Stainless Steel Grades Used in the Water Industry

  • Type 304L(1.4307) and 316L(1.4404) are the two grades of stainless steel most frequently used in the water industry. The 316L(1.4404) grade contains molybdenum, which provides a higher corrosion resistance and is therefore used for more exacting conditions. Both have an austenitic structure that in practical terms means they are ductile and strong and do not embrittle in freezing temperatures. A range of more highly alloyed “super”austenitic alloys is available for very critical applications. Their composition provides stronger alloys with very high corrosion resistance which means they can be used for handling higher chloride waters (even sea water) and higher levels of free chlorine in the waters than can be accommodated by the Type 304L(1.4307) and 316L(1.4404) grades.

The third most common grade used in the water industry is the duplex alloy 2205(1.4462). This has a higher corrosion resistance to waters than 316L(1.4404). The name duplex indicates that the alloy structure contains both austenite and ferrite in roughly similar amounts. This appreciably increases the alloy strength whilst retaining a reasonable ductility. It will embrittle at very low temperatures, but as this occurs at below -45°C there is no practical significance. A range of super-duplex grades is available which are similar to the super-austenitic alloys in having very high corrosion resistance and are used for exceptionally severe conditions.

Table 2. Typical Chemical Composition of Some Commonly Used Stainless Steels

Popular NameEuronorm  EN 10088-2Carbon max. %Nickel NiChromium CrMolybdenum MoOther ElementsUNS Equivalent

304L

1.4307

0.03

8.00-10.00

17.50-19.50

-

 

S30403

316L

1.4404

0.03

10.0-13.0

16.5-18.5

2.0–2.5

 

S31603

316Ti

1.4571

0.08

0.5-13.5

16.5-18.5

 2.0–2.5

Ti

S31635

22% Cr 

1.4462

0.03 

4.5-6.5

21.0-23.0

2.5-3.5

N

S31803*

duplex
(alloy 2205)

1.4462

0.03

4.5-6.5

22.0-23.0

3.0-3.5

N

S32205*

25% Cr

super-duplex

1.4507

1.4410

1.4501

0.03

0.03

0.03

5.5-7.5

6.0-8.0

6.0-8.0

24.0-26.0

24.0-26.0

24.0-26.0

2.7-4.0

3.0-4.5

3.0-4.0

Cu, N

N

Cu, N, W

S32550

S32750

S32760

904L

1.4539

0.02

24.0-26.0

19.0-21.0

4.0-5.0

Cu

N08904

6% Mo

super-austenitic

1.4529

1.4547

-

0.02

0.02

0.03

24.0-26.0

17.5-18.5

23.5-25.5

19.0-21.0

19.5-20.5

20.0-22.0

6.0-7.0

6.0-7.0

6.0-7.0

Cu, N

Cu, N

N

N08926

S31254

N08367

Table 3. Mechanical Properties taken from EN 10088-2(Cold rolled, solution annealed strip)

Popular Name 

0.2%Proof Stress* MPa Tensile Strength MPa Elongation*  %
304L

220

520-670

45

316L

 240

 530-680

 40

22% Cr Duplex 

 480

 660-950

 20

25% Cr Super-duplex
(1.4507) 

 570

 690-940

 17

Alloy 904L 

 240

 530-730

 35

6%MoSuper-austenitic
(1.4547)

 320

 650-850

 35

*Single values are minimum values.

The alloys listed are not exhaustive and further information can be found in: