Corrosion Flashcards
Define Corrosion
The destruction or deterioration of a material because of chemical or electrochemical reaction with the environment
What is the difference between wet and dry corrosion?
Dry corrosion occurs when a material is in contact with the air. Wet corrosion requires water or another solution to be present.
List the costs associated with corrosion
- Plant downtime
- Loss of product (Leakage)
- Loss of efficiency (Heat Transfer)
Define cathode
Metal which consumes electrons through reduction.
Define anode
Metal that is corroding, produces electrons through oxidation
Define electrolyte
Provides an aqueous environment, giving a path for ionic conduction (oxidation/reduction)
Name the nine general forms of corrosion
- Uniform attack
- Galvanic or two metal corrosion
- Crevice corrosion
- Pitting
- Inter-granular corrosion
- Selective leaching
- Erosion corrosion
- Stress corrosion cracking
- Hydrogen Damage
What are the four elements required for wet corrosion to occur?
- Cathode
- Anode
- Electrolyte
- A pathway for electron travel
What are two names for crevice corrosion?
1) Gasket
2) Filiform corrosion
Sacrificial materials should have _________ standard volt potential than the protected material.
Lower
What does it mean when material X is “more noble” than material Y?
Material X is less likely to corrode
What factors affect corrosion?
1) Metallurgical
2) Environmental
3) Operating conditions
What form of corrosion can not be detected?
Pitting corrosion
What is the most common type of corrosion that accounts for the highest metal loss annually?
Uniform corrosion
What are the requirements of galvanic corrosion?
Two dissimilar metals in physical contact with each other are exposed to a common electrolyte
What 2 factors affect galvanic corrosion?
1) Area
2) Distance
What are the 2 requirements for crevice corrosion?
A crevice must be wide enough to allow a solution to penetrate but not wide enough to allow circulation
How does pitting corrosion occur?
A mechanical or a corrosive force damages the passive layer of a material. This forms pits or small holes
What 2 steps does pitting corrosion occur in?
(Hint: same as the first 2 stages of fatigue)
1) Initiation
2) Propagation
What solution is responsible for most pitting?
Chloride solution
Describe intergranular corrosion
Intergranular corrosion forms along the grain boundary of a material. The grain boundary of one material acts as a small anode to a grain boundary of another material.
What is intergranular corrosion in Aluminum called?
Exfoliation
What causes selective leaching corrosion?
Selective leaching corrosion is caused by the loss of an alloying element in an alloy.
What are some other terms for selective leaching corrosion?
1) Dezincification
2) Graphitization
3) Dealuminization
