Is Coating Required On Steel Components?
Stainless steel is very popular for preparing corrosion-resisting alloys with 10.5% of chromium (Cr) and other alloying compounds, including Nickel (Ni), manganese (Mn), molybdenum (Mo), and nitrogen (N). Even though stainless steel has corrosion-resistant quality, the material can be damaged in certain harsh environmental conditions. So, it is important to use anti-corrosion coating for steel to protect the material in certain weather, particularly in the marine environment or under the soil.
Corrosion in stainless steel:
Stainless steel containing chromium more than 10.5% is perfect for forming a layer of chromium oxide (CR2O3). This layer plays as a protector of the underlying material from the damage. The layer stops further oxygen diffusion, protecting the base metal from corrosion in some environments. It is to remember that cutting or grinding can damage the passive chromium oxide layer. Since chromium shares a high affinity with oxygen, it forms the passive CR2O3 by responding to the surrounding oxygen.
The corrosion damage in the stainless is mostly due to the presence of halides, including chlorides and bromides. In the industrial areas, chloride presence is high, and it causes damage to the stainless steel also. The other locations that can harm stainless by forming corrosion are the close proximity of the marine environment and under soil or water atmosphere. The damage to the material is primarily because of the chloride presence.
A humid environment has chloride ions that bind with chloride presented in the passive layer, forming soluble chromium chloride. It dissolves the chloride, and the free iron (Fe) responds to the chlorides presented in the surrounding environment. It initiates the process of corrosion.
Different corrosion types:
Chloride ions cause corrosion on stainless steel, but the severity of the damage depends on chloride concentration, temperature, and more. Three common corrosion types for stainless steel are:
- Crevice corrosion
- Pitting corrosion
- Stress corrosion cracking
Crevice corrosion is a type of localized corrosion, occurring in the crevice or the shielded areas only. A common example of this type of corrosion is under-deposit corrosion.
Pitting corrosion is another type of corrosion that is extremely localized in nature and forms in holes on the surface. It is the most severe type of corrosion that can cause equipment failure. For both crevice and pitting corrosions, the passive chromium oxide layer gets damaged.
Stress corrosion causes more damage to equipment because such corrosion causes cracks or sudden rupture in the equipment.
The other factors related to the corrosion in stainless steel are chloride concentration, temperature, oxygen, PH, and more. Anti-corrosion coating for steel can protect the metal from such damages. You will learn here how the coating is important for stainless steel.
The coating can prevent corrosion:
For stainless steel, the internal coating can be avoidable because its corrosion-resistance quality will protect the material from the internal process fluids. But, the external atmosphere can damage the material and cause corrosion. This is why coating for the external surface is needed to protect the material from chloride corrosion damage.
In certain environmental conditions, your stainless steel requires coating as the external guards.
- When equipment is designed for the underground where wet soil containing chlorides and microbes bind to the stainless steel.
- When equipment is kept in wet pits, salty water and microbes respond to the presence of stainless steel.
- When equipment comes in contact with salty water or rainwater, especially for the insulation.
To protect from corrosion damage, the anti-corrosion coating for steel is one of the best choices that keep the material away from the direct connection with the corrosion-made compounds.
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