The corrosion of steel is a problem that occurs in all environments but it is particularly prevalent in coastal regions. Here we will explain how and why steel corrodes, why it is prevalent in coastal areas and marine environments and how stainless steel can be used to combat these degradation effects.
What does the corrosion of steel mean ?
Structure steel corrosion is an electrochemical process that requires both oxygen and moisture to be present at the same time, this forms rust. Rust is essentially created when the iron in steel oxidises, taking up roughly six times as much space as the initial substance. The 'micro-climate' immediately surrounding the structure, as well as a number of other elements, determines how quickly the corrosion process develops.
Fig.1: Rusty Fittings
Why is corrosion prevalent in Coastal Regions & Marine Environments?
Steel located in coastal & marine environments are more susceptible to corrosion due to the high levels of moisture in the air. The presence of pollutants, such as sulfur dioxide and carbon dioxide, in the atmosphere can also increase the rate of corrosion.
Stainless steel corrodes at least five times more quickly in saltwater than it does in freshwater. The cause is that salt, which is an electrolyte, disperses ions into water, accelerating corrosion. Steel corrodes 10 times more quickly as a result of this in combination with salty ocean air than it would in inland air with a normal humidity level.
According to a recent study, salt can still have an impact on the system up to 10 miles from the coast. Higher wind speeds, for instance, indicate that the salt air is spread out much farther than only the coastal regions in that location. Bacteria in the water is another environmental factor that will impact the rate of corrosion.
Effects of Steel Corrosion
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Reduction in Strength: Corrosion can weaken the steel structure, reducing its load-bearing capacity and compromising its safety.
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Aesthetic Degradation: Corrosion can also affect the appearance of the steel structure, making it look old and worn out.
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Maintenance Costs: The cost of repairing and maintaining corroded steel structures can be significant, especially if the damage is severe.
What is Stainless Steel and how it reduces the affects of corrosion.
Stainless Steel is an alloy of Iron that is resistant to rusting and corrosion. Our product ranges contain two grades of stainless steel, 304 (A2) and 316 (A4). Due to its corrosion resistance, stainless steel is a far better material than carbon steel or aluminium for many purposes. Chromium, nickel, and molybdenum are all present in stainless steel in varying quantities and all help to prevent corrosion. Due to varying grades and alloy compositions, some versions are more corrosion resistant than others and are therefore better suited to the harsh coastal climates. The 304 grade of stainless steel is more suited to inland conditions whereas 316 grade is more widely used in marine and coastal environments.
The below Figure.2 comparing 304 and 316 stainless steel to plain carbon steel (also known as mild steel) can illustrate the differences in their corrosion resistance properties.
Fig.2: Corrosion rates of different steel grades in coastal environments
As can be seen from the graph, both 304 and 316 stainless steel have much lower corrosion rates than plain carbon steel in saltwater. 316 stainless steel, in particular, has significantly lower corrosion rates than 304 stainless steel, making it more resistant to corrosion in harsh environments.