ogf aim course 3 module 1

7/30/2019 OGF AIM Course 3 Module 1

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MODULE 1CORROSION LANGUAGE

AND TERMINOLOGY


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Cost of Corrosion

Fundamental Chemistry

Cells and electrochemistry

Forms of Corrosion

OVERVIEW


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WHAT IS CORROSION?

Spontaneous , exothermic reaction of a metal with its

environment to form compounds.

The metal reverts back to the natural form found in nature.

In order to made metals (smelting, or reduction), chemical

energy is given to the ore material to make it a metal.

Thus metals contain more energy than rust.

The rusting process releases this energy back to the

environment.


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COST OF CORROSION

Annually, between 3~ 6% of GDP.

The US spends approx. 276 Billion annually (1999 figures).

( equal to the DOD budget!)

In the UAE the GDP in 2008 was 792 Billion Dhs. Cost of

corrosion was therefore between 24 and 48 Billion Dhs. But, of these costs, between 20 and 40% is preventable, using

current technology and best practices.

The UAE economy could therefore save between 5 and 10

Billion Dhs annually if best practices were implemented.

Current world annual cost of corrosion: $3.3 Trillion.


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DIRECT VERSUS INDIRECT COSTS

Direct costs:

Replacement of infrastructure.

Product loss.

Plant shutdown.

Corrosion resistant materials. Cathodic Protection.

Coatings.

Inhibitors.

Manpower.

Inspection. Loss of life/ injury.

Loss of reliability (redundancy).

Indirect costs:

Loss of consumerconfidence.

Disruption to society.

Litigation. Fines.

Increased regulation.

Failure analysis.

Research anddevelopment.

Education and training.


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FORMS OF CORROSION

Uniform

Galvanic

Dealloying

Pitting

Crevice

Stress Corrosion

Cracking Intergranular

Corrosion

Erosion Corrosion

Fretting

Microbiological

CorrosionHigh Temperature

Corrosion

Hydrogen Damage

Sulfide StressCorrosion


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CORROSION

FUNDAMENTALSChemistry


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ATOMS AND IONS

Elements are unique types of atoms.

Nucleus containing:

Protons

Neutrons

Orbiting electrons

Listed in the Periodic Table of elements

Chemistry involves adding and subtracting electrons to atoms.

Since electrons are charged, the resulting IONS have

electrical charge.


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THE PERIODIC TABLE OF THE ELEMENTS


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IONS

However, electrons are negatively charged, so removing

electrons makes the ion positively charged

Compounds are a positive ion and a negative ion held

together by electrostatic attraction. Overall the compound is

neutral. Fe3+ + 3Cl- FeCl3

In water, some ions are soluble and are surrounded by a

solvation sphere of water molecules. State symbol: ( aq)


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CHEMICAL REACTIONS AND SPONTANEITY

A chemical reaction may be spontaneous or non spontaneous.

Spontaneous reactions are exothermic.

Reverse the direction of reaction and change the energy

changes:

Spontaneous, exothermic

Fe (s) Fe2+(aq) + 2 e-

Non spontaneous, endothermic


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CORROSION

FUNDAMENTALS

2

Electroche

mistry


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ELECTROCHEMISTRY

Corrosion is electrochemical.

The transfer of electrons from one substance to another.

Spontaneous chemical react ions liberate energy. This energy

can be used to push electrons around a circuit, giving them a

voltage.

The materials proper ties change:

Fe (s) Fe2+ (aq) + 2 e-

In order for corrosion we need 4 things:

Anode

Cathode

Electrical path

electrolyte


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ELECTRODES NEEDED FOR CORROSION

ANODE CATHODE

Oxidation (loss of

electrons).

Corrosion.

Source of electrons.

More Active metals.

Low [O2].

Reduction (gain of

electrons).

Protection from

corrosion.

Consumption of

electrons.

More Noble metal.

High [O2].


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CONDUCTIVE PATHS NEEDED FOR

CORROSION

Metallic path Electrolytic path

Allows the movement of

ELECTRONS.

From the anode to the

cathode.

Must be made of metal.

REAL CURRENT.

Allows the movement of

IONS.

Positive ions flow from

the anode.

Must be an electrolyte

(water or a molten

salt).

CONVENTIONAL

CURRENT.


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ogf aim course 3 module 1

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