Ministry of Transportation Ontario has been using weathering steel for bridge girders since1968. The main advantage of using weathering steel is that, under normal weathering cycles, it will form a tough outer oxide layer referred to as ‘patina’ that will protect the steel from unabated corrosion. However, recently the ministry has observed that the patina formed on girders over the driving lanes is de-bonding from the parent steel material and often has to be physically removed before it becomes a safety hazard. In contrast, other locations of the girders (between the ends of girders and the driving lanes) exhibited a more stable patina.