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1. What Is ASTM A335 Pipe?
ASTM A335/A335M covers seamless ferritic alloy-steel pipe for high-temperature service. The specification defines requirements for chemical composition, mechanical properties, heat treatment and testing.
The conventional P11 and P22 grades use chromium-molybdenum alloy systems. P91 and P92 use a modified 9% chromium composition, with additions such as vanadium and niobium and, in P92, tungsten. Their alloy design and controlled heat treatment support the high-temperature strength and creep resistance required in demanding steam piping applications.
For P91 and P92, the tempered martensitic microstructure is central to their creep-strength performance. Material selection therefore requires grade-specific high-temperature allowable stress data, while fabrication procedures must preserve the specified material condition.
ASTM A335 P11 contains approximately 1.25% chromium and 0.5% molybdenum. It is commonly used in industrial boiler piping, auxiliary steam lines and refinery process piping where moderate chromium-molybdenum alloying is suitable for the operating conditions.
ASTM A335 P22 contains approximately 2.25% chromium and 1% molybdenum. Its higher chromium content distinguishes it from P11 and provides greater resistance to oxidation at elevated temperatures. Typical applications include boiler superheaters, reheaters, steam headers and refinery process piping.
ASTM A335 P91 is a creep-strength-enhanced ferritic steel containing approximately 9% chromium and 1% molybdenum, with additions of vanadium and niobium. It is widely used in power plant main steam lines, hot reheat piping and high-temperature headers where conventional Cr-Mo grades may not meet the required design conditions.
ASTM A335 P92 is a modified 9% chromium steel containing tungsten, molybdenum, vanadium and niobium. It is used in advanced steam piping systems, particularly in ultra-supercritical power plants, where it can serve as an alternative to other high-chromium steels subject to the applicable design requirements.
P11 and P22 are chromium-molybdenum steels, while P91 and P92 use modified 9% chromium alloy systems. The following table compares their specified chemical composition and minimum mechanical properties.
| Parameter | P11 | P22 | P91 Type 1 | P92 |
|---|---|---|---|---|
| UNS Designation | K11597 | K21590 | K90901 | K92460 |
| Carbon (%) | 0.05–0.15 | 0.05–0.15 | 0.08–0.12 | 0.07–0.13 |
| Chromium (%) | 1.00–1.50 | 1.90–2.60 | 8.00–9.50 | 8.50–9.50 |
| Molybdenum (%) | 0.44–0.65 | 0.87–1.13 | 0.85–1.05 | 0.30–0.60 |
| Vanadium (%) | — | — | 0.18–0.25 | 0.15–0.25 |
| Niobium (%) | — | — | 0.06–0.10 | 0.04–0.09 |
| Tungsten (%) | — | — | 0.05 max | 1.50–2.00 |
| Tensile Strength, min. (MPa) | 415 | 415 | 585 | 620 |
| Yield Strength, min. (MPa) | 205 | 205 | 415 | 440 |
| Longitudinal Elongation, min. (%) | 30 | 30 | 20 | 20 |
| Hardness, max. (HBW) | 163 | 163 | 250 | 250 |
ASTM A335 pipe dimensions are specified by nominal pipe size (NPS), outside diameter, wall thickness and Schedule.
For standard outside diameters, wall thicknesses and Schedule charts, see ANSI/ASME B36.10M Pipe Dimensions, Schedule & Size Chart.
Heat treatment is specified by grade under ASTM A335/A335M. The main requirements for common grades are summarized below.
| Grade | Heat Treatment | Temperature Requirements |
|---|---|---|
| P11 | Full annealing, isothermal annealing, or normalizing and tempering | Minimum tempering temperature: 650°C |
| P22 | Full annealing, isothermal annealing, or normalizing and tempering | Minimum tempering temperature: 675°C |
| P91 | Normalizing and tempering | Normalizing: 1040–1080°C; tempering: 730–800°C |
| P92 | Normalizing and tempering | Normalizing: 1040–1080°C; tempering: 730–800°C |
ASTM A335/A335M covers the following inspection and testing requirements, subject to the applicable grade and specification provisions:
Impact testing and additional nondestructive examination may be specified by the purchaser or applicable construction code.
ASTM A335 alloy steel pipe is used in power generation, refining, petrochemical processing and industrial steam systems.
Power generation: Boiler circuits, superheater and reheater systems, main steam piping and hot reheat lines.
Refining and petrochemical processing: Process piping in catalytic reforming and hydroprocessing units, subject to the operating temperature, pressure and process environment.
Industrial facilities: Steam distribution networks and thermal process systems requiring alloy steel pipe specified for elevated-temperature service.
When requesting a quote for ASTM A335 alloy steel pipe, specify the grade, NPS or outside diameter, wall thickness or Schedule, pipe length, quantity, and applicable inspection, heat treatment, and material certification requirements.
Eastern Steel supplies seamless steel pipe for industrial applications. See our Seamless Steel Pipe page for product details and inquiries.
Q1. What is ASTM A335 pipe used for?
ASTM A335 pipe is used in power generation, refinery, petrochemical and industrial steam systems operating at elevated temperatures.
Q2.What are the common grades of ASTM A335 pipe?
Common grades include P11, P22, P91 and P92. P11 and P22 are conventional chromium-molybdenum steels, while P91 and P92 are modified 9% chromium steels with additional alloying elements.
Q3.What is the difference between ASTM A335 and ASME SA335?
ASTM A335 is an ASTM material specification for seamless ferritic alloy-steel pipe for high-temperature service. ASME SA335 is the corresponding specification published by ASME for use within its code framework.
How to Read a MTC for Seamless Steel Pipes
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