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•  Dr. Winfried Heimann •  was heading varios division of R+D, quality control and application engineering in Thyssen Edelstahlwerke and

ThyssenKrupp Nirosta •  was being Senior Manager with Outokumpu Stainless •  after retirement he is acting as Consultant in this field

•  Christian Behrle •  is heading the Technical Department for R+D in Fischer-group •  specialised in SS-tubes for desalinations •  DME – Member of the Board •  Member of IDA •  Member of EDS

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Typical Relation of Corrosion Resistance und Mechanical Strength of some Stainless Steel Grades

Mechanical Strength

Cor

rosi

on R

esis

tanc

e

Austenitic grades Superferritic grades

Ferritic-Austenitic (Duplex)-Grades

Ferritic grades

1.4565

1.4404

1.4547

1.4162 1.4362

1.4410

1.4539

1.4521

28 Cr + Mo + Ni

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EN 10088

ASTM A 240

Cr %

Ni %

Mo %

Others PRE1

1.4162 S32101 21 1,5 0,3 N 26 19

1.4362 S32304 23 4,8 0,3 N 26 25

1.4410 S32750 25 7 4,0 N 43 85

1.4521 S44400 18 <0,5 1,90 Ti + Nb 24 22

1.4404 316 L 17 10 2,1 - 25 21

1.4547 S31254 20 18 6,1 N + Cu 43 87

1.4565 S34565 24 17 4,5 N + Mn 46 >87

1  PRE= %Cr + 3,3%Mo + 16x%N (Pitting Resistance Equivalent) 2  Critical Pitting Temperature acc. ASTM G 150

Ref.: Mikael Willför, Outokumpu: Materials selection for thermal plants DME-Workshop 2008, Duisburg

Stainless Steel Grades for Seawater Desalination Plants

Duplex stainless steel grades Austenitic stainless steel grades

CPT2

°C

Ferritic stainless steel grades

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EN 10088

ASTM A 240

Yield Strength Rp0,2

MPa EN(ASTM)

Tensile Strength

Rm MPa

EN(ASTM)

Elongation

A5

% EN(ASTM)

1.4162 S32101 (530) (700) (30)

1.4362 S32304 450(420) 650(600) 20(20)

1.4410 S32750 550(550) 750(750) 20(15)

1.4521 S44400 320(275) 420(415) 20(20)

1.4404 S31603 240 530 40

1.4547 S31254 320(310) 650(690) (35)

1.4565 S34565 420 800 30

Mechanical properties of Stainless Steel Cold rolled Strip Minimum Values

Duplex stainless steel grades Austenitic stainless steel grades Ferritic stainless steel grades

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Ferritic grades 17Cr 28Cr 2Mo 1-4Mo 0-2Ni (Superferritics)

Duplex grades Austenitic grades 1.4404 1.4547 1.4565 (Superaustenitics)

Density g/cm³ 7,7 7,7 7,8 8,0 8,1

Modulus of Elasticity GPa

220 200 200 200 195

Thermal Conductivity W/mK

23 17,5 15 15 12

Thermal Expansion RT - 300°C 10-6/K

11  10 14,0 17,0 16,5

Specific Heat J/kg°C

430 500 500 500 450

Physical Properties of Stainless Steel grades (Average values according to EN 10088 or ASTM A240)

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Corrosion of Materials in Sea Water Desalination Plants

Forms of corrosion

•  General corrosion

•  Pitting and crevice corrosion

•  Erosion corrosion

•  Galvanic corrosion

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Corrosion Resistance of Stainless Steel in Sea Water

•  Stainless Steels have negligible thinning in sea water

•  Chromium oxide film (passive layer) forms immediately on steel surface with exposure to air

•  Oxygen levels as low as 20 ppb are still sufficient to repair itself after being damaged

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Corrosion Resistance of Stainless Steel in Sea Water

• Pitting and Crevice Corrosion • Under certain conditions the protective surface film on stainless steels can break down locally:

oxyginated water high chloride too high chlorination level low pH-value pitting and crevice corrosion

more resistant grade has to be selected acc. to PRE = %Cr + 3,3% Mo + 30 (16)% N ranking of alloys can be carried out

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Critical Pitting and Crevice Corrosion Temperatures of Stainless Steel Grades

According to ASTM G 48

1.4404

1.4404

1.4439

1.4439

1.4462

1.4462

1.4539

1.4539

1.4410

1.4410

1.4565

1.4565

Pitting Crevice Corrosion

100

80

60

40

20

0

Tem

pera

ture

[°C

]

PRE (%Cr + 3.3 %Mo + 30 %N)

25 35 45 55

1.4547

1.4547

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Critical Pitting Temperature of Stainless Steel Grades (Values determined according to ASTM G 150)

Crit

ical

Pitt

ing

Tem

pera

ture

Duplex Stainless Steel Grades Austenitic Stainless Steel Grades

Ref.: Outokumpu Stainless Corrosion Handbook Ninth Edition, 2004

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20 Cr / 6,6 Mo

1.4529

1.4404 1.4438

20 Cr / 6,1 Mo

1.4462 1.4439 1.4539

90 unwelded TIG-welded, without filler TIG-welded, overalloyed filler (THERMANIT® 625) Laser-welded tubes (0,3x30)mm, minimum value

80

70

60

50

40

30

20

10

0 25 30 35 40

Test according to ASTM G48

PRE = % Cr + 3.3 • % Mo

Crit

ical

Pitt

ing

Tem

pera

ture

1.4565

%Cr + 3,3x%Mo on the CPT (Critical Pitting Temperature) of welded and unwelded Stainless Steels

°C

Influence of PRE (Pitting Resistance Equivalent)

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Erosion Corrosion in Sea Water Desalination Plants

Erosion corrosion is the most common failure, e.g. in the heat rejection

•  Copper alloys, brasses and bronzes are prone to impingement attack, at sea water velocities above 3m/s.

•  In sea water polluted with solids copper based alloys suffer severe erosion corrosion even at very low flow rates (< 0,5 m/s)

•  Stainless steels and especially high alloyed grades like Duplex and Superaustenitics are much better resistant to erosion corrosion than copper based alloys.

There is no risk of erosion corrosion with special stainless steels at velocities up 20 m/s even up to 40 m/s with high nitrogen containing Superaustenitic steel UNS S34565.

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Corrosion Resistance of Stainless Steel in Sea Water

•  Erosion and Erosion Corrosion

•  The passive layer is maintained at very high flow rates and

•  Sea water velocities in excess of 40 m/s can be accommodated (in praxis usually below 10m/s)

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Austenitic Mn-Steels

Ferritic Cr-Steels Duplex Stainless Steels

Superaustenitic Steels UNS S34565

1000

100

10

1 0 20 40 60

Flow velocity [m/s]

Cor

rosi

on ra

te [g

/m² d

]

Austenitic Steel

Corrosion of Stainless Steels in Contaminated (Solids) Flowing Sea Water

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Galvanic Corrosion in Sea Water Desalination Plants Multi-metal systems: Stainless steels, titanium, copper aloys

•  Titanium is cathodic to most of other metals.

•  Stainless steels are towards the more noble end of the galvanic series.

•  Superaustenitic stainless steels are compatible with titanium because their free corrosion potential is close together.

•  Galvanic corrosion occurs when using titanium or stainless steel tubing together with copper based alloy tube sheets, increasing corrosion attack to the tube sheet to a point where cathodic protection is required in the water boxes.

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Chlorination – Performance of Stainless Steel •  Chlorination is used to control microbiological films. To prevent the build-up of biofilms and remove settled biological species.

•  Practice of chlorination is the addition of a hypochloride solution to the sea water

•  Chlorination can be either continuous or intermittent (Chlorine is added for shorter periods e.g. twice a day 15 minutes)

•  Chlorination level - continuous: 0,1 - 0,4 ppm - intermittent: several ppm total amount of chlorine is less than with systems using continuous systems

•  The objective: Keep the residual chlorine level < 0,5 ppm

•  Stainless steel perform well up to 2ppm

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Condenser tubes UNS S34565

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Welding root planed Welding root sag < 0,2 mm

Welding root sag < 0,15 mm

Laser welding

Tungsten inert gas welding - TIG

Weld shape of TIG and Laser welded Stainless Steel – thin walled tubes, welded from 1,5 mm cold rolled strip

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Tube assembly specimen Methodes of joining: •  Welding to the tube plate •  Rolling into the tube plate

Corrosion Tests in Simulated MSF Desalination Plant Evironments Tests carried out by Cortest Laboratories, Sheffield

Material: •  UNS S34565, laser welded tube with 0,35 mm wall thickness, 20 mm and 30 mm diameter •  UNS S31603, S31803, S32760, and S34565, plate material

Test Environment: •  Alloy C276 autoclave •  Syntetic sea water heated to 90°C •  Three oxigen levels, 750, 150, and 65 ppb

Test Duration: 30 days

Experimental Test Program

Ref.: NACE Corrosion 2001, Paper No. 01484 NACE Corrosion 2002, Paper No. 02190

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Corrosion Tests in Simulated MSF Desalination Plant Evironments Tests carried out by Cortest Laboratories, Sheffield

Ref.: NACE Corrosion 2001, Paper No. 01484 NACE Corrosion 2002, Paper No. 02190

Results: •  UNS S34565 thin walled, laser welded tubing did not corrode in any of the tests •  No corrosion occurred at the welds of any tubeplate material studied. UNS S34565, S32760, S31603 •  Some corrosion was observed at non welded joints. Greatest on S32760 and least on S34565.

•  The extend of corrosion on the non-welded assemblies was not great. In particular for the S34565 the corrosion is insignificant at the lowest oxigen level tested of 65 ppb.

Conclusions: •  UNS S34565 thin walled laser welded tubes when welded to S34565, S32760 or S31603 tubeplates would be suitable for MSF plant evaporators.

•  UNS S34565 thin walled laser welded tubes when rolled into S34565 tubeplate would be suitable for MSF plant evaporators.

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Stainless Steel grades for Condenser Tubes for MSF-Desalination Plants

Superaustenitic stainless steels: 1.4565 (S34565)

Superduplex stainless steels: 1.4410 (S32750) 1.4501 (S32760)

Superferritic stainless steels: Seacure(S44660) 1.4592 (S44735)

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Stainless Steel grades for Condenser Tubes for MED-Desalination Plants

Austenitic stainless steels:

1.4404 (S31603)

Duplex stainless steels:

1.4162 (S32101) 1.4362 (S32304)

Ferritic stainless steels:

1.4521 (S44400)

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Stainless Steel thin walled Tubes for Desalination Plants

MSF Plants: •  Heat recovery stages •  Heat reject stages •  Brine heater •  Vacuum systems

MED Plants •  Evaporator shell

•  Condenser tubes

•  Tube and Tube support plates •  Vacuum ejectors

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Technical Data:

Capacity: Operating Temperature: Raw Water: Destillate : Effectiveness:

MED - HTE Multi Effect Distillation Horizontal Tube Evaporation

2 x 12.000 m³ / d <65°C

Brackish Water < 5µS/cm

>95 % 1,4 Million Meters

Condenser Tubes of 1.4565 (UNS S34565)

Producer: Fischer Edelstahlrohre GmbH

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Source: VA TECH WABAG

Stainless Steels in the Sea-Water-Desalination Condenser Tubes made of 1.4565

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Stainless Steels in the Sea-Water-Desalination Technology Heat-Exchanger Tubes

made of 1.4565

Windpowered seawater desalination Plant

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MSF and MED condenser tubing

Historically titanium and copper alloys •  Poor availability of titanium •  Environmental impact of toxic copper ions

Trends and options •  Decreasing use of copper alloys •  Use of corrosion resistant stainless steels

Duplex stainless steels Austenitic and superaustenitic stainless steels Ferritic and superferritic stainless steels

•  Reduction of wall thickness, e.g. heat exchanger tubes with 0,3 to 0,1 mm, UNS S34565 Ref. AVR Rotterdam

Ref.: DME-Seminar Materials and Corrosion in Desalination Plants, June 2007 Heike Glade, Bremen Jan Olsson, Outokumpu Stainless

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Reference List Fischer Edelstahlrohre GmbH

Rügen Evaporator-Condenser Tubes of UNS S34565 in Operation since 1998 at about 80°C

St. Martin Testing of Condenser Tubes of UNS S34565 since 1998 Rotterdam MED-Plant of AVR Rotterdam, NL in Operation since Dez. 1999, 1,4 Mio m Tubes of UNS S34565 Al-Taweelah A1 Condenser tubes of 316 L (1.4404) / MED

Creek Island Evaporator-Condenser Tubes of UNS S34565 will start up in 2009 at about 80°C South Korea Evaporator-Condenser Tubes of UNS S34565 Installation in a MED test plant Sharjah U.A.E. Layyah Station for Power Generation & Water Desalination – Intake Pump Cooling Coil