347 Stainless Steel Flanges

Niobium Stabilization (Nb ≥ 10×C): Prevents chromium carbide precipitation and sensitization in the 425–870°C temperature range, eliminating intergranular corrosion even after extended high-temperature exposure.

Superior Creep Strength: Better high-temperature creep-rupture resistance than 321, especially above 650°C, ensuring long-term bolted joint integrity in demanding service.

Outstanding Oxidation Resistance: Excellent resistance to scaling and oxidation up to 900°C (1652°F) in intermittent service and 870°C (1600°F) in continuous service.

Polythionic Acid SCC Resistance: Superior resistance to polythionic acid stress corrosion cracking, making 347 the preferred flange material for refinery equipment exposed to sulfur compounds during shutdowns.

Excellent Weldability: Niobium stabilization eliminates the need for post-weld heat treatment (PWHT), simplifying field installation and repair of flanged joints.

Full Range of Types: Weld neck (WN), slip-on (SO), blind (BL), socket weld (SW), threaded (TH), lap joint (LJ), plate flanges, and orifice flanges.

Pressure Ratings: Available in Class 150, 300, 600, 900, 1500, and 2500 (PN6 to PN400 in metric equivalents).

High-Temperature Strength: Maintains excellent mechanical properties up to 900°C (1652°F), significantly outperforming 304H, 316H, and 321H at elevated temperatures.

Excellent Resistance to Thermal Fatigue: Outstanding resistance to thermal cycling, making 347 flanges suitable for cyclic high-temperature service.

International Certifications: Flanges can be certified by ABS, BV, DNV, LR, GL, RINA, CCS, KR, and NK, and comply with NORSOK M-650, ASME, PED, and EN standards for high-temperature and creep-critical service.

These standards ensure that our 347 stainless steel flanges meet global requirements for chemical composition, mechanical properties, dimensional tolerances, and pressure-temperature ratings for extreme high-temperature service.

The niobium (columbium) addition (Nb ≥ 10×C) combines with carbon to form niobium carbides instead of chromium carbides, preventing chromium depletion at grain boundaries (sensitization). Compared to 321 (titanium-stabilized), 347 offers higher creep strength at temperatures above 650°C, better resistance to polythionic acid stress corrosion cracking, superior weldability with less risk of stabilization element segregation, and better high-temperature oxidation resistance.

Comparison of Stabilized Grades:

High-Temperature Tensile Properties (Typical Values – 347H Superiority):

Creep Rupture Strength (Typical at 100,000 hours):

Heat Treatment Condition:
All 347 flanges are solution annealed at 1050–1100°C followed by rapid cooling (water quenching or rapid air cooling). This heat treatment dissolves niobium carbides and puts niobium into solid solution, restores full corrosion resistance and ductility, relieves internal stresses from forging, and optimizes high-temperature creep resistance.

Critical Note: 347/347H has superior resistance to sensitization compared to 321 due to the higher stability of niobium carbides. This makes 347/347H the preferred flange material for welded connections operating in the most demanding high-temperature environments, including catalytic reformers, superheaters, and hydrocracker units.

Delivery Condition: Flanges normally supplied in solution annealed and pickled condition, providing a clean, smooth surface and excellent corrosion resistance. Upon request, bright annealed (BA) finish can be provided for applications requiring ultra-clean internal surfaces.

Reference: ASME B16.5 – 347 stainless steel. 347H has slightly higher ratings at elevated temperatures due to improved creep strength. Maximum continuous service temperature is 870°C (1600°F) for 347 and 900°C (1652°F) for 347H in oxidizing atmospheres.

Standard Dimensions: ASME B16.5 for sizes up to 24″, and ASME B16.47 Series A/B for large diameters up to 60″. EN 1092-1 dimensions available upon request.

Raw Material Selection: High-quality 347 stainless steel bars or billets from certified mills (Baosteel, TISCO, Outokumpu, Sandvik) with certified chemical composition including niobium content verification (Nb ≥ 10×C critical for stabilization). Raw material is VIM-VAR processed for optimal cleanliness.

Cutting & Heating: Material is cut to precise weight using band saws, then induction-heated to forging temperature (1100–1200°C). Temperature control is critical to prevent niobium carbide dissolution or segregation.

Forging: Hot forged using hydraulic presses (3000–8000 tons) with strict temperature control. Multiple forging steps with controlled reduction rates to maintain forgeability.

Heat Treatment – Solution Annealing: Solution annealing at 1050–1100°C to dissolve niobium carbides and put niobium into solid solution, followed by rapid cooling (water quenching or rapid air cooling).

Machining: CNC lathes and milling machines produce precise dimensions, bolt holes, and facing surfaces. Standard tooling suitable for austenitic stainless steel.

Surface Finishing: Raised face serration, flat facing, or RTJ groove machining per ASME B16.5 requirements.

Marking: Laser engraving or stamping with grade (347/347H), size (NPS), class, heat number, manufacturer identification, and standard.

Inspection & Testing: Dimensional check, PMI (including niobium verification), hardness test, and NDT as required.

Surface Treatment: Pickling and passivation to remove oxide scale and restore corrosion resistance.

Each 347 flange face is inspected for surface roughness, concentricity, and absence of defects.

Chemical Analysis: PMI 100% verification using handheld XRF spectrometer for Cr, Ni, Nb (niobium content ≥10×C verification critical for stabilization).

Mechanical Testing: Tensile strength (≥515 MPa), yield strength (≥205 MPa), elongation (≥35%), hardness (≤201 HBW).

Dimensional Inspection: OD, ID, bolt circle, bolt hole alignment, thickness, flatness using calibrated gauges and CMM.

Thread Inspection: NPT thread verification using GO/NO-GO gauges per ANSI B1.20.1.

NDT – Liquid Penetrant Testing (PT): 100% for surface defects.

NDT – Ultrasonic Testing (UT): For internal flaws upon request.

Intergranular Corrosion Test: ASTM A262 Practice C (nitric acid test) or Practice E – validates resistance to sensitization (mandatory for stabilized grades).

High-Temperature Tensile Testing (optional): Upon customer request.

Third-Party Inspection: SGS, BV, DNV, TUV, LR, or ABS on customer request.

Petrochemical & Refining (High-Temperature): Catalytic reformer flange connections, FCC unit flanges, hydrocracker feed/effluent flanges, delayed coker unit flanges, alkylation unit flanges (high-temperature sections), refinery heater connections, crude oil heater flanges.

Power Generation: Superheater header flanges, reheater flange connections, boiler nozzle flanges, economizer flanges, heat recovery steam generator (HRSG) connections (high-temperature zones), nuclear auxiliary boiler flanges, supercritical boiler flanges.

Heat Exchangers (High-Temperature Service): Shell-and-tube heat exchanger channel flanges, floating head flanges, tube sheet flange connections for service above 650°C, high-temperature gas-to-gas heat exchanger flanges.

Chemical Processing (High-Temperature): Organic chemical reactor flanges, acetic acid plant high-temperature connections, phthalic anhydride heat exchanger flanges, maleic anhydride reactor flanges, ethylene cracking furnace outlet flanges.

Industrial Furnaces: Radiant tube flanged connections, furnace door flanges, recuperator flanges, heat treatment furnace process piping flanges, annealing furnace flanges, carburizing furnace flanges.

Exhaust Systems (High-Temperature): High-temperature exhaust gas flanges, diesel engine exhaust connections, gas turbine exhaust flanges, industrial stack flanges, incinerator flue gas connections.

Hydrogen Production: Steam methane reformer (SMR) flange connections, high-temperature hydrogen piping flanges, ammonia plant reformer flanges, methanol reformer flanges, high-temperature shift converter flanges.

Aerospace & Defense: Engine test stand flanges, high-temperature gas flow flanges, exhaust system flanges for test cells, rocket engine propellant line flanges, hypersonic wind tunnel flanges.

Marine Engineering (High-Temperature): Boiler flanges on marine vessels (ABS/DNV/LR certified), exhaust gas heat exchanger flanges, high-temperature steam line flanges (classification society certified).

Waste-to-Energy (High-Temperature): Incinerator flanged connections, heat recovery boiler flanges, flue gas treatment system flanges, superheater flanges for waste-to-energy plants.

Small flanges (≤4″): Heavy-duty cartons with moisture barrier paper on pallets.
Medium flanges (6″–12″): Wooden crates with foam padding dividers, each flange wrapped in VCI paper.
Large flanges (≥14″): Individual wooden crates or steel-framed pallets with foam padding.

All shipments:

VCI paper interleaving between flanges

Plastic end caps for bore protection

Bolt hole protectors for RTJ facings

Individual tagging: Grade (347/347H), size, class, heat number, heat treatment condition, standard, PO number

Waterproof shipping marks for export containers

Moisture barrier wrapping for sea freight

Womic Steel's Delivery Strengths:

Ready stock: Class 150 and 300 347 flanges in sizes 1/2″–12″ – dispatch within 24–48 hours.

Direct cooperation with global shipowners for the most competitive freight rates.

Professional loading by in-house teams using padded slings.

Complete documentation package including EN 10204 3.1 MTR, PMI reports, IGC test reports (ASTM A262), heat treatment charts, and mechanical test reports.

Continuous cargo tracking and after-sales follow-up.

1. Why choose 347 instead of 321 for high-temperature flange applications?
347 offers 40% higher creep strength at 650°C (100,000 hours), better resistance to polythionic acid stress corrosion cracking, and higher maximum service temperature (900°C vs 800°C). For applications above 650°C, 347 is the preferred stabilized grade.

2. What is the difference between 347 and 347H flanges?
347H has higher carbon content (0.04-0.10% vs ≤0.08%), providing improved creep strength and higher tensile strength at elevated temperatures. 347H is recommended for prolonged service above 540°C. For most high-temperature flanged connections, 347H is the preferred grade.

3. Do 347 flanges require post-weld heat treatment (PWHT)?
No. Niobium stabilization eliminates the need for PWHT after welding to restore intergranular corrosion resistance. This makes 347 ideal for field welding where PWHT is impractical.

4. What is the maximum service temperature for 347 flanges?
Continuous service: 870°C (1600°F). Intermittent service: 900°C (1652°F). For 347H, continuous service up to 900°C (1652°F). For service above 900°C, consider 310/310S stainless steel flanges.

5. Are 347 flanges resistant to polythionic acid stress corrosion cracking?
Yes. Niobium stabilization provides superior resistance to polythionic acid SCC, which can occur in refinery equipment exposed to sulfur compounds during shutdowns when moisture is present.

6. Can 347 flanges be used in sour service (H₂S)?
347 is not typically NACE MR0175 certified. For sour service at high temperatures, consider duplex 2205 or super duplex 2507 flanges, or nickel alloys.

7. What facing is recommended for high-temperature gasket sealing?
Raised face with serrated finish (125–250 μinch) using spiral wound gasket with inner ring is standard for high-temperature applications. For critical high-pressure high-temperature service (Class 1500+), RTJ facing with octagonal ring gasket provides the most reliable seal.

8. What is the typical lead time for 347 flanges?
Stock sizes (1/2″–12″, Class 150/300 WN RF): 1–3 days. Non-stock or special facings: 2–4 weeks. Large diameter B16.47 flanges (≥26″): 3–5 weeks depending on thickness.

Complete Product Range: Weld neck, slip-on, blind, socket weld, threaded, lap joint, and plate flanges – one-stop purchasing solution.

Strict Quality Control: ISO 9001:2015, PED 2014/68/EU, and API Q1 certified facilities.

Stabilized Grade Expertise: Specialized knowledge in niobium-stabilized heat treatment and intergranular corrosion resistance.

Advanced Forging & Machining: 3000–8000 ton hydraulic presses and CNC machining centers.

Full Traceability: Heat number stamped on each flange – traceable back to original mill certificate including niobium content verification.

Niobium Verification: 100% PMI verification of Nb content (≥10×C) for stabilization.

ASTM A262 Intergranular Corrosion Testing: In-house testing capability for stabilized grade certification.

Flexible Customization: Non-standard sizes, special facings (T&G, M&F), custom bolt drilling, and high-temperature service modifications available.

Global Delivery: Exported to over 50 countries including petrochemical and refining facilities worldwide.

Competitive Pricing: Direct mill sourcing and in-house manufacturing reduce intermediate costs.

Tel / WhatsApp:
Victor: +86 15575100681
Jack: +86 18390957568

E-mail: info@womicstainless.com

Website: www.womicsteel.com

Contact Womic Steel today for a competitive quote on 347 stainless steel flanges. We offer certified quality, niobium-stabilized material verification, fast production lead times, and reliable global delivery to keep your high-temperature refinery and petrochemical projects running smoothly.

Stock Examples (Class 150 WN RF – 347/347H):

Stock Examples (Class 300 WN RF – 347/347H):

Stock Examples (Class 1500 and above – RTJ facing – 347H, High-Temperature Service):

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