ASME B16.48 Spectacle Blind Flange – High-Strength Figure 8 Pipeline Isolation

  Introduction to Spectacle Blind Flange (Figure 8 Blind / Line Blank)

ASME B16.48 Spectacle Blind Flange is a critical pipeline isolation device used in high-pressure industrial piping systems.

Also known as Figure 8 Blind Flange, Line Blank Flange, Paddle Blind or Ring Spacer Assembly, this component provides positive mechanical isolation by physically blocking or allowing fluid flow inside the pipeline.

Spectacle blinds are widely installed in:

• Oil & Gas transmission pipelines
• Petrochemical plants
• LNG terminals
• Refinery shutdown systems
• Offshore platforms
• Power generation pipeline networks

Compared with valves, spectacle blind flanges eliminate leakage risks because they create full metal isolation between pipeline sections.

  Working Principle of Spectacle Blind Flange

The assembly includes:

• One solid blind plate
• One spacer ring
• A connecting metal web

During maintenance or shutdown:

• Rotate the blind plate into position → pipeline flow completely blocked
• Rotate spacer ring into position → normal flow resumes

This enables safe switching without dismantling flange connections, significantly reducing downtime and maintenance cost.

  Advantages of Using Figure 8 Blind Flanges

• Provides absolute pipeline isolation
• Reduces maintenance time
• Enhances plant safety level
• Eliminates risk of valve internal leakage
• Reusable for multiple shutdown cycles
• Suitable for high-temperature and corrosive environments

  ASME B16.48 Spectacle Blind Flange Technical Specifications

Compatible with ASME B16.5 and ASME B16.47 flange systems.

  ASME B16.48 Spectacle Blind Flange Dimensions

Class 150 Dimension Table (Sample)

Available Pressure Classes

• Class 150 Spectacle Blind
• Class 300 Spectacle Blind
• Class 600 Spectacle Blind
• Class 900 Spectacle Blind
• Class 1500 Spectacle Blind
• Class 2500 Spectacle Blind

Full dimension drawings available upon request.

  Material Grades Available

Carbon Steel

ASTM A105
ASTM A350 LF2
ASTM A694 F52 / F60 / F65 / F70

Stainless Steel

ASTM A182 F304
ASTM A182 F316
ASTM A182 F321
ASTM A182 F347

Duplex & Super Duplex

F51
F53
F55

High Nickel Alloys

Inconel 625
Monel 400
Hastelloy C276

  Manufacturing Process of Spectacle Blind Flanges

• Raw material ultrasonic inspection
• Open die forging
• Heat treatment
• CNC turning & drilling
• Edge finishing
• Final dimensional inspection
• NDT testing

Ensures long-term performance in high-pressure pipeline isolation systems.

  Installation Guide for Pipeline Isolation

1. Depressurize the pipeline system
2. Remove flange bolts partially
3. Rotate spectacle blind assembly
4. Align flange faces
5. Tighten bolts using cross-torque method

Proper installation ensures zero leakage isolation condition.

  Spectacle Blind vs Spade Blind vs Ring Spacer

  Applications in Industrial Pipeline Systems

• Refinery turnaround maintenance
• LNG shutdown operations
• Offshore pipeline safety isolation
• Chemical plant process switching
• High-pressure steam pipeline systems
• Gas transmission line maintenance

  Quality Assurance & Certification

• EN10204 3.1 / 3.2 MTC
• NACE MR0175 compliance
• PMI positive material identification
• Third-party inspection available

  Packing & Shipment

• Wooden seaworthy case packing
• Flange face protection caps
• Export marking & heat number traceability
• Bulk shipment capability

  Related Flange Products

• Weld Neck Flange
• Blind Flange
• Ring Spacer
• Socket Weld Flange

  Request Technical Support & Quotation

Looking for reliable ASME B16.48 Spectacle Blind Flanges for your pipeline project?

Our engineering team can provide:

• Dimension drawings
• Weight calculations
• Material recommendations
• Bulk price quotation

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