Abstract
Hot-dip galvanized steel is one of the most used materials in equipment and metallic structures of the Brazilian electric sector. Although carbon steel is the main substrate in the galvanizing hot-dip process, recently, weathering steel has been used as an alternative material to be galvanized. In the transmission line segment of the Brazilian electric sector, for instance, compact towers made of galvanized weathering steel have been installed to conduct energy through urban sites. It is well known that weathering steel, depending on wet and dry cycles and on the pollutants present in the atmosphere, develops a protective patina made of its corrosion products. The patina is dense and strongly adhered to the substrate, blocking the active surface and, thus, reducing the corrosion rate of the base metal. However, when the weathering steel is galvanized, the substrate surface has a layer of zinc and zinc-iron intermetallic alloys. When the sacrificial layer is consumed by atmospheric corrosion, critical questions remain to be answered regarding the underlying substrate. Will the patina of weathering steel be formed? In what condition? Does the hot-dip galvanizing process modify the weathering steel microstructure? The present work carried out an experimental research to shed light on the anticorrosive behavior of hot-dip galvanized weathering steel, after the zinc layer is corroded. This was done by a controlled pickling process, where the zinc layer was removed simulating its consumption during real corrosion processes. The results, obtained through electrochemical techniques and different accelerated corrosion tests, showed that galvanizing weathering steel is a promising technology to enhance the lifetime of structures used in the Brazilian electric sector.
Highlights
Weathering steel is widely used as construction material for metallic structures under atmospheric exposure
It is well known that weathering steel, depending on wet and dry cycles and on the pollutants present in the atmosphere, develops a protective patina made of its corrosion products
Some alloying elements content slightly diverged from typical standardized values in weathering steels [16] [17], this aspect did not compromise the performance of this material, as will be presented ahead
Summary
Weathering steel is widely used as construction material for metallic structures under atmospheric exposure. Weathering steel contains alloying elements, such as Cu, Cr, P and Ni, that favors the formation of a compact layer of corrosion products on the metallic surface over time [2] [3]. This rust layer, known as patina, is thick, dense and highly adherent to the substrate. The protective features of the patina are usually attributed to the formation of corrosion products mainly comprised of α-FeOOH The structure of such rust layer is different from the usual layer of corrosion products formed when carbon steel is exposed to the atmosphere, as the latter is less compact and presents voids and microcracks, being unable to protect the steel. In atmospheres containing sulphur compounds, the corrosion rate of carbon steel shows appreciable increase, whereas weathering steel corrodes significantly slower, owing to the patina formation [4] [5]
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