TKp TKp Ferritic / Duplex / Austenitic Steel Grades for Condenser Tubes reported by Dr. Winfried Heimann Christian Behrle Ferritic Ferritic / / Duplex Duplex / / Austenitic Austenitic Steel Grades Steel Grades for for Condenser Condenser Tubes Tubes reported reported by by Dr. Winfried Heimann Dr. Winfried Heimann Christian Behrle Christian Behrle
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Dr. Winfried HeimannDr. Winfried HeimannChristian BehrleChristian Behrle
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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
onR
esis
tanc
e
Austenitic grades Superferritic grades
Ferritic-Austenitic(Duplex)-Grades
Ferritic grades
1.4565
1.4404
1.4547
1.41621.4362
1.4410
1.4539
1.4521
28 Cr + Mo+ Ni
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EN10088
ASTMA 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 plantsDME-Workshop 2008, Duisburg
Stainless Steel Grades for Seawater Desalination Plants
90unweldedTIG-welded,without fillerTIG-welded,overalloyed filler(THERMANIT® 625)Laser-welded tubes (0,3x30)mm, minimum value
80
70
60
50
40
30
20
10
025 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 suffersevere 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 thancopper based alloys.There is no risk of erosion corrosion with special stainless steelsat velocities up 20 m/s even up to 40 m/s with high nitrogen containingSuperaustenitic steel UNS S34565.
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Corrosion Resistance of Stainless Steelin Sea Water
• Erosion and Erosion Corrosion
• The passive layer is maintained atvery high flow rates and
• Sea water velocities in excess of 40 m/s canbe accommodated (in praxis usually below 10m/s)
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AusteniticMn-Steels
Ferritic Cr-SteelsDuplex Stainless Steels
Superaustenitic SteelsUNS S34565
1000
100
10
10 20 40 60
Flow velocity [m/s]
Cor
rosi
onra
te [g
/m²d
]
AusteniticSteel
Corrosion of Stainless Steelsin Contaminated (Solids) Flowing Sea Water
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Galvanic Corrosion in Sea Water Desalination PlantsMulti-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 titaniumbecause their free corrosion potential is close together.
• Galvanic corrosion occurs when using titanium or stainless steeltubing together with copper based alloy tube sheets, increasingcorrosion attack to the tube sheet to a point where cathodicprotection 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 solutionto the sea water
• Chlorination can be either continuous orintermittent (Chlorine is added for shorter periodse.g. twice a day 15 minutes)
total amount of chlorine is less than with systemsusing 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 planedWelding 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 specimenMethodes of joining:• Welding to the tube plate• Rolling into the tube plate
Corrosion Tests in Simulated MSF DesalinationPlant EvironmentsTests 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. 01484NACE Corrosion 2002, Paper No. 02190
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Corrosion Tests in Simulated MSF DesalinationPlant EvironmentsTests carried out by Cortest Laboratories, Sheffield
Ref.: NACE Corrosion 2001, Paper No. 01484NACE 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 assemblieswas not great. In particular for the S34565 the corrosion isinsignificant 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 tubeplatewould be suitable for MSF plant evaporators.
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Stainless Steel grades for Condenser Tubesfor MSF-Desalination Plants