ASME B16.9 is the standard for factory-made wrought buttwelding fittings: elbows, return bends, tees, crosses, reducers, caps and lap joint stub ends from NPS ½" to NPS 48". It fixes their overall dimensions, tolerances, pressure rating basis, marking and design-proof testing, so that a B16.9 fitting welds into pipe of the same size and schedule and carries the same pressure as the pipe.
Raaj Fittings manufactures ASME B16.9 fittings at our two plants in India in stainless steel, duplex and super duplex, nickel alloys, carbon, low-temperature and alloy steel, seamless and welded, in every schedule from 5S to XXS, and exports them to EPC contractors, fabricators and stockists in the Middle East, Europe and the Americas.
B16.9 does not give pressure classes. Instead, a fitting may be used at the same pressure–temperature rating as straight seamless pipe of the equivalent material and the same nominal wall thickness. Manufacturers prove each design by calculation or by a proof (burst) test. In practice, you order the fitting in the same schedule and material grade as the pipe, and the piping code (ASME B31.1, B31.3 and others) treats the fitting as being as strong as the pipe.
The fitting wall must match the pipe wall at the welding end. Common schedules and their nominal wall thicknesses (from the pipe standards ASME B36.10 and B36.19) are:
| NPS (OD) | SCH 10S | SCH 40 / 40S | SCH 80 / 80S | SCH 160 | XXS |
|---|---|---|---|---|---|
| 1" (33.4 mm) | 2.77 | 3.38 | 4.55 | 6.35 | 9.09 |
| 2" (60.3 mm) | 2.77 | 3.91 | 5.54 | 8.74 | 11.07 |
| 4" (114.3 mm) | 3.05 | 6.02 | 8.56 | 13.49 | 17.12 |
| 6" (168.3 mm) | 3.40 | 7.11 | 10.97 | 18.26 | 21.95 |
| 8" (219.1 mm) | 3.76 | 8.18 | 12.70 | 23.01 | 22.23 |
For each size, B16.9 sets the centre-to-end dimension of elbows and tees, the end-to-end length of reducers, the length of caps and the dimensions of stub ends. For example, a 90° long radius elbow has a centre-to-end of 1.5 times the nominal size (152 mm for a 4" elbow), and a short radius elbow 1.0 times. Tolerances cover outside diameter at the bevel, inside diameter at the end, wall thickness (not less than 87.5% of nominal), centre-to-end and overall dimensions, and angularity of the ends. Ends are bevelled for welding, normally to ASME B16.25.
B16.9 fittings are marked with the manufacturer's name or trademark, the material and grade symbol from the ASTM specification (for example WPB or WP316L-S), the schedule or wall thickness, and the size. Our fittings also carry the heat number, so every piece traces back to its EN 10204 3.1 certificate.
| Standard | Scope | Relation to B16.9 |
|---|---|---|
| MSS SP-43 | Light-wall stainless and nickel alloy fittings, mainly SCH 5S and 10S | Lighter, for low-pressure corrosion-resistant service; short-pattern stub ends |
| MSS SP-75 | High-yield steel fittings for pipelines (A860 WPHY) | Same fitting types, higher-strength materials, larger sizes |
| ASME B16.25 | Weld end preparation (bevels) | Used for the ends of B16.9 fittings |
| EN 10253 | European buttweld fittings | Metric dimensions; not always identical to B16.9 |
| DIN 2605 / 2615 / 2616 / 2617 | German elbows, tees, reducers, caps | Older national standards, largely replaced by EN 10253 |
ASME B16.9 covers factory-made wrought buttwelding fittings from NPS ½" to NPS 48". Larger sizes and high-yield pipeline fittings are usually made to MSS SP-75 or project specifications.
A B16.9 fitting is rated the same as straight seamless pipe of equivalent material and the same nominal wall thickness. That is why fittings are ordered in the same schedule and grade as the pipe.
ASME B16.28, which covered short radius elbows and returns, was withdrawn and its content incorporated into ASME B16.9. Short radius fittings are now ordered to B16.9.
MSS SP-43 covers light-wall stainless and nickel alloy fittings, mainly SCH 5S and 10S, for low-pressure corrosion-resistant service, with some shorter dimensions. ASME B16.9 fittings are designed for pressure piping in all schedules.
A 90° long radius elbow to ASME B16.9 has a centre-to-end dimension of 1.5 times the nominal pipe size for NPS ¾" and larger, for example 152 mm for a 4" elbow. Short radius elbows are 1.0 times the nominal size.