Page 562 - Corrosion Engineering Principles and Practice

CHAPTER 13

Cathodic Protection

13.1 Cathodic Protection Historical Notes
The first application of cathodic protection (CP) can be traced back to
1824, when Sir Humphrey Davy, in a project financed by the British
Navy, succeeded in protecting copper sheathing* against corrosion
from seawater by the use of iron anodes. This limited use of CP on
copper sheathing perdured and when wooden hulls were replaced by
steel the fitting of zinc protector blocks on the sterns of naval vessels
became traditional. These zinc slabs, although they offered some
protection to steel hulls against local galvanic effects due to the presence
of the bronze propellers, were generally not deemed to be effective.
This lack of efficiency was mainly due to the use of unsuitable zinc
alloys and other factors such as insufficient appreciation of the
technology of cathodic protection and the tendency to reduce the
efficiency of the zinc material to zero by painting their surfaces [1]. From
that early beginning, CP has grown to have many uses in marine and
underground structures, water storage tanks, gas pipelines, oil platform
supports, and many other facilities exposed to corrosive environments.
More recently, CP has been proved to be an effective method for
protecting and reinforcing steel from chloride-induced corrosion.
The CP effectiveness at protecting steel in soils has been
demonstrated in the early 1940s when CP was applied to an old
natural-gas piping network that had been developing leaks at a
rapidly increasing rate, enough so that abandonment was seriously
considered. The observed reduction in the number of leaks immediately
after the CP installation was impressive [2]. A similarly impressive
reduction in the frequency of leaks on a cast iron water main was
achieved at about the same period as shown in Fig. 13.1 [3].
Modern specifications for the cathodic protection of active ocean-
going ships were first described in 1950 [4]. Since that time progress
has been rapid. Considerable advances in cathodic protection
technology have been made, better sacrificial anode materials have

* Cladding with copper of the underwater hull of a ship was used on warships to
prevent attack of the wooden hull by the Teredo worm in tropical waters.
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