Stainless pipe fitting,stainless fitting,duplex stainless,31803,32750,32760,we are one of largest sour service stainless fitting supplier according to ISO 10156.
UNS N06625 | W.Nr. 2.4856 | GB/T 15007 NS3306
1. Material Overview
Alloy 625, widely known as Inconel 625, is a premium solid-solution strengthened austenitic nickel-chromium-molybdenum-niobium wrought superalloy. It conforms to unified global standards: ASTM B446, B475, B564, B619, B622; the ASME SB series; AMS 5599, 5666, 5837; European DIN W.Nr. 2.4856; and Chinese GB/T 15007 NS3306.
A dual solid-solution strengthening system of high molybdenum and niobium provides ultra-high tensile strength without the need for aging heat treatment. The carefully matched chromium-molybdenum ratio delivers all-round corrosion resistance.
Unlike conventional nickel alloys, Alloy 625 maintains excellent mechanical stability from cryogenic temperatures (-196 °C) up to 982 °C. It is virtually immune to chloride stress corrosion cracking (SCC), pitting, and crevice corrosion in seawater, brine, sour oil & gas, and mixed acid media.
Leveraging China’s complete industrial chain — vacuum induction melting (VIM), VIM+VAR double refining, hot forging, and seamless pipe extrusion — domestic manufacturers now offer fully localized raw materials and finished components, breaking import dependence. Our factory produces a full range of pressure-bearing products, including:
- Seamless high-pressure pipes
- Forged flanges
- Butt-weld fittings
- Threaded & socket-weld small-bore instrument fittings
- Plates, round bars, and custom special forgings
Our products fully match the requirements of global offshore, petrochemical, aerospace, and chemical EPC pipeline projects. Alloy 625 has become the designated priority material for deep-sea subsea equipment, sour gas wellhead assemblies, chemical high-pressure reactors, aerospace hot-section components, and waste flue gas desulfurization systems. It is widely recognized by domestic energy enterprises and overseas contractors in Europe, the Middle East, and Southeast Asia.
2. Standard Chemical Composition (wt%)
All chemical indexes strictly adhere to UNS N06625 registration values, ASTM international standards, the German Werkstoff specification, and the Chinese NS3306 national alloy norm. Our domestic factories adopt VIM+VAR double vacuum melting to strictly control trace harmful impurities such as phosphorus (P) and sulfur (S), balancing high strength, full-range corrosion resistance, and stable welding performance.
| Element | Specification (wt%) |
|---|---|
| C | ≤0.10 |
| Si | ≤0.50 |
| Mn | ≤0.50 |
| P | ≤0.010 |
| S | ≤0.012 |
| Cr | 20–23 |
| Mo | 8.0–10.0 |
| Al | ≤0.40 |
| Ti | ≤0.40 |
| Co | ≤1.0 |
| Fe | ≤5.0 |
Key element functions:
- High Chromium (20–23%) – Forms a dense passive film that resists oxidizing acids and high-temperature oxidation.
- High Molybdenum (8–10%) – Core element for resisting reducing acids, chloride pitting, and crevice corrosion.
- Niobium – Cooperates with molybdenum in solid-solution strengthening, greatly improving tensile and creep strength. Stabilizes grain boundaries to avoid welding sensitization.
- High Nickel matrix – Single-phase austenitic structure eliminates ductile-brittle transition at ultra-low temperatures, maintaining excellent impact toughness under cryogenic conditions.
- Ultra-low Carbon – Limits brittle carbide precipitation.
- Strict P & S control – Eliminates hot cracking risk during forging and welding.
3. Heat Treatment & Comprehensive Performance
3.1 Standard Heat Treatment Process
All Alloy 625 pipes, fittings, flanges, and forged blanks are delivered in the full solution-annealed condition — the universal mature process validated by domestic and international alloy manufacturers:
- Temperature: 1090–1175 °C
- Holding time: Adjusted to wall thickness (approximately 30 min for thin-wall parts, 1–2 h for heavy forgings)
- Cooling: Forced air cooling or rapid water quenching
This procedure completely dissolves intermetallic precipitates, homogenizes single-phase austenitic grains, and thoroughly eliminates residual stresses from forging, extrusion, and cold forming. It maximizes room-temperature ductility, cold forming performance, and long-term high-temperature creep rupture strength.
Optional supplementary heat treatments:
- Stabilization treatment (for welded assemblies) – 870 °C, hold 1 h, air cool. Reduces welding internal stress without damaging corrosion resistance.
- High-strength aging treatment (for high-load structural parts) – 705 °C, hold 20 h, air cool. Tensile strength can be increased by 10–15%.
Every production batch is supported by complete heat treatment curve records, PMI full-spectrum element inspection reports, tensile and hardness mechanical test certificates, and multi-standard NDT documents. These simultaneously satisfy Chinese GB, ASME Section VIII pressure vessel, and NACE MR0175 oil & gas certification audit requirements.
3.2 Room-Temperature Mechanical Properties (Solution-Annealed Delivery State)
| Mechanical Property | Standard Minimum Value |
|---|---|
| Ultimate Tensile Strength | ≥820 MPa |
| 0.2% Offset Yield Strength | ≥415 MPa |
| Elongation (50 mm gauge) | ≥30% |
| Brinell Hardness | ≤240 HB |
| Charpy V-notch Impact (20 °C) | ≥130 J |
| Fatigue Limit (10⁷ cycles) | ≥360 MPa |
3.3 Physical & High-Temperature Characteristics
| Physical Index | Test Data |
|---|---|
| Density | 8.44 g/cm³ |
| Melting Temperature Range | 1290 – 1350 °C |
| 20–1000 °C Average Linear Expansion Coefficient | 12.8×10⁻⁶ /°C |
| Room-Temperature Thermal Conductivity | 12.4 W/m·K |
| Maximum Continuous Oxidation Service Temperature | 982 °C |
| Intermittent Short-Term Service Limit | 1050 °C |
| 100 h Creep Rupture Strength @816 °C | ≥60 MPa |
| Magnetism | Non-magnetic at all temperatures |
The low linear expansion coefficient effectively relieves thermal stress and dimensional deformation during frequent cold-heat alternating cycles. The uniform grain structure resists abnormal coarsening even after thousands of hours of high-temperature exposure. The alloy maintains stable toughness from cryogenic liquid nitrogen environments up to medium-high temperature working conditions, adapting to the strictest deep-sea, aerospace, and chemical equipment service requirements.
4. Core Performance Advantages
4.1 All-Round Chloride Corrosion Resistance (Core Advantage)
The high Cr+Mo synergistic system provides an ultra-high Pitting Resistance Equivalent Number (PREN) of 45–48. The critical pitting temperature (CPT) exceeds 80 °C, and the critical crevice temperature (CCT) is above 50 °C. The alloy is almost completely immune to chloride-induced stress corrosion cracking. It operates stably in seawater, brackish water, underground brine, and sour oil & gas containing H₂S/CO₂. Its seawater corrosion resistance is far superior to 316L, Alloy 825, and other common corrosion-resistant alloys, making it the standard designated material for subsea Christmas tree components and underwater pipeline connectors.
4.2 Excellent Dual Resistance to Oxidizing & Reducing Mixed Acids
Alloy 625 performs stably in nitric, phosphoric, sulfuric, hydrochloric, and organic acid mixed environments. The corrosion rate in 5% dilute hydrochloric acid at room temperature is only 0.05–0.15 mm/year — 5 to 10 times lower than Alloy 825. It also exhibits excellent tolerance to high-temperature alkali solutions, suitable for multi-condition mixed acid chemical reactor pipeline accessories.
4.3 High Strength Without Aging Treatment
Molybdenum and niobium solid-solution strengthening delivers high tensile strength in the annealed state. No precipitation aging treatment is required for conventional pressure equipment, simplifying the production process and reducing post-processing deformation risk. The alloy retains stable strength and fatigue performance under long-term alternating loads, widely used for high-pressure flanges, thick-wall pipe fittings, and aerospace structural bearing parts.
4.4 Outstanding Cryogenic & Thermal Fatigue Stability
No ductile-brittle transition occurs at -196 °C (liquid nitrogen temperature); impact toughness remains high. The matched thermal expansion coefficient avoids thermal fatigue cracking after tens of thousands of hot-cold cycles, making it ideal for expansion joints, high-temperature flue dampers, and burner assemblies in waste incineration and power plants.
4.5 Mature Domestic Complete Industrial Supporting System
China has formed a closed-loop industrial chain covering vacuum melting, hot extrusion pipe making, open/closed die forging, CNC precision machining, and full NDT inspection. Matching ERNiCrMo-3 special welding wire is independently developed domestically. Welding crack sensitivity is extremely low; no strict preheating is required for field pipeline construction, and weld corrosion resistance is consistent with the base metal. All products support ISO 9001, AS9100, PED, and NACE MR0175 multi-certification. Delivery cycles are shorter than imported blanks, and quality certificates are mutually recognized by global EPC contractors.
5. Product Range & Complete Specifications
Leveraging China’s mature heavy forging and seamless pipe industrial advantages, we supply a full ASTM/ASME standard range of Alloy 625 finished pressure components and semi-finished blanks for extreme corrosion and high-temperature industrial systems.
- Seamless High-Pressure Pipes & Heat Exchanger Tubes – Hot extruded and cold drawn seamless tubes; outer diameter 12 mm–800 mm, wall thickness 2–100 mm, random or fixed cut lengths. Compliant with ASTM B446/B167.
- Forged High-Pressure Flanges – WN, SO, BL, SW, NPT threaded types; pressure class 150–2500; RF/RTJ full sealing surfaces. Mainstream specifications like DN300 WNRF and 2 IN 300 CL BL RF in stock.
- Butt-Weld Pipe Fittings – Standard 90°/45° elbows, equal/reducing tees, concentric/eccentric reducers, pipe caps. Size NPS 1/2 to NPS 48, wall thickness SCH10–SCH160; heavy-wall customization available.
- Forged Threaded & Socket Weld Small-Bore Fittings – Hex nipples, pipe plugs, reducing bushings, full couplings. Widely used for offshore and chemical high-pressure instrument sampling pipelines.
- Plates, Sheets, Round Bars & Custom Special Forgings – Plates 0.5–120 mm thick, solid round bars Φ5–320 mm, subsea connector blanks, aerospace hot structural forgings, furnace transition parts customized per drawings.
Factory Full Quality Assurance System: Full-batch PMI spectral composition inspection, room-temperature tensile & hardness mechanical testing, triple non-destructive flaw detection (UT ultrasonic, MT magnetic particle, PT penetrant), and full three-dimensional dimensional calibration. All finished products can be supplied with EN 10204 3.1 official mill test certificates, meeting both Chinese national standards and international dual acceptance requirements.
6. Main Application Fields
- Offshore & Oil & Gas Industry – Subsea Christmas tree components, deep-sea underwater pipeline connectors, sour gas wellhead flanges, offshore platform seawater cooling piping, high-pressure downhole instrument fittings (NACE MR0175 certified).
- Chemical & Pharmaceutical Industry – Mixed acid high-pressure reactor pipe fittings, phosphoric acid production heat exchanger tubes, alkali evaporation equipment components, waste flue FGD desulfurization liners and dampers.
- Aerospace & Aviation – Aero-engine hot section ducts, thrust reverser structural parts, high-temperature expansion bellows, thermocouple protection sleeves, hydraulic high-pressure pipe fittings.
- Cryogenic Equipment – Liquid nitrogen / LNG storage pipeline accessories, low-pressure vessel connecting flanges, ultra-low temperature valve bodies.
- Thermal Power & Environmental Protection – Waste incineration high-temperature flue pipelines, waste heat recovery heat exchanger components, high-temperature anti-corrosion dampers.
- Marine Desalination – Large seawater desalination heat exchange tubes, coastal platform anti-corrosion process piping.
7. Quality Control & Product Marking
All Alloy 625 / UNS N06625 products are manufactured under ISO 9001:2015 and aerospace AS9100D dual quality management systems. We implement a standardized full-process inspection workflow accumulated over decades by domestic special alloy manufacturers:
- Raw material incoming PMI spectral recheck
- Hot forging/extrusion forming
- Standardized solution annealing heat treatment
- Room-temperature mechanical performance testing
- Multi-type non-destructive flaw detection
- Full dimensional tolerance calibration
- Surface polishing & cleaning
- Laser permanent marking
- Vacuum moisture-proof plywood packaging
Finished product surface quality is strictly controlled: no cracks, folding layers, metal inclusions, oxidation scales, or mechanical scratch defects are permitted. Standard laser permanent marking includes manufacturer brand, grade (Alloy 625 / UNS N06625 / W.Nr. 2.4856), applicable ASTM/ASME standard, smelting heat batch number, product outer diameter & wall thickness, nominal size, and pressure class.
Laser marking and complete full-life quality traceability documents are mutually recognized by domestic energy clients and global overseas EPC engineering buyers, fully meeting the third-party independent inspection requirements of large offshore and chemical projects.
C&N / HONGCHENG PIPE FITTINGS LIMITED
📞 Tel: +86 021-31267504 | 86 0317 6287569
📱 WhatsApp/Cell: +86 186 1676 2200 | +86 1561278 9688
🌐 Web: www.cnpipefitting.com | www.pipefittingflange.com
Factory Address:
Wuliyao, Yanshan County, Cangzhou City, Hebei Province 061300, China
Office Address:
A8 Jinyu Group, Sunac Cultural Tourism City, High-tech Zone
