Duplex systems provide tremendous economic advantages because of the extended time to first maintenance and delayed maintenance cycle. Initially, the cost of a duplex system is high because you must pay for both corrosion protection systems. However, because of the synergistic effect the initial premium cost pays off over the life of the project and in the end is less expensive than coating bare steel.
For duplexed projects where the paint/powder system is used strictly to prolong life and the color finish is not critical, the initial cost can also be your final cost. But for most duplex projects, the top coat will be maintained and on these projects, the delayed maintenance cycle can significantly decrease the cost over the life-cycle.
Cost Case Study
To explore the economic benefits of utilizing a duplex system, consider the following case study of a two-coat paint system on black steel and galvanized steel. The study utilizes nationwide cost data collected from the galvanizing industry and paint manufacturers for initial costs, surface preparation, and maintenance costs.
Evaluating LCC can be cumbersome, so to facilitate the analysis, the AGA developed the Life-Cycle Cost Calculator lccc.galvanizeit.org/. The online calculator allows users to input the parameters for a project and compare the initial and life-cycle costs of hot-dip galvanizing or a duplex system to more than 30 other corrosion protection systems based on published cost data.
All of the financial equations used in the calculator are the same as those provided in the specification ASTM A1068 Practice for Life-Cycle Cost Analysis of Corrosion Protection Systems on Iron and Steel Products. Data Sources (costs, time to first maintenance based on in-field performance):
- Paint - KTA Tator, Inc Paper No. C2014-4088 Expected Service Life and Cost Considerations for Maintenance and New Construction Protective Coating Work (2016) - presented at NACE
- Hot-Dip Galvanizing - American Galvanizers Association National Survey (2016)
As stated before, the cost of utilizing a duplex system is more expensive initially because you are paying for both the HDG and the paint system. However, specifying a duplex system of paint over hot-dip galvanized steel means less money will be spent on maintenance over the life of the structure, as can be seen by the table indicating when maintenance is necessary. The delayed maintenance cycle of the duplex system resulted in four less maintenance cycles during the 60-year life, allowing the owner more time to earn interest on the money.
|Epoxy/Polyurethane (Black Steel)||$3.06||$152,750|
|Duplex System (HDG + epoxy/poly)||$5.22||$260,750|
|Maintenance (Years)||Black Steel||HDG Steel|
|Touch-Up Repaint||11 & 31 & 51||22 & 58|
|Maintenance Repaint||14 & 34 & 54||29|
|Full Repaint||20 & 40||51|
Life Cycle Cost
Due to the synergistic effect of delayed and even eliminated maintenance over a project's planned, useful life cost savings of a duplex system are often significantly greater than the initial 'premium' cost of the galvanizing and paint combination. Because of the additional maintenance cycles, the life-cycle cost of the paint system only is nearly double that of the structure that utilized a duplex system. Therefore, utilizing a duplex system for corrosion protection pays for itself - delivering maximum value and aesthetic appeal to project owners throughout the design life. In summation, decreased maintenance costs over the life of the project result in lower life-cycle costs for a structure utilizing a duplex system.
|Epoxy/Polyurethane (Black Steel)||$23.54||$1,777,000|
|Duplex System (HDG = epoxy/poly)||$12.95||$647,500|
|Duplex System life-Cycle Cost Savings = 44%|
Cost Case Study
MarketPlace Center: Boston, MA, 1985
Faneuil Hall, located on Boston's waterfront, is one of the city's major tourist attractions. It is an historic site that was in disrepair for decades until developed by the Rouse Company in the late 1960's. Marketplace Center, a 17 story high-rise mixed use building was the final component in the rebirth of Faneuil Hall.
One of the main features of Marketplace Center is the open "Walkway to the Sea." This is a steel framed, glass canopied structure designed to allow pedestrians to walk from Faneuil Hall directly to the waterfront. Since it is an architectural element and highly visible open structure constantly exposed to the moist sea air, the architect wanted a coating system that would not only protect the steel from corrosion, but would also provide the aesthetics required of the structure. Based on these criteria, a duplex system of hot-dip galvanizing and paint was specified.