Pitting resistance equivalent number: calculated from composition, most often as %Cr + 3.3 x %Mo + 16 x %N. Type 304 sits near 18 to 20, 316 near 24 to 26, duplex 2205 around 35, and super duplex and 6Mo austenitic grades above 40, the usual bar for seawater service. It ranks alloys quickly but ignores microstructure, welding and surface finish, so it is a screening tool, not a guarantee.
Seawater cooling wants PREN over 40, so 316 is out, go super duplex or 6-moly.
Also heard as
- PRE
- pitting resistance equivalent
Related terms
Pitting
Localized corrosion that drills small, deep cavities into metal while the surface around them stays nearly intact.
Crevice corrosion
Localized attack inside tight gaps under gaskets, deposits or lap joints where the solution stagnates.
Intergranular corrosion
Attack that runs along grain boundaries, often in stainless steel sensitized by welding heat.
Tea staining
Light brown surface discoloration on stainless steel exposed to salt air or pollution, mostly cosmetic.