Class 900 Blind Flange Dimensions — ASME B16.5 Chart, Bolting & Weights

A solid forged disc with the standard Class 900 drilling and facing but no bore — also called a blank flange. It bolts to any B16.5 flange of the same class, size and facing to close the end of a pipe, valve or vessel nozzle, and comes off again for inspection, cleaning, extension or hydrotest. Because it carries full line pressure on its unsupported centre, it is the most highly stressed of the B16.5 flange types.

They are tabulated in ASME B16.5-2020 Tables 16 and 17 and reproduced in full in the chart above: for each of the nineteen sizes, the flange OD, thickness, raised face diameter, bolt circle and bolting — all in millimetres — plus the approximate weight. A 6 in Class 900 blind flange, for example, is 380 mm OD and 55.6 mm thick (plus the 7 mm face) on a 317.5 mm bolt circle with twelve 1-1/8 in studs, at about 53 kg.

The rating depends on material and temperature. For Group 1.1 materials such as A105 carbon steel, ASME B16.5 allows 153.2 bar (roughly 2220 psig) at 38 °C, derating with temperature — the full bar table for carbon and stainless groups is on this page. The solid centre is rated for the full class pressure; always confirm the rating at your design temperature.

Yes — ASME B16.5 gives one thickness per class and size for all flange types, so the blind in this chart matches the weld neck, slip-on and socket weld of the same class and size. The OD, bolt circle and bolting match too: any B16.5 flange of one class and size bolts to any other.

Yes — tapped blinds with an NPT or socket-weld connection are common for vents, drains, gauges and chemical injection; specify the connection size and type with the order. The tapping reduces the flange rating only if it exceeds the reinforcement limits of B16.5 and B31.3, which a single small-bore tap in a thick blind rarely does.

Match class, size and facing to the mating flange, fit a new gasket of the same type, and tighten the studs in a cross pattern in at least three steps. Large blinds benefit from jack-screw holes for break-out and a tapped vent so the line can be depressurised safely before the joint is opened — both available on request.

A blind flange closes the end of a line; a spectacle or spade blind (ASME B16.48) slips between two existing flanges to positively isolate a live line without dismantling it. For a permanent closure, a welded pipe cap (B16.9) is the third option. End of line: blind flange. Isolation inside a run: spectacle blind.

It is the standard hydrotest closure — bolted on, tested against, removed. Confirm the blind's class rating covers the test pressure (typically 1.5 times design), use fresh gaskets, and fit a tapped vent and drain so filling and depressurising are controlled. We supply test blinds tapped to order.

No — at Class 400 and above the raised face is 7 mm, and the tabulated thickness B excludes it. That is the reverse of the Class 150 and 300 convention, where the 2 mm face is included in the thickness — worth checking whenever you compare charts from different sources.

From the weight column in our chart: a 2 in weighs about 10.1 kg, a 6 in about 53 kg, a 12 in about 189 kg and a 24 in about 875 kg. Blinds are the heaviest flange type per size — a solid disc, not a ring — and the weights are approximate for carbon steel, solid and untapped.

Carbon steel ASTM A105/A105N is the usual choice, with A350 LF2/LF3 for low temperature. Stainless A182 F304/L, F316/L, F321 and F347, alloy steel F5/F9/F11/F12/F22/F91 for high-temperature service, duplex F51 and super duplex F53/F55 — plus Monel 400, Inconel 600/625, Hastelloy C276 and copper-nickel 90/10 on request. EN equivalents such as P250GH, 1.4301 and 1.4404 are available — all with EN 10204 3.1 mill certificates.

A 7 mm raised face as standard, serrated to 125-250 microinch Ra (3.2-6.3 micrometre); flat face and RTJ are available on request. The facing must match the mating flange — state it with the enquiry.

Spiral wound gaskets to ASME B16.20 or non-metallic gaskets to B16.21 on RF and FF joints, ring gaskets on RTJ, with stud bolts and heavy hex nuts — A193 B7 / A194 2H for carbon steel, B8M Class 2 for stainless flanges. Counts, hole sizes and stud sizes per flange size are in the chart; each hole is drilled 3 mm larger than its stud.

Forged from certified bars and billets, normalised, quenched-and-tempered or solution annealed per the material specification. Dimensional inspection follows ASME B16.5 tolerances, face finish per MSS SP-6 and marking per MSS SP-25; UT of forgings is available for NPS 12 and above. Every batch ships with EN 10204 3.1 mill test certificates traceable by heat number; MPI/DPT, PMI, NACE MR0175, IBR and PED compliance and 3.2 endorsement are available on request.

ANSI B16.5 900 lb blind flange, 900# blank flange, BLRF Class 900 and blind raised face flange all describe the same product, at roughly PN 160 in metric terms. ANSI B16.5 and ASME B16.5 are also the same standard — custodianship moved from ANSI to ASME decades ago but the old name persists on drawings.

Because ASME B16.5 furnishes NPS 1/2 to 2-1/2 Class 900 flanges to the Class 1500 dimensions — the demand for true Class 900 small bore never justified its own table. The result is the chart's famous anomaly: the 2-1/2 in blind (245 mm OD, about 16 kg) is larger and heavier than the 3 in (240 mm OD, about 13 kg), which is a true Class 900 part. Order by the chart, not by intuition.