Ansi B16.48 Class 300 Spectacle Blind Flange

Shanxi Xinshunda Flange Manufacturing Co., Ltd. is a premier manufacturer of ANSI B16.48 Class 300 Spectacle Blind Flanges (Figure-8 Blinds), engineered to provide absolute, leak-tight isolation in medium-pressure piping systems. Covering pipe sizes from NPS ½" to NPS 24", the Class 300 rating represents a critical operational tier with a working pressure of approximately 740 psi (for Carbon Steel at ambient temperature). This pressure class is ubiquitous in refinery process lines, chemical transfer headers, and high-pressure utility systems where the safety margin provided by Class 150 is insufficient, but the extreme cost of Class 600 is unnecessary. Our B16.48 Class 300 Spectacle Blinds deliver the perfect balance of structural strength, sealing reliability, and operational visibility.

While visually similar to Class 150 units, a Class 300 Spectacle Blind is significantly more robust. The increased pressure rating demands thicker blind discs, heavier bridges, and precise machining to handle higher bolt loads without deformation:

• Enhanced Thickness: The solid "blind" side of a Class 300 unit is substantially thicker than its Class 150 counterpart to resist bowing under 740+ psi of internal pressure. We calculate thickness strictly per ASME B31.3 and B16.48 formulas, ensuring a safety factor that exceeds code minimums.
• Reinforced Bridge Design: The connecting bridge must withstand significant shear forces during the rotation of heavy discs, especially in larger sizes (NPS 12"–24"). Our forging and machining processes ensure the bridge integrity remains uncompromised after thousands of cycle operations.
• Facing Compatibility:

1. Raised Face (RF): The standard configuration for Class 300 steel piping. We machine a precise 1/16" (1.6mm) raised face with a serrated finish (125–250 AARH) to ensure optimal grip on spiral wound gaskets.
2. Flat Face (FF): Available upon request for specific applications involving cast iron valves or where full-face gaskets are required, though RF is dominant in Class 300 steel systems.

• Dimensional Rigor: Every Class 300 Spectacle Blind is manufactured to match the exact bolt circle diameter (BCD), outside diameter (OD), and bolt hole count of ASME B16.5 Class 300 flanges, guaranteeing seamless installation without field re-drilling.

At 740 psi, the consequences of a blind failure or leakage are severe. Shanxi Xinshunda implements a rigorous QA protocol for all Class 300 Spectacle Blinds:

• Material Traceability: 100% Positive Material Identification (PMI) via XRF analysis. Full EN 10204 3.1 Mill Test Certificates trace chemistry and mechanical properties to the original melt.
• Dimensional Verification: Precision measurement of disc thickness, bridge width, OD, BCD, and bolt hole alignment using calibrated micrometers and CMMs to ensure strict ASME B16.48 compliance.
• Surface Finish Control: Raised faces are machined to precise serration depths and flatness tolerances to prevent gasket blowout under high bolt loads.
• Non-Destructive Testing (NDT): While visual inspection is standard, we offer Ultrasonic Testing (UT) for thickness verification and Magnetic Particle (MT) or Liquid Penetrant (PT) testing for surface defect detection on demand, especially for critical alloy services.
• Permanent Marking: Each unit is permanently stamped with Size, Class (300), Material Grade, Heat Number, and Manufacturer ID as per code requirements.

• Weight Considerations: Class 300 blinds are notably heavier than Class 150. For sizes NPS 16" and above, we recommend using lifting lugs or specialized handling tools, which we can integrate into the design or packaging.
• Gasket & Bolting Advice: Our engineering team provides specific recommendations for gasket types (e.g., Spiral Wound with inner ring) and bolt torque values tailored to the Class 300 pressure rating and material combination.
• Protective Packaging: Blind faces are protected with durable plastic or wooden caps, and units are coated with anti-corrosion inhibitors and wrapped in VCI paper for long-term storage or overseas shipping.

Selecting Shanxi Xinshunda for your ANSI B16.48 Class 300 Spectacle Blind Flanges ensures you receive components engineered for safety, durability, and precision. Whether you require standard Carbon Steel for a refinery turnaround or exotic alloys for a corrosive chemical process, our manufacturing capabilities and quality systems guarantee performance. With nearly 20 years of experience serving global industries, our Class 300 Spectacle Blinds provide the visual confirmation and positive isolation your operations rely on. Contact our sales team today for technical data, dimensional drawings, and competitive pricing.