Why Choose Steel for a Split Case Casing?
While standard split case pumps often utilize Cast Iron (e.g., ASTM A48 Class 30) because it is cost-effective and dampens vibration well, steel is specified for more rugged applications due to the following advantages:
Higher Pressure Ratings: Carbon steel can handle much higher working and hydrostatic pressures without cracking.
Thermal Shock Resistance: Steel maintains its structural integrity under rapid or extreme temperature changes, whereas cast iron can be brittle and crack.
Weldability: Unlike cast iron, steel casings can be easily welded for repairs, nozzle modifications, or localized rebuilding.
Toughness: It offers significantly higher tensile strength and impact resistance, making it ideal for critical industrial environments like oil and gas, petrochemical, and high-pressure water transmission.
Common Steel Material Grades for HSC Pumps
Depending on the fluid and environment, manufacturers generally cast or fabricate split case casings using two main categories of steel:
1. Carbon Steel (Cast Steel)
Used for high-pressure, non-corrosive, or high-temperature applications (e.g., boiler feed water, oil transfer).
ASTM A216 Grade WCB: The industry standard for cast carbon steel. It balances excellent strength, weldability, and pressure containment.
2. Stainless Steel
Used when the application requires high-pressure capabilities plus excellent corrosion or erosion resistance (e.g., seawater desalination, chemical processing, brackish water).
Austenitic Stainless Steel (ASTM A351 CF8M / SS316): Offers superior resistance to pitting and crevice corrosion, especially in chlorated or mildly acidic fluids.
Duplex Stainless Steel (e.g., CD4MCu / ASTM A890): Provides twice the mechanical strength of standard stainless steel and exceptional resistance to stress corrosion cracking and abrasive wear.
Quick Comparison: Steel vs. Cast Iron Casings
| Feature | Cast Iron (ASTM A48) | Cast Carbon Steel (ASTM A216 WCB) | Stainless Steel (ASTM A351 CF8M) |
| Initial Cost | Low | Medium | High |
| Pressure Limits | Low to Moderate | High | High |
| Corrosion Resistance | Poor (Rusts easily) | Fair (Requires coatings) | Excellent |
| Repairability | Difficult to weld | Easy to weld | Easy to weld |
| Typical Use Case | HVAC, municipal clean water | Oil & gas, high-pressure industrial | Seawater, chemicals, mining |
Key Maintenance Note for Split Case Designs
Because a splitcase pump casing is split horizontally down the center, achieving a perfect seal between the upper and lower halves is critical.
When using carbon steel, the split flange faces must be carefully inspected during maintenance for any signs of wire-drawing (erosion paths caused by high-pressure fluid bypassing the gasket), which can be repaired via welding and machining—a major benefit over cast iron.