The range of duplex stainless steel allows them to be matched for corrosion resistance with the austenitic stainless steel and ferritic stainless steel grades. There is no single measure of corrosion resistance. However, it is convenient to use the Pitting Resistance Equivalent Number (PREN) as a means of ranking the grades.
PREN = %Cr + 3.3 x %Mo + 16 x %N
The following table shows how the duplex stainless steel compare with some austenitic stainless steel and ferritic stainless steel grades.
PREN = %Cr + 3.3 x %Mo + 16 x %N
The following table shows how the duplex stainless steel compare with some austenitic stainless steel and ferritic stainless steel grades.
| Grade | EN No/UNS | Type | Typical PREN |
| 430 | 1.4016/ S43000 | Ferritic stainless steel | 18 |
| 304 | 1.4301/ S30400 | Austenitic stainless steel | 19 |
| 441 | 1.4509/ S43932 | Ferritic stainless steel | 19 |
| RDN 903 | 1.4482/ S32001 | Duplex stainless steel | 22 |
| 316 | 1.4401/ S31600 | Austenitic stainless steel | 24 |
| 444 | 1.4521/ S44400 | Ferritic stainless steel | 24 |
| 316L 2.5 Mo | 1.4435 | Austenitic stainless steel | 26 |
| 2101 LDX | 1.4162/ S32101 | Duplex stainless steel | 26 |
| 2304 | 1.4362/ S32304 | Duplex stainless steel | 26 |
| DX2202 | 1.4062/ S32202 | Duplex stainless steel | 27 |
| 904L | 1.4539/ N08904 | Austenitic stainless steel | 34 |
| 2205 | 1.4462/ S31803/ S32205 | Duplex stainless steel | 35 |
| Zeron 100 | 1.4501/ S32760 | Duplex stainless steel | 41 |
| Ferrinox 255/ Uranus 2507Cu | 1.4507/ S32520/ S32550 | Duplex stainless steel | 41 |
| 2507 | 1.4410/ S32750 | Duplex stainless steel | 43 |
| 6% Mo | 1.4547/ S31254 | Austenitic stainless steel | 44 |
It must be emphasised that this table is only a guide to material selection. It is always important to assess the suitability of a particular with a full knowledge of the corrosive environment.
Source: Zhejiang Yaang Pipe Industry Co., Limited (www.yaang.com)
