ASTM A691 — High-temperature and high-pressure electrofusion welded alloy steel pipes
Grades
Gr.CM-65, Gr.CM-70, Gr.1-1/4Cr-1/2Mo, Gr.2-1/4Cr-1Mo, Gr.5Cr-1/2Mo, Gr.9Cr-1Mo-V
Chemical composition and mechanical properties
| Grade | Chemical composition | Mechanical properties |
|---|---|---|
| Gr.CM-65 | C≤0.20, Mn 1.05-1.50, P≤0.030, S≤0.030, Si 0.13-0.32, Mo 0.25-0.45 | Rm ≥450 MPa, Rp0.2 ≥260 MPa, A≥17%, Killed steel |
| Gr.CM-70 | C≤0.20, Mn 1.05-1.50, P≤0.030, S≤0.030, Si 0.13-0.32, Mo 0.25-0.45 | Rm ≥485 MPa, Rp0.2 ≥280 MPa, A≥15%, Killed steel |
| Gr.1-1/4Cr-1/2Mo | C≤0.15, Mn 0.40-0.70, P≤0.030, S≤0.030, Si 0.50-1.00, Cr 1.00-1.50, Mo 0.45-0.65 | Rm ≥415 MPa, Rp0.2 ≥205 MPa, A≥18%, Normalizing + Tempering |
Application scope
ASTM A691 specifies electrofusion welded alloy steel pipes for high-temperature and high-pressure applications, including carbon manganese steel and chromium-molybdenum steel, typically delivered after post-weld heat treatment. The grades cover the CM series and chromium-molybdenum grades such as 1-1/4Cr, 2-1/4Cr, and 9Cr. Higher chromium-molybdenum grades generally indicate better high-temperature strength, creep resistance, and heat resistance.
Typical applications
Primarily used in critical pressure-bearing pipelines such as high-temperature and high-pressure pipelines in power plants, oil refining and hydrogenation units, and petrochemical high-temperature and high-pressure process pipes. Chromium-molybdenum alloy electrofusion welded pipes combine the advantages of high-temperature strength, creep resistance, and large-diameter forming, making them suitable for thick-walled piping systems and manifolds in harsh high-temperature and high-pressure conditions such as main steam and hydrogen supply. They are a commonly used standard for large-diameter high-pressure alloy welded pipes.
