ASME B16.48 | Class 150 – 2500 | Figure-8 Blind · Paddle Blind · Paddle Spacer | PSM / Safety Isolation | ISO 9001:2015
A spectacle blind (also called a figure-8 blind) is a safety isolation device fabricated in the shape of a figure-8 — two circular discs joined by a connecting web. One disc is solid (blind disc) for complete pipeline isolation; the other is an open ring (spacer disc) that allows normal flow. The spectacle blind is permanently installed between two pipe flanges and can be rotated 180° in-place — without removing any pipe — to switch between isolated and open positions. This makes it the fastest and safest method for positive mechanical isolation in process plants.
Tesco Steel & Engineering, ISO 9001:2015 certified, manufactures and exports spectacle blinds to ASME B16.48 (Line Blanks) in Classes 150 through 2500, from ½″ NB to 56″ NB, across the full range of materials. We also supply paddle blinds (single solid disc with handle) and paddle spacers (single open ring). Spectacle blinds with jack screws are available for large-bore installations where manual rotation requires mechanical assistance. All products ship with dimensional inspection reports and EN 10204 3.1/3.2 Mill Test Certificates.
Unlike a closed valve, a spectacle blind provides positive double-block isolation — the solid disc physically blocks flow with zero leak path. This is the only method accepted under OSHA PSM (29 CFR 1910.119) and API 598 for isolation of hazardous process streams during maintenance.
The spectacle blind rotates in position between the two flanges. To isolate: unbolt, slide blind disc in, re-bolt. To restore flow: unbolt, rotate to spacer disc, re-bolt. No pipe spools need to be removed, cut, or displaced — saving hours on every line break-in.
The protruding connecting web (handle/tab) visually indicates whether the blind or spacer is in position, even from a distance — a critical safety feature that enables operators to confirm isolation status without disconnecting the joint.
Spectacle blind thickness is engineered per the ASME B16.48 formula accounting for bore diameter, design pressure, allowable material stress, and corrosion allowance — ensuring the blind disc withstands full system pressure without deflection or leakage.
For NPS 10″ and above, spectacle blinds can be supplied with jack screws threaded into the web, allowing the operator to mechanically push the blind into position and break the gasket seal during removal — eliminating the need for hammers and drift pins in confined spaces.
ASME B16.48 Classes 150–2500, ½″–56″ NB, in carbon steel, SS 316L, duplex 2205/2507, Inconel 625, Hastelloy C276, Titanium Gr.2, and all alloys — with NACE MR0175 compliance for sour service and EN 10204 3.1/3.2 certification.
| Parameter | Details |
|---|---|
| Size Range | ½″ NB to 56″ NB |
| Pressure Classes | 150#, 300#, 600#, 900#, 1500#, 2500# |
| Pressure Ratings | PN 1 – PN 400 |
| Standard | ASME B16.48 (Line Blanks) |
| Types | Spectacle Blind (Figure-8), Paddle Blind, Paddle Spacer |
| Options | Standard, With Jack Screw (NPS 10″+), RTJ Face |
| Carbon Steel | ASTM A516 Gr.60/70, ASTM A105 |
| LTCS | ASTM A350 LF2 |
| Alloy Steel | ASTM A182 F5, F9, F11, F21, F22, F91 |
| Stainless Steel | ASTM A182 F304/304H/304L, F316/316H/316L/316Ti, F309, F310, F317L, F321, F347, F904L |
| Duplex / Super Duplex | ASTM A182 F51 (2205), F53 (2507), F55 (Zeron 100) |
| Nickel Alloys | UNS N02200, UNS N02201 |
| Monel | UNS N04400, UNS N05500, Alloy 20 |
| Inconel / Incoloy | UNS N06600, N06601, N06625, N08800, N08810, N08825 |
| Hastelloy | UNS N10276, N06022, N10665, N06455 |
| Titanium | Gr.1, Gr.2, Gr.3, DTH 3.7035, DTH 3.7055 |
| Copper Nickel | C70600 (90/10), C71500 (70/30), C71640 |
| Surface Treatments | Hot Dip Galvanizing, Sand Blasting, Shot Peening, Epoxy Coating, FBE Coating |
| Test Certificates | EN 10204 3.1/3.2 MTC, PMI, Dimensional Report, NACE MR0175 |
| Factor | Spectacle Blind | Blind Flange | Paddle Blind |
|---|---|---|---|
| Standard | ASME B16.48 | ASME B16.5 | ASME B16.48 |
| Shape | Figure-8 (blind + spacer joined) | Single solid disc flange | Single solid disc with handle |
| Switching Position | Rotate in place — no pipe removal | Must remove and replace with spool | Must remove and insert/remove |
| Permanent Installation | Yes — stays in pipeline | No — end cap only | No — inserted as needed |
| Visual Status Indicator | Yes — web/tab shows blind or open | No | Yes — handle visible |
| Best For | Frequent isolation & line switching | Permanent end closure | Long-term single isolation event |
| Industry | Typical Application | Common Material |
|---|---|---|
| Oil & Gas Refineries | Battery limit isolation, unit turnaround blinding, PSM compliance | A105, A182 F316L |
| Petrochemical Plants | Mandatory positive isolation at HHC handling points per OSHA PSM | A182 F316L, Hastelloy C276 |
| Offshore Platforms | Production line isolation for subsea / topside maintenance | Duplex F51, Cu-Ni |
| Power Generation | Steam and cooling water line isolation during outages | A105, A182 F91 |
| LNG & Gas Processing | Cryogenic line isolation — LTCS or SS 304L blinds | A350 LF2, A182 F304L |
| Pharma & Food Processing | Hygienic isolation, CIP line switching | A182 F316L (Ra <0.8µm) |
ISO-certified manufacturer & exporter. ASME B16.48 Class 150–2500. Figure-8 blinds, paddle blinds, paddle spacers — all materials. Fast delivery worldwide from Mumbai, India.
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