What is a Copper Nickel Spectacle Blind Flange?
A Copper Nickel Spectacle Blind Flange (also called a Figure-8 Blind) is a combination of two elements in a single device: a solid blind disc and an open spacer ring, connected by a solid web bar — resembling a pair of spectacles/glasses in shape. It is installed between two flanges and can be flipped from the spacer position (open/flow) to the blind position (closed/isolated) to provide positive pipeline isolation without removing any piping.
Sunflex Metalloy manufactures CuNi Spectacle Blinds in CuNi 90/10 (UNS C70600) and CuNi 70/30 (UNS C71500) per ASTM B151, conforming to ASME B16.48, ASME B16.5, and API 6A standards.
Features & Benefits
- Combined blind disc and spacer ring in one unit — eliminates need to open flange joint to change from flow to blind position
- Visible isolation status — the handle/tab on the blind or spacer element is visible externally showing isolation state
- Critical safety isolation device — provides positive mechanical isolation required by safety regulations in process plants
- No process downtime for isolation — simply unbolt two flange bolts, flip the spectacle blind, and re-bolt
- CuNi 90/10 and CuNi 70/30 provide seawater and brine corrosion resistance for marine and offshore use
- Compliant with ASME B16.48, ASME B16.5, API 6A, BS 3799, EN 13942
- Available with Raised Face (RF) and Ring Type Joint (RTJ) facing options
- Full MTC per EN 10204 3.1 / 3.2 with hardness testing certificate
Industry Applications
Ship seawater cooling circuits, air conditioning sea water lines
Ballast water systems, bilge, fire main and general service piping
Low-pressure intake and outfall piping, auxiliary seawater circuits
Utility seawater headers, non-critical process piping on platforms
Cooling water distribution headers in coastal power generation facilities
Jetty seawater supply systems, port utility piping installations
Manufacturing Process
Raw Material
Billet Heating
Hot Forging
Heat Treatment
CNC Machining
NDT & Testing
Final Inspection
Dispatch
All CuNi flanges are forged from ASTM B151 billets, heat treated (annealed) to restore ductility per ASTM B151 requirements, then CNC machined to ASME B16.5 / B16.47 dimensional tolerances. Full quality records and heat treatment certificates accompany every delivery.
Quality Testing Program
PMI Testing
XRF-based Positive Material Identification per ASTM B151 for Cu, Ni, Fe, Mn chemistry verification on every heat number.
Hydrostatic Test
Shell hydrostatic testing at 1.5× rated pressure per ASME B16.5 / API 598 with hold time verification and certified results.
Ultrasonic Testing (UT)
Volumetric UT per ASTM A388 / EN 10228-3 on all forgings to detect internal flaws before and after machining.
Dye Penetrant (DPT)
Surface DPT per ASME Section V / ASTM E165 on flange faces and bore after final machining operations.
Dimensional Inspection
100% dimensional check per ASME B16.5 / B16.47 tables using calibrated vernier, micrometers, and CMM instruments.
Mechanical Testing
Tensile, yield, elongation, and Brinell hardness per ASTM B151 on test coupons from each production heat.
⚠ Important Note
Spectacle Blinds are subject to bending stress from the pipeline pressure acting on the blind disc. Thickness must be verified per ASME B16.48 Appendix calculations for each size and pressure class. Above Class 900, the spectacle blind weight becomes significant and a pipe support may be required adjacent to the spectacle blind installation.
Technical Specifications
Mechanical Properties — ASTM B151
| Property | CuNi 90/10 (C70600) | CuNi 70/30 (C71500) |
|---|---|---|
| Tensile Strength (UTS) | 275 MPa (40 ksi) min | 380 MPa (55 ksi) min |
| Yield Strength (0.2%) | 105 MPa (15 ksi) min | 170 MPa (25 ksi) min |
| Elongation (50 mm GL) | 30% minimum | 30% minimum |
| Brinell Hardness (HB) | ≤ 100 HB | ≤ 120 HB |
| Density | 8.94 g/cm³ | 8.94 g/cm³ |
| Modulus of Elasticity | 132 GPa | 152 GPa |
Chemical Composition — ASTM B151
| Element | CuNi 90/10 (C70600) | CuNi 70/30 (C71500) |
|---|---|---|
| Copper (Cu) | Remainder (~88–90%) | Remainder (~65–70%) |
| Nickel (Ni) + Co | 9.0 – 11.0% | 29.0 – 33.0% |
| Iron (Fe) | 1.0 – 1.8% | 0.40 – 1.0% |
| Manganese (Mn) | 1.0% max | 1.0% max |
| Lead (Pb) | 0.02% max | 0.02% max |
| Zinc (Zn) | 0.50% max | 0.50% max |
| Carbon (C) | 0.05% max | 0.05% max |
| Sulfur (S) | 0.02% max | 0.02% max |
Material Traceability
Every CuNi flange is manufactured with full heat traceability. Chemical composition is verified by OES (Optical Emission Spectrometry) on each heat and confirmed by XRF-based PMI prior to dispatch. MTC provided per EN 10204 3.1 (standard) or 3.2 (third-party witnessed) per project requirements.
Equivalent Grades — International Standards
| Standard | CuNi 90/10 Designation | CuNi 70/30 Designation |
|---|---|---|
| UNS (ASTM) | C70600 | C71500 |
| DIN / W.Nr. | CuNi10Fe1Mn / 2.0872 | CuNi30Mn1Fe / 2.0882 |
| EN (CW No.) | CW352H | CW354H |
| BS | CN102 | CN107 |
| MIL Spec | MIL-T-16420 (Comp B) | MIL-T-16420 (Comp A) |
| NORSOK MDS | C-600 (CuNi 90/10) | C-601 (CuNi 70/30) |
Frequently Asked Questions
A Spectacle Blind is a single Figure-8 shaped device combining blind and spacer in one piece — it is flipped from one position to the other by rotating it within the open flange joint. A Slip Blind (also called a paddle blind or figure blind) consists of two separate interchangeable elements: a blind plate and a spacer ring. To change from flow to isolation, the spacer is removed and the blind plate is inserted. Spectacle blinds are preferred when frequent switching between flow and blind positions is anticipated, as no separate component storage is required.
Spectacle Blind thickness is determined by ASME B16.48 formula which considers the full pipe bore diameter (as a simply supported circular plate under uniform pressure). For a given bore size and pressure class, the required thickness increases significantly with bore size — a Class 600, 12" spectacle blind requires considerably more thickness than a 4" blind in the same class. Sunflex Metalloy provides thickness calculations per ASME B16.48 for all spectacle blind orders.
Yes. The blind disc of a Spectacle Blind in vacuum service acts as a plate under negative pressure (vacuum suction). ASME B16.48 calculations apply for the vacuum condition as well. CuNi 90/10 and 70/30 mechanical properties are suitable for vacuum service applications in marine condensers and desalination vacuum evaporators.
Per ASME B16.48 and industry practice, the blind disc element has a solid (filled) handle tab, and the spacer ring element has an open (ring) handle tab. The tabs are positioned such that they are visible outside the flange bolting when the spectacle blind is installed. Additional color coding (red for blind, green for open) and nameplates (indicating line number, service, and position) are also applied per customer project specifications.