A387 Grade 22 Class 2 is a type of alloy steel plate designed for use in welded pressure vessels where improved toughness and creep resistance are required at elevated temperatures. It belongs to the chromium-molybdenum steel family, offering good strength retention and resistance to hydrogen attack in high-temperature service environments. This grade is typically employed in refinery equipment, petrochemical processing units, and power generation systems where reliable performance under thermal stress is essential.
Chemical Composition
| Grade | C | Mn | P | S | Si | Cr | Mo |
| A387 Gr.22 | 0.05-0.15 | 0.30-0.60 | 0.035 | 0.035 | 0.50 max | 2.00-2.50 | 0.90-1.10 |
Mechanical Properties
| Class | Tensile (MPa) | Yield (MPa) | Elong. (50mm) | Elong. (200mm) | Reduc'n of Area* |
| Class 1 | 415 - 585 | 205 min | 18% min | - | 40% min |
| Class 2 | 515 - 690 | 310 min | 18% min | - | 40% min |
Equivalent Grades
| COUNTRY | EU EN |
USA - | Germany DIN,WNr |
Japan JIS |
France AFNOR |
England BS |
Italy UNI |
China GB |
Sweden SS |
| STANDARDS | 10CrMo9-10 | A387Gr.22 Gr.P22 |
10CrMo9-10 | SCMV4 | 10CD9-10 12CD9-10 |
622 622Gr.31 |
10CrMo9-10 12CrMo9-10 |
12CrMo | 2218 |
processing
1. Steelmaking and Refining
The steel must be fully killed steel with a fine grain practice.
Melting: Typically produced via Electric Arc Furnace (EAF).
Secondary Refining: Modern plants use LF (Ladle Furnace) and VOD/VD (Vacuum Degassing) to minimize impurities like Sulfur (S), Phosphorus (P), and gases (O, H, N).
Chemical Control: Precise alloying of Chromium (2.00%–2.50%) and Molybdenum (0.90%–1.10%) is critical.
2. Casting
The molten steel is cast into slabs using Continuous Casting or Ingot Casting (for extra-thick plates) to ensure internal structural integrity.
3. Hot Rolling
Slabs are reheated to approximately 1150°C–1250°C.
The steel is rolled through multiple passes to achieve the target thickness and width.
Thermomechanical control processing (TMCP) may be applied to refine the grain structure during deformation.
4. Heat Treatment (Defining Class 2)
The difference between Class 1 and Class 2 lies in the heat treatment and resulting mechanical properties.
Normalizing: Heating to a temperature range (typically 900°C–960°C) and cooling in air.
Tempering: Reheating to a minimum of 720°C (1325°F) to achieve the required ductility and toughness while maintaining the higher strength levels of Class 2.
Accelerated Cooling: For heavy thicknesses, "Quench and Temper" (Q+T) may be used to ensure uniform properties throughout the plate.
5. Inspection and Testing
Mechanical Testing: Class 2 requires a higher Tensile Strength (515–690 MPa / 75–100 ksi) compared to Class 1.
Ultrasonic Testing (UT): Conducted per ASTM A435 or A578 to detect internal laminations or defects.
Charpy V-Notch Impact Test: Ensures the material remains tough at low temperatures.
Hardness Testing: Ensures the material does not exceed maximum hardness limits, which is vital for sour service (H2S) environments.
6. Post-Processing (Fabrication)
Cutting: CNC Flame or Plasma cutting.
Preheating: Essential before welding to prevent cold cracking.
PWHT (Post-Weld Heat Treatment): After the vessel is welded, it must undergo PWHT to relieve residual stresses and optimize the microstructure of the heat-affected zone (HAZ).
key applications
1. Oil & Gas and Petrochemical Industry
Due to its superior resistance to corrosion, oxidation, and sour gas (H₂S) environments, it is a standard choice for:
Petrochemical Reactors: Used in hydrogenation units and chemical processing reactors.
Storage Tanks: Specifically for pressurized chemicals, hot liquids, or sour gas.
Refineries: Applied in oil refining units and separators.
Offshore/Onshore Platforms: Used for high-pressure pipelines, process vessels, and condensers in harsh environments.
2. Power Generation
Its creep resistance and thermal stability make it essential for:
Industrial Boilers: Used for boiler drum shells and superheaters that handle steam at elevated temperatures.
Nuclear Power: Ideal for nuclear reactor pressure vessels due to its ability to maintain structural integrity under extreme thermal stress.
Turbines: Applied in gas and steam turbines in thermal power stations.
Heat Recovery Steam Generators (HRSG): Vital for efficient energy generation.
3. Equipment Components
The material's high tensile strength (515–690 MPa) allows for the fabrication of critical parts:
Heat Exchangers: Handling thermal fluids in chemical process heating systems.
Piping & Ducting: High-temperature piping and ducting for industrial furnaces.
Valves & Fittings: Including flanges, pipe clamps, and high-pressure valves.
4. Other Industrial Sectors
Heavy Machinery: Liners for chutes, tubs, bins, and truck body wear liners.
Shipbuilding: Used for structural components and pressure-retaining equipment in marine vessels.
Chemical & Pharmaceutical: Reactors and storage for corrosive chemical substances.
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What is the primary material composition of A387 Grade 22 Class 2?
It is a chromium-molybdenum (Cr-Mo) alloy steel, mainly containing 2.25% chromium and 1% molybdenum. Its carbon content is strictly controlled to guarantee excellent weldability and reliable high-temperature strength for industrial applications.
What is the maximum service temperature of A387 Grade 22 Class 2?
It can operate continuously at up to 593°C (1100°F) and intermittently at slightly higher temperatures. This high-temperature resistance makes it ideal for manufacturing high-temperature pressure vessels in various industries.
Is A387 Grade 22 Class 2 a weldable material?
Yes, it boasts good weldability. However, preheating and post-weld heat treatment (PWHT) are generally necessary during welding to avoid cold cracking and effectively relieve residual stresses in the welded joints.
In which industries is A387 Grade 22 Class 2 commonly used?
It is widely applied in oil and gas, petrochemical, power generation and chemical processing industries, mainly for making high-temperature pressure vessels, reactors and heat exchangers due to its excellent performance.
Can A387 Grade 22 Class 2 be used for low-temperature applications?
It is not ideal for service below -29°C (-20°F) as its impact toughness decreases at low temperatures. For low-temperature environments, A516 Grade 70 or stainless steels are more appropriate choices.
What is the recommended preheating temperature for welding A387 Grade 22 Class 2?
The recommended preheating temperature ranges from 150°C to 200°C (302°F to 392°F), which varies based on the material thickness and the specific welding process adopted to ensure welding quality.
What post-weld heat treatment (PWHT) is required for A387 Grade 22 Class 2?
PWHT is usually conducted at 620°C to 675°C (1150°F to 1247°F). The holding time depends on material thickness, aiming to relieve residual stresses and enhance the toughness of welded joints.
Can A387 Grade 22 Class 2 be normalized and tempered?
Yes, normalization and tempering are common for it. Normalization involves heating to 890-925°C then air cooling, and tempering follows PWHT parameters to optimize its mechanical properties comprehensively.
How does the thermal conductivity of A387 Grade 22 Class 2 compare to 304 stainless steel?
Grade 22 Class 2 has higher thermal conductivity (≈45 W/m·K at 20°C) than 304 stainless steel (≈16 W/m·K), making it more efficient in heat transfer applications.
What is the difference between A387 Grade 22 Class 1 and Class 2?
The key difference lies in manufacturing processes and mechanical requirements. Class 2 has stricter quality control, including extra impact testing and tighter limits on chemical composition than Class 1.