Iron Corrosion and Stainless Steel Corrosion

Wrought Iron

Most metal aquarium stands available in the market is made of wrought iron. It is a relatively tough metal and cheap to produce. However, it is almost guaranteed to rust within a very short time of use. To increase its rust resistance, you may want to find one with a thicker wall thickness (i.e. 3.2 mm shell thickness rather than 1.6mm)

You may also fully galvanise it after the welding process, followed by a coat of paint on top as an extra measure.

Stainless Steel

All stainless steel will rust, it is only a matter of how long it takes before it does, and the rate where it gets worse. The main factor that determines the resistance to corrosion is the grade of the metal. Most low grade stainless steel is grade 304, while most high grade stainless steel is 316 or 316L

The grade will be the major factor of corrosion resistance. Most commonly used high grade SS will be 316 or 316L which is the low carbon version.

Other than the grade, the resistance to corrosion is also affected by the process of manufacturing. If the workshop handles carbon steel and stainless steel, there is a high chance of contamination. Stainless steel, when in contact with carbon steel, results in galvanic corrosion which may cause pitting.

Most corrosion take place near the edges of the weld where improper heating or higher carbon stainless steel causes the forming of chromium carbide. Chromium when exposed to oxygen forms chromium oxide (which is the reason why stainless steel is corrosion resistant). Chromium carbide robs the chromium and creates a galvanic couple which will corrode the steel. Nobium or titanium can be added to form nobium carbide or titanium carbide to prevent this.

So how can we protect stainless steel? Paint it and keep it protected from moisture. Avoid contact with carbon steel and make sure that no other metals are electrically connected to it.





 

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