What Is A387 Grade 5 Class 1
ASTM A387 Grade 5 Class 1 is a chromium-molybdenum alloy steel plate for weldable pressure vessels and industrial boilers designed for elevated temperature service. The nominal composition is about 5 percent chromium and 0.5 percent molybdenum, and Class 1 is supplied in the annealed or normalized and tempered condition with lower strength than Class 2.
Chemical Composition
Heat analysis limits are carbon 0.15 percent maximum, manganese 0.30 to 0.60 percent, phosphorus 0.035 percent maximum, sulfur 0.030 percent maximum, silicon 0.50 percent maximum, chromium 4.00 to 6.00 percent, and molybdenum 0.45 to 0.65 percent, with wider product analysis ranges permitted.
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. The moderate strength of Class 1 provides excellent formability and simplified fabrication, making it suitable where the higher Class 2 properties are not required.
Heat Treatment and Properties
Plates supplied in the annealed condition are classified as Class 1 only. The 5Cr composition provides markedly better oxidation and sulfidation resistance at elevated temperatures than lower-chromium Cr-Mo grades, extending component life in corrosive high-temperature service.
Applications
The grade is used in the petrochemical industry for reactors, pressure vessels, and storage tanks handling high-temperature process fluids; in power generation for boilers, heat exchangers, and associated piping; in oil and gas for sour service equipment resisting sulfide stress corrosion cracking; in chemical processing for equipment handling aggressive acids; and in industrial boilers requiring continuous elevated-temperature service.
Fabrication Notes
Welding requires preheating and post-weld heat treatment because of the high chromium content. Low-hydrogen consumables and qualified procedures are essential to avoid hydrogen-induced cracking in the heat-affected zone. Hot forming is followed by the appropriate heat treatment to restore specified properties.
Frequently Asked Questions
Q: What is the composition of A387 Grade 5?
A: About 5 percent chromium and 0.5 percent molybdenum.
Q: What is the tensile strength of Grade 5 Class 1?
A: 415 to 585 MPa with a minimum yield of 205 MPa.
Q: How does Class 1 differ from Class 2?
A: Class 2 is normalized and tempered to higher strength; Class 1 may be annealed or normalized at lower strength.
Q: What environments suit A387 Grade 5 Class 1?
A: High-temperature, corrosive, and sour service environments.
Q: Is A387 Grade 5 Class 1 weldable?
A: Yes, with preheating, low-hydrogen consumables, and post-weld heat treatment.
Q: What applications use this grade?
A: Reactors, boilers, heat exchangers, and sour-service pressure equipment.
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