Class 1500 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 nineteen sizes from NPS 1/2 to 24, 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 1500 weld neck flange, for example, is 310 mm OD, 54 mm thick plus the 7 mm face, on a 241.3 mm PCD, at about 33 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, easing to about 199 bar at 300 °C and 144 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 1500 (also written #1500 or 1500 lb) is a pressure-temperature rating class, not a working pressure of 1500 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 1500 A105 flange is good for roughly 3705 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.

NPS 1/2 through 2-1/2. In those sizes ASME B16.5 furnishes Class 900 flanges to Class 1500 dimensions, so the first seven rows of this chart serve both classes and the two mate perfectly there — with the stamped rating still governing the joint. From NPS 3 upward the classes part company, and the Class 1500 pattern pulls away fast: at 5 in the thickness jumps to 73.1 mm against Class 900's 50.8.

The same two gaps as Class 900: NPS 3-1/2 and NPS 22 do not exist at Class 1500, so the chart runs nineteen sizes from 1/2 to 24. A take-off that carries a 3-1/2 in line into this class has to move to 4 in (or drop to 3 in) at the spec break.

From the weight columns in our chart: a 2 inch Class 1500 weld neck flange weighs about 11.3 kg (25 lbs), a 6 inch about 75 kg (165 lbs), a 12 inch about 313 kg (690 lbs) and a 24 inch about 1508 kg (3325 lbs) — a tonne and a half of forged steel, 203 mm thick, moved by crane and made up with hydraulic tensioners. 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 most Class 1500 hydrocarbon and wellhead 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.

With Class 2500, never — every size differs in OD, bolt circle and bolting. With Class 900 the identity runs small-bore only: in NPS 1/2 through 2-1/2 the two classes share these dimensions, so those sizes mate perfectly — the stamped rating still governs the joint. From NPS 3 upward, 900 and 1500 are different flanges and do not interchange.

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 1500 pressures the mating pipe runs Sch 160, XXS or heavier, 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 1500 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 — and the Class 1500 bolting pattern has its own signature: the stud count stays low while the diameters balloon. A 12 inch flange takes just 16 studs, but of 2 inch UNC; a 24 inch takes 16 studs of 3-1/2 inch UNC at 615 mm long — hardware made up exclusively with hydraulic tensioners. A193 B7 / A194 2H remain the standard grades on carbon-steel joints, B16 for high temperature.

RTJ dominates: most Class 1500 hydrocarbon, hydrogen and wellhead 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. Spiral wound gaskets to ASME B16.20 with inner and outer rings remain available for RF joints on milder services. Our RTJ gasket size chart on this site covers the ring numbers per flange size.

Because at 250-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. Slip-on and threaded flanges have no place in Class 1500 practice; blinds and spectacle blinds remain for isolation, and their Class 1500 charts are on this site.

For A105 at 38 °C the allowable working pressures are roughly 3705 and 2220 psig. Dimensionally the step is dramatic above the shared small bores: at 6 in, Class 1500 is 395 mm OD and 82.6 mm thick against Class 900's 380 and 55.6; at 12 in the stud diameter steps from 1-3/8 to 2 inches. Class 1500 belongs to synthesis loops, hydrogen compression and water injection — services where even Class 900 has run out of headroom.

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, slip-on, socket weld, lapped joint and spectacle blind dimension charts for Class 1500 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.

Ammonia and methanol synthesis loops, hydrogen compression and storage, high-pressure water injection offshore, wellhead and christmas-tree piping, hydrocracker reactor circuits and the highest-pressure steam — the territory between Class 900 and the rare Class 2500, where joints are engineered one by one.

Yes — "ANSI 1500", "ANSI B16.5" and "1500 lb" all refer to what is today the ASME B16.5 Class 1500 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.