Class 2500 Weld Neck Flange Dimensions — ASME B16.5 Chart, Weights & Bolting

They are tabulated in ASME B16.5 and reproduced in full in the chart above: for each of the fourteen sizes from NPS 1/2 to 12, the outer diameter, flange thickness, hub diameters at base and bevel, length through hub, raised face diameter and height (7 mm at this class), bolt circle and weld face — all in millimetres — plus the published weight. A 4 in Class 2500 weld neck flange, for example, is 355 mm OD, 76.2 mm thick plus the 7 mm face, on a 273 mm PCD, at about 66 kg.

The rating depends on material and temperature. For Group 1.1 materials such as A105 carbon steel, ASME B16.5 allows 425.5 bar (roughly 6170 psig) at 38 °C, easing to about 332 bar at 300 °C and 240 bar at 450 °C — the full bar table for carbon steel, 304 and 316 groups is reproduced on this page. Stainless and alloy grades have their own columns. Always confirm the rating at your design temperature.

Class 2500 (also written #2500 or 2500 lb) is a pressure-temperature rating class, not a working pressure of 2500 psi. Each class maps to a table in ASME B16.5 giving the maximum allowable working pressure at each temperature for each material group — a Class 2500 A105 flange is good for roughly 6170 psig cold, nearly two and a half times the number in its name, and less when hot.

No — for Class 400 and above, ASME B16.5 tabulates flange thickness C excluding the 7 mm raised face, while the length through hub V includes it. That is the reverse of the Class 150 and 300 convention, where the standard includes their 2 mm face in the thickness. Our charts follow the standard on every page and say so under each table — worth checking whenever you compare charts from different sources.

Because beyond that, a conventional bolted flange stops making engineering sense at these pressures. ASME B16.5 tabulates Class 2500 only through NPS 12 — a 12 in flange already weighs about 692 kg on twelve 2-3/4 in studs — and the forces on anything larger would demand bolting and ring sections outside sensible practice. Larger ultra-high-pressure connections move to other technologies: API 6A wellhead flanges, clamp-type hub connectors or welded construction. No NPS 3-1/2 exists at this class either, so the chart runs fourteen sizes.

From the weight columns in our chart: a 2 inch Class 2500 weld neck flange weighs about 19 kg (42 lbs), a 4 inch about 66 kg (145 lbs), an 8 inch about 263 kg (580 lbs) and a 12 inch about 692 kg (1526 lbs) — heavier than a 20 inch Class 900, at a third of the bore. These are published carbon-steel weights with a standard bore; the exact weight varies with the bore schedule and material density.

7 mm (nominally 1/4 inch) — the tall face shared by Class 400 and above. In practice nearly all Class 2500 line classes specify RTJ facings, where an octagonal ring gasket seats in a machined groove — state RF or RTJ with the enquiry, because the two are not interchangeable in the field.

No — and unlike Classes 400 and 900, Class 2500 shares no sizes with any neighbour: every size has its own OD, bolt circle and bolting, so a Class 2500 flange never mates with a Class 1500 flange of the same size. A spec break between the two classes always means matching flanges on both sides of the joint.

The bore of a weld neck flange is machined to match the inside diameter of the pipe it will be welded to, so state the pipe schedule with your order. At Class 2500 pressures the mating pipe runs Sch 160, XXS or heavier still, and the match is critical: a bore step at the butt weld concentrates turbulence and erosion exactly where the joint works hardest. That is why the Bore column in our chart reads "as per pipe schedule".

We manufacture Class 2500 weld neck flanges in carbon steel A105, low-temperature A350 LF2/LF3, stainless steel A182 F304/L, F316/L, F310, F321, F347 and F410, 254 SMO (F44), 904L, duplex 2205 (F51), super duplex 2507 (F53/F55), alloy steel F1/F5/F9/F11/F22/F91, Monel 400/K500, Inconel 600/625/825, Hastelloy C276/C22, titanium, copper nickel 90/10 and 70/30, and bimetal/clad — each with EN 10204 3.1 mill certificates.

Stud bolts with two heavy hex nuts, always — in the Class 2500 pattern of few but massive studs: just 8 studs up to NPS 6, but already 2 inch UNC at that size, and a 12 inch flange takes 12 studs of 2-3/4 inch UNC at 540 mm. Make-up is exclusively by hydraulic tensioner. A193 B7 / A194 2H remain the standard grades on carbon-steel joints, B16 for high temperature.

RTJ, almost without exception: Class 2500 line classes specify ring type joints with octagonal ring gaskets (soft iron or low-carbon steel for A105, stainless for stainless flanges) in machined grooves — at 400-plus bar, the self-energising metal ring is the only gasket culture that belongs. Spiral wound gaskets remain technically available for RF joints on milder duty. Our RTJ gasket size chart on this site covers the ring numbers per flange size.

Because at 400-plus bar the joint must be as strong as the pipe, and only the weld neck's tapered hub and full-penetration butt weld deliver that — with a weld geometry open to full radiography, which every line class at this rating demands. The proportions tell the story: a 10 in Class 2500 flange carries a 419 mm hub, longer than many complete flanges, purely to feed the load gently into the pipe. Slip-on and socket-weld flanges do not exist in B16.5 practice at this class; blinds and spectacle blinds remain for isolation.

For A105 at 38 °C the allowable working pressures are roughly 6170 and 3705 psig. Dimensionally the step is brutal: a 6 in flange grows from 395 to 485 mm OD and from 82.6 to 108 mm thickness, and the size range itself shrinks — Class 1500 runs to NPS 24 where Class 2500 stops at 12. Class 2500 belongs to urea and ammonia synthesis, hydrogen compression and injection service — the last stop in B16.5 before special joint designs take over.

Every batch is dimensionally inspected against ASME B16.5, marked per MSS SP-25 and supplied with EN 10204 3.1 mill test certificates traceable by heat number. We offer PMI, ultrasonic and magnetic particle examination, impact testing for low-temperature grades, NACE MR0175 compliance for sour service — a frequent requirement at this class — and third-party inspection by LR, BV, DNV, SGS, TÜV or IBR on request.

Yes — blind, lapped joint and spectacle blind dimension charts for Class 2500 are on this site (linked in the sidebar), alongside the weld neck charts for every class from 150 to 2500. Special bores, facings, RTJ grooves and flanges to customer drawings are quoted case-by-case.

Urea and ammonia synthesis high-pressure sections, hydrogen compression and storage, gas injection and water injection at extreme wellhead pressures, hyper-compressor circuits and high-pressure test facilities — the ultra-high-pressure corner of the process industries, where every joint is engineered, witnessed and documented one by one.

Yes — "ANSI 2500", "ANSI B16.5" and "2500 lb" all refer to what is today the ASME B16.5 Class 2500 table; the standard transferred from ANSI to ASME custodianship decades ago but the old name persists on drawings and enquiries. The dimensions on this page are the current ASME B16.5 values.