ASTM A234 WP91 Type 1 — Chemical Composition & Mechanical Properties
ASTM A234 WP91 Type 1 is a chrome-moly alloy steel grade for wrought butt-weld fittings (UNS K90901, EN / W.Nr 1.4903). It is also known as P91 / 9Cr-1Mo-V. This sheet summarises its chemical composition limits, minimum mechanical properties, heat treatment and typical service. Teshi Group manufactures flanges and fittings in this grade.
ASTM A234 WP91 Type 1 at a glance
| Specification | ASTM A234 WP91 Type 1 |
|---|---|
| Material family | Chrome-moly alloy steel |
| Product form | Wrought butt-weld fittings |
| UNS number | K90901 |
| EN / W.Nr equivalent | 1.4903 |
| Also known as | P91 / 9Cr-1Mo-V |
| Document | TG-MG-118 · Rev. 1 · October 2026 |
Typical service
Main steam and hot reheat lines in power plants
Heat treatment
Normalised 1040–1080 °C and tempered 730–800 °C
Chemical composition of ASTM A234 WP91 Type 1 (weight %)
Other elements and limits: V 0.18–0.25; Nb 0.06–0.10; Al 0.02 max
Single values are maximums unless shown as a range or “min”.
Mechanical properties
| Tensile strength, min | 585 MPa |
|---|---|
| Yield strength (0.2 % offset), min | 415 MPa |
| Elongation, min | 20 % |
| Tensile strength, max | 760 MPa |
| Hardness | 248 HBW max |
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 A234 WP91 Type 1
All equivalents| Standard system | Nearest equivalent grade |
|---|---|
| USA — ASTM / ASME | ASTM A234 WP91 Type 1 · ASME SA-234 WP91 Type 1 |
| 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 |
| Seamless pipe | ASTM A335 P91 |
| Pressure-vessel plate | ASTM A387 Grade 91 Cl.2 |
Standards for ASTM A234 WP91 Type 1
All material standardsFAQ
ASTM A234 WP91 Type 1: common questions
What is the minimum yield strength of ASTM A234 WP91 Type 1?
415 MPa, with a minimum tensile strength of 585 MPa.
What is the carbon content of ASTM A234 WP91 Type 1?
0.08–0.12 %.
What is the UNS number and EN equivalent of ASTM A234 WP91 Type 1?
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 A234 WP91 Type 1 heat treated?
Normalised 1040–1080 °C and tempered 730–800 °C.
What is the Chinese (GB) equivalent of ASTM A234 WP91 Type 1?
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 A234 WP91 Type 1?
The nearest Japanese (JIS) equivalent is STPA28 (JIS G3458) / SFVAF28 (JIS G3203).
Does Teshi Group supply ASTM A234 WP91 Type 1?
Teshi Group manufactures flanges and fittings in this grade. Send your size, rating and quantity to info@teshigroup.com for a quotation with EN 10204 3.1 certificates.
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