Butt-weld fittings glossary

Butt-weld fitting

Piping part (elbow, tee, reducer, cap) whose ends are bevelled to be welded end to end to the pipe, with no flange or thread. The weld goes through the full wall.

ASME B16.9

US standard for factory-made wrought butt-welding fittings: dimensions, tolerances and marking. Fittings are designated in inches (NPS) and by wall (STD, XS, schedule). See the dimension charts.

EN 10253-1

European standard for non-alloy steel butt-welding fittings for general use, without specific inspection requirements. Fittings are designated by outside diameter and wall in mm.

EN 10253-2

Part of EN 10253 covering non-alloy and ferritic alloy steel fittings with specific inspection requirements, for pressure applications.

DN (nominal size)

Unitless size designation (DN 50, DN 100…). It is not a dimension: each DN matches an outside diameter, which can differ between the European and US series. See the DN, NPS and outside diameter chart.

NPS (nominal pipe size)

The US size designation in inches (½", 4", 8"…). Like DN it names a size: a 4" pipe is 114.3 mm in outside diameter.

Outside diameter

The real dimension of pipe and fitting. EN 10220 series in Europe (26.9 – 33.7 – 76.1 – 139.7 mm…), ASME B36.10 series in the US (26.7 – 33.4 – 73.0 – 141.3 mm…). The two series match for several sizes, not all.

Schedule (Sch)

US designation of pipe wall thickness (Sch 40, Sch 80…) to ASME B36.10. For the same schedule, the wall grows with the diameter.

STD (Standard)

The "standard" wall of ASME B36.10. It matches Sch 40 up to 10"; above, STD stays at 9.53 mm. Example: 6.02 mm at 4".

XS (Extra Strong)

The heavier wall of ASME B36.10. It matches Sch 80 up to 8"; above, XS stays at 12.70 mm. Example: 8.56 mm at 4".

Centre-to-end

Distance from the centre of a fitting to the plane of its end: A or B for an ASME elbow, C and M for a tee, F on EN 10253-1 sheets. It is the dimension carried onto a drawing. See elbow dimensions.

Long radius elbow (1.5D)

ASME B16.9 elbow whose bend radius is 1.5 times the nominal size: 152 mm for a 4" 90° elbow.

Type 3D elbow (EN 10253)

European designation of the elbow whose dimensions match, from 1" up, those of the ASME long radius elbow. "3D" does not mean three times the outside diameter: at 114.3 mm the dimension is 152 mm.

Equal tee

Tee whose three outlets share the same size. Its centre-to-end is the same on all three. See tee dimensions.

Concentric / eccentric reducer

Fitting joining two sizes. Concentric: both axes are aligned. Eccentric: one side stays straight, which avoids air or liquid pockets. See reducer dimensions.

Form 1 / form 2 (EN 10253-1)

The two EN 10253-1 concentric reducers. Form 1 is a cone whose length depends on both diameters; form 2 has rounded transitions and a length set by the large end.

Cap

Dished closure welded to the end of a pipe to close it for good. Under ASME B16.9 its length increases above a limiting wall. See cap dimensions.

Dished end

A closure flatter than the cap, defined by EN 10253-1: 26 mm high at 114.3 mm, against 64 mm for the cap.

Bevel

Angle machined on the ends of a fitting to form a V with the pipe and allow a full-penetration weld. To ASME B16.25: 37.5° with a 1.6 mm ± 0.8 mm root face.

Root face

Small flat at the root of the bevel. It keeps the root from burning through and eases fit-up.

Seamless / welded

A seamless fitting is formed from seamless pipe, a welded fitting from welded pipe. Our EN 10253-1 catalog offers both for elbows, tees and reducers.

A234 WPB

ASTM A234 carbon steel grade for wrought fittings: 240 MPa minimum yield, 415 to 585 MPa tensile, 0.30% carbon maximum. See the A234 WPB page.

S235

Non-alloy structural steel used for our EN 10253-1 fittings: 235 MPa yield, 360 to 510 MPa tensile. See the S235 page.

Hot-dip galvanizing

Zinc coating by immersion to EN ISO 1461. Minimum mean thickness: 85 µm above 6 mm of steel, 70 µm from 3 to 6 mm, 55 µm from 1.5 to 3 mm.

EN 10204 certificate (2.1, 2.2, 3.1, 3.2)

Inspection documents for metallic products. The 3.1 gives the actual test results of the lot, validated by an inspection representative independent of production. See quality and certifications.

Heat number

Identifier of the steel melt the pipe comes from. Stamped on the fitting and carried onto the 3.1 certificate, it links the part to its original material.

Marking (MSS SP-25)

ASME B16.9 refers to MSS SP-25: manufacturer, grade, wall and size on every fitting. Our fittings also carry lot and heat, stamped by micro-percussion.

Wall tolerance (87.5%)

Under ASME B16.9 the wall of a fitting must be at least 87.5% of nominal at any point.