In addition to building structures that are environmentally-friendly, for true sustainability these structures must also be economically responsible for future generations. Hot-dip galvanized steel can provide economic savings both initially and throughout the life of a project, freeing up money for new construction rather than costly maintenance.
There has long been a perception in the specifying community that hot-dip galvanized steel is cost prohibitive on an initial basis. However, due to regular process improvements, galvanized steel is not only competitive but often less expensive than other corrosion protection systems initially. Furthermore, because of quick turnaround and erection, utilizing hot-dip galvanized steel often provides wider-ranging cost savings during construction.
Cost Case Study
Using the galvanizing cost data obtained through a 2016 survey of North American hot-dip galvanizers and paint cost data taken from a paper produced in 2016 by KTA-Tator (consulting firm specializing in protective coatings, specifically paint) the AGA developed an online tool called The Life-Cycle Cost Calculator (lccc.galvanizeit.org). This is an example using the online calculator, which follows the calculation in ASTM A1068, to conduct a quantitative analysis comparing hot-dip galvanizing to four paint systems, with defined maintenance schedules, in one of the ASTM classified environments.
For this case study, we are analyzing:
- Typical mix of steel shapes/sizes
- 50,000 square foot project
- 75-year design life
- Moderately Industrial (C3) Environment
So, this example could easily represent a short-span bridge, light rail station, stadium, petro-chem plant, etc. In this example, we will evaluate hot-dip galvanizing in comparison to various painted systems, a metallized solution, and duplex system.
Initial costs take into account the material (paint, metallizing, etc.), as well as the number of coats. Additionally, it examines the cleaning method, where the application will be done, and labor accordingly. All painted systems in this example were cleaned to an SP-10 Automated surface prep, the duplex was to SP-16 (same as ASTM D6386) and the Metallizing example to the standard near white metal required. Galvanizing is an all-inclusive price, as the way the galvanizer quotes the material includes the surface preparation, material and labor costs.
|Hot-Dip Galvanizing||$1.76||$ 88,000|
|Inorganic Zinc/Epoxy||$3.17||$ 158,650|
|Inorganic Zinc/Epoxy/Polyurethane||$4.53||$ 226,300|
|Galvanizing/Epoxy/Polyurethane (Duplex)||$5.28||$ 263,950|
As mentioned before, it is not recommended to analyze only the initial cost for a corrosion protection system. However, if it is the only analysis, galvanizing is still a solid choice, as it is often initially less expensive or very cost competitive with other coating systems. Keep in mind these costs are all coming from the manufacturer (paint manufacturer and/or galvanizer) and do not take into account fabricator markup which may be assigned at varying rates dependent on the material (i.e. galvanizing may be marked up more if the fabricator has his own paint facility). This example uses a typical mix of structural pieces, which will typically yield an initial galvanizing cost lower than most paint systems, as the galvanizing process efficiently accommodates bundles and groups of steel. However, even if you compare medium or large structural elements, the galvanizing cost is less expensive or within a few cents per square foot of each of these systems as well. The strongly held notion galvanizing is more expensive initially is no longer accurate, as the cost of HDG has remained relatively stable while the cost of paints and other systems have increased significantly over the last 5-10 years.
Although the initial cost of your corrosion protection system is important, the life-cycle cost per year should be the determining factor in the selection process. After all, if the cost per year to maintain a painted structure far exceeds another corrosion protection system such as galvanizing, the owner should logically make the decision to galvanize.
Comparing the life-cycle costs of a galvanizing system to five other systems as well as a duplex (galvanized + painted system), a practical maintenance cycle was used over the prescribed lifetime of the project. A 75-year lifetime for this analysis was selected as a realistic timeframe before modification. This is opposed to an ideal maintenance cycle, which would be even more costly for all of the other systems which require maintenance. When analyzing life-cycle costs, you must also account for the time value of money using Net Future Value (NFV) and Net Present Value (NPV) calculations.
For this example, we used:
- 3% inflation
- 2% interest
In this example, it is quite possible the galvanizing would not be in need of maintenance, even at the 75-year mark. However, using conservative estimates, this analysis includes a maintenance paint with an inorganic zinc at year 70 (when it is expected to have about 5% rusting of the substrate steel 95% of the steel still has zinc on it). Even with this one maintenance cycle near the end of the life of the project, hot-dip galvanizing is still significantly more economical than the other coating systems.
|Hot-Dip Galvanizing||$ 4.29||$214,500|
When life-cycle costs are considered, hot-dip galvanizing is the most economical system for corrosion protection. In fact, this analysis does not even include the hidden (or indirect) costs associated with touch-up, maintenance, and full repainting required for paint systems. If deviations from the practical maintenance schedule occur, life-cycle costs could be significantly higher than indicated.
After 75-years of life, the cost of the galvanizing only increased $120,500 due to the one painting/maintenance cycle at 5% rust (Year 70). It is highly possible in the real world no maintenance would even be done at that time, as 5% corrosion is very minimal and the life is nearly over. However, looking at the other systems, even if this maintenance was performed, the cost savings is still significant in comparison to the other coating options. The second best option over the life of the project in this example is actually the duplex system of paint over galvanizing because as mentioned before, the galvanized primer allows less maintenance cycles to the painted system than the same system (with IOZ primer) on bare steel.
Also, of note, often the least expensive systems initially (Epoxy/Polyurethane, Epoxy/Epoxy) are the most expensive in life-cycle cost (because they require more maintenance). Even though the metallizing system requires less maintenance, the cost to metallize (and touch up with metallizing in the field) is much higher than it is to use paint in the field. To break-down the cost increase over 75 years as well as the saving hot-dip galvanizing provides, consider the following:
- Duplex System (Galvanizing/Epoxy/Polyurethane) cost 81% more than just HDG; but provides a cost savings of 44% in comparison to painting bare steel (IOZ/Epoxy/Polyurethane)
- Inorganic Zinc/Epoxy cost 89% more than galvanizing
- Inorganic Zinc/Epoxy/Polyurethane cost 89% more than galvanizing
- Epoxy/Epoxy cost 91% more than galvanizing
- Epoxy/Polyurethane cost 92% more than galvanizing
- Metallizing cost 93% more than galvanizing