ASME B16.47 Series B Class 150 Weld Neck Flange — Dimensions, Bolting & Weights

A large diameter welding neck flange — NPS 26 through 60 — in the compact bolting pattern of ASME B16.47. Series B, formerly API 605, uses a smaller outside diameter, a thinner flange and many smaller bolts on a tight bolt circle, making it typically 40-60% lighter than the Series A counterpart at the same rating. The weld neck type carries a tapered hub butt-welded to the pipe, giving the best stress distribution and fatigue life of any flange type at these sizes.

They are tabulated in ASME B16.47-2020 and reproduced in full in the chart above: for each of the eighteen sizes from NPS 26 to 60, the outer diameter, flange thickness, hub diameters at base and bevel, raised face diameter, length through hub, bolt circle, stud count, hole diameter and stud size — all in millimetres — plus the approximate weight. A 36 in flange, for example, is 1055 mm OD and 52.5 mm thick on a 1009.6 mm bolt circle with forty-four 7/8 in studs, at about 109 kg.

Yes — both series use the ASME B16.5 Table 2 Class 150 ratings: 19.6 bar at 38 °C for A105, derating with temperature. Series B achieves the same rating with a thinner flange and more, smaller bolts on a tighter bolt circle — clever bolt-load distribution rather than brute steel. The full bar table for carbon and stainless groups is on this page.

Typically 40-60% at the same size and rating. A 26 in Series B Class 150 weld neck weighs about 54 kg against 136 kg for Series A; at 60 in it is about 386 kg against 928 kg. Across a tank farm or an offshore topside with dozens of large joints, the difference in steel, deck load, handling and bolting is why Series B exists.

Match the mating equipment. Series B (ex API 605) is common in refineries, tank farms and offshore topsides; valves, pumps and older MSS SP-44 pipeline systems are usually Series A. When in doubt, compare the bolt count and bolt circle of the mating flange against the chart — at Class 150 the two series never share a drilling at any size.

No — at every size the two series differ in outside diameter, bolt circle, bolt count and bolt size, so a Series B flange can never bolt to a Series A flange, nor to any B16.5 or B16.1 drilling. The series must be stated on every enquiry and drawing — "36 in Class 150 B16.47" alone is not a complete description.

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 flange made to our chart mates with it exactly.

Yes — for Class 150 the tabulated thickness C includes the 2 mm raised face, and the length through hub V is measured from the raised face. One Series B subtlety: the hub diameter at the bevel A is listed in B16.47 at roughly 1.5 mm above the pipe OD — the weld end is machined to match the pipe on the order.

Because ASME B16.47 deliberately leaves it to the purchaser. Large diameter pipe is ordered by wall thickness rather than schedule, so there is no standard bore to print — the flange is bored to match the pipe stated on the order. Give the pipe OD and wall thickness (or the exact ID) with your enquiry; our chart weights assume a bore for STD (9.53 mm) wall pipe.

From the weight column in our chart: a 26 inch weighs about 54 kg, a 36 inch about 109 kg, a 48 inch about 218 kg and a 60 inch about 386 kg — well under half the Series A figures at every size. These are approximate carbon-steel weights bored for STD wall pipe; the exact weight varies with the bore and material.

Because the stud size steps up at those sizes — from 3/4 to 7/8 in at NPS 34, to 1 in at 38, to 1-1/8 in at 46 and to 1-1/4 in at 58 — and fewer, larger studs replace many smaller ones. A 32 in flange carries forty-eight 3/4 in studs while a 34 in carries forty 7/8 in studs. It is a normal feature of the Series B pattern, but worth knowing when counting holes against a mating flange.

Spiral wound gaskets to ASME B16.20 (with inner ring at these diameters) or non-metallic full-face gaskets to B16.21 on flat-faced joints, with stud bolts and heavy hex nuts — A193 B7 / A194 2H for carbon steel, B8M Class 2 for stainless flanges. Studs run 3/4 to 1-1/4 in on this chart, 36 to 60 per flange, and the holes are drilled 3.2 mm larger than the stud — joints that ordinary tooling makes up without tensioners.

Carbon steel ASTM A105/A105N and A266 Cl.2 for large forgings, high-yield A694 F42 through F65 matched to API 5L X42-X65 pipeline pipe, low-temperature A350 LF2/LF3, stainless A182 F304/L, F316/L and F321, duplex F51 and super duplex F53, plus carbon-steel flanges with 316L, Inconel 625 or copper-nickel weld overlay on request. EN equivalents such as P250GH, P355NH and 1.4404 are available — all with EN 10204 3.1 certificates, 3.2 on request.

Because at 26 to 60 in even a low-pressure line carries serious piping loads, and large thin-wall pipe takes them better through a butt-welded tapered hub than through a slip-on fillet weld. The weld neck's full-penetration butt weld can also be radiographed — which matters on process headers and offshore topsides where joint integrity is documented.

A 2 mm raised face as standard, serrated to 125-250 microinch Ra (3.2-6.3 micrometre) for spiral wound and soft gaskets; flat face on request. State RF or FF with the enquiry.

Forged from certified ingots or blooms, or rolled-ring forged at the larger diameters, then normalised, quenched-and-tempered or solution annealed per the material specification. Dimensional inspection follows ASME B16.47 tolerances with face finish per MSS SP-6, and marking per B16.47 and MSS SP-25 including "B16.47 SER. B" and "CL 150". Every batch ships with EN 10204 3.1 certificates; UT per ASTM A388, MPI/DPT, PMI, Charpy impact testing, NACE MR0175, PED and IBR compliance and 3.2 endorsement are available on request.

ANSI B16.47 Series B 150 lb WNRF flange, API 605 Class 150 weld neck flange, 150# compact large diameter welding neck flange and 26-60 in WN flange all describe the same product, and the rating sits at roughly PN 20 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.

B16.47 covers NPS 26 through 60 — eighteen sizes in Series B at Class 150, all in the chart above. Below 26 in, large flanges are B16.5 territory: our Class 150 weld neck dimensions page carries NPS 1/2 to 24 with the same style of chart. For still lighter duty at these diameters, Series B also offers Class 75, unique to this series — its chart is linked below.