Page 330 - Challenges in Corrosion Costs Causes Consequences and Control(2015)

308 CORROSION CONTROL AND PREVENTION

4.33.3 Corrosion Control by Coatings and Paint
Liquid coatings (paints), powder coatings, porcelain enamel coatings are used to coat
appliances. Pretreatments that affect the performance level are used for surface clean-
ing and adhesion of coatings. Pretreatment systems consist of iron phosphate and zinc
phosphate. The cost of phosphate pretreatment depends on the following factors: (i)
continuous or intermittent manufacturing; (ii) geometry of the part; (iii) control of
chemical processing.
Liquid coatings are used for refrigerators as they are corrosion resistant and are
of low cost. In laundry washers and dryers, a primer coating is applied on galvanized
steel.
Powder coatings are organic coatings and are used primarily on boiler and furnace
steel sheets. These coatings are applied by depositing a mist of powder on the product
sample in the presence of an electrostatic field, followed by baking. Powder coatings
are more popular and widely recognized because of their advantage with respect to
environmental acceptability, quality of coating, coating requirement, and cost.
Porcelain enamel is used mainly in high-level performance appliances. The porce-
lain enamel coatings are more scratch resistant and heat resistant than the thinner
liquid and powder coatings; however, porcelain enamel is porous. Holidays are some-
times found in the porcelain (glass). Magnesium, zinc, and aluminum anodes are used
in combination with porcelain enamel coatings in water heating systems to act as a
sacrificial anode.

4.34 DEFENSE

Corrosion of military equipment and facilities has been a significant and ongoing
problem. Large yearly costs are incurred to protect these assets from corrosion, affect-
ing procurement, maintenance and operations. The effect of corrosion is a problem
that is becoming more serious as the acquisition of new equipment slows and more
reliance is placed on modifications and upgrades to extend the life of the current
systems. As the intention to operate the aging fleets of aircraft, ships, land combat
vehicles, and submarines continues into the 21st century the potential detrimental
effects of corrosion on the cost of ownership, safety and readiness must be taken
into account. The effects of corrosion of DOD equipment will continue to deteriorate
unless and until new technologies can be used. Within DOD, the annual costs are
very difficult to ascertain; however, from available data obtained from the individ-
ual services (Army, Air Force, Navy, and Marine Corps) the total estimated cost of
corrosion to the DOD is approximately $20 billion for systems and infrastructure.

4.34.1 Army
This major branch of the armed forces owns and operates a range of facilities and
equipment. These include buildings, vehicles, trucks, aircraft, helicopters, missiles,
and weapons storage facilities. Corrosion costs are a significant burden for the Army,
including the cost of maintenance of weapons systems.