Cathodic Protection - 13

Question 1

,,,,,,,,,,is a secondary line of defense against corrosion ;

Answer 1

• Cathodic protection

Question 2

,,,,,,,,,, the primary line of defense against corrosion ;

Answer 2

• Coating

Question 3

For CP to be applied, an ,,,,,,, must be present ;

Answer 3

• Electrolyte

Question 4

SAS system, sometimes called ,,,,,,,system ;

Answer 4

• galvanic anode

Question 5

SAS system works on the principle of,,,,, ;

Answer 5

• bimetallic corrosion, the natural potential between metals

Question 6

Any metal that is more electronegative (less noble), or below steel on the galvanic list can be used as ,,,,, ;

Answer 6

• an anode

Question 7

SAS systems only protect ,,,,, and the anodes need changing regularly as they corrode;

Answer 7

• small area

Question 8

: ICS system will protect long lengths of pipeline from one installation, a distance of ,,,,,, ;

Answer 8

• approximately 10 miles

Question 9

The current to run the ICS system comes from the national grid and is connected through ,,,, ;

Answer 9

• a transformer rectifier (TR).

Question 10

The national grid is very high voltage, very high amperage and also ,,,,, ;

Answer 10

• AC

Question 11

Anti-corrosion (ICS) currents need to be ,,,, ;

Answer 11

• DC

Question 12

The TR (transformer rectifier) rectifies the current to ,,,,, and transforms it to ,,,, ;

Answer 12

• DC

- ow voltage and amperage

Question 13

,,,,,,,,,,,, side of the TR is connected to a ground bed (anode system) and ,,,,,,,to the pipe, making the pipe the cathode;

Answer 13

• The positive side

- the negative side

Question 14

The current is released into the electrolyte at ,,,,,, passes through the electrolyte and is received at ,,,,, ;

Answer 14

• the ground beds

- areas of coating damage on the pipe

Question 15

A typical ground bed will be approximately ,,,,, in length, at the ,,,,, depth as and running ,,,,,,,, to the pipe ;

Answer 15

• 50m
• Same
• parallel

Question 16

The cables carrying the current are of ,,,,,,, to produce a circuit of little or no resistance at the anode.;

Answer 16

• substantial diameter and pure copper

Question 17

The resistance encountered comes in the soil/clay/rock bearing the electrolyte and governs the driving voltage
required and number of anodes required to maintain ,,,,,

Answer 17

• negative potential on the buried pipe

Question 18

The voltage required varies, usually ,,,,,,, Voltage at an amperage of around,,,,,, A ;

Answer 18

• 10 - 50V

- 0.15A

Question 19

The interference structure picks up the current released from the ,,,,,,and conducts it through a circuit of minimal resistance and re-releases the current into ,,,,,, near the protected line ;

Answer 19

• anode bed

- the electrolyte

Question 20

The interference therefore becomes ,,,,, anode and can suffer severe corrosion. ;

Answer 20

• a secondary

Question 21

It is considered that ,,,,,, mV will maintain a pipeline in a ,,,,, state but most CP engineers will require a more negative value, ,,,, to ,,,,, V being typical. ;

Answer 21

• -850mV
• passive state
• -1 to –2V

Question 22

One method of monitoring at interval is known as ,,,,,;

Answer 22

• Half-cell reference electrode

Question 23

Copper/copper sulphate half-cell electrode is used for measuring the ,,,,,, the other half of the circuit being ,,,,,, pipe to earth potential, ie cathode to earth

Answer 23

• anode to earth.

Question 24

Periodically along the line, CP monitoring posts are installed, with a direct wire connection ,,,,,, accessed from a stud on the CP post panel. A voltmeter is connected to ,,,, and to the ,,,,, which is then pushed into the ,,,,,,, providing a
circuit for electrons from ,,,,, into ,,,,, back to ,,,, bed ;

Answer 24

• to the pipe
• the stud and copper/copper sulphate half cell
• earth directly above the pipe
• the pipe, the electrolyte, the anode

Question 25

Part of the electrical circuit of the corrosion reaction is the release of hydrogen gas from ,,,, ;

Answer 25

• the cathode

Question 26

A ,,,,, diameter hole is drilled into a plate coated with the material to be tested, through the coating and into but not through the underlying steel. A short length, approximately ,,,, , of plastic tube approximately ,,,, diameter is fixed in position, typically using ,,,,,,, with the drilled hole central to the tube. This is then part filled with ,,,,,,,and a lid fitted. The lid can be machined from a block of polyethylene with a suitable diameter hole drilled through. The plate is connected to the ,,,,,,,of a battery, ,,,,,, connected to the positive pole and inserted through the hole in the lid into the salt solution. ;

Answer 26

• 6mm
• 50mm
• 50mm
• Araldite™ epoxy or elastomeric sealant
• 3% solution of common salt (sodium chloride)
• negative pole
• an anode connected

Question 27

When the circuit is switched on the plate is ,,,, and hydrogen (andchlorine) will be released from ,,,,, and also at,,,, ,, enabling hydrogen to penetrate under the coating, simulating ;

Answer 27

• areas of coating damage
• the cathode
• the steel
• the interface of the steel/coating,

Question 28

The circuit is stopped after ,,,, days ;

Answer 28

• 28 days

Question 29

The distance from the edge of the hole to the disbondment is measured and should not exceed the stated requirements, for example FBE maximum ,,,, after 28 days. ;

Answer 29

• 5mm