Cathodic Protection - 13 Flashcards
,,,,,,,,,,is a secondary line of defense against corrosion ;
- Cathodic protection
,,,,,,,,,, the primary line of defense against corrosion ;
- Coating
For CP to be applied, an ,,,,,,, must be present ;
- Electrolyte
SAS system, sometimes called ,,,,,,,system ;
- galvanic anode
SAS system works on the principle of,,,,, ;
- bimetallic corrosion, the natural potential between metals
Any metal that is more electronegative (less noble), or below steel on the galvanic list can be used as ,,,,, ;
- an anode
SAS systems only protect ,,,,, and the anodes need changing regularly as they corrode;
- small area
: ICS system will protect long lengths of pipeline from one installation, a distance of ,,,,,, ;
- approximately 10 miles
The current to run the ICS system comes from the national grid and is connected through ,,,, ;
- a transformer rectifier (TR).
The national grid is very high voltage, very high amperage and also ,,,,, ;
- AC
Anti-corrosion (ICS) currents need to be ,,,, ;
- DC
The TR (transformer rectifier) rectifies the current to ,,,,, and transforms it to ,,,, ;
- DC
- ow voltage and amperage
,,,,,,,,,,,, side of the TR is connected to a ground bed (anode system) and ,,,,,,,to the pipe, making the pipe the cathode;
- The positive side
- the negative side
The current is released into the electrolyte at ,,,,,, passes through the electrolyte and is received at ,,,,, ;
- the ground beds
- areas of coating damage on the pipe
A typical ground bed will be approximately ,,,,, in length, at the ,,,,, depth as and running ,,,,,,,, to the pipe ;
- 50m
- Same
- parallel
The cables carrying the current are of ,,,,,,, to produce a circuit of little or no resistance at the anode.;
- substantial diameter and pure copper
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 ,,,,,
- negative potential on the buried pipe
The voltage required varies, usually ,,,,,,, Voltage at an amperage of around,,,,,, A ;
- 10 - 50V
- 0.15A
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 ;
- anode bed
- the electrolyte
The interference therefore becomes ,,,,, anode and can suffer severe corrosion. ;
- a secondary
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. ;
- -850mV
- passive state
- -1 to –2V
One method of monitoring at interval is known as ,,,,,;
- Half-cell reference electrode
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
- anode to earth.
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 ;
- to the pipe
- the stud and copper/copper sulphate half cell
- earth directly above the pipe
- the pipe, the electrolyte, the anode
