ASTM A387 Grade 11 Class 1 Compare With Class 2
ASTM A387 Grade 11 Class 1 refers to a chromium-molybdenum (1.25% Cr, 0.5% Mo) alloy steel plate for pressure vessels supplied in the normalized or stress-relieved heat treatment condition. It is designed for high-temperature service where the fabricator will perform final post-weld heat treatment (PWHT) after manufacturing, making it suitable for components requiring extensive forming and welding in refineries and power plants.
ASTM A387 Grade 11 Class 2 is the same chromium-molybdenum alloy composition but supplied in the fully normalized and tempered (or quenched and tempered) heat treatment condition. This provides higher as-delivered strength and a more refined microstructure, making it suitable for applications where the final PWHT by the fabricator is impractical or where higher initial mechanical properties are required for the finished component.
The core difference between ASTM A387 Grade 11 Class 1 and Class 2 lies in their heat treatment condition at the time of plate supply and the resulting mechanical properties, which dictates their intended fabrication path.
Here is a detailed comparison:
| Feature | ASTM A387 Grade 11 Class 1 | ASTM A387 Grade 11 Class 2 |
|---|---|---|
| Heat Treatment | Normalized or Stress-Relieved | Normalized and Tempered (Quenched & Tempered is also permitted) |
| As-Delivered Strength | Lower minimum yield strength (205 MPa / 30 ksi). | Higher minimum yield strength (240 MPa / 35 ksi). |
| Microstructure | Less uniform, softer state suitable for subsequent heat treatment. | More refined, uniform, and stable tempered microstructure. |
| Primary Fabrication Path | Intended for the fabricator to perform final Post-Weld Heat Treatment (PWHT) on the completed vessel. | Often selected when full PWHT of the final vessel is not feasible or for simpler components. |
| Key Rationale for Selection | Chosen when the fabrication process (extensive welding, hot forming) necessitates a final, full PWHT to restore properties, relieve stresses, and ensure safety. The plate condition is optimized for this. | Chosen to provide higher, guaranteed as-received strength and properties, often for applications where a full vessel PWHT is impractical or for replacement parts that match the original equipment's higher strength condition. |
Practical Summary:
Think of Class 1 as the "fabricator's grade." It arrives in a softer, more malleable state, ready to be cut, formed, and welded. The fabricator then performs a final, uniform PWHT on the entire vessel, which acts as the tempering process, achieving the desired final properties, stress relief, and toughness.
Think of Class 2 as the "performance-ready grade." The steel mill has already performed the full heat treatment (tempering). It arrives at the fabrication shop with higher strength and a stabilized microstructure. It is used when the final vessel cannot undergo a full PWHT (e.g., due to size, lack of furnace, or complex internals) or when the design specifically calls for the higher as-supplied strength.
In essence, the choice is not about quality but about the manufacturing and engineering workflow. Class 1 is designed to get its final properties from the fabricator's PWHT, while Class 2 is designed to arrive with its final properties largely already established.
What is A387 grade 11 material?
The ASTM A387 specification is the Standard Specification for Pressure Vessel Plates, Alloy Steel, Chromium-Molybdenum intended primarily for use in welded boilers and pressure vessels designed for elevated temperature service. SSAB can supply A387 Grade 11 to the tension test requirements for Class 1 and/or Class 2.
What is the composition of A387 steel?
Composition: ASTM A387 steel plates typically contain chromium (up to 9% or more) and molybdenum (up to 2.25% or more), which enhance their strength and corrosion resistance at high temperatures.
What is the difference between A182 and A387?
Both ASTM A182 grade F11 class 2 and ASTM A387 grade 22 steel are iron alloys. They have a very high 99% of their average alloy composition in common. There are 32 material properties with values for both materials. Properties with values for just one material (1, in this case) are not shown.
What is ASTM A387 Grade 11 equivalent to?
ASTM A387 grade 11 equivalent steel is ASME SA387 grade 11. ASTM A387 grade 11 covers A387 grade 11 class 1 and A387 grade 11 class 2, which are equivalent to ASME SA387 grade 11 class 1 and SA387 grade 11 class 2 respectively.
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.
