Class 150 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 size from NPS 1/2 to 24, the outer diameter, flange thickness, hub and weld-neck diameters, neck length, raised face diameter and height (1.6 mm at this class), bolt circle and weld face — all in millimetres — plus the published weight. A 4 in Class 150 weld neck flange, for example, is 230 mm OD, 24 mm thick, on a 190.5 mm PCD, at about 7.9 kg.

The rating depends on material and temperature. For Group 1.1 materials such as A105 carbon steel, ASME B16.5 allows roughly 285 psig (about 20 bar) at 38 °C — and Class 150 derates faster with temperature than any other class, falling to roughly 100 psig around 340 °C. Stainless and alloy grades have their own tables. Always confirm the rating at your design temperature.

Class 150 (also written #150 or 150 lb) is a pressure-temperature rating class, not a working pressure of 150 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 150 A105 flange is good for roughly 285 psig cold, but far less when hot.

ASME B16.5 covers pipe flanges from NPS 1/2 to NPS 24 (DN 15 to DN 600) in classes 150, 300, 400, 600, 900, 1500 and 2500. Flanges larger than 24 inches are covered by ASME B16.47 (Series A and B). Our Class 150 weld neck chart on this page lists all twenty standard sizes with dimensions in millimetres.

From the weight columns in our chart: a 2 inch Class 150 weld neck flange weighs about 2.6 kg (5.7 lbs), a 6 inch about 12 kg (26 lbs), a 12 inch about 36 kg (79 lbs) and a 24 inch about 118 kg (260 lbs). These are published carbon-steel weights with a standard bore — the exact weight varies with the bore schedule and material density.

Class 150 and 300 use the light raised face — 1.6 mm (1/16 inch), shown in the RF Height column of our chart — whereas Class 400 and above use the taller 6.35 mm (1/4 inch) face. This matters for bolt and stud length calculations, and it is one of the details estimators most often miss when a take-off moves between classes.

Yes — Class 150 is the class most often ordered flat face (FF). A flat face with a full-face gasket is the correct joint against cast-iron, bronze or FRP equipment, where the concentrated load of a raised face could crack the softer or brittle mating flange. State RF or FF (and the mating equipment) with your enquiry.

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 (for example Sch 10, 40 or 80) with your order. A matched bore gives a smooth, unrestricted flow path and a clean butt-weld joint — that is why the Bore column in our chart reads "as per pipe schedule".

We manufacture Class 150 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.

Either — and Class 150 is the class where machine bolts are genuinely common, which is why our bolt chart gives both machine bolt and RF stud lengths per size. A 2 inch flange takes 4 bolts of 5/8 inch UNC; a 12 inch takes 12 of 7/8 inch; a 24 inch takes 20 of 1-1/4 inch. Studs with two nuts remain the refinery preference; machine bolts save cost on utility duty.

Sheet gaskets (CNAF, PTFE, graphite) are the everyday choice at Class 150 bolt loads, with spiral wound gaskets to ASME B16.20 on steam and cycling services. For flat-face joints, use a full-face gasket drilled to the same bolt pattern. RTJ facings are unusual at this class but available on request.

Even at low pressure, the weld neck's tapered hub and full-penetration butt weld give the joint the strength and fatigue life of the pipe itself, with a smooth bore and no crevice. Slip-on flanges are cheaper and fine for stable utility duty, which is why both are common at Class 150 — choose weld neck where cycling, vibration, temperature swings or critical media are involved.

For A105 at 38 °C the allowable working pressures are roughly 285 and 740 psig respectively — Class 300 more than doubles the rating for a modest increase in thickness, bolting and cost, on the same 1.6 mm raised face. When a service sits near the top of the Class 150 envelope, or sees temperature, stepping to Class 300 is the standard move.

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, and third-party inspection by LR, BV, DNV, SGS, TÜV or IBR on request.

Yes — slip-on, blind, socket weld, lapped joint, long weld neck and spectacle blind dimension charts for Class 150 are all on this site (linked in the sidebar), alongside the weld neck charts for classes 300 through 2500. Special bores, facings and flanges to customer drawings are quoted case-by-case.

Practically all of them: water and wastewater, HVAC and building services, air and utility systems, food and chemical plants, low-pressure steam and condensate in power and process plants, marine services — Class 150 is the default flange wherever pressures are modest, which is most of industry.

To quote quickly we need: size (NPS) and quantity, class (150) and standard (B16.5), type (weld neck), facing (RF or FF), bore schedule of the mating pipe, material grade, any impact-test or NACE requirement, and certification and inspection needs. Tesco Steel & Engineering is an ISO 9001:2015 certified flange manufacturer and exporter based in Mumbai, India, shipping worldwide.

Yes — "ANSI 150", "ANSI B16.5" and "150 lb" all refer to what is today the ASME B16.5 Class 150 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.