ASME SA387 Grade 12 Class 2 plate is a chromium‑molybdenum alloy steel plate covered by the ASME SA‑387/SA‑387M specification, intended mainly for welded boilers and pressure vessels that operate at elevated temperatures. The "Grade 12" designation signifies a composition dominated by moderate chromium and molybdenum content, which imparts good high‑temperature strength, creep resistance, and oxidation resistance. "Class 2" indicates that the material is supplied in the normalized and tempered condition, resulting in higher strength and toughness compared to the annealed Class 1. The chemical composition is tightly controlled to ensure these properties, with limits set on carbon, silicon, manganese, phosphorus, sulfur, chromium, and molybdenum. The mechanical properties are characterized by good tensile and yield strength, reasonable ductility, and an appropriate hardness level, making the material suitable for withstanding the stresses and thermal cycles encountered in high‑temperature service. Plates are produced in a range of standard thicknesses, widths, and lengths, and the heat treatment typically involves normalizing followed by tempering to refine the microstructure and optimize the balance of strength and toughness required for pressure vessel applications.
SA 387 GR.12 Equivalent Grades :
| BS | ASTM/ASME | UNS | EN | DIN |
| 620B | A387 / SA 387 | K11757 | 3 CRMO 45 | 13 CRMO 44 |
Chemical Composition of SA387 GR.12 CL.2 Plate
| C | Mn | P | S | Si | Cr | Mo |
| 0.04 - 0.17 | 0.35 - 0.73 | 0.035 | 0.035 | 0.13 - 0.45 | 0.74 - 1.21 | 0.4 - 0.65 |
Mechanical Properties of SA 387 GR.12 CL.2 Plate
| Tensile Strength | Yield Strength | Elongationin 200mm (%) | Elongation in 50mm (%) |
| 65-85 ksi, 450-585 MPa | 40 Ksi, 275 MPa | 19 |
22 |
ASME SA 387 Grade 12 Class 2 steel plates are typically subjected to a heat treatment of normalizing followed by tempering. In cases with special requirements, such as thick plates or high toughness demands, the process may involve normalizing, rapid cooling (such as water quenching), and then tempering. These procedures ensure the material possesses the necessary strength, toughness, and corrosion resistance for service in high‑temperature and hydrogenation environments, meeting the requirements of pressure vessels and boilers.
Normalizing:
The steel plate is heated to a temperature above the austenitizing range and then cooled in air. This step refines the grain structure, homogenizes the microstructure, and relieves residual stresses from casting or rolling.
Tempering:
After normalizing, tempering is performed at a lower temperature to further reduce internal stresses, improve toughness, and achieve the desired combination of mechanical properties.
Special treatment (optional):
For thicker plates, a sequence of normalizing, rapid cooling (such as water quenching), and tempering may be applied to achieve superior toughness and microstructure.
Objectives:
Enhance resistance to embrittlement and improve low‑temperature impact toughness.
Provide good high‑temperature performance along with resistance to oxidation and corrosion.
Suit applications in the oil and gas industry, including hydrogenation reactors, refinery equipment, and gas processing units.
Key Applications:
Oil & Gas Industry
ASME SA 387 Grade 12 Class 2 plates are widely used in sour service environments, where resistance to hydrogen sulfide and related forms of corrosion and embrittlement is critical. They are employed in both offshore and onshore facilities, including platforms, processing plants, and equipment such as reactors, separators, and pressure vessels involved in hydrocarbon production, refining, and gas processing.
Power Generation
These plates are commonly specified for steam boilers, heat recovery steam generators (HRSG), thermal power stations, and turbine-related components. Their ability to maintain strength and stability at elevated temperatures makes them suitable for withstanding the high-pressure and high-temperature conditions typical of power generation systems.
Chemical Processing
In the chemical industry, SA 387 Grade 12 Class 2 is used in reactors, pressure vessels, and heat exchangers that handle aggressive chemicals and operate under demanding temperature and pressure regimes. The material's resistance to creep, thermal fatigue, and oxidation contributes to reliable long-term performance in these applications.
General Industrial
Beyond the energy and chemical sectors, these plates find use in a range of general industrial equipment, including tanks, piping for hot liquids, separators, industrial boilers, and various pressure vessels. Their combination of strength, toughness, and weldability makes them a versatile choice for handling high-temperature and high-pressure service in diverse industrial settings.
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What is ASME SA 387 Grade 12 Class 2?
ASME SA 387 Grade 12 Class 2 is a low-alloy chromium-molybdenum (Cr-Mo) steel plate specification developed by the American Society of Mechanical Engineers (ASME). It is designed for elevated temperature and pressure service, primarily used in boiler, pressure vessel, and piping applications where resistance to creep, oxidation, and high-temperature strength are required.
What is the chemical composition of SA 387 Grade 12 Class 2?
The typical chemical composition (weight %) is as follows: Carbon (C) 0.05-0.17%, Manganese (Mn) 0.40-0.65%, Phosphorus (P) ≤0.035%, Sulfur (S) ≤0.035%, Silicon (Si) 0.15-0.40%, Chromium (Cr) 0.80-1.25%, Molybdenum (Mo) 0.45-0.60%, and the balance is Iron (Fe). Trace elements may be present within acceptable limits per ASME standards.
What are the minimum mechanical properties of SA 387 Grade 12 Class 2?
At room temperature, the minimum mechanical properties are: Tensile strength (σ) ≥ 415 MPa (60,000 psi), Yield strength (σ) ≥ 205 MPa (30,000 psi), Elongation (in 200 mm) ≥ 22%, and Reduction of area ≥ 50%. These values apply to material in the normalized and tempered condition.
What heat treatment is required for SA 387 Grade 12 Class 2?
The mandatory heat treatment for SA 387 Grade 12 Class 2 is normalizing and tempering. Normalization is performed at a temperature of 890-940°C (1635-1725°F), followed by air cooling. Tempering is conducted at a minimum temperature of 620°C (1150°F), with sufficient holding time to ensure uniform temperature throughout the plate, then cooled in air or water.
What is the maximum service temperature for SA 387 Grade 12 Class 2?
SA 387 Grade 12 Class 2 is suitable for continuous service at elevated temperatures up to approximately 593°C (1100°F). Beyond this temperature, its creep strength and oxidation resistance may degrade, limiting its long-term performance.
What are the common applications of SA 387 Grade 12 Class 2?
It is widely used in high-temperature, high-pressure industrial equipment, including: Boiler drums and headers, Pressure vessels for petrochemical, refinery, and power generation industries, Piping systems for steam and process fluids, Furnace components, and Heat exchangers.
How does SA 387 Grade 12 Class 2 differ from Class 1 of the same grade?
The key difference lies in toughness requirements. SA 387 Grade 12 Class 2 has stricter Charpy V-notch (CVN) impact toughness requirements compared to Class 1. Class 2 typically requires a minimum CVN value of 27 J (20 ft-lb) at -18°C (0°F), while Class 1 may have lower or no mandatory impact requirements, depending on the application.
Is SA 387 Grade 12 Class 2 weldable?
Yes, it is weldable, but proper welding procedures are critical due to its Cr-Mo composition. Preheating (typically 150-260°C / 300-500°F) is required to prevent cold cracking, and post-weld heat treatment (PWHT) is necessary to relieve residual stresses and restore material toughness. Compatible welding consumables include E7018-B2, E8018-B2, or ER80S-B2 for GTAW/SMAW processes.
What is the standard thickness range for SA 387 Grade 12 Class 2 plates?
Plates are typically available in thicknesses from 6 mm (0.25 in) up to 200 mm (8 in), depending on the manufacturer. For thicker plates, additional quality control tests (such as ultrasonic inspection) may be required to ensure internal integrity.