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
| % Cr | %Mo | %Ni | %N | PREN | FEATURES | |
|---|---|---|---|---|---|---|
| 410 | 11.5 - 13.5 | 0.75 | 11 | Can be hardened for self drilling | ||
| Hardtec | 13 | 1-2% | 16 | Hardened for self drilling and good corrosion resistance |
| % Cr | %Mo | %Ni | %N | PREN | FEATURES | |
|---|---|---|---|---|---|---|
| 304 | 18.0 - 20.0 | 8-10.5 | 0.1 | 19 | General purpose grade | |
| 316 | 16.0 - 18.0 | 2.0 - 3.0 | 10.0 - 14.0 | 0.1 | 24 | Medium corrosion resistance |
| 316LHiMo (BUMAX® 88 and 109) | 16.0 - 18.0 | 2.5 - 3.0 | 10.0 - 14.0 | 0.1 | 25 | Stronger and higher corrosion resistance |
| 254SMO (6Mo) | 20.0 | 6.1 | 18.0 | 0.2 | 43 | Very high corrosion resistance |
| 1.4529 (A8-80) | 19 - 21 | 6 - 7 | 24 - 26 | 0.15 - 0.25 | 47 | Highest corrosion resistance, suitable for tunnels and above indoor swimming pools as per EU standards |
| % Cr | %Mo | %Ni | %N | PREN | FEATURES | |
|---|---|---|---|---|---|---|
| 2202 (Class 80) | 21.0 - 23.0 | 0.2 - 0.6 | 4.5 - 6.5 | 0.05 - 0.20 | 23 | High strength and cost effective |
| 2205 | 22.0 - 23.0 | 3.0 - 3.5 | 4.5 - 6.5 | 0.14 - 0.20 | 36 | High strength and high corrosion resistance |
| BUMAX® DX 129 (2205 Class 120) | 22.0 - 23.0 | 3.0 - 3.5 | 4.5 - 6.5 | 0.14 - 0.20 | 36 | Highest strength and high corrosion resistance |
| BUMAX® DX 149 (2205 Class 140) | 22.0 - 23.0 | 3.0 - 3.5 | 4.5 - 6.5 | 0.14 - 0.20 | 36 | The highest strength - made to order |
| 2507 (Class 80) | 24.0 - 26.0 | 3.0 - 5.0 | 6.0 - 8.0 | 0.24 - 0.35 | 41 | High corrosion resistance for salt water |
| BUMAX® SDX 109 (2507 Class100) | 24.0 - 26.0 | 3.0 - 5.0 | 6.0 - 8.0 | 0.24 - 0.35 | 41 | Very high corrosion resistance and strength |
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 technical advice about stainless steel and grade selection, you can log a free enquiry with the Nickel Institute.
A grade's resistance to pitting corrosion can be estimated and calculated by a PRE value or PREN (Pitting Resistance Equivalent Number). This number is an approximate guide for the corrosion resistance of each Stainless grade.
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