DIN 2634 PN 25 Weld Neck Flange — Dimensions, Weights & Bolting

DIN 2634 is the German standard for welding neck (weld neck) flanges in nominal pressure class PN 25 — rated for roughly 25 bar at room temperature. It defines the flange outside diameter, thickness, bolt circle, drilling, neck dimensions and weights in millimetres for sizes DN 15 to DN 1000. The weld neck's tapered hub is butt-welded to the pipe, making it the standard construction for reliable, inspectable joints.

Formally, no — DIN 2634 was withdrawn and superseded by the European standard EN 1092-1, which absorbed its dimensions as the Type 11 weld neck in PN 25. In practice the number is very much alive: drawings, spares lists and enquiries across the enormous installed base of DIN-era plants still cite DIN 2634 daily. We manufacture to the dimensions and certify to either designation.

Yes, for practical purposes: EN 1092-1 carried the DIN dimensions over essentially unchanged, so a DIN 2634 flange mates with an EN 1092-1 Type 11 PN 25 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 (DIN 2526 Form C corresponds in practice to EN Form B1).

PN (“Pression Nominale”) is the nominal pressure class. A PN 25 flange is rated for a maximum working pressure of about 25 bar at room temperature, with the exact allowable pressure depending on the material group and falling as temperature rises. The DIN welding neck family ran PN 6, 10, 16, 25 and 40 — one DIN number per class, DIN 2631 through DIN 2635.

d1 is the pipe outside diameter (given for the ISO and old DIN pipe series), D the flange outside diameter, b the flange thickness, k the bolt circle (PCD), d2 the bolt hole diameter, h1 the length through hub, d3 the neck diameter at the weld end, s the neck wall thickness, r the corner radius, h2 the hub taper height, d4 the raised face diameter and f the raised face height. The lettered diagram above the chart shows each one.

Because two pipe systems were in use in the DIN era: the modern ISO pipe outside-diameter series and the older German DIN pipe series. For the smaller sizes the standard tabulates both — the pipe OD (d1) and matching weld-end neck diameter (d3) differ between the series, while every other dimension of the flange is identical. State which pipe series you are welding to when ordering; modern projects almost always use the ISO series.

The chart on this page runs from DN 15 to DN 1000, per the standard. Within that range the smaller sizes carry the dual ISO/DIN pipe-series rows described above. For sizes or classes outside the DIN series, orders move to EN 1092-1 Type 11, which continues the same dimensional system.

The chart's weight column gives the standard's published weights at 7.85 kg/dm³ (carbon steel), to which we have added the lbs conversion: a DN 50 weighs about 2.82 kg (6.2 lbs), a DN 100 weighs about 6.52 kg (14.4 lbs), a DN 200 weighs about 17 kg (37 lbs), a DN 500 weighs about 89.6 kg (198 lbs). Stainless runs marginally heavier and titanium roughly 42% lighter; certified weights are issued on order.

The Bolting columns give the count, metric thread and hole diameter per DN: a DN 15 takes 4 × M12, a DN 100 takes 8 × M20, a DN 400 takes 16 × M33 and a DN 1000 takes 28 × M52. The cross-class drilling matrix further down the page also lets you compare the drilling against the other PN classes when matching an unknown flange.

The classic facing is a raised face to DIN 2526 Form C — the d4 and f columns in the chart give its diameter and height. It corresponds in practice to EN 1092-1 Form B1, so gaskets and mating faces carry over. Smooth finishes and other facing forms are machined on request.

EN 1514-1 sheet or spiral wound gaskets sized for PN 25; spiral wound preferred on steam and thermal-cycling duty. Always match the gasket to the facing and PN class of both flanges.

We manufacture them in carbon steel A105/P250GH — the modern equivalent of the classic DIN grade C22.8 (1.0460) — low-temperature A350 LF2, stainless steel 304/L, 316/L, 321, 310, 347 and 410 with their EN numbers (1.4301, 1.4404, 1.4541…), 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.

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. DIN-era slip-on and plate flanges (DIN 2573/2576/2501 series) are cheaper and fine for undemanding, low-pressure duty, but for process lines, temperature cycling and critical media the welding neck construction is the engineering choice.

The DIN system gave each type its own numbers: DIN 2527 for blind flanges, DIN 2573/2576 for PN 6/PN 10 plate and slip-on flanges, DIN 2501 for the general dimension/drilling series, and DIN 2565/2566 for threaded flanges. The welding neck family is DIN 2631–2635 — one number per PN class — all now consolidated into EN 1092-1 with its type numbers.

Within the DIN welding neck family, DIN 2635 (PN 40) is the next and final step. Above PN 40 the DIN welding-neck series ends — higher classes are ordered to EN 1092-1 Type 11 (PN 63, PN 100 and up), which also carries the DIN dimensions for the classes below. See the EN 1092-1 charts linked on this page.

Every batch is dimensionally inspected against the standard, marked with size, class, material grade and heat number, and supplied with EN 10204 3.1 mill test certificates — issued to DIN or 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.

Yes. Besides standard dimensions we machine special bores for either pipe series or non-standard walls, extended hubs and long weld neck versions, special facings and drilling, and flanges to customer drawings — including matching worn or undocumented legacy flanges from a sample or field measurements. Send the drawing or datasheet and we will quote to it.

District-heating utilities, chemical and food plants, thermal-oil and hot-water system builders, power-station auxiliary systems and maintenance teams serving legacy DIN-standard plants.

Size (DN) and quantity, the standard (DIN 2634 or EN 1092-1 Type 11 PN 25), pipe series (ISO or DIN) or wall thickness, 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.