Basics of Corrosion

7/23/2019 Basics of Corrosion

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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:

[email protected]


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Copyright @ Dr. I. H.

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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The destruction of a metallic material by chemical,electrochemical, or metallurgical interaction with theenvironment

What is Corrosion?


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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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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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Silver Bridge connecting Ohio and WestVirginia over the Ohio River

collapsed,1967


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Copyright @ Dr. I. H. ToorADVANCED CORROSION ENGINEERING

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.



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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)



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Cathodic reactions/reduction reaction:


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

-

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

Documents

Basics of Corrosion