What are the properties and applications of SA387 Grade 22 Class 1?
SA387 Grade 12 Class 1 Chromium-Molybdenum (Cr-Mo) alloy steel plate, standardized by ASME/ASTM, designed for weldable pressure vessels and boilers operating at elevated temperatures, offering good strength, toughness, and improved corrosion resistance due to its chromium content, suitable for demanding oil & gas, petrochemical, and power generation applications.
SA387 Grade 22 Class 1 shares the same chemical composition as the more common Class 2, but its different heat treatment results in distinct properties and typical applications.
Properties of SA387 Grade 22 Class 1
The core defining feature is its heat treatment condition:
Class 1: Material is supplied in the Annealed condition.
Composition: Nominal 2.25% Chromium, 1% Molybdenum (identical to Class 2).
Key Mechanical Properties (Typical for Annealed Condition):
Lower Strength, Higher Ductility: Compared to Class 2 (Normalized & Tempered), Class 1 has lower yield and tensile strength but higher elongation and toughness in the as-supplied state.
Softer: It has a lower hardness, making it easier for machining and cold forming.
Microstructure: The annealing process produces a soft, uniform microstructure (typically ferrite with coarse carbides) that is stable and stress-relieved.
Typical Room-Temperature Property Ranges (For Reference - Actual values are mill-specific):
Tensile Strength: ~415-585 MPa (60-85 ksi)
Yield Strength: ~205 MPa (30 ksi) minimum (significantly lower than Class 2's 310 MPa min)
Elongation: Higher than Class 2, often >22-25%
Hardness: Typically ≤ 170 HBW
Primary Applications of SA387 Grade 22 Class 1
Class 1 is specifically chosen for components that require significant fabrication before their final heat treatment. Its applications are more niche than Class 2:
1.Heavy Cold Forming or Severe Fabrication: Used for parts that require extensive cold bending, spinning, or pressing after the plate is supplied. The soft, annealed state prevents cracking during these processes.
2.Complex Fabricated Components: For vessels or parts where extensive welding and forming will be done, and the entire finished assembly will undergo a final Post-Weld Heat Treatment (PWHT). The PWHT will ultimately develop the final mechanical properties in the component (approaching those of Class 2).
3.Interim Condition for Further Processing: Sometimes specified as a starting condition for parts that will be re-heat-treated by the fabricator to a different specification or condition after machining/forming.
1.Applications Where Ultimate Final Properties are Developed in Service: In some high-temperature equipment, the service conditions themselves act as a tempering cycle after the annealed component is put into operation.
Critical Consideration: The Final Heat Treatment
PWHT is Mandatory: After all welding and forming, SA387 Gr 22 Cl 1 components MUST undergo a full Post-Weld Heat Treatment (typically normalizing and tempering or a sub-critical tempering, per the design code). This relieves stresses and develops the required strength and creep resistance for high-temperature service.
End-Use Comparison: In the final, heat-treated state, a component made from Class 1 can achieve mechanical properties very similar to one made from Class 2. The choice often comes down to fabrication logistics and cost.
Summary: Class 1 vs. Class 2 (Quick Comparison)
| Feature | SA387 Grade 22 Class 1 (Annealed) | SA387 Grade 22 Class 2 (N&T) |
|---|---|---|
| Key Benefit | Superior formability & machinability in the as-supplied state. | Higher as-supplied strength; ready for moderate forming. |
| Typical Use Case | Complex fabrications needing heavy cold work before final PWHT. | Standard fabrications where the plate can be used as-supplied after moderate forming. |
| Final State | Requires full PWHT after fabrication to develop service properties. | May only require a stress relief after welding, depending on code. |
In essence, SA387 Grade 22 Class 1 is the preferred choice for fabricators who need a soft, workable starting material for complex components, with the understanding that the final heat treatment is an integral and necessary step to achieve the performance required for high-temperature pressure vessel service.
What is SA387 Grade 22 Class 1?
SA387 Grade 22 Class 1 is an annealed chromium-molybdenum alloy steel plate designed for high-temperature pressure vessel service, with a composition of 2.25% Cr and 1% Mo to resist oxidation and hydrogen attack in refinery and power plant applications.
What are the mechanical properties of SA387 Grade 22 Class 1?
In its annealed condition, SA387 Grade 22 Class 1 typically has a tensile strength of 415-585 MPa (60-85 ksi), a minimum yield strength of 205 MPa (30 ksi), and high ductility, making it suitable for severe forming before final heat treatment.
Where is SA387 Grade 22 Class 1 commonly used?
It is widely used in hydroprocessing reactors, hydrocrackers, heat exchangers, and high-temperature pressure vessels in the petrochemical and power generation industries, especially where resistance to hydrogen attack and creep is required.
How does SA387 Grade 22 Class 1 differ from Class 2?
Class 1 is supplied in an annealed state for better formability, while Class 2 is normalized and tempered for higher as-delivered strength. Class 1 is chosen when complex fabrication is needed before final PWHT.
What is the post-weld heat treatment (PWHT) for SA387 Grade 22 Class 1?
PWHT is mandatory and typically performed at 1250-1300°F (675-705°C) to relieve welding stresses, prevent hydrogen-induced cracking, and restore corrosion resistance in the weld zone for high-temperature service.
What are the equivalent materials to SA387 Grade 22 Class 1?
Common equivalents include UNS K21590, European 10CrMo9-10 (1.7380), and the generic designation 2.25Cr-1Mo steel. However, exact equivalency depends on heat treatment and certification requirements.
Can SA387 Grade 22 Class 1 be used in hydrogen service?
Yes, its 2.25% chromium and 1% molybdenum content provides excellent resistance to high-temperature hydrogen attack (HTHA), making it a standard choice for hydrogen processing units in refineries.
What are the forming and machining guidelines for SA387 Grade 22 Class 1?
Due to its annealed condition, it offers good cold formability but requires preheating for hot forming and controlled machining to avoid excessive work hardening, with tooling suitable for alloy steels.
What standards certify SA387 Grade 22 Class 1 plates?
Plates are certified to ASME SA387/SA387M and ASTM A387/A387M standards, with mill test reports (MTRs) providing chemical and mechanical properties per EN 10204 3.1 or 3.2.
How does SA387 Grade 22 Class 1 compare to Grade 11 or Grade 5?
Compared to lower-alloy grades like Grade 11 (1.25Cr-0.5Mo) or Grade 5 (5Cr-0.5Mo), Grade 22 offers superior high-temperature strength and hydrogen resistance, but requires stricter welding and heat treatment controls.
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.
