ASTM A234 WPB is the de-facto standard for carbon steel butt-welding pipe fittings in moderate-temperature pressure piping. If you've ever specified an elbow, tee, reducer, or cap for a process plant, refinery, or power station carbon steel piping system, the fitting was almost certainly A234 WPB. It's the fitting equivalent of ASTM A106 Grade B pipe — the workhorse grade that handles the majority of industrial piping applications before the temperature or pressure envelope demands a step up to alloy steel.
ZC Steel Pipe manufactures and exports ASTM A234 WPB butt-welding fittings from our Hai'an City facility, supplying elbows, tees, reducers, and caps in NPS ½ through NPS 48 to projects across Africa, the Middle East, and South America. Our fittings are produced to ASME B16.9 dimensional standards with full material test reports and third-party inspection available.
CONTENTS
Standard Scope — What A234 Covers
A234 Grades — WPB, WPC, and Alloy Grades
Mechanical Properties
Chemical Composition
Fitting Types Covered
Dimensions — ASME B16.9
Pressure-Temperature Ratings
Heat Treatment Requirements
Marking & Traceability
A234 WPB vs A105 — Butt-Weld vs Forged
Applications
Frequently Asked Questions
1. Standard Scope — What A234 Covers
STANDARD DEFINITIONASTM A234 / A234M covers wrought carbon steel and alloy steel fittings of seamless and welded construction for use in pressure piping and in pressure vessel fabrication for service at moderate and elevated temperatures. The standard covers butt-welding fittings in all sizes manufacturable from pipe, tube, or plate.
The key word is "wrought" — A234 fittings are formed from pipe, tube, or plate (not cast or forged from bar). This distinguishes them from ASTM A105 (forged fittings for flanges and socket-weld/threaded connections) and ASTM A216 (cast steel valves and fittings). In practice, A234 means butt-welding fittings: elbows, tees, reducers, and caps that are welded into the piping system using the same weld preparation and procedure as the adjacent pipe.
ASME equivalent designations are SA-234 and SA-234M, used when the fittings must comply with the ASME Boiler and Pressure Vessel Code. This is the specification you'll see on MTRs for fittings in ASME-coded pressure systems.
2. A234 Grades — WPB, WPC, and Alloy Grades
ASTM A234 covers both carbon steel and alloy steel fittings. The grade designation uses a "WP" prefix (Wrought Piping) followed by a letter or number identifying the alloy class.
WPB — Carbon Steel
Base material: Carbon steel (≈ A106 Gr.B)
Tensile (min): 60,000 psi (415 MPa)
Yield (min): 35,000 psi (240 MPa)
Max temp: 800°F (427°C)
Usage: ~90% of all carbon steel fittings
WPC — Higher Strength Carbon
Base material: Higher carbon steel
Tensile (min): 70,000 psi (485 MPa)
Yield (min): 40,000 psi (275 MPa)
Max temp: 800°F (427°C)
Usage: Where WPB wall is inadequate
WP11 — 1¼Cr–½Mo Alloy
Base material: 1.25Cr–0.5Mo alloy steel
Tensile (min): 60,000 psi (415 MPa)
Yield (min): 30,000 psi (205 MPa)
Max temp: 1,100°F (593°C)
Usage: High-temp steam, refinery furnace piping
WP22 — 2¼Cr–1Mo Alloy
Base material: 2.25Cr–1Mo alloy steel
Tensile (min): 60,000 psi (415 MPa)
Yield (min): 30,000 psi (205 MPa)
Max temp: 1,200°F (649°C)
Usage: Very high-temp refinery and power plant piping
WP9 — 9Cr–1Mo Alloy
Base material: 9Cr–1Mo alloy steel
Tensile (min): 60,000 psi (415 MPa)
Yield (min): 30,000 psi (205 MPa)
Max temp: 1,200°F+ (649°C+)
Usage: HPHT steam, hydrogen service
WP91 — Modified 9Cr–1Mo
Base material: 9Cr–1Mo–V alloy (P91 chemistry)
Tensile (min): 85,000 psi (585 MPa)
Yield (min): 60,000 psi (415 MPa)
Max temp: 1,200°F+ (649°C+)
Usage: Ultra-supercritical steam, nuclear
3. Mechanical Properties
| Grade | Tensile Strength min (psi / MPa) | Yield Strength min (psi / MPa) | Elongation in 2 in. min (%) | Reduction of Area min (%) |
| WPB | 60,000 / 415 | 35,000 / 240 | 22 | 35 |
| WPC | 70,000 / 485 | 40,000 / 275 | 22 | 35 |
| WP11 Cl.1 | 60,000 / 415 | 30,000 / 205 | 20 | 35 |
| WP11 Cl.3 | 75,000 / 515 | 45,000 / 310 | 20 | 35 |
| WP22 Cl.1 | 60,000 / 415 | 30,000 / 205 | 20 | 35 |
| WP9 Cl.1 | 60,000 / 415 | 30,000 / 205 | 20 | 35 |
| WP91 | 85,000 / 585 | 60,000 / 415 | 20 | 40 |
4. Chemical Composition
| Grade | C max | Mn | P max | S max | Si | Cr | Mo |
| WPB | 0.30 | 0.29–1.06 | 0.050 | 0.058 | 0.10 min | 0.40 max | 0.15 max |
| WPC | 0.35 | 0.29–1.06 | 0.050 | 0.058 | 0.10 min | 0.40 max | 0.15 max |
| WP11 | 0.05–0.15 | 0.30–0.60 | 0.030 | 0.030 | 0.50–1.00 | 1.00–1.50 | 0.44–0.65 |
| WP22 | 0.05–0.15 | 0.30–0.60 | 0.030 | 0.030 | 0.50 max | 1.90–2.60 | 0.87–1.13 |
| WP9 | 0.15 max | 0.30–0.60 | 0.030 | 0.030 | 0.25–1.00 | 8.00–10.00 | 0.90–1.10 |
Procurement Note — Heat Analysis vs Product Analysis
ASTM A234 reports chemistry on a heat (ladle) analysis basis. Product analysis (from a finished fitting) is permitted to vary slightly from heat analysis within defined tolerances. When your project specification requires product analysis (common on high-alloy grades WP11, WP22, WP91), state this explicitly — the default under A234 is heat analysis certification only. This matters most on alloy grades where Cr and Mo ranges are narrow.
5. Fitting Types Covered
ASTM A234 covers all standard butt-welding fitting geometries. Each type is available in all A234 grades and in the full NPS range from ½ inch to 48 inch:
Elbows (90° & 45°)
Long Radius (LR): Radius = 1.5 × NPS
Short Radius (SR): Radius = 1.0 × NPS
Standard: ASME B16.9 (LR), B16.28 (SR)
Tees
Equal tee: All three outlets same NPS
Reducing tee: Branch outlet smaller than run
Standard: ASME B16.9
Reducers
Concentric: Axis aligned — vertical lines
Eccentric: Flat bottom — pump suction
Standard: ASME B16.9
Caps
Type: Ellipsoidal or hemispherical head
Use: End closure on pipe runs
Standard: ASME B16.9
Stub Ends
Type: Lap joint stub end
Use: Lap joint flanges, rotating connections
Standard: ASME B16.9 Type A & B
Notes: Used with backing flanges
Bends
Type: Long-radius induction bends
Radius: 3D, 5D, 7D typical
Standard: ASME B16.49
6. Dimensions — ASME B16.9
All A234 butt-welding fittings are dimensioned per ASME B16.9 (Factory-Made Wrought Buttwelding Fittings) for long-radius elbows, tees, reducers, and caps, or ASME B16.28 for short-radius elbows and returns. Key dimensional parameters engineers need to confirm when ordering:
| NPS (in) | LR 90° Elbow Center-to-End A (in) | LR 45° Elbow Center-to-End (in) | Equal Tee C-to-E (in) | Reducer Overall Length (in) |
| 1 | 1.50 | 0.62 | 1.50 | 2.00 |
| 1½ | 2.25 | 0.94 | 2.25 | 2.50 |
| 2 | 3.00 | 1.25 | 3.00 | 3.00 |
| 3 | 4.50 | 1.88 | 4.50 | 3.50 |
| 4 | 6.00 | 2.50 | 6.00 | 4.00 |
| 6 | 9.00 | 3.75 | 9.00 | 5.00 |
| 8 | 12.00 | 5.00 | 12.00 | 6.00 |
| 10 | 15.00 | 6.25 | 15.00 | 7.00 |
| 12 | 18.00 | 7.50 | 18.00 | 8.00 |
| 16 | 24.00 | 10.00 | 24.00 | 10.00 |
| 20 | 30.00 | 12.50 | 30.00 | 12.00 |
| 24 | 36.00 | 15.00 | 36.00 | 14.00 |
Field Note — LR vs SR Elbows
Long-radius (LR, 1.5D) elbows are the default for process piping under ASME B31.3 because they produce lower pressure drop and lower erosion rates at the bend. Short-radius (SR, 1D) elbows under B16.28 are used only where space is critically constrained — they have higher pressure drop, more turbulence, and faster erosion in slurry or wet gas service. If your P&ID shows a tight 90° turn in a limited space, always verify with the piping designer whether SR is intentional or a drawing shorthand for LR.
7. Pressure-Temperature Ratings
ASTM A234 fittings do not have their own independent pressure-temperature ratings — they derive their ratings from the applicable piping code (ASME B31.1 or B31.3) using the allowable stress for the grade at the design temperature, combined with the fitting's wall thickness per ASME B16.9.
For WPB at key temperatures under ASME B31.3:
| Temperature °F (°C) | Allowable Stress S (psi) | Notes |
| −20 to 100°F (−29–38°C) | 15,000 | Full ambient rating |
| 400°F (204°C) | 14,400 | Minor reduction |
| 600°F (316°C) | 13,600 | Suitable for most process service |
| 800°F (427°C) | 11,800 | Upper practical limit for WPB |
| Above 800°F | Specify WP11 or WP22 | Carbon steel approaching creep regime |
Critical Engineering Point — Fitting Wall Thickness
ASME B16.9 specifies a minimum fitting wall thickness that is the same as the matching pipe schedule (e.g., an SCH 40 fitting has a minimum wall equal to SCH 40 pipe). However, the pressure design calculation for the fitting must also satisfy the burst pressure formula at the design temperature. For tees, the branch reinforcement geometry affects the permissible pressure rating. Never assume a fitting rated for the same schedule as the pipe is automatically adequate — confirm with your piping engineer on large-bore or high-pressure systems.
8. Heat Treatment Requirements
Heat treatment requirements under A234 vary by grade and wall thickness:
| Grade | Required Heat Treatment | Condition |
| WPB | Not mandatory for t ≤ 19 mm | Normalized or normalized+tempered for heavy wall |
| WPC | Not mandatory for t ≤ 19 mm | Normalized or normalized+tempered for heavy wall |
| WP11 | Mandatory | Annealed, normalized+tempered, or quenched+tempered |
| WP22 | Mandatory | Annealed or normalized+tempered |
| WP9 | Mandatory | Annealed or normalized+tempered |
| WP91 | Mandatory — specific range | Normalize 1040–1080°C + temper 730–800°C |
9. Marking & Traceability
Every A234 fitting must be marked with the following per the standard:
Manufacturer's mark — Identifies the mill or fabricator
Material grade — e.g., WPB or SA-234 WPB for ASME code applications
Schedule or wall thickness — e.g., SCH 40 or actual WT in inches
Heat number — Links the fitting to its MTR
Size — NPS designation
ASTM standard designation — A234 or SA-234
Engineering Insight — Verifying MTR Continuity
On pressure-critical piping, the heat number stamped or painted on the fitting must match the heat number on the MTR in your document package. In project audits, missing or illegible heat markings on fittings are among the most common NCRs raised by third-party inspectors. Specify that heat markings must be legible at time of delivery — not just at time of manufacture — and inspect before installation.
10. A234 WPB vs A105 — Butt-Weld vs Forged
Both A234 WPB and A105 are carbon steel fitting materials, but they serve different connection types:
| Parameter | A234 WPB | A105 |
| Manufacturing method | Wrought (formed from pipe/plate) | Forged from bar or billet |
| Connection type | Butt-weld | Socket weld, threaded, flanged |
| Size range | NPS ½ and above | NPS ½ to NPS 4 (typical) |
| Tensile strength (min) | 60,000 psi | 70,000 psi |
| Yield strength (min) | 35,000 psi | 36,000 psi |
| Applications | Mainline piping, large-bore systems | Small-bore branch connections, flanges |
| ASME equivalent | SA-234 WPB | SA-105 |
| ZC product | Elbows, Tees, Reducers → | Flanges → |
11. Applications
Refinery & Petrochemical Process Piping
A234 WPB elbows, tees, and reducers are used throughout refinery and petrochemical plant carbon steel piping systems under ASME B31.3 — from crude unit feed piping to storage tank headers. The fitting material matches the ASTM A106 Grade B pipe, ensuring a homogeneous material system with consistent welding characteristics and no concerns about differential thermal expansion.
Power Generation
SA-234 WPB fittings (the ASME designation) are used in steam and condensate piping under ASME B31.1. For high-temperature service in the same system, WP11 or WP22 fittings are specified where A106 pipe transitions to A335 alloy pipe — a common configuration in power plant steam main circuits.
Oil & Gas Facilities
A234 WPB butt-welding fittings are specified for oil and gas processing facility piping — separators, compressor stations, and metering skids — where process temperatures are moderate and the line pipe is ASTM A53 or A106 carbon steel. The fitting material matches the pipe, enabling a single welding procedure for the entire piping class.
Pipeline & Transmission
Field bends and fabricated tee connections on API 5L line pipe projects often use A234 WPB fittings manufactured to match the API 5L pipe chemistry and strength. For high-pressure gas transmission where SMYS matching is critical, ensure the WPB fitting yield strength is compatible with the pipe grade yield strength in your stress analysis.
12. Frequently Asked Questions
What is ASTM A234 WPB?
ASTM A234 WPB is the most widely used grade of carbon steel butt-welding pipe fitting for moderate-temperature pressure piping. "WP" stands for Wrought Piping and "B" designates the carbon steel grade. A234 WPB fittings — elbows, tees, reducers, caps — are made from base material equivalent to ASTM A106 Grade B pipe and are used in ASME B31.1 and B31.3 piping systems throughout the process, power, and oil and gas industries.
What is the difference between ASTM A234 WPB and WPC?
WPB and WPC are both carbon steel grades under A234, but WPC has higher minimum tensile strength (70,000 psi vs 60,000 psi) and yield strength (40,000 psi vs 35,000 psi). WPB covers the vast majority of carbon steel fitting applications. WPC is specified when higher strength is needed to maintain pressure capacity at a thinner wall — less common in practice.
What fittings are covered by ASTM A234?
ASTM A234 covers wrought carbon and alloy steel butt-welding fittings for pressure piping, including elbows (45° and 90°, long and short radius), equal and reducing tees, concentric and eccentric reducers, caps, and stub ends. All fittings are dimensioned to ASME B16.9 (standard) or B16.28 (short-radius).
What is the maximum temperature for A234 WPB fittings?
ASTM A234 WPB fittings are rated for service up to 800°F (427°C) per ASME B31.3 allowable stress tables. Above this temperature, creep becomes significant and alloy steel fittings — such as A234 WP11 (1¼Cr–½Mo) for up to 1,100°F or WP22 (2¼Cr–1Mo) for up to 1,200°F — should be specified instead.
Are ASTM A234 WPB fittings suitable for sour service?
A234 WPB fittings can be used in sour service (H₂S environments) provided they meet NACE MR0175 / ISO 15156 hardness requirements (maximum HRC 22 / 237 HBW). Hardness testing is not a default requirement under A234, so sour service purchasers must specify hardness testing as a supplementary requirement on the purchase order and confirm compliance on the MTR before installation.
Request A234 WPB Pipe Fittings — ZC Steel Pipe
ZC Steel Pipe manufactures and exports ASTM A234 WPB butt-welding fittings — elbows, tees, reducers, caps, and bends — from our Hai'an City facility. Full range NPS ½ to NPS 48, all schedules, ASME B16.9 dimensions. Full MTRs, heat treatment certification, and third-party inspection available. Active supply to refinery, power, and pipeline projects in Africa, Middle East, and South America.
Contact us: mandy.w@zcsteelpipe.com | WhatsApp: +86-139-1579-1813
→ Request a Quote
