Chapter 3 - CP - how it works

Question 1

The driving voltage of CP system must be greater than ………………. to provide effective cathodic protection.

Answer 1

driving voltage of corrosion cell

Question 2

The sole purpose of the cathodic protection grounded is to ……………

Answer 2

discharge current

Question 3

When cathodic protection current is applied to a structure, which direction does the potential of the structure shift?

Answer 3

negative direction

Question 4

List two methods utilized to produce cathodic protection current.

Answer 4

A. Impressed current

B. Galvanic/sacrificial

Question 5

CSE

Answer 5

Copper - Copper Sulfate reference electrode

Question 6

Pipe-to-soil potential

Answer 6

potential of a pipeline in a given location compared to reference electrode.

Question 7

On potential

Answer 7

potential of pipeline when CP system is energized.

Question 8

Off or Instant-Off Potential

Answer 8

estimates the polarized potential when the measurement is made within 1 second after simultaneously interrupting current output from all CP current sources.

Question 9

How does the use of underground pipeline coatings affect the current requirement to achieve cathodic protection?

Answer 9

more coating - less current.

Question 10

Why is it possible to protect more miles of large diameter pipelines from a single cathodic protection installation than small diameter pipelines?

Answer 10

resistivity inversely proportional to area.

Larger diameter pipe has lower resistance than small diameter pipe.
larger area and the resistance, conductor inversely proportional to cross sectional area.

Question 11

Cathodic disbondment can be avoided if the off-potentials are kept below what level?

Answer 11

-1.1 V (CSE)

Question 12

Which grounded construction method will produce the smallest area of full protection and provide the least effect on the potential compared to remote earth? (remote ground bed or closed ground bed)

Answer 12

close ground bed

close - smaller area
remote - larger area

Question 13

A plastic material loosely wrapped around a pipeline that blocks the effectiveness of the cathodic protection current is a example of which type of shielding? (Insulating barrier or Metallic shield)

Answer 13

insulating barrier

Question 14

A shorted pipeline casing on a pipeline road crossing which blocks the effectiveness of the cathodic protection current is an example of which shielding? (Insulating barrier or Metallic shield)

Answer 14

Metallic shields

Question 15

Is it good idea to insure that reinforcing wire in concrete be allowed to contact the underlying steel which is under cathodic protection to avoid shielding problems? (True or False)

Answer 15

False

Question 16

What is cathodic corrosion and give an example.

Answer 16

corrosion resulting from a cathodic condition of a structure, usually caused by the reaction of an atmospheric metal with the alkaline products of electrolysis.

if the metal is over-voltaged, its going to break down the passivating layer.

Question 17

Which type of cathodic protection system is most likely to cause stray current damage? (Galvanic anode system or impressed)

Answer 17

impressed

because they are putting large volume of current

Question 18

Describe 2 procedures that a corrosion engineer could use to avoid causing or experiencing damage from interference.

Answer 18

A. Select grounded sites accordingly

B. Inform neighbors, owners/facilities of the CP system

Question 19

Describe how you can determine if there is damaging interference at a point of crossing a foreign pipeline.

Answer 19

when surveying potential drop in the area of damage, the potential of foreign crossing measures at close intervals.

crossing - more electro+
distance - more electro_

Question 20

What is corrosion coordinating committee?

Answer 20

committee of representatives from many principle owners of underground metallic structures in an area that work together to solve corrosion problems.

Question 21

Steel potential range

Answer 21

0.2 - 0.8

Question 22

current shunt

Answer 22

resistor

calibrated - known restore value that does not change its value

Question 23

CP types

• Galvanic System
• Impressed Current

Answer 23

Galvanic (Mg, Zn, Al)
Mg, Zn - use in fresh and zinc water
Al - most electropositive

Impressed Current

• rectifiers
• photovoltaic solar panels
• thermo-electric

Question 24

linear scale

Answer 24

2,4,6,8,10,…….

Question 25

logarithmic scale

Answer 25

2, 4, 8, 16, 32, 64, ….

Question 26

current takes place of ….

Answer 26

least resistor

most of them but not at all