Corrosion Protection

Question 1

Corrosion protection.

Three main was to prevent corrosion.

Answer 1

Change the electrolyte ph
Make the electrode more positive
Make the electrode more negative.

Question 2

Sacrificial anodes

Mainly made up of
Aluminium ( uncontested structures)
Zinc. ( coated)
magnesium rare as they don’t last long.

Anode is the - structure is the + cathode

Answer 2

Pros of sacrificial

No danger of over protection
No running costa
Active from day one
Well proven methods.

Cons
Current decreases over time
Initial costs to start
Considerable weight added to structure.

Question 3

Impressed current cathodic protection

ICCP

Same as before. But the current is made from a dc generator rather then the galvanic coupling.

Answer 3

This way round the structure is at the - end and the anode is attached to the + end of the generator

These are made up of
Titanium
Platinised niobium
Lead/silver alloy.

Question 4

ICCP

Pros
The output is variable to react to changing current density.
Anodes are smaller less weight.
Fewer required.

Cons only works when switched on
There is running costs
Overprotection can cause hydrogen embrittlement
Safety zone required when diving.

Answer 4

Can increase certain types of marine growth.

Question 5

Reference electrodes.

Made from
Zinc
Silver/silver cholride.
Copper/ copper sulphate.

Answer 5

These determine the current required for the ICCP system