HOME  > Surface Finishing Tutorial  > #054 Contact Corrosion of Dissimilar Metals
Surface Finishing Tutorial

#054 Contact Corrosion of Dissimilar Metals

Category : Corrosion - Corrosion Protection
September 3, 2010

Suppose we submerge various metals in 3% salt water solution. When a standard electrode is submerged in this solution and electrical potentials are measured between the metals and the standard electrode, varying potentials can be seen. A series can be established when the potentials are put in an order from high to low. When two metals A and B are picked from this series and the electrical potentials are compared, A would be dubbed as more noble than B if the A potential is higher, or less noble if the A potential is lower than B.

As shown in [Fig. 1], when two metals pieces A and B are submerged and contacted in 3% salt water solution, the metal B will soon corrode. This is because the two metals form a battery circuit in the solution where A becomes a positive pole and B a negative pole, and the electrical current flows from A to B to the solution, then back to A. The corrosion occurs by the electrical current flowing from the metal to the environment. In other words, the less noble metal B would be corroded. The [Table 1] shows an order of electrical potentials of metals in sea water.

As can be seen in the table, carbon steel will exhibit more promoted corrosion in sea water if in contact with metals such as copper and stainless steel that are more noble than the carbon steel. Though carbon steel will corrode by itself in sea water, being in contact with copper and stainless steel results in formation of an electrical circuit and the electrical current flowing as a battery will increase the amount of corrosion. This phenomena is called "Contact Corrosion of Dissimilar Metals".

 [Fig. 1]