Page 181 - Challenges in Corrosion Costs Causes Consequences and Control(2015)

TELECOMMUNICATIONS 159

The fiberglass shelters consist of a foam core with two skins of fiber-reinforced
plastic. The fiberglass exterior is corrosion-resistant and requires low maintenance.
The price of fiberglass shelters is higher than the corresponding aluminum and carbon
steel shelters.
The largest and strongest shelters are those constructed using concrete. These are
usually secured shelters with steel doors. All concrete shelters have temperature and
humidity controlled environments; therefore, corrosion is not an issue for the equip-
ment placed in concrete shelters.
Degradation of equipment because of heat and humidity is possible for cellular
telephone equipment. A refrigerator-sized cabinet may be placed near the antenna.
The cabinets are made of steel or aluminum. Corrosion protection is applied for cos-
metic purposes as this type of technology generally becomes obsolete and is replaced
before corrosion becomes a structural issue. In some cases, a double system of
galvanizing and painting is applied for corrosion protection of steel cabinets. Surface
preparation through grinding and application of zinc chromate primer is essential for
galvanizing. The outdoor cabinets are built more robustly, that is, of thicker gauge
material than the indoor cabinets and can cost twice as much. Cabinets priced in the
range $1000–10,000 have an estimated corrosion cost of $200–2000. The estimated
total corrosion costs of the cabinets amount to $4 million (4000 × 5000 × 0.2).
A large majority of telecommunication towers are of the self-supporting type.
These have been constructed since the early 1960s and are made from hot-dipped
galvanized steel. For about 40 years, there is hardly any corrosion.
Guided (wire) towers belong to the second largest group. These are made from
carbon steel and were sandblasted and repainted regularly. The continued operation
of these aging guided towers is a major corrosion concern because corrosion may
affect the structural integrity of the towers.
The single largest corrosion problem in the telecommunications industry is the
degradation of buried grounding beds and grounding rings around towers and shelters.
The copper grounding systems are consumed over time by corrosive soil. Problems
occur when the electrical connection between the grounding bed and the structure is
interrupted or when the corrosion advances to the extent that the electrical resistance
of the bed becomes too great. To prevent electrical disconnection between the
grounding and the structure, the traditional mechanical connections must be replaced
with CADWELD connections (American Welding Society (AWS) designation:
Termit welding (TW) process). Galvanic corrosion because of connections between
dissimilar metals is another factor related to copper ground beds.
The copper cables used in the telecommunications industry’s electrical supply are
encapsulated in plastic to prevent electrical shorts. The plastic cover also provides
corrosion protection to the wires. The following anticorrosion protection measures
are recommended:
1. Check galvanization condition.
2. Check paint condition.
3. Check oxidization of the structure, bolting parts, and accessories.
4. Check for masts with guide wires and oxidation of wires.