Corrosion Prevention

1. Corrosion Prevention
Chapter 13
Instructor:
Dr. Md. Easir Arafat Khan
Associate Professor
Department of Chemical Engineering, BUET, Dhaka-
1000
July 2022
ChE 409

2. How to prevent or minimize corrosion?
• changing the metallic material to another one
• altering the environment making it less aggressive
• separating the metallic material from the environment
• changing the electrode potential of the metal/alloy
• appropriate design at the design stage

3. Methods of corrosion protections
Design Change
of Metal
Change of
Environment
Change of
Electrode
potential
Use of
Coating
Cathodic
Protection
Anodic
Protection

4. Methods of corrosion protections
Design Change
of Metal
Change of
Environment
Change of
Electrode
potential
Use of
Coating
Change of composition
change of structure
Elimination of stress
Introduction of surface compressive
stress

5. Methods of corrosion protections
Design Change
of Metal
Change of
Environment
Change of
Electrode
potential
Use of
Coating
Removal of
corrosives
Change in Operating
Conditions
Inhibitors
Removal of O2
Moisture Removal
Purification/salt removal

6. Methods of corrosion protections
Design Change
of Metal
Change of
Environment
Change of
Electrode
potential
Use of
Coating
Removal of
corrosives
Change in Operating
Conditions
Inhibitors
Chemical passivators
Adsorption passivators
Film forming passivators
Vapor phase passivators

7. Methods of corrosion protections
Design Change
of Metal
Change of
Environment
Change of
Electrode
potential
Use of
Coating
Removal of
corrosives
Change in Operating
Conditions
Inhibitors
pH
Temperature
Velocity

8. Factors affecting service life
Factors affecting the service life
Environmental factors affecting service
life

9. Corrosion prevention at the design stage:
Points to be considered
• Environment: corrosiveness
• Available fabrication and machining facilities
• Temperature, pressure and velocity of the environment
• Expected life of the component/equipment.
• Accessibility for preventive maintenance.
• Expected form of corrosion
• Is product contamination a factor?

10. Bimetallic corrosion

11. Avoid Crevices

12. Welding vs rivets??
• Welding is preferable to rivets.
• Riveted joints provide sites for crevice corrosion.

13. Flowing water
system

14. Accessibility for Maintenance

15. Suitability of design for uniform coating

16. Providing drain holes

17. Design for liquid containers

18. Drainage

19. The Most useful “Design Rule”
• The most useful rule is to avoid heterogeneity. At the design stage,
attempts should be made to make all conditions as uniform as
practicable throughout the whole system. Dissimilar metals, uneven
stress distribution, uneven heat distribution, vapor spaces, etc.
should be avoided.