EN 1092-1 Type 11 PN 2.5 Weld Neck Flange — Dimensions, Weights & Bolting

It is a weld neck flange made to the European standard EN 1092-1 in nominal pressure class PN 2.5. In EN 1092-1, “Type 11” is the designation for the weld neck (welding neck) flange — a flange with a long tapered hub that is butt-welded to the pipe. PN 2.5 is the lowest pressure class in the series, used for large-diameter, low-pressure lines, and the standard covers sizes from DN 10 up to DN 4000.

PN stands for “Pression Nominale” — 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, per the pressure-temperature tables in EN 1092-1. The PN series runs 2.5, 6, 10, 16, 25, 40, 63, 100, 160, 250, 320 and 400.

PN 2.5 is chosen for large, low-pressure services: raw and cooling water lines, sewage and wastewater treatment, HVAC and district-heating distribution, air and flue-gas ducting, penstocks and gravity pipelines. Because pressures are low, the class stays economical even at very large diameters — the dimension chart runs to DN 4000 — where a higher PN rating would make the flange needlessly heavy and expensive.

EN 1092-1 gives each flange construction a type number, and the combined dimension chart on this page carries columns for several of them: Type 01 is a plate flange, Type 02 a loose plate flange used with a collar, Type 05 a blind flange, Type 11 the weld neck, Type 21 an integral flange, and Types 32–37 are the weld-on and pressed collars. For this page the chart has been edited down to the Type 11 columns alone: the D, K and L mating dimensions with bolting, neck OD A, flange thickness C2/C3 and lengths H2 and H3.

Both are butt-welding neck flanges, but they belong to different systems: EN 1092-1 is metric, sized in DN with PN pressure classes, and its bolt circles, bolt sizes and facings (Form A, B1, B2, etc.) differ from the imperial ASME B16.5 system with its NPS sizes and Class 150–2500 ratings. The two are not interchangeable — an EN PN 2.5 flange will not bolt to an ASME flange of the same nominal size — so always match the standard of the mating equipment.

The PN 2.5 dimension chart on this page runs from DN 10 (about 3/8 inch) all the way to DN 4000 — a four-metre flange — which is the widest size range of any PN class. Small and mid sizes are machined from forgings; very large diameters are produced as forged rings or fabricated and machined to the standard, with dimensions per the chart.

From the weight columns in our chart: a DN 100 Type 11 flange weighs about 3.7 kg (8.2 lbs), a DN 300 about 17 kg (37 lbs), a DN 600 about 48 kg (106 lbs) and a DN 1000 about 92 kg (203 lbs). These are approximate carbon-steel weights calculated from the standard dimensions with a standard bore — actual weight varies with the bore and material.

EN 1092-1 defines facing forms by letter: Form A is a flat face, Form B1 the standard raised face with a normal serrated finish, Form B2 a raised face with a smooth finish, and Forms C–F cover tongue, groove, spigot and recess joints. For PN 2.5 service, Form A flat face and Form B1 raised face are the usual choices — flat face is common when mating with cast-iron or plastic-lined equipment. State the form required on your enquiry.

The bore is machined to match the inside diameter of the mating pipe so the joint has a smooth, unrestricted flow path and a clean butt weld. EN pipe walls vary, so state the pipe wall thickness or internal diameter (or the pipe standard and series) with your order. The chart's B1/B2 bore columns apply to the plate and loose flange types; for Type 11 the bore follows your pipe.

We manufacture them in carbon steel A105/P250GH and low-temperature A350 LF2, stainless steel 304/L (1.4301/1.4307), 316/L (1.4401/1.4404), 321 (1.4541), 310, 347 and 410, 254 SMO (1.4547), 904L (1.4539), duplex 2205 (1.4462), super duplex 2507 (1.4410), alloy steel F1–F91, Monel 400/K500, Inconel 600/625/825, Hastelloy C276/C22, titanium Gr. 2/5, copper nickel 90/10 and 70/30, and bimetal/clad — all with EN 10204 3.1 certificates.

It rises with size — the chart's bolting columns give the exact count and metric thread per DN: a DN 50 takes 4 × M12, a DN 150 takes 8 × M16, a DN 300 takes 12 × M20, a DN 600 takes 20 × M24, and a DN 1000 takes 28 × M27. Bolt holes (column L) and the bolt circle (column K) are also tabulated, so gasket and fastener take-offs can be made straight from this page.

For Form B1 raised-face PN 2.5 flanges, non-metallic sheet gaskets to EN 1514-1 sized for PN 2.5 are the norm — the low bolt loads of this class suit soft gaskets. Spiral wound gaskets can be used where specified. For Form A flat-face joints a full-face gasket is used, drilled to the same bolt pattern. Always match the gasket to the facing form and PN class of both flanges.

The tapered hub and full-penetration butt weld make the joint as strong and fatigue-resistant as the pipe itself, the weld is easy to examine by radiography, and the matched bore eliminates turbulence and crevice corrosion at the joint. Plate (Type 01) and loose flanges are cheaper and fine for undemanding services, but Type 11 is the engineering choice where reliability, temperature cycling or critical media are involved — even at PN 2.5 pressures.

When the line's design pressure (at design temperature, for your material group) exceeds the PN 2.5 rating of roughly 2.5 bar. Water hammer, surge allowances and test pressures should be included in that check. PN 6 and PN 10 share the same DN system with progressively heavier flanges and closer bolt pitches — see our PN 6 and PN 10 Type 11 charts linked on this page for direct comparison.

Every batch is dimensionally inspected against EN 1092-1, marked with size, PN class, material grade and heat number, and supplied with EN 10204 3.1 mill test certificates. 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.

Yes. Standard machined flanges are produced across the DN range, and very large diameters — DN 700 up to DN 4000 — are made as forged rings or fabricated-and-machined flanges to the same standard. Special bores, non-standard drilling, tongue/groove and recess facings, and flanges to customer drawings are regular work. Send the drawing or datasheet and we will quote to it.

Water and wastewater utilities, desalination plants, HVAC and district heating, power station cooling-water circuits, marine and shipbuilding, food processing, and any European-specification project handling large volumes at low pressure. EPC contractors ordering to EN piping classes use PN 2.5 Type 11 flanges on the largest, lowest-pressure lines of the plant.

Size (DN) and quantity, standard and type (EN 1092-1 Type 11), PN class, facing form (A, B1, B2…), pipe wall thickness or bore, 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.