Procurement Guide for Figure-8 Blanks (Spectacle Blinds) and Pipe Bends

Introduction

Figure-8 blanks (also known as spectacle blinds or 8-blanks) and pipe bends are essential components in industrial piping systems. Figure-8 blanks provide positive isolation for maintenance or flow control, while pipe bends allow directional changes without the pressure drop of a welded elbow. For EPC procurement engineers and industrial buyers, selecting the right design, material, and manufacturing standard is critical to system safety and longevity. This guide outlines key considerations for sourcing these components from global suppliers like Hebei Haihao Group.

Design and Function

A figure-8 blank consists of two discs connected by a handle: one solid (blind) and one open (spacer). When the solid disc is positioned in the flange gap, the line is positively isolated. Reversing the assembly aligns the spacer, allowing flow. This design eliminates the need for multiple gasket changes and provides rapid isolation. Pipe bends, on the other hand, are formed by bending a straight pipe to a specified radius—commonly 90° or 45°—offering a smooth flow path with minimal turbulence compared to multiple butt-weld elbows.

Applicable Standards

Procurement specifications should reference recognized international standards:

Ensure the supplier's quality system complies with ISO 9001 and that all components are traceable to the applicable standard batch.

Material Selection and Quality Risks

Select material based on operating pressure, temperature, and fluid corrosiveness. Common material grades include:

• Carbon steel (ASTM A105) for general service.
• Stainless steel (304/316) for corrosive or hygienic applications.
• Alloy steel (F11/F22) for high-temperature services.

Quality risks to mitigate:

• Undersized thickness: Verify that the blank or bend matches the required schedule (e.g., Sch 40, Sch 80).
• Improper heat treatment: Figure-8 blanks should be normalized or quench-and-tempered per material spec.
• Weld defects in bends: For induction bends, ensure no cracks or laminations via NDT.
• Gasket surface finish: Blank faces must be smooth (125-250 μin RMS) to prevent leaks.

Inspection Documents Required

Before shipment, request the following documentation:

• Material test certificates (MTC) per EN 10204 3.1 or 3.2.
• Dimensional inspection report (including thickness, diameter, bolt holes, and bend radius).
• Hardness test report.
• Visual inspection report.
• For critical service: PMI (Positive Material Identification) report, ultrasonic thickness, or radiography for bends.

RFQ Checklist

When requesting a quotation, include the following details to minimize errors:

1. Component type: figure-8 blank (spectacle blind) or pipe bend.
2. Quantity and size: e.g., 10 pcs of 8" class 150 figure-8 blank.
3. Pressure class: 150, 300, 600, etc.
4. Facing: Raised face (RF), flat face (FF), ring joint (RTJ).
5. Standard: ASME B16.48 (blanks) or ASME B16.9 (bends).
6. Material grade: ASTM A105, A182 F304, etc.
7. Bend angle and radius: 90° long radius or short radius, 45°.
8. End preparation: Beveled (for weld) or plain (for screwed).
9. Certification requirements: MTC, NDT, PMI.
10. Packaging and delivery terms.

Conclusion

Figure-8 blanks and pipe bends are simple yet critical components. By specifying the correct standards, materials, and inspection criteria, procurement professionals can ensure long-term reliability. Hebei Haihao Group manufactures these components in accordance with ASME, ASTM, and other international standards. Our quality team provides full traceability and third-party inspection support.

Request a Quotation

Optimize your next project with compliant figure-8 blanks and pipe bends from Hebei Haihao Group. Send your RFQ with the checklist above to our engineering team for a prompt response with drawings, certifications, and competitive pricing.