Ity to have long term protection on exposed

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ity to have long-term protection on exposed structural steel has allowed many of today's innovative architects to express a wide variety of ideas through the structure itself. Properly specified and applied coating systems can be expected to give 20 to 25 years of initial service life that can be extended almost indefinitely and with subsequent maintenance painting. Coatings technology continues to evolve with paint systems being developed to meet more and more stringent requirements. This is a blessing in the sense that owners and architects can expect continually improving per- formance, but it also means that developing a proper specification for a given project requires keeping up with the most recent product developments. Paint specifications for building structures should be performance-based to allow competition within a perform- ance standard. Paint specifications should also be project specific and take into account the following three fac- tors: ! Building end-use—Is it a factory where the structure will be exposed to corrosive processes or high humidity ? Is it a public facility subject to abrasion and vandalism (graffiti) ? Is it a swimming pool with high humidity and heat ? Or, is it an office building that is well-protected and subject to benign usage ? ! Environment—Is the building located on the coast in a saline atmosphere, at an inland location sur- rounded by industrial plants, or is it in a desert-dry climate but subjected to relentless attack by the ultra- violet rays of the sun ? ! Is the structure to be exposed on the exterior, interior or both ? This portion of the guide is intended to inform architects of issues that should be considered in the development of a proper paint specification for building structures. In addition, there is considerable background information intended to help specifiers understand coating systems in general so that they can make informed and intelligent choices. Several coating references are provided at the end of this section. BASICS OF PROTECTIVE COATINGS The Corrosion Process A clear understanding of the corrosion process is essential to understand the steps to inhibit corrosion with pro- tective coatings.
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SYSTEMS PAGE 26 Oxygen combines with iron, the major element in steel, to form rust. This electrochemical process returns the iron metal to the state that it existed in nature—iron oxide. The most common form of iron oxide or iron ore found in nature is hematite (Fe 2 0 3 ), which is equivalent to what we call rust. Iron in iron ore is separated from the oxide to yield usable forms of iron, steel and various other alloys through rigorous electrochemical reduction process- es. Because the iron has a strong affinity for oxygen, it is necessary to deal with the ever-present tendency to form the more electrochemically stable iron oxides.
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  • Fall '19
  • Structural steel

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