This document provides information on corrosion and cathodic protection. It discusses how corrosion degrades metals through chemical or electrochemical reactions. Corrosion costs over $2 trillion annually worldwide. Cathodic protection works by reducing the potential difference between anodic and cathodic sites on a metal surface to stop corrosion. There are two main types of cathodic protection systems - galvanic systems which use sacrificial anodes and impressed current systems which use an external current source. Both systems have advantages and limitations for different corrosion protection applications.

2. CORROSION BASICS
• Corrosion is the degradation or destructive attack of a
metal by chemical or electrochemical reaction with its
environment.
Fe ------- Fe++ + 2e-
(1)
O2 + 2H2O + 4e- ------- 4OH-
(2)
2H2O + 2e- -------- H2 + 2OH-
(3)
• Return of metal to the low energy oxide form in which it
originally existed as an ore with complete loss of its
metallic properties.

3. THE IMPACT OF CORROSION ON PIPELINES

4. WHY CORROSION IS IMPORTANT TO COMBAT?
Corrosion Effects:
• The world is loosing 2.2 trillion dollars every year – equivalent
to 3% of the world’s GDP.
• The plants spends more than 600 thousand dollars each year
and corrosion control.
• Watching corrosion is like watching grass grow – slower in
motion, but it definitely grows, and it grows in such an extent,
that one day, it will become disaster and starts giving
sleepless nights to operators of plants, pipelines and other
structures affected by corrosion.

5. CORROSION CONTROL
• Protective Coatings
• Environmental Control

6. BASIC ELECTRICITY
VOLTAGE
• Voltage is an electromotive force or a difference in
potential expressed in volts.
CURRENT
• Current is the flow of charges along a conducting path
and is measured in amperes.
RESISTANCE
• Resistance is the opposition to current flow through a
material.

7. • Current flows in
only one direction
DIRECT CURRENT

8. ALTERNATING CURRENT
• Current reverses direction on a cyclic basis.
• A full cycle is completed in 50th or 60th of a second,
represented in Hertz.

9. UNDERGROUND CORROSION AND ITS CONTROL

10. CATHODIC PROTECTION
• The concept of cathodic protection involves
reducing the potential difference between local
anodic and cathodic sites on a metal surface to
zero, resulting in zero corrosion current flow.

11. CORROSION CELL (CONSTITUENTS OF CP)

12. CRITERIA FOR CATHODIC PROTECTION
• A negative (Cathodic) potential of at least 850mV
• A minimum of 100mV of Cathodic polarization

13. TYPES OF CATHODIC PROTECTION
G A L V A N I C A N O D E
S Y S T E M
I M P R E S S E D C U R R E N T
S Y S T E M

14. GALVANIC SERIES
Metal
Potential wrt Cu:CuSO4
reference electrode (Volts)
Carbon, Graphite, Coke +0.3
Platinum 0 to -0.1
Mill scale on Steel -0.2
High Silicon Cast Iron -0.2
Copper, Brass, Bronze -0.2
Mild Steel in Concrete -0.2
Lead -0.5
Cast Iron (not Graphitized) -0.5
Mild Steel (Rusted) -0.2 to -0.5
Mild Steel (Clean) -0.5 to -0.8
Commercially Pure Aluminium -0.8
Aluminum Alloy (5% Zinc) -1.05
Zinc -1.1
Magnesium Alloy (6% Al, 3% Zn, 0.15% Mn) -1.6
Commercially Pure Magnesium -1.75

15. CONNECTION DIAGRAM
G C P I C C P

16. ADVANTAGES OF GCP/SACP SYSTEM
• No external power source required.
• Low maintenance requirements.
• Easy to install.

17. LIMITATIONS OF GCP/SACP SYSTEM
• Low driving voltage/current output.
• May be ineffective in high – resistivity
environments.
• Higher cost per unit ampere than impressed current
due to lower efficiency (self – consumption).
• May be difficult or expensive to replace spent
anodes.

18. ADVANTAGES OF ICCP SYSTEM
• Flexible with capability to handle a wide range of voltage
and current outputs.
• Satisfy high current requirements with a single
installation.
• Effective in high – resistivity environments.
• Less anode consumption than with galvanic anodes.

19. LIMITATIONS OF ICCP SYSTEM
• Higher inspection and maintenance cost than with
galvanic system.
• Requires external power.
• Constant power supply cost.
• May cause overprotection resulting in hydrogen
embrittlement and coating damage.

20. TTPS CATHODIC PROTECTION (TANK FARM)

21. PERMANENT RE PORTABLE RE
CU/CUSO4 REFERENCE CELL/ELECTRODE

22. TRANSFORMER RECTIFIER UNIT

23. COOLING TOWER BURRIED PIPES

24. GAS TURBINE BURIED CCW PIPES

25. UNDERGROUND GAS PIPELINE

26. THANK YOU