At a Glance
Key Grades
P11 · P22 · P91 · P92
Scope
ASTM A335 covers seamless ferritic alloy steel pipe for high-temperature service. All A335 grades are seamless only — there is no welded equivalent. The specification covers a range of chromium-molybdenum alloys from P1 through P92, each optimized for specific temperature ranges, pressure levels, and corrosion environments.
Heat treatment is mandatory for all grades — A335 pipe cannot be used in the as-rolled condition. All grades require either full annealing or normalizing and tempering to achieve the required microstructure and mechanical properties.
Grade Availability — Know Before You Specify
P11K11597
Common · Widely StockedMax 1050°F
Cr 1.00–1.50%
Mo 0.44–0.65%
SMYS 30,000 PSI
The most commonly specified chromium-molybdenum alloy pipe.
P22K21590
Common · Widely StockedMax 1100°F
Cr 1.90–2.60%
Mo 0.87–1.13%
SMYS 30,000 PSI
2¼Cr-1Mo alloy pipe — the refinery workhorse for high-temperature, high-pressure service.
P5K41545
Less CommonMax 1200°F
Cr 4.00–6.00%
Mo 0.45–0.65%
SMYS 30,000 PSI
5Cr-½Mo alloy with significantly higher chromium content than P11 or P22.
P9K90941
Less CommonMax 1200°F
Cr 8.00–10.00%
Mo 0.90–1.10%
SMYS 30,000 PSI
9Cr-1Mo alloy — the predecessor to P91.
P91 Type 1K91560
High-Temp Critical ServiceMax 1200°F
Cr 8.00–9.50%
Mo 0.85–1.05%
SMYS 60,000 PSI
Modified 9Cr-1Mo-V alloy — one of the most important high-temperature pipe materials in modern power generation and petrochemical service.
P91 Type 2K91560
High-Temp Critical · Tighter ControlsMax 1200°F
Cr 8.00–9.50%
Mo 0.85–1.05%
SMYS 60,000 PSI
P91 Type 2 was introduced in ASTM A335/A335M-19a to address long-term creep performance concerns observed in Type 1 material with chemistry near the allowable range extremes.
P92K92460
Specialty · Power GenMax 1200°F
Cr 8.50–9.50%
Mo 0.30–0.60%
SMYS 64,000 PSI
Advanced 9Cr alloy with tungsten (1.
Critical: Heat Treatment is Mandatory
⚠ All A335 Grades Require Heat Treatment
Unlike carbon steel pipe (A106, A53) where heat treatment is optional and PO-driven, ASTM A335 requires heat treatment as a base specification requirement for every grade. Pipe shipped without proper heat treatment is non-conforming — regardless of chemistry and mechanical test results. For P91 and P92, the heat treatment parameters (temperature, soak time, cooling rate) are critical to achieving the required tempered martensite microstructure.