Corrosion remains a significant challenge in the longevity and reliability of buried piping systems, particularly for ductile iron pipes (DIP). Among the various corrosion mitigation strategies, the application of polyethylene encasement, commonly known as polywrap, has emerged as a cost-effective and efficient solution. This article delves into the principles, types, applications, and advancements of polywrap for pipe corrosion protection, with a focus on polywrap for pipe, polywrap ductile iron pipe, and polywrap pipe.
Understanding Polywrap and Its Protective Mechanism
Polywrap serves as a physical barrier between the pipe surface and the surrounding soil, effectively mitigating corrosion by preventing direct contact with corrosive elements. This encasement is not designed to be airtight or watertight but functions by creating a controlled environment around the pipe, reducing the availability of oxygen and moisture that facilitate corrosion processes. The American Water Works Association (AWWA) standard C105/A21.5 outlines the specifications for polyethylene encasement, ensuring consistency and reliability in its application.
Types of Polywrap and Their Applications
Polywrap is available in various forms to cater to different installation requirements:
Low-Density Polyethylene (LDPE) Polywrap: This standard form is widely used for general applications, providing basic corrosion protection by isolating the pipe from the soil.
High-Density Polyethylene (HDPE) Polywrap: Offering enhanced mechanical strength, HDPE polywrap is suitable for installations where additional durability is required.
Enhanced Polywrap: This advanced variant incorporates additional corrosion-inhibiting properties. For instance, V-Bio® Enhanced Polyethylene Encasement consists of a three-layer co-extruded film infused with a volatile corrosion inhibitor (VCI) and a biocide to combat microbiologically influenced corrosion (MIC).
Polywrap for Ductile Iron Pipe: A Standard Practice
Ductile iron pipes are commonly protected using polywrap due to their susceptibility to corrosion in aggressive soils. The application of polywrap for ductile iron pipe involves encasing each pipe segment with polyethylene film, ensuring overlaps at joints and securing the ends to prevent soil ingress. This method has been standard practice since its introduction in the mid-20th century and continues to be endorsed by industry standards and organizations.
Installation Considerations and Best Practices
Proper installation of polywrap is crucial to its effectiveness. Key considerations include:
Surface Preparation: Ensuring the pipe surface is clean and free from debris before application.
Wrapping Technique: Applying the polywrap with appropriate overlaps and securing it to prevent movement during backfilling.
Damage Prevention: Avoiding tears or punctures in the polywrap during handling and installation, as these can compromise its protective function.
Adhering to these practices ensures the longevity and effectiveness of the polywrap in corrosion protection.
Advancements in Polywrap Technology
Recent developments have led to the creation of enhanced polywrap materials with superior protective properties. For example, V-Bio® Enhanced Polyethylene Encasement not only serves as a physical barrier but also actively combats corrosion through its infused VCI and biocide components. These advancements address limitations of traditional polywrap, such as susceptibility to MIC and the potential for corrosion under intact wraps.
Performance and Longevity of Polywrap Systems
Studies have demonstrated the effectiveness of polywrap in extending the service life of ductile iron pipes. Field tests and long-term evaluations indicate that properly installed polywrap can significantly reduce corrosion rates, even in highly aggressive soils. The Ductile Iron Pipe Research Association (DIPRA) has conducted extensive research confirming the durability and protective capabilities of polyethylene encasement over several decades.
Conclusion
Polywrap remains a vital component in the corrosion protection strategy for ductile iron pipes. Its cost-effectiveness, ease of installation, and proven performance make it a preferred choice for many utilities and engineers. With ongoing advancements enhancing its protective properties, polywrap continues to play a crucial role in ensuring the longevity and reliability of buried piping systems.
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References:
1- Northtown Company – Polywrap: https://www.northtowncompany.com/polywrap.html
2- U.S. Pipe – Polyethylene Encasement for Ductile Iron Pipe: https://www.uspipe.com/special-coatings-linings/polyethylene-encasement-for-ductile-iron-pipe/
3- Pollardwater – Polyethylene Polywrap Product Details: https://www.pollardwater.com/product/24-in-x-400-ft-x-8-mil-polyethylene-polywrap-a70003/_/R-4822225
4- McWane Ductile – Corrosion Control for Ductile Iron Pipe: https://www.mcwaneductile.com/blog/corrosion-control-inside-and-out-for-ductile-iron-pipe/
5- McWane Pocket Engineer – Polyethylene Encasement: https://pe.mcwane.com/upl/downloads/dipra/dip-polywrap-2b98cc86.pdf
