Class 600 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 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 600 weld neck flange, for example, is 275 mm OD, 38.1 mm thick plus the 7 mm face, on a 215.9 mm PCD, at about 19.1 kg.

The rating depends on material and temperature. For Group 1.1 materials such as A105 carbon steel, ASME B16.5 allows 102.1 bar (roughly 1480 psig) at 38 °C, easing to about 80 bar at 300 °C and 57 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 600 (also written #600 or 600 lb) is a pressure-temperature rating class, not a working pressure of 600 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 600 A105 flange is good for roughly 1480 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 ASME B16.5 furnishes Class 400 flanges in NPS 1/2 through 3-1/2 to Class 600 dimensions — at small bores a dedicated lighter pattern saves nothing worth tooling for. Seen from this page, it means the first nine rows of the Class 600 chart serve both classes, and small-bore Class 600 stock covers a Class 400 requisition dimensionally. The two charts part company at NPS 4, where Class 600 steps up to its own heavier pattern — 275 mm OD against Class 400's 255 at 4 inches.

From the weight columns in our chart: a 2 inch Class 600 weld neck flange weighs about 5.4 kg (12 lbs), a 6 inch about 37 kg (81 lbs), a 12 inch about 102 kg (225 lbs) and a 24 inch about 376 kg (829 lbs) — in the larger bores roughly 30 to 40 percent heavier than Class 400 and half as heavy again as Class 300. 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, against the 2 mm face of Class 150 and 300. The taller face adds to every stud length, which is why bolting assumptions must never cross a 300-to-600 spec break. Our stud chart below already allows for the 7 mm face.

No — for every size, Class 600 differs from both neighbours in OD, bolt circle and bolting, so a Class 600 flange never mates with a Class 300 or Class 900 flange of the same size. The one identity in the family runs the other way: small Class 400 flanges (NPS 1/2 to 3-1/2) are furnished to Class 600 dimensions, so those mate with Class 600 perfectly — the stamped rating still governs the joint.

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 600 weld neck chart on this page lists twenty-one sizes with dimensions in millimetres, NPS 22 included.

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 600 pressures the mating pipe is commonly Sch 80, 160 or heavier, and the match matters: 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 600 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 — machine bolts have no place at Class 600 bolt loads, which is why our chart lists stud lengths only. A 2 inch flange takes 8 studs of 5/8 inch UNC, a 12 inch takes 20 of 1-1/4 inch — note the jump to twenty studs that Class 600 makes at 12 inches — and a 24 inch takes 24 of 1-7/8 inch, with A193 B7 / A194 2H the standard grades on carbon-steel joints.

Spiral wound gaskets to ASME B16.20 with inner and outer rings are the standard at Class 600 bolt loads — the inner ring matters here, preventing inward buckling of the winding at high seating stress. Graphite-filled for steam and hydrocarbons, PTFE-filled for chemical duty. RTJ facings with octagonal ring gaskets are routine at this class on hydrocarbon and wellhead service — state RF or RTJ with the enquiry.

At Class 600 there is no real choice to make: most line classes at this rating specify the weld neck outright, because the tapered hub and full-penetration butt weld give the joint the strength and fatigue life of the pipe itself, with a smooth bore and a weld open to radiography. Slip-on flanges exist in the Class 600 tables but are rare in practice at these pressures.

For A105 at 38 °C the allowable working pressures are roughly 1480 and 740 psig — Class 600 doubles the rating. Dimensionally everything steps up: a 6 inch flange grows from 320 to 355 mm OD, from 36.6 to 47.7 mm thickness, and the 2 mm face becomes 7 mm, which lengthens every stud. When a service outgrows Class 300 — high-pressure steam, hydroprocessing, boiler feed discharge — Class 600 is the standard destination, and stockists carry it nearly as deep as 150 and 300.

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 and spectacle blind dimension charts for Class 600 are all on this site (linked in the sidebar), alongside the weld neck charts for every class from 150 to 2500. Special bores, facings and flanges to customer drawings are quoted case-by-case.

Refinery hydroprocessing and high-pressure process units, boiler feedwater discharge and high-pressure steam in power plants, gas processing and compression, wellhead and manifold piping onshore and offshore — Class 600 is the standard high-pressure class of the process industries, the third of the three classes the trade stocks deep.

Yes — "ANSI 600", "ANSI B16.5" and "600 lb" all refer to what is today the ASME B16.5 Class 600 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.