Prevent Steel Corrosion with Protective Coatings

Anti-corrosion coating for steel will protect from deterioration

Anti-corrosion coating for steel assets is essential

According to the latest data from NACE (the Worldwide Corrosion Authority), the global cost of corrosion is estimated at $2.5 trillion. In the US alone, the cost is nearly $500 billion, most of those costs incurred in the industry sector. However, 15-35% of the cost of corrosion costs could be saved by the implementation of corrosion control practices, and a corrosion management system. Anti-corrosion coating for steel is a vital part of a corrosion protection system.


Anti-corrosion coating: What, where, why

Corrosion can be uniform, galvanic, pitting, crevice, and exfoliation, and each have different mechanisms. Galvanic corrosion is an important one; it is triggered when two metals of different electrochemical potentials come into electrical (or physical) contact in presence of an electrolyte, such as saltwater. Current flows through the electrolyte from one metal to the other (the anode to the cathode), and the anode will corrode. Coatings form a protective barrier, and depending on the coating type and the substrate, they do this in different ways.

Anti-corrosion coating for steel extends the life of your asset

Non-metallic corrosion protection systems can be applied like any other paint

1. Barrier coatings

A protective coating system that forms an insulating barrier between the substrate and corrosive elements. Thick film application o f two-pack epoxies and coal tar epoxies work in this way.

2. Inhibitor coatings

These contain a pigment that releases a chemical which interferes with the electrolyte and stops the corrosion process. Applied as primers directly to the steel surface. Zinc phosphate is an example of an inhibitive pigment.

3. Galvanic coatings

Also called sacrificial protection, these are metal-rich coatings applied as a primer which provide a sacrificial layer or use the principle of cathodic protection to prevent corrosion. Cathodic protection is a method of preventing galvanic corrosion by providing a more easily corroded metal (such as zinc) to be the anode to the protected metal’s cathode. The most widely used metal for the protection of steel is zinc.

4. Metal coatings

Metal coatings contain a metallic element or alloy, and are applied electrochemically, , mechanically, or with a sprayer. This group includes includes hot dip galvanizing, thermal spraying, and electroplating.


Understanding the environmental factors for anti-corrosion coating

Choosing which corrosion protection system is right for you is a matter of understanding your substrate, your substrate’s intended environment and use, and the type of application (on-site or off-site) your project will need. Whether a bridge, pipeline, or building, you need to understand which corrosive elements it will need protection from. Steel corrosion is a chemical reaction that occurs in the presence of water and oxygen, and is accelerated by the presence of certain pollutants, such as chlorides or sulfur dioxide These elements are all present in the atmosphere, even more so closer to the coast, which is why corrosion is so pervasive. Environmental factors which increase the risk of corrosion include:

Anti-corrosion coating for steel works to prevent this kind of deterioration

An anti-corrosion coating system works to prevent deterioration

  • Exposure to salt or fresh water (and degree of immersion)
  • Humidity and condensation
  • Exposure to UV radiation
  • Exposure to chemicals and acids
  • Pollutants such as smog or sewage
  • Soil chemistry (acidic or alkaline, the presence of salts)
  • Temperature fluctuations
  • Proximity to electrochemical activity (high-voltage lines, for example)

Preparation of your steel substrate

The correct preparation of the substrate is of paramount importance with any corrosion protection system. A coating will perform at its best only if it can properly adhere, and any surface contaminants can lead to a coating failure. Surface treatment steps are cleaning (with a solvents or chemicals), removing loose materials, abrading, cleaning again, priming and surface hardening. The abrading process roughens the surface of the steel, which gives the coating better adhesion.


Anti-corrosion coating for steel is a multi-layer system

The typical high performance coating system is multi-layered. Specifications usually comprise a series of layers of different paints, or the application of paints over metal coatings to form a ‘duplex system‘. The paint layers form a particular sequence: primers, intermediate/build coats, and finally the finish or top coat. All paints within a system need to be compatible, and they may all be of the same type or all different.

Anti-corrosion coating for steel is multi-layered

By building up the layers, the steel substrate can be more protected, and with a variety of mechanisms

  1.  Primer: Applied directly to the steel substrate, a primer wets the surface, provides good adhesion for subsequent coats, and protects the substrate from corrosion.
  2. Intermediate/build coats: These build the film thickness of the system, as generally the thicker the coating the longer the life. Intermediate coats increase overall protection and decrease permeability to oxygen and water.
  3. Finish/top coat: The finish provides the required appearance and surface resistance of the coating system. It is the first line of defense against the corrosive elements of the environment. As such, it needs to be able to withstand UV, humidity, condensation, pollutants, and all other corrosive factors.

The duplex system: Double up your protection

A duplex system is a form of corrosion protection where a steel substrate is protected using a metal coating and a non-metallic coating. First the steel undergoes hot dip galvanization, and then an additional anti corrosion system, whether paint or powder coating, is applied on top. By doubling up the coatings, the substrate is better able to withstand corrosion and it increases the lifespan of the asset.

Step 1: Hot dip galvanization

This is the process of immersing steel in a bath of molten zinc. The zinc and the steel form a metallic bond and create a layer of alloy, and so the coating creates a barrier that is actually part of the substrate, not just layered on top. As the steel is removed from the zinc bath an additional layer of zinc is deposited. Galvanizing uses the principle of cathodic protection, as the zinc coating acts as a sacrificial anode.

Step 2: Non-metallic coating

If you choose to use liquid paint over your galvanizing, it is is applied just as it would be on raw steel. A primer coating such as an epoxy is applied, cured, and followed by the over coats. The top coat could be a vinyl, alkyd, acrylic or others, but once applied may also be cured. Powder coating is a process where a powdered coating is sprayed onto a substrate. The gun used to spray the powder gives it an electrostatic charge, which attracts and sticks it to the substrate. The piece is then baked, and the coating melts into a solid film over the substrate.


Anti-corrosion coating for steel protects your assets

Whether you use a non-metallic coating, a metal coating or a duplex system, it is of paramount importance that you protect your steel. A corrosion protection system is of vital importance for the durability, lifespan, and viability of your project. Applying an anti-corrosion coating for steel properly now can save huge costs in the future in the case of failure.  Do it once, do it right.


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