Corrosion Types and Rust-Preventive Coatings
Transcript of Corrosion Types and Rust-Preventive Coatings
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Corrosion Types and
Rust-PreventiveCoatings
Preparing byEfekan BakIR
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Contents
Definition of Corrosion
Types of Corrosion
Definition of Rust
Prevention of Rust
Rust-Preventive Coatings
Conclusion References
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What is the Corrosion ?
Corrosion is the gradual destruction of material, usuallymetals, by chemical reaction with its environment. In the most
common use of the word, this means electrochemical oxidation of
metals in reaction with an oxidant such as oxygen. Rusting, the
formation of iron oxides, is a well-known example of
electrochemical corrosion.
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This type of damage typically produces oxide or salt of the
original metal. Corrosion can also occur in materials other thanmetals, such as ceramics or polymers, although in this context, the
term degradation is more common. any types and causes of
corrosion and depending on a particular scientist's or corrosion
engineer's tendencies to look upon the subject more broadly or
narrowly there is no clear and exact total for the number ofcorrosion types. Most corrosion experts however can agree on the
basic varieties of corrosion listed and described.
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As a result, methods to reduce the activity of the exposedsurface, such as passivation and chromate conversion, can increase
a material's corrosion resistance. However, some corrosion
mechanisms are less visible and less predictable.
Example of Corrosion
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Types of Corrosion
Corrosion comes in many different forms and can be classified
by the cause of the chemical deterioration of a metal. Listed beloware 8 common types of corrosion:
Galvanic Corrosion, Environmental Cracking, Erosion
Corrosion , Intergranular corrosion, De-Alloying, Fretting corrosion,
Pitting Corrosion,High-Temperature Corrosion.
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Fretting corrosion
Fretting corrosion refers to corrosion damage at the asperities
of contact surfaces. This damage is induced under load and in the
presence of repeated relative surface motion, as induced for
example by vibration. Pits or grooves and oxide debris characterize
this damage, typically found in machinery, bolted assemblies and
ball or roller bearings. Contact surfaces exposed to vibration during
transportation are exposed to the risk of fretting corrosion.
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Galvanic Corrosion
When dissimilar metals are connected in the presence of an
electrolyte a galvanic corrosion reaction occurs. Both the presenceof an electrolyte solution and a bi-metallic coupling is required for
this type of corrosion to occur.
Example of Galvanic Corrosion
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Environmental Cracking
Environmental cracking is a corrosion process that can result
from a combination of environmental conditions affecting the
metal. Chemical, temperature and stress-related conditions canresult in the following types of environmental corrosion:
Stress Corrosion Cracking (SCC)
Corrosion fatigue
Hydrogen-induced cracking Liquid metal embrittlement
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Erosion Corrosion
Erosion corrosion is an acceleration in the rate of corrosion
attack in metal due to the relative motion of a corrosive fluid and a
metal surface. The increased turbulence caused by pitting on the
internal surfaces of a tube can result in rapidly increasing erosion
rates and eventually a leak. Erosion corrosion can also be
aggravated by faulty workmanship. For example, burrs left at cut
tube ends can upset smooth water flow, cause localized turbulence
and high flow velocities, resulting in erosion corrosion. A
combination of erosion and corrosion can lead to extremely high
pitting rates.
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Intergranular corrosion
The microstructure of metals and alloys is made up of grains,
separated by grain boundaries. Intergranular corrosion is localized
attack along the grain boundaries, or immediately adjacent to grain
boundaries, while the bulk of the grains remain largely
unaffected. This form of corrosion is usually associated with
chemical segregation effects (impurities have a tendency to be
enriched at grain boundaries) or specific phases precipitated on the
grain boundaries. Such precipitation can produce zones of reduced
corrosion resistance in the immediate vicinity.
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De-Alloying
Dealloying or selective leaching refers to the selective removal
of one element from an alloy by corrosion processes. A common
example is the dezincification of unstabilized brass, whereby a
weakened, porous copper structure is produced.
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High-Temperature Corrosion
Under very high temperature metals need only the presence
of oxygen or other oxidizing gases to corrode. This type of corrosionis referred to as high temperature oxidation, scaling or tarnishing
and requires neither moisture nor dissolved electrolytes (salts,
acids) to proceed.
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Definition of Rust
Rust is another name for iron oxide, which occurs when iron or
an alloy that contains iron, like steel, is exposed to oxygen and
moisture for a long period of time. Over time, the oxygen combineswith the metal at an atomic level, forming a new compound called
an oxide and weakening the bonds of the metal itself. Although
some people refer to rust generally as "oxidation," that term is
much more general; although rust forms when iron undergoes
oxidation, not all oxidation forms rust. Only iron or alloys thatcontain iron can rust, but other metals can corrode in similar ways.
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Prevention of RustBecause of the widespread use and importance of iron and steelproducts, the prevention or slowing of rust is the basis of major
economic activities in a number of specialized technologies. A briefoverview of methods is presented here; for detailed coverage, seethe cross-referenced articles.
Rust is permeable to air and water, therefore the interior metalliciron beneath a rust layer continues to corrode. Rust prevention thusrequires coatings that preclude rust formation.
There are kinds 7 of prevention
of rust : Rust-resistant alloys, Galvanization,
Cathodic protection, Coatings and painting,
Bluing, Inhibitors, Humidity control
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Rust-Preventive Coatings
Stop rust before it starts with water based rust preventive dip
coating. In just one coat, corrosion control is achieved by using
water based rust proofing that contains a balanced rust inhibitor
system. This rust prevention product is a cream colored liquid when
applied but upon drying turns to a translucent light brown dry to
the touch wax coating. Dyes can be added if color coding is desired.
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This corrosion resistant coatings will not transfer, abrade or
run under normal handling. Therefore neither the floor of your
packaging area, storage bins or the packages you send to yourcustomers will be oil stained and messy. Some materials active rust
inhibitor system neutralizes metal corrosion normally attributed to
fingerprints from parts handling. This protective coating and its rust
inhibitor system are compatible with lube oil so they do not need to
be removed from internal parts before assembly.
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Rust formation can be controlled with coatings, such as paint,
lacquer, or varnish that isolate the iron from the environment. Large
structures with enclosed box sections, such as ships and modern
automobiles, often have a wax-based product (technically aslushing oil) injected into these sections. Such treatments usually
also contain rust inhibitors. Covering steel with concrete can
provide some protection to steel because of the alkaline pH
environment at the steel-concrete interface. However rusting of
steel in concrete can still be a problem, since expanding rust can
fracture or slowly "explode" concrete from within.
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Conclusion
Corrosion comes in many different forms and can be classified
by the cause of the chemical deterioration of a metal. However,some corrosion mechanisms are less visible and less predictable.
Rusting, the formation of iron oxides, is an example of
electrochemical corrosion. Rust-Preventive Coatings is a well-known
method for preventing the rust.
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References
http://www.corrosion-doctors.org/pict-type.htm
http://www.counteractrust.com/types%20of%20corrosion.htm http://metals.about.com/od/metallurgy/a/Types-Of-Corrosion.htm
http://www.corrosionist.com/Corrosion_Types_Uniform_Corrosion.
htm
http://en.wikipedia.org/wiki/Corrosion
http://www.tis-gdv.de/tis_e/misc/korro.htm
http://www.authorstream.com/Presentation/hitiboy-410714-
corrosion-hiti-science-technology-ppt-powerpoint/
http://www.sanchem.com/safegard_uses.html
http://en.wikipedia.org/wiki/Rust#Prevention
http://www.metaltreaters.net/rust-preventives.html