The rich patina of Weathering Steel is being seen more often in unpainted applications for bridges, utility and sign poles, structures and highway guardrails. The aesthetic values of this weathered and textured material, and more importantly, the practical values of Weathering Steel make this steel particularly useful for applications where strength, ease of fabrication and appearance are paramount. This brochure provides owners, designers, structural engineers, bridge engineers and contractors important information about Weathering Steel including its use, handling, fabrication, availability, properties and specifications. Design Considerations Weathering Steel has a unique, natural oxide coating that when fully mature is dense, tightly adherent and relatively impervious to further atmospheric corrosion. Minor damage to this oxide coating heals itself; therefore, maintenance is greatly reduced. Bare Weathering Steel is suitable for many atmospheric environments, including moderate industrial and select marine exposures. It is compatible with other construction materials – brick, stone and wood – when appropriate details are incorporated in the design. Weathering Steel is available with yield strengths of 50 ksi, 70 ksi and 100 ksi allowing designs with relatively light sections. When combined with the fact little or no painting is required, Weathering Steel provides significant first cost and life cycle cost savings.
Weathering Steel has been successfully used in many applications. Growing use in bridges has resulted in over 40% of all structural steel used in bridges to be weathering steel. However, there are conditions where bare unpainted weathering steel may have problems developing a protective oxide patina. Examples of these conditions are:
• Atmospheres containing concentrated, corrosive industrial or chemical fumes
• Locations subjected to salt-water spray or saltladen fog
• Applications where the steel is continuously submerged in water, buried in soil or installed where water run-off is contaminated with deicing salts (during winter months) or drains through leaky seals, open joints or expansion dams.
• Applications where the steel is in direct contact with timber decking. Timber retains moisture and may be treated with salt bearing preservatives.
• Bridges over enclosed highways where concentrated salt-laden road sprays under the bridge accumulate on the superstructure.