SA 387 Gr. 11 Cl. 2 is a chromium-molybdenum alloy steel designed for high-temperature pressure vessels, offering good weldability, oxidation, and corrosion resistance due to its ~1.25% Chromium and ~0.50% Molybdenum content, making it ideal for oil, gas, and power generation industries. Class 2 indicates higher strength (75-100 ksi tensile) than Class 1, requiring normalization and tempering for enhanced performance in demanding elevated-temperature service.
Specifications for ASME SA387 Grade 11 Alloy Steel Plates
| Designation | Nominal Chromium Content (%) |
Nominal Molybdenum Content (%) |
| SA387 Grade 11 | 1.25% | 0.50% |
SA387 Grade 11 Chemical Composition
|
Grade |
Nominal Chromium Content, % |
Nominal Molybdenum Content, % |
|---|---|---|
|
11 |
1.25 |
0.50 |
|
22, 22L |
2.25 |
1.00 |
|
5 |
5.00 |
0.50 |
|
9 |
9.00 |
1.00 |
|
91 |
9.00 |
1.00 |
Applications
Oil & Gas:Widely used in upstream, midstream, and downstream operations, including petrochemical plants, sour gas processing facilities, offshore platforms, and onshore installations. It is suitable for equipment handling high-temperature hydrocarbons, hydrogen-rich fluids, and sour gas containing H2S. Common applications include reactors, separators, heat exchangers, and storage tanks for hot liquids and gases, where resistance to hydrogen attack and sulfidation is essential.
Power Generation:Used in both conventional and nuclear power plants for components that operate at elevated temperatures and pressures. Typical applications include boiler membranes, headers, pressure vessels, and high-temperature piping systems. Its good creep resistance and strength retention make it ideal for use in superheater and reheater sections, as well as in auxiliary equipment such as heat recovery steam generators (HRSGs).
Chemical Processing:Valued for its ability to withstand corrosive media and high-temperature process conditions. It is commonly used in pressure vessels, reactors, columns, and heat exchangers handling acids, hydrocarbons, and other aggressive chemicals. Its resistance to oxidation and hydrogen attack also makes it suitable for hydrogenation and reforming processes in chemical plants.
General Industrial Applications:Beyond the major sectors, SA 387 Gr.11 Cl.2 is used in a wide range of high-pressure and high-temperature industrial equipment. This includes high-pressure storage vessels, industrial boilers, waste heat recovery systems, heat exchangers, and pipelines transporting hot fluids such as steam, oil, and process gases. Its combination of strength, toughness, and weldability makes it a versatile choice for many demanding industrial applications.
Advantages
High-Temperature Performance: Excellent strength, creep, and oxidation resistance at elevated temperatures.
Corrosion Resistance: Enhanced resistance to corrosion, particularly important in sour gas environments.
Mechanical Strength: High tensile and yield strength, especially for Class 2 compared to Class 1.
Weldability & Toughness: Good forming ability, toughness, and weldability, with suitable post-weld heat treatment (PWHT).
Reliability: Meets stringent ASME/ASTM specifications, ensuring safety and performance in demanding conditions.
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What are the main alloying elements in SA 387 Grade 11 Class 2?
The key alloying elements are chromium (Cr) and molybdenum (Mo). Chromium improves oxidation resistance and high-temperature strength, while molybdenum enhances creep resistance and toughness. Other elements include carbon, manganese, silicon, phosphorus, and sulfur, with strict limits on impurities to ensure weldability and toughness.
What is the typical chemical composition range of SA 387 Grade 11 Class 2?
Typical ranges include: carbon 0.05–0.17%, manganese 0.40–0.65%, silicon 0.50–0.80%, chromium 1.00–1.50%, molybdenum 0.45–0.65%, phosphorus ≤ 0.035%, and sulfur ≤ 0.035%. These ranges are carefully controlled to balance strength, toughness, and weldability.
What is the minimum yield strength of SA 387 Grade 11 Class 2?
For plates up to 50 mm thick, the minimum yield strength is 310 MPa (45 ksi). For thicker plates, the yield strength may decrease slightly, but it remains sufficient for most high-temperature pressure vessel applications. The yield strength is a critical parameter for ensuring structural integrity under pressure.
What is the tensile strength range of SA 387 Grade 11 Class 2?
The tensile strength typically ranges from 515 to 690 MPa (75 to 100 ksi). This range ensures good load-bearing capacity while maintaining adequate ductility and toughness, even at elevated temperatures.
What preheat and PWHT temperatures are typical for SA 387 Grade 11 Class 2?
Preheat temperatures typically range from 200–300°C, depending on plate thickness and welding consumables. PWHT is usually performed at 620–680°C to relieve residual stresses and improve the toughness of the weld and heat-affected zone (HAZ).
What types of pressure vessels use SA 387 Grade 11 Class 2?
It is used in a variety of pressure vessels, including boilers, heat exchangers, reactors, reformers, and hydrogenation units. It is particularly suitable for equipment operating at high temperatures and pressures where creep resistance and hydrogen attack resistance are essential.
In which industries is SA 387 Grade 11 Class 2 commonly used?
It is widely used in the oil and gas industry, petrochemical plants, chemical processing facilities, and power generation plants. It is also found in refineries, where it is used for equipment handling high-temperature hydrocarbons and hydrogen-rich fluids.
What is the difference in chemical composition between SA 387 Grade 11 Class 2 and SA 387 Grade 22?
SA 387 Grade 11 Class 2 is a 1.25Cr-0.5Mo steel, while Grade 22 is a 2.25Cr-1Mo alloy. The higher chromium and molybdenum content in Grade 22 provides better high-temperature strength and creep resistance, making it suitable for higher service temperatures than Grade 11 Class 2.
How does the maximum service temperature of SA 387 Grade 11 Class 2 compare to that of SA 387 Grade 91?
SA 387 Grade 11 Class 2 is typically used up to around 500°C, whereas SA 387 Grade 91 can operate at temperatures up to approximately 600°C or higher. Grade 91's higher chromium content and advanced heat treatment give it superior creep strength at elevated temperatures compared to Grade 11 Class 2.