What Is A387 Grade 22 Class 1
A387 Grade 22 Class 1 is a chromium-molybdenum alloy steel plate with a nominal composition of 2.25 percent chromium and 1 percent molybdenum, specified in ASTM A387 for welded pressure vessels in high-temperature service. It is supplied in the normalized or stress-relieved condition and is intended for fabrications where the completed vessel will undergo a full post-weld heat treatment to develop its final tempered microstructure and optimum properties.
Chemical Composition
Heat analysis limits are carbon 0.05 to 0.15 percent, manganese 0.30 to 0.60 percent, silicon 0.50 percent maximum, phosphorus 0.035 percent, sulfur 0.035 percent, chromium 2.00 to 2.50 percent, and molybdenum 0.90 to 1.10 percent. The tight composition control preserves weldability and toughness in heavy sections.
Mechanical Properties
Class 1 plates have a tensile strength of 415 to 585 MPa, a minimum yield strength of 205 MPa, and a minimum elongation of 18 percent in 50 mm. Impact testing is optional and specified per project requirements. The as-supplied condition is deliberately softer to support subsequent hot forming and fabrication.
High-Temperature and Hydrogen Resistance
The 2.25Cr-1Mo composition provides excellent high-temperature strength and creep resistance, superior to Grade 11 alloys, and outstanding resistance to hydrogen attack and high-temperature oxidation up to about 600 degrees C, assessed using the Nelson curve guidelines. This makes it the established choice for high-pressure hydrogen service.
Applications
A387 Grade 22 Class 1 is specified for severe-service welded pressure vessels where the fabrication route allows full vessel post-weld heat treatment: critical reactors in hydrocracking, hydrodesulfurization, and hydrotreating units; high-pressure boiler drums and headers in power generation; and reactors and vessels in chemical and petrochemical plants exposed to aggressive high-temperature and high-hydrogen partial pressure environments.
Why Choose Class 1 over Class 2
Class 1 is selected when the manufacturing route includes hot forming, extensive welding, and a final full furnace post-weld heat treatment. This complete thermal cycle transforms the normalized plate into a finished component with a fully tempered, tough microstructure, making it the fabrication-friendly form of the alloy for large and complex heavy-wall reactors.
Frequently Asked Questions
Q: What is the composition of A387 Grade 22?
A: About 2.25 percent chromium and 1 percent molybdenum.
Q: What is the yield strength of Grade 22 Class 1?
A: 205 MPa minimum in the as-supplied condition.
Q: Why is Grade 22 Class 1 supplied soft?
A: To support hot forming and fabrication before a full post-weld heat treatment develops final properties.
Q: What applications use Grade 22 Class 1?
A: Hydrocracking reactors, hydrotreating vessels, boiler drums, and high-temperature hydrogen equipment.
Q: What temperature limit applies to Grade 22?
A: Continuous service up to about 600 degrees C depending on pressure and environment.
Q: Is post-weld heat treatment mandatory?
A: Yes for Cr-Mo steels per the governing pressure vessel code.
Contact us for A387 Grade 22 Class 1 plates with certified composition and properties for your hydrogen service project.