Objective 01: Corrosion Definition and Electrochemical Principles

Question 1

What is the definition of Corrosion?

Answer 1

The chemical or electrochemical reaction between a material, usually a metal, and its environment that produces a deterioration of the material and its properties

Question 2

What are examples of problems caused by Corrosion?

Answer 2

1. Loss of production due to downtime for repair
2. Leakage of process fluid to the atmosphere or within a process vessel, leading to contamination of the environment or process fluids
3. Rupture of pressurized piping or vessels, with possible consequences for the safety of the site personnel or the public (in extreme cases)
4. Blockage of flow passages due to deposits of corrosion products
5. Loss of heat transfer efficiency, due to corrosion products collecting on heat transfer surfaces
6. High cost of installing and maintaining equipment (plus chemicals) necessary to monitor and control corrosion
7. High cost of manpower to manage a corrosion program
8. High cost of corrosion related repairs
9. Increased equipment costs, due to over-design for corrosion allowance and corrosion prevention

Question 3

Electrochemistry

Answer 3

Process that involves a flow of electrons plus chemical reactions between substances

Question 4

How does corrosion involve electrochemistry?

Answer 4

Corrosion involves chemical reactions occuring at the interface of a metal and an electrolyte, resulting in or caused by an electric current, which transfers electrons between the metal and the electrolyte. When electrons are lost from a metal, corrosion occurs and the metal is weakened.

Question 5

What substances do most metals readily react with electrochemically?

Answer 5

1. Oxygen
2. Water
3. Aqueous substances

Question 6

Oxidation

Answer 6

Any reaction in which atoms of a substance lose one or more electrons

Question 7

What is the product of oxidation?

Answer 7

Electrically charged ion that is available for chemical reaction with other ions

Question 8

Reduction

Answer 8

Chemical reaction in which the atoms of a substance gain one or more electrons

Question 9

How does Redox normally apply in Corrosion?

Answer 9

The environment adjacent to the metal surface reacts with the metal and gains electrons at the expense of the metal

Question 10

Redox

Answer 10

Involves a reaction in which a reduction and oxidation both occur

Question 11

How does the reduction fluid react in a redox reaction if it is acidic?

Answer 11

1. Hydrogen ions in the fluid adsorb onto the metal surface
2. Electrons in the metal are free to react with these hydrogen ions
3. Results in loss of metal ions and formation of hydrogen gas

Question 12

How does the reduction fluid react in a redox reaction if it is neutral?

Answer 12

1. Air, disolved in the fluid, makes oxygen available

2. Oxygen reacts with water and metal electrons in a reduction reaction to produce hydroxide

Question 13

Electrodes

Answer 13

The locations at which electrons are discharged or received

Question 14

Anodic Electrodes

Answer 14

Electrodes that discharge electrons

Question 15

Cathodic Electrodes

Answer 15

Electrodes that receive electrons

Question 16

Anode

Answer 16

The location at which oxidation occurs

Question 17

Cathode

Answer 17

The location at which reduction occurs

Question 18

Corrosion Cell

Answer 18

Combination of all components necessary for corrosion

Question 19

What are the 4 components that must be present for corrosion to occur?

Answer 19

1. Cathode
2. Anode
3. Electrical connection for electron flow
4. Electrolyte on surface of the metal

Question 20

Electrolyte

Answer 20

Solution which connects the anode and the cathode and readily conducts ions