basics of corrosion
TRANSCRIPT
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WELCOME TO ME 575
(Advanced Corrosion Engineering)
(6.30~7.45 PM / MW)
Instructor: Dr. Ihsan-Ul-Haq Toor
Office: 63-358/Phone:7493
Office Hours: 12.30~1.30 (UTR)
or appointment via E-mail:
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ToorADVANCED CORROSION ENGINEERING
Lecture Contents
Why Study Corrosion?
Economic impact of corrosion?
Environmental factors for corrosion?
Corrosion Basics (what, why and how)
Electrochemical nature of corrosion
Forms of Corrosion
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ToorADVANCED CORROSION ENGINEERING
The destruction of a metallic material by chemical,electrochemical, or metallurgical interaction with theenvironment
What is Corrosion?
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ToorADVANCED CORROSION ENGINEERING
Why Study Corrosion?
Almost every engineer/scientist will at one time or another be
exposed to MATERIALS (design, synthesis, application etc)
Examples: gear, building, oil refinery component, or an integrated
circuit chip, oil and gas etc, desalination, power, nuclear, etc
Metals are the most abundant and each has different
properties (80 known elements are metals)
These different elements have been combined to develop
roughly > 40000 different alloys and still going on
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ToorADVANCED CORROSION ENGINEERING
Importance of this subject
?Human life and safety
ALOHA incident 1998/ Pilot managed to land the plane on the island ofMaui, Hawaii (one flight attendant was died)
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ToorADVANCED CORROSION ENGINEERING
Silver Bridge connecting Ohio and WestVirginia over the Ohio River
collapsed,1967
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Importance of this subject?
The oil-drilling rig that burned for 36 hours in the Gulf of Mexico sankThursday, April 22, 2010/ 11 ppl died and major oil spill occured
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3~5% of GNP of Developd country
Economic Impact of Corrosion
Importance of this subject?
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Direct Cost:
Capital costs cost of replacement parts, e.g., automobile mufflers, water lines, hot
water heaters, sheet metal roofs.
Control costs maintenance, repair, painting.
Design costs extra cost of using corrosion-resistant alloys, protective coatings,
corrosion inhibitors.
Indirect loss
Plant shutdown.
Loss of product.
Loss of efficiency
Contamination.
Economic Impact of Corrosion
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Economic Impact of Corrosion
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Materials & Environment
Corrosion is an interdisciplinary area
embracing chemistry, materials science,
and mechanics
The study of aqueous corrosion
processes involves the intersection ofchemistry and materials science.
But the science of mechanics must be
added to understand mechanically
assisted corrosion processes (SCC, HIC,
FAC, CF)
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Defining the environment is very important
Some environments are more corrosive than others,
but there can be exceptions
Moist air is more corrosive than dry air
Hot water is more corrosive than cold water
Polluted air is more corrosive than clean air
Acids are more corrosive than bases (alkalies) to steels
Salt water is more corrosive than fresh water
No corrosion will occur in a vacuum, even at very high temperatures
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Challenge for Corrosion Engineers
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1. The development ofprotective surface treatmentsand corrosion inhibitors to replace inorganic chromates,
whichare environmentally objectionable.
2. An improved conservation of materials through the development of corrosion-resistant surface alloys which
confine alloying elements to the surface rather than employing conventionalbulk alloying.
3. The formulation of a newgeneration of stainless steels containingreplacements for chromium and other
critical metals.
4. An improved understandingof passivityso as to use our fundamental knowledge to guide the development
of alloys having improved corrosion resistance.
5. Understanding the mechanism of thebreakdown of passive oxide filmsby chloride ions and subsequent
pitting of the underlying metal.
6. The development of smartorganic coatingswhich candetect a break in thecoating andautomatically
dispatch an organicmolecule to the required site to both heal the coating and inhibit corrosion.
7. The ability to predict the lifetime of metals and components from short-term experimental corrosion data.
Challenge for Corrosion Engineers
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Why Corrosion?
Corrosion is natural process and it returns the metal to its oxidized state or combined state in the form of
chemical compounds that are simi lar to the minerals from wh ich they are extracted
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Corrosion process requires a complete corrosion cell/circuit, which
includes;
How Corrosion Takes Place?
Electrochemical Cell
1. Anode2. Cathode
3. Electrolyte
4. Electrical path
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Anodic reactions/Oxidation reaction takes place at anode
(generation of electrons)
General Reaction (metal oxidation)
MMn+ + ne- (gives off electrons))
Zn Zn2+ + 2e- (Zn corrosion)
Fe Fe2+ + 2e- (Fe corrosion)
Al Al3+ + 3e- (Al corrosion)Fe2+ Fe3+ + e- (Ferrous ion oxidation)
How Corrosion Takes Place?
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Cathodic reactions/reduction reaction:
How Corrosion Takes Place?
O2 + 2H2O + 4e- 4OH- (oxygen reduction in water/bases)
O2 + 4H+ + 4e- 2H2O (oxygen reduction in acids)
2H2O + 2e- H2 + 2OH- (hydrogen evolution in water/bases)
2H+ + 2e- H2 (hydrogen evolution in acids)
Cu
2+
+ 2e
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Cu (metal deposition=>copper plating)
Fe3+ + e- Fe2+ (metal/ferric ion reduction)
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Consider what happens when Zn is placed in aerated dilute HCl solution
(acidic solution):
Electrochemical nature of Corrosion
CR or ?
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ActivePassive
Behavior of Active and Passive metals
Corrosion of Metals
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Corrosion Types
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Corrosion Types
SCC in DSS