Corrosion II / Objectives

1. Define activation polarization and concentration polarization.

Corrosion II / Objectives

1. Define activation polarization and concentration polarization.

2. Explain galvanic corrosion.

Corrosion II / Objectives

1. Define activation polarization and concentration polarization.

2. Explain galvanic corrosion.

3. Describe basic general rules for good corrosion preventing design.

Corrosion II / Objectives

1. Define activation polarization and concentration polarization.

2. Explain galvanic corrosion.

3. Describe basic general rules for good corrosion preventing design.

4. Calculate the cell potential for a redox pair.

Corrosion II: Protection Methods

1. Material Selection

2. Inhibitors

- Remove oxidizing agents

- Interfere with a step in activation

Protection Methods3. Cathodic & Anodic Protection – supply

electrons to structure to be protected

a. External power supply

Protection Methods3. Cathodic & Anodic Protection – supply

electrons to structure to be protected

b. Galvanic coupling (sacrificial anode)

Anode Consumption/Current

Anode Current capacity (lb/A-year)

Mg 18

Zn 25

Al-Sn 16-20

Anode Consumption/Current

Required Currents

Structure Media Velocity Current

Pipeline Fresh water flowing 5-10 mA/ft2

Piling Salt water tidal 6-8 mA/ft2

Reinforcing rod Concrete static 0.1-0.5 mA/ft2

In general: polarize to a potential of – 0.85 volts with

respect to copper/copper sulfate reference electrode.

Protection Methods4. Coatings

A. Metallic – Often dual function

cladding

flame spraying

electro-deposition

hot-dipping

vapor deposition

Protection Methods4. Coatings

B. Organic

Corrosion Protection

1. Weld rather than rivet

Corrosion Protection

1. Weld rather than rivet

2. Containers should be designed for easy draining

Corrosion Protection

1. Weld rather than rivet

2. Containers should be designed for easy draining

3. Design for easy replacement of expected failures

Corrosion Protection

1. Weld rather than rivet

2. Containers should be designed for easy draining

3. Design for easy replacement of expected failures

4. Avoid stresses in corrosion exposed components

Corrosion Protection

1. Weld rather than rivet

2. Containers should be designed for easy draining

3. Design for easy replacement of expected failures

4. Avoid stresses in corrosion exposed components

5. Avoid electrical contact between dissimilar materials

Corrosion Protection

1. Weld rather than rivet

2. Containers should be designed for easy draining

3. Design for easy replacement of expected failures

4. Avoid stresses in corrosion exposed components

5. Avoid electrical contact between dissimilar materials

6. Avoid heterogeneity (metals, vapor spaces, heat, stress)