Spectacle blind flanges (also called figure-8 blinds) in carbon steel, stainless steel and alloy steel, NPS 1/2″ – 24″ per ASME B16.48, class 150 – 2500. Custom sizes and materials manufactured to order.
What Is a Spectacle Blind Flange?
A spectacle blind is a pipe spool isolation device that combines a solid spade (blind disc) and an open spacer (ring) joined by a web, shaped like a pair of spectacles – hence the name. Bolted between two flanges, it can be rotated 180° to either stop the flow (blind side) or allow full flow (open side) without dismantling the joint. This makes it the standard choice for lines that must be periodically isolated for maintenance, sampling or safety blanking.
Specifications
| Item | Range |
|---|---|
| Size | NPS 1/2″ – 24″ (DN15 – DN600), larger on request |
| Pressure class | Class 150 – 2500 / PN2.5 – PN400 |
| Standard | ASME B16.48 (line blanks), DIN 86044 / customer drawings |
| Materials | A105, A350 LF2, A182 F304/F304L/F316/F316L, alloy steels |
| Facing | FF, RF, MFM, TG, RTJ to match mating flanges |
| Thickness | Calculated per ASME B16.48 / B31.3 for the design pressure |
Why Use a Spectacle Blind Instead of a Valve?
- Positive shut-off – a metal plate gives absolute isolation; valves can leak
- No joint dismantling – rotate 180° in the flange gap, re-torque and restart
- Visible status – the open or closed side is always visible from outside the line
- Lower cost than a double-block-and-bleed valve arrangement
Applications
Refineries and petrochemical plants use spectacle blinds on transfer lines, pump suctions and burner lines; power plants on boiler feed and cooling circuits; water treatment and chemical plants wherever sections of pipe need routine isolation. They are also installed at battery-limit tie-ins so operators can blank a line during turnaround.
Manufacturing & Customization
Our Hebei factory cuts discs from certified plate, machines the web and handle, and drills to match your flange bolt pattern. Every blank is thickness-stamped with size, class and material for traceability. Non-standard thicknesses, PTFE-coated surfaces, special handle orientations and third-party inspection (PMI, hardness, EN 10204 3.1/3.2 certificates) are available on request.
FAQs
What is the difference between a spectacle blind and a spade blind?
A spectacle blind combines the spade (solid) and spacer (open) in one figure-8 piece that rotates; a spade blind is the solid plate alone, and the spacer is a separate ring. Spectacle blinds suit lines isolated repeatedly; spades suit longer-term blanking.
How do I choose the thickness?
Thickness follows ASME B16.48 tables for your size and class, or is calculated from pipe design pressure per ASME B31.3. Send us the line class and we will confirm the correct thickness before quoting.
Which side is which?
The open ring (spacer) side allows flow; the solid disc side blocks it. Handles are stamped so operators can read the position at a glance.
Request a spectacle blind quote with your size, class and material – drawings reviewed before quotation.
Related Blind Flange Products
Standard Blind Flanges (blank flanges) · Spectacle Blinds · Spade / Paddle Blinds · RTJ Blinds · Tapped Blinds · All Flange Types