Corrosion handbook

26 06/21
3.3 Prevention of galvanic corrosion
Galvanic corrosion (described in section 1.2.6) can be avoided by the right choice
of material combinations. This, however, is not always possible and sometimes
other measures have to be considered. One example is galvanic separation of the
different materials, as shown in Fig. 34.
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Fig. 35: Corrosion potential of various metals in sea water.
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Fig. 34: Conditions for metal combinations without risk of galvanic corrosion.
To minimize galvanic corrosion, the difference in free corrosion potential between
the materials should be as low as possible, and/or the surface ratio of less noble
metal to nobler metal should be very high. The free corrosion potential depends
on the standard potential, a given thermodynamic value for each metal and the
corrosive environment.
Fig. 35 shows the free corrosion potential of various materials when immersed in
seawater. The higher the potential, the nobler is the metal. Contact with a metal
of a lower potential leads to galvanic corrosion of that less noble metal. The
differences in corrosion potentials between Zn and ZM are small enough not to
cause any contact corrosion issues.