Can A193 Grade B7 bolts be galvanized?

Yes they can. A common misconception is that B7 bolts cannot be galvanized. That misconception is wrong. A193 Grade B7 bolts are considered high strength and have developed their strength through a heat treating process. There are two concerns when galvanizing high strength bolts. One issue is the potential for hydrogen embrittlement and the other issue is altering the mechanical properties of the fastener during the galvanizing process.

Hydrogen embrittlement is a phenomenon in which hydrogen can become trapped in the surface of some fasteners during the galvanizing process leading to premature failure. However, this is only of concern for bolts exceeding 150 ksi in tensile strength. Since A193 Grade B7 has a maximum hardness requirement of Rockwell C35, it is highly unlikely that the tensile strength for a given lot would exceed 150 ksi.

The other concern is the effect that the heat of the molten zinc might have on the strength of the A193 Grade B7 bolts. When quenched and tempered bolts are heated to within 100 degrees of the tempering temperature, you run the risk of altering the strength of the bolts. Since hot-dip galvanizing is performed at 840 degrees Fahrenheit and the minimum tempering temperature of A193 Grade B7 bolts is 1,100 degrees Fahrenheit, there is no risk of altering the mechanical properties of the bolt during the hot-dip galvanizing process.

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