Cathodic Protection
The table below shows the
galvanic series of metals and alloys
arranged in decreasing order of electrical
activity. Metals toward the top of the
table, often referred to as “less noble”
metals, have a greater tendency to lose
electrons than the more noble metals at the
bottom of the table. Thus, metals higher in
the series provide cathodic (or sacrificial)
protection to those metals below them.
Because zinc is anodic to
steel, the galvanized coating provides
cathodic protection to exposed steel. When
zinc and steel are connected in the presence
of an electrolyte, the zinc is slowly
consumed while the steel is protected.
Zinc’s sacrificial action offers protection
where small areas of steel are exposed, such
as cut edges, drill-holes, scratches, or as
the result of severe surface abrasion.
Cathodic protection of the steel from
corrosion continues until all the zinc in
the immediate area is consumed.
To learn more about cathodic
protection
view this paper by Gregory Zhang.
Figure 1 below shows how
corrosion will begin and immediately
progress at a scratch or gap in a
paint/epoxy coating. Figure 2 shows how
corrosion will be prevented at a scratch or
gap in a zinc coating.
Figure 1
Figure 2
