What is an ASTM A234 WPB buttweld fitting?
ASTM A234 WPB is the carbon steel grade for wrought buttweld piping fittings — elbows, tees, reducers, caps and stub ends — used in moderate and elevated-temperature service. Dimensions follow ASME B16.9 and the fitting is specified to match the schedule of the pipe it joins.
Key Takeaways
- A234 is the material specification; ASME B16.9 supplies the dimensions. Both belong on the purchase order.
- WPB is the carbon steel grade; WP11, WP22 and WP91 are the chrome-moly grades for elevated temperature.
- The stainless equivalent is ASTM A403, in grades WP304, WP304L, WP316 and WP316L.
- Fittings are rated by matching pipe schedule, not by a flange class — a SCH 40 elbow belongs on SCH 40 pipe.
- Long radius elbows have a centreline radius of 1.5 times the nominal diameter and are the default choice.
- Short radius elbows at 1.0D produce higher pressure drop and are used only where space forces it.
The fitting range
Buttweld fittings are welded directly into the run with a full-penetration butt weld, which makes the joint as strong as the pipe and allows it to be radiographed. That is why they dominate process piping above 2 inch.
| Fitting | Configurations | Notes |
|---|---|---|
| Elbow | 45°, 90°, 180° return; long radius (1.5D) and short radius (1D) | Long radius is the default; short radius only where space forces it |
| Equal tee | Branch equal to run | Full-bore branch connection |
| Reducing tee | Branch smaller than run | State run size then branch size when ordering |
| Concentric reducer | Common centreline | Used on vertical lines and where the centreline must be held |
| Eccentric reducer | Offset centreline, flat on one side | Used on horizontal lines to avoid trapping vapour or liquid |
| Cap | Domed end closure | Closes a line end with a butt weld |
| Stub end | Used with a lap joint flange | Allows the flange to rotate for bolt-hole alignment |
| Pipe bend | 3D, 5D and custom radius | Made to drawing for low-pressure-drop or pigged lines |
Grades within and alongside A234
WPB is the carbon steel workhorse and by volume the most-ordered buttweld grade in the world. Where temperature rises, the chrome-moly grades in the same specification take over: WP11 and WP22 for refinery heater and steam service, WP91 for high-temperature power plant headers.
Stainless buttweld fittings are not covered by A234 at all — they fall under ASTM A403, in WP304, WP304L, WP316 and WP316L. Duplex fittings fall under ASTM A815. Specifying “A234 WP316” is a common but incorrect combination that will be queried at order entry.
Seamless and welded construction are both permitted. Seamless is normally specified on high-pressure, cyclic and sour service; welded fittings made to the specification are fully tested and code-acceptable for most duties and become more economical in larger sizes.
Why the schedule must be stated
A buttweld fitting is rated by its wall thickness, and that wall is specified by matching the schedule of the pipe it joins. There is no equivalent of a flange pressure class. A fitting ordered by nominal size alone arrives with an unspecified wall, and if it does not match the run the fabricator is left with a mismatched weld preparation and either a transition weld or a rejection.
The correct line item states type, size, schedule, material specification and grade, and the dimensional standard: 90° long radius elbow, 6 inch, SCH 40, ASTM A234 WPB, ASME B16.9, seamless. On a reducing item, state both sizes in run-then-branch order.
Wall thickness by schedule is given on the pipe schedule chart, and the material specification is covered in more detail on the ASTM A234 WPB standard page.
Frequently Asked Questions
WP denotes a wrought piping fitting and B is the carbon steel grade designation within the specification. WP11, WP22 and WP91 are the chrome-moly grades covered by the same standard.
A long radius elbow has a centreline radius of 1.5 times the nominal diameter and is the default because it produces less pressure drop. A short radius elbow at 1.0 times the diameter is used only where installation space forces it.
No. ASTM A234 covers carbon and alloy steel. Stainless buttweld fittings are supplied to ASTM A403 in grades such as WP304 and WP316, and duplex fittings to ASTM A815.
Yes, where the project specification distinguishes. Seamless is normally required on high-pressure, cyclic and sour service. Welded fittings to the same specification are fully tested and acceptable for most other duties.
NPS 1/2 inch to 48 inch, in schedules from SCH 10 through SCH XXS, with heavier walls and custom bends produced to drawing.
An EN 10204 3.1 mill test certificate as standard with chemical and mechanical results, heat number traceability and a dimensional report. EN 10204 3.2 with third-party inspection is arranged where required.