Different types of corrosion

Question 1

Uniform corrosion

Answer 1

also known as general corrosion, is a type of corrosion that occurs uniformly over the entire exposed surface of a material. This type of corrosion is easy to notice since it is uniform and constant.

How to prevent:
* Apply paint coatings, like zonc
* Inhibitors of H+
* Make the surface to a cathode

Question 2

Galvanic corrosion

Answer 2

can happen if one metal is more active (lower in the galvanic series) than the other metal.

How to reduce it:
* Try to make the anode as large as possible as it will then take longer time.

Question 3

Differential alteration

Answer 3

when a metal is locally exposed to difference in oxygen content.
The less oxygenated part assumes a lower corrosion potential and acts as the anode of the cell.

How to prevent it: Soil is inherently porous and rich in moist and electrolytes (e.g. mineral salts). Therefore, soil is the perfect environment to provide corrosion to metals.

Question 4

Crevice corrosion

Answer 4

This occurs in areas with restricted oxygen access, such as under deposits
Example reinforcing bars in concrete

Question 5

Pitting corrosion

Answer 5

Is a localized attack that occurs at specific points on the metal surface, resulting in small but deep cavities. It often starts where the protective oxide film on the surface has been damaged, or due to metallurgical inhomogeneity. Small anode and big cathode, it is very aggressive

Question 6

Intergranular corrosion

Answer 6

corrosion that occurs along the grain boundaries of a metal, particularly alloys. This form of corrosion can be detrimental as it can lead to severe structural weakening and failure of the material

Question 7

Stress corrosion cracking

Answer 7

combination of stress applied and corrosion actions. A typical feature of stress corrosion cracking is the occurrence of multiple cracking and that the cracks have lateral tree-like cracks.

Consequence: bearing section reduces since the cracks travels radius.

Question 8

Describe the Stress Corrosion stages

Answer 8

The process is that a crack that has opened under tension lets a corrosive solution enter the opening which becomes anodic.
The most obvious Anode mechanism: metal that is being removed
The most obvious cathodic mechanism is hydrogen evolution, absorption, diffusion, and embrittlement.

1. Crack initiation - a delayed process
2. Constant crack propagation
3. Crack propagation of final failure

Question 9

How to mitigate Stress Corrosion Cracking

Answer 9

check the aqueous environment and the load applied

• Work with the right materials
• Reduce stresses
• Remove critical environmental species such as hydroxides, chlorides, and oxygen
• Avoid stagnant areas and crevices in heat exchangers where chloride and hydroxide might become concentrated.

Question 10

What is brass dizincification?

Answer 10

is a typical example of selective corrosion.

As a consequence of this corrosion type, a porous copper layer is formed. Pure copper is less resistant than an alloy, especially if porosity are present. As a result, pipes or components will fail under normal loading condition.

Corrosion can be diffused (layer corrosion) or localized (Plug corrosion)