ASTM A387 / ASME SA387 Grade 22 Class 2: The Definitive Guide for High-Temperature Pressure Vessel Steel
ASTM A387 / ASME SA387 Grade 22 Class 2 is a premium 2.25% Cr–1.0% Mo alloy steel plate designed for elevated-temperature and high-pressure service in boilers and pressure vessels. As the higher-strength grade of A387 Gr.22, it features excellent creep resistance, oxidation and corrosion resistance, as well as good weldability compared to Class 1. It is widely adopted across global oil & gas, petrochemical and power generation industries for critical components operating at a maximum service temperature up to 600°C (1112°F). This guide covers official specifications, mechanical & chemical properties, cross-standard equivalents, typical applications and fabrication guidelines in line with ASTM and ASME standards.
1. Standard Overview & Core Definition
1.1 Governing Standards
ASTM A387 / A387M: Standard Specification for Chromium-Molybdenum Alloy Steel Plates for Pressure Vessels.
ASME SA387 / SA387M: Equivalent standard under ASME Boiler and Pressure Vessel Code (BPVC), fully interchangeable with ASTM A387 for industrial applications.
UNS Number: K21590 (universal material identification for global traceability).
1.2 Grade & Class Distinction
Grade 22: Specifies nominal chemical composition of 2.25% Chromium and 1.0% Molybdenum, delivering better high-temperature performance than Grade 11 (1.25% Cr, 0.5% Mo).
Class 2: Requires mandatory Normalized and Tempered (N&T) heat treatment, providing higher tensile and yield strength than Class 1 (no mandatory N&T).
ASME P-Number: P5 (defined in ASME Section IX for welding procedure qualification of Cr-Mo steels).
2. Chemical Composition (Weight %)
Strict chemical control ensures stable performance at high temperatures. Values below apply to heat analysis (ladle sample) and product analysis (finished plate).
| Element | Carbon (C) | Manganese (Mn) | Silicon (Si) | Phosphorus (P) | Sulfur (S) | Chromium (Cr) | Molybdenum (Mo) |
|---|---|---|---|---|---|---|---|
| Min | 0.05 / 0.04 | 0.30 / 0.25 | - | - | - | 2.00 / 1.88 | 0.90 / 0.85 |
| Max | 0.15 | 0.60 / 0.66 | 0.50 | 0.035 | 0.035 | 2.50 / 2.62 | 1.10 / 1.15 |
Carbon Equivalent Formula: Ceq = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15
Key Functions of Alloy Elements:
Chromium (2.00–2.50%): Forms dense protective oxide film to improve oxidation resistance and general corrosion resistance, suitable for sour gas and high-temperature working environments.
Molybdenum (0.90–1.10%): Greatly enhances creep strength and resistance to hydrogen attack at 400–600°C, avoiding premature failure under long-term high temperature and pressure.
3. Mechanical Properties (Room Temperature)
All mechanical tests are conducted in accordance with ASTM A370. Comparison between Class 2 and Class 1 is listed below for reference.
| Property | Unit | Class 2 | Class 1 (Reference) |
|---|---|---|---|
| Tensile Strength | MPa (ksi) | 515–690 (75–100) | 415–585 (60–85) |
| Minimum Yield Strength (0.2% Offset) | MPa (ksi) | 310 (45) | 205 (30) |
| Elongation (50mm Gauge Length) | % | ≥18 | ≥18 |
| Reduction of Area (Round Specimen) | % | ≥45 | ≥40 |
| Typical Brinell Hardness (HB) | - | 130–170 | 140–200 |
Mandatory Heat Treatment: Normalized at 890–950°C (air cooling), then Tempered at 650–720°C (air cooling). This process balances mechanical strength and material toughness.
Impact Test: Charpy V-Notch (CVN) impact test is required at -52°C to verify low-temperature toughness.
4. Global Equivalent Grades
Below are internationally recognized equivalent grades with matched chemical composition and mechanical properties for engineering substitution.
| Standard System | Equivalent Grade | Region |
|---|---|---|
| EN 10028-2 / DIN 17155 | 10CrMo9-10 (1.7380) | Europe, Germany |
| BS 622 | 622-515B | United Kingdom |
| JIS G3103 | SCMV4 | Japan |
| GB/T 713 | 12Cr2Mo1R | China |
| AFNOR | 10CD9-10 | France |
| GOST | 10KH2M | Russia |
| SS Standard | SS 2218 | Sweden |
Important Reminder: When replacing materials, always confirm the material is supplied in Class 2 (N&T) condition. Most equivalent grades only provide Class 1 products with lower mechanical strength.
5. Key Advantages & Performance Features
High-Temperature Creep Resistance: Maintains structural stability under long-term high temperature and pressure, maximum operating temperature up to 600°C.
Excellent Oxidation & Corrosion Resistance: Resists scaling and corrosion in high-temperature steam, hydrogen medium and sour gas environments.
Reliable Weldability: Compatible with low-hydrogen welding processes. Proper preheat and post-weld heat treatment can effectively prevent welding cold cracks.
High Strength-to-Weight Ratio: Higher yield strength allows thinner plate design for pressure vessels, saving material cost and overall equipment weight.
6. Industrial Applications
This Cr-Mo alloy steel plate is primarily used for critical high-temperature and high-pressure equipment:
Petrochemical & Refinery: Hydrocracking reactors, catalytic reformers, hot separators, coke drums, hydrogen service pressure vessels.
Power Generation: Boiler drums, superheater headers, industrial heat exchangers.
Oil & Gas: Onshore & offshore high-pressure separators, LPG storage tanks, sour service piping systems.
Chemical Industry: Ammonia converters, sulfur recovery units, high-temperature heat exchange equipment.
7. Product Specifications & Quality Control
7.1 Dimension Range
Thickness: 6mm – 300mm
Width: 1000mm – 4500mm
Length: 3000mm – 18000mm
Product Form: Hot Rolled (HR) steel plates, customized cut pieces
7.2 Quality Assurance & Testing
Ultrasonic Testing (UT): Inspected per ASTM A435 / A578 to eliminate internal defects.
Low-temperature Impact Test: Charpy V-Notch test at -52°C.
Third-Party Certification: Available with SGS, TUV, BV, Lloyd's Register certification for global project approval.
8. Welding & Fabrication Guidelines
Follow the below requirements to avoid material cracking and comply with ASME BPVC codes:
Preheat Temperature: 150–250°C. Higher preheat is required for plates over 25mm in thickness.
Welding Filler Metal: AWS E8018-B2 for SMAW; EB3 / FB3 for SAW, matching Cr-Mo chemical composition.
Post-Weld Heat Treatment (PWHT): Hold at 680–710°C, 1 hour per 25mm plate thickness (minimum holding time: 2 hours) for residual stress relief.
Thermal Cutting: Laser cutting or plasma cutting with 150–200°C preheat to prevent edge cracks.
9. Frequently Asked Questions (FAQ)
Q1: What is the maximum continuous service temperature for A387 Gr.22 Cl.2?
A: The peak temperature reaches 600°C (1112°F). For long-term safe operation, continuous service temperature is recommended not to exceed 550°C.
A: They are interchangeable for most working conditions. A387 Gr.22 Cl.2 contains higher chromium and molybdenum content, delivering better high-temperature performance.
Q3: Is A387 Gr.22 Cl.2 identical to 10CrMo9-10?
A: Yes. EN/DIN standard 10CrMo9-10 is the direct equivalent grade with consistent chemical and mechanical properties.
Conclusion
ASTM A387 / ASME SA387 Grade 22 Class 2 is a benchmark high-temperature pressure vessel steel in the global steel industry. Combining outstanding creep resistance, oxidation resistance and stable weldability, it fully complies with ASTM and ASME international standards. With widely recognized cross-standard equivalent grades, it remains the preferred material for engineers, fabricators and procurement teams for critical high-temperature pressure equipment projects worldwide.
For detailed quotations, Material Test Reports (MTRs) or custom processing services, please contact professional and qualified A387 Gr.22 Cl.2 steel suppliers.
