Page 326 - Challenges in Corrosion Costs Causes Consequences and Control(2015)

304 CORROSION CONTROL AND PREVENTION

is a problem when stainless steels are exposed to the chlorine used in sanitizers and
hydrochloric acid used in cleaning agents and processing liquids. Corrosion products
must be removed before they can contaminate the food products and impede proper
cleaning of surfaces.
Stainless steel consumption in the food processing industry is 370,000 ton or about
15.3% of the overall market for stainless steel of 2.4 million tons/year. The estimated
cost of stainless steel for the food-processing industry was determined to be nearly
$1.8 billion. Aluminum is often used in processing equipment and is less expensive
than stainless steel. Aluminum alloys are usually used in processing, handling, and
packaging of foods and beverages. Nearly one quarter of all aluminum is used in
packaging. High corrosion resistance and the nontoxic nature of aluminum and its
salts and freedom from catalytic effects that cause product discoloration are features
suited to the food packaging industry.
Aluminum cans contain both internal and external coatings, primarily for decora-
tion and protection of product taste. Oxygen is removed before the can is filled with
the product. This prevents oxidation and the potential risk of toxicity.
The shiny appearance, low-weight per volume, favorable mechanical properties
such as material strength, ease of forming, and handling are some favorable features
of aluminum and hence its use in the food industry. In addition, aluminum has a
better corrosion resistance than carbon steel as it readily forms a protective film that
prevents further atmospheric corrosion. Aluminum is also lighter than stainless steel
and hence its use in beverage cans.
Inhibitors are used in severe and harsh environments encountered in rotary cook-
ers and hydrostatic sterilizers. The medium consists of hot water, steam, and cooling
water. A single approach to this problem may not provide the solution. A combina-
tion of anodic, cathodic, and filming inhibitors was selected for corrosion prevention
depending on the water composition and equipment material.
Coatings used in food-processing plants must withstand high-pressure cleaning
and microbial attack. Microbial attack is a major problem in breweries and bever-
age bottling plants. Antimicrobial additives are used to control bacterial activity and
growth. Urethane coatings instead of epoxy coatings are preferred in the food pro-
cessing industry because they are resistant to cleaning compounds.

4.32 CORROSION FORMS IN THE ELECTRONICS INDUSTRY

Anodic corrosion between components of integrated circuits with voltaic gradients
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of the order of 10 –10 v/cm occurs in the case of positively biased aluminum metal-
lization. The combination of electric fields, the atmospheric moisture, and the halide
contamination leads to corrosion attack on aluminum. Gold and copper metallizations
are also prone to corrosion under these conditions.

4.32.1 Cathodic Corrosion
Negatively biased aluminum metallizations, as those with positive bias, can also cor-
rode in the presence of moisture and the high pH produced because of the cathodic