Piping standards old and new: reading DIN, ASA and ND correctly on as-built drawings
In existing plants, isometrics, bills of materials and nameplates still show DIN 2448, DIN 2633, ND 16 or St 35.8 – yet today materials are ordered and inspected to EN, ISO and ASME. This overview sets the old designations against the standards that apply today: pipes, fittings, flanges, flange facings, gaskets, welding standards and materials. Each entry includes a note on what to watch for when replacing parts on site.
Designations and pressure ratings
| Formerly (existing plant) | Today | Subject | Practical note |
|---|---|---|---|
| NW (nominal size) | DN | Nominal size, dimensionless | DN 100 is not a dimension in millimetres – the outside diameter is 114.3 mm. |
| ND (nominal pressure) | PN | Nominal pressure rating | PN is a rating, not a permissible operating pressure – that depends on material and temperature. |
| 150 lb, 300 lb … | Class 150, Class 300 … | Pressure classes to ASME B16.5 | ‘lb’ is not a pressure unit in bar; Class 150 does not correspond to PN 16. |
| Inch nominal size (e.g. 4″) | NPS 4 | US nominal size | NPS 4 and DN 100 have the same outside diameter (114.3 mm), but the wall thickness series differ (schedule). |
Pipes
| Formerly (existing plant) | Today | Subject | Practical note |
|---|---|---|---|
| DIN 2448 / DIN 2458 | DIN EN 10220 | Dimensions and weights of seamless / welded steel pipes | Outside diameters have stayed the same; some wall thicknesses in the preferred series differ. |
| DIN 1629 / DIN 17175 | DIN EN 10216-1 / -2 | Technical delivery conditions for seamless pipes (non-alloy / elevated-temperature) | |
| DIN 1626 / DIN 1628 | DIN EN 10217-1 / -2 | Technical delivery conditions for welded pipes | |
| DIN 17458 / DIN 17457 | DIN EN 10216-5 / DIN EN 10217-7 | Seamless / welded stainless steel pipes | |
| DIN 2440 / DIN 2441 | DIN EN 10255 | Threaded pipes | |
| ASA B36.10 | ASME B36.10M (B36.19M for stainless steel) | US pipe dimensions with schedule series | XS corresponds to Sch 80 only up to NPS 8; XXS is not generally Sch 160. |
Fittings
| Formerly (existing plant) | Today | Subject | Practical note |
|---|---|---|---|
| DIN 2605 / 2615 / 2616 / 2617 | DIN EN 10253-1 / -2 | Butt-welding elbows, tees, reducers and caps | For stainless steel fittings, EN 10253-3 / -4 apply. |
| ASA B16.9 / B16.11 | ASME B16.9 / B16.11 | US fittings for butt welding and socket welding |
Flanges and flange facings
| Formerly (existing plant) | Today | Subject | Practical note |
|---|---|---|---|
| DIN 2631 – DIN 2638 | DIN EN 1092-1, type 11 | Weld-neck flanges PN 6 – PN 160 | Connection dimensions have stayed the same; in existing plants, old and new flanges of the same PN mate. |
| DIN 2573 / DIN 2576 | DIN EN 1092-1, type 01 | Plate flanges for welding | |
| DIN 2527 | DIN EN 1092-1, type 05 | Blind flanges | |
| DIN 2641 / DIN 2642 | DIN EN 1092-1, type 02 with collar | Loose flanges with weld-neck collar | |
| DIN 2526 form C / form E | DIN EN 1092-1 form B1 / B2 | Raised face (coarse / fine roughness) | Today the flange facing is part of the order designation (see example below). |
| DIN 2512 tongue / groove | DIN EN 1092-1 form C / D | Tongue and groove facing | |
| DIN 2513 male / female | DIN EN 1092-1 form E / F | Male and female (spigot and recess) | |
| ASA B16.5 | ASME B16.5 (NPS 26 and above: ASME B16.47) | US flanges in pressure classes | PN and Class flanges have different bolt patterns – do not mix them. |
Gaskets
| Formerly (existing plant) | Today | Subject | Practical note |
|---|---|---|---|
| DIN 2690 / 2691 / 2692 | DIN EN 1514-1 | Flat gaskets for PN flanges | |
| API 601 | ASME B16.20 | Metallic gaskets (spiral wound, corrugated, ring joint) | |
| ASA B16.21 | ASME B16.21 | Flat gaskets for Class flanges |
Welding
| Formerly (existing plant) | Today | Subject | Practical note |
|---|---|---|---|
| DIN 2559 | DIN EN ISO 9692-1 | Weld preparation (joint types) | Joint dimensions refer to the tack-welded condition. more on this → |
| DIN 1912 | DIN EN ISO 2553 | Symbolic representation of welds | |
| DIN 8563 | DIN EN ISO 5817 | Quality levels for imperfections | |
| DIN 8560 | DIN EN ISO 9606-1 | Welder qualification testing |
Bolts and nuts
| Formerly (existing plant) | Today | Subject | Practical note |
|---|---|---|---|
| DIN 931 / 933 / 934 | DIN EN ISO 4014 / 4017 / 4032 | Hexagon bolts, screws and nuts | For M10, M12, M14 and M22 the width across flats has changed. more on this → |
Materials: old DIN names and current EN designations
For materials, the material number is the key: in most cases it has stayed the same, making it the quickest way to cross-check in existing plants. The exceptions are, of all things, the most common elevated-temperature pipe steels – St 35.8 and St 45.8 were given new numbers with P235GH and P265GH.
| Formerly | Mat. no. old | Today | Mat. no. today | Application |
|---|---|---|---|---|
| St 37.0 | 1.0254 | P235TR1 | 1.0254 | Line pipe without test requirements |
| St 35.8 | 1.0305 | P235GH | 1.0345 * | Elevated-temperature carbon steel (pipe) |
| St 45.8 | 1.0405 | P265GH | 1.0425 * | Elevated-temperature carbon steel (pipe) |
| C 22.8 | 1.0460 | P250GH | 1.0460 | Forging steel for flanges |
| 17 Mn 4 | 1.0481 | P295GH | 1.0481 | Elevated-temperature C-Mn steel |
| 15 Mo 3 | 1.5415 | 16Mo3 | 1.5415 | Elevated-temperature Mo steel |
| 13 CrMo 4 4 | 1.7335 | 13CrMo4-5 | 1.7335 | Elevated-temperature CrMo steel (P11/P12) |
| 10 CrMo 9 10 | 1.7380 | 10CrMo9-10 | 1.7380 | Elevated-temperature CrMo steel (P22) |
| 12 CrMo 19 5 | 1.7362 | X11CrMo5 | 1.7362 | Elevated-temperature 5% Cr steel (P5) |
| 14 MoV 6 3 | 1.7715 | 14MoV6-3 | 1.7715 | Power plant steel |
| X 20 CrMoV 12 1 | 1.4922 | X20CrMoV11-1 | 1.4922 | Power plant steel |
| St 37-2 | 1.0037 | S235JR | 1.0038 * | Structural steel (supports, steelwork) |
| St 52-3 | 1.0570 | S355J2 | 1.0577 * | Structural steel (supports, steelwork) |
| X 5 CrNi 18 9 | 1.4301 | X5CrNi18-10 | 1.4301 | Stainless (304) |
| X 6 CrNiMoTi 17 12 2 | 1.4571 | X6CrNiMoTi17-12-2 | 1.4571 | Stainless (316Ti) |
* Material number has changed.
Old and new materials do not always match exactly in chemical composition and strength values. For pressure-bearing components, the inspection certificate (EN 10204 3.1) against the current standard is decisive. ASTM materials (e.g. A106 Gr. B, A335 P11) are only approximately comparable and are not substituted as equivalents.
How an order designation changes
Two typical items from an old bill of materials and how they are ordered today:
What matters when replacing parts on site
- Connection dimensions of PN flanges: A flange to DIN 2633 and one to EN 1092-1 PN 16 of the same nominal size mate – bolt circle, number of bolts and bolt size are the same. Differences lie in overall height, facing roughness and material marking.
- Do not mix PN and Class: An ASME Class 150 flange and a PN 16 flange look similar but have different bolt circles and bolt holes. If in doubt, measure the bolt circle and bolt hole diameter.
- Check the wall thickness: DN 100 to EN and NPS 4 to ASME have the same outside diameter but different wall thickness series. When welding an ASME fitting into an EN line, the wall thickness must be matched (counterboring or bevelling to EN ISO 9692-1 or ASME B16.25).
- The welding procedure takes precedence: If the material changes, the welding procedure specification (WPS) may change too – preheating, filler metal, heat treatment. Any material substitution must therefore be agreed with the welding coordinator.
English terms on isometrics? See the piping glossary English–German →
Frequently asked questions
May I replace an old DIN flange with an EN 1092-1 flange?
As a rule yes, provided nominal size, pressure rating, facing type and material match: the connection dimensions of PN flanges were retained in the changeover. Check the flange facing (form B1 or B2 depending on the gasket), the overall height – it changes the make-up piece – and the material certificate. For pressure-bearing lines, the piping class or the plant operator has the final say.
What does ND 16 on an old drawing mean today?
ND (nominal pressure) is now called PN. ND 16 corresponds to PN 16. Both are a pressure rating, not a permissible operating pressure – which pressure is permissible at which temperature follows from the material and the standard (pressure-temperature ratings in EN 1092-1).
Is a 150 lb flange the same as PN 16?
No. Class 150 (formerly “150 lb”) to ASME B16.5 and PN 16 to EN 1092-1 have different bolt circles, numbers of bolts and bolt sizes. They cannot be joined without an adapter flange.
Which standard applies to weld preparation now that DIN 2559 has been withdrawn?
DIN EN ISO 9692-1 (part 2 for submerged arc welding). For lines to ASME, ASME B16.25 applies with the familiar 37.5° bevel angle. Our bevel overview compares both.
To the bevel overview: joint types to EN ISO 9692-1 and ASME →
Compiled to the best of our knowledge from standards catalogues, without guarantee. Standards are revised continually; the edition agreed in the project, the piping class and the welding procedure specification are authoritative.
Existing plant, new parts – we make them fit
HSOS cuts, bevels and machines pipes, flanges and flange faces directly in the plant – including where old DIN parts meet new EN or ASME components.