductile, Roy served as Lead Executive with the American Water System, retiring as President/CEO of Kentucky-American Water Co. Roy has served as Section Chair and is on several national committees of AWWA, Board of Directors and national committees of NAWC, Chair of ORSANCO, member of Kentucky Infrastructure Authority. He is currently serving on AWWA – Business Practices Standards Committee, the KY/TN Section Management Committee, and the Water/Wastewater and Legislative Committees of DBIA. Roy is a member of AWWA, NSPE, KSPE, ASCE, DBIA, and KYRWA.
"I joined McWane Ductile 5 years ago after spending most of my career in the water industry in the private water utility sector," said Mundy. "I enjoy the opportunity to work with engineering firms and utilities in assisting with value engineering projects and providing education on aspects of our products. I enjoy restoring classic cars, but foremost enjoy time with my family traveling and working around our small farm in Kentucky."
https://www.linkedin.com/in/roy-mundy-7b/
Want more information on flanged ductile iron pipe? Feel free to contact us.