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CORROSION
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Introduction
Forms of Corrosiono Uniform Corrosion
o Pitting Corrosion
o Stress Corrosion Cracking
o Crevice Corrosiono Erosion Corrosion
o Intergranular Corrosion
o Hydrogen Damage
o Corrosion Fatigueo Concentration Cell Corrosion
o Fretting Corrosion
o Dealloying
o Corrosion in Concrete
CONTENTS
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Electrochemical cell
The components in an electrochemicalcell
A cell in which electrons and ions can flow by separate pathsbetween two materials, producing a current which, in turn, leadsto corrosion or plating.
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Electrochemical corrosion
Corrosion produced by the development of a current in an electrochemical
cell that removes ions from the material.
CORROSION:
Degradation of metals and is often called RUST
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Car Corrosion
Examples
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Corrosion of Implants
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Portion Of Different Forms Of Corrosion
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Uniform Corrosion
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Pitting Corrosion
Potential(Volts)
Current Densit
A/cmicrit2
a - activation control
Epp
Passive region
Transpassive region
101
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Examples of stress cells
Cold work required to bend a steel bar introduces high residual stressesat the bend, which then is anodic and corrodes.
Stress Corrosion Cracking
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Because grain boundaries have a high energy, they are anodic and corrode.
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River Branching Pattern
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Intergranular SCC Of An Aluminum Aerospace Part
The arrows indicate the primary crack
shown in both pictures
Changes in alloy heat treatment recommended
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Corrosion occurs at the tip of a crevice because of limited access to oxygen.
Crevice Corrosion
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Erosion Corrosion
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In austenitic stainless steel, precipitation of chromium carbide makes the low Craustenite in the grain boundaries anodic.
Intergranular Corrosion
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Exfoliation Corrosion
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Example of microgalvanic cells in two-phase alloys :
In steel, ferrite is anodic to cementite
Galvanic Corrosion
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Hydrogen Damage
Hydrogen Embrittlement of ValveCapscrew Fasteners
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Corrosion Fatigue
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Corrosion fatigue cracks on the I.D. ofa Admiralty brass exchanger tube
Corrosion Fatigue Cracks In AISI1020 Steel In Oil And GasDownhole Service
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Concentration Cell Corrosion
Corrosion occurs beneath a water droplet on a steel plate due to low oxygenconcentration in the water.
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Fretting Corrosion
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Dealloying
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Photomicrograph of a copperdeposit in brass, showing theeffect of dezincification (x50).
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Filiform Corrosion
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Corrosion in Concrete
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THANK YOU FOR YOUR KIND ATTENTION
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References :
1. http://corrosion.ksc.nasa.gov
2. http://www.corrosion-doctors.org
3. http://www.hghouston.com
4. The Science and Engineering of Materials, 4th ed Donald R. AskelandPradeep P. Phuile