The differences between SA 537 Class 1 (SA537CL1) and Class 2 (SA537CL2) lie primarily in their heat treatment processes, mechanical properties, and applications. These distinctions are critical for material selection in pressure vessel and industrial equipment manufacturing. Here’s a detailed comparison:
1. Heat Treatment
SA537CL1:
Delivered in a normalized state (heated to a high temperature and cooled in air)
Normalization refines grain structure and improves uniformity in mechanical properties
SA537CL2:
Undergoes quenching and tempering (heated, rapidly cooled, then reheated to a lower temperature)
This process enhances strength and toughness compared to normalization
2. Mechanical Properties
Yield Strength (σ₀.₂) ≥345 MPa (≤65mm thickness) ≥415 MPa (≤65mm thickness) Tensile Strength (σb) 485–620 MPa550–690 MPa
Elongation (δ4%)
≥22% ≥22% Impact Toughness Lower due to normalization Higher due to quenching and temperingClass 2’s higher strength makes it suitable for thicker sections (up to 150mm) and high-stress applications
3. Applications
SA537CL1:
Used for moderate-pressure vessels, boilers, and structural components where high strength is not critical
Example: Storage tanks, low-temperature reactors
SA537CL2:
Ideal for high-pressure and high-temperature environments, such as nuclear reactor pressure vessels, liquefied gas tanks, and critical petrochemical equipment
Preferred for components requiring superior fatigue resistance and load-bearing capacity
4. Cost and Availability
SA537CL2 is approximately 400 RMB/ton more expensive than Class 1 due to the complex heat treatment process .
Class 2’s quenching and tempering also increase production time and energy consumption
5. Additional Considerations
Standards Compliance: Both classes follow ASME/SA537M standards, but Class 2 often requires stricter ultrasonic testing and impact verification
Weldability: Class 2’s higher carbon equivalent may necessitate preheating during welding to avoid cracking
In summary, SA537CL2 offers enhanced mechanical performance for demanding applications but at a higher cost, while SA537CL1 provides a cost-effective solution for less critical environments. The choice depends on design requirements, operating conditions, and budget constraints
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