CORROSION IN MARINE ENVIRONMENTS
Marine Grade Steel
This type of stainless steel is known as “marine grade” thanks to its extreme resistance to any sort of atmospheric agent, in particular the corrosive nature of marine environments. It is classified as stainless steel 316 or AISI 316 by the authoritative classifying body.
The corrosive effects of salt water.
The composition of sea water and its physical and chemical properties are constant throughout the world, with a few small but significant local variants. Some of the most important factors related to corrosion are the amount of dissolved oxygen in, the pH level, the temperature, turbulence, micro-organism activity, and the balance between carbonates and bicarbonates in the water. Stainless steel’s resistance to corrosion is thanks to the formation of a passive film on its surface, made from chromium- molybdenum. These materials are resistant to corrosion in water neutral environments. In order for a stainless steel to remain resistant to corrosion in marine environments, it must possess a PREN greater than 40. Once the passive film has been broken, the corrosion will spread only if oxygen is present in the solution.