Corrosion of structural steel
The corrosion of structural steel is an electrochemical process that requires the simultaneous presence of moisture and oxygen. Essentially, the iron is oxidised to produce rust, which occupies about six times the volume of the original material. The rate at which the corrosion process progresses depends on a number of factors, but principally the ‘micro-climate’ immediately surrounding the structure.

Corrosion in concrete structures
The water penetration helps corrosion of the steel reinforcement. As the rust has more volume then the original steel bar, the rust causes tension in the surrounding concrete. As the cover of concrete is limited on the outer side, the resultant tensile force causes cracks formation and the crack permit more easier entry of water and oxygen to form more rusting. Resulting leads to increase in volume and the cracks in concrete get wider and wider. The surrounding concrete becomes partly disintegrated which finally causes spalling.

Corrosion resistant coatings
Corrosion resistant coatings ensure metal components have a longer life. Metal coatings are ideally used coatings in the industry. The function of the coating is to act as a barrier that inhibits contact between chemical compounds or corrosive materials with the metal housing. STP offers a variety of anti-corrosion coatings which include:
• Rust remover: ShaliRustoff
• Rust converter: ShaliPrime RC
• Zinc rich primer: ShaliPrime ZnR
• Zinc phosphate primer: ShaliPrime Zn Ph
• Micacious iron oxide: ShaliPoxy MIO
• Novolac based epoxy: ShaliKote NES
• Bituminous coatings: Tank Mastic HB
• Pipe coatings: ShaliUrethane PC
• Coal tar epoxy coatings: ShliPrime CTE HB LB.

Rusting of reinforcement bars lead to spalling of concrete
Corrosion control of metals is technically, economically, environmentally, and aesthetically important. The good option is to use inhibitors for protecting metals and alloys against corrosion. Lot of people are using migratory corrosion inhibitor (ShaliPlast RCI) in concrete at the time of pouring concrete to prevent rusting of reinforcement bars in the future. These are mainly amine based bipolar migratory corrosion inhibitors. Effect of addition of ShaliPlast RCI, migratory corrosion inhibitor in concrete block would result in corrosion free rebar. They are widely used in concrete repairs.

Precaution for concrete corrosion
Protection of concrete from highly corrosive environment in chemical plant by using ShaliKote NES, it protects the reinforced concrete in the neutralisation pit. Coal Tar Epoxy (ShaliPoxy CTE LB /HB) are quite often used in Marine structures like Jetties. PU Coatings (ShaliUrethane PC) for metal structures and anti-corrosive coating for pipelines. 

Conclusion
When it comes to corrosion protection, different kinds of material are available. The usage depends on the kind of environment the structure is exposed. Choosing the right methodology for the treatment is very important. At STP Ltd there is a range of anti-corrosive treatments for various applications. STP also provides customised solutions to clients regarding, the various corrosion and repair problems.

Authored by__

Hasan Rizvi, Vice President, STP Ltd
Email: hasan@stpltd.com