This document discusses methods for cathodic protection to control corrosion. It describes two main methods: (1) sacrificial anodes (galvanic action) which use more active metals like zinc or magnesium that corrode instead of the protected structure; and (2) impressed current systems which use an external DC power source to force the structure to act as a cathode. The document provides examples of applications for each method and notes their advantages and disadvantages. Sacrificial anodes are best for small, well-coated structures while impressed current is used for large, complex structures.

4. 4Methods to Control Corrosion
 Use of Corrosion resistant materials (plastic, stainless alloys, fiberglass).
 Use of the same or similar metals per the galvanic series.
 Altering the environment (utilizing homogeneous high resistivity backfill or
inhibitors).
 Utilize coatings and linings that electrically insulate the structure from the
electrolyte (paints, plastic films, etc)

5. Cathodic Protection (CP)
Cathodic protection (CP) is a technique to
control the corrosion of a metal surface by
making it work as a cathode of an
electrochemical cell.
or
Minimize corrosion by utilizing an external
source of electrical current which forces the
entire structure to become a cathode.

6.  Sir Humphrey Davy’s work on
protecting the copper sheathing on
wooden hulls in the British(London)
Navy by sacrificial zinc or iron anodes
in 1824.
 Firstly Considered impressed current
process.
In USA by 1945 CP was applied to oil &
natural gas industry.
Earliest practical use of cathodic protection
History

7. Quay structures and sheet pile curtains
Concrete bridges placed in seawater
Water or Fuel Pipelines buried in soil
Vessels/tanks buried in soil
Oil Platforms in steel and concrete
Subsea Pipelines
Hull
storage tanks
steel pier piles
offshore oil platforms
onshore oil well casings
Cathodic protection systems are most commonly used to protect
Applications of cathodic protection

8. Commonly Affected Structures
 Buried Piping
 Steel Piles
 Storage Tanks - Above Ground / Underground
 Reinforcing Steel in Concrete
 Ships/Boats
 Hulls
 Jetties
 Offshore and onshore platforms

9. Commonly Affected Structures

10. Why Need Cathodic Protection
LET’S SEE A VIDEO

11. Cathodic Protection Types
1. Use of sacrificial anodes (Galvanic Action)
2. Impressed currents

12. Sacrificial Anodes or Galvanic Action
sacrificial anodes (zinc, magnesium or aluminum)
• The sacrificial anodes are more active (more negative potential) than the
metal of the structure they’re designed to protect.
• The anode pushes the potential of the steel structure more negative and
therefore the driving force for corrosion halts.
• The anode continues to corrode until it requires replacement

13. Sacrificial or Galvanic System Deficiencies
 Anode ribbons are too far apart
 Anode ribbons do not deliver sufficient current
 Sand used as fill is conductive and corrosive
 Water enters sand causing it to become corrosive
 Galvanic anode ribbons are depleted
 Reference cells are inaccurate or inoperable Let’s see a video

14. Application Of Cathodic protection by Sacrificial anodes

15. Anodes Used for Sacrificial/Galvanic CP
 Magnesium – Magnesium is often used in soil to
protect small electrically isolated structures, such as
underground storage tanks, and well coated
pipelines.
 Zinc – Zinc is often used in marine environments.
They are commonly found on boats.
 Aluminum – Aluminum can be used for a variety of
marine applications.

16. Visualization of Sacrificial anode process

17. Advantages of Sacrificial anode process
 Inexpensive
 Little Maintenance cost
 No external Power source
 A variety of install methods can be used or simple to install
 Suitable for localized protection
 Independent of any source of electric power

18. Impressed Current CP
Pros of Impressed Current CP
 Unlimited driving potential.
 Capable of protecting large steel structures when designed
properly.
 Requires less anodes then a galvanic system.
 Output can be controlled using a permanent reference electrode,
desirable when the electrolyte resistivity is known to change.
Done for large structures (pipes, offshore platforms, etc) where a
galvanic (or sacrificial) anode can not economically deliver enough
current.

19. Impressed Current Deficiencies
 Rectifier inoperable or not properly adjusted
 Cables between rectifier and anode box are severed
 Anodes are spaced too far apart
 Anode ratings are too low
 Anodes are grounded to tank bottom
 Reference cells are inacurate or inoperable
 Positive and negative cables are connected with the wrong polarity
 Sand is too dry

20. Application of cathodic protection by an impressed current

21. Visualization of Sacrificial anode process

22. Pros & Cons of Impressed Current CP
 Initial costs can be more expensive.
 Requires an external DC power source along with an AC
supply.
 System requires routine maintenance and monitoring.
 Anode wires can be susceptible to damage.
 Comparatively few anodes are needed.
 The voltage may be adjusted to allow for environment and
coating change.

23. Pros & Cons of Impressed Current CP
 Initial costs can be more expensive.
 Requires an external DC power source along with an AC
supply.
 System requires routine maintenance and monitoring.
 Anode wires can be susceptible to damage.
 Comparatively few anodes are needed.
 The voltage may be adjusted to allow for environment and
coating change.

24. Choise of Cathodic Protection System
Which method is superior
Generally,
 sacrificial anode schemes have found favour for well-
coated low current demand structure,
 Impressed current being utilized for large complex
structure which may be poorly coated.
Morever,
 sacrificial anodes offer easily installed but Impressed
current is complex process.
So, sacrificial anode is Superior