III. Feature Description

A. Floating Ball Design for Cryogenic Sealing

B. SS304 Stainless Steel: Cryogenic Toughness & Corrosion Resistance

• Cryogenic Toughness: Unlike carbon steel, which becomes brittle at low temperatures, SS304 retains ductility at -196℃. This prevents valve body or ball fracture under thermal shock (e.g., rapid filling with liquid nitrogen).
• Corrosion Resistance: In cryogenic systems handling liquefied gases (e.g., LNG, which contains trace moisture and acids), SS304 resists pitting, crevice corrosion, and stress corrosion cracking, ensuring long-term material integrity.

C. Socket Weld Connection: Leak-Tight Integrity in Cryogenic Systems

• Welded Seamlessness: By welding the valve socket to the pipeline, the joint becomes a monolithic structure, eliminating gasket interfaces that could leak or fail under thermal cycling (a common issue in cryogenic systems where temperature swings cause gasket compression loss).
• High-Pressure Capability: Socket weld’s mechanical strength exceeds that of threaded connections, making it suitable for 800LB pressure ratings while maintaining leak-tightness at -196℃.

D. Ultra-Low Temperature Compatibility of Soft Seals

• PTFE: Maintains chemical inertness and low friction at cryogenic temperatures, with a service temperature range of -196℃ to 260℃. It doesn’t harden or lose sealing ability in liquid nitrogen or liquid oxygen service.
• Cryogenic Elastomers: For applications requiring elastomeric sealing (e.g., better conformability to seat irregularities), perfluoroelastomers can operate down to -100℃, providing flexible sealing in less extreme cryogenic ranges.

IV. Manufacturing Processes

A. Material Inspection & Preparation

• SS304 Verification: Raw SS304 bars undergo spectral analysis to confirm chemical composition (Cr: 18-20%, Ni: 8-10.5%) and mechanical testing (tensile, impact at -196℃) to ensure cryogenic toughness meets ASTM A182 standards.
• Seal Material Testing: Soft seals (PTFE/RPTFE) are tested for dimensional stability and compression set at -196℃ to verify they retain sealing properties after prolonged cryogenic exposure.

B. Precision Machining of Components

• Valve Body & Ball: The body is CNC-machined from SS304 bar stock, with socket weld ends machined to ASME B16.11 dimensions (socket depth, wall thickness). The ball is turned to a spherical tolerance of ±0.02mm, then lapped to a surface roughness of Ra ≤0.8μm for uniform seal contact.
• Stem & Handle: The stem is ground to a diameter tolerance of h7 (±0.015mm) and polished to reduce friction with packing. The handle is machined with internal threads matching the stem, ensuring secure attachment and smooth torque transmission.

C. Assembly & Sealing Integration

• Seal Installation: PTFE seals are precision-cut and installed into the valve seat pockets, with spring-loading (optional) to compensate for thermal contraction. The ball is inserted, and the stem is connected, with packing (graphite-impregnated PTFE) installed to prevent cryogenic media leakage along the stem.
• Socket Weld Preparation: The valve’s socket ends are machined to ensure proper fit-up with pipeline ends, with beveled edges for full penetration welding.

D. Quality Testing & Cryogenic Validation

• Hydrostatic Test: The valve is pressurized to 20.7MPa (1.5×800LB) for 30 minutes (shell) and 15.2MPa (1.1×800LB) for 15 minutes (seat), with no leakage or deformation allowed.
• Cryogenic Cycle Test: The valve is cooled to -196℃ using liquid nitrogen, held for 4 hours, then subjected to 100 open-close cycles. Leakage is tested before and after cooling to ensure ANSI/FCI Class VI compliance.
• Torque Testing: Manual operation torque is measured at room and cryogenic temperatures to ensure it remains within acceptable limits (≤150 N·m for 3/4” 800LB valve).