Alloy 20 Stainless Steel Flanges

Exceptional Sulfuric Acid Resistance: Outstanding resistance to sulfuric acid (H₂SO₄) across a wide range of concentrations and temperatures, making Alloy 20 the premier flange material for sulfuric acid plants, acid coolers, and heat exchangers.

Excellent Phosphoric and Nitric Acid Resistance: Superior performance in phosphoric acid (H₃PO₄) and nitric acid (HNO₃) service, suitable for fertilizer production, chemical processing, and pickling operations.

Superior Chloride Stress Corrosion Cracking Resistance: High nickel content (32-38%) provides excellent resistance to chloride-induced SCC, significantly outperforming 304L, 316L, and 317L stainless steel flanges.

Good Pitting and Crevice Corrosion Resistance: Molybdenum (2-3%) and copper (3-4%) additions provide enhanced resistance to pitting and crevice corrosion in chloride-containing environments.

Excellent Weldability – Niobium Stabilized: Niobium stabilization (8×C max) prevents sensitization and intergranular corrosion after welding, eliminating the need for post-weld heat treatment for most applications.

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).

Good Mechanical Properties: Tensile strength ≥550 MPa, yield strength ≥240 MPa, with excellent ductility for forming and machining.

Cost-Effective Alternative to Higher Alloys: More economical than Alloy 825, Alloy 625, and Hastelloy C276 for sulfuric acid service where those grades are over-specified.

International Certifications: Flanges can be certified by ABS, BV, DNV, LR, GL, RINA, CCS, KR, and NK, and comply with NACE MR0175/ISO 15156 (limited sour service), ASME, PED, and EN standards.

These standards ensure that our Alloy 20 stainless steel flanges meet global requirements for chemical composition, mechanical properties, dimensional tolerances, and pressure-temperature ratings for extreme corrosive service.

Alloy 20 (UNS N08020) is a nickel-iron-chromium alloy with controlled additions of molybdenum and copper for enhanced corrosion resistance in sulfuric acid service. The copper content (3-4%) provides exceptional resistance to sulfuric acid, while molybdenum (2-3%) enhances pitting resistance. Niobium stabilization (Nb addition) prevents sensitization and intergranular corrosion after welding, making Alloy 20 suitable for welded flange connections without post-weld heat treatment.

Comparison with Other Corrosion-Resistant Alloys for Flange Applications:

High-Temperature Tensile Properties (Typical Values):

Maximum Recommended Service Temperatures:

Critical Note: Alloy 20 is niobium-stabilized, which prevents sensitization and intergranular corrosion after welding. Unlike many stainless steels, Alloy 20 can be used in the as-welded condition without post-weld heat treatment for most corrosive environments, including sulfuric acid service. This is a significant advantage for field fabrication and repair of flanged connections.

Heat Treatment Condition:
All Alloy 20 flanges are solution annealed at 925–1010°C followed by rapid cooling (water quenching or rapid air cooling). This heat treatment:

l  Dissolves precipitated carbides and intermetallic phases.

l  Relieves internal stresses from forging.

l  Restores optimum corrosion resistance and ductility.

l  Ensures niobium stabilization is effective.

Delivery Condition: Flanges normally supplied in annealed and pickled condition, providing a clean, smooth surface and excellent corrosion resistance. Upon request, bright annealed (BA) finish or polished finishes can be provided for high-purity and pharmaceutical applications.

Reference: Based on ASME B16.5 for nickel alloys. These ratings are similar to 316L stainless steel, but Alloy 20 offers significantly better corrosion resistance in sulfuric acid environments.

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 Alloy 20 (UNS N08020) nickel-iron-chromium billets from certified premium mills (Special Metals, VDM Metals, Carpenter) with certified chemical composition (Ni 32-38%, Cr 19-21%, Mo 2-3%, Cu 3-4%, Nb stabilization verification) and traceability.

Cutting & Heating: Material is cut to precise weight using band saws, then induction-heated to forging temperature (1100–1200°C). Temperature control is critical for nickel alloys.

Forging: Hot forged using hydraulic presses (3000–8000 tons) with strict temperature control. Alloy 20 has good forgeability.

Heat Treatment – Solution Annealing: Solution annealing at 925–1010°C followed by rapid cooling (water quenching) to dissolve carbides and restore properties.

Machining: CNC lathes and milling machines produce precise dimensions, bolt holes, and facing surfaces.

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

Marking: Laser engraving or stamping with grade (Alloy 20/N08020), size (NPS), class, heat number, manufacturer identification, and standard.

Inspection & Testing: Dimensional check, PMI, hardness test, and NDT as required.

Surface Treatment: Pickling and passivation using specialized pickling acids optimized for nickel-iron-chromium alloys; thorough rinsing required.

Each Alloy 20 flange face is inspected for surface roughness, concentricity, and absence of defects.

Chemical Analysis: PMI 100% verification using handheld XRF spectrometer for Ni (32-38%), Cr (19-21%), Mo (2-3%), Cu (3-4%), Nb (stabilization verification).

Mechanical Testing: Tensile strength (≥550 MPa), yield strength (≥240 MPa), elongation (≥30%), hardness (≤200 HBW).

Intergranular Corrosion Test: ASTM G28 – validates resistance to intergranular corrosion and niobium stabilization effectiveness (mandatory).

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.

Sulfuric Acid Corrosion Test: ASTM G31 – weight loss in H₂SO₄ upon request (copper advantage verification).

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

Sulfuric Acid Production & Handling: Sulfuric acid plant heat exchanger flanges, sulfuric acid cooler flanges and heaters, acid piping system flanges, storage tank manway flanges, acid dilution system flanges, spent acid recovery flanges, metallurgical acid plant flanges.

Phosphoric Acid Service: Phosphoric acid evaporator flanges, heat exchanger flanges, fertilizer production equipment flanges (DAP/MAP), wet-process phosphoric acid plant flanges, gypsum slurry handling flanges.

Nitric Acid Service: Nitric acid cooler flanges and heaters, piping system flanges, ammonium nitrate production equipment flanges, stainless steel pickling lines.

Chemical Processing (Aggressive): Chemical reactor flanges, process vessel connections, piping systems for aggressive chemicals, organic acid processing flanges (acetic, formic, citric), chlorinated hydrocarbon handling flanges, chlor-alkali heat exchanger flanges.

Pharmaceutical: High-purity process line flanges, API (Active Pharmaceutical Ingredient) reactor flanges, sterile transfer line flanges, clean steam system flanges, chemical synthesis equipment flanges, vitamin C production flanges.

Food & Beverage: Food processing equipment flanges, citric acid service flanges, pickling system flanges, food-grade chemical handling flanges, fruit juice processing flanges, edible oil processing flanges (fatty acid resistance).

Petrochemical (Limited Corrosive Service): Amine service flanges, glycol service flanges, sour water stripper flanges, catalytic cracking unit components flanges (non-chloride service).

Marine Engineering (Chemical Tankers): Chemical tanker cargo piping system flanges, acid handling line flanges (ABS, BV, DNV, LR, GL, RINA, CCS, KR, NK certified).

Pollution Control: Flue gas desulfurization (FGD) system flanges, scrubber component flanges, waste treatment heat exchanger flanges, acid gas cleaning flanges.

Metal Finishing & Pickling: Pickling line flanges, acid recovery system flanges, spent acid handling equipment flanges, steel mill pickling flanges, titanium dioxide production flanges.

Fertilizer Production: Phosphoric acid and sulfuric acid heat exchanger flanges, chemical reactor flanges, fertilizer granulation equipment flanges.

Small flanges (≤4″): Heavy-duty cartons with moisture barrier paper on pallets, individual plastic bagging for high-purity flanges.
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 (Alloy 20/N08020), size, class, heat number, manufacturer identification, 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 Alloy 20 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 G28), sulfuric acid corrosion test reports (optional), and inspection certificates.

Continuous cargo tracking and after-sales follow-up.

1. What is Alloy 20 best suited for in flange applications?
Alloy 20 is the premier material for sulfuric acid (H₂SO₄) service, offering excellent resistance across a wide range of concentrations and temperatures. It is also highly suitable for phosphoric acid, nitric acid, and chloride stress corrosion cracking resistance where 316L and 317L are insufficient.

2. How does Alloy 20 compare to 316L stainless steel for acid service?
Alloy 20 offers significantly better resistance to sulfuric acid (H₂SO₄), phosphoric acid (H₃PO₄), and chloride stress corrosion cracking. While 316L is acceptable for mild chemical service, Alloy 20 is required for concentrated sulfuric acid, hot acid service, and environments where SCC is a concern.

3. Is Alloy 20 resistant to hydrochloric acid (HCl)?
Limited. Alloy 20 has fair resistance to dilute HCl but is not recommended for concentrated or aerated HCl. For hydrochloric acid service, consider Hastelloy C276.

4. Can Alloy 20 flanges be welded without post-weld heat treatment?
Yes. Alloy 20 is niobium-stabilized, which prevents sensitization and intergranular corrosion after welding. This is a major advantage over non-stabilized grades, eliminating the need for PWHT for most applications.

5. What is the maximum temperature for continuous service?
400°C (752°F) for general corrosive service. For sulfuric acid service specifically, limit to 150°C (302°F) depending on acid concentration. Above 400°C, mechanical properties degrade, and other nickel alloys should be considered.

6. Are Alloy 20 flanges suitable for sour service (H₂S)?
Limited. Alloy 20 is not typically NACE MR0175 certified for sour service. For H₂S environments, consider duplex 2205, super duplex 2507, or nickel alloys such as Alloy 825.

7. What facing is recommended for sulfuric acid service flanges?
Raised face (RF) with serrated finish (125–250 μinch) using PTFE envelope gasket or spiral wound gasket with PTFE filler is recommended for sulfuric acid service to ensure leak-tight sealing.

8. Can you supply Alloy 20 flanges with EN 1092-1 dimensions?
Yes. We can manufacture Alloy 20 flanges to EN 1092-1 Type 01, 02, 05, 11, 12 with PN6 to PN400 pressure ratings. Please specify your standard.

9. What is the typical lead time for Alloy 20 flanges?
Stock sizes (1/2″–12″, Class 150/300 WN RF): 2–4 days. Non-stock or special facings: 3–4 weeks. Large diameter B16.47 flanges (≥26″): 4–6 weeks depending on thickness.

10. How does Alloy 20 compare to Alloy 825?
Alloy 20 has lower nickel (32-38% vs 38-46%), similar copper (3-4% vs 1.5-3.0%), and is generally more cost-effective for sulfuric acid service. Alloy 825 has slightly better overall corrosion resistance in mixed acids and sour service, but at higher cost. For dedicated sulfuric acid applications, Alloy 20 is often the more economical choice.

Complete Product Range: Weld neck, slip-on, blind, socket weld, threaded, lap joint, and plate flanges – one-stop sourcing for acid service projects.

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

Premium Mill Sources: Special Metals, VDM Metals, Carpenter certified raw materials – 100% traceable.

Niobium Stabilization Verified: ASTM G28 intergranular corrosion testing available to validate stabilization.

Acid Service Expertise: Proven supply record for sulfuric acid, phosphoric acid, and pickling plants worldwide.

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.

Flexible Customization: Special facing types (RTJ, T&G, M&F), custom bolt drilling, and non-standard sizes available.

Cost-Effective Solution: More economical than Alloy 825 and nickel alloys for dedicated sulfuric acid service.

Global Delivery: Exported to major chemical plants, fertilizer facilities, and acid handling projects worldwide.

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 Alloy 20 stainless steel flanges. We offer certified quality, niobium-stabilized material verification, ASTM G28 corrosion testing, fast production lead times, and reliable global delivery to keep your acid service and chemical processing projects running smoothly.

Stock Examples (Class 150 WN RF – Alloy 20, Annealed + Pickled):

Stock Examples (Class 300 WN RF – Alloy 20, Annealed + Pickled – Higher Pressure Acid Service):

Stock Examples (Sulfuric Acid Plant Service – Alloy 20, Class 150, RF – Heat Exchanger Connections):

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