Page 230 - Challenges in Corrosion Costs Causes Consequences and Control(2015)

208 CORROSION CONTROL AND PREVENTION

Silicones. Chemically, silicones vary greatly; however, the corrosion-resistant
coatings based on silicones are baked to create an inorganic silicone backbone
that withstands very high temperatures. In applications such as furnaces and
boilers, silicone-based coatings are often the only option.
Fusion-Bonded Epoxies. These are powder-based epoxies applied to hot sub-
strates. The powder on contact with the hot substrate melts followed by a
chemical reaction. On cooling, the solid film is formed. Fusion-bonded epoxies
are widely used in pipelines and concrete rebar applications.
Hydrolysis-Induced Polymerized Coatings: Inorganic Zinc. Zinc metal powder is
dispersed in a zinc silicate binder, and the zinc silicate uses the moisture from
the air to form a cured matrix. The zinc particles behave like individual anodes
to sacrificially protect the steel from corrosion. Many steel bridges and free-
standing structured steel members are coated with inorganic zinc, which has
a characteristic gray-green color. For other applications, the zinc is top-coated
with an epoxy and/or polyurethane to provide an excellent system for corrosion
control. There are also water-based inorganic zinc coatings, which react with
CO to cure.
2
Moisture-Cured Polyurethanes. Some polyurethane coatings form their protective
cured film by reaction with the moisture from the air. The properties of the
resulting film are different from two-component polyurethanes, but contain a
basic urethane side group that classifies them as polyurethanes.

The selection of coating for the different industrial applications is based on the
intended service, application, intended service life, and cost. According to the US
Department of Commerce, Census Bureau, the total amount of organic coating mate-
rial sold in the United States in 1997 was 5.56 billion liters (1.47 billion gallons) at a
cost of $16.56 billion.
The four types of coatings are the following:

1. Architectural coatings
2. Original equipment manufacturers’ coatings
3. Special-purpose coatings
4. Miscellaneous allied paint products

Architectural coatings are applied on new and existing residential, commercial,
institutional, and industrial buildings. Small percentages of these are used as primers
and undercoats and may be classified as corrosion control coatings. Architectural
coatings are water-based and water-thinned. Some data on architectural coatings sold
in 1997 in the United States are as follows in Table 4.2.
This value of $486 million spent on corrosion-related architectural coatings
amounts to nearly 8% of the total $6.2649 billion spent on all architectural coatings
in 1987.
Original Equipment Manufacture (OEM) Coatings are factory-applied to manu-
factured goods as part of the manufacturing process. There is an element of decoration