A387 Grade 12 Class 2 is a chromium‑molybdenum alloy steel plate intended for welded pressure vessels that require enhanced strength and toughness at moderately elevated temperatures. It offers good resistance to creep and oxidation under heated service conditions and is commonly used in boilers, heat exchangers, and other pressure‑containing equipment operating above the typical range of carbon steels. Produced with controlled chemistry and heat treatment, it achieves a balanced combination of strength, ductility, and impact performance. Its favorable weldability allows it to be joined by standard welding methods while preserving structural integrity in high‑temperature environments.
Specifications for ASTM A387 Grade 12 Alloy Steel Plates
| Designation | Nominal Chromium Content (%) |
Nominal Molybdenum Content (%) |
| A387 Grade 12 | 1.00% | 0.50% |
Chemical Requirements for ASTM A387 Grade 12 Alloy Steel Plates
| Element | Chemical Composition (%) | |
| ASTM A387 Grade 12 | ||
| Carbon: | Heat Analysis: | 0.05 - 0.17 |
| Product Analysis: | 0.04 - 0.17 | |
| Manganese: | Heat Analysis: | 0.40 - 0.65 |
| Product Analysis: | 0.35 - 0.73 | |
| Phosphorus: | Heat Analysis: | 0.035 |
| Product Analysis: | 0.035 | |
| Sulphur (max): | Heat Analysis: | 0.035 |
| Product Analysis: | 0.035 | |
| Silicon: | Heat Analysis: | 0.15 - 0.40 |
| Product Analysis: | 0.13 - 0.45 | |
| Chromium: | Heat Analysis: | 0.80 - 1.15 |
| Product Analysis: | 0.74 - 1.21 | |
| Molybdenum: | Heat Analysis: | 0.45 - 0.60 |
| Product Analysis: | 0.40 - 0.65 |
processing flow
1. Steelmaking & Casting
The process begins with melting high-quality raw materials, often in an Electric Arc Furnace (EAF) or via Vacuum Oxygen Decarburization (VOD).
Killed Steel: The steel must be "fully killed" (deoxidized) to ensure a uniform chemical composition and high internal soundness.
Refining: Vacuum treatment is often used to remove dissolved gases (hydrogen, nitrogen), improving the steel's purity and toughness.
2. Rolling & Heat Treatment
The steel is hot-rolled into plates and must undergo mandatory thermal treatments to achieve its "Class 2" strength levels.
Austenitizing: Heating the plates to approximately 870°C – 950°C to transform the microstructure into austenite.
Cooling Methods:
Normalizing: Cooling in air to refine grain size.
Accelerated Cooling: If agreed upon, air blasting or liquid quenching may be used to achieve higher hardness.
Tempering (Critical): To reduce brittleness, the plates are reheated. For Grade 12, the minimum tempering temperature is 620°C (1150°F).
3. Fabrication & Welding
Once the plates are produced, they are fabricated into pressure vessel components:
Preparation: Edges are beveled (e.g., single or double V-joints) for full penetration welds.
Welding: Standard processes include Submerged Arc Welding (SAW) and Gas-Shielded Flux-Cored Arc Welding (FCAW-G).
Post-Weld Heat Treatment (PWHT): Essential to relieve internal stresses created during the welding process, ensuring the joint remains ductile under high-temperature service.
4. Testing & Quality Control
Final products undergo rigorous 2026-standard testing to verify mechanical properties:
Tensile Testing: Verifies the Class 2 strength range (450–585 MPa).
Charpy V-Notch: Assesses impact toughness and resistance to brittle fracture, often tested at low temperatures like -20°C.
Non-Destructive Testing (NDT): Includes ultrasonic and magnetic particle examinations to detect any internal defects.
Primary Industry Applications
Oil & Gas Refining: It is extensively used in "sour service" environments where high levels of hydrogen sulfide (H2S) are present. Common components include:
Separator vessels and accumulators.
Refinery process vessels.
Hydrocrackers and high-temperature storage tanks.
Power Generation: Favored for fossil fuel and nuclear power stations because it can operate effectively up to 575°C. Key uses include:
Industrial boilers and boiler drums.
Heat recovery steam generators (HRSG).
Steam pipelines, headers, and turbine components.
Chemical & Petrochemical Processing: Its resistance to oxidation and corrosion makes it suitable for equipment handling corrosive media:
Reactors and chemical processing vessels.
Shell-and-tube heat exchangers, reheaters, and coolers.
Fertilizer production equipment.
Component-Specific Uses
Beyond large vessels, this steel grade is used to manufacture specialized parts that require mechanical reliability under high pressure:
Piping Systems: High-temperature ducting, manifolds, and pipe supports.
Fittings: Flanges, valves, and heavy-duty pipe clamps.
Storage: Oxygen cylinders and large metallic tanks for high-pressure gas.
Secondary Applications
Aerospace & Defense: Utilized for thermal fatigue-resistant components in military vehicles and naval ships.
Pulp & Paper Industry: Applied in specialized processing equipment that faces elevated heat and mild chemical exposure.
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.
Is this steel suitable for marine environments?
It is not ideal for marine environments directly due to poor seawater corrosion resistance, but it can be used after anti-corrosion coating.
What parts of boilers are made of A387 Grade 12 Class 2?
It is often used to make boiler tubes, furnace walls, and header components that bear high temperature and pressure, ensuring stable operation of boiler systems.
Can A387 Grade 12 Class 2 be welded?
Yes, it is weldable, but preheating (150-200°C) and post-weld heat treatment are required to avoid cold cracks and improve joint toughness.
What welding methods are suitable for this alloy steel?
Common methods include shielded metal arc welding, gas tungsten arc welding and submerged arc welding, adapting to different welding scenarios and quality requirements.
Is heat treatment necessary after welding?
Yes, post-weld tempering at 620-670°C is essential to eliminate welding residual stress and restore the mechanical properties of the weld zone.
Can it be cold-formed?
It can be cold-formed with proper procedures, but preheating may be required for thick plates to prevent cracking and ensure forming quality.
Can it be machined easily?
It has moderate machinability. Sharp tools and proper cutting parameters are needed, and cooling lubricants should be used to reduce tool wear.
What is the recommended preheating temperature before forging?
The recommended preheating temperature is 815-870°C, which softens the material and reduces deformation resistance during forging.
What is the main function of molybdenum in this alloy steel?
Molybdenum improves its high-temperature strength, creep resistance and corrosion resistance, making it adaptable to harsh working environments.
Is it suitable for making pressure vessel shells?
Yes, it is widely used for pressure vessel shells in petrochemical plants, as it can withstand high internal pressure and stable high temperatures.
What is the hardness of A387 Grade 12 Class 2 after heat treatment?
After normalizing and tempering, its Brinell hardness is about 187-229 HB, balancing hardness and toughness for industrial applications.