Advanced Corrosion

Question 1

Corrosion Definition

Answer 1

Deterioration of a substance, usually metal, or its properties because of a reaction with its environment

Question 2

What is corrosion?

Answer 2

Corrosion is the reverse process of steel manufacturing

Question 3

What is passivation?

Answer 3

The formation of a protective oxide film on the surface reducing its chemical activity and its ability to corrode.

Question 4

What elements are in the corrosion cell?

Answer 4

• Anode
• Cathode
• Return Path (Metallic Pathway)
• Electrolyte

Question 5

What is an anode?

Answer 5

Part of the metal that corrodes (i.e. dissolves in the electrolyte)

Question 6

What is the cathode?

Answer 6

The more noble region on the electrode where the electrons are consumed

Question 7

What is the return path (metallic pathway)?

Answer 7

Connection of the anode and cathode and allows passage of the electrons, generated at the anode, to the cathode

Question 8

What is the eletrolyte?

Answer 8

A medium that conducts ionic (rather than electron) current

Question 9

How does oxygen affect the rate of corrosion?

Answer 9

Oxygen increases the rate of corrosion.

Question 10

How does temperature affect the rate of corrosion?

Answer 10

Corrosion usually accelerated with increasing temperature.

Question 11

How does chemical salts affect the rate of corrosion?

Answer 11

Increase the rate of corrosion by increasing the efficiency of the electrolyte.

Question 12

How does humidity (or wetness) affect the rate of corrosion?

Answer 12

The wetter the environment, the more corrosion is likely to occur.

Question 13

How does pollutants or acid gases affect the rate of corrosion?

Answer 13

Acid rain, chemical byproducts, and chlorides all promote corrosion.

Question 14

What are the two broad types of corrosion?

Answer 14

General & Localized

Question 15

What is general corrosion?

Answer 15

Relatively uniform loss of material

Question 16

What is localized corrosion?

Answer 16

Corrosion that occurs at discrete sites on the metal surface. Areas adjacent are normally corroded to a much lesser extent, if at all.

Question 17

What is pitting corrosion?

Answer 17

Corrosion that does not proceed uniformly but primarily at distinct spots

Question 18

What is crevice corrosion?

Answer 18

Occurs on a metal surface that is shielded from full exposure to the environment because of the close proximity of another material that forms a narrow gas between substances

Question 19

Of the two broad classifications of corrosion, what type represents the most significant in terms of potential for unplanned maintenance?

Answer 19

Localized

Question 20

What is galvanic corrosion?

Answer 20

An electrochemical reaction of two dissimilar metals in the presences of an electrolyte and an electron conductive path, which occurs when dissimilar metals come into contact.

Question 21

What is cathodic protection?

Answer 21

The reduction or elimination of corrosion by making the structure to be protected a cathode by means of an impressed current or attachment to a galvanic anode.

Question 22

What are the two types of cathodic protection systems?

Answer 22

• Galvanic
• Impressed current

Question 23

What materials are suitable for use as galvanic anodes?

Answer 23

• Aluminum
• Magnesium
• Zinc

Question 24

What is an impressed current system?

Answer 24

An external source of direct current power is connected (or impressed) between the structure to be protected and the ground bed.

Question 25

What are the various materials are for impressed current anodes?

Answer 25

• Scrap Steel
• Graphite
• Iron Oxide
• High-silicon chromium-bearing cast iron
• Platinized niobium & mixed metal oxide titanium

Question 26

Name impressed current power sources

Answer 26

• Rectified commercial power
• Solar cells
• Generators
• Fuel cells
• Wind powered cells
• Thermoelectric cells

Question 27

What is cathodic disbondment?

Answer 27

The separation of the coating from the surface through hydroxyl (OH-) formation due to increased (made more negative) potential.

Separation of coating due to increased current

Question 28

The formation of a thin surface layer on metals, whether an oxide, carbonate, or other compound, that slows the rate of corrosion process is called?

Answer 28

Passivation

Question 29

The principal component of mild carbon steel is __________?

Answer 29

Iron (Fe)

Question 30

Which is the part of the corrosion cell where metal dissolves?

Answer 30

Anode

Question 31

Which of these elements is likely to accelerate corrosion on a steel structure?
A. Salts
B. Low temperature
C. High temperatures
D. Pollutants

Answer 31

A. Salts
C. High temperatures
D. Pollutants

Question 32

In a cathodic protection system the metal being protected is the _________?
A. Anode
B. Cathode
C. Ground bed
D. Rectifier

Answer 32

B. Cathode

Question 33

When parts of a metal surface are shielded from full exposure to the environment because of the close proximity of another metal, corrosion at that location is identified as __________?
A. Fretting corrosion
B. Cavitation-erosion corrosion
C. Pitting corrosion
D. Crevice corrosion

Answer 33

D. Crevice corrosion

Question 34

Cathodic protection using impressed current is most commonly used on __________?
A. Off-shore drilling platforms
B. High voltage transmission towers
C. Pipelines
D. Trucks

Answer 34

C. Pipelines

Question 35

Impressed current ground bed anodes are likely to include ______?
A. Graphite
B. Zinc
C. High silicon cast iron
D. Aluminum

Answer 35

A. Graphite
C. High silicon cast iron