ASME B16.47 Series B Class 75 Blind Flange — Dimensions, Bolting & Weights

A solid forged disc with ASME B16.47 Series B drilling and facing and no bore — the removable closure for pipeline ends, tank and vessel nozzles, large valve connections, hydrotest and isolation. Series B, formerly API 605, is the compact B16.47 bolting pattern: smaller OD and more, smaller bolts than Series A. Because the disc carries full pressure on its unsupported centre, B16.47 makes most blinds thicker than the matching weld neck flange.

They are tabulated in ASME B16.47-2020 and reproduced in full in the chart above: for each size, the flange OD, thickness, raised face diameter, bolt circle and bolting — all in millimetres — plus the approximate weight. A 36 in Series B Class 75 blind, for example, is 1034 mm OD and 42.5 mm thick on a 992.1 mm bolt circle with 40 studs of 3/4 in, at about 235 kg.

Class 75 is rated in ASME B16.47 Table 3, not the B16.5 tables the other classes borrow: for Group 1.1 carbon steel such as A105, 9.6 bar (140 psig) from -29 to 38 °C, decreasing with temperature. It is not an ASME B16.5 class and has no B16.5 equivalent. Refer to B16.47 Table 3 for the full curve and other material groups, and confirm for your bolting and gasket.

Not always — and this is where B16.47 differs from B16.5. The large-diameter standard tabulates blind flange thickness separately, and in most sizes the blind is thicker than the weld neck of the same class and size, because a flat disc carries pressure less efficiently than a hubbed ring. Use the B column of this chart, not the weld neck table, when specifying a blind.

Match the mating equipment. Series B (ex API 605) is the compact pattern, common on storage tanks, process plants and offshore topsides; Series A (ex MSS SP-44) is the heavier pipeline pattern. When in doubt, compare the bolt count and bolt circle of the mating flange against the chart.

No. Class 75 exists only in Series B — there is no Series A counterpart — and its bolt circles match neither Class 150 of either series nor any B16.5 or B16.1 flange. A Class 75 blind mates only with a Series B Class 75 joint, which is why the class and series must appear on every drawing and enquiry.

API 605 was the American Petroleum Institute's standard for large-diameter carbon steel flanges on refinery and tank-farm piping — compact, economical patterns for moderate pressures. When ASME consolidated large diameter flanges into B16.47 in 1990, API 605 became Series B, dimension for dimension. Drawings still call up API 605 regularly, and a blind made to our chart mates with it exactly.

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 rating only if it exceeds the reinforcement limits of B16.47 and B31.3, which a single small-bore tap in a disc this thick rarely does.

Match series, 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. These blinds weigh hundreds of kilograms to tonnes — specify lifting lugs for handling and jack-screw holes for break-out, and fit a tapped vent so the line depressurises safely before the joint is opened.

They are the standard large-bore hydrotest closure — bolted on, tested against, removed. Confirm the class rating covers the test pressure (typically 1.5 times design), use fresh gaskets, and fit a tapped vent and drain for controlled filling and depressurising. We supply test blinds tapped to order.

Yes — for Class 75 the tabulated thickness B includes the 2 mm raised face. Our charts follow the ASME B16.47 convention on every page and say so under each table.

From the weight column in our chart: a 26 in weighs about 116 kg, a 36 in about 235 kg and a 60 in about 1134 kg — large blinds are rigging jobs, not hand lifts. Weights are approximate, carbon steel, solid and untapped.

Carbon steel ASTM A105/A105N, with A266 Cl.2/Cl.4 for large disc forgings and A694 F42-F65 matched to pipeline systems; A350 LF2 for low temperature. Stainless A182 F304/L, F316/L, F321 and F347, alloy F5-F91, duplex F51 and super duplex F53/F55 — plus Monel, Inconel, Hastelloy and copper-nickel on request. EN equivalents such as P250GH, 1.4301 and 1.4404 are available — all with EN 10204 3.1 certificates, 3.2 on request.

A 2 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 with inner ring at these diameters, or non-metallic gaskets to B16.21, 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 3.2 mm larger than its stud.

Forged from certified bars, billets or disc forgings, normalised, quenched-and-tempered or solution annealed per the material specification. Dimensional inspection follows ASME B16.47 tolerances, face finish per MSS SP-6 and marking per B16.47 and MSS SP-25 including "B16.47 SER. B"; UT of disc forgings per ASTM A388 is available on request. Every batch ships with EN 10204 3.1 certificates; MPI/DPT, PMI, NACE MR0175, IBR and PED compliance and 3.2 endorsement on request.

ANSI B16.47 Series B 75 lb blind flange, API 605 Class 75 blind, large diameter 75# blank flange and 26-60 in BLRF all describe the same product, at roughly PN 10 in metric terms. ANSI and ASME B16.47 are the same standard — custodianship moved to ASME but the old names, API 605 especially, persist on drawings.

Weight and money, exactly as with the Class 75 weld neck: large-bore water, air, vent and flare lines rarely see more than a few bar, and a Class 150 blind there carries steel the service never uses. A 36 in Class 75 blind weighs about 310 kg against roughly 760 kg for Series A Class 150 — across a tank farm of closures the saving is substantial. When the duty outgrows 9.6 bar, step up to Series B Class 150.