Steel corrosion: Causes, impact and prevention

Steel is a key raw material used in a number of industries due to its advantages such as durability and strength. However, the flip side of the material is that it is prone to corrosion.

In fact, steel corrosion is one of the key challenges that the steel industry is facing. However, with the help of treatments and mindful usage, it can be restricted. This article will highlight the meaning of corrosion, the causes of steel corrosion, the types of corrosion-resistant steel and prevention tips.

Meaning and causes of steel corrosion

Let us begin by understanding what is steel corrosion? And what causes corrosion in steel?

Steel corrosion is an electromechanical process. In simple terms, the iron in steel is oxidised and produces rust. There are multiple causes why corrosion happens. Some of the key causes of steel corrosion include:

• Temperature
• Humidity
• Water (especially salt water)
• Chemical fumes
• Vapour
• Oxygen in the air
• Stress, etc.

Such oxidisation causes permanent deterioration of steel making it weaker. As a result, the structures made of steel may become weak. Globally, corrosion is one of the common concerns of the steel industry.

Types of corrosion in steel

Corrosion can occur in various ways. Here are some common types of corrosion in steel metal:

• Uniform corrosion: It is one of the most common corrosions, where the whole steel surface is exposed to a corrosion agent. As a result, it affects the large area of the steel structure. Usually, it is caused by the presence of certain chemicals. As a result of the corrosion, steel loses its thickness, deteriorating steel.
• Pitting corrosion: Pitting corrosion begins from a small area or a pit. It is one of the most common types of corrosion in steel. Usually, this area is in contact with water or soil which starts the corrosion and forms a hole, cavity or pit. Many times, pitting corrosion is a result of a coating chip-off or damage to the protective coating. Since it is a localised type of corrosion, it might get unnoticed. However, it is dangerous for steel structures.
• Galvanic corrosion: Such corrosion happens at the places of joints or intersections, etc., when two kinds of electrochemically dissimilar materials are in contact with the moisture. For example, copper and steel are in contact with salt water. The likelihood of galvanic corrosion taking place is higher in areas like fasteners, etc., as two dissimilar metals come in contact.
• Stress corrosion: Stress corrosion happens when there is constant static tensile stress and the presence of a corrosive environment. The stress concentration areas become anodic. This type of corrosion is not common in steel though stainless steel can get deteriorated with it.
• Crevice corrosion: This kind of corrosion happens in the closed and smaller areas where oxygen is trapped. These may include washers, gaskets, etc.

In addition to the kinds of corrosion mentioned above, there are a few more types of steel corrosion including biochemical corrosion, bimetallic corrosion, fretting corrosion and so on. In order to avoid corrosion, one can select the right type of steel for the project depending on the environment it will be into.

Impact of steel corrosion

So, what happens when steel corrodes? A quick answer to this question is steel does not meet quality expectations and damages may turn out to be harmful in many ways. Here is how steel deterioration impacts the quality of steel.

• Reduced strength: As steel corrodes, it loses strength. This is especially harmful in the construction industry as weaker structures are not stable and are prone to fall. For example, corrosion on steel girders can make the bridge weaker and hence unsafe.
• Reduced ductility: Reduced ductility can lead to the breakage of steel which is again harmful, especially in the construction industry.
• Decreased safety: Reduced strength and ductility mean compromised safety. Corrosion compromises safety in any industry including using steel in automotive, aerospace, marine, construction, food and beverages, home appliances, and so on.

Types of corrosion-resistant steel

Steel is a key material in the construction industry. Therefore, it is important to understand the application and weather conditions of the geography and use steel wisely. Similarly, in the industrial application of steel, it is important to understand the application and use the right kind of steel.

Here are some of the types of type of steel according to the steel corrosion treatment. One can select the right one for the project depending on the application.

• Stainless steel: It is one of the most widely used materials in the construction industry as stainless steel is known for its strength, lightweight and resistance to corrosion. This makes it an ideal choice for the construction as well as the food and beverage industry. This is also why stainless steel is the preferred material for modern steel railing designs for balconies and gates. However, some types of stainless steel corrode when it comes in contact with salt water, certain chemicals and moisture.
• TMT bars: Thermo Mechanically Treated bars popularly known as TMT bars are critical for Reinforced Cement Concrete (RCC) projects. They are corrosion-resistant and are used in construction as well as marine applications. Fe 550, Fe 550S and Fe 600 are types of TMT bars used in marine application where steel in constantly in contact with salt water.
• Galvanised steel: Steel treatment of galvanisation protects steel from rust and corrosion. Galvanised steel is applied with a zinc coating that improves and protects steel from rust and corrosion and hence increases the durability of steel. However, it is not the right choice when steel is expected to be in contact with salt water.
• Colour coated steel: Colour coated steel is used in a wide range of industries such as automotive, home appliances, construction and so on. It offers protection to steel from atmospheric corrosive agents hence improving durability.

Apart from the treatments mentioned above, there are multiple other treatments that makes steel corrosion resistant. It is a matter of application that determines the kind of treatment.

Prevention tips: How to stop corrosion in steel metal?

Selecting the right type of steel for your project does not offer 100% protection against corrosion. It only reduces the chances of corrosion. Here are some of the preventive tips for preventing steel corrosion.

• Periodic monitoring: After the steel application, it is important that conduct close monitoring of all parts to check if there is any corrosion.
• Improving environmental conditions: This may or may not be in the user’s control. However, if it is, the best thing to do is to improve environmental conditions and eliminate steel that is in contact with the corrosive agent.
• Keeping corrosion in mind while designing: Elimination of cracks and pits at the designing stage can help to control corrosion at the later stage.
• Regular maintenance: It is best to conduct regular maintenance of steel structures, components and appliances. Regular cleaning, avoiding water leakages, repair any damages, avoiding contact with any corrosive agent can help in avoiding corrosion.

Closing remarks

The use of the right type of steel can help you avoid corrosion. Additionally, regular maintenance and preventive steps are must steps for keeping steel structures and components corrosion-free. Moreover, as technology advances, innovations in steel are expected to offer better corrosion resistance.