The question of galvanic corrosion can arise when dissimilar metals, or different methods of corrosion protection (such as galvanized bolts and weathering steel), come into contact. One example application involves galvanized bolts and angles supporting conduits on a bridge made of 350A (atmospheric corrosion-resistant, weldable) steel or its notch-tough counterpart, 350AT steel. Can galvanized high-strength ASTM F3125 A325 bolts be used on weathering steel?
Galvanized Bolts
While A325 Type 3 (weathering) bolts are usually used in weathering steel structures, hot-dip galvanized A325 bolts may also be used despite galvanic reaction. According to the American Galvanizers Association (www.galvanizeit.org):
“When galvanized bolts are used on weathering steel, the zinc will initially sacrifice itself until a protective layer of rust develops on the weathering steel. Once this rust layer develops, it forms an insulating layer that prevents further sacrificial action from the zinc. The zinc coating has to be thick enough to last until the rust layer forms, usually several years. Most hot-dip galvanized bolts have enough zinc coating to last until the protective rust layer develops on the weathering steel, with only a minimal loss in coating life.”
It should be noted that galvanized A490 bolts are not permitted. High-strength bolts covered in ASTM F3125 (A325, A490, F1852 and F2280) are available in weathering steel (Type 3).
