1. Corrosion Control Must be addressed at the design stage
Understand the exposure (environment) – pollution, repeated wetting & drying, humidity, the presence of salts etc.
Design life – maintenance programmes – repair & replacement
Methods of control – longest life for the minimum cost

2. Corrosion Protection
Corrosion occurs at ambient temperatures in the presence of moisture
Design to protect from exposure & if wetted aid drying process – run off surfaces – laps in joints arranged to avoid channels for water – sealant used in joints
Previously rusted steel left on site will be liable to further corrosion as rust pits are difficult to remove even after aggressive cleaning – protect site steel with primer – prevent initial corrosion

3. Isolation Methods
Application of protective coatings to specially prepared surfaces
Metallic coatings:
protective barrier - steel protected by nickel or chromium
Anodic coatings – sacrificial protection – steel protected by zinc, cadmium or aluminium

4. Cont’d
Organic coatings – protective barrier - paints, pitch & tar – usually applied over a metallic primer
Application must be to clean & dry surfaces that have been properly prepared

5. Cathodic Protection This can be achieved in two ways:
1.) Sacrificial Anode
2.) Impressed current
It has been shown that a combination of cathodic protection & coating is the most economical means of protecting steel structures

6. Sacrificial Anode Use of sacrificial anodes – Zinc, lead, etc.
Used on small structures
Anodes welded or bolted to fixtures
Need regular checks for wastage
Recently aluminium oxides have become more popular due to better performance to weight

7. Example Sacrificial Anodes

8. Cont’d Pipelines buried underground are protected in this way
Method relies on conductive pathways through the soil
Spacing coating design and coupling are important factors
Anodes are fixed in bands weighing 300 to 400kg at intervals of about 150m

9. Impressed Current (ICCP)
Involves the use of an external power source – metal to be protected is made cathodic to its surroundings – inert anodes used which are virtually non-consumable – insulated from structure
Early anodes made from scrap steel but most modern ICCP systems use lead silver alloy, titanium or niobium

10. Transformer Rectifier Unit

11. Cont’d
Has been used in the protection of steel reinforcement in concrete
The use of modern electronics makes the system self regulating
Very costly to run – mainly used in marine applications – oil rigs – large anodes placed on sea bed approximately 100m away

12. Impressed Current System

13. Typical Alternatives for a Buried PipelineMg
Magnesium Anode
Impressed current