Chapters 22 and 23 Cont Wet Corrosion Key Concepts

1
Chapters 22 and 23 (Cont)Wet Corrosion Key
Concepts

• Hour Exam Wed. Oct 18 (In-class)
• Help Session
• Monday, Oct. 16
• 530-700 pm
• Rm U113 MME
• Assign App. Prob. 45 (Calc. uniform corrosion
  rate first!)
• The Eight Forms of Corrosion
• Common Corrosion Environments
• Corrosion Protection

2
Voltage Differences Drive Corrosion
3
The Eight Forms of Corrosion

• Uniform Attack
• Galvanic Corrosion
• Crevice Corrosion
• Pitting
• Selective Leaching
• Intergranular Corrosion
• Erosion-Corrosion
• Stress Corrosion
• Corrosion Fatigue

4
Intergranular Corrosion
Source W. Callister, Materials Science and
EngineeringAn Introduction, New York, John Wiley
Sons, 1997.
5
Weld Decay(Stainless Steel)
6
Weld DecayAn Example(Stainless Steel)
7
Erosion-Corrosion
Source W. Callister, Materials Science and
EngineeringAn Introduction, New York, John Wiley
Sons, 1997.
8
Stress Corrosion(The Process)
9
Stress Corrosion(The Result)

• (A few)
• Dangerous Combinations
• Chloride ions with
• stainless steel
• Ammonia with
• brass
• Caustic soda with
• mild steel

Source W. Callister, Materials Science and
EngineeringAn Introduction, New York, John Wiley
Sons, 1997.
10
Corrosion Fatigue
11
Common Corrosion Environments

• The Atmosphere
• Primarily moisture with dissolved oxygen
• Acid rain, sodium chloride (marine atms) and
  industrial pollutants may aggravate corrosion
• Commonly-used metals include aluminum, copper and
  galvanized steel
• Water
• Fresh waterCast iron, steel, aluminum, copper,
  brass and some stainless steels generally
  suitable
• Sea water (3.5 NaCl)Titanium, brass, some
  bronzes, Cu-Ni alloys, and Ni-Cr-Mo alloys often
  acceptable

12
Common Corrosion EnvironmentsII

• Soils
• Wide range in compositions and susceptibilities
  for corrosion
• Cast iron and plain carbon steelswith and
  without coatingsgenerally most cost-effective

13
Corrosion Protection

• Materials Selection
• Modify the Environment
• Design Practices
• Galvanic, Crevice, Erosion corrosion
• Drainage
• Physical barriers
• Inhibitors
• Cathodic Protection

14
Cathodic Protection
Sacrificial Anode
Applied Voltage
Source W. Callister, Materials Science and
EngineeringAn Introduction, New York, John Wiley
Sons, 1997.
15
Galvanized Steel
16
Anodized Aluminum

• Aluminum Metal
• Oxide Layer
• Colored Die

17
Area Effects
Large cathodes with very small anodes lead to
VERY rapid corrosion of the anode.
Avoid It ! !
18
ReviewFast Fracture

• Fast Fracture
• What is it?
• Relative toughness of different classes of
  materials (metals, ceramics, polymers,
  composites common metals)
• Fracture mechanisms (ductile tearing, cleavage,
  crack blunting)

19
Fatigue and Crack Growth

• Fatigue
• What is fatigue? (Ds, sm, sa)
• Mechanisms of fatigue crack initiation and growth
• Basquins Law
• Coffin-Manson Law
• Goodmans Rule

20
Diffusion, Creep and Creep Fracture

• Primary, secondary and tertiary creep
• Creep damage time to fracture
• Mechanism of diffusion (incl. fast diffusion
  paths)
• Power law creep
• Diffusion creep
• Material design to resist creep
• Materials for common temperature ranges

21
Oxidation

• What is it?
• Linear, parabolic and linear loss behavior
• Micromechanisms of oxidation
• Stainless steels and superalloys
• Coatings and protective scales

22
Corrosion

• Anodic and cathodic reactions
• Ranking of common materials in galvanic series
• Mg
• Zn
• Aluminum
• Iron and steel
• Copper
• Titanium
• Types of corrosion
• Ways to control corrosion (incl. cathodic
  protection)
• Thin wall pressure vessels