TKp. Dr. Winfried Heimann

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2 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

3 Typical Relation of Corrosion Resistance und Mechanical Strength of some Stainless Steel Grades Corrosion Resistance Austenitic grades Superferritic grades 28 Cr Mo + Ni Ferritic grades Ferritic-Austenitic (Duplex)-Grades Mechanical Strength

4 Stainless Steel Grades for Seawater Desalination Plants EN ASTM A 240 Cr % Ni % Mo % Others PRE 1 CPT 2 C S ,5 0,3 N S ,8 0,3 N S ,0 N S <0,5 1,90 Ti + Nb L , S ,1 N + Cu S ,5 N + Mn 46 >87 1 PRE= %Cr + 3,3%Mo + 16x%N (Pitting Resistance Equivalent) 2 Critical Pitting Temperature acc. ASTM G 150 Duplex stainless steel grades Austenitic stainless steel grades Ref.: Mikael Willför, Outokumpu: Materials selection for thermal plants DME-Workshop 2008, Duisburg Ferritic stainless steel grades

5 Mechanical properties of Stainless Steel Cold rolled Strip Minimum Values EN ASTM A 240 Yield Strength Rp0,2 MPa EN(ASTM) Tensile Strength Rm MPa EN(ASTM) Elongation A5 % EN(ASTM) S32101 (530) (700) (30) S (420) 650(600) 20(20) S (550) 750(750) 20(15) S (275) 420(415) 20(20) S S (310) 650(690) (35) S Duplex stainless steel grades Ferritic stainless steel grades Austenitic stainless steel grades

6 Physical Properties of Stainless Steel grades (Average values according to EN or ASTM A240) Ferritic grades 17Cr 2Mo 28Cr 1-4Mo 0-2Ni (Superferritics) Duplex grades Austenitic grades (Superaustenitics) Density g/cm³ 7,7 7,7 7,8 8,0 8,1 Modulus of Elasticity GPa Thermal Conductivity Thermal Expansion W/mK RT C 10-6 /K 23 17, ,0 17,0 16,5 Specific Heat J/kg C

7 Corrosion of Materials in Sea Water Desalination Plants Forms of corrosion General corrosion Pitting and crevice corrosion Erosion corrosion Galvanic corrosion

8 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

9 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

10 Critical Pitting and Crevice Corrosion Temperatures of Stainless Steel Grades 100 According to ASTM G Temperature [ C] Pitting Crevice Corrosion PRE (%Cr %Mo + 30 %N)

11 Critical Pitting Temperature of Stainless Steel Grades (Values determined according to ASTM G 150) Critical Pitting Temperature Duplex Stainless Steel Grades Austenitic Stainless Steel Grades Ref.: Outokumpu Stainless Corrosion Handbook Ninth Edition, 2004

12 Influence of PRE (Pitting Resistance Equivalent) %Cr + 3,3x%Mo on the CPT (Critical Pitting Temperature) of welded and unwelded Stainless Steels Critical Pitting Temperature C unwelded TIG-welded, without filler TIG-welded, overalloyed filler (THERMANIT 625) Laser-welded tubes (0,3x30)mm, minimum value Cr / 6,6 Mo Test according to ASTM G48 20 Cr / 6,1 Mo PRE = % Cr % Mo

13 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.

14 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)

15 Corrosion of Stainless Steels in Contaminated (Solids) Flowing Sea Water Corrosion rate [g/m² d] Ferritic Cr-Steels Duplex Stainless Steels Austenitic Mn-Steels Austenitic Steel Superaustenitic Steels UNS S Flow velocity [m/s]

16 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.

17 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

18 Condenser tubes UNS S34565

19 Weld shape of TIG and Laser welded Stainless Steel thin walled tubes, welded from 1,5 mm cold rolled strip Tungsten inert gas welding - TIG Welding root sag < 0,2 mm Welding root planed Laser welding Welding root sag < 0,15 mm

20 Corrosion Tests in Simulated MSF Desalination Plant Evironments Tests carried out by Cortest Laboratories, Sheffield Experimental Test Program 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 Tube assembly specimen Methodes of joining: Welding to the tube plate Rolling into the tube plate Ref.: NACE Corrosion 2001, Paper No NACE Corrosion 2002, Paper No

21 Corrosion Tests in Simulated MSF Desalination Plant Evironments Tests carried out by Cortest Laboratories, Sheffield 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 S 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. Ref.: NACE Corrosion 2001, Paper No NACE Corrosion 2002, Paper No

22 Stainless Steel grades for Condenser Tubes for MSF-Desalination Plants Superaustenitic stainless steels: (S34565) Superduplex stainless steels: (S32750) (S32760) Superferritic stainless steels: Seacure(S44660) (S44735)

23 Stainless Steel grades for Condenser Tubes for MED-Desalination Plants Austenitic stainless steels: (S31603) Duplex stainless steels: (S32101) (S32304) Ferritic stainless steels: (S44400)

24 Stainless Steel thin walled Tubes for Desalination Plants MSF Plants: Heat recovery stages Heat reject stages Brine heater Vacuum systems MED Plants Evaporator shell Tube and Tube support plates Vacuum ejectors Condenser tubes

25 Technical Data: 1,4 Million Meters Condenser Tubes of (UNS S34565) Producer: Fischer Edelstahlrohre GmbH MED - HTE Multi Effect Distillation Horizontal Tube Evaporation Capacity: 2 x m³ / d Operating Temperature: <65 C Raw Water: Brackish Water Destillate : < 5µS/cm Effectiveness: >95 %

26 Stainless Steels in the Sea-Water-Desalination Condenser Tubes made of Source: VA TECH WABAG

27 Stainless Steels in the Sea-Water-Desalination Technology Heat-Exchanger Tubes made of Windpowered seawater desalination Plant

28 MSF and MED condenser tubing Historically titanium and copper alloys Trends and options Poor availability of titanium Environmental impact of toxic copper ions 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

29 Reference List Fischer Edelstahlrohre GmbH Rügen St. Martin Rotterdam Evaporator-Condenser Tubes of UNS S34565 in Operation since 1998 at about 80 C Testing of Condenser Tubes of UNS S34565 since 1998 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 South Korea Sharjah U.A.E. Evaporator-Condenser Tubes of UNS S34565 will start up in 2009 at about 80 C Evaporator-Condenser Tubes of UNS S34565 Installation in a MED test plant Layyah Station for Power Generation & Water Desalination Intake Pump Cooling Coil