AGA Cost Case Study
The parameters:
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- Typical mix of steel shapes/sizes
- 50,000 square foot short-span bridge
- 75-year design life
- Moderately Industrial (C3) Environment
Using the AGA Life-Cycle Cost Calculator, a quantitative analysis was conducted comparing hot-dip galvanizing to four paint systems, as well as a duplex system and metallizing with defined maintenance schedules.
Initial Cost:
Including materials (paint, metallizing, etc.), the number of coats, the surface prep cleaning method (painted systems: SP-10; duplex: SP-16/ASTM D; metallizing: standard near white metal), where the application was performed, and labor costs versus galvanizing&#;s all-inclusive price:
Coating System$/ft2TotalHot-Dip Galvanizing$1.76$ 88,000Epoxy/Epoxy$2.92$ 146,150Epoxy/Polyurethane$3.35$ 167,650Inorganic Zinc/Epoxy$3.17$ 158,650Inorganic Zinc/Epoxy/Polyurethane$4.53$ 226,300Galvanizing/Epoxy/Polyurethane (Duplex)$5.28$ 263,950Metallizing$8.37$ 418,550
These findings indicate that when all the costs are considered, galvanizing is often less expensive and at the very least, exceedingly competitive with other coating systems.
Life Cycle Cost:
Utilizing a practical maintenance cycle over the prescribed 75-year lifetime of the project based on Net Future Value (NFV) and Net Present Value (NPV) calculations at 3% inflation and 2% interest, and accounting for a very unlikely needed maintenance paint with an inorganic zinc at year 70 for the galvanized steel:
Coating System$/ft2TotalHot-Dip Galvanizing$ 4.29$ 214,500Galvanizing/Epoxy/Polyurethane (Duplex)$22.84$1,142,000Inorganic Zinc/Epoxy$39.92$1,996,000Inorganic Zinc/Epoxy/Polyurethane$41.53$2,076,500Epoxy/Epoxy$51.91$2,595,500Epoxy/Polyurethane$61.63$3,031,500Metallizing$62.80$3,140,000
Even with the one maintenance cycle near the end of the life of the project, hot-dip galvanizing was proven to have a significantly more economical lifecycle than that of the other coating systems.
Galvanized Steel Protects Your Investment
To maximize return on investment, it&#;s critical that buyers ensure the longevity of their purchase. Enhanced over 200 years, galvanizing is a process that best protects steel for long-lasting, corrosion-free performance. In fact, galvanized components can potentially last up to a century without the need for costly maintenance, delivering a significantly lower lifecycle cost, especially when compared to alternatives like stainless steel, aluminum, and epoxy coating. And research suggests that non-galvanized structures incur indirect costs as much as 11 times higher than those that utilize galvanized products. In an economy where steel prices are expected only to rise, buyers are wise to protect their investment and achieve cost savings by galvanizing.
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AZZ&#;s GalvXtra four-step, hot-dip galvanizing process uses a proprietary formulation of molten metals to deliver consistent, high-quality zinc coatings on ferrous materials. At the preparation stage, steel arrives at AZZ&#;s galvanizing plant and is inspected to ensure that drainage and venting requirements are met. Then, the metal is cleaned by immersion in a hot alkali solution, acid pickled to remove rust or scale, and fluxed to eliminate surface oxides. Next, the steel is hot-dip galvanized&#;submerged in a bath of molten zinc to form a shield of zinc/iron intermetallic layers on all surfaces. Finally, the newly galvanized steel is cleaned, weighed, and carefully inspected with calibrated instrumentation to ensure quality standards.
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Am I (customer) being charged for thick coatings? Why do I keep getting thick coatings from the galvanizer&#; are they trying to inflate the total selling price by putting more zinc on the steel?
This is a question the AGA receives from time to time over concerns related the thickness of the hot-dip galvanized coating. Although sometimes a thick coating can be desired to achieve greater longevity of the hot-dip galvanized coating, other times an excessive coating thickness potentially results in issues related to fit-up between parts, appearance concerns, or flaking of the coating.
However, it is not true that galvanizers provide thick coatings in an attempt to charge more for their services on a per-pound basis. Zinc is the largest material cost factor in the hot-dip galvanizing process, and thick coatings result in lower profit margins. If we look at the cost of zinc used in the hot-dip galvanizing process, it is possible to see the impact zinc prices and thick coatings have on the galvanizer&#;s bottom line.
Prices of zinc over the last year (USD):
- 52-week low: $1.04/lb
- 52-week high: $1.64/lb
- Current: $1.19/lb
Galvanizers charge for their services by weighing the part after it has been galvanized, and this results in pricing anywhere from $0.20 to $0.50 (USD) per pound of finished weight. This pricing information is general to the industry in North America and based on survey data obtained from AGA galvanizing members. Though an increase in coating thickness adds extra weight (and therefore cost) to the final product, the zinc prices referenced above mean the galvanizer actually loses $0.69 to $0.99 for each additional pound of zinc on a part which is beyond the minimum needed to meet the specification requirements. This explains why it is not in the galvanizer&#;s best interest (financial or otherwise) to provide excessively thick coatings. Instead, the galvanizer&#;s profit margins increase when the minimum average coating thickness is met while overall zinc consumption is minimized.
Then why does the galvanizer occasionally provide thick coatings when it is not desired by either the galvanizer or the customer? The primary challenge occurs when the customer provides the following types of steels or steel assemblies that make limiting the coating thickness very difficult. The list below contains links to additional Dr. Galv articles explaining why these conditions may result in thick coatings:
When specifying these steels or assembly types, there are some methods the galvanizer can employ to try and limit the coating thickness. It is important to note not all of these methods may be applicable to a project, and a thinner coating is never guaranteed:
- Reduce immersion time
- Request the customer blast clean the parts before hot-dip galvanizing
- Move/agitate the part as much as possible while immersed in the bath
- Increase immersion rate and decrease withdrawal rate from the zinc bath (effectiveness limited by poor venting/drainage design)
- Add elements to the zinc bath known to reduce the surface tension of the zinc and/or reduce reactivity for Sandelin Steels with 0.04 &#; 0.15 % Si content (impractical to change existing bath chemistry for one customer)
- Lower the bath temperature (often impractical)
In order for these methods to be used successfully, steel chemistry and/or assembly make-up should be provided to the galvanizer ahead of time in order to evaluate the steel chemistry, review the overall design, and then determine which measures are appropriate to limit the coating thickness.
To avoid future concerns about thick coatings and pricing in the future, direct communication with the galvanizer is critical to ensure a successful combination of design, fabrication, and galvanizing practices are employed. These practices help ensure your expectations are met regarding cost, fit-up, appearance, and overall quality.
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