Understanding Corrosion in Nitric Acid Environments: Evolution of Corrosion Resistant Stainless Steels

摘要

The materials for use in nitric acid service have to be resistant to intergranular corrosion. For stainless steels, the main reason for intergranular corrosion is sensitization, a process that has been thoroughly investigated and understood in the last few decades. Apart from the carbon, the alloying elements like nickel and chromium also affect the resistance to sensitization. Even non-sensitized stainless steels are known to undergo intergranular corrosion due to segregation of silicon and phosphorus at grain boundaries. End grain corrosion resulting from sulphide inclusions and due to segregation along dislocation bands needs to be minimized. This paper describes the strategies used in combating corrosion due to these factors. The experience gained at Bhabha Atomic Research Centre in optimizing the Nitric Acid Grade stainless steel has been described. The influence of contamination of the process fluid due to chloride and fluoride ions on corrosion behaviour has been described to emphasise the strong passivating action of nitric acid on stainless steels.