Procurement Guide for Figure 8 Blanks (Spectacle Blinds): Specifications, Quality Checks & RFQ Tips

Introduction

Figure 8 blinds, also known as spectacle blinds or spectacle flanges, are critical components in piping systems. Their distinctive shape—one solid blind and one open spacer connected by a tie—allows quick isolation of sections during maintenance, testing, or shutdowns. For EPC engineers and procurement professionals, specifying the correct figure 8 blind is essential to avoid leaks, ensure safety, and comply with industry standards. This guide covers the key procurement considerations, from material selection to quality inspection, helping you make informed decisions.

Key Standards to Confirm

When sourcing figure 8 blinds, always verify that the manufacturer adheres to applicable standards. The most common are:

• ASME B16.48: This standard covers line blanks in sizes NPS 1/2 through NPS 24 for Classes 150, 300, 600, 900, 1500, and 2500. It defines dimensions, tolerances, facings, and materials.
• ASME B16.5 / B16.47: For flange dimensions and facing types (e.g., raised face, flat face, ring joint) that must match the mating flanges.
• Material Standards:

- Carbon steel: ASTM A105 or ASTM A516 Gr. 70 (for high-temperature service)
- Stainless steel: ASTM A240 Gr. 304/304L or 316/316L
- Alloy steel: ASTM A182 F11, F22, etc., depending on pressure and temperature.

Request the manufacturer's material test certificates (MTC) to confirm chemical and mechanical properties.

RFQ Checklist: What to Send Before Quotation

To get accurate, competitive quotes, include the following in your request for quotation (RFQ):

• Nominal pipe size (NPS) and pressure class (e.g., NPS 6, Class 300)
• Facing type: Raised face (RF), flat face (FF), ring joint (RTJ), etc.
• Material grade: Specify both the blank (blind) and spacer material if different.
• Required certifications: e.g., EN 10204 3.1, NACE MR0175, PMI testing.
• Quantity and packaging requirements (wooden crates, pallets, etc.).
• Delivery schedule and destination (incoterms).

Providing a clear specification sheet avoids back-and-forth and reduces risk of incorrect supply.

Quality Risks and Inspection Documents

Figure 8 blinds must seal when the solid side is installed, so dimensional accuracy and surface finish are critical. Common quality risks include:

• Incorrect thickness: The blind thickness must match the pressure class. Too thin can cause deformation under pressure.
• Gasket face finish: Raised face finish (125–250 μin Ra typical) must be consistent to prevent leaks.
• Misalignment: The two ends (blank and spacer) must align perfectly with the bolt holes of the mating flanges.
• Material substitution: Some manufacturers may use lower-grade material. Always demand MTC and third-party inspection if possible.

Inspection documents to request:

• Material Test Reports (MTR)
• Dimensional inspection report (with actual measurements)
• Visual inspection report (surface defects, cracks, etc.)
• Non-destructive testing reports (ultrasonic, dye penetrant if required)
• Hardness test report (for alloy steels)
• Pressure test certificate (if hydrostatic testing is specified)

A reputable supplier will provide these documents without hesitation.

Manufacturing Process Overview

Understanding the production steps helps you evaluate supplier capability. While the process varies by manufacturer, typical steps include:

1. Material preparation – Plate cutting to rough shape.
2. Forging or machining – For high-pressure classes, forging is preferred over plate cutting for better grain structure.
3. Heat treatment (if required for alloy steels) – Normalizing, quenching, and tempering to achieve mechanical properties.
4. Machining – Final dimensions, facing, and drilling of bolt holes.
5. Surface treatment – Anti-corrosion coating (e.g., oiling, painting) as per customer spec.
6. Inspection and testing – Dimensional, NDT, pressure tests.
7. Marking – Permanent stamping with size, material, pressure class, and heat number.
8. Packaging – Secure packing for export.

When auditing a supplier, check that they have CNC machining centers, heat treatment furnaces, and in-house NDT capabilities. Third-party certification (e.g., ISO 9001) is a good baseline.

Conclusion

Figure 8 blinds are simple yet mission-critical components. Spending time on proper specification and supplier qualification pays off in reduced downtime and safer operations. Always confirm the applicable standard (ASME B16.48), review material certificates, and include a detailed RFQ checklist.

For reliable figure 8 blinds with full traceability and third-party inspection options, contact Hebei Haihao Group. They offer a wide range of sizes and materials, ensuring compliance with ASME and other international standards. Submit your RFQ today for a prompt quotation.