UNS K11597 - ASME SA-335 / ASTM A335 P11 is a seamless 1.25% Chromium - 0.5% Molybdenum (1.25Cr-0.5Mo) ferritic alloy steel pipe, engineered for continuous service in boilers, superheaters, pressure vessels, and high-temperature steam piping. Known in the industry as chrome-moly or Cr-Mo pipe, P11 delivers reliable creep and oxidation resistance above 400°C, making it the standard material choice across power generation, petrochemical plants, oil refineries, and industrial heating systems worldwide.
Chromium in the 1–1.5% range builds a stable chromium oxide layer that shields the pipe against high-temperature oxidation and scaling. Molybdenum at 0.44–0.65% strengthens the ferrite matrix and slows dislocation creep under sustained load at elevated temperatures. Together, these two alloying elements give P11 its characteristic combination of heat resistance and long-term mechanical stability.
The table below lists the closest material equivalents to ASTM A335 P11 across major international standards. These grades are functionally similar and are often accepted as substitutes in global projects where one standard system is specified and another is sourced.
ASTM A335 mandates that P11 pipe be delivered in the normalized and tempered condition (full or isothermal annealing is also permitted).
The resulting ferrite-carbide microstructure delivers the creep strength, ductility, and toughness required for long-term high-temperature pressure service.
The table below reflects a portion of our current stock. Contact us for updated availability, additional sizes, or non-standard specifications.
Length: 5800mm / 6000mm / 6096mm / 7315mm / 11800mm / 12000mm (custom available)
Max length: 16000mm; U-bending also available.
Note: The above table shows a portion of our current stock. For additional sizes, quantities, or non-stock grades, please contact us.
