Joining dissimilar metals: Some precautions Joining different metals - even different grades of steel - may induce galvanic corrosion. Galvanic corrosion occurs when two metals with different electrolytic potential come into contact in the presence of an electrolyte such as water. The metals form a galvanic couple. In the couple, the anode corrodes faster than it would alone, while the cathode corrodes at a slower rate than it does alone. The cathode is the ‘noble’ metal: the one with the highest electrolytic potential. Metals frequently found in the building industry are ranked from noblest to least noble as follows: Stainless steel > Weathering or carbon steel > Galvanised steel > Aluminium The galvanic corrosion rate depends on the ratio of cathode area to anode area. The following overview summarises the risks of pairing weathering steels with the other metals commonly found in building and construction applications.
• Stainless steel and weathering steels
• Galvanised steel and weathering steels
• Carbon steel and weathering steels Risk
• Galvanic corrosion of the weathering steels. There is usually no significant galvanic corrosion from stainless steel nuts and bolts as the cathode area remains small.
• Galvanic corrosion of the galvanised steel.
• No significant risk of galvanic corrosion if their chemical composition remains close.