1. Corrosion II / Objectives 1.Define activation polarization and concentration polarization.

2. Corrosion II / Objectives 1.Define activation polarization and concentration polarization. 2.Explain galvanic corrosion.

3. 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. 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.

5. Corrosion II: Protection Methods 1.Material Selection 2.Inhibitors - Remove oxidizing agents - Interfere with a step in activation

6. Protection Methods 3. Cathodic & Anodic Protection – supply electrons to structure to be protected a. External power supply

7. Protection Methods 3.Cathodic & Anodic Protection – supply electrons to structure to be protected b. Galvanic coupling (sacrificial anode)

8. Anode Consumption/Current Anode Current capacity (lb/A-year) Mg18 Zn25 Al-Sn16-20

9. Anode Consumption/Current Required Currents Structure MediaVelocityCurrent Pipeline Fresh water flowing 5-10 mA/ft 2 Piling Salt water tidal 6-8 mA/ft 2 Reinforcing rod Concretestatic 0.1-0.5 mA/ft 2 In general: polarize to a potential of – 0.85 volts with respect to copper/copper sulfate reference electrode.

10. Protection Methods 4. Coatings A. Metallic – Often dual function cladding flame spraying electro-deposition hot-dipping vapor deposition

11. Protection Methods 4. Coatings B. Organic

12. Corrosion Protection 1.Weld rather than rivet

13. Corrosion Protection 1.Weld rather than rivet 2.Containers should be designed for easy draining

14. Corrosion Protection 1.Weld rather than rivet 2.Containers should be designed for easy draining 3.Design for easy replacement of expected failures

15. 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

16. 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

17. 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)