Measure the full wall – not the root face: where wall thickness and outside diameter are really measured at the welding end

Rule of thumb

Wall thickness T and outside diameter D of a fitting, pipe or weld neck flange apply at the welding end – and exactly as the standard enters them in its figure: at the end plane, between the extended outside surface and the inside surface. The welding bevel only appears to cut into the wall; the root face of 1.6 ± 0.8 mm is not a wall thickness. Anyone who reaches across the bevel with a caliper measures too little and wrongly rejects a conforming part.

Where does the rule come from?

From the standards’ own figures. EN 10253-2 and EN 10253-4 dimension the welding end in figure 11: D on the extended cylindrical outside surface, T as the full wall to the inside surface, both at the end plane; the bevel angle α of 30° +5/−0 and the root face C of 1.6 ± 0.8 mm are separate dimensions next to them. EN 10216-2, 10216-5, 10217-1 and 10217-7 show the same bevel for pipes in figure 1 – supplied only on order, and without T, because the pipe standard inspects the wall at both pipe ends (EN 10216-2 clause 11.9) without entering it in the figure. EN 1092-1 likewise enters ØA and the wall thickness S of the weld neck flange at the end plane in annex A (figures A.1 to A.3). So the rule is not a workshop convention but the way the standard drawing is read.

What is technically correct?

A welding end has three zones: the cylindrical outside surface, the welding bevel and the root face. The wall thickness the standard tolerances is the wall that will later carry the weld – the full wall, extended to the end plane. In practice you take it with the caliper where the wall is still cylindrical, i.e. directly behind the end of the bevel, and read the same value as in the standard’s figure. The outside diameter is taken at the welding end across the cylindrical outside surface, not across the edge of the bevel. If a fitting end is machined (chamfered outside up to 30° and inside up to 18°, permitted by EN 10253-2 clause 11.3), T runs from the edge of the outer chamfer to the edge of the inner chamfer – the wall may become thinner at the end, and it is measured where both chamfers end. On a weld neck flange with a bore taper (EN 1092-1 figure A.3, 15° +5/−0 to the pipe wall) the reduced wall Sp stands at the end plane and must equal the pipe wall T; S is read only behind the taper.

Where does the rule end?

• On the body of an elbow or tee only the lower limit of the welding ends applies (type A to EN 10253-2 table 12); the body has no upper limit – there you do not measure to check dimensional conformity, at most to find thin spots.
• On pipe the standard inspects at both pipe ends (EN 10216-2 clause 11.9); the wall in the middle of the pipe is inspected only if the option for it was ordered (EN 10216-2 option 15, EN 10216-5 option 23, EN 10217-1 option 11, EN 10217-7 option 22).
• Pipe has a bevel only on order (EN 10216-2 option 10, EN 10216-5 option 17, EN 10217-1 option 7, EN 10217-7 option 16) and, under the last three standards, only from 3.2 mm wall – the default is a square cut, and then the question does not arise.
• Below 3.2 mm ordered wall EN 10253-2 supplies square-cut or lightly chamfered ends, above 20 mm the joint preparation is agreed – then the agreed drawing applies.
• The flange taper Sp is not a shortfall of S but intended; only on a flange without taper is the wall at the end plane also S.

What does the standard say?

EN 10253-2:2021-11 (and EN 10253-4:2025 with identical wording): 11.2.1.1 outside diameter at the welding ends, 11.2.3 and table 12 wall thickness at the welding ends, 11.3 and figure 11 weld preparation with angle α, root face C and the dimensions T/T1 and D/D1 at the end plane. EN 10216-2:2020-04: 8.6 and figure 1 (option 10), 11.9 measurement at the pipe ends, option 15. EN 1092-1:2018-12: 5.6, table 22 (A and S with plus tolerances only, footnote c) and normative annex A, figures A.1 to A.3. ASME B16.9 tolerances outside diameter and wall thickness at the welding end, ASME B16.25 sets the bevel at 37.5° ± 2.5° with a root face of 1.6 ± 0.8 mm.

DIN/EN versus ASME/ASTM

The measuring point is the same in both worlds: at the welding end on the full wall, not at the root face. What differs is the bevel – 30° +5/−0 to EN, 37.5° ± 2.5° to ASME B16.25 – and because the ASME bevel is longer, the error from measuring across it is larger. The nominal wall of an ASME fitting is the ordered schedule wall of the matching pipe; the bore B of an ASME weld neck flange follows the order, not the table (the rule of thumb “DN is not NPS” applies to the sizes, not to the measuring point).

Worked example

Goods inward, elbow 88.9 × 3.2 to EN 10253-2 type A, 3D. The inspector sets the caliper at the end, the jaws slide across the bevel onto the root face, reading 2.4 mm – “too thin, complaint”. Directly behind the end of the bevel, on the cylindrical wall, the same caliper reads 3.2 mm; the outside diameter across the cylindrical outside surface is within tolerance. The elbow conforms; the 2.4 mm were the root face plus part of the bevel. The same trap exists on the weld neck flange when the inspector takes the wall across the bore taper and compares it with S – there Sp applies.

Relevance for Zickwolff

From daily business: the query “the wall is too thin” regularly comes from the customer’s goods inward – almost always it was measured across the bevel. That is why our dimensional drawing pages for fittings and pipes show the box “Where it is measured – at the welding end” with our own drawing detail after the standard’s figure, and the dimension finder gives the tolerances for the ordered wall. Anyone who sends us a photo with the caliper at the right place gets the assessment the same day.

Checked today

Traffic light: applies (class A). The rule reproduces the standards’ figures literally (EN 10253-2 figure 11, EN 10216-2 figure 1, EN 1092-1 annex A) and was checked against the page image of the standards.

Further reading

• Steel elbow EN 10253-2: dimensions – table, dimensional drawing and tolerances – Elbows to EN 10253-2 with dimensional drawing and measuring box
• Boiler tubes EN 10216-2: dimensions – table, dimensional drawing and tolerances – Seamless tubes to EN 10216-2
• Welding neck flange type 11 EN 1092-1: dimensions – table, dimensional drawing and tolerances – Weld neck flange type 11 to EN 1092-1
• DN is not NPS, PN is not Class – why translating between the standards worlds is only an approximation – DN is not NPS
• Mixing standards worlds: what fits, what only appears to fit, what does not fit – Mixing standards worlds: EN and ASME in one project