ASME SA350 LF2 Class 1 Nozzle Cover Flange , Low Temperature Forged Flanges

Low Temperature​ Forgings , ASTM A350 Grade LF2 Class 1 Forged Nozzle Cover Flange

ASME SA350 LF2 Class 1 is a low-temperature carbon steel forging specification specifically designed for flanges, fittings, valves, and pressure components operating in cryogenic service. 

Specification of ASTM A350/ASME SA350 LF2 CLASS1 Nozzle Cover Flange

1. Material: SA350 LF2

• Base Composition: Low-carbon steel alloyed with Nickel (Ni) for improved low-temperature toughness. Typical Ni content is 0.40-1.06%.

• Purpose: Nickel shifts the material's Ductile-to-Brittle Transition Temperature (DBTT) lower, preventing brittle fracture at sub-zero temperatures.

• Form: Supplied as forgings (not castings or plate).

2. Class: Class 1

• Critical Requirement: This designates the lowest service temperature the material is certified for.

• Temperature Rating: -46°C (-50°F). The material must demonstrate adequate impact toughness (via Charpy V-notch testing) at this temperature.

• Testing: Mandatory Charpy V-notch impact testing is performed at -46°C (-50°F) on each heat lot. Strict minimum average energy absorption requirements must be met (e.g., 20 J avg. for standard sizes)

3. Component: Nozzle Cover Flange

• Function: This is essentially a specialized blind flange (ASME B16.5 Type: Blind) used to seal the end of a nozzle on a pressure vessel, heat exchanger, or piping system.

• Purpose:

  • Isolate sections for maintenance, inspection, or safety.

  • Provide future connection points ("nozzle covers" are often temporary).

  • Serve as permanent seals on unused nozzles.

• Design: Manufactured to dimensions and pressure ratings specified in standards like ASME B16.5 (Pipe Flanges and Flanged Fittings) or ASME B16.47 (Large Diameter Flanges). Key features include bolt holes, facing (e.g., raised face - RF, ring-type joint - RTJ), and thickness rated for pressure.

Chemical Composition of ASTM A350 LF2 Nozzle Cover Flange

Mechanical Properties of ASTM A350 LF2 Nozzle Cover Flange

Key Characteristics & Requirements

• Low-Temperature Toughness: The core reason for specifying SA350 LF2 Cl. 1. Ensures resistance to brittle fracture at -46°C/-50°F.

• Pressure Rating: The flange's pressure capacity at various temperatures is defined by its ASME B16.5/B16.47 Class rating (e.g., Class 150, 300, 600, 900, 1500, 2500). The LF2 Cl.1 material must be suitable for the design pressure/temperature.

• Heat Treatment: Forgings are typically Normalized or Normalized and Tempered to achieve the required grain structure, mechanical properties, and impact toughness.

• Mandatory Impact Testing: As mentioned, Charpy testing at -46°C/-50°F is required for each heat lot.

• NDE (Non-Destructive Examination): Requires 100% Ultrasonic Testing (UT) to detect internal flaws. Surface inspection (MT or PT) is also common practice.

• Chemical & Mechanical Properties: Must meet strict compositional limits and tensile/yield strength requirements defined in SA-350.

Applications:

• Liquefied Natural Gas (LNG) Facilities: Piping, storage tanks, processing units.

• Refrigeration & Cryogenic Plants: Ammonia systems, ethylene plants, air separation units.

• Petrochemical & Gas Processing: Equipment handling cold gases or liquids.

• Power Generation: Certain components in cryogenic systems.

• Pressure Vessels & Heat Exchangers: Nozzle closures in vessels operating below -29°C.