Written by Igsaan Jamie, Product Manager
Corrosion is a destructive process that significantly affects various metallic materials, including mild steel. One effective way of limiting corrosion and prolonging the life of mild steel surfaces is paint which acts as a protective coating. However, understanding the effects of corrosion on painted mild steel surfaces is crucial for adequate maintenance and care of the steel surfaces.
The following is an overview of the corrosion process and the effects of corrosion on painted mild steel surfaces to assist in best caring for your enclosures.
Corrosion is the gradual destruction of metallic materials by a chemical or electrochemical reaction with the surrounding environment. In the case of mild steel, corrosion occurs when the iron in the metal reacts with oxygen and moisture in the air to form iron oxide (rust). Rusting weakens the steel and affects its mechanical properties, making it more prone to structural failure.
Painting is an effective method of protecting mild steel surfaces from corrosion. An adequately coated mild steel surface acts as a protective coat and barrier, preventing oxygen and moisture from coming into contact with the metal. The paint also prevents the formation of rust by isolating the steel surface from the environment.
However, painted mild steel surfaces are not entirely immune to corrosion. Several factors can cause the paint to fail, exposing the steel surface to the elements and promoting corrosion. For instance, mechanical damage, such as scratches or chips on the paint, can expose the underlying steel surface to oxygen and moisture. Additionally, exposure to harsh chemicals or extreme temperatures can cause the paint to deteriorate, further exposing the steel surface to corrosion.
The effects of corrosion on painted mild steel surfaces can be profound:
- Corrosion weakens the steel, reducing its load-bearing capacity and making it more prone to structural failure.
- Rusting causes the paint to peel, crack, or bubble, exposing even more of the steel surface to corrosion.
- Rust stains, often reddish-brown streaks, can appear on the painted surface, spoiling its appearance.
- Corrosion can increase maintenance costs, as the steel surfaces require frequent repair and repainting.
The IEC Standard IEC 62208 allows for a degree of rusting Ri1, in accordance with ISO 4628-3, and although in practice this degree of rusting does not affect the function or mechanical properties of the enclosure, regular maintenance to avoid its aesthetic deterioration and to prolong its useful life is recommended.
The IPD range of mild steel enclosures complies with corrosion resistance standard UNE-EN 62208.
General enclosure selection guide (recommended):
| Installation Environment |
Mild Steel |
Stainless Steel or Polymer |
| Indoors - normal environmental conditions, low dust, dry |
☒ |
☐ |
| Outdoors - normal environmental conditions, minimal road pollution, no chemical exposure, moderate temperature, low dust, minimal direct sunlight, dry |
☒ |
☐ |
| Indoors - exposure to chemicals and high humidity, dusty |
☐ |
☒ |
| Outdoors – exposure to sea air/sea breeze, high temperatures, direct sunlight |
☐ |
☒ |
| Outdoors – direct sunlight, dusty, wet |
☐ |
☒ |
 For mild steel enclosures installed outdoors, it is recommended to install an enclosure canopy to provide additional shielding from the weather.
Even though the IP rating may be suited for the intended application, the correct enclosure must be selected to suit the environmental conditions so corrosion is minimised.
When in doubt, choose stainless steel or polymer, as the additional investment will outweigh the ongoing maintenance costs.
In conclusion, corrosion is a significant problem that affects mild steel surfaces. Paint and corrosion inhibitors effectively protect mild steel surfaces from rusting. However, painted mild steel surfaces are not entirely immune to corrosion, and several factors can cause the paint to fail, exposing the steel surface to corrosion. Understanding the effects of corrosion on painted mild steel surfaces is essential for adequate maintenance and care of the steel surfaces, reducing costs and ensuring their longevity.
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