Is A387 Grade 12 Class 2 a low-alloy or high-alloy steel?

A387 Grade 12 Class 2 is a chromium‑molybdenum alloy steel plate intended for welded pressure vessels that require enhanced strength and toughness at moderately elevated temperatures. It offers good resistance to creep and oxidation under heated service conditions and is commonly used in boilers, heat exchangers, and other pressure‑containing equipment operating above the typical range of carbon steels. Produced with controlled chemistry and heat treatment, it achieves a balanced combination of strength, ductility, and impact performance. Its favorable weldability allows it to be joined by standard welding methods while preserving structural integrity in high‑temperature environments.

Chemical Requirements for ASTM A387 Grade 12 Alloy Steel Plates

Tensile Requirements for ASTM A387 Grade 12 Alloy Steel Plates Class 2 Plates

processing

1. Heat Treatment (Core Process)

According to ASTM A387 standards, Grade 12 Class 2 must undergo specific heat treatments to achieve its mechanical properties:

Method: Typically Normalized and Tempered (N+T). Alternatively, if accelerated cooling is used (liquid quenching), it must still be followed by tempering.

Tempering Temperature: The minimum tempering temperature is 1150°F (620°C).

Purpose: This process refines the grain structure and eliminates internal stresses, ensuring the material can withstand temperatures up to approximately 550°C without significant creep deformation.

2. Welding Procedure

Due to the alloy content (Cr and Mo), this material is susceptible to cold cracking and requires careful welding management:

Preheating: Preheating the base metal is mandatory before welding. The specific temperature depends on the plate thickness and the welding method used.

Post-Weld Heat Treatment (PWHT): PWHT is generally required to relieve residual stresses in the weld zone and restore the toughness of the Heat Affected Zone (HAZ).

3. Mechanical Properties (Class 2)

Class 2 indicates a higher strength level compared to Class 1:

Tensile Strength: 450 to 585 MPa (65 to 85 ksi).

Yield Strength: Minimum 275 MPa (40 ksi).

Elongation: Minimum 18% to 22% (depending on gauge length).

4. Technical Specifications

Chemical Composition: Contains 0.80%–1.15% Chromium (for oxidation and corrosion resistance) and 0.45%–0.60% Molybdenum (for high-temperature strength).

Delivery Condition: Usually supplied in the N+T condition. Additional tests like HIC (Hydrogen Induced Cracking) or SSCC (Sulfide Stress Corrosion Cracking) may be required if used in sour service environments.

Key Advantages

High-Temperature Performance: It maintains mechanical stability and creep resistance at elevated temperatures, with an effective working range typically up to 575°C (1,070°F).

Corrosion and Oxidation Resistance: The addition of 1.25% Chromium provides excellent protection against scaling and oxidation, making it suitable for "sour service" (H2S-rich) environments in the oil and gas industry.

Superior Thermal Conductivity: Compared to higher chromium grades like Grade 11, Grade 12 conducts heat more efficiently, which is a critical advantage for heat exchangers where minimizing temperature gradients is necessary.

Enhanced Strength (Class 2): As a Class 2 material, it undergoes additional heat treatment (Quenching and Tempering) to achieve higher yield and tensile strength than Class 1, allowing for higher pressure ratings.

Cost Efficiency: It serves as a balanced solution for large-scale projects, offering reliable high-temperature service at a lower cost than premium grades like Grade 22 or 91.

Primary Applications

Oil & Gas and Petrochemical: Used extensively in the fabrication of reactors, separators, and storage tanks that handle corrosive media at elevated temperatures.

Power Generation: Essential for high-pressure components such as boiler drums, steam pipelines, and superheaters in thermal and nuclear power plants.

Heat Transfer Equipment: Its high thermal conductivity makes it ideal for shell-and-tube heat exchangers, condensers, and reheaters.

Industrial Infrastructure: Utilized for high-temperature ducting, pipe supports, valves, flanges, and fittings in various heavy industries including chemical processing and refineries.

Specialized Tanks: Employed in the construction of large metallic tanks and oxygen cylinders designed for high-pressure gas storage.

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If you have project requirements for A387 Grade 12 Class 2, we welcome your inquiry. GNEE maintains a large inventory of commonly used high strength steel grades for your selection.For detailed mechanical properties, chemical composition, and technical data, as well as free samples, please contact our factory immediately. We offer competitive prices, stable quality, and professional service. Email:beam@gneesteelgroup.com.

Is heat treatment necessary after welding? 

Yes, post-weld tempering at 620-670°C is essential to eliminate welding residual stress and restore the mechanical properties of the weld zone.

Can it be machined easily? 

It has moderate machinability. Sharp tools and proper cutting parameters are needed, and cooling lubricants should be used to reduce tool wear.

What is the recommended preheating temperature before forging?

The recommended preheating temperature is 815-870°C, which softens the material and reduces deformation resistance during forging.

What is the delivery condition of A387 Grade 12 Class 2? 

It is usually delivered in normalized and tempered condition, ensuring stable mechanical properties and meeting industrial application requirements.

Can it be used in nuclear power plants?

It is not commonly used in core areas of nuclear power plants but can be used in auxiliary high-temperature and high-pressure pipelines and equipment.

 What is the impact toughness of this steel at room temperature? 

Its Charpy V-notch impact toughness is above 35 J at room temperature, ensuring good anti-impact performance in normal working conditions.

What is the elongation rate of this steel?

Its minimum elongation rate is 20% in the longitudinal direction, ensuring good ductility and avoiding brittle fracture under external forces.

Is it suitable for making pressure vessel shells? 

Yes, it is widely used for pressure vessel shells in petrochemical plants, as it can withstand high internal pressure and stable high temperatures.

What is the hardness of A387 Grade 12 Class 2 after heat treatment? 

After normalizing and tempering, its Brinell hardness is about 187-229 HB, balancing hardness and toughness for industrial applications.

What welding methods are suitable for this alloy steel? 

Common methods include shielded metal arc welding, gas tungsten arc welding and submerged arc welding, adapting to different welding scenarios and quality requirements.

Is heat treatment necessary after welding? 

Yes, post-weld tempering at 620-670°C is essential to eliminate welding residual stress and restore the mechanical properties of the weld zone.

Can it be machined easily? 

It has moderate machinability. Sharp tools and proper cutting parameters are needed, and cooling lubricants should be used to reduce tool wear.