S2 · Duplex Flange & Desalination

Double Phase Steel Flanges for Desalination (List of Media, Grades, and Conditions)

List the media, grades, and boundary conditions related to desalination double phase steel flanges: 5 typical components/processes with recommended grades, specifications, failure reasons, and standards.

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Metal Products: Cold Rolled Sheets, Plates, Fasteners, and Flanges (Illustration; actual selection based on media, temperature, and drawings)

Five Parts and Material List

Part / ComponentRecommended GradeSpecification / ThicknessSurfaceMain Failure ModesReference Standards
Double-Phase Steel Welded/Threaded Flanges2205（F51/S31803）/2507（F53/S32750）/Zeron 100（F55/S32760）Class 150–2500；DN15–DN15002507 PREN 41–43；2205 PREN 34–36Yield Strength of 2507 is approximately twice that of 316L, allowing for thinner wall under the same pressure; long-term service above 250℃ requires evaluation of σ phaseASTM A182；ASME B16.5；NACE MR0175/ISO 15156
RO High Pressure Seawater Feed Pipes/Crude Water Pipes2507 Seamless or Welded TubesOperating Pressure: 5.5–7.0MPa ; Design PN100 ; Outer Diameter: Φ6–530mmMinimum Yield Strength of 2507: 550MPa ; CPT > 50℃ ; Continuous Wear Resistance to 6m/sErosion/Corrosion on 316L in SWRO High-Pressure Section Within Months;, Reduce Wall Thickness of 2507 by Over 30%.ASTM A789/ASME SA789；ASTM A240
RO Membrane Shell/Pump Impellers/Energy Recovery Devices2507 Forgings/Castings;2205High-Pressure Pump Shell/Letter/Valves; Energy Recovery2507 forged parts tensile strength ≥ 800MPa, yield ≥ 550MPa, impact at -40℃ ≥ 100J2507 forged parts lifespan is more than three times that of 316L castings; casting defects are a major risk for high-pressure pumpsASTM A182 F53；ASTM A995
MSF/MED heat exchanger tubes/tube sheets2507 tube/plateMSF Salt Water Up to 110℃; MED Shell Side 60–70℃Concentrated Salt Water Cl⁻ 60,000–80,000ppm2507 Superior SCC Resistance in MSF Hot Salt Water Compared to 304L/316L; Lower Cost Than 6Mo and TitaniumASTM A789/A815；ASTM A240
Seawater Desalination Flanges/Nipple2507/2205Class 150–2500；RF/RTJBy project NACE applicabilitySame material as pipe, avoid galvanic corrosion; seal face roughness per MSS SP-6ASTM A182；MSS SP-6；NACE MR0175
Here areStandard configurationMaterial selection

Consider usage conditions instead of grades

  • The most common grades in this industry are 2507 (5), 2205 (3) —— numbers in parentheses indicate the number of affected areas, useful for quoting and material procurement.
  • Watch out for sensitization and chloride-ion stress corrosion cracking (SCC) (2/5 hit).
  • Minimum thickness 5.5–2500 mm: Thin plates are mostly formed parts (considering bend rebound and deep drawing cracking), thick plates are mostly welded structures (considering heat input and sensitization).

Common Questions

Double-phase steel flanges for seawater desalination: Which stainless steel is used most often in the pressure-temperature-corrosion boundary of 2205/2507?
Out of the total 5 parts, 2507 appears most frequently (5 times), followed by 2205 (3 times). Specific to a part still depends on the medium and temperature, for example, stainless steel countertops that come into contact with salt water should switch from 304 to 316L.
What parts are most prone to issues?
By failure description, typical is "duplex steel weld/threads flanges": yield strength of 2507 is twice that of 316L at the same pressure; wall thickness can be reduced for equivalent pressure. Long-term service above 250°C requires evaluation of σ phase; recommended grades 2205 (F51/S31803), 2507 (F53/S32750), Zeron 100 (F55/S32760); pressure classes Class 150–2500; DN15–DN1500. For this type of condition, specify medium concentration, temperature, and cleaning method on the drawings.
How thick should the material be?
Thickness ranges in the list are 5.5–2500 mm. Thin plates consider forming and surface quality, while thick plates look at welding and structural strength; different manufacturers may have varying values for the same part, so review your drawing or conditions to confirm.

Related materials and adjacent industries

2205Material specificationsStainless fasteners: A2-70/A4-70/A4-80/D series and latest standardsStainless FastenersSanitary diaphragm valves/clean valves: ASME BPE, Ra, temperature boundarySanitary ValvesPeroxide stress corrosion cracking: Temperature-time-concentration boundarySensitization & Chloride SCC
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