BS 4504 PN 2.5 Weld Neck Flange — Dimensions, Weights & Bolting

BS 4504 is the British Standard for metric PN-series pipe flanges — the UK's issue of the dimensional system shared with DIN 2501-family standards. It tabulates flanges by DN size and PN class with metric dimensions and bolting; this page covers the weld neck series in PN 2.5, rated for roughly 2.5 bar at room temperature and spanning DN 10 to DN 2000.

Formally, no — BS 4504 was withdrawn and superseded by BS EN 1092-1, which absorbed its dimensions (the weld neck as Type 11). In practice the number is very much alive: plants engineered to British-metric specifications across the UK, Middle East, Africa and Asia still cite BS 4504 on drawings, spares lists and enquiries daily. We manufacture to the dimensions and certify to either designation.

Yes, for practical purposes: EN 1092-1 carried the dimensions over essentially unchanged, so a BS 4504 PN 2.5 weld neck flange mates with an EN 1092-1 Type 11 PN 2.5 flange of the same DN — same outside diameter, bolt circle and drilling. On critical joints, confirm details such as facing form and tolerances, which the EN standard defines slightly differently.

They are two national issues of one dimensional system: BS 4504 in Britain and the DIN 2501 family in Germany (whose welding neck standards are DIN 2631–2635, one per PN class). Outside diameters, bolt circles and drilling correspond class-for-class, and both were consolidated into EN 1092-1. A BS 4504 flange therefore mates with its DIN counterpart of the same DN and PN.

PN (“Pression Nominale”) is the nominal pressure class. A PN 2.5 flange is rated for a maximum working pressure of about 2.5 bar at room temperature, with the exact allowable pressure depending on the material group and falling as temperature rises. BS 4504 covered the classes PN 2.5 through PN 40 tabulated on this site, with the EN successor adding higher classes.

A is the flange outside diameter; C, C1 and C2 the thicknesses for the plate, boss/slip-on and weld neck constructions respectively; D the boss or hub length and D1 the weld neck's length through hub; G and X the raised face diameter and height; N the boss diameter; No., I and J the bolt count, hole diameter and bolt circle (PCD); M the hub base diameter; F the weld-end OD (it matches the pipe OD); E the straight neck length; r the corner radius; S the neck wall; and Bore the bore diameter.

Because BS 4504 tabulated several flange constructions in one table: C is the plate-flange thickness, C1 the boss and slip-on thickness, and C2 the weld neck thickness. For the weld neck flanges on this page, read C2 together with D1 (length through hub) and the Neck group (M, F, E, r, S). The shared columns — A, drilling, bolting — apply to every construction of the class.

The chart on this page runs DN 10 to DN 2000. The weld neck series covers DN 10 to DN 600 — rows outside it carry other-construction or mating data only, as noted under the chart.

From the weight columns in our chart: a DN 50 weighs about 1.6 kg (3.5 lbs), a DN 100 weighs about 3.7 kg (8.2 lbs), a DN 200 weighs about 8.8 kg (19.5 lbs), a DN 300 weighs about 16 kg (36 lbs). These are approximate carbon-steel weights calculated from the chart's own dimensions with a standard bore — actual weight varies with the bore and material.

The No., I and J columns give the count, hole diameter and bolt circle per DN, with the metric thread alongside: a DN 10 takes 4 × M10, a DN 100 takes 4 × M16 and a DN 600 takes 20 × M24. Metric stud bolts are used throughout the PN system.

A raised face is the standard — the G and X columns give its diameter and height per size. It corresponds in practice to EN 1092-1 Form B1, so gaskets and mating faces carry over to the successor standard. Smooth finishes and other facings are machined on request.

Non-metallic sheet gaskets sized for PN 2.5; full-face where flat-faced mating parts are involved. Always match the gasket to the facing and PN class of both flanges.

We manufacture them in carbon steel A105/P250GH, low-temperature A350 LF2, stainless steel 304/L, 316/L, 321, 310 and 347 with their EN numbers, 254 SMO, 904L, duplex 2205 and super duplex 2507, alloy steel F1–F91, Monel, Inconel, Hastelloy, titanium, copper nickel and bimetal/clad — all with EN 10204 3.1 certificates, PMI and heat-number traceability.

The weld neck's tapered hub and full-penetration butt weld give the joint the strength and fatigue life of the pipe itself, and the weld can be examined by radiography. The slip-on and plate constructions sharing this chart are cheaper and fine for undemanding duty, but for process lines, temperature cycling and critical media the weld neck is the engineering choice.

Step up through PN 6, PN 10, PN 16, PN 25 and PN 40 as design pressure rises — all charted on this site. The successor standard BS EN 1092-1 continues the same dimensions and adds classes above PN 40; see the EN 1092-1 Type 11 charts linked on this page.

Every batch is dimensionally inspected against the standard, marked with size, PN class, material grade and heat number, and supplied with EN 10204 3.1 mill test certificates — issued to BS 4504 or BS EN 1092-1 designation as your paperwork requires. PMI verification, ultrasonic and magnetic-particle examination, impact testing for low-temperature grades, NACE MR0175 compliance and third-party witness inspection by LR, BV, DNV, SGS, TÜV or IBR are available on request.

Water and utility contractors, HVAC companies and plant-maintenance teams replacing flanges in legacy British-metric installations across the UK, Middle East, Africa and Asia.

Size (DN) and quantity, the standard (BS 4504 or BS EN 1092-1 Type 11 PN 2.5), pipe wall or bore, facing, material grade, any impact-test or NACE requirement, and the certification and inspection you need. Tesco Steel & Engineering is an ISO 9001:2015 certified flange manufacturer and exporter in Mumbai, India, shipping worldwide with sea-worthy packing.