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Protecting critical infrastructure with hot-dip galvanizing

5 min read
May 13, 2023
Quality infrastructure is critical to support the transportation, electricity, communication and agricultural needs of today’s communities. The escalating severity of natural disasters and extreme weather patterns add to the urgency for more sustainable infrastructure. History shows hot-dip galvanized (HDG) steel structures are fully equipped to weather the trials and tests of time, reaching the most sustainable finish for up to 100 years.
  • Project
    Hot-dipped galvanized (HDG) steel transmission tower
  • Location
    Omaha, Nebraska
  • Challenge
    Building materials that last, are highly recyclable and minimize future environmental impacts are in high demand as the world progresses toward a more sustainable future.
  • Solution
    With a strong zinc coating, Valmont® hot-dip galvanized (HDG) steel creates a long-lasting building material that can be easily recycled once it has outlived its use.

Over more than five decades, Valmont has aided in the creation of durable, enduring infrastructure through its hot-dip galvanized (HDG) steel products, including irrigation center pivots, transmission and distribution towers, commercial lighting and communication structures, and bridges. In 1969, Valmont produced an innovative HDG steel transmission tower for the Omaha Public Power District (OPPD). The 120-foot (36.5-meter) transmission tower was galvanized and erected in Omaha, Nebraska, as part of a larger transmission line grid that stretches from Minneapolis to Kansas City. It featured a new, octagonal design and replaced a round, painted structure. Over 50 years later, it is still standing as tall and strong as ever, with little to no maintenance over the decades. And Omaha, Nebraska, has had its fair share of extreme weather over this timespan — tornadoes, blizzards, ice and wind storms, and more. Using an online program to compare the average atmospheric conditions and the coating thickness readings measured a few years ago, after more than 50 years of service, the galvanized coating on the tower still averaged 6.5 mils, far exceeding the minimum industry standard of 3.8 mils. Had this been a painted tower, it would likely have had corrosion on the steel due to the paint degrading or undercut rusting, prompting maintenance cycles that could remove the tower from service, potentially disrupting utility service to homes and businesses. Maintenance cycles to reapply and touch up paint coatings also result in additional greenhouse gas emissions, such as CO2, and pollutants, such as volatile organic compounds (VOCs), known to cause smog. It all comes down to the chemistry for this HDG steel tower to maintain its strength over time. In the HDG process, the steel is dipped in molten zinc, forming multiple metallurgically bonded iron-zinc layers, with a layer of pure zinc on top. Zinc is more active than steel and sacrifices itself, protecting the underlying steel from corrosion. While producing HDG steel is comparable to the initial cost of paint, the total can continue to add up for painted products because of these regular maintenance cycles. For example, when the HDG steel of the 1969 OPPD transmission tower is compared to two common paint options — epoxy primer with an epoxy topcoat and zinc epoxy primer with two epoxy topcoats — the life cycle cost for HDG steel has resulted in a cost savings of more than 80% over each painted option. Our analysis shows that the OPPD tower could last for another 195 years, well into the early 2200s. In addition to multiple real-life, standing examples of durability like the OPPD tower, Valmont regularly contributes data and insight for HDG steel studies completed by the American Galvanizers Association (AGA), a nonprofit trade organization of which Valmont is a longtime member. Extensive AGA research has proven, time and time again, how HDG steel is unique, in part because its environmental impacts are isolated to the initial production phases—meaning zero emissions after installation for its 75-year (or more) life span. For example, an independent study cited by the AGA found that the HDG process contributed 16% (23,700 MJ) (30.5 MJ/kg) of the total energy demand over a 60-year estimated lifecycle for identical balcony systems. In contrast, paint contributed 69% (64,700 MJ) (83.2 MJ/kg). The energy demand was much higher for the painted balcony because of the three maintenance cycles needed to maintain the finish over time. The maintenance to keep the coating intact resulted in higher greenhouse gas emissions and higher contributions of other pollutants that cause acid rain and smog. Ultimately, the energy used to perform the maintenance was equal to the expenditure for the original production of the balcony. Adding to the sustainable results of little to no maintenance and zero emissions after production, HDG steel is 100% recyclable. Both zinc and steel can be infinitely recycled and reused because the metals maintain their original properties. In comparison, painted steel must be treated to remove the paint beforehand, resulting in more energy use, emissions and waste. When the total benefits are tabulated and compared to other coatings, it is clear why HDG steel is often the top choice for infrastructure worldwide. Many decades-old Valmont-produced structures, like OPPD’s transmission tower, are models of this sustainable finish in action. The more than 550,000 MT of HDG steel produced by Valmont in 2022 will add to this sustainable effort to reimagine infrastructure for communities worldwide — conserving resources and improving lives. Valmont has taken the conservation of resources in the HDG process a step further and reduced its zinc usage by 1 million lbs (453,592 kg) annually with GalvTrac, a proprietary program that uses artificial intelligence (AI) for more precise zinc measurements. Additionally, in 2022, Valmont recycled nearly 12,000 metric tons (MT) of skims, dross and crystals as part of its commitment to sustainable production.