The Family of Duplex Stainless Steels
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The Family of Duplex Stainless Steels
GRADES OF DUPLEX
Duplex stainless steel grades are indeed listed in three groups; standard, lean, and super. This classification is made according to the composition of the alloy, its corrosion resistance, and its mechanical properties. The standard grade has a balanced composition, while the lean grade has a lower nickel content for improved cost-effectiveness. The super grade, on the other hand, has a higher content of chromium, molybdenum, and nitrogen for superior resistance to corrosion and higher strength.
The grades are listed in three groups; standard, lean and super.
The major difference between each grade is corrosion resistance. This is based on a Pitting Equivalent Number:
(PREN) = %Cr + 3.3 x %Mo + 16 x %N.
This is a comparative rating that relates to the critical pitting and crevice corrosion temperatures in hi chloride environments (CPT and CCT respectively).
| DUPLEX TYPE | PREN |
| Standard | Approximately 35 |
| Lean | 25-30 |
| Duplex | Above 40 |
USES OF DUPLEX STAINLESS STEELS
Stress corrosion cracking (SCC) is a form of corrosion that occurs with a particular combination of factors:
- Tensile stress;
- Corrosive environment;
Sufficiently high temperatures: Normally above 60°C but can occur at lower temperatures (around 30°C in specific environments, notably unwashed atmospheric exposures above indoor chlorinated swimming pools).
Unfortunately, the standard austenitic steels like 304 (1.4301) and 316 (1.4401) are the most susceptible to SCC. The following materials are much less prone to SCC:
- Ferritic stainless steels;
- Duplex stainless steels;
- High nickel austenitic stainless steels;
The resistence to SCC makes duplex stainless steels suitable for many processes operating at higher temperatures. Examples of the successful use of duplex stainless steel are hot water tanks, brewing tanks and thermal desalination vessels.
GNEE Steel has been committed to the stainless steel industry for many years and is an expert in stainless steel. GNEE Steel provides high-quality stainless steel products to solve various needs for you.
