Corrosion II: Protection Methods

1
Corrosion II / Objectives

• Define activation polarization and concentration
  polarization.

2
Corrosion II / Objectives

• Define activation polarization and concentration
  polarization.
• Explain galvanic corrosion.

3
Corrosion II / Objectives

• Define activation polarization and concentration
  polarization.
• Explain galvanic corrosion.
• Describe basic general rules for good corrosion
  preventing design.

4
Corrosion II / Objectives

• Define activation polarization and concentration
  polarization.
• Explain galvanic corrosion.
• Describe basic general rules for good corrosion
  preventing design.
• Calculate the cell potential for a redox pair.

5
Corrosion II Protection Methods

• Material Selection
• 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

• 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)
• Mg 18
• Zn 25
• Al-Sn 16-20

9
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.
10
Protection Methods
4. Coatings A. Metallic Often dual
function cladding flame spraying electro-dep
osition hot-dipping vapor deposition
11
Protection Methods
4. Coatings B. Organic
12
Corrosion Protection

• Weld rather than rivet

13
Corrosion Protection

• Weld rather than rivet
• Containers should be designed for easy draining

14
Corrosion Protection

• Weld rather than rivet
• Containers should be designed for easy draining
• Design for easy replacement of expected failures

15
Corrosion Protection

• Weld rather than rivet
• Containers should be designed for easy draining
• Design for easy replacement of expected failures
• Avoid stresses in corrosion exposed components

16
Corrosion Protection

• Weld rather than rivet
• Containers should be designed for easy draining
• Design for easy replacement of expected failures
• Avoid stresses in corrosion exposed components
• Avoid electrical contact between dissimilar
  materials

17
Corrosion Protection

• Weld rather than rivet
• Containers should be designed for easy draining
• Design for easy replacement of expected failures
• Avoid stresses in corrosion exposed components
• Avoid electrical contact between dissimilar
  materials
• Avoid heterogeneity (metals, vapor spaces, heat,
  stress)