A234 WPB vs WPC

ASTM A234 WPB and WPC are both carbon steel grades for buttweld pipe fittings used in moderate and high-temperature service. WPB is the industry standard. WPC offers higher strength but is less commonly stocked. The choice between them depends on the matching pipe grade and the required mechanical properties.

When to Use Each Grade

WPB fittings pair with ASTM A106 Grade B pipe. WPC fittings pair with ASTM A106 Grade C pipe. The pipe grade drives the fitting grade. Mixing grades (e.g., WPC fittings on Grade B pipe) is generally unnecessary and complicates procurement.

Mechanical Properties

Property	A234 WPB	A234 WPC
Min yield strength	240 MPa (35 ksi)	275 MPa (40 ksi)
Min tensile strength	415 MPa (60 ksi)	485 MPa (70 ksi)
Min elongation (2”)	22%	19%
Hardness (max)	197 HBW	197 HBW

WPC is approximately 15% stronger in yield and 17% stronger in tensile than WPB. However, this extra strength comes with slightly lower ductility (19% vs 22% minimum elongation).

Chemical Composition

Element	WPB (max %)	WPC (max %)
Carbon	0.30	0.35
Manganese	0.29-1.06	0.29-1.06
Phosphorus	0.035	0.035
Sulfur	0.035	0.035
Silicon	0.10 min	0.10 min
Chromium	0.40	0.40
Molybdenum	0.15	0.15
Nickel	0.40	0.40

The primary difference is carbon content: WPC allows up to 0.35% vs 0.30% for WPB. Higher carbon increases strength but can reduce weldability and increase susceptibility to hydrogen-induced cracking in sour environments.

Weldability

WPB has a lower carbon equivalent (CE), making it easier to weld without preheat in most ambient conditions. WPC may require preheat above 100°C (212°F) for wall thicknesses above 25 mm, depending on the welding procedure and ambient temperature. For sour service per NACE MR0175, WPB is preferred because its lower carbon content reduces hardness in the heat-affected zone.

Availability and Cost

WPB dominates global inventory. Most pipe fitting stockists carry WPB in standard sizes (NPS 1/2 to NPS 24) across common schedules. WPC is typically manufactured to order, leading to longer lead times and higher unit costs.

Factor	WPB	WPC
Stock availability	Widely stocked worldwide	Mostly made to order
Lead time	Short (ex-stock or 4-8 weeks)	Longer (8-16 weeks)
Relative cost	Base	5-15% premium
Project usage	~85%+ of carbon steel fittings	<15% of carbon steel fittings

Selection Summary

Use WPB unless the piping specification explicitly calls for A106 Grade C pipe (and therefore WPC fittings). WPB meets the vast majority of carbon steel service requirements in oil and gas, provides better weldability, and is available off the shelf.

For alloy steel grades (WP5, WP11, WP22, WP91) within the same ASTM A234 standard, see the BW fittings materials guide.

Read the full guide to pipe fittings