ASME B16.47 Series A Class 400 Weld Neck Flange — Dimensions, Bolting & Weights

A large diameter welding neck flange made to ASME B16.47, the standard that takes over where B16.5 stops: NPS 26 through 60. Series A — formerly the MSS SP-44 standard — is the heavier of the two bolting patterns in B16.47, with larger outside diameters, thicker flanges and fewer but larger bolts than Series B. The weld neck type carries a long 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 1270 mm OD and 114.3 mm thick (plus the 7 mm face) on a 1168.4 mm bolt circle with thirty-two 2 in studs, at about 608 kg.

Because from NPS 38 upward, B16.47 defines Series A Class 400 with the Series B (API 605) dimensions — the two series converge. The step is dramatic: a 38 in flange is smaller and lighter than the 36 in one (1205 vs 1270 mm OD, about 424 vs 608 kg), on a tighter bolt circle with smaller studs. It is the strangest-looking row boundary in any flange chart, and the reason to always confirm the mating flange's bolt circle and count in this range.

Match the mating equipment. Series A (ex MSS SP-44) is the heavier pattern and the usual choice for pipelines, large valves, pumps, vessel nozzles and any system built around older MSS SP-44 piping; Series B (ex API 605) is the compact pattern, seen on tanks and some process plants. At Class 400 the question only bites at NPS 26-36, where the two differ — from 38 up the standard gives them identical dimensions.

At NPS 26 to 36, no — different OD, bolt circle, bolt count and bolt size, so they can never bolt together. At NPS 38 to 60, yes: B16.47 defines the two series with identical Class 400 dimensions there. The series must still be stated on every enquiry and drawing, because at other classes and sizes the difference is real.

MSS SP-44 was the Manufacturers Standardization Society's steel pipeline flange standard, and when ASME consolidated large diameter flanges into B16.47 it became Series A, dimension for dimension. Drawings and valve catalogues still call up MSS SP-44 regularly, and a flange made to our chart mates with it exactly — the two names describe the same flange.

B16.47 adopts the ASME B16.5 Table 2 ratings, so Class 400 here rates the same as Class 400 in B16.5: for Group 1.1 materials such as A105, 68.1 bar at 38 °C, easing to 53.1 bar at 300 °C — the full bar table for carbon and stainless groups is on this page. A694 high-yield grades are rated per Group 1.1 unless otherwise agreed. Always confirm the rating at your design temperature.

No — Class 400 is where the raised face grows to 7 mm (1/4 in), and the tabulated thickness C excludes it, while the length through hub V includes 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. The hub diameter at the bevel A equals the pipe outside diameter per ASME B36.10M.

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 295 kg, a 36 inch about 608 kg — then the Series B convergence resets the curve, so a 38 inch drops to about 424 kg before climbing again to about 1733 kg at 60 inch. These are approximate carbon-steel weights bored for STD wall pipe; the exact weight varies with the bore and material.

The rating steps from 51.1 to 68.1 bar at 38 °C for A105, and two conventions change with it: the raised face grows from 2 mm to 7 mm, and the tabulated thickness switches from including the face to excluding it. Dimensionally a Class 400 flange is thicker and heavier on larger studs — a 36 in grows from 104.8 to 114.3 mm in thickness and from about 578 to 608 kg. Our Series A Class 300 page carries the companion chart.

Spiral wound gaskets to ASME B16.20 with inner ring — compulsory thinking at these diameters and this class — with stud bolts and heavy hex nuts: A193 B7 / A194 2H for carbon steel, B8M Class 2 for stainless flanges. Studs run 1-3/4 to 2-3/4 in on this chart, 28 to 36 per flange, and the holes are drilled 3.2 mm larger than the stud. RTJ facings are available on request for critical service, and hydraulic tensioning is the sensible make-up method at these stud sizes.

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 400 pressures the piping loads are enormous and the joint lives on its fatigue performance. The weld neck's long tapered hub feeds bending and pressure loads gradually from flange ring into pipe wall, and its full-penetration butt weld can be radiographed — which is why gas transmission systems, compressor stations and processing headers standardise on it at this class.

A 7 mm (1/4 in) raised face as standard — the tall face that Class 400 and above carry — serrated to 125-250 microinch Ra (3.2-6.3 micrometre) for spiral wound gaskets; RTJ on request 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. A". 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 A 400 lb WNRF flange, MSS SP-44 Class 400 weld neck flange, large diameter 400# welding neck flange and 26-60 in WN flange all describe the same product, and the rating sits at roughly PN 64 in metric terms. ANSI and ASME B16.47 are the same standard — custodianship moved to ASME but the old name persists on drawings.

B16.47 covers NPS 26 through 60 — eighteen sizes in Series A at Class 400, all in the chart above. Below 26 in, large flanges are B16.5 territory: our Class 400 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.