A387 Gr 11 Cl 1 is an ASTM alloy steel plate (Chromium-Molybdenum) for high-temperature pressure vessels and boilers, offering excellent heat resistance, creep strength, and weldability, with Class 1 indicating a specific heat treatment (normalized/normalized & tempered) that provides slightly lower strength than Class 2 but is ideal for demanding petrochemical and power-generation applications.
Chemical Composition :
| C | Mn | P | S | Si | Cr | Mo |
| 0.04 - 0.17 | 0.35 - 0.73 | 0.035 | 0.035 | 0.44 - 0.86 | 0.94 - 1.56 | 0.40 - 0.7 |
Mechanical Properties :
| Grade | Thickness | Yield strength | Tensile strength | Elongation in 2" 1) (min %) |
Elongation in 8" 1) (min %) |
|---|---|---|---|---|---|
| Grade 11 Class 1 | 0.185 - 3.60 4.70 - 91.4 |
35 | 60 - 85 | 22 | 19 |
| Grade | Product type | Thickness in |
Width | Length in |
|---|---|---|---|---|
| Grade 11 | Plate | 0.185 - 3.60 4.70 - 91.4 |
60 - 131.9 1500 - 3350 |
73 - 590 1900 - 15000 |
Tensile Requirements
| 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 % | ––– |
processing
1. Steelmaking and Casting
Melting Process: The steel is typically produced using the electric furnace or basic oxygen process. It must be fully killed steel to ensure a fine grain structure and high durability.
Rolling: The steel is hot-rolled to the required thickness (ranging from 4mm to over 150mm depending on application).
2. Heat Treatment (Mandatory)
Per ASTM A387 standards, Class 1 material must undergo specific heat treatments to achieve its mechanical properties:
Normalizing: Heating the plates to a temperature range of 900°C - 950°C (1650°F - 1750°F) followed by air cooling.
Tempering: Heating to a minimum of 650°C (1200°F) to improve ductility and relieve internal stresses.
Annealing: Alternatively, the plates can be supplied in an annealed condition.
3. Fabrication and Machining
Cutting: CNC flame cutting or plasma cutting is used. Since Cr-Mo steel is prone to hardening, preheating may be required before thermal cutting to prevent edge cracking.
Forming: Cold or hot bending/rolling into cylindrical shells for pressure vessels. If hot formed, the temperature must be strictly controlled to avoid degrading the material's properties.
4. Welding Process
A387 Gr 11 belongs to the P-No. 4 group in ASME codes, requiring specific welding controls:
Preheating: A minimum preheat temperature of 121°C (250°F) is generally required to prevent cold cracking in the Heat Affected Zone (HAZ).
Filler Metals: Low-hydrogen electrodes or wires (e.g., E8018-B2 for SMAW or ER80S-B2 for GTAW/GMAW) are used to match the 1.25% Cr - 0.5% Mo composition.
Post-Weld Heat Treatment (PWHT): Mandatory for most thicknesses to reduce hardness and restore toughness. The typical PWHT temperature range is 650°C - 700°C (1200°F - 1300°F).
5. Testing and Inspection
Mechanical Testing: Tensile strength must be within 60–85 ksi (415–585 MPa), with a minimum yield strength of 35 ksi (240 MPa).
NDT (Non-Destructive Testing): 100% Ultrasonic Testing (UT) for plate laminations and Radiographic Testing (RT) for weld integrity.
Hardness Testing: Often required to ensure the PWHT was effective (typically keeping the HAZ below 225 HBW).
Core Applications
The material is primarily used for equipment in the energy and chemical processing sectors:
Petrochemical & Refining: Fabrication of hydrogenation reactors, hydrocracking units, separators, and high-pressure storage tanks.
Power Generation: Used in industrial boilers, steam headers, superheater tubes, and boiler drums where continuous operation at 400–550°C is required.
Heat Transfer: Widely applied in shell-and-tube heat exchangers and industrial furnaces.
Piping Systems: High-pressure pipelines and refinery manifolds exposed to thermal cycling and aggressive process media.
Sour Gas Service: Suitable for hydrogen-rich environments and H₂S-containing media due to its resistance to hydrogen-induced cracking (HIC).
Key Advantages
Compared to standard carbon steels or higher-alloy stainless steels, A387 Gr 11 CL 1 offers a unique balance of properties:
High-Temperature Stability: The addition of 0.5% molybdenum significantly enhances creep resistance, preventing structural deformation under long-term thermal stress.
Oxidation & Corrosion Resistance: Approximately 1.25% chromium provides superior protection against high-temperature oxidation and sulfidation.
Resistance to Hydrogen Attack: The alloy chemistry is designed to withstand "hydrogen attack" (decarbonization) in severe refinery environments.
Optimized Strength & Ductility: Class 1 provides a lower tensile strength (60–85 ksi) compared to Class 2 but offers higher elongation and ductility, which can be advantageous for specific forming processes and thermal cycling resistance.
Cost Efficiency: It serves as an economical alternative to more expensive high-alloy materials when moderate strength at elevated temperatures is sufficient.
Excellent Weldability: When proper preheat and post-weld heat treatment (PWHT) are applied, it maintains reliable structural integrity at the weld joints.
If you want to learn more about (A387 Gr 11 CL 1)GNEE's products, you can send an email to beam@gneesteelgroup.com. We are more than happy to assist you.
What type of material is A 387 Gr 11 CL 1?
A 387 Gr 11 CL 1 is a low-alloy chromium-molybdenum (Cr-Mo) steel plate, primarily designed for pressure vessel applications under elevated temperatures.
What are the main chemical components of A 387 Gr 11 CL 1?
The key chemical components (typical values) include: Carbon (C) 0.15-0.25%, Manganese (Mn) 0.40-0.65%, Phosphorus (P) ≤0.035%, Sulfur (S) ≤0.035%, Silicon (Si) 0.50-0.80%, Chromium (Cr) 1.00-1.50%, and Molybdenum (Mo) 0.45-0.65%.
What does "CL 1" stand for in A 387 Gr 11 CL 1?
"CL" refers to "Class". CL 1 indicates that this grade has a lower tensile strength requirement compared to CL 2 of the same A 387 Gr 11 series, suitable for less demanding high-temperature service conditions.
Which standard specifies A 387 Gr 11 CL 1?
A 387 Gr 11 CL 1 is specified by the American Society of Mechanical Engineers (ASME) Standard SA-387, which covers alloy steel plates for pressure vessels and boilers operating at elevated temperatures.
Can A 387 Gr 11 CL 1 be welded?
Yes, it is weldable. However, preheating (typically 150-260°C/300-500°F) and post-weld heat treatment (PWHT) are required to prevent cold cracking and reduce residual stresses, ensuring weld joint integrity.
What welding processes are suitable for A 387 Gr 11 CL 1?
Common suitable welding processes include shielded metal arc welding (SMAW), gas tungsten arc welding (GTAW/TIG), gas metal arc welding (GMAW/MIG), and submerged arc welding (SAW).
Is cold forming possible for A 387 Gr 11 CL 1?
Yes, it can be cold formed, but it has higher strength than carbon steel, so higher forming forces are needed. It is recommended to perform forming at room temperature and avoid excessive deformation to prevent cracking.
What is the difference between A 387 Gr 11 CL 1 and A 387 Gr 12 CL 1?
The main difference is the molybdenum content: Gr 11 CL 1 has 0.45-0.65% Mo, while Gr 12 CL 1 has 0.87-1.13% Mo. Gr 12 CL 1 offers better high-temperature strength and creep resistance but is more expensive.