AMERICAN Ductile Iron Pipe has the high-impact strength and toughness to withstand shocks usually encountered in transportation, handling and installation. These characteristics also provide added security against stresses induced by water hammer, highway traffic and unexpected adverse forces. Excellent impact resistance is confirmed by tests made at regular intervals in accordance with ANSI/AWWA C151/A21.51 standard.
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Head losses in piping are directly related to inside diameters, and energy consumption and accompanying pumping costs are directly related to head losses. Therefore, the use of ductile iron piping having inside diameters greater than nominal can result in significant energy savings over the years. In addition to helping keep operating costs and utility rates reasonable, this conservation of energy is also helpful to the environment.
AMERICAN uses a combination of chemical analysis and heat treatment to produce a pipe with desirable strength and ductility—a pipe that will withstand high internal pressure and deep cover—a pipe providing added reliability and safety for normal and unusual conditions, such as expansive soils and earth movement due to freezing and thawing.
Historical records document centuries of proven service of gray cast iron pipe. Extensive laboratory and field tests under various installation conditions prove the soil corrosion resistance of ductile iron is as good, if not better than, grey cast iron. The corrosion resistance of ductile iron pipe is verified by more than four decades of service.
Design
The design basis behind DI pipe is the most conservative of products on the market today. Decades of reliable service is evidence of DI pipe’s success. Design calculations are found in the ANSI/AWWA C151/A21.51 Standard Design for Ductile Iron Pipe.
The most notable difference is the safety factor. The safety factor for DI pipe is 2.0 versus the safety factor for steel, ranging from 1.33 to 2.0, depending on the percent of yield strength used.
Notice the two different equations used to calculate thickness design. Allowing the stress to escalate to 75 percent of yield strength lowers the steel pipe's safety factor to 1.33 when including surge, compared to the 2.0 safety factor used in the DI pipe design. The difference in percentages to yield affect the thickness design of the pipe.
Let’s stick with the more conservative and trustworthy calculations. Take the example of a 24-inch water line with a working pressure of 150 psi. Calculating the thickness:
Required Thickness
Steel Pipe (50% Yield) = .086 Thickness
Steel Pipe (75% Yield) = .095 Thickness
Ductile Iron Pipe = .157 Thickness
The thickness of the DI pipe is much greater than steel. The minimum thickness for a 24-inch Class 200 pipe is .24 inch. This is well beyond the calculated thickness design for internal pressure.
There is a comfortable feeling knowing the product chosen is designed well above the intended use. We do not know what the future will bring 100 years down the road, but we know that the design of DI pipe helps to ensure your water delivery system's longevity.
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Everyone would like to see a return on investment. These annual savings could be put to practical use. For more information on the these calculations, check out McWane's Pocket Engineer.
Additionally, DI pipe is also SMaRT certified with as much as 95 percent recycled content used in the manufacturing process. It also has no "end of use," which means that when replaced, it can be recycled over and over again. Choosing a sustainable product like Ductile iron not only benefits the end-user, but also our environment long term.
Corrosion and Protection
Ductile iron pipe is unique when it comes to corrosion control. An oxide layer is formed on the inside as well as the outside of all DI pipe during the manufacturing process. This oxide layer provides adequate corrosion protection (in many circumstances.) Utilization of the 10 Point Soil System will determine if there is a need for additional corrosion protection. The next step in corrosion protection for DI pipe is polyethylene encasement, better known as V-Bio®.
V-Bio is formed by bonding three layers of co-extruded, linear, low-density polyethylene into one. The inside surface contains an antimicrobial biocide to control microbiologically influenced corrosion and a volatile corrosion inhibitor to prevent galvanic corrosion.
V-Bio is easily installed in the field prior to pipe installation, making it cost-effective and easy to use. DI pipe and V-Bio can be installed in nearly any weather condition. No other product on the market compares.
Polyethylene encasement has proven to control corrosion in aggressive soils for more than 50 years and is cost-effective. The investment in V-Bio is minimal compared to the project's overall cost, especially when compared to the vastly more expensive alternative of bonded coatings used by the steel pipe industry. Not to mention the even higher costs associated with cathodic protection that is widely used in conjunction with steel.
Bonded coatings used to protect steel pipe are very expensive. Other issues that plague bonded coatings are handling and patching. The thin wall of steel pipe may not have enough beam strength to support its own weight, making for difficult handling.
It is difficult to handle a steel pipe section through installation without some damage to the bonded coatings. Any void in the bonded coating dramatically increases corrosion's potential, and these voids must be repaired. Contractors do not have the luxury of waiting until the sun shines to get the job done.
Time is money, and these folks need a product that is easy to work with, such as DI pipe. Some steel pipes are also coated with cement mortar, which is porous and subject to cracking. Again, any void in the coating increases the potential for corrosion of steel pipe.
Installation Factors
Ductile iron pipe can be installed in the rain, sleet, snow, high heat, or freezing temperatures. Because steel pipe needs to be welded together, a rainstorm can shut down any progress being made.
Ductile iron pipe joints come in 18-to 20-foot lengths, which are much easier to handle in the field than 40- to 50-foot steel joints. Do the math. Four joints of 24-inch ductile per hour = 72 feet, versus one joint of steel at 40 feet.
18-foot DI joints also provide a better opportunity for deflection. This deflection capability reduces the number of fittings. Again, reducing the overall cost of a project.
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/
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