What does PREN stand for?

• A. Pitting Reduction Environmental Number
• B. Protection Rating Equivalent Number
• C. Pit Reactivity Equivalent Number
• D. Pitting Resistance Equivalent Number

Answer: (D)

Pitting resistance in stainless steels is estimated with PREN, a simple index that captures how alloying elements influence the protective passive film against localized attack in chloride environments. PREN stands for Pitting Resistance Equivalent Number. It combines chromium, molybdenum, and nitrogen to reflect their contributions to resisting pit initiation, with higher values indicating better resistance. A common form is PREN = Cr + 3.3 Mo + 16 N (percent by weight), so increasing Cr, Mo, or adding N raises PREN and typically improves pitting resistance. For example, adding molybdenum to a Cr-rich stainless steel raises PREN and enhances resistance to chloride-induced pits. The other phrases don’t represent the standard term used to describe this metric.