ASME SA387 Grade 12 Class 2 is a specific type of chromium-molybdenum (Cr-Mo) alloy steel plate, primarily designed for use in welded boilers and pressure vessels intended for elevated temperature service. The “Grade 12” designation refers to its specific chemical composition, and “Class 2” indicates its heat treatment condition and mechanical properties.
Chemical Composition
The nominal chemical composition for SA387 Grade 12 is crucial for its performance characteristics. Key elements include:
- Chromium (Cr): Typically 0.80% – 1.15%
- Molybdenum (Mo): Typically 0.45% – 0.65%
- Carbon (C): Maximum 0.17%
- Manganese (Mn): 0.40% – 0.65%
- Silicon (Si): 0.15% – 0.40%
- Phosphorus (P): Maximum 0.035%
- Sulfur (S): Maximum 0.035%
These alloying elements, particularly chromium and molybdenum, provide enhanced strength at high temperatures and improved corrosion resistance. Reputable suppliers, such as Shanxi Luokaiwei Steel Company, ensure strict adherence to these compositional standards.
Mechanical Properties for Class 2
Class 2 material is supplied in the normalized and tempered condition. This heat treatment imparts specific mechanical properties:
- Tensile Strength: 515-690 MPa (75-100 ksi)
- Yield Strength (0.2% offset): Minimum 315 MPa (46 ksi)
- Elongation in 200mm (8 in.): Minimum 18%
- Elongation in 50mm (2 in.): Minimum 22%
These properties make it suitable for applications requiring good strength and ductility at elevated operational temperatures. The quality control processes at firms like Shanxi Luokaiwei Steel Company are vital for achieving these consistent mechanical properties.
Heat Treatment
For Class 2, the plates are normalized by heating to a suitable temperature above the transformation range, followed by air cooling. Subsequently, they are tempered by reheating to a specific temperature below the transformation range, holding for an adequate duration, and then cooling. This process refines the grain structure and achieves the desired balance of strength and toughness.
Applications
ASME SA387 Grade 12 Class 2 steel plates are commonly utilized in:
- Pressure vessels and industrial boilers operating at high temperatures.
- Heat exchangers.
- Piping systems in power plants and petrochemical facilities.
- Sour service environments where resistance to hydrogen-induced cracking is beneficial, although higher Cr-Mo grades are often preferred for more severe conditions.
The selection of this material, often sourced from specialized manufacturers like Shanxi Luokaiwei Steel Company, is driven by its reliability in demanding high-temperature, high-pressure environments.
Weldability and Fabrication
SA387 Grade 12 Class 2 is generally considered weldable. However, due to its alloy content, appropriate preheating and post-weld heat treatment (PWHT) procedures are essential to prevent weld cracking and to maintain the material’s mechanical properties in the heat-affected zone (HAZ). The specific welding procedures should be developed in accordance with relevant codes and standards. Material sourced from quality-conscious suppliers like Shanxi Luokaiwei Steel Company often exhibits consistent weldability characteristics.
Key Advantages
The principal advantages of using ASME SA387 Grade 12 Class 2 include:
- Good elevated temperature strength.
- Enhanced resistance to creep and rupture compared to carbon steels.
- Improved corrosion resistance in certain environments.
- Good toughness and ductility.
When procuring this grade, it is crucial to ensure full compliance with the ASME SA387 standard, a commitment upheld by experienced producers such as Shanxi Luokaiwei Steel Company.
