SA387 Grade 11 Class 1 is a chromium-molybdenum alloy steel plate specified under the ASME SA387 standard, primarily used for welded pressure vessels and boiler components that operate at elevated temperatures. It contains a nominal composition of around 1.00–1.50% chromium and 0.45–0.65% molybdenum, which provides good high-temperature strength, creep resistance, and oxidation resistance. Class 1 indicates the standard level of carbon content and mechanical properties, with a minimum tensile strength typically in the range of 60–80 ksi and a minimum yield strength of 30 ksi. This grade is commonly applied in refinery equipment, petrochemical reactors, heat exchangers, and power plant boilers where reliable performance under high pressure and temperature is required.
Equivalents
| BS | EN | ASTM/ASME | DIN |
| 621 B | ––– | SA387-11-1 | ––– |
Specifications for ASME SA387 Grade 11 Alloy Steel Plates
| Designation | Nominal Chromium Content (%) |
Nominal Molybdenum Content (%) |
| SA387 Grade 11 | 1.25% | 0.50% |
Tensile Requirements for ASME SA387 Grade 11 Alloy Steel Plates Class 1 Plates
| Designation: | Requirement: | Grade 11 |
| SA387 Grade 11 | Tensile strength, ksi [MPa] | 75 to 100 [515 to 690] |
| Yield strength, min, ksi [MPa]/(0.2% offset) | 43 [310] | |
| Elongation in 8 in. [200mm], min % | 18 | |
| Elongation in 2 in. [50mm], min, % | 22 | |
| Reduction of area, min % | ––– |
Chemical Requirements for ASME SA387 Grade 11 Alloy Steel Plates
| Element | Chemical Composition (%) | |
| SA387 Grade 11 | ||
| Carbon: | Heat Analysis: | 0.05 - 0.17 |
| Product Analysis: | 0.04 - 0.17 | |
| Manganese: | Heat Analysis: | 0.40 - 0.65 |
| Product Analysis: | 0.35 - 0.73 | |
| Phosphorus: | Heat Analysis: | 0.035 |
| Product Analysis: | 0.035 | |
| Sulphur (max): | Heat Analysis: | 0.035 |
| Product Analysis: | 0.035 | |
| Silicon: | Heat Analysis: | 0.50 - 0.80 |
| Product Analysis: | 0.44 - 0.86 | |
| Chromium: | Heat Analysis: | 1.00 - 1.50 |
| Product Analysis: | 0.94 - 1.56 | |
| Molybdenum: | Heat Analysis: | 0.45 - 0.65 |
| Product Analysis: | 0.45 - 0.70 |
Key Processing Aspects
Heat Treatment:
The material is supplied in specific conditions, often Normalized & Tempered (N&T) or Quenched & Tempered (Q&T).
Preheating:
Required for welding to prevent cracking, typically at temperatures around 1100°F (593°C) for Grade 11.
Post-Weld Heat Treatment (PWHT):
Mandatory for many applications, involving holding at specific temperatures (e.g., 1150°F min for Grade 11) for a set time based on thickness, followed by controlled cooling.
Controlled Cooling:
Essential after heat treatment, with specific rates to achieve desired microstructures and properties.
Key Applications
Oil & Gas:
Pressure vessels, storage tanks, reactors, and piping for processing and storing high-temperature liquids and gases.
Petrochemical Industry:
Equipment in refineries and chemical plants that operates under extreme thermal conditions.
Power Generation:
Components in thermal power plants, boilers, and steam piping systems.
Heat Exchangers:
Used where high temperatures and corrosive media are present.
Why It's Used
High-Temperature Service: Specifically designed for elevated temperature applications.
Corrosion Resistance: Chromium content provides excellent resistance to oxidation and sour gas environments.
Creep Resistance: Molybdenum enhances its ability to resist deformation under sustained stress at high temperatures.
Key Advantages:
High-Temperature Performance:
Excellent mechanical strength and stability at elevated temperatures and under high pressure.
Corrosion Resistance:
Chromium content provides superior resistance to oxidation and hydrogen attack, crucial for sour service (H₂S) environments.
Strength & Toughness:
Offers good tensile strength and toughness for reliable performance in stress-induced conditions.
Weldability & Fabricability:
Can be readily cut, formed, and welded using appropriate procedures, enabling complex designs.
Enhanced Safety & Durability:
Its properties reduce failure risk and extend service life in harsh conditions, leading to lower maintenance.
Cost-Effective:
Provides excellent long-term value and performance for demanding applications compared to less specialized materials.
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What is the impact toughness of SA387 Grade 11 Class 1?
Its Charpy V-notch impact energy is ≥27 J at room temperature, ensuring good toughness to resist sudden impact loads in service.
Is this steel grade used in nuclear power plants?
Rarely, as nuclear power requires stricter material standards. It is mainly used in conventional thermal power and petrochemical fields instead.
Is SA387 Grade 11 Class 1 magnetic?
Yes, it is magnetic. Due to its ferritic structure caused by chromium content, it exhibits magnetic properties, unlike austenitic stainless steels.
What standard does SA387 Grade 11 Class 1 comply with?
It complies with the ASTM A387 standard, which specifies requirements for low-alloy steel plates for pressure vessels in high-temperature service.
What is the difference between Class 1 and Class 2 of SA387 Grade 11?
Class 1 has lower carbon content and stricter impurity control than Class 2, offering better weldability and toughness, suitable for thicker components.
What is the heat treatment process before delivery?
Typical delivery heat treatment is normalizing + tempering. Normalizing refines grains, while tempering reduces brittleness and adjusts mechanical properties.
What is the microstructure of SA387 Grade 11 Class 1 after heat treatment?
After normalizing and tempering, its microstructure is tempered bainite or ferrite-pearlite, which provides good strength and toughness.
Can SA387 Grade 11 Class 1 be machined easily?
It has moderate machinability. Using high-speed steel or carbide tools with proper cutting parameters ensures smooth machining without excessive tool wear.
How does temperature affect the strength of this steel?
Strength decreases with increasing temperature. Below 593°C, it maintains stable strength; beyond that, the decline accelerates, affecting service safety.
What is the maximum carbon content allowed in this steel grade?
The maximum carbon content is 0.20%. Exceeding this will reduce weldability and toughness, increasing the risk of cracks during processing.
What are the alternatives to SA387 Grade 11 Class 1?
Alternatives include SA387 Grade 12 Class 1 (lower Cr content) and SA387 Grade 22 Class 1 (higher Cr-Mo content), chosen based on service conditions.