ASME B16.47 Series B Class 300 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 more, smaller bolts on a tight bolt circle, making it typically 30-50% lighter than the Series A counterpart at the sizes where the two patterns differ. 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 1170 mm OD and 103.2 mm thick on a 1089 mm bolt circle with thirty-two 1-5/8 in studs, at about 381 kg.

Yes — both series use the ASME B16.5 Table 2 Class 300 ratings: 51.1 bar at 38 °C for A105, derating with temperature. Series B achieves the same rating with a smaller OD and more, smaller bolts on a tighter bolt circle. Note that at NPS 38-60, B16.47 defines Series A Class 300 with the Series B dimensions, so the two series coincide in that range.

Typically 30-50% at the sizes where the two patterns differ, NPS 26 to 36: a 26 in Series B Class 300 weld neck weighs about 181 kg against 274 kg for Series A, and a 36 in about 381 kg against 578 kg. From NPS 38 upward the standard gives the two series identical Class 300 dimensions, so the saving applies to the 26-36 in range.

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 NPS 26-36 the two series never share a Class 300 drilling.

At NPS 26 to 36, no — different OD, bolt circle, bolt count and bolt size, so they can never bolt together there, nor to any B16.5 or B16.1 drilling. At NPS 38 to 60 the standard defines the two series with identical Class 300 dimensions. The series must still be stated on every enquiry and drawing, because at other sizes and classes the difference is real.

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 300 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 slightly 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 181 kg, a 36 inch about 381 kg, a 48 inch about 714 kg and a 60 inch about 1302 kg. These are approximate carbon-steel weights bored for STD wall pipe; the exact weight varies with the bore and material.

The Series B Class 300 pattern balances bolt load size by size rather than in long runs, so count and stud size alternate as the chart climbs — a 36 in flange carries thirty-two 1-5/8 in studs while a 38 in carries thirty-six of the same size, and a 32 in steps down to thirty-two studs where the 30 in had thirty-six. Always count holes and measure the bolt circle against the mating flange rather than assuming a trend.

Spiral wound gaskets to ASME B16.20 with inner ring — standard thinking at these diameters and this class — or non-metallic gaskets to B16.21 on milder duty, with stud bolts and heavy hex nuts: A193 B7 / A194 2H for carbon steel, B8M Class 2 for stainless flanges. Studs run 1-1/4 to 2-1/4 in on this chart, 32 to 48 per flange, and the holes are drilled 3.2 mm larger than the stud. RTJ facings are available on request for critical service.

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 and Class 300 pressures the piping loads are serious and the joint lives on its fatigue performance. The weld neck's tapered hub feeds bending and pressure loads gradually from flange ring into pipe wall, and its full-penetration butt weld can be radiographed — which matters on process headers, compressor connections 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; RTJ or flat face on request — RTJ for critical hydrocarbon service. State the facing 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 300". 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 300 lb WNRF flange, API 605 Class 300 weld neck flange, 300# compact large diameter welding neck flange and 26-60 in WN flange all describe the same product, and the rating sits at roughly PN 50 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 300, all in the chart above. Below 26 in, large flanges are B16.5 territory: our Class 300 weld neck dimensions page carries NPS 1/2 to 24 with the same style of chart, and the drilling families line up so systems transition cleanly at the 24/26 in boundary.