ASME SA387 Grade 11 Class 1 is a premium chromium-molybdenum alloy steel plate engineered specifically for use in boilers, pressure vessels, and heat exchangers operating at elevated temperatures.
ASME SA387 Grade 11 Class 1
In the boiler manufacturing industry, it is recognized for its balance of high-temperature strength, oxidation resistance, and excellent weldability.
Chemical Composition of ASME SA387 Grade 11 Class 1
The addition of Chromium (Cr) and Molybdenum (Mo) provides the necessary resistance to creep and hydrogen attack.
| Element | Composition (%) |
| Chromium (Cr) | 1.00 – 1.50 |
| Molybdenum (Mo) | 0.44 – 0.65 |
| Carbon (C) Max | 0.05 – 0.17 |
| Manganese (Mn) | 0.40 – 0.65 |
| Silicon (Si) | 0.50 – 0.80 |
| Phosphorus (P) Max | 0.035 |
| Sulfur (S) Max | 0.035 |
For high-end boiler applications, P and S levels are often restricted to lower levels (e.g., P ≤ 0.010%) to prevent temper embrittlement.
Mechanical Properties of ASME SA387 Grade 11 Class 1
Class 1 plates are characterized by lower tensile strength but higher ductility compared to Class 2, making them ideal for complex forming operations in boiler shops.
| Property | Value (Metric Units) | Value (Imperial Units) |
| Tensile Strength | 515 – 690 MPa | 75 – 100 ksi |
| Yield Strength (Min) | 310 MPa | 45 ksi |
| Elongation in 50mm (Min) | 22% | 22% |
| Reduction of Area (Min) | 45% (for heavy plates) | 45% |
Advantages for Boiler Manufacturers Of SA387
A. High-Temperature Creep Resistance
Boiler components operate under constant pressure at temperatures often exceeding 400°C (750°F). While carbon steel suffers from "creep" (slow permanent deformation), the Molybdenum in Grade 11 locks the crystalline structure, ensuring dimensional stability and preventing long-term structural failure.
B. Superior Weldability and Fabrication
The lower hardness of Class 1 (compared to Class 2) reduces the risk of cold cracking during the welding of thick-walled boiler drums.
Weldability: Compatible with standard SMAW, SAW, and GTAW processes.
Formability: Highly suitable for the rolling of shells and the deep drawing of dished ends.
C. Post-Weld Heat Treatment (PWHT) Stability
Grade 11 Class 1 maintains its mechanical integrity after the mandatory PWHT cycles required by ASME Section I or Section VIII codes. It is designed to withstand typical soaking temperatures of 620°C to 700°C without significant loss of yield strength.
Comparative Analysis of SA387
For a boiler plant, choosing the right class is a trade-off between design pressure and ease of manufacturing.
| Feature | Class 1 | Class 2 |
| Tensile Strength | Lower (Max 690 MPa) | Higher (Max 725 MPa) |
| Ductility/Toughness | Superior | Moderate |
| Welding Risk | Lower (Less prone to cracking) | Higher (Requires stricter pre-heat) |
| Typical Use | Complex geometries, thick headers | High-pressure shells, thinner walls |
Applications in Boiler Systems
Steam Drums: The primary pressure-retaining component for water/steam separation.
Superheater Headers: Distribution manifolds for high-temperature steam.
Boiler End Caps (Dished Ends): Components requiring significant cold or hot forming.
Main Steam Piping Flanges: Connections exposed to constant thermal cycling.
To ensure compliance for boiler projects, plates must be delivered with the following:
MTC (Material Test Certificate): According to EN 10204 3.1 or 3.2.
Heat Treatment: Usually supplied in Normalized and Tempered (N+T) condition.
Testing Standards:
Ultrasonic Testing (UT): Per ASTM A435 or A578 to ensure internal soundness.
Charpy V-Notch Impact Test: To verify low-temperature toughness and resistance to brittle fracture.
Simulated PWHT: Test coupons subjected to the customer's specific heat treatment cycle to verify final properties.
ASME SA387 Grade 11 Class 1 provides the optimal safety margin for high-temperature boiler construction. By choosing Class 1, manufacturers benefit from a material that is not only resistant to creep and steam oxidation but also significantly reduces the risk of rework during welding and forming.
This grade ensures a design life of 20+ years in the most demanding thermal environments, fully compliant with ASME BPVC Section II Part A requirements.
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What is SA 387 GR 12 material?
Engineered for use in elevated temperature service, ASME SA387 Grade 12 is a chrome molybdenum carbon alloy steel for use in weldable pressure vessels and industrial boilers.
What is the difference between A387 GR 11 and A387 GR 22?
Grade 11: Contains approximately 1% chromium and 0.5% molybdenum. Grade 22: Contains about 2.25% molybdenum and 1% chromium. This higher molybdenum content enhances its strength and resistance to high temperatures.
Is SA 387 low alloy steel?
ASTM A387, ASME SA 387, is one of our most popular products. It is a Low Alloy sSteel pressure vessel quality steel for high temperatures. We have a wide range of plate sizes available and Thickness range from 6 - 100mm.
What is SA 387 GR 11 Cl 2 equivalent material?
Sa 387 Gr 11 Equivalent Material is the ASME SA387 in the US markets with the European Union having modules in 13CrMoSi5-5 grade. The Sa 387 Gr 11 Cl 2 Equivalent Material is the SA387-11-2 of the ASME and ASTM standard.
What is the temperature range for SA 387 GR 11?
In the lower end of the temperature range SA 387 Gr 11 (1150 °F min tempering temperature) , and SA 387 Gr 22 (1250 °F min tempering temperature) are used. These grades can be specified in either class 1 or 2 and can also be provided in the Normalized & Tempered or Quenched and Tempered.