Made By :

Mahmoud Ali Agmay

Adham Ahmed Hassan

Mohamed Ali Mohamed

Kareem Tharaa Kamel

Presented To: Dr. Mona Osman

• is a technique used to control the corrosion of a

metal surface by making it the cathode of

an electrochemical cell.

I.By Galvanic Anodes.

II.By Impressed Current.

• Positive current to flow in the electrolyte, from

the anode to the steel. Thus, the whole surface of

the steel becomes more negatively charged and

becomes the cathode.

• Some requirements to make galvanic anodes:

1. Sacrificial anodes.

2. Direct welding to the structure or a conductor

connecting the anode to the structure

3. Secure and minimum resistance connections

between conductor and structure, and between

conductor and anode.

• Impressed-current systems employ inert (zero or low

dissolution) anodes and use an external source of dc power

(rectified ac) to impress a current from an external anode onto

the cathode surface.

• Some requirements to make impressed current:

1. Inert anodes.

2. A dc power source.

3. Electrically well insulated.

4. Secure and minimum resistance connections between power

source and structure.

1. Pipelines.

2. Ships and boats.

3. Marine.

4. Steel in concrete.

5. Internal cathodic protection.

6. Galvanized steel.

7. Automobiles.

1. The corrosion of steel embedded in

reinforced concrete structures (bridges,

buildings, port and harbour structures,

etc.)

2. Protection can be applied to copper-

based alloys in water systems.

3. To lead-sheathed cables and to

aluminium alloys.

I. Production of hydrogen ions.

II. Cathodic disbonding.

III. Cathodic shielding.

• Under normal conditions, the atomic

hydrogen will combine at the metal surface to

create hydrogen gas, which cannot penetrate

the metal. Hydrogen atoms, however, are

small enough to pass through the crystalline

steel structure, and lead in some cases to

hydrogen embrittlement.

• This is a process of disbondment of

protective coatings from the protected

structure (cathode) due to the formation of

hydrogen ions over the surface of the

protected material

• Cathodic disbonding occurs rapidly in

pipelines that contain hot fluids because the

process is accelerated by heat flow.

• This phenomenon occurs because of the high

electrical resistivity of these film backings.

• Protective electric current from the cathodic

protection system is blocked or shielded from

reaching the underlying metal by the highly resistive

film backing.