When specifying steel corrosion protection systems, it is important to consider not only the initial cost, but also the life-cycle costs (including all future maintenance). The following information will provide the considerations when determining initial and life-cycle costs, and provide a real-world comparison. Performing life-cycle assessments can be a difficult and cumbersome practice, but the online calculator www.galvanizeit.org/galvanizingcost will automate the process.
This is an example of the use of the online calculator for one particular situation. A quantitative analysis comparing hot dip galvanizing to four paint systems used data collected from recent surveys. The galvanizing cost data was obtained through a 2008 survey of North American hot-dip galvanizers and the paint cost data is taken from a paper produced in 2008 by KTA-Tator (consulting firm specializing in protective coatings, specifically paint) that lists costs of paint systems as well as their maintenance schedules in numerous ASTM classified environments.
It is important to note that the mix of steel products are inclusive of mostly small structural steel and/or fabrications and a typical job size of 30,000 sq. ft. was used to perform the analysis. We will also assume the steel will be used in a moderately industrial environment and we are going to look at a 60-year life-cycle.
Initial costs for paint systems include four components: material, shop cleaning labor, shop/field application, and field labor. All of these costs are included in the initial price for galvanizing as the cleaning process is a built-in part of the galvanizing process.
As mentioned before, it is not recommended to analyze only the initial cost for a corrosion protection system. However, if it is, galvanizing is still a solid choice, as it is initially less expensive than all but the minimal-protection, one-coat inorganic zinc paint system (see table below). As is common, projects with many smaller components and structural steel will yield an initial galvanizing cost lower than most paint systems, as the galvanizing process efficiently accommodates bundles and groups of steel.
|Acrylic WB Primer/Acrylic WB Intermediate/Acrylic WB Topcoat||$2.55||$76,630|
|Inorganic Zinc Primer/H-B Epoxy/Acrylic Urethane||$3.17||$94,950|
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 four paint systems, a practical maintenance cycle was used over the prescribed lifetime of the project. A 60-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 paint systems. Since galvanizing requires no maintenance during this period of performance in a moderately industrial environment, it is not affected by the choice of a 60-year lifetime.
When life-cycle costs are considered, hot-dip galvanizing is the most economical system for corrosion protection (see table below). 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.
|Acrylic WB Primer/Acrylic WB Intermediate/Acrylic WB Topcoat||7.98|
|Inorganic Zinc Primer/H-B Epoxy/Acrylic Urethane||6.43|
What Does All of this Mean?
So, bringing our analysis to life, using the example of a 30,000 sq. ft. steel bridge, the cost of the corrosion protection system over the 60-year life of the bridge would be as shown in the table below. Even if you think designing bridge members to fit into the galvanizing kettle may mean more erection time in the field and slightly more steel and connections, (by the way, 60’ kettles are now common) those costs are generally small when compared to the savings indicated. When the hidden costs associated with the maintenance of paint systems is added to the analysis, galvanizing is clearly the preferred choice.
|Coating System||Total Cost|
|Acrylic WB Primer/Acrylic WB Intermediate/Acrylic WB Topcoat||$301,200|
|Inorganic Zinc Primer/H-B Epoxy/Acrylic Urethane||$444,600|