Ch 5 Related Science

Question 1

Define the term corrosion.

Answer 1

Corrosion is the deterioration and destruction of a substance, usually a metal, or its properties because
of a reaction with its environment.

Question 2

What are the three basic kinds of corrosion.

Answer 2

1. Chemical
2. Physical
3. Electrochemical

Question 3

Corrosion created by ____ causes is sometimes referred at as ____.

Answer 3

physical, corrosion-erosion

Question 4

High velocities of liquids can affect the corrosion rate of a pipeline. Explain.

Answer 4

Where a high velocity condition continues to cause removal of the corrosion coating as it is formed,
the metal becomes progressively thinner until finally it is completely eaten through.

Question 5

A chemical reaction involving oxidation, reduction and transfer of electrons is defined as
____ corrosion.

Answer 5

electrochemical

Question 6

The term ____ is used to describe that portion of the metal surface which is corroded, and it is
the location where current leaves the metal to enter the solution (electrolyte).

Answer 6

anode

Question 7

The term ____ is used to describe the metal surface from which current leaves the solution
(electrolyte) and returns to the metal.

Answer 7

cathode

Question 8

The most common type of localized corrosion is ____.

Answer 8

pitting

Question 9

Reddish-brown iron rust on uncoated cast iron pipe is a form of ____.

Answer 9

oxidation

Question 10

T or F

Answer 10

Local action cells may be responsible for corrosion of buried pipelines that contain a
solution which can conduct electricity.

Question 11

What are the three main types of corrosion cells that take part in the electrochemical corrosion
reaction?

Answer 11

1. Different temperature cells
2. Concentration cells
3. Dissimilar electrode cells

Question 12

Define the term “galvanic” cell.

Answer 12

A galvanic cell is two electrodes and an electrolyte capable of producing electricity by chemical
action. It consists of two dissimilar metals in contact with an electrolyte, or two similar metals in
contact with dissimilar electrodes. A galvanic cell converts energy liberated by a chemical action
directly into electrical energy.

Question 13

The galvanic series rate the ____ activity of metals.

Answer 13

relative

Question 14

Electrochemical corrosion will take place if ____ is present to conduct an electric current.

Answer 14

water

Question 15

Corrosion may result because of the ____ of soils.

Answer 15

variation

Question 16

The formation of a ____ cell is possible where two different soils are in contact with a
single piece of metal.

Answer 16

concentration

Question 17

Water is a piping system with a pH below 7 would be considered ____.

Answer 17

corrosive

Question 18

Usually the rate at which a material corrodes ____ as the temperature increases.

Answer 18

increases

Question 19

What are six kinds of corrosion resistant materials commonly used in the pipe trades?

Answer 19

1. Cast iron 7. Glass
2. Brass 8. Terracotta
3. Copper 9. Bituminous fiber
4. Aluminum 10. Plastic
5. Stainless steel 11. Cement
6. Non-metallic or synthetic 12. Copper alloys

Question 20

How is electric current produced by galvanic corrosion in a dry cell battery?

Answer 20

Electric current produced by galvanic corrosion in a dry cell is created by wasting away of two
dissimilar metals in electrical contact when exposed to an electrolyte. The current obtained from a dry
cell is generated by the chemical action of the chemicals used to form the electrolyte. The flow and
amount of electrical current produced results in corrosion of the anode.

Question 21

How can cathodic protection be used to control corrosion of buried or immersed metallic waterlines
and tanks?

Answer 21

Cathodic protection prevents corrosion of metallic structures buried or immersed in a continuous
electrolyte by making them the cathode and applying direct current to the electrolyte from an anode
source. By making waterlines or tanks the cathode, all anode areas from local corrosion cells are
eliminated and direct current is prevented from leaving the tanks or pipes thereby stopping further
corrosion.

Question 22

What are the two proven methods of applying cathodic protection to a buried pipeline?

Answer 22

The two proven methods of applying cathodic protection to a buried pipeline are with galvanic anodes
(usually magnesium or zinc) and impressed current systems.

Question 23

Cathodic protection prevents corrosion of metallic structures buried or immersed in a continuous
electrolyte by making them the ____ and applying direct current to the electrolyte from an
____ source.

Answer 23

cathode, anode

Question 24

List four methods of corrosion control that can be used on piping systems.

Answer 24

1. Cathodic protection
2. Coatings
3. Dielectric insulation
4. Test stations

Question 25

Stray electric current ___corrosion__ can be caused by the effects of direct current source from a
cathodic protection rectifier.

Answer 25

corrosion

Question 26

How can piping systems be protected against stray electrical currents?

Answer 26

1. Bonding the pipe system to the source
2. Cathodic protection
3. Insulating coupling in the pipe lines
4. Coatings

Question 27

Instantaneous hot water heaters should be provided with the necessary connections for
____ to remove sediment.

Answer 27

backwashing

Question 28

Instantaneous hot water heaters should be provided with the necessary connections for
____ to remove sediment.

Answer 28

backwashing

Question 29

A ____ is a substance which can be added to an environment to decrease the rate
of attack on a metal.

Answer 29

corrosion inhibitor

Question 30

Bituminous coatings containing ____ are used on underground pipelines.

Answer 30

asphaltum

Question 31

A common problem associated with coatings on pipelines is ____to the coating after it has
been applied.

Answer 31

damage

Question 32

List three materials that are commonly used as sacrificial anodes in piping systems.

Answer 32

1. Magnesium
2. Aluminum
3. Zinc

Question 33

T or F: Zinc offers the same type of cathodic protection as aluminum.

Answer 33

T

Question 34

T or F: Corrosion of metals themselves can form a protective coating to prevent further corrosion.

Answer 34

T

Question 35

T or F: The impressed current system of cathodic protection is externally powered usually by an
AC-DC rectifier.

Answer 35

T

Question 36

T or F: Test stations are the most practical method which can be used for cathodic protection
of pipelines.

Answer 36

F

Question 37

T or F: The solution forming an electrolyte is called the corrodent.

Answer 37

T

Question 38

T or F: Oxygen can be removed from piping systems by heating or neutralizing.

Answer 38

T

Question 39

T or F: Ground joint unions with brass seats should be used in galvanized piping systems.

Answer 39

F