Weathering Steel Next to Other Metals: Avoiding Galvanic Corrosion Problems

Weathering steel builds its own protective patina in wet-dry cycles, so most corrosion questions stop being a problem once the surface matures. The exceptions appear where another metal touches it. In a wet joint, two different metals form a galvanic couple, and the less noble one gives up material to protect the other.

Which pairings cause trouble.

Weathering steel sits in the middle of the galvanic series. Zinc is less noble, so galvanized fasteners, flashings and drip edges in constant contact with wet weathering steel corrode noticeably faster than they would alone, losing their sacrificial layer years earlier. Stainless steel and copper are more noble; here the weathering steel becomes the anode, so its surface can pit or stain exactly at the contact line, even though the rest of the panel looks healthy.

Detailing that solves it.

One rule covers most cases.

Either separate the metals with an insulating layer, or make sure the contact point never stays wet. Occasional rain on a bolted connection is harmless; a trapped drip line is where every bimetallic problem starts. Detail the joint so water leaves it quickly, and the patina will handle the rest.

We supply weathering steel plates, coils and sections for facades, bridges and landscape structures, and are glad to review connection details before you order.