Forged Flanges for Power Generation Industry

Grade 91 (ASTM A182 F91) is a 9%Cr-1%Mo steel modified with vanadium (V), niobium (Nb), and nitrogen (N) to achieve exceptional creep strength. It was developed specifically for steam service above 540°C where conventional 2¼Cr-1Mo steel exhausts its allowable stress.

Critical properties:

• Allowable stress at 600°C: ~85 MPa for F91 vs. ~45 MPa for F22 — allowing much smaller flange wall thickness
• PWHT requirements: 730–780°C, minimum 1 hr per 25mm wall thickness. Skipped or incorrect PWHT leads to "Type IV cracking" at weld heat-affected zones after 50,000–100,000 hours of service.
• Hardness limits: After PWHT, hardness must be 190–250 HBW. Values outside this range indicate incorrect heat treatment.
• Oxidation resistance: 9Cr forms a protective oxide film superior to 2–3% Cr steels at 560–620°C

JIAJI supplies F91 flanges with full chemistry traceability, hardness test reports, and PWHT simulation certificates on request.

Both are ASME piping codes but cover different systems in a power plant:

• ASME B31.1 (Power Piping): Governs steam, water, oil, and gas piping in power plants at temperatures above 50°C (or pressures above 1 MPa). Applies to main steam, feedwater, condensate, extraction steam, and boiler blowdown.
• ASME B31.3 (Process Piping): Used in petrochemical plants and, in some plants, for auxiliary systems (fuel gas, cooling water chemicals). Generally has higher allowable stress values than B31.1 for the same material.

Key difference: B31.1 requires stress-relieving (PWHT) for high-alloy steels that B31.3 may allow to omit. B31.1 also mandates full radiography for most Class I joints, while B31.3 uses a normal/category D fluid service classification system. Our flanges are supplied to either code on request.

Creep is time-dependent plastic deformation that occurs when materials are subjected to sustained stress at elevated temperatures (typically above 0.4× the melting temperature in Kelvin). For power plant flanges:

• Creep range for Cr-Mo steels: Above approximately 450°C (F11), 480°C (F22), 540°C (F91)
• Design life: Power plant flanges are designed for 100,000–300,000 hours (25–75 years) of continuous service in the creep range
• Bolt relaxation: High-temperature creep causes flanged joint bolts to relax, reducing gasket seating stress and potentially causing leaks after 5–10 years. High-strength alloy bolting (B7/B16/L7M) is required with proper retorquing schedules.
• Type IV cracking: A specific failure mode in Grade 91 welds where creep cracks initiate in the fine-grained outer heat-affected zone after 50,000–200,000 hours. Proper PWHT and weld geometry minimizes risk.

JIAJI's F91 and F92 flanges are supplied with chemistry reports showing compliance to the "enhanced" specification per EPRI P91 Guidelines, minimizing long-term creep risk.

Main steam (MS) and hot reheat (HRH) are the highest-energy piping systems in a power plant. Standard flange specifications:

• Weld Neck Flanges: Exclusively used for MS / HRH. The tapered hub provides superior fatigue performance and smooth stress transition at the hub-to-pipe interface — critical for thermal cycling service.
• Pressure Class: MS typically Class 1500 or 2500 LB (ASME B16.5). HRH: Class 600–1500 LB depending on reheat pressure.
• Face type: Ring Type Joint (RTJ) preferred for Class 900 LB and above. Class 600 may use RF with spiral wound gasket.
• Bore: Schedule matching (sch 80–160 or XS/XXS) to ensure smooth bore and minimize turbulence / erosion.
• NPS range: Typically NPS 8"–20" for subcritical MS headers, NPS 6"–14" for USC plants (higher pressure = smaller pipe).

Yes. Geothermal brine is one of the most corrosive natural fluids encountered in power generation. Our approach to geothermal flange supply:

• Fluid analysis first: We request the geothermal brine chemistry report (pH, Cl⁻ ppm, H₂S partial pressure, CO₂ concentration, temperature) to guide material selection
• Material options: 316L (mild brine, low Cl⁻), F51 duplex 2205 (moderate H₂S + Cl⁻), F53 super duplex 2507 (high Cl⁻, >5,000 ppm), Titanium Gr.2 (most aggressive — e.g., Iceland, Philippines geothermal)
• NACE MR0175 compliance: For H₂S-containing brine, material hardness and heat treatment must comply with ISO 15156 Part 3 (for stainless and nickel alloys)
• Testing: G48 Method A (pitting resistance in FeCl₃), ASTM G28 intergranular corrosion test for duplex grades

Lead time for Grade 91 and Grade 92 flanges depends on size, pressure class, and quantity:

• Small bore (NPS 2"–6", Class 150–600): 4–6 weeks from confirmed order (raw material often in stock)
• Medium bore (NPS 8"–16", Class 900–1500): 8–12 weeks (forging + machining + PWHT + testing)
• Large bore (NPS 18"–24", Class 1500–2500): 12–18 weeks (custom forging die + qualification)
• ASME B16.47 Series A (NPS 26"–60"): 16–24 weeks (block forging + roughing + finish machining)

For planned outages or turnaround shutdowns with fixed schedules, we recommend placing orders 6+ months in advance for critical F91 flanges. Emergency stock of common sizes (NPS 2"–10") may be available — contact our export team with your requirement list.