JANUARY 31 2003
Advantages and Disadvantages of Galvanic Anode Systems
Economically feasible when installed with the structure.
Very little operation or maintenance requirements (very small chance of
premature failure or breakdown).
Extremely small possibility of overprotection (which may cause coating
Small likelihood of stray current causing interference damage to other
metallic (foreign) structures.
Small driving voltage available (limited potential difference).
Extremely small current available in higher resistivity electrolytes.
Not economically feasible to install or replace anodes on large or
extensive existing structures.
Installation of Galvanic Anodes. Galvanic anodes used to protect buried
structures are normally buried a short distance from the structure and connected to the
structure using an insulated copper wire. Chemical backfill material is almost always
used around sacrificial anodes in soil. The backfill may be installed dry, as a water
slurry, or as part of a prepackaged unit. The special backfill is used to provide a uniform
electrolyte, maintain moisture, and lower the resistance to earth to allow the anode to
produce the required electrical current in an efficient and reliable manner. This backfill
is normally 75 percent gypsum, 20 percent bentonite, and 5 percent sodium sulfate.
Figure 2-20 shows the desired result of the installation of a sacrificial anode with
backfill. It is not normally necessary to remove the consumed anodes.