1. What Is EN 10253?
EN 10253 is the European standard series governing wrought steel fittings for butt welding. Published by the European Committee for Standardisation (CEN) and adopted as a national standard by all EU and EEA member states, it is the European equivalent of ASME B16.9 but with important structural differences in both dimensional requirements and quality documentation.
The standard is divided into four parts, each addressing a different material category or inspection regime:
| Part | Scope | Arshya Supply |
|---|---|---|
| EN 10253-1 | Non-alloy steels with specific inspection requirements (plain carbon grades, e.g. P235GH, P265GH) | On request |
| EN 10253-2 | Austenitic and austenitic-ferritic (duplex) stainless steels, and nickel alloys — the most widely specified part for process piping | Standard supply |
| EN 10253-3 | Alloy steels with specific inspection requirements — chromium-molybdenum grades (P11, P22, P5, P9, P91, P92 equivalents) | Standard supply |
| EN 10253-4 | Supplementary inspection requirements applicable to Parts 1–3; used when the application demands additional NDE, PMI, or impact testing beyond the base parts | Available on PO |
Arshya Pipe Fittings manufactures to EN 10253-2 (stainless and nickel alloy) and EN 10253-3 (CrMo alloy steel) as standard production. In both cases, every order is supplied as Type B — not Type A — a distinction that defines bore geometry, wall thickness, and ultimately pressure integrity.
2. Type A vs Type B — The Dimensional Difference
The single most important concept in EN 10253 procurement is the distinction between Type A and Type B. Both types share the same external geometry — centre-to-end dimensions, outside diameter, and bevel angle. The difference lives entirely at the bore (inside diameter).
Type A — Nominal Bore
- Bore: Not machined to any specific pipe schedule. The inside diameter is a nominal value with relatively wide tolerance — it is not matched to the connecting pipe wall.
- Wall thickness: Lighter, broadly equivalent to the ASME B16.9 nominal wall at the same NPS/schedule combination.
- Bore step: A measurable step between the fitting bore and the pipe bore is normal and expected. This step affects flow characteristics and can impede ultrasonic inspection.
- Weld joint: The weld root may sit on a slight bore mismatch, which increases the risk of turbulence, crevice corrosion, and incomplete fusion in root passes.
- Typical use: General utilities, lower-pressure systems, applications where PED Cat I–II is the design limit.
Type B — Precision-Machined Bore
- Bore: Precision-machined after forming to match the exact inside diameter of the mating pipe at the specified pipe standard (EN 10216, EN 10217) and wall thickness. The bore machining is an explicit manufacturing step.
- Wall thickness: Heavier than Type A before machining; after bore machining the net wall at the end is exactly that of the connecting pipe — flush joint, zero step.
- Bore step: Zero. The bore-machined end is dimensionally identical to the cut pipe end it mates with.
- Weld joint: Flush bore permits full-penetration root pass without backing ring, enables orbital TIG welding, and opens the bore for post-weld UT inspection from either end.
- Typical use: PED Cat III–IV process piping, pharmaceutical, food-grade, high-pressure power piping, any system where weld quality is subject to documented inspection.
3. Pressure Rating Comparison
Because Type B has a heavier pre-machined wall, the net wall at the fitting body (away from the bored ends) is thicker than in Type A. Under EN 13480 (European Metallic Industrial Piping standard), allowable pressure is directly proportional to wall thickness, so Type B always achieves a higher allowable working pressure than Type A in the same material, at the same temperature.
The table below illustrates a worked example for a 4" (DN100) 90° long-radius elbow in grade 1.4404 (316L stainless) at a metal temperature of 150°C. Wall values are indicative; always calculate to EN 13480-3 for actual design.
| Parameter | Type A | Type B |
|---|---|---|
| Nominal size | DN100 (4") | DN100 (4") |
| Material grade | 1.4404 (316L) | 1.4404 (316L) |
| Bore reference pipe | Not machined | EN 10216-5, SCH 40 equivalent |
| Fitting body wall (approx.) | ~6.0 mm | ~6.7 mm |
| Allowable pressure at 150°C (EN 13480, approx.) | ~4.5 MPa | ~5.2 MPa |
| Bore step at weld joint | Present (variable) | Zero (flush) |
| Orbital TIG welding feasible | Restricted | Yes |
| Post-weld UT from bore | Impeded by step | Full access |
Values are approximate and for illustration only. Always perform design calculations to EN 13480-3 using the actual material allowable stress at design temperature and the measured minimum wall thickness of the fitting supplied.
4. PED 2014/68/EU Category and Fitting Type
The Pressure Equipment Directive 2014/68/EU (PED) categorises pressure equipment into four risk categories — I (lowest) through IV (highest) — using Annex II tables that cross-reference fluid group against the product of maximum allowable pressure (PS in bar) and nominal size (DN).
PED Fluid Groups
Group 1 (higher risk)
Flammable, explosive, or toxic fluids. Includes hydrocarbons, acids, ammonia, chlorine. Triggers lower PS×DN thresholds for Cat III–IV uplift.
Group 2 (lower risk)
All other fluids — steam, compressed air, water above 110°C, inert gases. Higher PS×DN thresholds before Cat III–IV applies.
For buttweld pipe fittings, the PED category determines the required conformity assessment route:
| PED Category | Typical Conformity Route | Fitting Type Acceptable | Notes |
|---|---|---|---|
| Category I | Module A (internal production control) | Type A or Type B | Lowest risk — self-declaration by manufacturer |
| Category II | Module A1 or Module D1/E1 | Type A or Type B | Notified Body involvement in surveillance only |
| Category III | Module B+D, B+F, or G | Type B strongly required | EU-type examination by Notified Body; traceable docs essential |
| Category IV | Module G or Module H1 | Type B mandatory | Individual unit verification; full traceability, NDE, Notified Body sign-off |
Practical implication for procurement
For fluid group 1 applications at pressures above 25 bar on line sizes above DN50, PED Category III or IV is common. In this regime, specifying EN 10253-2 Type A can invalidate the system-level PED Declaration of Conformity (DoC). The DoC for the assembled pipe system depends on every component meeting the applicable EN standards at the required type — a Type A fitting in a Type B design basis is a non-conformance that may require component removal and replacement after pressure testing.
5. Weld Bevel and End Preparation
The heavier wall of a Type B fitting means the weld bevel preparation at each end follows a more substantial geometry than its Type A counterpart. End preparation for EN 10253-2 Type B fittings conforms to EN ISO 9692-1 (Welding and allied processes — Joint preparation — Part 1: Manual metal-arc welding, gas-shielded metal-arc welding, gas welding, TIG welding and beam welding of steels).
Standard bevel geometry (EN ISO 9692-1 Type 1.3)
- Bevel angle: 37.5° ± 2.5° (total included angle ~75°)
- Root face (land): 1.6 mm ± 0.8 mm
- Surface finish: Ra ≤ 12.5 µm on the bevel face
- Perpendicularity: Squareness tolerance of 0.5 mm across the face
Type B bore advantage for welding
- Flush bore — no internal step to trap contamination or act as a stress riser
- Orbital TIG welding is feasible without a backing ring — critical for pharmaceutical, food-grade and ultra-pure process lines
- GTAW root pass achieves full-penetration without bridging a bore mismatch
- Post-weld radiography (RT) and ultrasonic testing (UT) from the bore give unobstructed access to the weld root
For high-alloy stainless steel applications (duplex, super-duplex, 6Mo), the bore alignment offered by Type B is not a luxury — it is the only geometry that allows the weld procedure qualification to remain valid for orbital GTAW. Specifying Type A in these services and then attempting orbital welding typically results in weld procedure deviations that must be re-qualified at significant cost.
6. Ordering Requirements for Type B Fittings
A correctly written EN 10253-2 Type B purchase order requires six specific data points. Missing any one of them creates ambiguity that — at best — results in an RFI to the manufacturer, and — at worst — results in a shipment that cannot be accepted against the design specification. The most common error is omitting the bore reference pipe standard and wall thickness.
Standard designation — explicitly state Type B
Write “EN 10253-2 Type B” — not just “EN 10253” and not just “EN 10253-2”. Without the Type B designation, the manufacturer may legally supply Type A and the order is technically filled.
Bore reference pipe standard
State which pipe standard the bore is machined to match. Common choices: EN 10216-5 (seamless stainless, most common for process), EN 10217-7 (welded stainless), EN 10216-2 (seamless alloy for CrMo). This is mandatory — without it the bore diameter cannot be determined.
Outside diameter series
EN 10253 uses DN sizes that map to OD series from EN ISO 1127. Most European process piping uses OD Series 1 (matching the OD of the connecting pipe). State this explicitly: “OD Series 1” or “EN ISO 1127 Series 1”.
Wall thickness
State the wall thickness as either the pipe schedule (e.g. SCH 40, SCH 80) or the actual wall in mm (e.g. T = 6.3 mm) as defined in the reference pipe standard. This value determines the bore diameter after machining.
Material grade with EN Werkstoffnummer
Do not rely on grade names alone (e.g. “316L”) — state the full EN designation: 1.4404 (316L), 1.4301 (304), 1.4462 (duplex 2205), 1.4410 (super-duplex 2507). For alloy steel to EN 10253-3: e.g. 13CrMo4-5 (1.7335).
Certificate type — EN 10204 3.1 or 3.2
For PED Cat II–IV, EN 10204 3.1 (material test report validated by the manufacturer's own authorised inspection representative, independent of production) is the minimum. EN 10204 3.2 (validated additionally by a third-party inspector appointed by the purchaser or by an independent inspectorate) is required for some Cat IV applications and for nuclear or offshore projects.
Example correct PO line item
EN 10253-2 Type B, 90° LR Elbow, DN100 (4"), OD Series 1, bore matched to EN 10216-5 T=6.3mm (SCH 40 equiv.), Material 1.4404 (316L), EN 10204 3.1 certificate required, PED 2014/68/EU DoC required.
7. Arshya's EN 10253-2 Type B Capability
Arshya Pipe Fittings Pvt Ltd manufactures EN 10253-2 Type B as the exclusive standard — Type A is not offered. This position reflects our focus on European process piping, power generation, and petrochemical customers who require PED compliance and full bore traceability on every order.
Size range
- DN15 (½") to DN1200 (48")
- Wall thickness: SCH 10 through SCH XXS
- Fittings: 90° LR / SR elbows, 45° elbows, 180° return bends, equal and reducing tees, concentric and eccentric reducers, pipe caps, stub ends
Material grades (EN 10253-2)
- Austenitic: 1.4301 (304), 1.4307 (304L), 1.4306, 1.4401 (316), 1.4404 (316L), 1.4432, 1.4571 (316Ti), 1.4541 (321), 1.4550 (347)
- Duplex / Super-duplex: 1.4462 (2205), 1.4410 (2507), 1.4501 (Zeron 100)
- 6Mo / High-alloy: 1.4547 (254 SMO), 1.4529 (Incoloy 926)
- Nickel alloys: Alloy 625, Alloy 825, Alloy C276
3.1
EN 10204 3.1 certificate on every heat — standard, not optional
DoC
PED 2014/68/EU Declaration of Conformity available on request
TPI
Third-party inspection by TUV, Lloyd's Register, Bureau Veritas on request
Additional certifications available