Is A 387 Gr 11 CL 1 a carbon steel or alloy steel?

A387 Grade 11 Class 1 is a chromium-molybdenum alloy steel plate specified under the ASTM A387 standard, widely used in the fabrication of pressure vessels and boiler components that operate at elevated temperatures. It belongs to the family of low-alloy steels containing a moderate amount of chromium and molybdenum, which imparts good strength, creep resistance, and resistance to hydrogen attack in high-temperature service environments. Class 1 indicates a normalized and tempered heat treatment condition, resulting in a refined microstructure that balances toughness and strength for reliable performance under thermal and mechanical stress.

applications

Pressure vessels and boilers

Used in the fabrication of pressure vessels, boilers, and related components that operate under high temperatures and pressures, where good creep resistance and strength retention are required.

Oil refinery equipment

Applied in refinery units such as reactors, heat exchangers, and piping systems that handle hot hydrocarbons and process fluids.

Petrochemical and chemical processing

Utilized in reactors, columns, and heat exchangers within petrochemical and chemical plants, particularly in services involving elevated temperatures and hydrogen-containing environments.

Power generation systems

Found in components of power plants, including boilers, steam generators, and associated pressure parts, where resistance to high-temperature oxidation and creep is essential.

Other high-temperature service equipment

Used in various industrial applications requiring steel plates with good elevated-temperature strength and resistance to hydrogen attack, such as in certain process heaters and furnace components.

advantages

Good high-temperature strength

Retains significant strength at elevated temperatures, making it suitable for long-term service under heat and pressure.

Resistance to creep

Exhibits improved resistance to creep deformation, an important property for components operating at high temperatures over extended periods.

Resistance to hydrogen attack

The chromium-molybdenum alloying provides better resistance to hydrogen-induced damage in high-temperature hydrogen-containing environments.

Favorable toughness and ductility

Proper heat treatment results in a balance of toughness and ductility, helping to prevent brittle failure under thermal and mechanical stress.

Weldability and fabricability

Generally considered weldable with appropriate procedures, allowing for the fabrication of large and complex pressure vessels and structures.

Proven performance in industry

Has a long history of reliable use in refineries, petrochemical plants, and power generation facilities, demonstrating consistent performance in demanding service conditions.

processing flow

1. Material Inspection & Preparation

Verification: Confirm the Mill Test Certificate (MTC) complies with ASTM A387/A387M standards. Class 1 requires a Tensile Strength of 60–85 ksi (415–585 MPa).

Cutting: CNC Flame or Plasma cutting is used.

Preheating: It is highly recommended to preheat the plate to 100-150°C before thermal cutting to prevent edge cracking due to the material's hardenability.

2. Forming (Cold or Hot)

Cold Forming: Applicable for thinner plates. If the strain exceeds 5%, a subsequent stress relief or heat treatment may be required.

Hot Forming: Usually performed between 900°C and 1050°C. If the temperature drops below the transformation point during forming, a full Normalizing and Tempering (N+T) cycle must be repeated to restore mechanical properties.

3. Welding Process (Critical Phase)

A387 Gr 11 is sensitive to delayed cracking.

Preheating: Must maintain a minimum preheat temperature of 150°C to 250°C depending on thickness.

Interpass Temperature: Should be controlled between 150°C and 300°C.

Post-Heating (Dehydrogenation): Immediately after welding, heat the joint to 300-350°C for 2-4 hours to allow hydrogen to escape, followed by slow cooling.

4. Heat Treatment

The material must be in the Normalized and Tempered condition to meet Class 1 specifications:

Normalizing: Heat to 900-950°C, then air cool.

Tempering: Minimum tempering temperature is 620°C (1150°F).

Post-Weld Heat Treatment (PWHT): To relieve residual stresses in the vessel, PWHT is typically conducted at 650°C to 700°C.

5. NDT & Quality Control

Non-Destructive Testing (NDT): 100% Radiographic Testing (RT) or Ultrasonic Testing (UT) of all pressure-retaining welds.

Hardness Testing: The hardness of the weld and Heat Affected Zone (HAZ) is generally restricted to ≤ 225 HBW to ensure ductility and resistance to stress corrosion cracking.

Mechanical Testing: Impact tests and tensile tests are often performed on "Production Test Coupons" that have undergone a Simulated PWHT (SPWHT) cycle.

Contact now

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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.

Can A 387 Gr 11 CL 1 be replaced with A 516 Gr 70?

Only for low-temperature or ambient-temperature applications. A 516 Gr 70 is carbon steel with poor high-temperature properties, so it cannot replace A 387 Gr 11 CL 1 in elevated-temperature service.

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 purpose of post-weld heat treatment (PWHT) for A 387 Gr 11 CL 1?

PWHT reduces residual welding stresses, improves the toughness and ductility of the weld joint, eliminates hydrogen-induced cracking, and enhances the material's resistance to stress corrosion cracking at elevated temperatures.

What are the main applications of A 387 Gr 11 CL 1?

It is widely used in the manufacture of pressure vessels, boilers, heat exchangers, and petrochemical equipment that operate at elevated temperatures, such as refinery reactors, steam generators, and catalytic crackers.

What is the maximum service temperature for A 387 Gr 11 CL 1?

Its maximum continuous service temperature is approximately 593°C (1100°F). Beyond this temperature, its creep and oxidation resistance decline significantly.

Can A 387 Gr 11 CL 1 be used in low-temperature environments?

It is not ideal for low-temperature service (below -20°C/-4°F) because its impact toughness decreases at low temperatures, increasing the risk of brittle fracture. For low-temperature applications, other grades like A516 Gr 70 or low-temperature alloy steels are preferred.

How does temperature affect the mechanical properties of A 387 Gr 11 CL 1?

At elevated temperatures (up to 593°C/1100°F), it retains excellent tensile strength, creep resistance, and fatigue strength compared to carbon steel. Beyond this temperature, its properties gradually degrade.

What is the Brinell hardness (HB) range of A 387 Gr 11 CL 1?

The typical Brinell hardness range is 130-180 HB, which reflects its moderate hardness and machinability.

 Is A 387 Gr 11 CL 1 resistant to corrosion?

It has moderate corrosion resistance in atmospheric and mild corrosive environments. However, it is not suitable for strong corrosive media (e.g., acids, alkalis) unless additional protection (e.g., coating, cladding) is applied.

What is the certification requirement for A 387 Gr 11 CL 1 plates?

Plates must be certified in accordance with ASME SA-387, including material test reports (MTRs) with chemical composition, mechanical properties, and heat treatment records. Third-party inspection (e.g., ABS, DNV) may be required for critical applications.

What is the typical thickness range of A 387 Gr 11 CL 1 plates?

The standard thickness range is 6 mm to 200 mm (0.24 inches to 7.87 inches). Thicker plates may be available on request but require special heat treatment to ensure uniform mechanical properties.