What is the main chemical composition of A387 Gr 11 CL 2?

A387 Gr 11 Cl 2 is a specification for a chrome-molybdenum (Cr-Mo) alloy steel plate used in welded boilers and pressure vessels for elevated temperature service, offering good corrosion/oxidation resistance, weldability, and strength at high temperatures. The "Class 2" indicates higher strength and requires a normalized and tempered condition, unlike "Class 1".

A387 GR 11 CLASS 2 Plate Specification

ASTM A387 GR 11 CLASS 2 Chemical Composition

ASTM A387  GR 11 CLASS 2 Mechanical Properties

Equivalent Grades 

The manufacturing and processing technologies  involved are as follows:

1. Steelmaking & Refining

Melting Process: It is produced using Electric Arc Furnace (EAF) followed by Ladle Refining (LF) and Vacuum Degassing (VD). This process is critical to minimize impurities like Sulfur (S), Phosphorus (P), and harmful trace elements (like Sb, Sn, As), which helps reduce temper embrittlement sensitivity.

Casting: Typically produced via Continuous Casting or ingot casting followed by hot rolling.

2. Heat Treatment (Most Critical Process)

According to the ASTM A387 standard, Class 2 plates must undergo specific heat treatments to achieve the required mechanical properties (Higher tensile strength than Class 1):

Normalizing + Tempering (N+T):

Normalizing: Heated to approximately 900–950°C (1650–1740°F) and cooled in air to refine grain structure.

Tempering: Must be performed at a minimum temperature of 620°C (1150°F), typically between 650°C and 750°C, to achieve the desired toughness and ductility.

Quenching + Tempering (Q+T): Accelerated cooling (liquid quenching) is permitted if agreed upon, followed by tempering.

3. Welding Process

Consumables: Low-hydrogen welding consumables matching the 1.25%Cr-0.5%Mo chemistry are required.

Preheating: Preheating is mandatory (typically 150°C to 250°C) to prevent cold cracking due to the material's hardenability.

Post-Weld Heat Treatment (PWHT): Essential for stress relief and restoring ductility in the Heat Affected Zone (HAZ). Typical PWHT temperatures range from 650°C to 700°C.

4. Cutting and Forming

Cutting: Can be processed via Flame (Oxy-fuel) Cutting, Plasma Cutting, or Laser Cutting.

Forming: Can be cold or hot formed. If Hot Forming is performed, the material must undergo a full re-heat treatment (Normalizing and Tempering) to ensure the mechanical properties are restored.

5. Technical Specifications Comparison (Class 2)

Compared to Class 1, the Class 2 process focuses on achieving a higher tensile strength (515–690 MPa or 75–100 ksi) through controlled cooling and tempering cycles.

applications

1. Petrochemical and Oil & Gas Industries

This is the most common application area due to the material's resistance to hydrogen-induced cracking and sour gas (H₂S) environments.

Reactors: Used in hydrogenation reactors and hydrocracking units.

Processing Vessels: High-pressure separators, fractionation columns, and gas-handling systems.

Storage: Large-scale storage tanks for high-temperature liquids and gases.

2. Power Generation

Its thermal stability makes it a standard for systems exposed to sustained steam pressure.

Boiler Components: Boiler drums, steam headers, and high-temperature piping systems.

Turbines: Critical parts for steam and gas turbines.

Nuclear Power: Used in nuclear reactor pressure vessels and high-pressure steam generators.

3. High-Temperature Heat Exchange

Heat Exchangers: Specifically shell-and-tube and high-pressure heat exchangers that undergo continuous thermal cycling.

Ducting: High-temperature industrial ducting systems.

4. Specialized Fittings and Hardware

Because it is a pressure-vessel-grade steel, it is also fabricated into smaller but critical components for pressurized systems:

Piping Systems: Flanges, valves, pipe clamps, and high-pressure pipelines.

Cylinders: High-pressure industrial cylinders.

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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.

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.

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.

What is the thermal conductivity of A387 Gr 11 CL 2?

At 20°C (68°F), thermal conductivity is about 42 W/(m·K), decreasing slightly with increasing temperature, suitable for heat transfer applications.

Is A387 Gr 11 CL 2 suitable for hydrogen service?

Yes, it is widely used in hydrogen service (e.g., hydrocracking units) due to its resistance to hydrogen embrittlement at high temperatures and pressures.

What is the delivery condition of A387 Gr 11 CL 2?

Usually delivered in normalized and tempered (N&T) condition, optimizing its mechanical properties and ensuring uniformity across the plate.

What is the coefficient of thermal expansion of A387 Gr 11 CL 2?

From 20°C to 500°C, it is approximately 12.5 × 10⁻⁶/°C, important for thermal stress calculations in high-temperature equipment.

Can A387 Gr 11 CL 2 be normalized only without tempering?

No, tempering after normalizing is mandatory to reduce hardness, relieve stress, and improve toughness, meeting ASTM A387 requirements.

What is the difference between A387 Gr 11 and Gr 22?

Gr 22 has higher Mo content (2.25%), better high-temperature creep resistance, while Gr 11 is cost-effective for moderate-temperature applications.

What standards should be followed for welding A387 Gr 11 CL 2?

Follow AWS D1.1/D1.1M (Structural Welding Code) and ASME BPVC Section IX, selecting matching Cr-Mo electrodes for weld joint strength.