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Ductile Iron Pipe’s superiority

Introduction
Ductile iron is a graphite cast iron that has been spheroidized. The ductile iron’s reliability stems mostly from its great durability, strength, corrosion resistance and impact. Ductile iron pipes are typically utilized for the distribution of potable water, pumping of slurries, sewage, and process chemicals.
The high operational dependability of ductile iron pipe originates from its key benefits such as machinability, corrosion resistance and high strength making it a pipe material that is sturdy and durable with high resistance that requires almost little to no maintenance.
As a result of these factors, it has supplanted cast iron as the preferred pipe material among waterworks specialists. The high reliability of ductile iron pipes is due to their many superior qualities, which we will talk about below.

The History of Ductile Iron Pipes
In 1948, the first ductile iron pipe was produced as an experiment by the American Cast Iron Pipe Company. Years of refinement in metallurgical, casting, and quality control procedures followed. With the first shipment in 1955, the ductile iron pipes were finally introduced into the market. Since then, the manufacturing of ductile iron pipes has constantly increased, and it is today the most often used pipeline material for transporting water and other fluids.
After 1955, Ductile iron pipes were recognised as a pipe with all the desirable features of cast iron plus added ductility and strength. These pipes were initially utilized for exceptional and difficult circumstances of high pressure, water hammer, and heavy external stresses. Ductile iron pipes have proven themselves to be nearly maintenance-free pipe material, and it is now employed in the transportation of potable water, sewage, slurries, and process chemicals. The ductile iron pipe’s strength and tough durability results in a high level of operating reliability in any terrain.
As a pipe which can be easily handled and installed without damage, it has gained popularity among engineers and utility authorities. Zero to no pipe damage.

Benefits of DI pipes

  • They require very little maintenance once placed or installed.
  • Ductile iron pipes can last more than a decade, more than any other pipe.
  • DI pipes are machineable, which means they can be cut, drilled or welded with proper precaution.
  • Can withstand high impact and traffic load.
  • Ductile iron pipes are not easily damaged until they are mishandled.
  • Installation is easy and safe for engineers because of its socket design. Also, DI pipes can be cut and reused when required.
  • Weight is 30 to 40% less than cast iron pipes.
  • DI pipes are more than capable of withstanding difficult terrains and abnormal service conditions.
  • Highly resistant to internal and external corrosion.
  • DI pipes offer high specific damping capacity (15%-40%) coupled with low notch sensitivity due to the presence of graphite nodules.
  • Ductile Iron Pipes are 100% recyclable.
  • Having tremendous burst strength makes these pipes ideally suited for the high-pressure application and also provides additional safety against water hammers.

Superior properties-

Corrosion
Iron is notoriously prone to rust and corrosion but ductile iron is more flexible and corrosion-resistant than other forms of the iron pipe due to its unique composition. Graphite in ductile iron forms spherical nodules rather than the flakes observed in grey iron. This spherical shape provides structural stability to the iron, preventing fracture development and boosting ductility (flexibility). Originally developed for gas industry purposes, ductile iron is now frequently employed in the water industry.
Underground ductile iron pipe may survive for more than a century if properly planned and placed. One distinguishing feature of ductile iron pipe is that its physical properties do not alter over time. Corrosion is the sole hazard to the pipe’s usable life if it is not subjected to a higher pressure than it was designed to withstand.
Even though ductile iron pipes are ferrous metal (containing iron) and may be used in a variety of applications, the same surface preparation and coatings cannot be used on them as on other pipes such as steel pipes, composite pipes, and so on.
Attempting to prepare ductile iron in the same manner as any other pipe may harm the pipe’s outside and render the coating ineffective. In some situations, such as chemical environments, corrosive wet wells, or aggressive soil, these coatings are needed. Ductile iron pipes are manufactured with 130 or 200 gm/m2 external metallic zinc coating and 2nd part Bitumen coating or epoxy coating to increase protection against corrosion. Polyethene sleeves may be applied during installation to enhance protection in an aggressive environment. Ductile iron pipes are also highly resistant to electrical corrosion. In general, if the prerequisites are not satisfied, this coating is not necessary. The corrosion rate of ductile iron pipes is around 0.005 per year, and because it is so low, these pipes are almost corrosion-free.

Laying – Jointing
Ductile iron pipes are easier and less expensive to install than other pipe materials, due to the flexibility and strength it offers. Due to its flexibility, ductile iron pipes offer 2° – 5° deflection after jointing depending on the pipe diameter, unlike steel pipes where the joints are rigid. For example, DI pipes can be laid with less severe bedding and backfill specifications. Other pipe materials, such as PVC, concrete, and clay, need stringent designed fill and bedding specifications to reduce settlement and long-term creep. Steel pipes during installation require external soil support and extra bracing.
Furthermore, because ductile iron pipes can be machined, they can be simply cut, drilled, and easily tapped in the field. Rubber gaskets are used as a sealing agent in DI pipe jointing, the same as concrete pipes.

Storage and safety
Pipeline materials, such as PVC, might break catastrophically due to high pressures or ground movement. This failure poses a danger of drinking water pollution in potable water pipes. Ruptured wastewater pipelines can potentially pollute the surrounding environment.
Ductile iron pipes have high bending, tensile, and impact resistance. Ductile iron pipes offer a minimum elongation of 10% and have minimum yield strength of 30000 psi and tensile strength of 60000 psi.
When these properties are paired with normal wall thicknesses, ductile iron pipes can withstand ground movement caused by heaving, settlement, and seismic activity. Ductile iron pipes have a high bursting strength, allowing them to endure high-pressure surges such as water hammers.

Maintenance/ Cost Effective
The maintenance of any pipeline is a big factor when considering or planning to install them, as sometimes the maintenance cost, in the long run, can cost double or even triple the cost of the pipe itself.
The maintenance required in DI pipes is very minor due to the increased longevity. Impact failure or bursting due to a crack or water hammer is extremely rare. As ductile iron pipes can last more than a decade, the frequency of damage is very low.

While Ductile Iron pipes are virtually maintenance-free, they are also very cost-effective.

  • Reduced Pumping costs
  • DI pipes are more energy-efficient than other materials used in pipelines thanks to their big inside diameter. This allows DI pipes to push the liquids through the pipe with reduced force. Ductile Iron pipe’s relatively low coefficient of friction (K=0.03mm) can result in high flow capacity, low head loss, low pumping cost and significant energy savings over the life of the pipeline.

  • Reduced Tapping costs
  • Due to its inherent strength, DI pipes are more economically convenient and reliable for future connections. Typical service taps can be installed directly into the pipe, which is called ‘direct tapping’. This eliminates the need for tapping saddles. DI pipes can be ‘hot tapped’ with ease. This avoids the issue of unsatisfied consumers as their service and pressure are not impacted by adding a new tap.

  • Repairs Costs
  • Repairs on a ductile iron pipe are much easier to assess and settle.
    When such minor issues arise, they point towards source repairs which then can be easily fixed with a stainless steel repair clamp and a couple of restrained Mechanical Joint sleeves, reducing the overall cost by a landslide.

Sustainability (environment)
Sustainability is a big issue for manufacturers when it comes to the production of pipes. Production of pipes such as PVC contains tons of chemicals that are very harmful. Furthermore, toxic gasses are released during the production process, affecting nearby flora and fauna.
When it comes to how environment-friendly ductile iron pipes are there is no comparison. Ductile Iron Pipes are made from recycled steel and iron scraps. Having as much as 98% recycled content, Ductile Iron Pipe is itself 100% recyclable, and decades of extensive use have demonstrated it presents no adverse health risks. Pumping through a Ductile Iron Pipe instead of PVC can save about 40% of energy consumption. This also means less CO2 production and an overall fall in carbon emissions. A ductile iron pipe is not vulnerable to pollutants creeping their way into drinking water, but a plastic pipe is, which can contaminate the water. A plastic pipe was linked to 98 % of permeation occurrences in a study conducted by the EPA. Toxic substances cannot find their way into drinking water if ductile iron pipes are used.

References:

  1. https://www.electrosteel.com/products/ductile-iron-pipes-jointing-systems.php
  2. https://dipra.org/about-ductile-iron-pipe
  3. https://www.mcwaneductile.com/blog/ductile-iron-vs-steel-pipe-how-to-make-the-best-choice/
  4. Kubota.com
  5. https://cdn.ymaws.com/www.isawwa.org/resource/resmgr/handouts_for_seminars/joints.pdf
  6. https://www.awwa.org/portals/0/files/publications/documents/m41lookinside.pdf