What is electrochemical and chemical corrosion? How to protect metal from corrosion?

What is electrochemical and chemical corrosion? How can metal be protected against corrosion?

Corrosion is a common phenomenon that has a direct impact on the durability of buildings, bridges, machinery, vehicles, industrial installations and many other metal components. This process cannot be completely eliminated, but it can be effectively slowed down and controlled. To protect metal properly, it is essential to understand the difference between electrochemical corrosion and chemical corrosion, as well as the practical methods used to prevent both.

Key takeaways

✅ Corrosion is a natural process of metal degradation caused by interaction with the environment

✅ The most common causes include moisture, salts, acidic or alkaline media, and contact between dissimilar metals

✅ Electrochemical corrosion occurs in the presence of an electrolyte and a potential difference

✅ Chemical corrosion results from the direct chemical reaction between the material and its environment

✅ Effective corrosion protection usually combines several methods: protective coatings, proper material selection, environmental control and regular maintenance

What is corrosion?

Corrosion is a natural degradation process affecting materials, most commonly metals, as a result of their reaction with the surrounding environment. It is typically caused by contact with oxygen, water, salts, acids, alkalis or other chemical substances. As a result, the material gradually loses its original properties.

Corrosion may manifest itself in different ways, including rusting, surface dulling, cracking, flaking or structural weakening. In practice, this does not only reduce the visual quality of a component, but also lowers its mechanical strength, shortens service life and increases maintenance costs.

The corrosion rate depends on many factors, including temperature, humidity, pH, salt concentration, metal type and operating conditions. For this reason, in industrial applications both material selection and appropriate surface protection are critical.

What most often causes corrosion?

• moisture and standing water on the surface,
• high air humidity,
• rain and snow exposure,
• salt, including marine environments,
• acids and alkalis,
• contact between metal and other metals or materials,
• contact with soil,
• chemically aggressive water,
• industrial contamination and severe operating conditions.

What is electrochemical corrosion?

Electrochemical corrosion is a type of corrosion that occurs when a metal is in contact with an electrolyte, for example water containing dissolved salts, acids or alkalis. Under such conditions, local corrosion cells are formed and the metal begins to degrade gradually.

In practice, part of the metal surface becomes the anode and undergoes dissolution, while another part acts as the cathode. These reactions generate corrosion products such as oxides, hydroxides and metal salts.

A specific case is galvanic corrosion, which occurs when two different metals are in electrical contact in the presence of an electrolyte. The metal with the lower potential becomes the anode and corrodes faster, while the more noble metal is protected.

This type of corrosion is particularly important in industrial installations, pipelines, marine structures, tanks and wherever metal operates in humid or chemically aggressive environments.

What is chemical corrosion?

Chemical corrosion, sometimes referred to as dry corrosion, is a degradation process resulting from the direct chemical reaction between the material and its environment. Unlike electrochemical corrosion, it does not require the presence of an electrolyte or electrical current.

It occurs, for example, when a metal reacts with oxygen, sulphur, acids, alkalis or other aggressive substances. One of the most well-known examples is the oxidation of iron leading to the formation of rust.

Some metals, such as aluminium and chromium, form a thin oxide layer on the surface that partially protects the base material against further degradation. Others, such as ordinary carbon steel, are more susceptible to ongoing corrosion because the resulting corrosion products do not form a dense protective barrier.

The effects of chemical corrosion may be severe, ranging from visual deterioration to a significant reduction in mechanical strength and increased maintenance, repair or replacement costs.

Metal corrosion – how can metal be protected effectively?

Metal protection against corrosion cannot usually be based on one universal solution. The best results are achieved when the method is selected according to the specific material, service environment and operating requirements. In practice, corrosion prevention usually involves several complementary approaches.

Protective coatings

One of the most common solutions is the use of protective coatings, such as paints, varnishes, epoxy coatings or other barrier layers that isolate metal from the environment. Such a barrier reduces contact with moisture, oxygen and chemicals. However, the condition of the coating is critical – even minor damage may lead to local corrosion development.

Corrosion inhibitors

Corrosion inhibitors are chemical substances that reduce the corrosion rate. They may act by passivating the metal surface, forming a protective film, or modifying the properties of the corrosive environment.

Environmental control

In many cases, a great deal can be achieved simply by controlling the operating environment. This includes reducing humidity, controlling temperature, lowering salt concentration or maintaining an appropriate pH. The less aggressive the environment, the slower the corrosion process.

Cathodic protection

Cathodic protection is an electrochemical method used, among other applications, for pipelines, tanks, underground installations and submerged structures. It works by ensuring that the protected metal acts as the cathode and therefore does not undergo anodic dissolution.

Use of corrosion-resistant materials

In some applications, the best solution is to select a material with greater inherent corrosion resistance, such as stainless steel, aluminium, suitable alloys or non-ferrous metals. Material selection should always take into account the actual service environment, loads and process conditions.

Regular maintenance and inspection

Even the best protection systems require inspection. Regular checks make it possible to identify coating damage, environmental changes or early signs of corrosion before the problem becomes serious and costly.

Proper design of structures and systems

The corrosion rate is also influenced by the design of the component or installation itself. It is advisable to avoid geometries that retain water, contaminants or chemicals. It is equally important to reduce crevices, moisture traps and poorly considered combinations of dissimilar metals.

Education and personnel training

Personnel awareness is also essential. Employees should understand the basic corrosion risks, know how protection systems are selected and be able to monitor the condition of surfaces and components operating in demanding environments.

Anti-corrosion solutions – what can help in practice?

In industrial practice, various anti-corrosion solutions are used: from protective coatings and temporary corrosion prevention products to specialist agents designed to protect metal surfaces during transport, storage and operation.

If you are looking for such solutions, see the category: ANTI-CORROSION AGENTS FOR INDUSTRY.

Summary

Electrochemical corrosion and chemical corrosion are two different degradation mechanisms, but in practice both can lead to serious technical issues and costly repairs. That is why effective corrosion protection should include not only the selection of a suitable coating or protective agent, but also environmental control, proper design and regular maintenance.

The earlier an appropriate anti-corrosion strategy is implemented, the greater the chance of extending service life, reducing failures and lowering operating costs.