The pitting resistance equivalent number (PREN) is a theoretical metric derived from a stainless steel's chemical composition, primarily its chromium, molybdenum, and nitrogen content. A higher PREN indicates better resistance to localized pitting in chloride-rich environments like seawater. Engineers use this number to select appropriate alloys for specific corrosive services, with values above 40 generally required for severe marine or offshore applications.
We need a super duplex with a PREN over 40 for this seawater injection line.
The standard formula is PREN = %Cr + 3.3(%Mo) + 16(%N). If an alloy's PREN is below 32, it will likely pit in warm seawater.
Related terms
Pitting
Localized corrosion that drills small, deep cavities into metal while the surface around them stays nearly intact.
PREN
Pitting resistance equivalent number: an index of a stainless alloy's chloride pitting resistance from its chemistry.
Crevice corrosion
Localized attack inside tight gaps under gaskets, deposits or lap joints where the solution stagnates.