How to Order Buttweld Fittings
Buttweld (BW) fittings are manufactured to match the OD and wall thickness of the connecting pipe, so every fitting in your purchase order must reference the correct pipe size, schedule, and material specification. An elbow ordered without the schedule or with the wrong material grade cannot be welded to the piping system.
This checklist covers the parameters required to specify BW elbows, tees, reducers, caps, and return bends for RFQs and purchase orders.
Core Attributes
These parameters must appear in every buttweld fitting line item.
| Parameter | What to Specify | Example |
|---|---|---|
| Fitting type | 90° long radius (LR) elbow, 90° short radius (SR) elbow, 45° elbow, equal tee, reducing tee, concentric reducer, eccentric reducer, cap, 180° return bend | 90° LR elbow |
| Dimensional standard | ASME B16.9 (wrought steel BW fittings, NPS 1/2–48), ASME B16.28 (short radius elbows and returns), MSS SP-75 (large diameter fittings for pipeline use) | ASME B16.9 |
| Nominal size | NPS for elbows and caps. Run × branch for reducing tees (e.g., NPS 6 × 4). Large end × small end for reducers (e.g., NPS 8 × 6). | NPS 6 × Sch 40 |
| Wall thickness | Must match the connecting pipe schedule: Sch 5S, 10S, STD, 40, XS, 80, 120, 160, XXS | Sch 40 |
| Material specification | Carbon steel: ASTM A234 WPB. Alloy steel: ASTM A234 WP11, WP22, WP5, WP9, WP91. Stainless steel: ASTM A403 WP304, WP304L, WP316, WP316L. Duplex: ASTM A815 UNS S31803 (2205), UNS S32750 (2507). | ASTM A234 WPB |
| End finish | Always Beveled End (BE) per ASME B16.25. Standard bevel: 37.5° ± 2.5° with 1.6 mm (1/16”) root face. | BE per ASME B16.25 |
Optional / Special Attributes
Include these when the project specification or service conditions require it.
| Parameter | What to Specify | When Required |
|---|---|---|
| Elbow tangent length | Long tangent or short tangent (affects straight portion beyond the arc). Standard tangent per ASME B16.9 Table dimensions. | When clearance or welding access is a concern |
| Testing requirements | PMI (positive material identification), Charpy impact test at a specific temperature, UT (ultrasonic testing), RT (radiographic testing) per ASME B16.9 supplementary requirements S1–S7 | Alloy/CRA fittings, cryogenic service, critical piping classes |
| NACE MR0175 / ISO 15156 compliance | Sour service compliance: max hardness 22 HRC for CS (ASTM A234 WPB), restricted chemistry for alloy and CRA grades | H₂S-containing environments |
| Heat number traceability | Each fitting traceable to the original heat number of the raw material (plate, pipe, or forging) | Critical piping, nuclear, high-energy lines |
| Certificates | EN 10204 Type 3.1 (manufacturer’s inspection certificate) or Type 3.2 (third-party witnessed certificate) | Always specify; 3.2 for critical and sour service |
| Marking | Per ASME B16.9 Sec. 6 or MSS SP-25 (standard marking system). Specify if low-stress stamps or paint marking are required. | All orders (standard marking is default, but state preferences) |
Example Line Item
Correct:
20 pcs - 90° LR elbow, ASME B16.9, NPS 6 × Sch 40, ASTM A234 WPB, BE, MTR EN 10204 3.1
This line item defines: quantity and UOM, fitting type and geometry (90° long radius), dimensional standard, size, wall thickness (matching pipe schedule), material specification, end finish, and certification.
Incorrect:
20 - CS elbow 6 inch
This is missing the fitting geometry (LR vs SR), dimensional standard, schedule, material grade (WPB vs WP11 vs WP22), end finish specification, and certification. The supplier will either reject the inquiry or make assumptions that may not match your piping class.
Common Pitfalls
- Forgetting to specify LR vs SR. A 90° long radius elbow has a center-to-end dimension of 1.5 × NPS; a short radius elbow is 1.0 × NPS. They are not interchangeable; the piping isometric is designed for one or the other. LR elbows are standard in process piping (ASME B31.3); SR elbows are used only where space is restricted. If you do not specify, the supplier will typically quote LR, but the risk of mismatch remains.
- Mismatching the schedule between pipe and fitting. A Sch 80 fitting welded to a Sch 40 pipe creates a wall thickness mismatch at the weld joint that requires a taper per ASME B31.3 Para. 328.4.2. Always verify that the fitting schedule matches the connecting pipe schedule in your piping class.
- Not stating reducing dimensions for tees and reducers. A “6-inch reducing tee” is incomplete. You must specify run and branch sizes (e.g., NPS 6 × 4) for reducing tees and both ends (e.g., NPS 8 × 6) for reducers. For eccentric reducers, confirm whether the flat side is on top (FOT) or bottom (FOB) per the piping arrangement.
- Omitting NACE requirements for alloy fittings. ASTM A234 WP11 and WP22 fittings for sour service must meet hardness and chemistry limits per NACE MR0175/ISO 15156. Standard mill production may not meet these limits unless explicitly requested in the purchase order.
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