ASTM Material Specifications: WCB vs WCC

Both WCB and WCC are grades specified under ASTM standards for carbon steel castings used in valve manufacturing. Understanding their fundamental definitions and standards is the first step in making an informed selection.

ASTM A216 Grade WCB Definition

WCB stands for “Weldable Cast Steel with B grading” and is defined under ASTM A216 standard. This specification covers carbon steel castings suitable for fusion welding, intended for high-temperature service. WCB is the most commonly used grade in this standard due to its balanced properties and cost-effectiveness.

ASTM A216 Grade WCC Definition

WCC represents “Weldable Cast Steel with C grading” and is also covered under ASTM A216. It offers higher manganese content and improved mechanical properties compared to WCB, making it suitable for more demanding applications where higher yield strength is required.

Chemical Composition Comparison

The key chemical difference lies in the manganese-to-carbon ratio. For WCB, for every 0.01% reduction of carbon below the maximum (0.30%), the manganese can be increased by 0.04% without exceeding 1.28%. For WCC, the same carbon reduction allows manganese to increase without exceeding 1.40%, resulting in higher overall strength.

Mechanical Properties Comparison

The mechanical properties of valve materials directly impact their performance in various operating conditions. WCB and WCC have distinct mechanical characteristics that make them suitable for different applications.

Tensile and Yield Strength

WCC’s higher yield strength (40 ksi vs 36 ksi) is its primary mechanical advantage over WCB. This higher yield strength means WCC valves can withstand greater pressure before permanent deformation occurs, making them more suitable for high-pressure applications.

Hardness and Impact Resistance

Both materials typically have Brinell hardness values between 140-170 HB, with WCC often testing slightly higher due to its increased manganese content. The impact resistance of both materials is adequate for standard industrial applications, though neither is specifically designed for extreme impact conditions.

Brinell hardness testing on valve material sample

Temperature and Pressure Service Ranges

Operating temperature and pressure capabilities are critical factors in valve selection. WCB and WCC materials have different performance characteristics under various conditions.

Temperature Range Comparison

WCC offers better low-temperature performance compared to WCB, making it more suitable for colder environments. Both materials have similar upper temperature limits, with performance degradation occurring beyond 425°C (800°F).

Pressure Class Capabilities

Due to its higher yield strength, WCC valves typically offer better performance in higher pressure class applications. However, both materials are commonly used across standard pressure classes:

• Class 150 (PN 20): Both WCB and WCC suitable
• Class 300 (PN 50): Both WCB and WCC suitable
• Class 600 (PN 100): Both suitable, WCC preferred for upper range
• Class 900 (PN 150): WCC generally preferred over WCB
• Class 1500 (PN 250) and above: WCC strongly preferred over WCB

For applications requiring both high pressure and low temperature, WCC provides a clear advantage over WCB due to its superior yield strength and better low-temperature performance.

Corrosion Resistance Properties

Laboratory corrosion testing of valve materials

Both WCB and WCC are carbon steel materials with similar corrosion resistance characteristics. Neither offers exceptional corrosion resistance without additional protection.

Corrosion Resistance Limitations

Protective Measures

For applications where corrosion is a concern, both WCB and WCC valves typically require additional protection:

• Surface treatments (painting, powder coating)
• Electroplating (nickel, chrome)
• Chemical treatments (phosphating, bluing)
• Cathodic protection systems for buried or submerged applications

For highly corrosive environments, alternative materials such as stainless steel (CF8, CF8M) or specialized alloys may be more appropriate than either WCB or WCC.

Industrial Applications and Selection Guidelines

Industrial applications for WCB and WCC valves across various sectors

WCB and WCC valves are used across numerous industries, but their specific properties make them more suitable for certain applications.

Typical Applications by Industry

Valve Types Commonly Manufactured with WCB and WCC

Common valve types manufactured with WCB and WCC materials

Cost Comparison and Maintenance Considerations

Cost and maintenance requirements are important factors in the valve selection process. WCB and WCC have different cost implications and maintenance needs.

Cost Comparison

WCB valves are generally more cost-effective and widely available, making them the preferred choice when their performance characteristics meet application requirements. The premium cost of WCC is typically justified only when its superior yield strength or low-temperature performance is necessary.

Maintenance Considerations

Both WCB and WCC valves have similar maintenance requirements:

• Regular inspection for corrosion, especially in outdoor installations
• Periodic lubrication of moving parts
• Maintenance of protective coatings where applied
• Checking for leakage at connections and seals
• Replacement of soft parts (seals, gaskets) according to manufacturer schedules

From a maintenance perspective, there is little difference between WCB and WCC valves. Both materials have similar durability and service life when properly maintained and operated within their design parameters.

Decision-Making Guidelines for Engineers

When selecting between WCB and WCC valve materials, engineers should consider several key factors to ensure optimal performance and cost-effectiveness.

Key Selection Criteria

Recommended Selection Process

1. Evaluate temperature requirements: If operating below -29°C (-20°F), WCC is the better choice. For standard temperatures, either material is suitable.
2. Assess pressure class needs: For higher pressure applications (Class 900 and above), WCC’s superior yield strength provides an advantage.
3. Consider application criticality: For critical service where failure consequences are severe, WCC’s superior mechanical properties may justify the additional cost.
4. Analyze corrosion environment: If corrosion is a significant concern, consider whether either material is appropriate or if alternative materials like stainless steel should be considered.
5. Review budget constraints: If cost is a primary concern and the application falls within WCB’s performance envelope, WCB offers better value.

Conclusion: Making the Right Choice Between WCB and WCC

Both WCB and WCC valve materials offer reliable performance for industrial applications, but their specific properties make them better suited for different scenarios. WCB provides cost-effective performance for standard operating conditions, while WCC offers enhanced yield strength and better low-temperature performance at a premium price.

When selecting between these materials, engineers should carefully evaluate the specific requirements of their application, including temperature range, pressure class, and criticality of service. In many standard applications, WCB provides sufficient performance at a lower cost, making it the more common choice. However, for applications with higher pressure requirements or lower operating temperatures, WCC’s superior mechanical properties justify its higher cost.

By understanding the key differences between WCB valve vs WCC valve materials outlined in this guide, engineers and procurement specialists can make informed decisions that balance performance requirements with cost considerations, ensuring optimal valve selection for their specific industrial applications.