ASTM A182 Duplex Stainless Steel Flange

Introduction to ASTM A182 Standard

ASTM A182 is a standard developed by the American Society for Testing and Materials (ASTM) for forged/rolled alloy and stainless steel pipe fittings used in high-temperature and high-pressure applications. The current effective version is ASTM A182/A182M-24. This standard not only regulates product forms, including flanges, forged pipe fittings, valves, and components but also establishes a strict control system covering material properties and the entire manufacturing process:

Material Classification:ASTM A182 duplex stainless steel flange is categorized into multiple "grades" (e.g., F51, F53, F55, F60) based on chemical composition and performance requirements. Each grade specifies the chemical composition content and allowable deviations.  

Mechanical Properties:The standard defines tensile properties (tensile strength, yield strength, elongation), impact toughness, and hardness limits for different materials.  

Testing and Certification:The standard specifies methods and requirements for chemical composition analysis and mechanical performance testing. Products must be marked with the standard number, material grade, nominal size, pressure rating, and manufacturer identification to ensure traceability.

What is Duplex Stainless Steel Flange

ASTM A182 duplex stainless steel flanges are pipe connectors made from duplex stainless steel material (with a ferritic + austenitic dual-phase structure, typically controlled at a 40-60% ratio) through forging, machining, and other processes. Their core advantages include the high strength and excellent chloride stress corrosion cracking resistance of the ferritic phase, combined with the good toughness and weldability of austenitic stainless steel. The synergistic effect of alloying elements such as Cr, Mo, and N significantly enhances the material's corrosion resistance, thereby reducing the overall weight and cost of the piping system.

Material Analysis of ASTM A182 Duplex Stainless Steel Flange

ASTM A182 F51 (UNS S31803)

Applications:The most widely used ASTM A182 duplex stainless steel flange in industrial fields. It resists neutral salt spray and weakly acidic solutions, offers good weldability, and costs only 70-80% of F53. Suitable for moderate corrosion environments, such as pretreatment pipeline flanges in seawater desalination, inlet flanges for chemical storage tanks, and connection flanges for municipal wastewater treatment equipment.  

Chemical Composition

Mechanical Properties

ASTM A182 F53 (UNS S32750)

Applications:A high-alloy-content duplex steel with significantly better chloride corrosion resistance than F51. It withstands 10% NaCl solutions and H₂S-containing oil and gas media. The high Mo content effectively inhibits pitting and crevice corrosion. Suitable for highly corrosive, high-temperature, and high-pressure environments, such as wellhead flanges in oil and gas extraction (for sour crude transportation), pipeline flanges for high-concentration pickling solutions (≤20% sulfuric acid), and circulating water pipeline flanges in conventional islands of nuclear power plants.  

Chemical Composition

Mechanical Properties

ASTM A182 F55 (UNS S32760)

Applications:A high-end material grade for ASTM A182 duplex stainless steel flanges. The addition of W (0.5-1.0%) further enhances pitting and crevice corrosion resistance, while W refines the grain structure and improves low-temperature toughness. The inclusion of Cu enhances resistance to sulfuric acid corrosion.  

Chemical Composition

Mechanical Properties

ASTM A182 F60 (UNS S32205)

Applications:Higher nitrogen content than F51 (0.14-0.20% vs. 0.08-0.20%). As an interstitial strengthening element, N improves strength and corrosion resistance without compromising toughness. It offers excellent weldability and maintains a balanced dual-phase structure after welding without requiring stabilization annealing, reducing subsequent processing costs.  

Chemical Composition

Mechanical Properties

Heat Treatment Methods for ASTM A182 Duplex Stainless Steel Flange

Based on the standard microstructural characteristics of ASTM A182 duplex stainless steel flanges, a solution annealing process at appropriate temperatures followed by immediate quenching achieves an austenitic-ferritic phase balance. Minimizing the time between removal from the furnace and water quenching is critical to reduce heat loss.  

Solution Annealing: High-temperature heating dissolves alloy elements (Cr, Mo, N, etc.) into the matrix, forming a uniform ferritic-austenitic duplex structure. This process eliminates internal stresses from forging and inhibits the precipitation of brittle phases (e.g., σ-phase, χ-phase). The σ-phase is a brittle intermetallic compound (mainly composed of Cr and Mo). Prolonged exposure to the 600-900°C range can cause a sharp decline in toughness (impact energy may drop below 10J) and worsen corrosion resistance.  

Heating Temperature:1020-1080°C for F51/F60; 1050-1100°C for F53/F55 (higher Mo and Cr content in F53/F55 requires higher temperatures for full dissolution of alloy elements). The heating rate should be controlled at 50-100°C/h to avoid cracking due to excessive temperature gradients, with uniform heating above 800°C.  

Holding Time:Determined based on flange wall thickness (t). Formula: "Holding time = 1h + (t-25mm) × 0.2h/25mm." For example, a flange with a 50mm wall thickness requires a holding time of 1h + (50-25) × 0.2h/25mm = 1.2h. The minimum holding time is 30 minutes (for small flanges with wall thickness ≤10mm), and uniform temperature distribution must be ensured (monitored in real-time with thermocouples).  

Cooling Method:Water quenching is mandatory (cooling rate ≥50°C/min from solution temperature to 400°C). Specific requirements: Immediately immerse the forged part into flowing water (water temperature ≤30°C, water volume ≥5 times the part volume) and continuously agitate to avoid uneven cooling. For large flanges with wall thickness ≥100mm, a combination of water mist cooling and spray cooling may be used to ensure the core cooling rate meets requirements. Air cooling or slow cooling is prohibited (to prevent σ-phase precipitation).  

Inspection Requirements:After solution annealing, microstructural examination (40-60% dual-phase ratio, no significant σ-phase), hardness testing (must meet the hardness limits of the corresponding material grade, e.g., F53 ≤ 310 HB), and tensile testing (yield strength and tensile strength must meet standard requirements) are required.  

Temperature-Pressure Rating Parameters

The table below lists the pressure-temperature ratings for these materials. The values indicate the allowable working pressure (in psi) at the corresponding temperature (in °F). Linear interpolation is permitted for intermediate temperatures. Important: Due to the potential embrittlement of duplex stainless steels after exposure to moderate high temperatures, their use above 600°F [315°C] is not permitted.

Differences Between ASTM A182 and ASTM A312 Materials

Although both ASTM A182 and ASTM A312 are standards for stainless steel materials, they differ fundamentally in product positioning, process requirements, and performance focus:

Product Form and Application

ASTM A182 focuses on forged products, including flanges, forged elbows, forged tees, valve bodies, and valve cores. Its primary purpose is to enable pipeline connections and system control, withstanding bolt preloads from flange connections and pipeline system pressure. These products are typically non-continuous components and must be used in conjunction with pipes, valves, and other equipment.  

ASTM A312 focuses on seamless and welded steel pipes, which are long, hollow tubular products primarily used for fluid or gas transport. These products are continuous components and can be custom-cut to length (e.g., 6m or 12m per piece). They require connection to other components via flanges or welding.  

Material Processing Technology

ASTM A182 uses forging processes, including open-die forging and closed-die forging, where metal billets are plastically deformed under pressure.  

ASTM A312 seamless pipes are produced through hot rolling or cold drawing processes, while welded pipes are made using electric resistance welding or submerged arc welding. The welded seams undergo non-destructive testing. After processing, the pipes are sized and straightened to ensure diameter tolerance and straightness meet requirements.  

Specifications and Dimensional Indicators

ASTM A182 products are labeled by "Nominal Diameter (DN) + Pressure Rating (PN)." Dimensional indicators include flange outer diameter, bolt hole circle diameter, sealing face dimensions (e.g., raised face height of 2mm or 3mm), and flange thickness (e.g., DN100 PN16 flange thickness ≥20mm). They must comply with ASME B16.5 dimensional tolerances, such as a bolt hole diameter tolerance of ±0.5mm.  

ASTM A312 products are labeled by "Outer Diameter (OD) + Wall Thickness (SCH)." Dimensional indicators include outer diameter (e.g., 108mm, 219mm), wall thickness (e.g., SCH40 corresponds to 4.0mm wall thickness, SCH80 corresponds to higher wall thickness), and length tolerance (fixed length tolerance ±50mm). They must meet the dimensional accuracy requirements specified in ASTM A999, such as an outer diameter tolerance of ±0.3mm.

Application 

ASTM A182 duplex stainless steel flanges, with their varied material properties, can adapt to demanding conditions across multiple industries. Specific application scenarios and material selection recommendations are as follows:

Petrochemical Industry  

Seawater Desalination Industry

Nuclear Power Industry

Food and Pharmaceutical Industry  

New Energy Industry