SA387 Grade 11 Class 1 is a chromium-molybdenum alloy steel plate for high-temperature pressure vessels, offering good strength and corrosion resistance, particularly for oil/gas/petrochemical uses with sour gas; it has lower tensile strength than Class 2 (60-85 ksi) and a specific composition with ~1.25% Cr and ~0.5% Mo, designed for elevated service conditions.
Key Characteristics:
Type: Chromium-Molybdenum Alloy Steel Plate.
Application: Welded boilers, pressure vessels, high-temperature equipment, especially in oil, gas, and petrochemical industries.
Properties: Excellent strength, heat resistance, and resistance to corrosion/oxidation, particularly from sour gas (H2S).
Composition (Approx.): ~1.25% Chromium (Cr), ~0.5% Molybdenum (Mo).
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 |
processing workflow
1. Heat Treatment (Most Critical Step)
Class 1 material is processed to achieve specific mechanical properties (lower strength but higher ductility compared to Class 2).
Normalizing: The plates are heated to an austenitizing temperature (typically 1650°F - 1750°F / 900°C - 955°C) and cooled in air.
Tempering: Following normalizing, the steel must be tempered at a minimum temperature of 1150°F (620°C) to refine the microstructure and relieve internal stresses.
Annealing: Alternatively, the material can be fully annealed to achieve maximum softness for complex forming.
2. Cutting and Forming
Thermal Cutting: Can be cut using oxy-fuel or plasma. Due to the chromium content, the heat-affected zone (HAZ) can harden; therefore, preheating the plate before cutting is often recommended to prevent edge cracking.
Cold Forming: Suitable for minor bending. However, because it is an alloy steel, spring-back is more pronounced than in carbon steel.
Hot Forming: Usually performed between 1650°F and 1900°F (900°C - 1040°C). If hot forming is performed, the material generally requires a complete re-heat treatment (Normalizing & Tempering) to restore its certified properties.
3. Welding Requirements
SA387 Gr. 11 is classified as P-Number 4 material under ASME Section IX.
Preheating: Essential to prevent hydrogen-induced cracking. Preheating temperatures typically range from 300°F to 500°F (150°C - 260°C) depending on thickness.
Post-Weld Heat Treatment (PWHT): This is mandatory for most pressure vessel applications. The typical PWHT range is 1200°F to 1300°F (650°C - 705°C) to ensure weld ductililty and stress relief.
4. Machining
Characteristics: The alloy's toughness makes it slightly more difficult to machine than standard carbon steel.
Tooling: High-speed steel (HSS) or carbide tools are recommended with consistent coolant flow to prevent work hardening.
5. Quality Inspection (Testing)
After processing, the material must be verified through:
Mechanical Testing: Confirming Tensile Strength (60–85 ksi) and Yield Strength (min 35 ksi).
Nondestructive Examination (NDE): Utilizing Ultrasonic Testing (UT) per SA435 or SA578 to ensure internal soundness.
Charpy V-Notch Impact Test: Conducted if low-temperature toughness is required by the specific project code.
Primary Industrial Applications
Due to its chromium-molybdenum (Cr-Mo) composition, this steel grade is widely utilized in the following sectors:
Oil and Gas & Petrochemicals:
Pressure Vessels: Used as a primary material for vessel shells and heads in refineries.
Sour Gas Service: Its resistance to hydrogen sulfide (𝐻2𝑆) makes it essential for handling "sour" oil and gas media.
Reactors & Storage Tanks: Fabrication of high-temperature chemical reactors and tanks for hot media.
Power Generation:
Industrial Boilers: Used in the construction of welded boilers and steam drums.
Heat Exchangers: Preferred for condenser tubes and heat exchanger shells due to thermal stability.
Nuclear & Thermal Plants: Employed in auxiliary systems and high-temperature ducting.
Chemical Processing:
Piping Systems: Used for high-temperature steam and gas piping.
Valves & Flanges: Manufacturing of forged components like flanges, valves, and pipe clamps.
Request a professional quotation for SA387 Grade 11 Class 1 from GNEE Steel.
What is SA387 Grade 11 Class 1?
It is a low-alloy steel plate for pressure vessels, mainly composed of carbon and chromium. It has good high-temperature strength and corrosion resistance, widely used in petrochemical equipment.
What is the main chemical composition of this steel grade?
The key components are about 0.15-0.20% C, 0.80-1.10% Cr, with small amounts of Mn, Si, P and S, ensuring its mechanical and high-temperature properties.
What is the maximum service temperature of SA387 Grade 11 Class 1?
Its maximum continuous service temperature is around 593°C (1100°F). Beyond this, its strength and structural stability will decrease significantly.
Which industry is this steel grade most commonly used in?
It is widely applied in the petrochemical, refinery and power generation industries, especially for pressure vessels, boilers and heat exchangers.
What is the tensile strength range of SA387 Grade 11 Class 1?
Its tensile strength is typically between 415-585 MPa. This range ensures it can withstand high pressure in harsh working environments.
How to improve the weldability of this steel grade?
Preheating to 150-200°C before welding and post-weld heat treatment (PWHT) can reduce welding stress and prevent cold cracks, enhancing weldability.
What is the minimum yield strength of SA387 Grade 11 Class 1?
The minimum yield strength is 205 MPa. This index reflects its ability to resist plastic deformation under load, critical for pressure-bearing parts.
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.