Home / Services / Rohrtrennen / Bevel overview

Pipe bevel geometries – finding the right weld preparation

Overview for our customers' site managers and planners: which bevel applies under which code, and how to choose the right geometry by wall thickness, accessibility and material – incl. unequal wall thicknesses and branch openings (nozzles/probes).

Everything from a single source at HSOS. We deliver all of the variants shown here in practice for our customers – cutting, bevelling and machining pipe, on site and cold (no ignition source, no metallurgical change). This overview is intended to give you a quick orientation on the common geometries. Which variant is actually used is agreed with your WPS / project specification.

The key point first: For the geometry of weld preparation there is no country-by-country patchwork in Europe. All EU/EFTA countries have adopted the same standard EN ISO 9692-1 – identical content, only a different national prefix (DIN, BS, NF, UNI, UNE …). The old DIN 2559-1 was withdrawn in 2004. The real difference comes not from the country but from the project code – and that depends on the industry. The WPS / project specification always takes precedence.

Which code applies in which industry?

The legal framework in Europe is the Pressure Equipment Directive PED 2014/68/EU. Alongside the harmonised EN standards it expressly permits equivalent codes – which is why, depending on the industry, work is sometimes done to ASME (guidance: CEN/TR 14549, ISO 15649). Rough assignment:

General industrial/plant engineering, chemicals (conventional), district heating, HVAC, mechanical engineering → EN 13480 / AD 2000 → bevel to EN ISO 9692-1.
Oil & Gas, refinery, petrochemicals, LNG (also in the EU – usually an operator/EPC requirement) → ASME B31.3 → bevel to ASME B16.25 (37.5°).
Power plants / power → ASME B31.1 or EN 12952 + EN 13480.
Transmission pipelines → API 1104, ASME B31.4/B31.8; EU gas EN 12732 / EN 1594.
Offshore (North Sea) → NORSOK / DNV (combined with ASME/API).

Rule of thumb: “It is not the country that decides, but the industry → the project code → the WPS.”

Systematic approach

1Clarify the code

Which code does the project / country require? EN ISO 9692-1 (European standard) or ASME (typical for Oil&Gas / international)?

2Choose the geometry

By accessibility (one-/two-sided) and wall thickness t determine the joint form – see the selection table.

3Dimensions & material

Set included angle, gap and root face within the standard range; the material mainly affects the angle/access, not the joint family.

1 · Differentiation by project code

Because the geometry is unified across Europe via EN ISO 9692-1, the bevel is determined by the project code – not the national border. The table below compares the relevant codes with their current edition (as of 2026, without warranty).

Project code	Typical industry	Preparation standard (current edition)	Angle principle	Region
EN / PED EN 13480, AD 2000	Industrial/plant engineering, chemicals, district heating, HVAC, mechanical engineering	EN ISO 9692-1:2013 · ends: EN 12627 / EN 10253	α = included (V 40–60°)	EU
ASME B31.3 Process Piping	Oil&Gas, refinery, petrochemicals, LNG	ASME B16.25-2022 (ends) · B31.3-2022 §328.4	37.5° per face (~75° incl.)	US
ASME B31.1 Power Piping	Power plants / power	ASME B16.25-2022 · B31.1-2022	37.5° per face	US
API 1104 B31.4 / B31.8	Transmission pipelines	API 1104 (22nd ed. 2021); EU gas EN 12732 / EN 1594	usually 30°–37.5° per face	EUUS
NORSOK / DNV	Offshore (North Sea)	NORSOK M-101 (+ ASME/API)	per project specification	US

National = identical content: EN ISO 9692-1 appears as DIN / BS / NF / UNI / UNE / ÖNORM / NEN / SS / PN … – same content, only a different prefix (DIN 2559-1 withdrawn in 2004).
Rule of thumb: “Same geometry across Europe – the difference comes from the project code (EN vs. ASME), not the national border.”

Component ends (fittings/pipe) vs. weld preparation: EN ISO 9692-1 describes the joint form at the weld. The factory bevel on pipe/fittings is governed in Europe by EN 12627 (welding ends) and the EN 10253 series – the European counterpart to ASME B16.25.

2 · Joint form by wall thickness & accessibility (EN ISO 9692-1)

First branch: one-sided (accessible only from outside – the usual case on pipe) or two-sided weldable (access inside & outside)? Then the wall thickness t decides. The dimensions are standard ranges (empirical values) – the exact value is in the WPS.

α included angle β angle of bevel / U flanks (included) b gap / root opening c root face height t wall thickness R radius (U groove)

Angle convention: All angles here are given as included (full) opening angles. DIN EN specifies some angles to the vertical (half the value – recognisable in the standard's drawing by a drawn vertical); those values are converted here consistently to the full angle (e.g. β 8–12° to the vertical → 16–24° included).

Underlying standards (current edition, as of 2026): EN ISO 9692-1:2013 · ASME B16.25-2022 · ASME B31.3-2022 (§328.4) · ASME B31.1-2022 · API 1104 (22nd ed. 2021) · EN 13480:2017 · EN 12627 · EN 10253 · PED 2014/68/EU (guidance CEN/TR 14549, ISO 15649).
All data without warranty – the dimensions are standard ranges/empirical values. The Welding Procedure Specification (WPS) always takes precedence.

One-sided welding (Table 1) – the usual case on pipe

Joint form	Wall thickness t	Angle	Gap b	Root c	Practitioner's note
1.2 I-Fuge square butt	≤ 3–4 mm (up to 8 MAG)	–	b ≈ t	–	Thin-walled; no bevel, just cut & deburr.
1.3 V-Fuge single-V	3 – 10 (12) mm	α 40–60°	≤ 4 mm	≤ 2 mm	The standard on pipe. Fully weldable from outside.
1.5 Y-Fuge V mit Steg	5 – 40 mm	α ≥ 60°	1–4 mm	2–4 mm	Root face > 2 mm secures the root; good for manual welding.
1.6 U-Fuge auf V-Wurzel U on V root	> 12 mm	α 60–90° / β 16–24°	1–3 mm	≥ 4 mm	Heavy wall, less weld metal than V; secure root. Colloquially known as the “tulip”.
1.7 V-Fuge auf V-Wurzel V on V root	> 12 mm	α 60–90° / β 20–30°	2–4 mm	> 2 mm	Combines V access with a defined V root; for heavy walls.
1.8 U-Fuge single-U	> 12 mm	β 16–24°	1–3 mm	≤ 4 mm	Pure U groove; minimal weld metal for very heavy walls.
1.4 Steilflanken-V narrow-gap V	> 16 mm	β 10–40°	5–15 mm	–	Only with backing; economical weld fill.
1.9 HV-Fuge single-bevel	3 – 10 mm	β 35–60°	2–4 mm	1–2 mm	One member bevelled (T-/branch and nozzle welds).

Two-sided welding (Table 2) – with inside & outside access / heavy wall

Joint form	Wall thickness t	Angle	Gap b	Root c	Practitioner's note
2.1 I-Fuge square, 2-seitig	≤ 8 mm	–	0–3 mm	–	Capping run on both sides, no bevel.
2.5 Doppel-V (X) double-V	> 10 mm	α 40–60°	1–3 mm	≥ 2 mm	Less distortion & fill volume than a single-sided V on heavy wall.
2.4 Doppel-Y double-Y	> 10 mm	α 40–60°	1–4 mm	2–6 mm	X with root face – robust root, two-sided.
2.9 Doppel-HV (K) double-bevel	> 10 mm	β 35–60°	1–4 mm	≤ 2 mm	One member bevelled on both sides (heavy T-joints).
2.7 Doppel-U double-U	≥ 30 mm	β 16–24°	1–3 mm	≥ 3 mm	Very heavy wall: minimal weld metal, most expensive preparation.

3 · International: ASME B16.25 (Oil&Gas / worldwide)

When the site manager moves to an ASME-based project (refinery, pipeline, offshore – also in Europe), the pipe ends follow ASME B16.25 (referenced in B31.3/B31.1). The main difference from the EN: the angle is measured per face from the vertical.

Standard bevel 37.5°

Wall 3.2–22.2 mm · root face (land) ≈ 1.6 mm · two ends → ~75° included

Compound bevel

Wall > 22.2 mm · a second, shallower angle at the bottom saves weld metal

U/J bevel

Heavy wall thicknesses · curved flank, minimal fill volume

Feature	EN ISO 9692-1 (Europe)	ASME B16.25 (international)
Angle definition	α = included opening angle (V: 40–60°)	37.5° per face from the vertical → ~75° included
Root face	c 1–4 mm (form-dependent)	≈ 1.6 mm (±0.8)
Heavy-wall transition	U/double-U, steep-flank groove	compound bevel / J-bevel above 22.2 mm
Practical consequence	narrower V → fewer passes/weld metal	wider 75° V → more weld metal, more passes
Typical use	industrial/plant engineering in the EU	Oil&Gas, petrochemicals, pipeline, offshore worldwide

When/where is ASME bevelling used in Europe? Whenever an operator or EPC specifies the project to ASME – typically in Oil&Gas, refinery, petrochemicals and LNG, often with internationally operating groups and on offshore projects. This is legally permissible via the PED (proof of equivalence, CEN/TR 14549, ISO 15649). Rule of thumb: classic EU plant engineering → EN; process / Oil&Gas → ASME. Recognisable on the isometric/WPS: an angle of 37.5° and a root face of ≈ 1.6 mm point to ASME, an included α 40–60° to EN.

Material – what changes?

EN ISO 9692-1 applies to all steel grades. The material determines the joint family less than the fine details:

Unalloyed / low-alloy steels: standard ranges apply directly.
Stainless / high-alloy steels: same forms, usually a somewhat larger included angle for access and due to heat input; often a TIG root.
Very heavy / high-strength walls: U or steep-flank/narrow-gap forms to limit weld metal, distortion and residual stresses.

4 · Unequal wall thickness: internal boring & external turning

When two pipe pieces of different wall thickness are joined (e.g. old/new pipe or pipe to valve/fitting), the transition must be matched – otherwise a bore mismatch (hi-lo), flow/erosion problems and misinterpretation on radiographic testing occur. Code basis: ASME B16.25 and ASME B31.3 §328.4.3 (Fig. 328.4.3); EN 13480 has analogous transitions (taper max. 30°).

When? A transition is required when the internal mismatch exceeds the permissible hi-lo or one wall is significantly thicker (guide value ratio > 1.5 : 1). The thicker part is machined to match – internally (internal boring) for ID mismatch, externally (turning) for OD mismatch. Internal boring is especially important with erosive/aggressive media and for radiography.

Internal boring (ID matching on the thicker pipe)

Direct taper

Taper directly at the joint, ~15° (ASME max. 30°). Short, simple.

Straight then tapered

First cylindrical (e.g. ~3×t), then tapering out at ~15°. Smoother force flow.

Bore taper 1:4

Continuous cone max. 1:4 (~14°) over ≥ 2×t (ASME alternative).

Variant	Geometry	Angle / length	Use
Direct taper	taper straight from the root	~15° (max. 30°)	Standard for moderate mismatch; short length.
Straight then tapered	cylindrical land, then taper	land ~3×t, then ~15°	Smoother transition, less notch effect; often specified by the project.
Bore taper	continuous conical bore	max. 1:4 (~14°), ≥ 2×t	ASME alternative for larger ID differences.

External turning (OD matching)

If the outside diameters differ (with the same bore), the OD of the thicker part is turned down externally; alternatively the transition is made via the weld cap. Slope in each case ≤ 30°.

External taper ≤ 30°

OD of the thicker part turned down; slope max. 30°.

Tapered weld cap

Transition via the cap, taper ≤ 30° (no material removed from the pipe).

Values to ASME B16.25 / B31.3 §328.4.3 – guide values, without warranty; the WPS is binding.

5 · Bevelling on un-cut pipe: branches, nozzles & probe openings

When a branch, nozzle or measuring probe is connected to an un-cut pipe, an opening must be made in the pipe wall and its edge bevelled – on a doubly curved “saddle” surface. This is not trivial: the local dihedral angle ψ (angle between the branch and run-pipe wall) changes around the circumference – acute at the “toe”, ~90° at the sides, obtuse at the “heel”. So the bevel geometry must also be adjusted around the circumference.

Code basis: AWS D1.1 (tubular T-/Y-/K-connections: bevel detail by local dihedral angle ψ, zones, Tab. 3.5/3.6, Fig. 3.8–3.10) · ASME B31.3 §328.5.4 (Fig. 328.5.4: set-on/set-in branches, full penetration + cover fillet t_c = the lesser of 0.7·T_b or 6 mm) · EN 1708-1 (European catalogue of weld details for pressurised branches/nozzles).

The three connection variants

Set-on

Branch saddle-bevelled onto the run pipe; weld running around the outside + cover fillet.

Set-in / set-through

Hole in the run pipe, branch inserted; full-penetration weld + cover fillet.

With welding outlet (olet)

Factory-bevelled fitting (e.g. Weldolet) – defined, constant bevel, no saddle problem.

Why the bevel changes around the circumference: local dihedral angle ψ

According to AWS D1.1, the preparation is divided into zones around the circumference by the local dihedral angle ψ. Rule of thumb:

Toe – acute

Tight access → larger bevel angle, grind out the root if needed.

Side – right-angled

Standard bevel (HV-like), easily accessible.

Heel – obtuse

Smaller bevel angle; a partial fillet weld is possible.

Position on the circumference	Local dihedral angle ψ	Preparation (AWS D1.1)
Toe / crown (acute)	small (< 90°, down to ~30°)	Larger bevel angle, create root access; for very acute ψ, full penetration may not be possible.
Sides	≈ 90°	Standard bevel (HV-like), root + fill passes from outside.
Heel (obtuse)	large (> 90°)	Smaller bevel angle; transition to a (partial) fillet weld.

In practice this means: the opening is profiled (saddle cut) and the bevel adjusted around the circumference – demanding by hand, ideal for machine/CNC-assisted bevelling. HSOS performs both routes.

The WPS always takes precedence. The Welding Procedure Specification (WPS), or the project specification and isometric, is binding – the tables here are for orientation (standard ranges = empirical values, not manufacturing limit deviations). All data without warranty. HSOS bevels on site to size, cold and to the required code (EN or ASME).

Frequently Asked Questions

Which standard applies to pipe bevels in Europe?

For the bevel geometry, EN ISO 9692-1 applies Europe-wide (adopted nationally as DIN/BS/NF/UNI/UNE … – identical content). In Oil & Gas, petrochemicals and offshore, bevelling is often to ASME B16.25 / B31.3 – also in Europe. The project's WPS governs.

What bevel angle is common?

To EN ISO 9692-1 the single-V has an included opening angle of 40–60°. ASME B16.25 specifies 37.5° per face (two ends give ~75° included), root face ≈ 1.6 mm. The exact values are set by the Welding Procedure Specification (WPS).

When is internal boring done for unequal wall thickness?

For a significant internal mismatch or a wall-thickness ratio above about 1.5 : 1 (ASME B31.3 §328.4.3 / B16.25). The transition is internal at approx. 15° or a 1:4 cone, external at a maximum of 30°.

How is a nozzle bevelled on an un-cut pipe?

The opening is profiled on the curved saddle surface; the dihedral angle changes around the circumference (AWS D1.1, ASME B31.3 §328.5.4, EN 1708-1). HSOS mills/bevels it by machine on site – cold and to size.

Can HSOS cut and bevel pipe on site?

Yes. HSOS cuts, bevels and machines pipe mobile and cold on site (no ignition source, no metallurgical change) – to the required code (EN or ASME) and the customer's WPS.