SA 387 Grade 12 Class 2 is a specific type of weldable, chromium-molybdenum alloy steel plate designed for high-temperature pressure vessel and boiler applications, offering excellent resistance to oxidation, corrosion, and high pressure, with Class 2 denoting higher mechanical strength (tensile/yield) than Class 1. It's a robust material used in demanding oil & gas, petrochemical, and industrial settings.
SA387 Alloy Steel Gr.12 CL 2 Sheet & Plate Specification :
| Specifications | ASTM A387 / ASME SA387 |
|---|---|
| Thickness | 5mm-150mm |
| Width | 1000mm-4500mm |
| Length | 3000mm -18000mm |
| Hardness | As per ASME A & NACE MR 175 |
| Impact Tested | Impact tested -52° C |
| Finish | Hot rolled plate (HR), Cold rolled sheet (CR) |
Equivalent Grades For SA387 Alloy Steel Gr.12 CL 2 Sheets & Plates
| BS | EN | ASTM/ASME | UNS | DIN |
| – | – | A387 / SA 387 | K11757 | – |
Chemical Composition of SA387 Alloy Steel Gr.12 CL 2 Sheets and Plates
| 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 For A387 Alloy Steel Gr.12 CL 2 Sheets & Plates
| A387 / SA387 Grade 12 | Class 1 | Class 2 |
| Tensile Strength (ksi) | 50-80 | 65-85 |
| Tensile Strength (MPa) | 380-550 | 450-585 |
| Yield Strength (ksi) | 33 | 40 |
| Yield Strength (MPa) | 230 | 275 |
| Elongation in 200mm (%) | 18 | 19 |
| Elongation in 50mm (%) | 22 | 22 |
| Reduction of area in % | – | – |
Technical Processing
1. Heat Treatment (Thermal Processing)
Under ASME SA 387, plates must be thermally treated using one of the following methods:
Annealing: Heating above the critical point and cooling slowly to improve ductility and relieve stress.
Normalizing and Tempering (N&T): The most common condition for project requirements. The minimum tempering temperature for Grade 12 is 1150°F (620°C).
Quenched and Tempered (Q&T): Permitted only with purchaser agreement, involving liquid quenching or air blasting from the austenitizing temperature followed by tempering.
2. Welding Procedures
Due to its alloy content, SA 387 Grade 12 requires specific care to prevent cold cracking and ensure joint integrity:
Preheating: A minimum preheat temperature of 250°F (120°C) is generally required, especially for thicknesses exceeding 5/8 inch (16 mm).
Edge Preparation: Plates should be beveled (e.g., 60° V-groove) and polished to remove oil, rust, and moisture.
Methods: Common methods include TIG (Gas Tungsten Arc), Stick (SMAW), and Submerged Arc Welding (SAW).
Post-Weld Heat Treatment (PWHT): Essential after welding to relieve residual stresses and restore mechanical properties.
3. Mechanical Properties (Class 2)
Class 2 plates are distinguished by higher strength requirements compared to Class 1:
Tensile Strength: 65 to 85 ksi (450 to 585 MPa).
Yield Strength (min): 40 ksi (275 MPa).
Elongation (min): 22% in 2 inches (50 mm).
4. Manufacturing & Inspection
Process: Plates are typically produced via hot rolling.
Testing: Quality control includes Ultrasonic Testing (UT) for internal defects, Charpy Impact Tests (often at -20°C or -46°C), and chemical analysis.
Surface Treatment: Grooves may be processed by flame or plasma cutting; however, PT (Penetrant Testing) should follow to check for cracks.
Key Applications
This steel is a benchmark material for equipment operating under high stress, high pressure, and high temperature:
Oil & Gas / Petrochemical: Fabrication of reactors, separators, distillation towers, and spherical storage tanks for crude oil and refined products.
Power Generation: Critical components for thermal and nuclear power plants, including boiler drums, steam pipelines, turbine volutes, and heat recovery steam generators (HRSG).
Chemical Processing: Construction of heat exchangers, pressure vessels, and vessels containing high-pressure gas or corrosive media.
Sour Service Environments: Ideal for "sour gas" applications where the material must resist hydrogen-induced cracking and corrosion from sulfur compounds.
General Heavy Industry: Used in high-temperature ducting, pipe supports, valves, flanges, and fittings.
Core Advantages
SA 387 Grade 12 Class 2 offers several technical benefits over standard carbon steels like SA 516 Grade 70:
Superior High-Temperature Strength: The addition of molybdenum significantly enhances tensile and yield strength at temperatures up to approximately 575°C (1067°F).
Exceptional Corrosion & Oxidation Resistance: Chromium content provides a protective layer that resists pitting, crevice corrosion, and oxidation in demanding industrial environments.
Higher Mechanical Performance (Class 2 vs. Class 1): Class 2 is specifically heat-treated to provide higher tensile strength (450–585 MPa) and yield strength (≥275 MPa) compared to Class 1, allowing for thinner, more efficient vessel walls.
Excellent Weldability and Formability: Despite its high strength, the alloy remains easily weldable and fabricable, which is critical for constructing complex industrial structures.
Reliability & Longevity: Known for its durability and resistance to thermal fatigue, it ensures stable service over extended operational periods, reducing maintenance costs.
Full specification and details are available on request. The above information is provided for guidance purposes only. For specific design requirements please contact our technical sales staff.
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.
What is the difference between ASME SA 387 and ASTM A 387?
ASME SA 387 and ASTM A 387 are technically identical in terms of chemical composition and mechanical properties. The only difference is their application scope: ASME SA 387 is part of the ASME Boiler and Pressure Vessel Code (BPVC), used for equipment certified to ASME standards. ASTM A 387 is a general-purpose standard for industrial applications not requiring ASME certification. Manufacturers often produce material that complies with both standards.
What is the creep strength performance of SA 387 Grade 12 Class 2 at elevated temperatures?
SA 387 Grade 12 Class 2 exhibits reliable creep strength at service temperatures up to 593°C (1100°F). For example, at 538°C (1000°F), its 100,000-hour creep rupture strength is approximately 34.5 MPa (5,000 psi), which is sufficient for most medium-temperature high-pressure applications like refinery heaters and steam boilers. Creep strength decreases gradually with increasing temperature beyond 593°C (1100°F) due to microstructural changes.
Can SA 387 Grade 12 Class 2 be cold-formed?
It can be cold-formed, but its ductility at room temperature requires careful handling. Cold forming should be performed at temperatures above -18°C (0°F) to avoid brittle fracture, and the material should not be strained beyond its yield strength excessively. Post-forming heat treatment may be necessary if the forming process introduces significant residual stresses, especially for components used in critical pressure service.