Galvanic Corrosion occurs at the junction of dissimilar metals when they are joined together in a suitable electrolyte, such as a moist or aqueous environment, or soils containing moisture.
Galvanic Corrosion | Materials And Corrosion Control
Damage Mechanism |
Galvanic Corrosion Upstream |
Damage Description |
· Occurs at the junction of dissimilar metals when they are joined together in a suitable electrolyte, such as a moist or aqueous environment, or soils containing moisture. |
Affected Materials |
· All metals with the exception of most noble metals |
Control Methodology |
· Avoid contact of different alloys in conductive environments unless the anode/cathode surface area ratio is favorable.
· Rivets, bolts, and fasteners should be of as more noble metal that the material to be fastened. · Use metallic coatings, such as inert barrier, organic or vitreous for the more noble material. · Use nonmetallic inserts, washers, fittings at the joint between the materials to eliminate their electrical connection. · Provide an appropriate corrosion allowance of the more active metal · Avoid dissimilar-metal crevices such as those that occur at threaded connections. Crevices should be sealed preferably by welding or brazing. · Use of corrosion inhibitors can be effective in some aqueous systems. |
Monitoring Techniques |
· Visual Inspection · UT Survey |
Inspection Frequency |
· Annually |
KPIs |
· Corrosion Rate: <3 mpy |
Reference Resources (Standards/GIs/BPs) |
· API RP 571 (DM#53)
· Corrosion Basics – An Introduction,” NACE International |
Atmospheric Corrosion | Materials And Corrosion Control(Opens in a new browser tab)
Sour Water Corrosion | Materials And Corrosion Control(Opens in a new browser tab)
Hydrogen Embrittlement | Materials And Corrosion Control(Opens in a new browser tab)
Notes:
- For galvanic corrosion, three conditions must be met:
-
- Presence of an electrolyte, a fluid that can conduct a current. Moisture or a separate water phase is usually required for the solution to have enough conductivity.
- Two different materials or alloys known as the anode and the cathode, in contact with an electrolyte.
- An electrical connection must exist between the anode and the cathode.
- The more noble material (cathode) is protected by sacrificial corrosion of the more active material (anode). The anode corrodes at a higher rate than it would if it were not connected to the cathode.