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As a trusted supplier of high-performance alloy piping solutions, we specialize in ASTM A335 Grade P91 Pipe (conforming to ASME SA335 P91), an advanced chromium-molybdenum-vanadium seamless alloy steel pipe engineered for extreme high-temperature and high-pressure applications. With a optimized chemical composition including 8.0-9.5% Chromium, 0.85-1.05% Molybdenum, and strengthened by micro-alloying elements like Vanadium (0.18-0.25%) and Niobium (0.06-0.10%), this grade delivers exceptional creep strength, thermal fatigue resistance, and long-term structural stability at temperatures up to 650°C (1200°F). Widely specified in modern ultra-supercritical power plants, heat exchangers, and refinery transfer lines, P91 alloy pipe offers significant advantages over conventional grades like P22, enabling thinner wall designs and improved operational efficiency. Our ASTM A335 P91 seamless pipes are manufactured to strict quality standards, with full traceability and supporting documentation for global project compliance.
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Products Description
ASTM A335 Grade P91 is a chromium-molybdenum alloy steel enhanced with elements such as vanadium, niobium (columbium), and nitrogen, which collectively contribute to its superior high-temperature performance. The material composition includes controlled amounts of carbon, manganese, phosphorus, sulfur, silicon, chromium, molybdenum, vanadium, nitrogen, nickel, aluminum, niobium, titanium, and zirconium.
P91 pipes are available in both seamless and welded forms. Seamless pipes are extruded from a single billet, ensuring uniform structure and enhanced pressure integrity. Welded pipes, including those produced as ERW (Electric Resistance Welded) types, are fabricated from strip or plate, with longitudinal or spiral welding techniques employed to form the pipe body.
The mechanical properties of ASTM A335 P91 include a minimum yield strength of 415 MPa and a minimum tensile strength of 585 MPa, making it suitable for high-pressure and high-temperature applications in power generation and petrochemical industries.
For detailed information on Alloy Steel P91 ERW Pipe specifications or to request a quotation, please feel free to contact us. We are ready to support your project needs with reliable products and competitive pricing.
ASME SA335 Grade P91 Alloy Steel Pipe Specification Format
| Size in Inch | 1/8NB TO 24NB inch |
| ASTM Standards | ASTM A 335, and ASME SA 335 |
| Type | Seamless Pipes |
| Specialized in Size | Large Diameter Size |
| Outer Dimensions Chart | 19.05milimeter – 114.3milimeter |
| Wall Thickness Chart | 2.0milimeter – 14 milimeter |
| Length in milimeter | max 16000milimeter |
| Schedule Chart | Schedule 20 - XXS up to 250 milimeter thk. |
| Pipe Form | Round, Rectangular, Square, Hydraulic Etc. |
| Length | Single, Double Random & Cut to Length. |
| Pipes & Tube End | Plain, Beveled, Treaded. |
Chemical Properties of ASTM A335 Gr P91 Welded Pipe
| C, % | Mn, % | P, % | S, % | Si, % | Cr, % | Mo, % | V, % | N, % | Ni, % | Al, % | Nb, % |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 0.08-0.12 | 0.3-0.6 | 0.02 max | 0.01 max | 0.2-0.5 | 8.0-9.5 | 0.85-1.05 | 0.18-0.25 | 0.03-0.07 | 0.4 max | 0.04 max | 0.06-0.10 |
Mechanical And Physical Properties of Alloy Steel P91 ERW Pipe
| Tensile Strength , MPa | A335 P91 Yield Strength, MPa | Elongation, % | A335 P91 Hardness, HB |
|---|---|---|---|
| 585 min | 415 min | 20 min | 250 max |
Comparison with Other ASTM A335 Grades
| ASTM A335 Grades | BSi Equivalent Ref. | Material Focus |
|---|---|---|
| Gr. P5 | 3604/625 | 5% Cr 1/2% Mo |
| Gr. P9 | 3604/629 | 9% Cr 1% Mo |
| Gr. P11 | 3604/621 | 1 1/4% Cr 1/2% Mo |
| Gr. P12 | 3604/620 | 1% Cr 1/2% Mo |
| Gr. P22 | 3604/622 | 2 1/4% Cr 1% Mo |
| Gr. P91 | N/A (Modern CSEF) | ~9% Cr 1% Mo + V, Nb, N (Modified) |
ASTM A335 P91 Pipe Size Chart
| O.D.(mm) x Thk(mm) | O.D.(mm) x Thk(mm) | O.D.(mm) x Thk(mm) |
|---|---|---|
| 38.1 x 3.2 | 57.0 x 4.9 | 76.2 x 4.0 |
| 38.1 x 4.0 | 57.0 x 6.3 | 76.2 x 5.0 |
| 38.1 x 6.3 | 57.0 x 7.9 | 76.2 x 6.3 |
| 42.4 x 3.2 | 60.3 x 3.2 | 82.5 x 4.5 |
| 42.4 x 4.0 | 60.3 x 3.6 | 88.9 x 3.2 |
| 44.5 x 3.2 | 60.3 x 5.0 | 88.9 x 3.6 |
| 44.5 x 6.3 | 63.5 x 3.2 | 88.9 x 4.0 |
| 48.3 x 3.2 | 63.5 x 3.6 | 101.6 x 3.6 |
| 48.3 x 3.6 | 63.5 x 4.0 | 101.6 x 4.5 |
| 50.8 x 4.5 | 63.5 x 6.3 | 101.6 x 6.3 |
| 51.0 x 3.2 | 63.5 x 7.9 | 114.3 x 3.6 |
| 51.0 x 3.6 | 70.0 x 3.2 | 114.3 x 5.0 |
| 51.0 x 6.3 | 70.0 x 3.6 | 139.7 x 4.0 |
| 57.0 x 3.2 | 70.0 x 6.3 | 139.7 x 5.0 |
| 57.0 x 3.6 | 76.2 x 3.6 | 139.7 x 6.3 |
Alloy Steel P91 Seamless Pipe Wall Thickness
| NPS [DN] Designator | Tolerance, % from Specified | |
|---|---|---|
| Over | Under | |
| 1/8 to 2 1/2 [6 to 65] incl., all t/D ratios | 20.0% | 12.5% |
| Above 2 1/2 [65], t/D < or = 5% | 22.5% | 12.5% |
| Above 2 1/2 [65], t/D > 5% | 15.0% | 12.5% |
| (t = Specified Wall Thickness; D = Specified Outside Diameter) | ||
Frequently Asked Questions (FAQ): ASTM A335 Grade P91 / ASME SA335 P91 Alloy Steel Pipe
Q1: What is the key advantage of using ASTM A335 P91 over other chrome-moly grades like P22 or P9?
A: The primary advantage of P91 is its significantly higher strength at elevated temperatures. Due to its advanced chemical composition (including Vanadium, Niobium, and Nitrogen), P91 offers superior creep strength and thermal fatigue resistance. This allows for the design of piping systems with thinner wall thicknesses compared to P22 or P9, leading to material cost savings, reduced weight, and lower thermal stresses, especially in ultra-supercritical power plants and high-pressure piping.
Q2: What is the complete chemical composition of ASTM A335 P91?
A: P91 is a complex alloy with a carefully balanced composition for optimal performance:
Chromium (Cr): 8.00 - 9.50%
Molybdenum (Mo): 0.85 - 1.05%
Vanadium (V): 0.18 - 0.25%
Niobium (Cb/Columbium): 0.06 - 0.10%
Nitrogen (N): 0.030 - 0.070%
Carbon (C): 0.08 - 0.12%
Manganese (Mn): 0.30 - 0.60%
Silicon (Si): 0.20 - 0.50%
Nickel (Ni): ≤ 0.40%
Aluminum (Al): ≤ 0.02%
Phosphorus (P): ≤ 0.020%
Sulfur (S): ≤ 0.010%
Q3: What are the minimum mechanical properties of A335 P91 pipe?
A: The guaranteed minimum mechanical properties as per the standard are:
Tensile Strength: 585 MPa (85,000 psi)
Yield Strength: 415 MPa (60,000 psi)
Q4: What is the difference between Seamless and Welded P91 pipe?
A: The difference lies in the manufacturing process:
Seamless P91 (ASTM A335): Manufactured by piercing a solid billet, resulting in a homogeneous pipe with no longitudinal weld. This is the preferred choice for the most critical high-pressure applications.
Welded P91 (e.g., ASTM A691): Formed from plate or sheet and welded longitudinally (ERW or SAW). While cost-effective for large diameters, the weld seam is a critical area that requires extensive non-destructive testing (NDT) to ensure integrity.
Q5: What are the correct standards for P91 fittings, flanges, and plate?
A: For a fully code-compliant P91 piping system, specify these matching material standards:
Pipe Fittings (Elbows, Tees): ASTM A234 WP91
Flanges & Forged Fittings: ASTM A182 F91
Steel Plate for Fabrication: ASTM A387 Grade 91
Q6: Why is heat treatment so critical for P91 material?
A: P91 requires a precise Normalizing (at 1040-1080°C) and Tempering (at 730-780°C) heat treatment to develop its unique tempered martensitic microstructure. This structure is responsible for its high-strength and creep-resistant properties. Improper heat treatment will result in failed mechanical tests and severely reduced service life.
Q7: What are the specific welding challenges with P91 and what procedures are required?
A: Welding P91 is highly complex due to its hardenability. It demands:
Strict Pre-heat & Interpass Control: To prevent cracking.
Precise Filler Metal Selection: Typically ER90S-B9 for TIG or E9015-B9 for SMAW.
Mandatory Post-Weld Heat Treatment (PWHT): Must be performed immediately after welding within a strict temperature range (~760°C) to temper the weld zone and achieve the required toughness.
Controlled Cooling Rates: After welding and before PWHT.
Q8: What certifications and testing do you provide with your P91 pipes?
A: We supply all material with a full Material Test Certificate (MTC) per EN 10204 3.1/3.2, which includes certified chemical analysis and mechanical test results. Standard hydrostatic testing is included, and we can provide additional NDE certifications such as Ultrasonic Testing (UT) and Radiographic Testing (RT) as per project requirements.
Q9: In which applications is A335 P91 most commonly used?
A: P91 is the material of choice for the most demanding high-energy applications, including:
Main Steam Lines & Hot Reheat Lines in ultra-supercritical power plants.
High-Pressure Boiler Components and headers.
Critical Piping in petrochemical and process industries with extreme temperature/pressure conditions.
Q10: Do your P91 products support compliance with international pressure equipment codes?
A: Absolutely. Our materials and comprehensive documentation are designed to support your compliance with major international codes and directives, including the ASME Boiler & Pressure Vessel Code, the European Pressure Equipment Directive (PED 2014/68/EU), and other regional standards, ensuring global project acceptance.
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