The performance of flanges in high-temperature environments varies significantly depending on the material used, primarily in terms of strength retention, oxidation resistance, creep resistance, thermal stability, and compatibility with media. Below is an analysis of typical material categories:
1. Carbon Steel Flanges (e.g., Q235, 20# Steel) – Basic Choice for Low to Medium Temperatures
Strength Degradation at High Temperatures
Carbon steel flanges are typically limited to temperatures below 425°C. Beyond 350°C, their yield strength drops significantly (e.g., 20# steel’s yield strength decreases from 245 MPa at room temperature to 180 MPa at 400°C). Above 450°C, pearlite spheroidization occurs, leading to grain coarsening and eventual creep rupture.
Poor Oxidation Resistance
Rapid oxidation begins above 300°C, forming a loose Fe₃O₄ layer. At 500°C, the oxidation rate is five times faster than at 300°C. Exposure to sulfur or water vapor further accelerates corrosion.
2. Austenitic Stainless Steel Flanges (304/316, etc.) – Preferred for High-Temperature Corrosion Resistance
Better High-Temperature Strength and Oxidation Resistance
304 stainless steel can withstand up to 870°C, while 316L (with molybdenum) maintains good strength (yield strength ≥ 120 MPa) below 650°C.
The Cr₂O₃ oxide layer (from 18-20% chromium) provides superior oxidation resistance (e.g., 90% lower oxidation rate than carbon steel at 800°C).
High-Temperature Risks
Sensitization (450-850°C): Carbide precipitation may cause intergranular corrosion (mitigated by stabilization treatments, e.g., 321 stainless steel with titanium).
Creep Limitations: Above 650°C, creep deformation accelerates, requiring reduced allowable stress (e.g., 316L at 700°C has only 15% of its room-temperature strength).
3. Duplex Steel Flanges (2205, 2507, etc.) – Cost-Effective for High-Temperature Corrosion
Intermediate High-Temperature Performance
2205 duplex steel is usable up to 300°C, while super duplex 2507 extends to 350°C (yield strength > 400 MPa at 300°C, twice that of 304 stainless steel).
Beyond 350°C, ferrite phase degradation accelerates, reducing creep resistance faster than austenitic steels.
4. Chromium-Molybdenum Steel Flanges (15CrMo, P91, etc.) – Ideal for High-Temperature, High-Pressure Conditions
Enhanced Strength and Creep Resistance
15CrMo (1-1.5% Cr, 0.5% Mo) operates up to 550°C (yield strength > 200 MPa at 500°C).
P91 (9% Cr, 1% Mo) withstands 650°C long-term, with twice the creep rupture strength of 15CrMo (e.g., 100 MPa vs. 40 MPa at 600°C for 100,000 hours).
5. Nickel-Based Alloy Flanges (Inconel 625, Hastelloy C-276, etc.) – Ultimate Solution for Extreme Conditions
Unmatched High-Temperature Performance
Inconel 625 retains > 100 MPa tensile strength at 1093°C.
Hastelloy C-276 resists oxidation up to 1200°C, with creep life exceeding 100,000 hours (e.g., 5x stronger than 316L at 800°C).
Resistance to Complex Corrosion
High nickel (≥50%), chromium (20-30%), and molybdenum (10-16%) content enables resistance to:
Oxidation, stress corrosion, and intergranular attack in harsh environments (e.g., 650°C coal gasifiers with H₂S/CO₂).
Suitable for 20+ years of service in extreme conditions like high-temperature sulfuric acid or sulfur-rich oil/gas.
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