Why SA387 Cr-Mo Plates Dominate Petrochemicals
In environments characterized by high temperatures, elevated pressures, and highly corrosive media such as hydrogen service and sour gas atmospheres containing hydrogen sulfide, ASME SA387 chromium-molybdenum alloy steel plates remain the premier material choice for fabricating welded pressure vessels and industrial boilers. The precisely engineered balance of chromium and molybdenum gives this series exceptional elevated-temperature tensile strength, superior creep-rupture performance, and outstanding resistance to oxidation and hydrogen attack in the 400 to 600 degrees C range.
Grade 5: 5Cr-0.5Mo
SA387 Gr. 5 is a 5Cr-0.5Mo alloy steel engineered for petrochemical equipment under high-temperature and corrosive conditions. Its higher chromium content delivers superior resistance to oxidation and high-temperature sulfidation atmospheres, making it ideal for furnaces, reactors, heat exchangers, and refinery processing units. It has the highest nominal chromium of the three grades, giving the best resistance to oxidation and sulfidation, though moderate creep strength.
Grade 11: 1.25Cr-0.5Mo
SA387 Gr. 11 is a 1.25Cr-0.5Mo alloy steel, one of the most widely used chromium-molybdenum grades. It offers an excellent balance of high-temperature strength, weldability, and formability, serving as a cost-effective choice for moderate-to-high-temperature pressure vessels. It has the lowest chromium content, highest elongation, and is widely used in mid-temperature service such as sour gas equipment, boiler drums, and heat exchangers.
Grade 22: 2.25Cr-1Mo
SA387 Gr. 22 is a 2.25Cr-1Mo alloy steel developed for pressure vessels under more severe high-temperature and hydrogen service environments. Its increased chromium and molybdenum content significantly enhances creep resistance, oxidation resistance, and elevated-temperature strength, making it the preferred material for hydrotreating and hydrogen-refining units. With the highest molybdenum content, it offers the best creep and high-temperature hydrogen attack resistance, with long-term service up to about 595 degrees C.
Chemical Composition and Mechanical Properties
Grade 5 has chromium of 4.00 to 6.00 percent and molybdenum of 0.45 to 0.65 percent; Grade 11 has chromium of 1.00 to 1.50 percent and molybdenum of 0.45 to 0.65 percent; Grade 22 has chromium of 2.00 to 2.50 percent and molybdenum of 0.90 to 1.10 percent. Class 2 conditions provide yield strength of 310 MPa minimum and tensile strength of 515 to 690 MPa for Grades 5 and 22, and 485 to 620 MPa for Grade 11. Class 1 conditions provide 205 or 240 MPa yield with correspondingly lower tensile values.
Heat Treatment and Applications
Class 1 is annealed at 845 degrees C or higher; Class 2 is normalized and tempered or quenched and tempered, with minimum tempering temperatures of 705 degrees C for Grade 5, 620 degrees C for Grade 11, and 675 degrees C for Grade 22. Applications: Grade 5 for high-temperature pressure vessels and aggressive corrosive media; Grade 11 for mid-temperature oil and gas pressure vessels and sour gas equipment; Grade 22 for hydrocracking reactors, hydrodesulfurization vessels, high-pressure separators, ammonia synthesis, and coal gasification equipment.
Frequently Asked Questions
Q: Which SA387 grade offers the best oxidation resistance?
A: Grade 91 with about 9 percent chromium, followed by Grade 5 with 4 to 6 percent chromium.
Q: Can Gr.22 replace Gr.11?
A: Generally not recommended without engineering approval, because of differences in design temperature and toughness.
Q: What is the difference between Gr.5 and Gr.11?
A: Gr.5 has 5 percent chromium for superior oxidation resistance; Gr.11 has 1.25 percent chromium as a lower-cost mid-temperature grade.
Q: What are the welding requirements?
A: Preheat of 150 to 260 degrees C, controlled interpass temperature, and mandatory post-weld heat treatment to prevent hydrogen cracking.
Q: What is the service temperature range of Gr.22?
A: Typical continuous service from about 350 to 550 degrees C, with short-term exposure to about 600 degrees C per design code limits.
Q: What thickness range is available?
A: 6 to 250 mm with widths of 1500 to 4000 mm and lengths of 3000 to 18000 mm.
For ASME SA387 Gr.5, 11, and 22 plate quotations with EN 10204 certification, contact our sales team.
