Page 5 - Corrosion & Harsh Environment Protection

Corrosion & Harsh Environment Protection 5
Galvanic Corrosion
Galvanic corrosion results from contact between
electrochemically dissimilar metals. If you
connect bare copper and aluminum — two
metals commonly used for electrical wiring and
connectors — the aluminum, being the less
noble and more anodic of the two metals, will
be attacked by galvanic corrosion. However,
connectors for code construction are typically
tin plated, which prevents galvanic corrosion,
and tin-plated aluminum connectors that are
UL ® Listed as dual-rated may be used safely
on either aluminum or copper conductors.
The white rust that forms on galvanized steel
is also an example of galvanic corrosion. The
more anodic and less noble zinc applied over
steel during galvanizing is intended to act as a
sacrificial layer to protect the steel underneath.
White rust is evidence that the zinc coating is
serving its purpose; the appearance of red rust
indicates corrosion of the steel.
The Effects of Corrosion
on the Electrical System
Corrosion in electrical systems typically represents only a fraction of the direct costs for
many industries, but it yields a disproportionately large share of the indirect costs. Corrosion
in electrical contacts creates high resistance and unreliable connections, which lead to poor
power quality. In production and manufacturing, where downtime can be very costly, failure of a
relatively inexpensive electrical component that leads to loss of power and control to production
equipment can quickly add up to thousands of dollars in lost productivity. In aircraft, corrosion
that causes electrical system failure can result in loss of life.
Electrical systems, therefore, are a prime area in which an upfront investment in corrosion
protection returns significant cost savings, as well as increased safety and other benefits, over
the long term. This means selecting electrical conduit, fittings, support systems and accessories
in corrosion-resistant materials appropriate for the environment in which they’ll be installed.
The chart above provides a general guide for the end user to choose the most suitable material
for corrosion protection. Compatibility with chemical environment should be thoroughly evaluated
for each installation.
Chemical Compatibility Legend
SUITABILITY DESCRIPTION COMPATIBILITY RATING
Rated for all Fumes, Splash & Liquid L
Rated only for Fumes & Splash S
Rated for Fumes only F
Not Recommended NR
Corrosion Protection Options
CHEMICAL
CATEGORY
CHEMICAL
EXAMPLES
PVC URETHANE
304
STAINLESS
STEEL
316
STAINLESS
STEEL
POLY
CARBONATE CAST IRON BRASS ALUMINUM
COMPATIBILITY RATING
Solvents (excluding
alcohols and aliphatic) Acetone, toluene, ketones, etc. NR NR L L NR L L L
Fuels Jet fuel (alcohol based and
aliphatic solvent based) L L L L L L L L
Plating Solutions Chrome, nickel, copper, brass,
gold, zinc, etc. L F F F F NR NR NR
Salts and Alkaline
Materials
Caustic soda, caustic potash,
alkaline cleaners, etc. L F L L F NR NR NR
Mild Acids Low-concentration hydrochloric,
sulfuric, fruit acids, glycolic, citric, etc. L S L L S NR NR NR
Strong or High-
Purity Acids Nitric, hydrofluoric, etc. S S F F S NR NR NR
Oxidizing Agents Bleach, chlorine,
hydrogen peroxide, etc. L S L L S NR NR NR
Corrosion Protection of Electrical Conduit Systems