Page 285 - Challenges in Corrosion Costs Causes Consequences and Control(2015)

AIRPORTS 263

4.15.5 Underground Storage Tanks – Cathodic Protection
CP depends on the reversal of electrochemical current that occurs during corro-
sion process. The two CP systems used are: (i) sacrificial anode systems and (ii)
impressed-current systems.
The sacrificial anode system consists of burial of anodes in the electrical proximity
of the tank. The anodes are made of magnesium or aluminum, which are less noble
than the steel tank. This enables the flow of current from the sacrificial anode (Al
or Mg) to the cathodic steel tank. Over a period of time, the anodes are consumed
and hence replaced with new anodes in order for continued corrosion protection of
the tank.
The second system is based on the application of impressed current that is forced
through anodes to the protected structure such as the tank by a current source of
sufficient potential. Properly designed CP systems that are well maintained and oper-
ate at the correct current density are a proven method of protecting tanks from the
corrosive effects of contact with corrosive soils. In addition to protection of under-
ground tanks, CP is also useful for aboveground double-bottom tanks and for internal
corrosion protection.

4.15.6 Polymer Tanks
These are used when avoiding maintenance problems. This involves use of a
corrosion-resistant material. High-density polyethylene (HDPE) is commonly used
for chemical storage. For storage at higher temperatures, fiberglass reinforced tanks
∘
made with vinylester or epoxy can be used. For temperatures greater than 200 C
metal storage tanks are used.

4.16 AIRPORTS

A typical airport infrastructure is relatively complex, and the components that might
be subject to corrosion are the following:
1. Natural gas distribution system
2. Jet fuel storage and distribution system
3. Deicing storage and distribution system
4. Water distribution systems
5. Vehicle fueling systems
6. Natural gas feeders
7. Dry fire lines
8. Parking garages
9. Runways and runway lighting

In general, each of these infrastructure components is owned and/or operated
by different organizations and companies. Given the above, airports do not have