Corrosion – Types, Prevention, and Case Studies-GRK

 Seminar Topic: Corrosion – Types, Prevention, and Case Studies

Course Relevance: Mechanical Engineering / Materials Engineering / Manufacturing Technology

1. Introduction to Corrosion

Definition: Corrosion is the gradual deterioration of a metal due to chemical or electrochemical reactions with its surrounding environment.

Simple Example: Rusting of iron when exposed to air and moisture.

Why Corrosion is Important

• Reduces strength of components

• Causes machine failures

• Increases maintenance cost

• Leads to safety hazards

• Reduces service life of structures

2. Basic Mechanism of Corrosion

Electrochemical Corrosion Process

In the presence of water (electrolyte), small anodic and cathodic regions form on the metal surface.

Anode

Metal dissolves

Fe → Fe²⁺ + 2e⁻

Electrolyte

Water / Moisture

Conducts ions between regions

Cathode

Oxygen reacts

O₂ + H₂O + e⁻ → OH⁻

3. Types of Corrosion

3.1 Uniform Corrosion

Description: Corrosion occurs evenly over the entire surface.

Examples:

• Rusting of steel sheets

• Weathering of iron structures

Characteristics:

• Easy to detect

• Predictable material loss

3.2 Galvanic Corrosion

Description: Occurs when two dissimilar metals are electrically connected in an electrolyte.

Anode (Corrodes)	Cathode (Protected)
Steel	Copper
Zinc	Steel

Example: Steel bolt connected to a copper plate.

3.3 Pitting Corrosion

Description: Small localized holes or pits form on the metal surface.

Common in:

• Stainless steel

• Aluminum alloys

Danger: Difficult to detect but can cause sudden failure.

3.4 Crevice Corrosion

Description: Occurs in narrow gaps where oxygen concentration becomes low.

Locations:

• Bolted joints

• Gaskets

• Lap joints

3.5 Intergranular Corrosion

Description: Corrosion occurs along grain boundaries.

Common in: Improperly heat-treated stainless steel.

3.6 Stress Corrosion Cracking (SCC)

Description: Combination of tensile stress + corrosive environment.

Examples:

• Boilers

• Pipelines

• Aerospace components

3.7 Erosion Corrosion

Description: Corrosion accelerated by fast-moving fluids.

Common in:

• Pumps

• Turbines

• Pipe bends

4. Factors Affecting Corrosion

Factor	Effect
Moisture	Increases corrosion
Oxygen	Promotes oxidation
Salt	Accelerates corrosion
Temperature	Increases reaction rate
pH	Acidic solutions increase corrosion
Stress	May cause cracking

5. Prevention of Corrosion

5.1 Material Selection

Use corrosion-resistant materials such as:

• Stainless Steel

• Aluminum Alloys

• Titanium

• Brass

5.2 Protective Coatings

Method	Example
Painting	Steel structures
Galvanizing	Zinc coating on steel
Electroplating	Chrome plating
Powder coating	Machine parts

5.3 Cathodic Protection

Principle: Make the structure act as a cathode.

Methods:

• Sacrificial anode (Zn, Mg)

• Impressed current system

Used in:

• Pipelines

• Ship hulls

• Underground tanks

5.4 Design Modification

Good design practices:

• Avoid water traps

• Provide drainage

• Avoid crevices

• Use welded joints instead of lap joints

5.5 Corrosion Inhibitors

Chemicals added to reduce corrosion.

Applications:

• Cooling water systems

• Boilers

• Oil & gas pipelines

6. Case Studies

Case Study 1: Rusting of the Howrah Bridge (India)

Problem: Continuous exposure to humid and polluted environment caused corrosion of steel members.

Solution:

• Regular inspection

• Protective painting

• Replacement of damaged members

Learning: Maintenance is essential for large steel structures.

Case Study 2: Pipeline Corrosion in Oil & Gas Industry

Problem: Internal corrosion due to water, CO₂, and H₂S.

Consequences:

• Leakage

• Environmental damage

• Economic loss

Prevention:

• Internal coatings

• Corrosion inhibitors

• Cathodic protection

Case Study 3: Aircraft Aluminum Corrosion

Problem: Pitting and intergranular corrosion in aluminum alloys.

Prevention:

• Protective coatings

• Controlled environment

• Regular inspection

Importance: Aircraft safety depends heavily on corrosion control.

7. Economic Impact of Corrosion

Corrosion causes enormous financial losses worldwide.

Estimated Global Cost

3–4% of GDP

Infrastructure repair

Equipment replacement

Production shutdown

Accident prevention

8. Modern Trends in Corrosion Control

• Nanocoatings

• Smart coatings

• Self-healing materials

• Corrosion monitoring sensors

• Advanced stainless steels

9. Conclusion

“Corrosion cannot be completely eliminated, but it can be effectively controlled through proper material selection, protective coatings, good design, and regular maintenance.”

10. Viva Questions

• Define corrosion.

• What is galvanic corrosion?

• Differentiate between pitting and uniform corrosion.

• What is cathodic protection?

• Why is stainless steel corrosion-resistant?

• What are corrosion inhibitors?

• Explain stress corrosion cracking.

• State two industrial applications of cathodic protection.

• What are the effects of corrosion?

• Explain any one corrosion case study.

Short Seminar Summary (2-Minute)

Corrosion is the deterioration of metals due to environmental reactions. Major types include uniform, galvanic, pitting, crevice, intergranular, stress corrosion cracking, and erosion corrosion. Corrosion can be prevented by selecting suitable materials, applying protective coatings, using cathodic protection, improving design, and adding corrosion inhibitors. Real-world examples include bridges, pipelines, and aircraft structures. Effective corrosion control improves safety, reliability, and service life of engineering components.