Role of nitrite addition in chloride stress corrosion cracking of a super duplex stainless steel

This paper presents the role of addition of nitrite ions in susceptibility of a super duplex stainless steel, SAF 2507 to stress corrosion cracking (SCC) in chloride environment, which has a particular industrial relevance. Slow strain rate testing (SSRT) in 30 wt.% MgCl2 solution established SCC susceptibility, as evidenced by post-SSRT fractography. However, the addition of nitrite has interesting influence. At their lower concentrations, nitrite additions seem to decrease SCC susceptibility, whereas, at a higher concentration, it has an accelerating effect on SCC. Attempts have been made to understand this behaviour on the basis of the role of nitrite in passivation and pitting characteristics of SAF 2507 in chloride solution.