Page 299 - Challenges in Corrosion Costs Causes Consequences and Control(2015)

MOTOR VEHICLES 277

painting. The largest and strongest shelters are those constructed using concrete
with steel doors. Because of controlled temperature and humidity, corrosion is not a
problem for the equipment in these shelters.
The cabinets for cellular telephones are made of steel or aluminum. A double
system of galvanizing and painting steel cabinets is applied for corrosion protection.
Surface preparation by grinding and the application of zinc chromate primer is done
prior to galvanizing. There are nearly 4000 cabinets for cellular telephones in use,
and the estimated cost for corrosion is approximately $4 million.
Transmission of the signal is done from antennas mounted at high places achieved
by towers such as tapered steel monopoles. Hot-dipped galvanized steel has been used
in making the towers. Painting of the towers is done for aesthetic reasons and not for
mitigating corrosion. Guided (wire) towers form the second largest group of towers;
they are made from carbon steel and are sandblasted and repainted. The continued
operation of the aging guided towers is a major corrosion concern because corrosion
of the steel members may affect the structural integrity of the towers.
The single major corrosion problem in the telecommunication industry is the
degradation of buried grounding beds and grounding rings around towers and shel-
ters. These copper grounding systems are prone to attack by corrosive soil. Problems
occur when the electrical connection between the grounding bed and the structure
are interrupted or when the corrosion advances to such an extent that the electrical
resistance of the bed becomes too large. To prevent electrical disconnection between
the grounding bed and the structure, the traditional mechanical connection must be
replaced with CADWELD connections (American Welding Society Designation
Termi Welding (TW) Process). Galvanic corrosion because of connection between
two dissimilar metals is another factor related to copper ground beds.
The copper cables used for the telecommunications industry’s electrical supply
are encapsulated in plastic to prevent electrical shorts as well as corrosion protection
of the wires. The following anticorrosion protection measures should be taken.

1. Check galvanization condition
2. Check paint condition.
3. Check the oxidizing condition of the structure, bolting parts, and accessories
4. For masts with guide wires, check oxidization of the wires.

4.21 MOTOR VEHICLES

The most important change in materials over the years has been the transition from
uncoated mild steel to zinc pre-coated steel and other corrosion-resistant metals.
Hot-dip galvanized steels were used in the early stages in the motor vehicle industry.
Hot-dipped galvanized steels were corrosion resistant but had a spangled surface that
resulted in poor appearance after painting. Hot-dipped galvanized steel is still used
on most body parts and interior surface of body outer panels.
From the mid-1980s, most exterior body panels were made of electro-galvanized
steel, which was coated on both sides and served both cosmetic and perforation