Alloy 825 Stainless Steel Flanges

Superior Sulfuric and Phosphoric Acid Resistance: Outstanding performance in H₂SO₄ (all concentrations up to moderate temperature), H₃PO₄, and mixed acids, making Alloy 825 the premier flange material for fertilizer and chemical processing applications.

NACE MR0175 / ISO 15156 Compliant: Fully qualified for sour service (H₂S) up to 232°C (450°F), with documented HIC and SSC test reports available for oil and gas applications.

Excellent Chloride Stress Corrosion Cracking Resistance: High nickel content (38-46%) provides outstanding resistance to chloride-induced SCC, outperforming all austenitic and duplex stainless steel grades.

Good Pitting and Crevice Corrosion Resistance: Molybdenum (2.5-3.5%) and chromium (19.5-23.5%) provide enhanced resistance to localized corrosion in chloride-containing environments.

Titanium Stabilization: Titanium addition (0.6-1.2%) stabilizes the alloy against intergranular corrosion after welding or high-temperature exposure, eliminating the need for post-weld heat treatment.

Excellent Resistance to Reducing and Oxidizing Acids: Performs well in both reducing acids (sulfuric, hydrochloric) and oxidizing acids (nitric, chromic), as well as mixed acid environments.

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 Weldability: Nickel-iron-chromium alloy offers good weldability with matching filler metals (ERNiCrMo-3 or ERNiCrMo-10). No preheat or post-weld heat treatment required for most applications.

International Certifications: Flanges can be certified by ABS, BV, DNV, LR, GL, RINA, CCS, KR, and NK, and comply with NORSOK M-650, NACE MR0175, ASME, and EN standards.

These standards ensure that our Alloy 825 stainless steel flanges meet global requirements for chemical composition, mechanical properties, dimensional tolerances, and pressure-temperature ratings for extreme corrosive service.

Alloy 825 is a nickel-iron-chromium alloy with controlled additions of molybdenum and copper for enhanced corrosion resistance. The copper content (1.5-3.0%) provides exceptional resistance to sulfuric acid, while molybdenum (2.5-3.5%) enhances pitting resistance. Titanium stabilization (0.6-1.2%) prevents sensitization and intergranular corrosion after welding, making Alloy 825 suitable for welded flange connections without post-weld heat treatment.

Comparison of PREN (Pitting Resistance Equivalent) Values:

High-Temperature Tensile Properties (Typical Values):

NACE MR0175 / ISO 15156 Compliance:
Alloy 825 is fully compliant with NACE MR0175/ISO 15156 for sour service applications up to the limits specified for nickel-based alloys. The alloy is resistant to sulfide stress cracking (SSC) and hydrogen induced cracking (HIC) in H₂S-containing environments. Maximum sour service temperature: 232°C (450°F).

Maximum Recommended Service Temperatures:

Critical Note: Alloy 825 is titanium-stabilized, which prevents sensitization and intergranular corrosion after welding. Unlike many stainless steels, Alloy 825 can be used in the as-welded condition without post-weld heat treatment for most corrosive environments. This is a significant advantage for field fabrication and repair of flanged connections.

Heat Treatment Condition:
All Alloy 825 flanges are solution annealed at 925–1040°C followed by rapid cooling (water quenching or rapid air cooling). This heat treatment dissolves precipitated carbides and intermetallic phases, relieves internal stresses from forging, restores optimum corrosion resistance and ductility, and ensures titanium 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 applications.

Reference: Based on ASME B16.5 for nickel alloys. These ratings are similar to 316 stainless steel but Alloy 825 offers superior corrosion resistance in 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 825 (UNS N08825) nickel alloy billets from certified premium mills (Special Metals, VDM Metals, Carpenter) with certified chemical composition (Ni 38-46%, Cr 19.5-23.5%, Mo 2.5-3.5%, Cu 1.5-3.0%, Ti 0.6-1.2% verification) and traceability.

Cutting & Heating: Material is cut to precise weight using band saws, then induction-heated to forging temperature (1150–1200°C). Temperature control is critical for nickel alloys.

Forging: Hot forged using hydraulic presses (3000–8000 tons) with strict temperature control. Nickel alloys require careful reduction rates to maintain forgeability.

Heat Treatment – Solution Annealing: Heat treatment at 925–1040°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. Special tooling and slower cutting speeds may be required for nickel alloys.

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

Marking: Laser engraving or stamping with grade (N08825/Alloy 825), 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 alloys; thorough rinsing required.

Each Alloy 825 flange face is inspected for surface roughness, concentricity, and absence of defects.

Chemical Analysis: PMI 100% verification using handheld XRF spectrometer for Ni, Cr, Mo, Cu, Ti (titanium verification critical for stabilization).

Mechanical Testing: Tensile strength (≥585 MPa), yield strength (≥240 MPa), elongation (≥30%), hardness (≤200 HBW).

Intergranular Corrosion Test: ASTM G28 – validates resistance to intergranular corrosion (mandatory for stabilized grades).

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.

Sour Service Qualification (upon request): HIC per NACE TM0284, SSC per NACE TM0177.

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

Chemical Processing (Acid Service): Sulfuric acid (H₂SO₄) piping flanges, phosphoric acid (H₃PO₄) evaporator connections, nitric acid (HNO₃) heat exchanger flanges, acetic acid reactor flanges, chlor-alkali heat exchanger flanges.

Fertilizer Production: Wet-process phosphoric acid (WPA) evaporator flanges, diammonium phosphate (DAP) and monoammonium phosphate (MAP) production flanges, gypsum slurry handling flanges, fertilizer storage tank manways.

Oil & Gas (Sour Service): Sour gas pipeline flanges, H₂S-containing heat exchanger flanges, produced water cooler flanges, glycol reboiler flanges, amine regenerator flanges (NACE MR0175 compliant, NORSOK M-650 certified).

Offshore Platforms: Chemical injection line flanges, topside acid service flanges, offshore produced water treatment flanges (ABS, BV, DNV, LR certified).

Pharmaceutical: High-purity API reactor flanges, sterile transfer line flanges, clean steam system flanges, high-purity water-for-injection (WFI) flanges.

Pickling Plants: Acid recovery system flanges, spent acid heater flanges, rinse water heat recovery flanges.

Hydrometallurgy: Pressure acid leaching (PAL) flanges, solvent extraction flanges, electrowinning solution flanges, nickel/cobalt/copper processing equipment connections.

Marine Engineering: Chemical tanker cargo piping flanges, marine acid handling systems (classification society certified).

Power Generation: Flue gas desulfurization (FGD) flanges, scrubber reheat flanges, condenser flanges (aggressive cooling water with low pH).

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:

Rust preventive oil coating (optional – may be omitted for pickled finish).

Plastic end caps for bore protection.

Individual tagging: Grade (Alloy 825/N08825), size, class, heat number, heat treatment condition, standard, PO number.

Waterproof shipping marks for export containers.

Full documentation for customs clearance including EN 10204 3.1 MTR, NACE compliance certificates, corrosion test reports, and inspection certificates.

Womic Steel's Delivery Strengths:

Ready stock: Class 150 and 300 Alloy 825 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 to prevent surface damage.

Complete documentation package including MTR, PMI reports, IGC test reports, NACE certificates.

Continuous cargo tracking and after-sales follow-up.

1. How does Alloy 825 compare to 316L stainless steel for acid service?
Alloy 825 offers significantly better resistance to sulfuric acid (H₂SO₄), phosphoric acid (H₃PO₄), and sour gas (H₂S). While 316L is acceptable for mild chemical service, Alloy 825 is required for concentrated acids, reducing acid environments, and sour gas where 316L would fail rapidly.

2. Is Alloy 825 resistant to hydrochloric acid (HCl)?
Limited. Alloy 825 has fair resistance to dilute HCl but is not recommended for concentrated HCl. For hydrochloric acid service, consider Hastelloy C276 which has excellent resistance to HCl.

3. Can Alloy 825 flanges be used in seawater?
Yes, but Super Duplex 2507 is more cost-effective for seawater applications. Alloy 825 is typically specified for acid service rather than primarily for seawater.

4. What is the difference between Alloy 825 and Alloy 625?
Alloy 825 has lower nickel (38-46% vs ≥58%), lower molybdenum (2.5-3.5% vs 8-10%), and contains copper (1.5-3.0%) which improves sulfuric acid resistance. Alloy 825 is more cost-effective for acid service; Alloy 625 is preferred for high-strength seawater applications.

5. Do Alloy 825 flanges require post-weld heat treatment (PWHT)?
No. Titanium stabilization prevents sensitization, and PWHT is not required for most corrosive environments. This is a significant advantage for field fabrication.

6. 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.

7. Can you supply Alloy 825 flanges with NACE MR0175 documentation?
Yes. We supply full NACE MR0175 / ISO 15156 compliance documentation including material certification, MTRs, and optional HIC/SSC test reports.

8. Are Alloy 825 flanges available in EN 1092-1 dimensions?
Yes. We can manufacture Alloy 825 flanges to EN 1092-1 Type 01, 02, 05, 11, 12 with PN6 to PN400 pressure ratings. Please specify your standard.

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

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

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

NACE MR0175 / ISO 15156 Compliant: Full documentation for sour service applications with HIC/SSC test reports on request.

Titanium Stabilization Verified: Ensuring resistance to intergranular corrosion after welding.

Advanced Forging & Machining: Modern CNC equipment and heat treatment furnaces.

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.

Global Delivery: Exported to over 50 countries including chemical plants 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 825 stainless steel flanges. We offer certified quality, NACE MR0175 compliance, fast production lead times, and reliable global delivery to keep your acid service and sour gas pipeline projects running smoothly.

Stock Examples (Class 150 WN RF – Alloy 825):

Stock Examples (Class 300 WN RF – Alloy 825):

Common Stock Examples for Acid Service (Class 150 WN RF – Alloy 825):

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