1. Cathodic Protection of Tower Anchors
Presented by Tom McKigney
Brance-Krachy Co., Inc.
Houston Texas
to The Society of Broadcast Engineers
September 10, 2002

2. THE CORROSION CELL
When two dissimilar metals are connected in an electrolyte such as soil, a corrosion cell is formed. One metal becomes the anode and suffers corrosion while other metal becomes the cathode and corrosion is prevented.
Anodic and cathodic areas exist on the surface of all steel structures due to slight variations in material. Composition, local stresses, differences in coating condition and availability of oxygen are all factors in creating this. In the absence of cathodic protection corrosion will eventually occur.

3. ELEMENTS OF A CORROSION CELL
ANODE & CATHODE
ELECTRICAL POTENTIAL
ELECTROLYTE
METALLIC PATH

4. THE GALVANIC SERIES

5. Anchor Corrosion Cell

6. Stray Current Corrosion

7. ANCHOR CORROSION MITIGATION
1. Galvanizing and Epoxy Coatings
2. Concrete Encasement.
3. Electrical Isolation.
4. Cathodic Protection.
Galvanic Anodes
Impressed Current
When used in conjunction with Cathodic Protection the other methods
can be beneficial in mitigating corrosion problems.

8. Galvanizing and Epoxy Coatings
Not a solution
Galvanizing depletes rapidly underground
Only effective against atmospheric corrosion
Epoxy coatings can accelerate failure if used alone
Holidays give rise to the small anode large cathode effect

9. Concrete Encasement Used for structural strength
May provide some corrosion protection
Corrosion can cause concrete failure
Cracks in concrete may set up corrosion cells

10. Electrical Isolation

11. CATHODIC PROTECTION SYSTEMS
The cathodic protection of metals has been around since 1824.
Sir Humphrey Davy attached zinc plates on the hulls of British naval vessels to retard corrosion of the copper sheathing.
Cathodic Protection continues to be an effective method for mitigating the destructive action of corrosion.
The principal of cathodic protection involves the introduction into the electrical circuit a metal that is more electro-negative than the existing anodic and cathodic areas.
This additional metal becomes the anode and will corrode while providing current to the metal it is protecting, thereby overcoming the local anodic area and making them cathodic.

12. CATHODIC PROTECTION

13. GALVANIC SYSTEMS
The classic Cathodic Protection solution to a galvanic corrosion problem is to introduce an anode of a suitable alloy of magnesium or zinc which will suffer corrosion and can be sacrificed in protecting the cathode. This approach is used in galvanic systems.

14. Anchor Cathodic Protection

15. IMPRESSED CURRENT SYSTEMS
As an alternative solution, the protective current needed to make the structure cathodic may be obtained by applying low voltage Direct Current derived from normal ac mains supply.
This is achieved by transformer /rectifiers which supply DC to specially designed anodes which will dissipate large currents without themselves suffering significant wastage.

16. IMPRESSED CURRENT SYSTEM

17. Cathodic Protection System
Design Requirements
Anode Selection depends on:
Soil Resistivity
Current Requirement
Design Life

18. Maintenance and Record Keeping
Check system and record
Potential Readings on a regular schedule.
This should be done at least once a year.