Galvanized Steel

Typically and for best performance the steel should conform to the mechanical and chemical properties listed in American Society for Testing and Materials (ASTM) specification A572. We also recommend the maximum silicon content for steel substrate be 0.06 % to ensure an adequate free zinc and uniform galvanized finish. The mechanical strength requirements for structural performance, such as tensile strength, (assuming the inherent material strength remains constant), is then dependent upon the material cross-sectional area.  If inadequate, tensile failures could occur at locations where corrosion has produced localized reductions in cross-sectional areas and created stress raisers. Higher tensile strength steels have less ductility and toughness.  These steels are considered notch sensitive. Normal constructional steels would not typically be notch sensitive but high strength low alloy (HSLA) steels can be notch sensitive. Corrosion pitting can create the notch which then becomes the location of crack initiation. Pitting or reduced thickness areas due to corrosion can also initiate mechanical fatigue cracks.

We have inspected galvanized roofs, galvanized pipes, galvanized lattices in service which date back to the early 20th century. Upon inspection, we found out that the galvanized layer is present even after 100 years of service. The key point in long service life is that the soil in that location provided the protective layer on the galvanized surface. However, both white rust and paint failures have been observed on galvanized steel components in service after a few years in service.