Spectacle Blind Manufacturer & Exporter — India
ASME B16.48 | Class 150 – 2500 |
Figure-8 Blind · Paddle Blind · Paddle Spacer |
PSM / Safety Isolation | ISO 9001:2015
✓ ASME B16.48
✓ Class 150 – 2500
✓ Figure-8 Blind
✓ Paddle Blind / Spacer
✓ ½″ – 56″ NB
✓ PSM Safety Isolation
✓ Jack Screw Available
✓ EN 10204 3.1/3.2 MTC
✓ ISO 9001:2015
Tesco A182 F91 Line Blank (Spectacle Blind) — RJ 2″ × 1500# × 48 mm — Laser-Marked, Made in India
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.
At a glance: a spectacle blind = a figure-8 plate installed permanently between two flanges — one end solid (line blinded), one end an open ring (line running) — swung from one position to the other for positive isolation without breaking the joint apart. Governed by ASME B16.48. Specify it by five things: size, pressure class, facing (RF/FF/RTJ), material grade and standard.
Why Spectacle Blinds Are the Industry Standard for Positive Isolation
▶ Positive Mechanical Isolation
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.
▶ In-Place Rotation — No Pipe Removal
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.
▶ Visual Confirmation of Status
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.
▶ ASME B16.48 Thickness Calculated
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.
▶ Jack Screw Option for Large Bore
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.
▶ Full Material & Standard Range
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.
How Our Spectacle Blinds Are Manufactured
1
Plate or forging — certified heats are profiled from normalized plate or forged discs, thickness selected per ASME B16.48 for the size and class, keeping full heat traceability.
2
Profiling — the figure-8 shape is cut with the solid blank, open spacer ring and web in one piece; the jack-screw gap and pivot hole machined to suit the flange bolting.
3
Facing — both gasket faces on the blank end and the ring end machined to RF serrated, FF or RTJ groove — the RTJ version visible in the photo above carries a full ring groove in each eye.
4
Heat treatment — as the grade requires: normalizing/tempering for carbon and chrome-moly steel (F91 line blanks are supplied N+T), solution annealing for stainless and nickel alloys.
5
Testing & marking — mechanical and chemical verification against the heat, PMI and NACE hardness where specified, then permanent marking of grade, size, class, thickness and heat number on the web.
6
Certification & packing — EN 10204 3.1 MTC (3.2 witnessed on request), faces protected, export-packed.
Spectacle Blind Specifications
| 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 |
Spectacle Blind Dimensions — ASME B16.48
ANSI / ASME B16.48 Spectacle Blind Dimensions
Spectacle Blind vs Blind Flange vs Paddle Blind
| 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 |
Industries & Applications
| 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) |
Spectacle Blinds by Material Grade
How to Specify & Order a Spectacle Blind
A complete spectacle blind specification has five elements — plus one decision: spectacle blind, or separate spade and spacer for large bores:
1
Size & standard — nominal bore and governing standard, e.g. 2″ NB ASME B16.48 (B16.5 bolting pattern).
2
Pressure class — Class 150/300/600/900/1500/2500; thickness follows from B16.48 tables.
3
Facing — RF (default), FF, or RTJ with ring number — matching the flanges it sits between.
4
Form — spectacle (figure-8) for sizes handled by swing; spade + ring spacer as separate pieces where the assembled blind would be too heavy to swing.
5
Material grade & certification — e.g. ASTM A516 Gr.70 plate, A182 F316L, F91, A350 LF2 — plus EN 10204 3.1 or 3.2, NACE MR0175 or project specs, then quantity, sent to
sales@tescosteel.com or the
inquiry form.
Example of a complete line item: “Spectacle Blind, 2″ NB, ASME B16.48 Class 1500, RTJ (R-24), ASTM A182 F91, EN 10204 3.1 — 4 pcs.”
Frequently Asked Questions — Spectacle Blinds
What is a spectacle blind?▼
A spectacle blind (also called a figure-8 blind) is a single plate fabricated in the shape of a figure-8 — two circular discs joined by a connecting web. One disc is solid (blind disc) for complete isolation; the other is an open ring (spacer disc) that allows normal flow. Installed permanently between two pipe flanges, it can be rotated 180° in place — without removing any pipe — to switch between isolated and open positions. Governed by ASME B16.48, Class 150 through 2500.
What is the difference between a spectacle blind and a blind flange?▼
A
blind flange (ASME B16.5) is a solid disc bolted as the end cap of a pipe run — it must be unbolted and removed to restore flow. A
spectacle blind (ASME B16.48) is a figure-8 plate permanently installed between two flanges. To isolate, rotate the blind disc in; to restore flow, rotate the spacer disc in — no pipe removal needed. The spectacle blind is
faster and safer for frequent isolation switching, especially in hazardous services where positive isolation is a PSM requirement.
What is ASME B16.48 and how does it govern spectacle blinds?▼
ASME B16.48 — Line Blanks is the ASME standard governing the dimensions, pressure-temperature ratings, materials, and thickness calculations for spectacle blinds, paddle blinds, and paddle spacers. It covers NPS ½ through NPS 24 in Classes 150, 300, 600, 900, 1500, and 2500 (note: Class 400 is not included). The standard provides a specific formula for calculating the minimum required blind disc thickness based on bore, design pressure, allowable material stress, and corrosion allowance.
How is spectacle blind thickness calculated?▼
Per ASME B16.48, minimum blind disc thickness: t = d × √(3P / 16S) + c, where d = bore diameter, P = design pressure (psi), S = allowable stress at design temperature (psi), and c = corrosion allowance. Spectacle blinds are therefore generally thicker than blind flanges of the same class, because the blind disc spans the full bore without the stiffening provided by a raised face. Thickness increases significantly at Classes 900, 1500, and 2500 and at larger bore sizes — Tesco Steel provides thickness calculations on request for any NPS and class.
What is the difference between a spectacle blind and a paddle blind?▼
A spectacle blind is a figure-8 plate with both a blind disc and a spacer disc joined together — it stays in the pipeline and the operator rotates it between isolated and open positions. A paddle blind (line blank) is a single solid disc with a handle, inserted between flanges only when isolation is needed and removed to restore flow. A paddle spacer is a single open ring disc used to maintain the flange gap when no isolation is required. Spectacle blinds are preferred for frequent switching; paddle blinds are used for longer-term isolation events (e.g., plant turnarounds).
When is a spectacle blind required by safety regulations?▼
Spectacle blinds are required for positive mechanical isolation under OSHA's Process Safety Management (PSM) standard (29 CFR 1910.119) and EPA's Risk Management Program (RMP) for highly hazardous chemicals. A closed valve alone is not acceptable as positive isolation under PSM — only a physical barrier (spectacle blind, paddle blind, or blind flange) that completely blocks flow meets the requirement. ASME B31.3 and API 598 also require positive isolation during maintenance on live process lines. The visual tab/handle of the spectacle blind enables supervisors to confirm isolation status at a glance.
What materials are available for spectacle blinds?▼
Spectacle blinds are manufactured from the same grades as pipe flanges: ASTM A105 (carbon steel), A350 LF2 (LTCS, to -46°C), A182 F304/316/316L (stainless), F51/F53 (duplex/super duplex), F5/F9/F22/F91 (alloy steel), Inconel 625 (N06625), Hastelloy C276 (N10276), Titanium Gr.2, Monel 400 (N04400), and Copper Nickel C70600/C71500. All materials conform to ASME B16.48 allowable stress tables and ship with EN 10204 3.1/3.2 MTCs, NACE MR0175 compliance where required.
Which industries use spectacle blinds?▼
Spectacle blinds are used in virtually every process industry requiring positive isolation: Oil & Gas Refineries (battery limit blinding, unit turnaround isolation); Petrochemical Plants (PSM-required isolation at HHC handling points); Offshore Platforms (production line isolation for maintenance); Power Generation (steam and cooling water line isolation during outages); LNG & Gas Processing (cryogenic line isolation); Pharmaceutical & Food Processing (hygienic CIP line switching with SS 316L blinds); and Water Treatment (large-bore isolation with epoxy-coated carbon steel blinds).
How do you know which position a spectacle blind is in?▼
By sight — that is the point of the figure-8 shape. The unused eye always projects visibly outside the flange joint: if the open ring shows, the solid blank is inside and the line is positively isolated; if the solid disc shows, the spacer ring is inside and the line is open. Operators and safety auditors can walk a unit and read every blind's status without instruments, which is why permit-to-work systems and pre-startup safety reviews rely on spectacle blinds rather than removable spades that leave no external indication.
When should I use a spade and spacer instead of a spectacle blind?▼
Above roughly 12 inches or Class 600 the one-piece figure-8 becomes too heavy to swing by hand, so the same function is split into two separate pieces: a spade (paddle blank) and a ring spacer, exchanged one for the other when isolation status changes. The choice is weight and handling, not function — ASME B16.48 covers both forms. Tesco manufactures spectacle blinds, spades and ring spacers in matching materials and facings; state the line size and class and we advise which form your crew can realistically handle.
How much does a spectacle blind weigh?▼
It rises steeply with size and class, because B16.48 thickness grows with pressure: a 2" Class 150 spectacle blind weighs about 2 kg, a 6" Class 300 about 15 kg, and an 8" Class 600 around 40 kg — the practical reason large or high-class isolations switch to separate spade and spacer. Alloy density differences are minor. Every Tesco quotation states the exact unit weight for the size, class and facing ordered.
Do spectacle blinds need their own gaskets?▼
Yes — two per installation. A spectacle blind sits between two flanges, so there is a gasket on each side of it (flange-to-blind and blind-to-flange), and both must be replaced every time the blind is swung. The gasket type matches the facing: spiral wound or CNAF for RF, full-face for FF, and a metal ring each side for RTJ blinds. Longer bolts are also required to span the added blind thickness — state the blind on the bolting take-off.
What details are needed to get an accurate spectacle blind quotation?▼
Five elements plus commercial terms: (1) size and standard — e.g. 2" NB ASME B16.48; (2) pressure class — thickness follows from the B16.48 tables; (3) facing — RF, FF or RTJ with ring number, matching the mating flanges; (4) form — spectacle blind, or separate spade and ring spacer; (5) material grade and certification — e.g. A516 Gr.70, A182 F316L, F91, with EN 10204 3.1 or 3.2, NACE MR0175 or project specs stated. Add the quantity and destination and we return price, weight and delivery — normally within 24 hours.
Who manufactures spectacle blinds in India?▼
Tesco Steel & Engineering is an ISO 9001:2015 certified manufacturer based in Mumbai, India, producing spectacle blinds, spades and ring spacers to ASME B16.48 in Class 150 through 2500 — in carbon steel, LTCS, stainless and duplex A182 grades, chrome-moly F91, and nickel alloys including Monel and Inconel. Units are supplied with EN 10204 3.1/3.2 certification and NACE MR0175 compliance where required, and exported to more than 50 countries.
GET A QUOTE FOR SPECTACLE BLINDS
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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