Class 1500 Socket Weld Flange Dimensions — ASME B16.5 Chart, Socket Bore & Weights

A forged flange with a counterbored socket: the pipe slips into the socket and is fillet-welded on the outside of the hub, leaving a smooth bore with no weld protrusion inside the line. ASME B16.5 standardises socket weld flanges in small bore only — NPS 1/2 to 2-1/2 at Class 1500 — and they are the preferred welded small-bore flange where a butt weld is impractical: instrument and sample lines, hydraulics, steam tracing, chemical injection and auxiliary piping.

They are tabulated in ASME B16.5-2020 Tables 18 and 19 and reproduced in full in the chart above: for each of the seven sizes, the flange OD, thickness, hub diameter and length, socket bore and depth, through-bore, raised face diameter, bolt circle and bolting — all in millimetres — plus the approximate weight. A 2 in Class 1500 socket weld flange, for example, is 215 mm OD and 38.1 mm thick (plus the 7 mm face) on a 165.1 mm bolt circle with eight 7/8 in studs, at about 9.8 kg.

The rating depends on material and temperature. For Group 1.1 materials such as A105 carbon steel, ASME B16.5 allows 255.3 bar (roughly 3705 psig) at 38 °C, derating with temperature — the full bar table for carbon and stainless groups is on this page. Remember that the fillet weld and the pipe, not just the flange, must suit the duty; always confirm the rating at your design temperature.

Because ASME B16.5 provides socket dimensions only for NPS 1/2 to 3 — and only to 2-1/2 at Class 1500. Above small bore, a fillet-welded socket joint is less economical and less robust than a butt-welded weld neck flange, so the standard simply stops tabulating sockets and the weld neck takes over.

Insert the pipe to the bottom of the socket, then pull it back about 1.6 mm (1/16 in) before tacking. The gap lets the pipe expand as the weld cools; without it the shrinking fillet weld can crack at the root. ASME B31.1 (par. 127.3) and B31.3 (par. 328.5.2) both require the gap, and it is the single most important detail of socket weld fit-up.

The socket bore ID fits the pipe OD, which is the same for every schedule — but the through-bore ID 2 must match the pipe ID so the socket shoulder lines up with the pipe wall and the bore stays smooth. Our chart shows the STD bore; state the schedule (XS, Sch 80, Sch 160, XXS) or the exact ID on the order.

Yes — the socket bore ID and socket depth D are fixed per pipe size in ASME B16.5, because they fit the same pipe OD whatever the class. What grows with the class is everything around the socket: flange OD, thickness, hub and bolting. Compare our Class 150 and Class 1500 charts and the ID and D columns match line for line.

No — at Class 400 and above the raised face is 7 mm, and the tabulated thickness T1 excludes it, while the length through hub T 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 from different sources.

Both take the pipe into the flange and seal with fillet welds, but the socket weld has a machined shoulder that locates the pipe and needs only one external fillet, leaving a smooth internal bore; the slip-on has a plain through-bore, takes two fillet welds (inside and out) and is rated lower. In small bore, the socket weld is the stronger, cleaner joint; the slip-on earns its keep at larger sizes where sockets are not standardised.

Three cases: where the crevice between pipe and socket invites crevice corrosion or traps product (corrosive and hygienic service), where severe erosion attacks the internal shoulder, and where the piping class demands radiography of the weld — a fillet weld cannot be meaningfully radiographed. In all three, a weld neck flange with a full-penetration butt weld is the right answer.

Per ASME B31.3: throat at least 0.7 times the pipe wall, leg at least 1.09 times the wall or 3.2 mm, whichever is greater, welded all round. Two passes are good practice above Class 300. The weld is external only — nothing intrudes into the bore, which is the point of the socket design.

From the weight column in our chart: a 1/2 in weighs about 1.8 kg, a 2 in about 9.8 kg and a 2-1/2 in about 16.4 kg. These are approximate carbon-steel weights with a STD bore; the exact weight varies with the bore schedule and material.

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. State the facing with the enquiry.

Keep the socket and pipe end clean and dry before fit-up; standard ASTM A106 and A312 pipe OD tolerances fit B16.5 sockets. Avoid socket weld joints in cyclic-vibration service without proper support — small-bore vibration fatigue is the classic failure — and for sour service limit the hardness of weld and HAZ per NACE MR0175.

Forged from certified bars and billets, normalised, quenched-and-tempered or solution annealed per the material specification, with the socket bore and depth gauged on every piece. Dimensional inspection follows ASME B16.5 tolerances, face finish per MSS SP-6 and marking per MSS SP-25. 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 1500 lb SW flange, 1500# socket welding flange, SWRF Class 1500 and socket weld raised face flange all describe the same product, at roughly PN 260 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.

ASME B16.5 ends the Class 1500 socket weld table at NPS 2-1/2 — seven sizes instead of the eight the lower classes carry. At 255 bar a 3 in fillet-welded socket joint no longer makes engineering sense, so above 2-1/2 in the standard expects a butt-welded weld neck flange; our Class 1500 weld neck chart carries those sizes.