The Fundamental Difference: Manufacturing Process
While both materials are chemically similar carbon steels, their manufacturing DNA defines their mission in a piping system:
WCB (ASTM A216): A Cast Steel. Molten steel is poured into a mold to form the shape.
A105 (ASTM A105): A Forged Steel. Solid steel is hammered or pressed into shape under extreme heat and pressure.
1. Structural Integrity: Why Forging Wins on Strength
A105 (Forged): The forging process mechanically deforms the metal, creating a continuous grain flow. This eliminates internal porosity and voids, making A105 significantly more resistant to fatigue, impact, and high-pressure surges.
WCB (Cast): During the cooling of molten metal, tiny gas pockets (Porosity) or “sand holes” can form. While high-quality foundries use non-destructive testing (NDT) to manage this, a casting’s internal density is inherently lower than a forging’s.
2. Size and Geometry: Why Casting Wins on Economy
WCB (Large & Complex): The biggest advantage of casting is geometric freedom. For valves larger than 2 inches (DN50), especially complex Gate or Globe bodies, casting is the only cost-effective method.
A105 (Small & Simple): Forging costs increase exponentially with size. Therefore, A105 is primarily used for small-diameter valves (DN50 and below), flanges, and fittings.
3. Technical Comparison Table
| Feature | ASTM A216 WCB (Cast) | ASTM A105 (Forged) |
| Manufacturing | Poured into molds (Casting) | Mechanically pressed (Forging) |
| Typical Size | DN50 (2″) and above | DN50 (2″) and below |
| Internal Defects | Potential for sand holes/porosity | Virtually none (Dense structure) |
| Strength | Balanced | Superior (High impact resistance) |
| Welding | Excellent | Excellent |
| Cost | Economical for large sizes | Higher for large sizes |
4. Critical Selection Scenarios: Which to Choose?
Scenario A: High-Pressure Power Systems
In Class 1500 or Class 2500 ultra-high-pressure steam lines, engineers almost always mandate A105 Forged Steel. At these pressures, even a microscopic casting defect in a WCB body could escalate into a catastrophic crack or blowout.
Scenario B: Large Midstream Oil Pipelines
In a 24-inch crude oil pipeline, manufacturing a forged body is technically difficult and prohibitively expensive. In this case, a high-quality WCB Casting subjected to 100% Radiographic Testing (RT) is the industry standard for balancing safety and budget.
5. Quality Checklist for Global Buyers
The “Cast-as-Forged” Scam: Some low-end suppliers sell castings and claim they are forgings.
How to spot it: Check the surface. Forgings have a smoother, refined finish with no “sand-like” texture. Verify the hardness; A105 is usually more uniform and slightly harder than WCB.
NDT Requirements: If you choose WCB for critical service (like medium-pressure steam), always demand RT (X-ray) or UT (Ultrasonic) reports to ensure the internal casting is sound.
Heat Treatment: Ensure your WCB has been Normalized. Without proper heat treatment, cast steel retains internal stresses that lead to body failure under thermal cycling.
Conclusion: The Selection Logic
Large Bore (DN > 50mm) + Low/Medium Pressure = Choose WCB (Best ROI).
Small Bore (DN ≤ 50mm) + High Pressure/Critical Service = Choose A105 (Safety First).
