Due to hydrogen embrittlement concerns ASTM recommends against hot-dip galvanizing , mechanical deposition, or electroplating with zinc or other metallic coatings on high strength bolts ultimate tensile strengths that exceed 150 ksi. So what are the alternatives to provide corrosion resistance for A490 structural bolts?
Protective Coatings
ASTM recommends that if a protective coating is required for A490 bolts a Zinc/Aluminum Corrosion Protective Coating should be used in accordance with F 1136 Grade 3. This recommendation is based on findings from research conducted by the Industrial Fastener Institute (IFI 144). No other metallic coating is allowed unless authorized by ASTM’s fastener Committee F16. One trade name of this coating is Dacromet.
Weathering Steel
Another option is to specify ASTM A490 Type 3. This fastener is made from weathering steel which is inherently corrosion resistant. However, these fasteners are not as readily available in the marketplace as A490 Type 1.
Consulting a structural engineer involved in the project is always the best solution.
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