A387 Grade 12 Class 1
A387 Grade 12 Class 1 is a chromium-molybdenum alloy steel plate designed for pressure vessel service at elevated temperatures.
Alloy Composition: Its defining chemistry is approximately 1% Chromium (Cr) and 0.5% Molybdenum (Mo), placing it between carbon steel and the more common 1.25Cr-0.5Mo (Grade 11) in performance and cost.
Heat Treatment (Class 1): The "Class 1" designation means the plate is supplied in the normalized or stress-relieved condition, intended for the fabricator to perform a final Post-Weld Heat Treatment (PWHT) on the completed vessel.
Properties: It offers improved high-temperature strength, oxidation, and corrosion resistance compared to carbon steel, but lower than that of Grade 11. It has good weldability and formability with proper procedures.
Applications: It is typically used in moderate-temperature pressure vessels such as certain boilers, heat exchangers, and process equipment in power generation and petrochemical industries, where the environment is less severe than what requires Grade 11 or 22. Its use has declined in favor of more capable or cost-competitive grades.
Key Distinction: A387 Grade 12 is a lower-alloy, lower-cost alternative to Grade 11 for less demanding elevated temperature service.
Equivalents of A387 Grade 12 Class 1
| BS | EN | ASTM/ASME | DIN |
| 620 B | 13 CRMO 45 | A387-12-1 | 13 CRMO 44 |
Specifications for ASTM A387 Grade 12 Alloy Steel Plates
Chromium & Molybdenum content (according to the ASME specification)
| Designation | Nominal Chromium Content (%) |
Nominal Molybdenum Content (%) |
| A387 Grade 12 | 1.00% | 0.50% |
Tensile Requirements for ASTM A387 Grade 12 Alloy Steel Plates Class 1 Plates
| Designation: | Requirement: | Grade 12 |
| A387 Grade 12 | Tensile strength, ksi [MPA] | 65 to 85 [450 to 585] |
| Yield strength, min, ksi [MPa]/(0.2% offset) | 40 [275] | |
| Elongation in 8 in. [200mm], min % | 19 | |
| Elongation in 2 in. [50mm], min, % | 22 | |
| Reduction of area, min % | ––– |
Chemical Requirements for ASTM A387 Grade 12 Alloy Steel Plates
| Element | Chemical Composition (%) | |
| ASTM A387 Grade 12 | ||
| Carbon: | Heat Analysis: | 0.05 - 0.17 |
| Product Analysis: | 0.04 - 0.17 | |
| Manganese: | Heat Analysis: | 0.40 - 0.65 |
| Product Analysis: | 0.35 - 0.73 | |
| Phosphorus: | Heat Analysis: | 0.035 |
| Product Analysis: | 0.035 | |
| Sulphur (max): | Heat Analysis: | 0.035 |
| Product Analysis: | 0.035 | |
| Silicon: | Heat Analysis: | 0.15 - 0.40 |
| Product Analysis: | 0.13 - 0.45 | |
| Chromium: | Heat Analysis: | 0.80 - 1.15 |
| Product Analysis: | 0.74 - 1.21 | |
| Molybdenum: | Heat Analysis: | 0.45 - 0.60 |
| Product Analysis: | 0.40 - 0.65 |
1. What are the main advantages of choosing A387 Grade 12 Class 1 over carbon steel for a pressure vessel?
This question focuses on the economic and performance rationale for upgrading from carbon steel, typically for moderate temperature service where Grade 12 offers improved strength and oxidation resistance at a reasonable cost increase.
2. Why might an engineer specify Grade 12 instead of the more common Grade 11?
This question explores the trade-off between material performance and project economics, as Grade 12 offers a cost-saving option when the service conditions are within its more limited high-temperature and corrosion resistance capabilities.
3. What are the primary high-temperature limitations of A387 Grade 12 compared to Grade 11?
This question addresses the technical boundaries of the alloy, focusing on its lower chromium and molybdenum content which results in reduced oxidation resistance, creep strength, and hydrogen attack resistance at elevated temperatures.
4. How does the heat treatment and welding procedure for Grade 12 Class 1 compare to that for carbon steel?
This question highlights the fabrication implications of using a low-alloy steel, noting that while similar to carbon steel, it generally requires stricter preheat, controlled cooling, and mandatory Post-Weld Heat Treatment (PWHT) to achieve optimal properties.
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.
