PREN (Pitting Resistance Equivalent Number)
A single number that ranks a stainless steel's resistance to chloride pitting, calculated as %Cr + 3.3 x %Mo + 16 x %N.
Why PREN decides the grade
Pitting is driven by chromium, molybdenum and nitrogen. PREN collapses those three into one comparable figure: 304L sits near 19, 316L near 25, duplex 2205 above 34, and super duplex 2507 and 254 SMO above 42.
How to use it
PREN ranks grades against each other — it does not predict a service life. Use it to shortlist, then check the actual chloride concentration, temperature and pH. A rule of thumb for seawater is that a PREN above 40 is needed for crevice-free service at ambient temperature.
Related terms
Where this applies
Duplex & Super Duplex Plate, Super Austenitic & High Alloy Plate
Need help applying this?
Stancor Stainless engineers answer specification questions directly. Contact us.