Corrosion Resistance - PREN Values

Pitting Corrosion Resistance

The Pitting Resistance Equivalence Number (PREN) is a measure of relative pitting corrosion resistance of stainless steel in a chloride-containing environment.

Higher PREN values indicate greater corrosion resistance.

The Ferritic, Austenitic & Martensitic Stainless Steel grade formula for PREN is:

PREN = %Cr + 3.3 x %Mo + 16 x %N

The Duplex SS grade formula for PREN is:

PREN = %Cr + 3.3 x %Mo + 30 x %N

Martensitic Grades

	% Cr	%Mo	%Ni	%N	PREN
410	11.5 - 13.5		0.75		11

Austenitic & Ferritic Grades

	% Cr	%Mo	%Ni	%N	PREN
304	18.0 - 20.0		8-10.5	0.1	19
316	16.0 - 18.0	2.0 - 3.0	10.0 - 14.0	0.1	24
316LHiMo (Bumax)	16.0 - 18.0	2.5 - 3.0	10.0 - 14.0	0.1	25
254SMO (6Mo)	20.0	6.1	18.0	0.2	43

Duplex Grades

	% Cr	%Mo	%Ni	%N	PREN
2205	22.0 - 23.0	3.0 - 3.5	4.5 - 6.5	0.14 - 0.20	36
2507	24.0 - 26.0	3.0 - 5.0	6.0 - 8.0	0.24 - 0.35	41

If the PREN value for a SS is over 40, the SS should be fully resistant to localised corrosion (pitting/crevice corrosion) when immersed in seawater.

NB:This information is provided as a guide only. Anzor does not accept liability for the application of this information.

For advice about stainless steel contact the Nickel Institute.