A387 Grade 11 Class 2 is a chromium-molybdenum alloy steel plate designed for use in welded pressure vessels and high-temperature service. It belongs to the family of heat-resistant low-alloy steels, offering improved creep strength and resistance to hydrogen attack compared to plain carbon steels. The material is typically supplied in the normalized and tempered condition, which enhances its toughness and structural stability under elevated temperatures and high-pressure conditions. Its chemical composition, particularly the balanced addition of chromium and molybdenum, provides good oxidation resistance and durability in environments involving hydrogen, hydrocarbons, and other process fluids. This grade is commonly specified for components in refineries, petrochemical plants, and power generation systems where reliable performance under prolonged thermal stress is required.
Equivalents
| BS | EN | ASTM/ASME | DIN |
| 621 B | ––– | A387-11-2 | ––– |
Specifications for ASTM A387 Grade 11 Alloy Steel Plates
| Designation | Nominal Chromium Content (%) |
Nominal Molybdenum Content (%) |
| A387 Grade 11 | 1.25% | 0.50% |
Tensile Requirements for ASTM A387 Grade 11 Alloy Steel Plates Class 1 Plates
| Designation: | Requirement: | Grade 11 |
| A387 Grade 11 | Tensile strength, ksi [MPa] | 75 to 100 [515 to 690] |
| Yield strength, min, ksi [MPa]/(0.2% offset) | 43 [310] | |
| Elongation in 8 in. [200mm], min % | 18 | |
| Elongation in 2 in. [50mm], min, % | 22 | |
| Reduction of area, min % | ––– |
Chemical Requirements for ASTM A387 Grade 11 Alloy Steel Plates
| Element | Chemical Composition (%) | |
| A387 Grade 11 | ||
| 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: | 0.50 - 0.80 |
| Product Analysis: | 0.44 - 0.86 | |
| Chromium: | Heat Analysis: | 1.00 - 1.50 |
| Product Analysis: | 0.94 - 1.56 | |
| Molybdenum: | Heat Analysis: | 0.45 - 0.65 |
| Product Analysis: | 0.45 - 0.70 |
fabrication process
1. Steelmaking & Casting
Killed Steel Process: The material must be produced using a "killed" (deoxidized) steel process to ensure uniform density and prevent porosity.
Forming: Typically produced via Hot Rolling (HR) to achieve desired plate thicknesses (commonly ranging from 5mm to 150mm).
2. Primary Heat Treatment (Mill Stage)
To achieve Class 2 mechanical properties (higher strength than Class 1), the plates undergo specific thermal treatments:
Normalizing & Tempering (N+T): The most common method. Normalizing at 900–950°C (1650–1740°F) followed by tempering at a minimum of 620°C (1150°F).
Annealing: Full or isothermal annealing may also be used.
Quenching & Tempering (Q+T): Permitted if agreed upon by the purchaser, using accelerated cooling (air blasting or liquid) followed by tempering.
3. Fabrication & Processing
Cutting: Plates can be processed using CNC plasma cutting, laser cutting, or oxy-fuel cutting.
Welding:
Preheating: Required to prevent cracking. According to ASME Section VIII, a minimum preheat of 121°C (250°F) is typically required for P-No. 4 materials like Gr 11.
Post-Weld Heat Treatment (PWHT): Essential for stress relief in pressure-retaining components. Standard PWHT temperatures are often around 620°C–700°C.
4. Quality Control & Testing
To verify compliance with ASTM/ASME standards, the following tests are performed:
Mechanical Testing: Tensile tests (75–100 ksi for Class 2), yield strength, and elongation.
Non-Destructive Testing (NDT): 100% Radiographic Testing (RT), Ultrasonic Testing (UT), and Magnetic Particle Testing (MT).
Chemical Analysis: Verification of Chromium (1.00%–1.50%) and Molybdenum (0.45%–0.65%) content.
Key Applications
Petrochemical & Refining: Widely used for hydrogenation reactors, hydrocracking units, and fractionation columns. Its resistance to high-temperature hydrogen attack (HTHA) is essential for these environments.
Power Generation: Employed in boiler drums, steam headers, and heat exchangers within thermal and nuclear power plants. It is ideal for pressure systems operating between 350°C and 480°C.
Industrial Equipment: Used for separators, high-pressure storage tanks, and large-diameter pipelines handling corrosive fluids or gases.
Main Advantages
High-Temperature Strength: The addition of 0.5% Molybdenum ensures excellent creep resistance, allowing the steel to maintain structural integrity under sustained heat and load.
Corrosion & Oxidation Resistance: The 1.25% Chromium content provides superior protection against oxidation and sour gas corrosion (H2S environments) compared to standard carbon steels like SA 516 Gr 70.
Superior Mechanical Properties: As a Class 2 material, it offers higher tensile strength (515–690 MPa) and yield strength (min 310 MPa) than Class 1, enabling the design of thinner, lighter high-pressure vessels.
Resistance to Embrittlement: Specifically engineered to resist temper embrittlement and hydrogen-induced cracking (HIC), ensuring long-term durability in harsh process environments.
Fabricability: Despite its high strength, it maintains good weldability and can be easily cut or formed using standard industrial procedures when proper preheating and post-weld heat treatment (PWHT) are applied
Request a professional quotation for A387 Grade 11 Class 2 from GNEE Steel.
Is A387 Gr 11 CL 2 weldable?
Yes, it is highly weldable. Proper preheating (150-260°C) and post-weld heat treatment (PWHT) are needed to avoid cold cracks and ensure joint integrity.
What post-weld heat treatment (PWHT) is required for A387 Gr 11 CL 2?
Typical PWHT: Tempering at 620-677°C (1150-1250°F) for sufficient time, relieving welding residual stress and improving toughness.
What are the common applications of A387 Gr 11 CL 2?
Used in refineries, petrochemical plants, boilers, and nuclear power equipment, such as reactor vessels, heat exchangers, and steam pipes.
What is the thickness range of A387 Gr 11 CL 2 plates?
Common thickness ranges from 6mm to 200mm, customizable for specific pressure vessel designs and load-bearing requirements.
What is the impact toughness requirement for A387 Gr 11 CL 2?
At -18°C (-0.4°F), minimum Charpy V-notch impact energy is 27 J (20 ft-lb), ensuring resistance to brittle fracture in low-temperature environments.
What NDT methods are suitable for A387 Gr 11 CL 2?
Common methods: ultrasonic testing (UT) for internal defects, magnetic particle (MT) and liquid penetrant (PT) for surface flaws, and radiography (RT) if needed.
Can A387 Gr 11 CL 2 be used in corrosive environments?
It resists mild to moderate corrosion, especially high-temperature oxidation and hydrogen attack, but not suitable for strong acidic or chloride-rich
environments.
What is the melting point of A387 Gr 11 CL 2?
Its melting point ranges from 1427°C to 1482°C (2600°F to 2700°F), similar to other low-alloy chromium-molybdenum steels.
What is the density of A387 Gr 11 CL 2?
The density is approximately 7.85 g/cm³ (0.284 lb/in³), a standard value for carbon and low-alloy steels used in structural calculations.
Can A387 Gr 11 CL 2 be cold-formed?
It can be cold-formed with proper techniques, but preheating may be required for thick plates to avoid work hardening and potential cracking.
Is A387 Gr 11 CL 2 magnetic?
Yes, it is ferromagnetic due to its iron-based composition, which can be used for non-destructive testing (NDT) methods like magnetic particle inspection.
What is the thickness range of A387 Gr 11 CL 2 plates?
Common thickness ranges from 6mm to 200mm, customizable for specific pressure vessel designs and load-bearing requirements.
What is the hardness limit of A387 Gr 11 CL 2 after PWHT?
Maximum Brinell hardness (HBW) is 207 after PWHT, preventing excessive hardness that may cause cracking and ensuring structural reliability.