Page 205 - Challenges in Corrosion Costs Causes Consequences and Control(2015)

ELECTRONICS 183

The food processing industry uses water for washing, transporting, blanching,
cooking, cooling, and cleaning. In particular, heating and cooling processes require
large amounts of water. Underdeposit corrosion is caused by using water in boilers,
rotary cookers, and hydrostatic sterilizers.
Aluminum alloys are susceptible to underdeposit corrosion. Stainless steels are
also susceptible to underdeposit corrosion as well as deep pitting. Anodic, cathodic,
and filming inhibitors are used to mitigate corrosion (40).
Both aluminum alloys and stainless steels are susceptible to underdeposit corro-
sion and stainless steels are prone to deep pitting. Both anodic and cathodic as well
as filming inhibitors are used to mitigate corrosion.
Biocides such as chlorine dioxide and bromine compounds (oxidizers) are used
for sterilization. The biocides might interfere with the performance of inhibitors and
hence the concentration of biocides must be controlled.
Galvanic corrosion is an accelerated attack between two dissimilar metals that
are in electrical contact and exposed to an electrolyte. In hydrostatic sterilizers, the
flight bars are made of aluminum or stainless steel, and the transport chain is made of
carbon steel, and both are exposed to hot water and steam (40). Aluminum, the less
noble metal, will corrode.
SCC in AISI 304 and AISI 316 steel piping and tanks is a problem in water lines
in brewery applications (41). A common form of SCC occurs at temperatures higher
than ambient in the presence of chlorides. Cracking may occur from the process or
from the outside, for example, under insulation.

3.29 ELECTRONICS

The common electronic components consist of integrated circuits (ICs), printed cir-
cuits (PCs), and connectors and contacts. IC conductors are made from aluminum
alloys, often alloyed with silicon and copper. PC boards such as conductors and con-
nectors are made of copper with solders consisting of lead–tin alloys. Contacts are
made from copper covered with electroplated nickel or gold for improved corrosion
resistance.
Electronic devices are common and are exposed to much harder conditions than
air-conditioned rooms. The small dimensions of a microchip and the silicon-based IC
elements spaced less than 0.2 μm show that the tolerance for corrosion loss is as small
as a picogram (10 −12 g). Submicron dimensions of electronic circuits, high-voltage
gradients, and a fairly high sensitivity to corrosion lead to a unique corrosion-related
issues.
Environmental contaminants can cause failure in electronics. The contaminants
are fine and coarse particles of salts such as chlorides, sulfates of sodium, ammonium,
potassium, magnesium, and calcium. The environmental condition of importance is
relative humidity, which in combination with sulfur dioxide or nitrogen oxide will
cause a great deal of corrosion damage.
According to the Instruments System Automation Society standard there are four
classes as given in Table 3.15.