Enclosures are often located in dusty, wet, hot or humid areas. Under these kinds of conditions, the enclosure housing is subject to significant stresses and can be damaged over time.
When subjected to external influences, steel has shown itself to be a particularly robust material for enclosures in many different areas. However, one specific problem that particularly affects steel is rust. This eats its way through the metal until the enclosure’s protection class is no longer met and the electrical components inside are exposed to environmental influences. The resulting damage to the electrics causes the system to stop working. All this is reason enough to take a closer look at why rust forms on enclosures and what measures are effective in preventing it.
Steel and rust
The first thing to be aware of is that no two steels are the same. The properties of a steel alloy depend on which constituents are added – e.g. molybdenum, chromium, nickel, vanadium, titanium and/or manganese. The official Register of European Steels (“Stahl-Eisen-Liste”) includes over 2,400 different grades of steel. As different as these steels are, though, they all have the same Achilles’ heel – they can rust under certain conditions.
Why does steel rust?
Rust forms due to a chemical reaction. If the iron contained in the steel comes into contact with water and oxygen, it oxidises. Referred to as “corrosion”, this reaction produces hydrated iron oxide, which is commonly known as “rust”. Besides looking unsightly, this also has an adverse effect on the steel’s stability. As it flakes off, the rust continuously exposes fresh layers of metal, working its way down until nothing is left. This raises the question of what measures can be taken to provide effective protection against rust.
Protecting steel from rust
The most effective way of protecting steel from rust is to prevent simultaneous contact with water and oxygen. This is virtually impossible in the locations where enclosures are typically used, which leaves two established methods of protection.
Applying paint to steel adds a protective layer to help stop the iron reacting with oxygen and water. If this layer of paint is damaged, though, rust can form in the affected areas. Consequently, using stainless steel is a more effective solution.
Stainless steel
Stainless steels contain a high proportion of chromium, which forms a natural protective layer of chromium oxide on the steel’s surface. This layer protects the steel from rust and even repairs itself. If scratches occur, the chromium in the damaged area oxidises very quickly to restore the previous level of protection.
Wherever corrosion resistance and the good cleaning properties of stainless steel play an important role, enclosures made from this type of steel are used in the majority of cases nowadays. Typical areas of application include the chemical and food industries and medical technology.
Even stainless steel can rust
The term “stainless” should not be misinterpreted. Although it suggests corrosion can be eliminated altogether, even stainless steel can rust under certain conditions.
| Cause | Description |
| Mechanical damage | Scratches or abrasion caused by ferrous objects can damage the chromium oxide layer and introduce tiny particles of iron, which then rust. |
| Chemical influences | Acids, salty air and aggressive cleaning agents permanently damage the protective chromium oxide layer and increase the likelihood of rust forming. |
| Iron fallout | Metal-containing particles in the ambient air are deposited on the surface and start to rust. |
To maintain its corrosion resistance, stainless steel must be treated appropriately, undergo regular cleaning and have any iron fallout on the surface removed. Having a very smooth surface finish will make steel even less susceptible to rust.
Stainless steel for enclosures
If handled correctly, stainless steel provides excellent protection from rusting and has therefore become established as the material of choice for enclosures in challenging environments. Besides specially painted sheet steel, the enclosure specialist Rittal also offers a comprehensive portfolio of stainless steel enclosures.
Typical areas of application
Whether or not a stainless steel enclosure is needed always depends on the relevant location of use. The examples in the table below indicate typical areas of application and the associated conditions.
| Area of application | Ambient conditions |
| Food and pharmaceutical industries | Stringent hygiene requirements, frequent cleaning with aggressive cleaning agents |
| Chemical industry | Aggressive chemicals |
| Maritime industry | Salt water, moisture, large temperature fluctuations, strong vibrations |
| Steelworks and heavy industry | High temperatures, dusty conditions |
| Traffic and transport | Weathering |
It is also important to note that not all stainless steels are the same. The right stainless steel to use depends on the conditions at the site of installation. For example, V2A steel is suitable for environments with moderate ambient conditions, while V4A steel is designed for much more extreme requirements. To further increase the level of protection and prevent deposits of foreign particles, Rittal enclosures have smooth surfaces. This ensures long-term corrosion resistance. For particularly harsh environments, painting the enclosure is also recommended.
| Steel grade | Properties |
| Grade 1.4301: V2A steel | Contains 18% chromium and 10% nickel and is resistant to water vapour, humidity and weak acids. |
| Grade 1.4404: V4A steel | Besides chromium and nickel, also contains around 2 to 2.5% molybdenum, which significantly increases resistance to chlorides and aggressive media. Particularly resistant to salty environments and stronger acids. |
Reliable protection for electronics
Although rust can even form on the surface of high-quality stainless steel enclosures under extreme conditions, rusting all the way through, which poses a risk to the electronic components inside, is all but ruled out.
Summary
Enclosure rust is the result of a chemical reaction, during which water and oxygen react with the iron contained in the steel. In harsh industrial environments, preventing this from happening is practically impossible. Stainless steel’s protective chromium oxide layer makes it a resilient enclosure material that exhibits excellent resistance to corrosion. If the surface has a smooth finish, is cleaned regularly and does not sustain any mechanical damage, its rust protection is maintained even under extreme conditions. This means the enclosure remains airtight and retains its stability, providing the electronics inside with long-term protection from outages.
FAQs
1. Why do steel enclosures rust?
Rust forms when the iron contained in the steel comes into contact with water and oxygen at the same time. This chemical reaction results in oxidation and, consequently, the formation of iron oxide, which damages the surface and penetrates ever deeper into the steel.
2. What conditions typically increase the likelihood of rust forming on enclosures?
Moisture, high humidity, aggressive cleaning agents, salty air, dust and large temperature fluctuations all increase the risk of corrosion. They are a permanent feature in many industrial environments.
3. How can enclosures be protected from rust effectively?
Minimising contact with water and oxygen is the most effective form of protection. High-quality paint coatings and the use of stainless steel are practical ways of achieving this. Damage to the layer of paint should be repaired promptly, as corrosion is more likely to start here.
4. Why is stainless steel particularly resistant to corrosion?
Stainless steels contain a high proportion of chromium. This forms a thin, self-healing layer of chromium oxide that protects the surface from corrosion. If this layer is damaged, it normally repairs itself – provided the environment is not overly aggressive.
6. For which areas of application is stainless steel particularly suitable?
It is the preferred choice for sectors with stringent hygiene standards, extreme ambient conditions or a requirement for resistance to chemicals. Examples include the food and pharmaceutical industries, maritime applications, the chemical industry and heavy industry.
Dr. Dirk Pieler
Executive Vice President Business Unit Industry Solutions at Rittal
With his many years of industry experience, Dirk Pieler is helping to advance the digital transformation and automation in enclosure manufacturing.