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

SA 387 Grade 5 Class 2 is a chromium-molybdenum alloy steel plate specified in the ASME Boiler and Pressure Vessel Code. It is primarily used for welded pressure vessels and boiler components operating at elevated temperatures. This material offers good strength, creep resistance, and oxidation resistance, making it suitable for refineries, petrochemical plants, and power generation applications. Its chemical composition and mechanical properties are tightly controlled to ensure reliability under high-temperature and high-pressure conditions.

Equivalents

Specifications ASME SA387 Grade 5 Alloy Steel Plates

Tensile Requirements for ASME SA387 Grade 5 Alloy Steel Plates Class 2 Plates

Chemical Requirements for ASME SA387 Grade 5 Alloy Steel Plates

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.

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What is SA 387 Grade 5 Class 2?

SA 387 Grade 5 Class 2 is a chromium-molybdenum alloy steel plate specified in the ASME Boiler and Pressure Vessel Code. It is primarily used for welded pressure vessels and boiler components operating at elevated temperatures. This material offers good strength, creep resistance, and oxidation resistance, making it suitable for refineries, petrochemical plants, and power generation applications. Its chemical composition and mechanical properties are tightly controlled to ensure reliability under high-temperature and high-pressure conditions.

What standards cover SA 387 Grade 5 Class 2?

SA 387 Grade 5 Class 2 is covered by ASME SA-387, which is part of the ASME Boiler and Pressure Vessel Code, Section II, Part A. This standard defines requirements for chromium-molybdenum steel plates used in pressure vessels. It specifies chemical composition, mechanical properties, heat treatment, and testing methods. Compliance with SA-387 ensures that the material meets the necessary safety and performance criteria for high-temperature service in critical applications.

How does SA 387 Grade 5 Class 2 differ from Grade 5 Class 1?

SA 387 Grade 5 Class 1 and Class 2 have similar chemical compositions but differ in mechanical property requirements. Class 2 has higher specified minimum yield and tensile strength compared to Class 1. Class 2 also undergoes more stringent heat treatment and testing to achieve better strength and toughness. As a result, Class 2 is preferred for more demanding applications where higher strength at elevated temperatures is required.

What welding processes are commonly used for SA 387 Grade 5 Class 2?

Common welding processes for SA 387 Grade 5 Class 2 include SMAW, GTAW, GMAW, and SAW. The choice depends on joint design, thickness, and production needs. Low-hydrogen electrodes and fluxes are preferred to minimize cracking risk. Proper procedure qualification and welder certification are essential to ensure reliable welds. Each process has specific advantages, such as GTAW for root passes and SAW for high-deposition filling in thick plates.

What are the typical forms and dimensions of SA 387 Grade 5 Class 2?

SA 387 Grade 5 Class 2 is primarily produced as steel plates in various thicknesses and widths, as specified by ASME SA-387. Plates can range from thin sheets to several inches thick, depending on the application. The material may also be available as forgings or castings for specialized components. Dimensions and tolerances are controlled to meet pressure vessel fabrication and design code requirements.

How does SA 387 Grade 5 Class 2 compare to carbon steel plates like SA 516?

Compared to carbon steel plates such as SA 516, SA 387 Grade 5 Class 2 offers higher strength and better creep resistance at elevated temperatures due to its chromium-molybdenum alloying. SA 516 is more suitable for lower-temperature pressure vessel applications, while SA 387 Grade 5 Class 2 is preferred for high-temperature service in refineries and power plants. The alloy steel also requires more stringent welding and heat treatment procedures.

What is the equivalent material of SA 387 Grade 5 Class 2 in other standards?

SA 387 Grade 5 Class 2 is equivalent to ASTM A387 Grade 5 Class 2. In European standards, it may be comparable to certain Cr-Mo steel grades, although exact equivalents depend on chemical and mechanical property requirements. When selecting equivalent materials, it is important to verify compliance with the relevant design code and application needs to ensure compatibility in strength, toughness, and weldability.

What is the typical chemical composition of SA 387 Grade 5 Class 2?

SA 387 Grade 5 Class 2 generally contains chromium and molybdenum as key alloying elements, along with carbon, manganese, silicon, sulfur, and phosphorus. Chromium provides oxidation and corrosion resistance, while molybdenum enhances high-temperature strength and creep resistance. Carbon is controlled to maintain weldability and toughness. Trace elements are limited to prevent embrittlement and ensure consistent mechanical properties across different product forms.

What are the key mechanical properties of SA 387 Grade 5 Class 2?

SA 387 Grade 5 Class 2 typically has specified minimum yield and tensile strength, along with good elongation and reduction of area. It also exhibits reasonable impact toughness, especially after proper heat treatment. These properties make it suitable for pressure vessels and boiler components subjected to high temperatures and moderate to high pressures. The material maintains its strength and ductility under long-term thermal exposure, ensuring reliable performance.