What Is ASTM A234? BW Fittings Material

Quick Answer

ASTM A234 is the material specification for wrought carbon steel and alloy steel buttweld pipe fittings used in moderate and high-temperature service. The most common grade, WPB, matches ASTM A106 Grade B pipe and is the default carbon steel fitting material in oil and gas process piping. Alloy grades (WP5, WP11, WP22, WP91) match the corresponding ASTM A335 alloy pipe grades.

The full standard title is “Standard Specification for Piping Fittings of Wrought Carbon Steel and Alloy Steel for Moderate and High Temperature Service.” It covers elbows, tees, reducers, caps, and other ASME B16.9 buttweld fittings.

Key Grades

Grade	Type	Matching Pipe Spec	Min Yield (MPa)	Min Tensile (MPa)	Max Temp
WPB	Carbon steel	ASTM A106 Gr. B	240	415	~425°C
WPC	Carbon steel	ASTM A106 Gr. C	275	485	~425°C
WP1	C-Mo alloy	ASTM A335 P1	205	380	~480°C
WP5	5Cr-0.5Mo	ASTM A335 P5	205	415	~590°C
WP11	1.25Cr-0.5Mo	ASTM A335 P11	205	415	~540°C
WP22	2.25Cr-1Mo	ASTM A335 P22	205	415	~590°C
WP91	9Cr-1Mo-V	ASTM A335 P91	415	585	~620°C

Manufacturing

ASTM A234 fittings are manufactured by two methods:

• Seamless: Formed from seamless pipe or forged/rolled billets. No weld seam. Required by many piping specs for high-pressure and sour service.
• Welded: Formed from welded pipe or plate. The original weld seam is typically subjected to radiographic examination. Welded fittings must meet the same mechanical requirements as seamless.

The manufacturing process involves hot forming (pressing or drawing) followed by heat treatment per the applicable grade. WPB fittings are typically normalized or quenched-and-tempered. Alloy grades require specific post-forming heat treatment to achieve the required microstructure.

Chemical Composition (WPB)

Element	Max %
Carbon	0.30
Manganese	0.29-1.06
Phosphorus	0.035
Sulfur	0.035
Silicon	0.10 min
Chromium	0.40
Molybdenum	0.15
Nickel	0.40

The chemistry of WPB is virtually identical to A106 Gr. B pipe, ensuring weldability without pre-heat in most conditions (carbon equivalent typically below 0.42).

Testing Requirements

ASTM A234 mandates:

• Tensile test (one per heat or lot)
• Chemical analysis (ladle and product)
• Hydrostatic test (if specified in the order)
• NDE per the applicable fitting standard (ASME B16.9)
• Mill test certificate (EN 10204 Type 3.1 standard in oil and gas)

For a full comparison between WPB and WPC, see the A234 WPB vs WPC guide. For the broader material landscape including stainless steel and nickel alloys, see the BW fittings materials overview.

Read the full guide to pipe fittings