PREN – Pitting Resistance Equivalency Number
Pitting resistance equivalent numbers (PREN) are a theoretical way of comparing the pitting corrosion resistance of various types of stainless steels, based on their chemical compositions.
The PREN (or PRE) numbers are useful for ranking and comparing the different grades, but cannot be used to predict whether a particular grade will be suitable for a given application, where pitting corrosion may be a hazard.
Actual or specified range compositions can be used and usually involve chromium, molybdenum and nitrogen in the calculations.
| Grade | Type | Cr Min |
CR Max |
Mo Min |
Mo Max |
N Min |
N Max |
PREN Min |
PREN Max |
|---|---|---|---|---|---|---|---|---|---|
| 1.4301 | Austenitic 304S31 | 17.5 | 19.5 | 0.11 | 17.5 | 21.3 | |||
| 1.4362 | Lean Duplex | 22 | 24 | 0.1 | 0.6 | 0.05 | 0.2 | 23.1 | 29.2 |
| 1.4401/4 | Austenitic 316/316L | 16.5 | 18.5 | 2.0 | 2.5 | 0.11 | 23.1 | 28.5 | |
| 1.4436 | Austenitic 316S33 | 16.5 | 18.5 | 2.5 | 3.0 | 0.11 | 24.8 | 30.2 | |
| 1.4429 | 316LN | 16.5 | 18.5 | 2.5 | 3.0 | 0.12 | 0.22 | 26.7 | 31.9 |
| 1.4462 | Duplex F51 | 21 | 23 | 2.5 | 3.5 | 0.1 | 0.22 | 30.9 | 38.1 |
