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Alloy Steel T91 tube is a 9Cr-1Mo martensitic-ferritic chromium-molybdenum-vanadium steel tube manufactured under the ASTM A213 / ASME SA213 specification for seamless ferritic and martensitic alloy-steel boiler, superheater and heat-exchanger tubes. T91 is micro-alloyed with vanadium and niobium (columbium) and produced with tightly controlled nitrogen content, which refines the grain structure and gives the alloy outstanding creep strength and high-temperature tensile strength at metal temperatures up to approximately 600°C (1112°F).
The grade is internationally cross-referenced as UNS K91560, DIN / Werkstoff Nr. 1.4903 and the EN designation X10CrMoVNb9-1. The pipe equivalent of the same chemistry is known as ASTM A335 / ASME SA335 Grade P91. Thanks to its high chromium content (8–9.5%), T91 alloy steel offers excellent oxidation resistance, corrosion resistance, low thermal expansion and high heat-transfer efficiency, which is why it has largely replaced lower-alloy grades such as T22 and T9 in modern supercritical boilers and high-pressure piping systems.
Solitaire Overseas is a manufacturer, stockist, supplier and exporter of ASME SA213 T91 and ASTM A213 T91 alloy steel seamless tubes, part of our wider range ofAlloy Steel Products andAlloy Steel Tubes. For a broader introduction to alloy steel grades and classification, see our guide onWhat is Alloy Steel and Its Types.
| Parameter | Specification |
|---|---|
| Tube Standard | ASTM A213 / ASME SA213 (Seamless Ferritic & Martensitic Alloy-Steel Boiler, Superheater & Heat Exchanger Tubes) |
| Equivalent Pipe Standard | ASTM A335 / ASME SA335 Grade P91 |
| Dimensional Standards | ASTM, ASME, API, EN 10216-2 |
| Outer Diameter (OD) | 6mm – 219.1mm (½" OD up to 5" OD); custom diameters available on request |
| Wall Thickness (WT) | 1mm – 50mm (up to 200mm for special applications) |
| Schedule / Pressure Rating | SCH 20, SCH 30, SCH 40, STD, SCH 60, XS, SCH 80, SCH 120, SCH 140, SCH 160, XXS |
| Type | Seamless (ERW/welded available on request) |
| Form | Round, Square, Rectangular, U-Bend, Hydraulic, Finned |
| Length | Single Random, Double Random & Cut-to-Length |
| End Finish | Plain End, Beveled End, Threaded |
| Surface Finish | Hot Finished / Cold Drawn, Annealed & Pickled, Bright Annealed, Polished |
| Heat Treatment Condition | Normalized and Tempered (N&T) |
Buyers most frequently search for the “T91 material composition” or “T91 chemical composition” before placing an order — the table below gives the full SA 213 T91 chemical composition.
| Element | C | Mn | P (max) | S (max) | Si | Cr | Mo | Ni (max) | V | Nb (Cb) | N | Al (max) |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| T91 / UNS K91560 | 0.08–0.12 | 0.30–0.60 | 0.020 | 0.010 | 0.20–0.50 | 8.00–9.50 | 0.85–1.05 | 0.40 | 0.18–0.25 | 0.06–0.10 | 0.030–0.070 | 0.04 |
| Tensile Strength (MPa) | Yield Strength (MPa) | Elongation (%) | Hardness (HB) |
|---|---|---|---|
| 585 min | 415 min | 20 min | 250 max |
| Physical Property | Typical Value |
|---|---|
| Density | ≈ 7.75 g/cm³ |
| Maximum Recommended Service Temperature | ≈ 600°C (1112°F) |
| Thermal Conductivity (at room temp.) | ≈ 28–30 W/m·K |
| Melting Range | ≈ 1480–1530°C |
| Standard / Grade | UNS | Werkstoff Nr. | EN Designation | Trade Name | Pipe Equivalent |
|---|---|---|---|---|---|
| ASTM A213 / ASME SA213 T91 | K91560 | 1.4903 | X10CrMoVNb9-1 (EN 10216-2) | 9Cr-1Mo-V | ASTM A335 / SA335 P91 |
T91 and P91 share the same chemical composition (UNS K91560 / DIN 1.4903) and the same 9Cr-1Mo-V chrome-moly alloy system. The only difference is the product form covered by the specification: “T91” refers to seamless tubes manufactured to ASTM A213 / ASME SA213 (used for boiler, superheater, reheater and heat-exchanger tubing), while “P91” refers to seamless pipes manufactured to ASTM A335 / ASME SA335 (used for steam piping, headers and manifolds). Both grades are interchangeable in terms of chemistry, mechanical properties and heat treatment.
| Process | Outside Diameter (mm) | Tolerance |
|---|---|---|
| Hot Rolled | OD ≤ 101.6 | +0.4 / −0.8 mm |
| Hot Rolled | 101.6 < OD ≤ 190.5 | +0.4 / −1.2 mm |
| Hot Rolled | 190.5 < OD ≤ 228.6 | +0.4 / −1.6 mm |
| Cold Drawn | OD < 25.4 | ± 0.10 mm |
| Cold Drawn | 25.4 ≤ OD ≤ 38.1 | ± 0.15 mm |
| Cold Drawn | 38.1 < OD < 50.8 | ± 0.20 mm |
| Cold Drawn | 50.8 ≤ OD < 63.5 | ± 0.25 mm |
| Cold Drawn | 63.5 ≤ OD < 76.2 | ± 0.30 mm |
| Cold Drawn | 76.2 ≤ OD ≤ 101.6 | ± 0.38 mm |
| Cold Drawn | 101.6 < OD ≤ 190.5 | +0.38 / −0.64 mm |
| Cold Drawn | 190.5 < OD ≤ 228.6 | +0.38 / −1.14 mm |
| Process | Condition | Tolerance |
|---|---|---|
| Hot Rolled | OD ≤ 101.6, WT ≤ 2.4 | +40% / −0 |
| Hot Rolled | OD ≤ 101.6, 2.4 < WT ≤ 3.8 | +35% / −0 |
| Hot Rolled | OD ≤ 101.6, 3.8 < WT ≤ 4.6 | +33% / −0 |
| Hot Rolled | OD ≤ 101.6, WT > 4.6 | +28% / −0 |
| Hot Rolled | OD > 101.6, 2.4 < WT ≤ 3.8 | +35% / −0 |
| Hot Rolled | OD > 101.6, 3.8 < WT ≤ 4.6 | +33% / −0 |
| Hot Rolled | OD > 101.6, WT > 4.6 | +28% / −0 |
| Cold Drawn | OD ≤ 38.1 | +20% / −0 |
| Cold Drawn | OD > 38.1 | +22% / −0 |
Solitaire Overseas supplies Alloy Steel T91 tubes in multiple forms to suit boiler, heat exchanger and piping applications:
Every batch of Alloy Steel T91 tube supplied by Solitaire Overseas is manufactured from certified 9Cr-1Mo-V raw material, hot extruded or cold drawn to size, and given a normalizing-and-tempering heat treatment to develop the specified tensile strength, yield strength and creep properties. After sizing, tubes are cooled under a controlled atmosphere to preserve surface finish and avoid unwanted oxide scale.
Before dispatch, each lot undergoes dimensional inspection, chemical composition verification (spectro-analysis), mechanical testing (tensile, hardness, flattening, flaring) and non-destructive testing such as hydrostatic testing, ultrasonic testing (UT) and eddy-current testing (ECT). Every consignment is supplied with an EN 10204 3.1 Mill Test Certificate (MTC/MTR) recording heat number, chemical composition and mechanical properties. To understand how to read and verify these reports, see our guide How to Read a Mill Test Report (MTR) for Heat Exchanger Tubes.
Finished Alloy Steel T91 Seamless Tubes are packed in bundles with end caps or bubble-wrapped to prevent transit damage, clearly marked with grade, heat number, dimensions and standard, and shipped worldwide with full export documentation.
Because of its superior creep strength and oxidation resistance at up to 600°C, Alloy Steel T91 tube is specified primarily in high-temperature, high-pressure environments:
For supercritical boiler applications, also see our dedicated Alloy Steel T91 Boiler Tubes and Alloy Steel Boiler Tubes category pages, and our blog All You Need to Know About Alloy Steel Boiler Tubes for a complete buyer's overview.
| Grade | Cr / Mo (approx.) | Max. Service Temp. | Tensile Strength (MPa) | Best Suited For |
|---|---|---|---|---|
| T9 | 9% Cr / 1% Mo (no V/Nb) | ≈ 540°C | 415 min | Moderate temperature boiler tubes |
| T22 | 2.25% Cr / 1% Mo | ≈ 540°C | 415 min | Economical mid-temperature superheater/reheater tubes |
| T91 | 9% Cr / 1% Mo / V, Nb | ≈ 600°C | 585 min | High-pressure, high-temperature superheater/reheater tubes |
| T92 | 9% Cr / 0.5% Mo / W, V, Nb | ≈ 620°C+ | 620 min | Ultra-supercritical boilers requiring the highest creep strength |
| P91 (pipe) | Same as T91 | ≈ 600°C | 585 min | Pipe equivalent of T91 for steam headers & piping |
ASTM A213 T91 tubes are seamless, high-performance 9Cr-1Mo-V chrome-moly alloy steel tubes designed for boilers, superheaters, reheaters and other high-temperature, high-pressure industrial applications. They are produced without seams or welds for superior strength and consistency.
The SA213 / ASTM A213 T91 chemical composition is: 0.08–0.12% C, 0.30–0.60% Mn, max 0.020% P, max 0.010% S, 0.20–0.50% Si, 8.00–9.50% Cr, 0.85–1.05% Mo, max 0.40% Ni, 0.18–0.25% V, 0.06–0.10% Nb, 0.030–0.070% N and max 0.04% Al. This same composition applies to ASTM A335 P91 pipe.
T91 and P91 have identical chemistry (UNS K91560 / 1.4903) and mechanical properties. T91 refers to seamless tube under ASTM A213 / ASME SA213, used for boiler and heat-exchanger tubing, while P91 refers to seamless pipe under ASTM A335 / ASME SA335, used for steam headers and piping.
Alloy Steel T91 corresponds to UNS K91560 and DIN/Werkstoff Nr. 1.4903 (EN designation X10CrMoVNb9-1).
T91 tubes have a minimum tensile strength of 585 MPa, minimum yield strength of 415 MPa, minimum elongation of 20%, and a maximum hardness of 250 HB.
T91 alloy steel tubes offer outstanding creep strength and oxidation resistance at metal temperatures of up to approximately 600°C (1112°F), making them suitable for supercritical and ultra-supercritical boiler applications.
We supply T91 tubes from ½" OD up to 5" OD (custom diameters available), with wall thicknesses from 1mm to 50mm and schedules from SCH 20 through XXS, in single random, double random or cut lengths.
Yes. Custom outside diameters, wall thicknesses, lengths, end finishes (plain, beveled, threaded) and surface finishes (cold drawn, bright annealed, polished) are available on request, subject to minimum order quantities and lead time. Share your exact dimensions, tolerances and quantity for an accurate quotation.
For less severe service conditions, ASTM A213 T22 or T9 tubes can be used at lower cost. For even higher creep strength in ultra-supercritical boilers, T92 is preferred. The final choice depends on design temperature, pressure and project specification.
Yes, every consignment is supplied with an EN 10204 3.1 Mill Test Certificate (MTC/MTR) confirming heat number, chemical composition and mechanical test results, along with third-party inspection on request.
We regularly export Alloy Steel T91 seamless tubes to over 60 countries including the UAE, Saudi Arabia, Iran, Turkey, the USA, the UK, Germany, Singapore, Malaysia, South Korea, South Africa and across the Middle East, Europe, Asia, Africa and the Americas.
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