Buyers new to pipe fittings often ask why their elbow is quoted as A234 WPB but their flange as A105 — aren’t they both carbon steel? They are, but the two specifications cover different product forms and manufacturing processes. Ordering the wrong one is a costly mistake.
The Short Answer
| ASTM A234 WPB | ASTM A105 | |
|---|---|---|
| Product form | Wrought butt-weld fittings (elbows, tees, reducers, caps) | Forged components (flanges, socket-weld & threaded fittings) |
| Process | Formed from seamless pipe or plate | Forged from steel billet |
| Typical products | 90°/45° elbows, tees, reducers, caps | WN/SO/blind flanges, couplings, unions |
| Matching pipe | A106 Gr.B / A53 Gr.B | A106 Gr.B / A53 Gr.B |
| Temperature range | Moderate & high temperature service | Ambient & high temperature service |
Both grades are designed to be welded to the same carbon steel pipe systems, which is why they appear together on almost every piping bill of materials.
Why the Distinction Matters
A234 WPB (“WPB” = Wrought Pipe fitting, grade B) covers fittings made by bending and forming pipe or plate — hot pushing an elbow over a mandrel, for example. The standard controls chemistry and mechanical properties after forming and heat treatment.
A105 covers forgings. Flanges need the strength and grain structure of forged steel to handle bolt loads and pressure at the joint, so they are forged from billet, machined, then drilled.
How to Specify Correctly
- For butt-weld elbows, tees, reducers and caps: ASTM A234 WPB, ASME B16.9
- For flanges: ASTM A105, ASME B16.5 (state pressure class and face type, e.g. Class 150 RF)
- For low temperature service (below −29°C): use A420 WPL6 fittings and A350 LF2 flanges instead — do not substitute WPB/A105
One More Trap: WPB vs WPL6
The letters matter. WPB is standard carbon steel; WPL6 is a low temperature grade with impact testing requirements. They look similar on paper but are different materials with different prices. Always confirm the grade in writing before production starts — a reputable supplier will insist on it.
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