Corrosion Types and Rust-Preventive Coatings

7/28/2019 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

Corrosion Types and Rust-Preventive Coatings

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