What are the mechanical properties of SA387 Grade 22 Class 1?
SA387 Grade 22 Class 1 is a chromium-molybdenum (Cr-Mo) alloy steel plate specifically designed and standardized for the construction of welded pressure vessels and high-temperature components in demanding industrial applications. Its defining characteristic is its annealed heat treatment condition.
Mechanical Properties of SA387 Grade 22 Class 1
The mechanical properties of SA387 Grade 22 Class 1 are defined by its annealed condition and the ASTM/ASME A/SA387 standard. The key characteristic is a combination of moderate strength with high ductility, optimized for formability.
Here are the specified minimum mechanical properties per the standard, along with critical context for their application.
1. Room Temperature Mechanical Properties (As-Supplied, Annealed Condition)
| Property | Value (Minimum or Range) | Metric Units | Imperial Units |
|---|---|---|---|
| Tensile Strength (Rm) | 415 - 585 MPa | 415 - 585 MPa | 60,000 - 85,000 psi |
| Yield Strength (Rp0.2) | Minimum 205 MPa | ≥ 205 MPa | ≥ 30,000 psi |
| Elongation (A) | Minimum 22% | ≥ 22% (in 50 mm gauge length) | ≥ 22% (in 2 in. gauge length) |
| Hardness (Typical) | Not directly specified, but generally ≤ 197 HBW | ≤ 197 Brinell (typical) | ≤ 197 Brinell (typical) |
Key Interpretation:
Lower Strength, Higher Ductility: Compared to Class 2 (N&T: YS ≥ 275 MPa / 40 ksi), Class 1 has ~25% lower minimum yield strength but significantly greater elongation. This is the direct result of the annealing process, which produces a soft ferrite-pearlite microstructure.
The primary purpose of these properties is fabricability, not final design strength.
2. The Critical Role of Post-Weld Heat Treatment (PWHT)
The as-delivered properties above are not the final in-service properties. This is the most important concept.
After fabrication (welding and forming), the component must undergo a mandatory PWHT (typically 1250-1350°F / 675-730°C).
This PWHT acts as a tempering cycle, which will:
Increase the yield and tensile strength from the as-annealed values.
Slightly reduce the ductility.
Relieve stresses and ensure a stable microstructure.
Final In-Service Strength: The exact final mechanical properties after PWHT depend on the specific time-temperature cycle but will generally fall between the Class 1 (annealed) and Class 2 (N&T) values. For design, engineers use the ASME Section II, Part D maximum allowable stress values, which are identical for both Class 1 and Class 2 at all temperatures.
3. High-Temperature Mechanical Properties
For elevated-temperature design, the critical properties are Creep Strength and Stress Rupture Strength, not room-temperature yield strength.
The 2.25% Cr and 1% Mo composition provides excellent creep resistance and long-term strength at temperatures up to ~1050°F (~565°C).
The ASME Code provides identical maximum allowable stress (S) values for Grade 22 Class 1 and Class 2 at all temperatures, confirming that after proper PWHT, their high-temperature performance is equivalent.
4. Impact Properties (When Specified)
Charpy V-Notch impact testing is not a mandatory requirement of the base A387 specification.
It is almost always specified for pressure vessel applications. Common requirements are:
Test Temperature: +10°F to -20°F (-12°C to -29°C) or lower.
Minimum Absorbed Energy: 20 J (15 ft-lbf) average per three specimens.
Summary: Understanding the Property Philosophy
The mechanical properties of SA387 Grade 22 Class 1 should be viewed in two stages:
Stage 1 (Manufacturing/As-Delivered):
Tensile: 415-585 MPa | Yield: ≥205 MPa | Elongation: ≥22%
Purpose: To provide a soft, ductile, and highly formable material for complex fabrication.
Stage 2 (In-Service/After PWHT):
Strength increases, ductility slightly decreases.
High-temperature creep strength is fully realized.
Design Basis: Engineers use the code-approved allowable stress values (ASME Sec. II, Part D), which account for the final heat-treated state.
In essence, the "mechanical properties" on the mill certificate represent the starting point for fabrication, not the finish line for performance. The final, governing properties are achieved through the mandatory post-weld heat treatment.
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.
