Procurement Guide for Figure-8 Blinds (Spectacle Blinds) in Piping Systems

What Is a Figure-8 Blind?

A figure-8 blind (also called spectacle blind or 8字盲板 in Chinese standards) is a piping isolation device consisting of a solid plate (blind) and a ring (spacer) connected in a figure-8 shape. It allows quick conversion between open and closed positions by rotating the assembly. Unlike a simple blind flange, the spectacle blind provides a permanent, leak-tight closure without removing the fitting from the line.

Applications in Industrial Piping

Figure-8 blinds are used when a positive isolation is required during maintenance, testing, or temporary shutdown. Common applications include:

• Refineries and petrochemical plants: isolating equipment like heat exchangers, pumps, and compressors.
• Pipelines: providing a visible break for safety during pigging or hydrotesting.
• Chemical processing: preventing cross-contamination between process streams.
• Utility systems: separating steam, water, or gas lines for repair.

Key Standards to Confirm

When specifying figure-8 blinds, ensure compliance with the following standards:

For Chinese projects, GB/T 9126.1, GB/T 9126.2, or HG/T 21547 are also common.

Inspection and Documentation Requirements

Procurement of figure-8 blinds must include proper documentation. Request from the supplier:

• Material test certificates (MTC) per EN 10204 3.1 or 3.2
• Heat number traceability on all pressure-retaining parts
• Dimensional inspection report confirming flange thickness, diameter, bolt hole alignment per applicable standard
• Pressure test certificate if required by project specification
• Visual and NDT reports (e.g., PT, MT, UT for critical service)
• Coating/painting specification (e.g., zinc-rich primer for carbon steel)

RFQ Checklist for Buyers

To ensure accurate quotation and avoid delays, include these details in your request for quotation:

• Size: Nominal pipe size (NPS) and pressure class (e.g., 150#, 300#, 600#, 900#, 1500#)
• Material: Carbon steel (A105, A516 Gr.70), stainless steel (F304, F316L), alloy (F11, F22), or duplex.
• Face finish: Raised face (RF), flat face (FF), ring-type joint (RTJ), or male/female (M&F).
• Standard: ASME B16.48, GB, or other.
• Quantity: Number of spectacle blinds.
• Coating / surface treatment: Mill varnish, hot-dip galvanizing, or special coating.
• End connection: Flanged, butted weld ends, or other.
• Special requirements: Handling lugs, bleed rings, extension handles.
• Certification requirements: MTC, NDE, PED, IBR, etc.

Common Quality Risks

• Incorrect thickness: Blind thickness must match flange rating. Too thin can cause failure under pressure.
• Bolt hole misalignment: Holes must align with mating flanges; verify per ASME tolerances.
• Material substitution: Ensure grade matches spec, especially in sour service (NACE MR0175).
• Surface defects: Sharp edges, pitting, or weld repairs on solid plate can reduce integrity.
• Missing identification: Each spectacle blind should be stamped with size, rating, material, heat number.

How to Get a Reliable Quote

Send a concise but complete RFQ to Haihao Group with the above checklist. Include your project standards and any specific NDE or coating requirements. This helps us provide an accurate delivery timeline and competitive price.

Need a Quote for Figure-8 Blinds?

Hebei Haihao Group manufactures ASME B16.48 spectacle blinds in carbon steel, stainless steel, and alloys. We can supply with full documentation and third-party inspection. Contact our sales team with your RFQ for a prompt quotation.