Wrought stainless steel elbows, tees, reducers, caps and stub ends with bevelled ends, welded directly into the pipe run. Dimensions to ASME B16.9 (NPS 1/2 to 48) or EN 10253-4 for austenitic and duplex grades.
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Butt-weld fittings are wrought elbows, tees, reducers, caps and lap-joint stub ends with bevelled ends, welded straight into the pipe run so that the fitting bore matches the pipe bore. The joint is a full-penetration weld with no crevice and no mechanical seal, which is why butt-welding is the standard construction for pressure and process piping.
Dimensions come from ASME B16.9, which covers factory-made wrought buttwelding fittings in sizes NPS 1/2 through NPS 48 (DN 15 through DN 1200), or from EN 10253-4 for wrought austenitic and austenitic-ferritic (duplex) stainless steels. A long-radius elbow has a centre-to-end dimension of 1,5 times the nominal size: 76 mm at NPS 2, 152 mm at NPS 4, 229 mm at NPS 6.
A butt-weld fitting carries no pressure class of its own. ASME B16.9 rates it as straight seamless pipe of equivalent material and wall thickness under the applicable ASME B31 code, and the fitting is marked with the schedule number or nominal wall in millimetres, the material grade and the size in place of a pressure rating; conformance is shown by the prefix WP in the grade marking. EN 10253-4 instead distinguishes type A fittings, whose wall at the welding ends equals that of pipe of the same specified thickness, from type B fittings, thickened in the body so that they resist the same internal pressure as a straight pipe of the same dimensions.
When ordering, state the fitting type and angle; the nominal size, and both sizes for a reducing fitting; the pipe schedule or wall thickness the fitting must match, referred to ASME B36.19M for stainless or ASME B36.10M; the material grade - ASTM A403 under the ASME system, or 1.4301, 1.4307, 1.4404 or 1.4571 under EN 10253-4; whether seamless or welded construction is required; and whether an EN 10204 inspection document is needed.
| Dimensional Standard (ASME system) | ASME B16.9 - factory-made wrought buttwelding fittings, NPS 1/2 through NPS 48 (DN 15 through DN 1200): overall dimensions, tolerances, ratings, testing and marking |
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| Dimensional Standard (EN system) | EN 10253-4 - butt-welding fittings of wrought austenitic and austenitic-ferritic (duplex) stainless steel, for pressure and corrosion-resisting purposes at room, low and elevated temperature |
| Fitting Types | 45 and 90 degree elbows (long and short radius), returns, equal and reducing tees, concentric and eccentric reducers, caps, lap-joint stub ends |
| Long-Radius Elbow Geometry | Centre-to-end = 1,5 x nominal size: 38 mm at NPS 1, 76 mm at NPS 2, 114 mm at NPS 3, 152 mm at NPS 4, 229 mm at NPS 6, 305 mm at NPS 8 |
| Pressure Rating Basis | The fitting has no class of its own. It is rated as straight seamless pipe of equivalent material and wall thickness under the applicable ASME B31 code; schedule or wall thickness and material identity are marked on the fitting in lieu of a pressure rating |
| Type A and Type B (EN 10253-4) | Type A has the same wall thickness at the welding ends as pipe of the same specified wall thickness; type B has increased wall thickness in the body so that it resists the same internal pressure as a straight pipe of the same dimensions |
| Material Grades | ASTM A403 (and A234, A420, A815, B361, B363, B366) under ASME B16.9. Under EN 10253-4: 1.4301 (X5CrNi18-10), 1.4307 (X2CrNi18-9), 1.4404 (X2CrNiMo17-12-2), 1.4571 (X6CrNiMoTi17-12-2) |
| Marking | Manufacturer's name or trademark, material grade (ASTM or ASME designation), schedule number or nominal wall in mm, and NPS size. Conformance to the standard is certified by the prefix WP in the grade marking |
| Wall Thickness Reference | Ordered to a pipe schedule - ASME B36.19M for stainless steel pipe (5S, 10S, 40S, 80S) or ASME B36.10M |
