ASTM A387 Grade 12 Class 2 chrome moly steel plate

A387 Grade 12 Class 2 is a type of alloy steel plate designed for use in welded pressure vessels where improved toughness and strength at moderately elevated temperatures are required. It belongs to the chromium-molybdenum steel family, which provides good resistance to creep and oxidation under service conditions involving heat. This grade is suitable for applications in boilers, heat exchangers, and other pressure-containing equipment operating at temperatures higher than those typically handled by carbon steel plates. The steel is produced with specific chemical compositions and heat treatment procedures to achieve the desired combination of strength, ductility, and impact properties. Its weldability is an important characteristic, allowing it to be joined using common welding processes while maintaining structural integrity in high-temperature service environments.

Equivalents

Specifications

Tensile Requirements for Class 2 Plates

Chemical Requirements

Primary Manufacturing & Heat Treatment

The material is a chrome-molybdenum alloy steel, and its processing is defined by the following key stages:

Steel Making: The steel must be "killed" (deoxidized) to ensure a uniform chemical structure.

Rolling: Plates are typically produced via Hot-Rolling (HR).

Heat Treatment: This is the critical stage that distinguishes Class 2 from Class 1. For Grade 12 Class 2, the standard processing includes:

Annealing: Slow cooling to improve ductility.

Normalizing & Tempering: Heating to a specific temperature and air cooling (normalizing), followed by reheating to at least 1150°F (620°C) (tempering) to achieve the required strength.

Accelerated Cooling: Liquid or blast quenching from the austenitizing temperature is permitted if agreed upon by the buyer, provided it is followed by tempering.

Essential Testing Procedures

After manufacturing, A387 Grade 12 Class 2 plates undergo rigorous Destructive and Non-Destructive Testing (NDT) to verify mechanical properties:

Mechanical Testing: Tensile strength (required: 450–585 MPa) and yield strength (min: 275 MPa).

Impact Analysis: Often tested at low temperatures (e.g., -52°C) via Charpy V-Notch tests.

Non-Destructive Tests: Includes Ultrasonic testing, Radiography (X-ray), and Hydrostatic analysis to ensure no internal defects.

Spectro Analysis: Confirms the Chemical Composition meets the 0.80–1.15% Chromium and 0.45–0.60% Molybdenum standards.

Secondary Processing

The steel is highly versatile for further fabrication:

Cutting & Shaping: Plates can be supplied as custom cut-to-size shapes or beveled for welding.

Welding: It is designed for Weldable Pressure Vessels, offering good weldability even in "sour service" (corrosive) environments.

Formability: The material supports cold or hot forming for the construction of reactors, separators, and storage tanks.

applications

Pressure vessels: Used in a wide range of industrial pressure vessels that operate at elevated temperatures, where reliable strength and resistance to creep are essential for long‑term service.

Boilers and boiler components: Applied in boiler drums, headers, and other structural parts that must withstand high heat and internal pressure while maintaining structural integrity.

Heat exchangers: Utilized in shell‑and‑tube and other heat exchanger designs, where good thermal conductivity and stability under cyclic heating are required.

Oil and gas processing equipment: Found in upstream and downstream oil and gas facilities, including separators, reactors, and process vessels exposed to moderate to high temperatures.

Refinery vessels and piping systems: Used in refinery columns, tanks, and associated piping that handle hot fluids and require resistance to oxidation and thermal stress.

Petrochemical plant equipment: Applied in reactors, distillation units, and other process equipment involved in the production and treatment of chemicals at elevated temperatures.

Power generation systems: Utilized in power plant boilers, steam generators, and auxiliary equipment that operate under continuous high‑temperature conditions.

Components operating at elevated temperatures: Selected for various high‑temperature service parts where carbon steel may lack sufficient strength or creep resistance.

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What material is A387 Grade 12 Class 2?

It is a chromium-molybdenum alloy steel, mainly composed of Fe, Cr (1.00-1.50%) and Mo (0.45-0.65%), with excellent high-temperature strength and corrosion resistance.

What is the minimum tensile strength of A387 Grade 12 Class 2?

Its minimum tensile strength is 485 MPa, and the minimum yield strength is 260 MPa, meeting the requirements of high-pressure and high-temperature working environments.

 What is the maximum service temperature of this alloy steel? 

It can work stably at a maximum service temperature of 593°C, making it suitable for high-temperature equipment in petrochemical and power industries.

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

It belongs to low-alloy steel. The total content of alloying elements (Cr, Mo) is less than 5%, balancing cost and performance effectively.

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

After normalizing and tempering, its microstructure is fine pearlite and ferrite, which enhances its toughness and creep resistance.

Can A387 Grade 12 Class 2 be welded? 

Yes, it is weldable, but preheating (150-200°C) and post-weld heat treatment are required to avoid cold cracks and improve joint toughness.

What welding methods are suitable for this alloy steel? 

Common methods include shielded metal arc welding, gas tungsten arc welding and submerged arc welding, which adapt 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.