ASME SA 387 Grade 5 Class 2 is a high-strength chromium-molybdenum alloy steel plate specifically engineered for use in weldable pressure vessels and industrial boilers operating at elevated temperatures. With a significant chromium content (4% to 6%) for enhanced corrosion and oxidation resistance, and molybdenum (0.45% to 0.65%) for superior creep strength, Class 2 plates are heat-treated to achieve higher tensile and yield properties than Class 1. This material is indispensable in the petrochemical, oil and gas, and power generation industries, where it is used to fabricate critical equipment like heat exchangers, reactors, and high-pressure storage tanks that must maintain structural integrity under extreme thermal and corrosive conditions.
Chemical Composition
| Element | Melt Analysis (%) | Product Analysis (%) | Standard Limit | Test Method | Role | Keywords |
| Carbon (C) | 0.05-0.15 | 0.04-0.16 | 0.15 max | ASME SA-350 | Strength without brittleness | SA387 Gr 5 Cl 2 carbon |
| Manganese (Mn) | 0.30-0.60 | 0.27-0.66 | 0.30-0.60 | ASME SA-350 | Toughness, hardenability | SA387 Gr 5 Cl 2 manganese |
| Phosphorus (P) | ≤0.025 | ≤0.025 | 0.025 max | ASME SA-350 | Reduces brittleness | SA387 Gr 5 Cl 2 phosphorus |
| Sulfur (S) | ≤0.025 | ≤0.025 | 0.025 max | ASME SA-350 | Improves weldability | SA387 Gr 5 Cl 2 sulfur |
| Silicon (Si) | 0.50-0.80 | 0.44-0.86 | 0.50-0.80 | ASME SA-350 | Deoxidation, fluidity | SA387 Gr 5 Cl 2 silicon |
| Chromium (Cr) | 4.00-6.00 | 3.90-6.10 | 4.00-6.00 | ASME SA-350 | Corrosion resistance | SA387 Gr 5 Cl 2 chromium |
| Molybdenum (Mo) | 0.45-0.65 | 0.40-0.70 | 0.45-0.65 | ASME SA-350 | Creep resistance | SA387 Gr 5 Cl 2 molybdenum |
Mechanical Properties
| Property | Value | Test Method | Temperature (°C) | Thickness Effect | Keywords |
| Tensile Strength | 515-690 MPa | ASME SA-370 | Ambient | -5% >100mm | SA387 Gr 5 Cl 2 tensile |
| Yield Strength | 310 MPa (min) | ASME SA-370 | Ambient | Stable to 100mm | SA387 Gr 5 Cl 2 yield |
| Elongation | 18% (min) | ASME SA-370 | Ambient | 16-20% (6-25mm) | SA387 Gr 5 Cl 2 elongation |
| Impact Energy | 27J typical | ASME SA-23 | Ambient | All thicknesses | SA387 Gr 5 Cl 2 impact |
| Modulus of Elasticity | 200 GPa | ASME SA-111 | Ambient | Constant | SA387 Gr 5 Cl 2 modulus |
| Fatigue Limit | 220 MPa (est.) | ASME SA-466 | Ambient | Varies with surface | SA387 Gr 5 Cl 2 fatigue |
Tolerances
| Factor | Value/Condition | Standard | Recommended | Keywords |
| Thickness Tolerance (<40mm) | ±1.5mm | ASME SA-20 | 6-40mm | SA387 Gr 5 Cl 2 tolerance |
| Flatness | 3mm per meter | ASME SA-20 | All | SA387 Gr 5 Cl 2 flatness |
Primary Energy and Processing Sectors
Petrochemical and Refining: Extensively used in oil refineries and petrochemical plants to construct machinery and vessels that handle corrosive fluids and gases. They are foundational for:
Reactors and Distillation Columns: Components that must withstand high heat and potential hydrogen attack.
Heat Exchangers: Facilitating critical thermal management in volatile chemical processes.
Power Generation: Essential for fossil fuel and nuclear power facilities, particularly in high-thermal zones:
Industrial Boilers and Boiler Drums: Withstanding continuous steam pressure and elevated operating temperatures.
Steam Generators: Used in systems where material strength must remain stable under long-term heat exposure.
Oil and Gas Production: Utilized in upstream and midstream operations for equipment like separation tanks and high-pressure storage vessels.
Specialized Industrial Equipment
High-Pressure Components: Fabrication of specialized industrial hardware, including:
Flanges, Fittings, and Valves: Designed to match the temperature and pressure ratings of the primary piping system.
High-Temperature Ducting: For transporting extreme-heat exhaust or process gases.
Manufacturing and Infrastructure:
Pulp and Paper Industry: Machinery for chemical processing and freshwater environments where moderate corrosion resistance is required.
Heavy Machinery: Liners for chutes, tubs, and bins, as well as wear liners for truck bodies in abrasive environments.
Aerospace and Defense: Specialized components requiring high-strength-to-weight ratios at elevated temperatures.
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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 carbon equivalent of SA 387 Grade 5 Class 2?
The carbon equivalent of SA 387 Grade 5 Class 2 is typically moderate, reflecting a balance between strength and weldability. Carbon equivalent calculations help assess hardenability and welding cracking susceptibility. A moderate carbon equivalent indicates that preheating and post-weld heat treatment are necessary, especially for thicker sections, to prevent cold cracking and ensure sound welds in critical applications.
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 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 are common defects in SA 387 Grade 5 Class 2 welds and how to prevent them?
Common defects in SA 387 Grade 5 Class 2 welds include porosity, slag inclusions, incomplete fusion, and cracking. Porosity and slag can be minimized by proper cleaning and correct welding parameters. Incomplete fusion requires adequate joint preparation and heat input. Cracking, especially cold cracking, can be prevented by preheating, using low-hydrogen consumables, and applying post-weld heat treatment. Regular inspection helps detect and address defects early.
What non-destructive testing methods are used for SA 387 Grade 5 Class 2 welds?
Non-destructive testing methods for SA 387 Grade 5 Class 2 welds include radiographic testing, ultrasonic testing, magnetic particle testing, and liquid penetrant testing. RT and UT detect internal defects, while MT and PT find surface and near-surface flaws. The selection of NDT methods depends on joint type, thickness, and code requirements. Proper NDT ensures the integrity of welds in critical pressure vessel applications.
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 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.
What are the quality control measures for SA 387 Grade 5 Class 2 production?
Quality control for SA 387 Grade 5 Class 2 production includes strict control of chemical composition, careful melting and refining, and precise heat treatment. Plates undergo tensile, bend, impact, and ultrasonic tests to ensure they meet ASME requirements. Welding procedures and personnel must be qualified, and NDT is performed on welds to detect defects. Comprehensive documentation, including material test reports, ensures traceability and compliance with standards.