In what applications is SA 387 Grade 5 Class 2 commonly used?

SA 387 Grade 5 Class 2 is a chromium-molybdenum alloy steel plate specified under the ASME SA 387 standard, widely used in the fabrication of pressure vessels and boiler components that operate at elevated temperatures. With its nominal chromium content providing enhanced oxidation resistance and molybdenum contributing to improved creep strength and thermal stability, Grade 5 Class 2 is particularly suitable for service conditions where materials must withstand prolonged exposure to high heat and pressure. The steel is typically supplied in the normalized and tempered condition, ensuring a good combination of toughness, strength, and weldability. Its consistent mechanical properties and heat-resistant characteristics make it a preferred choice in industries such as oil and gas, petrochemical, and power generation.

specification

Chemical Composition

Equivalent Grades

processing

1. Primary Manufacturing

Hot-Rolling: The plates are primarily manufactured through hot-rolling (HR), where steel slabs are heated and passed through rollers to achieve thicknesses typically ranging from 5mm to 150mm.

Cold-Rolling: Some sheets are cold-rolled (CR) to achieve tighter dimensional tolerances and a smoother surface finish for specific industrial applications.

2. Critical Heat Treatment

To reach Class 2 strength levels-which are significantly higher than Class 1-the material must undergo specific thermal processing:

Normalizing & Tempering (N+T): The plate is heated above its critical temperature and cooled in still air to refine grain structure.

Quenching & Tempering (Q+T): When specified, liquid quenching (accelerated cooling) is used before tempering to maximize hardness and tensile strength.

Minimum Tempering Temperature: Grade 5 requires a minimum tempering temperature of 1300°F (705°C) to ensure structural stability at high operating temperatures.

3. Fabrication Processes

Precision Cutting: Suppliers utilize computer-controlled plasma cutting, laser, or waterjet methods to meet exact client dimensions.

Forming: Despite its high strength, the alloy has good formability, allowing it to be bent or shaped into vessel shells and heads.

Welding: It is designed for high weldability using TIG, MIG, and SMAW methods. Preheating and post-weld heat treatment (PWHT) are standard to prevent cracking and relieve internal stresses.

4. Specialized Testing 

Processed plates undergo rigorous inspection to verify integrity:

Non-Destructive Testing (NDT): Ultrasonic Examination (UT) for internal flaws and Magnetic Particle Examination (MPI) for surface cracks.

Mechanical Verification: Includes high-temperature tension tests and Charpy V-Notch impact testing, often conducted at temperatures as low as -52°C.

Key Advantages

High Tensile Strength: Class 2 offers superior mechanical properties compared to Class 1, with a tensile range of 515–690 MPa and a minimum yield strength of 310 MPa, ensuring structural stability under high pressure.

Thermal Stability & Creep Resistance: The addition of molybdenum allows the steel to maintain its strength at temperatures up to and exceeding 1300°F (705°C), resisting deformation (creep) over long service lives.

Enhanced Corrosion and Oxidation Resistance: The high chromium levels protect the material against aggressive oxidation and various forms of corrosion, including pitting and stress-corrosion cracking.

Excellent Weldability: Despite its high alloy content, it can be welded using standard methods (TIG, MIG, SMAW), provided proper preheating and post-weld heat treatment (PWHT) are applied.

Cost-Effectiveness: Its durability and resistance to harsh environments reduce the frequency of maintenance and replacements, offering lower long-term operational costs.

Primary Applications

Oil & Gas Industry: Used in refineries for hydrocracking units, catalytic reformers, and pipelines, particularly those in "sour service" (high H2S) environments.

Petrochemical Processing: Essential for the construction of high-pressure vessels, heat exchangers, and storage tanks for volatile chemicals.

Power Generation: Widely used for boiler drums, steam generators, and specialized piping in both fossil fuel and nuclear power plants.

Chemical & Fertilizer Production: Used for reactors such as ammonia and urea synthesis towers that operate under extreme heat and corrosive conditions.

Heavy Machinery & Industrial Equipment: Found in high-temperature ducting, flanges, and structural components for manufacturing and defense applications.

Contact now

If you have project requirements for SA 387 Grade 5 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.

What is the role of molybdenum in SA 387 Grade 5 Class 2?

Molybdenum is a key alloying element in SA 387 Grade 5 Class 2, significantly enhancing high-temperature strength and creep resistance. It stabilizes the microstructure and prevents softening under prolonged heat exposure. Molybdenum also improves resistance to temper embrittlement, which is important for long-term service in refineries and petrochemical plants. Its controlled addition ensures a good balance of mechanical properties and weldability.

What are the storage and handling recommendations for SA 387 Grade 5 Class 2 plates?

SA 387 Grade 5 Class 2 plates should be stored in a dry, covered area to prevent moisture absorption and surface corrosion. They should be separated from other materials to avoid contamination. Plates must be handled carefully to prevent scratches, gouges, or distortion, especially for thin plates. Proper lifting equipment and procedures are necessary to maintain plate flatness and surface quality before fabrication.

What are the testing requirements for SA 387 Grade 5 Class 2 plates?

SA 387 Grade 5 Class 2 plates undergo tensile, bend, impact, and ultrasonic tests. Tensile tests verify strength properties, while bend tests assess ductility. Impact tests evaluate toughness and resistance to brittle fracture. Ultrasonic testing detects internal defects. Additional tests such as hardness and chemical analysis may be performed to ensure compliance with standards. These tests help guarantee the material's quality and reliability for critical applications.

What is the hardness range of SA 387 Grade 5 Class 2?

The hardness of SA 387 Grade 5 Class 2 is typically between 170 and 220 HB after proper heat treatment. This range provides a good balance of strength and toughness, suitable for high-temperature pressure vessel service. Hardness testing is done on base material and welds to check for excessive hardening in the heat-affected zone, which could indicate potential cracking issues.

How does SA 387 Grade 5 Class 2 perform in terms of creep resistance?

SA 387 Grade 5 Class 2 has good creep resistance at elevated temperatures due to its chromium and molybdenum content. These elements stabilize the microstructure and reduce deformation under long-term stress and heat. The material is used in components where creep must be minimized, such as steam headers and high-temperature pressure vessels. Proper heat treatment and design are necessary to ensure reliable creep performance over the service life.

Can SA 387 Grade 5 Class 2 be used in low-temperature applications?

SA 387 Grade 5 Class 2 is primarily intended for high-temperature service and may not be ideal for low-temperature use where high toughness is needed. Its impact resistance can decrease at low temperatures, increasing brittle fracture risk. For cryogenic or low-temperature service, materials like SA 516 Grade 70 or nickel-alloyed steels are more suitable. The design temperature range must be carefully evaluated for code compliance.

What is the fatigue resistance of SA 387 Grade 5 Class 2?

SA 387 Grade 5 Class 2 has acceptable fatigue resistance for many pressure vessel and boiler applications when properly designed and fabricated. Fatigue performance depends on stress level, temperature, surface finish, and weld quality. Welded joints can reduce fatigue life due to stress concentrations and residual stresses. Proper welding, post-weld heat treatment, and quality control are essential to maximize fatigue resistance under cyclic loading.

What surface preparation is required before welding SA 387 Grade 5 Class 2?

Before welding, the surface of SA 387 Grade 5 Class 2 plates must be cleaned to remove oil, grease, rust, mill scale, and other contaminants. Mechanical methods such as grinding, blasting, or wire brushing are commonly used. Joint edges should be prepared to the specified bevel angle and root opening to ensure proper fusion. A clean surface and correct joint geometry are essential for high-quality welds with good mechanical properties.

What is the role of chromium in SA 387 Grade 5 Class 2?

Chromium in SA 387 Grade 5 Class 2 provides oxidation resistance and increases hardenability. It forms a protective oxide layer on the surface, reducing material loss at high temperatures. Chromium also contributes to strength and corrosion resistance in certain environments. The combination of chromium and molybdenum gives the material its ability to perform well under prolonged heat and mechanical stress in pressure vessel applications.