Sulfuric acid corrosion resistance of high gary cast iron

Sulfuric acid corrosion resistance of cast iron

    The corrosion resistance of common cast iron in sulfuric acid is similar to that of common carbon steel. However, gray cast iron will crack in concentrated sulfuric acid. This is because acid can infiltrate into the cast iron along the continuous sheet graphite structure, causing corrosion inside the cast iron (official account: Pump housekeeper).

     Due to the increase of the volume of corrosion products, the local stress is very high. With the increase of corrosion products, the local internal stress increases continuously, which finally leads to the cracking and damage of cast iron. Therefore, it is not suitable to use ordinary gray cast iron in sulfuric acid. If the continuous flake graphite structure is transformed into discontinuous spherical structure by heat treatment, the sulfuric acid will not penetrate into the cast iron, thus the cracking of cast iron in sulfuric acid can be prevented. Therefore, the so-called malleable cast iron, ductile cast iron or ductile cast iron have better performance in sulfuric acid.
Galvanic corrosion may occur when cast iron and carbon steel are used together in about 100% sulfuric acid. Because of the brittleness of cast iron and the consideration of safety, it is better to use carbon steel than cast iron when possible

     Grey cast iron is essentially an alloy of primarily iron, carbon and silicon with manganese, sulphur and phosphorus in minor amounts.  The carbon is present as free carbon or graphite interspersed throughout the mass of metal.  In grey cast iron, the graphite is in the form of flakes while in ductile cast iron, the graphite is in the form of nodules.  Cast iron is easily machined because the graphite in the iron acts as a lubricant during machining.

    Grey cast iron is no longer recommended for use in sulphuric acid plants.  in the past, there have been instances where acid lines have been accidentally struck and have failed catastrophically.   Ductile iron should only be used in sulphuric acid service.