Corrosion Protection for Steel

Steel is a proven durable and efficient building material that has been used since the Industrial Revolution. It is cost effective, aesthetically pleasing, sustainable, and strong. However, like all metals, steel corrodes when exposed to the atmosphere. Therefore, it is important to consider corrosion protection methods when constructing projects with exposed steel. There are a number of different corrosion protection systems to consider including:

1) Hot-Dip Galvanizing

2) Duplex Systems

3) Zinc Coatings

4) Protective Coatings

5) Special Steels

6) Sacrificial Anodes

This section will provide information on the various methods of corrosion protection, including application, performance characteristics, corrosion resistance and other information important to consider before specifying your corrosion protection system.

Classification of corrosion protection methods [German version]

1) Active corrosion protection

2) Passive corrosion protection

3) Permanent corrosion protection

4) Temporary corrosion protection

Active corrosion protection

The aim of active corrosion protection is to influence the reactions which proceed during corrosion, it being possible to control not only the package contents and the corrosive agent but also the reaction itself in such a manner that corrosion is avoided. Examples of such an approach are the development of corrosion-resistant alloys and the addition of inhibitors to the aggressive medium.

Passive corrosion protection

In passive corrosion protection, damage is prevented by mechanically isolating the package contents from the aggressive corrosive agents, for example by using protective layers, films or other coatings. However, this type of corrosion protection changes neither the general ability of the package contents to corrode, nor the aggressiveness of the corrosive agent and this is why this approach is known as passive corrosion protection. If the protective layer, film etc. is destroyed at any point, corrosion may occur within a very short time.

Permanent corrosion protection

The purpose of permanent corrosion protection methods is mainly to provide protection at the place of use. The stresses presented by climatic, biotic and chemical factors are relatively slight in this situation. Machines are located, for example, in factory sheds and are thus protected from extreme variations in temperature, which are frequently the cause of condensation. Examples of passive corrosion protection methods are:

1) Tin plating

2) Galvanization

3) Coating

4) Enameling

5) Copper plating

Temporary corrosion protection

The stresses occurring during transport, handling and storage are much greater than those occurring at the place of use. Such stresses may be manifested, for example, as extreme variations in temperature, which result in a risk of condensation. Especially in maritime transport, the elevated salt content of the water and air in so-called sea-salt aerosols may cause damage, as salts have a strongly corrosion-promoting action. The following are the main temporary corrosion protection methods:

A corrosion inhibitor is a chemical compound that, when added to a liquid or gas, decreases the corrosion rate of a material, typically a metal or an alloy.[1] The effectiveness of a corrosion inhibitor depends on fluid composition, quantity of water, and flow regime. A common mechanism for inhibiting corrosion involves formation of a coating, often a passivation layer, which prevents access of the corrosive substance to the metal. Permanent treatments such as chrome plating are not generally considered inhibitors, however. Instead corrosion inhibitors are additives to the fluids that surround the metal or related object.

Corrosion inhibitors are common in industry, and also found in over-the-counter products, typically in spray form in combination with a lubricant and sometimes a penetrating oil.

Cathodic protection

Cathodic protection is often used to mitigate corrosion damage to active metal surfaces. Cathodic protection is used all over the globe to protect pipelines, water treatment plants, above and underwater storage tanks, ship and boat hulls, offshore production platforms, reinforcement bars in concrete structures and piers, and more.

Cathodic protection is often used to protect steel from corrosion. Corrosion is caused when two dissimilar metals are submerged in an electrolytic substance such as water, soil, or concrete. This type of metal conducting path between the two dissimilar metals allows a pathway through which free electrons move from the more active metal (anode) to the less active metal (cathode). If free electrons from the anode do not reach active sites on the cathode before the arrival of oxygen, ions at the active sites can then recombine to produce ferrous hydroxide, i.e. rust.