Cathodic Protection

Question 1

What is corrosion?

Answer 1

• An electro-chemical process that involves current flow
• The change from a metallic form to a combined form occurs by an anodic reaction, this process produces free electrons which pass within the metal to another site on the metal surface where it is consumed by cathodic reaction

Question 2

Where does corrosion occur?

Answer 2

At the Anode

• The anode is the point in a corrosion cell where current flows by chemical means, form the surface of the metal to the electrolyte

Question 3

What are the four part of the corrosion process?

Answer 3

1. Anode
2. Cathode
3. Electrolyte
4. Metallic Path

Question 4

What needs to be present in order for corrosion to occur?

Answer 4

1. Anode
2. Cathode
3. Electrolyte
4. Metallic Path

Question 5

Where does the protection occur?

Answer 5

The Cathode

• The cathode is the point in a corrsoion cell where current flows by chemical means from the electrolyte to the metal
• This is a reduction reaction which involves the cathode gaining electrons from the electrolyte

Question 6

What purpose does the electrolyte serve?

Answer 6

• This is where ions flow
• The electrolyte is any material in contact with both the anode and the cathode that will allow oxidization and reduction reactions to occur
• This includes the source of the elements or atoms that are required for ion transfer to and from the metal electrodes

Question 7

What purpose does the metal path serve?

Answer 7

• The metallic path is any metal that completes the path between the anode and the cathode allowing electrons to flow
• This electron flow must be present corrosion to occur

Question 8

What are the two most common types of cathodic protection systems?

Answer 8

1. Sacrificial(Galvanic) Anode
   
   1. Most common materials used: Aluminum, Zin and Magnesium
2. Impressed Current Systems

Question 9

What are the two types of rectifier stacks used in Cathodic Protection Rectifier Circuits?

Answer 9

1. Selenium Plates
   
   1. Higher Voltage drop, less efficient
   2. Less affected by voltage surges
   3. Age over time and must be replaced
2. Silicon Diodes
   
   1. Susceptible to damage by voltage or current spikes
   2. Must be protected from these surges by a Metal Oxide Varistor (surge protector)

Question 10

In a sacrificial anode system, the anode always loses electrons

true or false?

Answer 10

true

Question 11

Cathodic protection is a way of controlling the corrosion of a metal surface. How is this achieved?

Answer 11

• By making the metal surface the cathode of an electrochemical cell

Question 12

What are the two methods of control used in Cathodic Protection rectifiers?

Answer 12

1. Manual
2. Automatic

Question 13

What are the two types of construction used in the manufacturing of cathodic protection rectifiers?

Answer 13

1. Selenium Plates
2. Rectifier Diodes

Question 14

What section of the code book deals with Cathodic Protection?

Answer 14

Section 80

Question 15

On which surface does reduction occur?

Answer 15

The Cathode

Question 16

On which surface does Oxidation occur?

Answer 16

The Anode

Question 17

Does a Cathodic Protection system require its own branch circuit?

Answer 17

Yes

Section 80 of the code book