ASTM A335 P91 — Chemical Composition & Mechanical Properties
ASTM A335 P91 is a chrome-moly alloy steel grade for seamless pipe (UNS K90901, EN / W.Nr 1.4903). It is also known as 9Cr-1Mo-V. This sheet summarises its chemical composition limits, minimum mechanical properties, heat treatment and typical service. Teshi Group supplies this grade as a stockist and supplier, and manufactures matching flanges and fittings.
ASTM A335 P91 at a glance
| Specification | ASTM A335 P91 |
|---|---|
| Material family | Chrome-moly alloy steel |
| Product form | Seamless pipe |
| UNS number | K90901 |
| EN / W.Nr equivalent | 1.4903 |
| Also known as | 9Cr-1Mo-V |
| Document | TG-MG-029 · Rev. 1 · October 2026 |
Typical service
9Cr-1Mo-V main-steam / hot-reheat piping
Heat treatment
Normalized 1040–1080 °C and tempered 730–800 °C
Chemical composition of ASTM A335 P91 (weight %)
Other elements and limits: V 0.18–0.25; Nb 0.06–0.10; Al 0.02 max; Ti 0.01 max; Zr 0.01 max
Single values are maximums unless shown as a range or “min”.
Mechanical properties
| Tensile strength, min | 585 MPa |
|---|---|
| Yield strength, min | 415 MPa |
| Elongation, min | 20 % |
| Hardness | 190–250 HBW |
About chrome-moly alloy steel
Chrome-moly steels are low-alloy steels with 1–9 % chromium and 0.5–1 % molybdenum. Chromium gives oxidation and sulphidation resistance; molybdenum gives creep strength at high temperature. They are the standard choice for steam and hot hydrocarbon service above the carbon-steel range.
Reference information compiled from the published standard for convenience. It does not replace the current edition of the governing standard, which takes precedence. Verify critical dimensions and properties before design, purchase or fabrication. Teshi Engineers & Sales Promoters (P) Ltd accepts no liability for errors or omissions.
International equivalents of ASTM A335 P91
All equivalents| Standard system | Nearest equivalent grade |
|---|---|
| USA — ASTM / ASME | ASTM A335 P91 · ASME SA-335 P91 |
| USA — UNS | K90901 |
| Europe — EN designation | X10CrMoVNb9-1 |
| Europe — W.Nr | 1.4903 |
| Japan — JIS | STPA28 (JIS G3458) / SFVAF28 (JIS G3203) |
| China — GB / NB | 10Cr9Mo1VNbN (GB/T 5310) |
Equivalents are the nearest commonly cited grades. Chemistry, mechanical properties and testing differ between standards — compare them before substituting one for another.
Same alloy in other product forms
| Product form | Specification / grade |
|---|---|
| Forged flanges & fittings | ASTM A182 F91 |
| Wrought butt-weld fittings | ASTM A234 WP91 Type 1 |
| Pressure-vessel plate | ASTM A387 Grade 91 Cl.2 |
Standards for ASTM A335 P91
All material standardsFAQ
ASTM A335 P91: common questions
What is the minimum yield strength of ASTM A335 P91?
415 MPa, with a minimum tensile strength of 585 MPa.
What is the carbon content of ASTM A335 P91?
0.08–0.12 %.
What is the UNS number and EN equivalent of ASTM A335 P91?
UNS K90901; the nearest European designation is W.Nr 1.4903. Equivalents are close but not identical — check the specification if substituting.
How is ASTM A335 P91 heat treated?
Normalized 1040–1080 °C and tempered 730–800 °C.
What is the Chinese (GB) equivalent of ASTM A335 P91?
The nearest Chinese equivalent is 10Cr9Mo1VNbN (GB/T 5310). Equivalents are close but not identical — compare chemistry and properties before substituting.
What is the JIS equivalent of ASTM A335 P91?
The nearest Japanese (JIS) equivalent is STPA28 (JIS G3458) / SFVAF28 (JIS G3203).
Does Teshi Group supply ASTM A335 P91?
Teshi Group supplies this grade as a stockist and supplier, and manufactures matching flanges and fittings. Send your size, rating and quantity to info@teshigroup.com for a quotation with EN 10204 3.1 certificates.
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