What is the difference between SA387 Grade 22 Class 2 and Grade 11?
SA387 Grade 22 Class 2 is a normalized and tempered chromium-molybdenum alloy steel plate with a nominal composition of 2.25% chromium and 1% molybdenum, designed for high-temperature and high-pressure service in applications like heavy-wall reactors and hydrocrackers where superior creep strength and resistance to hydrogen attack are required.
SA387 Grade 11 is a lower-alloy chromium-molybdenum steel plate, typically with about 1.25% chromium and 0.5% molybdenum, commonly supplied in normalized and tempered condition, used in moderate-temperature pressure vessels and boiler components where good elevated-temperature properties are needed but at a more economical cost compared to higher-grade alloys.
The key difference between SA387 Grade 22 Class 2 and Grade 11 lies in their chromium content and the resulting high-temperature strength, corrosion resistance, and cost.
| Feature | SA387 Grade 22 Class 2 | SA387 Grade 11 |
|---|---|---|
| Common Name | 2¼ Chrome - 1 Moly (2.25Cr-1Mo) | 1¼ Chrome - ½ Moly (1.25Cr-0.5Mo) |
| Typical Composition | Cr: ~2.25%, Mo: ~1.0% | Cr: ~1.25%, Mo: ~0.5% |
| Primary Distinction | Higher alloy content for superior performance. | Lower alloy content, a more economical choice. |
| High-Temperature Strength | Significantly higher creep strength and allowable stress values at elevated temperatures. | Good, but lower than Grade 22 at temperatures above ~450°C (850°F). |
| Max. Useful Temp. | Up to ~590°C (~1100°F) for some applications. | Typically up to ~540°C (~1000°F). |
| Corrosion/Oxidation Resistance | Better due to higher chromium content. Resists hydrogen attack more effectively. | Good, but less resistant than Grade 22 in severe environments. |
| Cost | Higher due to greater alloy content (Cr & Mo). | More economical, often the preferred choice when its properties suffice. |
| Common Applications | Heavy-wall reactors, hydrocracker units, high-temperature/high-pressure hydrogen service. | Boiler drums, heat exchangers, superheater headers, lower-temperature pressure vessels. |
How to Choose:
Choose Grade 22 Class 2 when: The design requires higher strength at temperatures above 450°C (850°F), involves high-pressure hydrogen service (better resistance to hydrogen attack), or demands greater oxidation resistance in corrosive flue gases.
Choose Grade 11 when: The operating conditions are moderate (typically below 450°C), and the design codes allow its lower allowable stress values. It offers a cost-effective solution for many refinery and power boiler applications.
Key Similarities:
Both are chromium-molybdenum alloy steels for pressure vessels.
Both are available in Class 1 (Annealed) and Class 2 (Normalized & Tempered) conditions.
Both require careful welding and Post-Weld Heat Treatment (PWHT).
In summary
Grade 22 is a higher-grade, more capable (and more expensive) alloy used for the most demanding high-temperature/high-pressure services, while Grade 11 is a workhorse alloy for less severe conditions where cost is a greater factor. The selection is ultimately dictated by the design temperature, pressure, and corrosive environment as per the applicable engineering codes (e.g., ASME BPVC).
1. What is SA387 Grade 22 Class 2?
SA387 Grade 22 Class 2 is a specification for chromium-molybdenum alloy steel plates primarily used in pressure vessels and other high-temperature service applications.
2. What is the chemical composition of SA387 Grade 22 Class 2?
Its typical composition includes chromium (2.00-2.50%), molybdenum (0.90-1.10%), with carbon, manganese, phosphorus, sulfur, and silicon making up the remainder.
3. What are the mechanical properties of SA387 Gr 22 Cl 2?
Key mechanical properties include a minimum tensile strength of 515 MPa (75 ksi) and a minimum yield strength of 310 MPa (45 ksi) for plates over 65mm thick.
4. What is the difference between SA387 Grade 22 Class 1 and Class 2?
The primary difference is heat treatment; Class 2 material is required to be supplied in the normalized and tempered condition, while Class 1 does not have this mandatory requirement, affecting its strength and microstructure.
5. What is the maximum service temperature for SA387 Grade 22?
SA387 Grade 22 is commonly used for service temperatures up to approximately 550°C (1022°F), but specific limits depend on the pressure and stress conditions.
6. Is SA387 Grade 22 Class 2 equivalent to any other material grade?
Yes, it is broadly equivalent to ASTM A387 Gr22 Cl2, ASME SA387 Gr22 Cl2, and the common wrought material grade UNS K21590.
7. How to weld SA387 Grade 22 Class 2 steel?
Welding typically requires pre-heat and post-weld heat treatment (PWHT). Common filler metals include AWS E9015-B3 for SMAW or corresponding grades for other processes to match the base metal's properties.
8. What is the heat treatment for SA387 Gr22 Cl2?
SA387 Grade 22 Class 2 plates are supplied in the normalized (at 1650-1750°F) and tempered (at 1250-1350°F) condition to achieve the required mechanical properties.
9. Where is SA387 Grade 22 Class 2 commonly used?
It is extensively used in the fabrication of pressure vessels, boilers, and reactors for the power generation, petrochemical, and oil & gas industries, especially for components exposed to high temperatures and pressures.
10. What are the hardness requirements for SA387 Grade 22 Class 2?
While the ASTM/ASME specification does not mandate a specific hardness, it is typically controlled during heat treatment. A common requirement in service is to maintain a maximum hardness, often 225 Brinell (HBW) or lower, to prevent issues like hydrogen-induced cracking.
Full specification and details are available on request. The above information is provided for guidance purposes only. For specific design requirements please contact our technical sales staff.
