ASTM A335 P91 seamless alloy steel tubes are engineered for high-pressure and extreme-temperature applications up to 600°C (1112°F). Containing 9% Chromium and 1% Molybdenum, alloyed with Vanadium and Niobium, P91 provides superior elevated-temperature creep strength, oxidation resistance, and microstructural stability compared to standard carbon steel or P22 grades.
Commonly deployed in critical power generation and refinery circuits, these tubes allow for reduced wall thickness and weight while maintaining structural integrity under severe thermal stress.
Specifications
|
Parameter |
Standard / Specification |
|
Material Grade |
ASTM A335 Grade P91 (UNS K91560) |
|
Manufacturing Process |
Seamless (Hot finished or cold drawn) |
|
Size Range |
Outer Diameter: 1/2" to 24" (21.3 mm to 610 mm) |
|
Wall Thickness |
Schedule 40 to XXS / Up to 100 mm |
|
Standard Length |
SRL (5-7m), DRL (10-12m), or cut to exact project lengths |
|
Heat Treatment |
Normalized and Tempered (1040°C min normalizing, 730°C min tempering) |
|
Associated Standards |
ASME SA335 P91, EN 10216-2 (X10CrMoVNb9-1) |
Material & Manufacturing
Chemical Composition (%)
|
C |
Mn |
P (max) |
S (max) |
Si |
Cr |
Mo |
V |
Nb |
N |
|
0.08–0.12 |
0.30–0.60 |
0.020 |
0.010 |
0.20–0.50 |
8.00–9.50 |
0.85–1.05 |
0.18–0.25 |
0.06–0.10 |
0.030–0.070 |
Mechanical Properties
|
Tensile Strength (min) |
585 MPa (85 ksi) |
|
Yield Strength (min) |
415 MPa (60 ksi) |
|
Elongation (min) |
20% (longitudinal), 20% (transverse) |
|
Hardness (max) |
248 HBW / 250 HV |
Manufacturing Process & Production Capability
• Raw Material Sourcing: Vacuum-degassed, fully killed steel billets with controlled sulfur and phosphorus limits to prevent reheat cracking.
• Piercing & Rolling: High-precision rotary piercing mills followed by multi-stand mandrel mills ensure uniform wall thickness eccentricity within ±10%.
• Controlled Heat Treatment: Fully automated, continuous roller-hearth furnaces equipped with multi-point thermocouple logging to maintain precise soaking and cooling rates, securing the tempered martensitic microstructure required for P91.
Quality Inspection & Testing
Every production lot undergoes rigorous destructive and non-destructive examination (NDE) prior to dispatch:
Non-Destructive Testing (NDT): 100% Ultrasonic Testing (UT) per ASTM A450 / A1016 and Hydrostatic Testing at pressures calculated per ASME B31.1/B31.3.
Mechanical Testing: Tension test, flattening test, hardness test, and impact (Charpy V-notch) testing at ambient or elevated temperatures per project specification.
Metallographic Examination: Microstructure evaluation (ensuring tempered martensite) and grain size determination (ASTM E112). PMI (Positive Material Identification) via XRF analyzer on 100% of finished tubes.
Certification: Mill Test Certificates (MTC) supplied in accordance with EN 10204 3.1. Third-party inspection (TPI) by Lloyds Register, SGS, or Bureau Veritas available upon request.
Applications
ASTM A335 P91 tubes are specified for high-energy piping systems where failure is not an option:
Power Generation: Main steam piping, hot reheat lines, boiler feed pump lines, and superheater headers in supercritical and ultra-supercritical coal/gas-fired power plants.
Petroleum Refining: Hydrotreater furnace tubes, high-pressure hydrogen transfer lines, and catalytic cracking unit (CCU) effluent piping operating above 500°C.
Petrochemicals: Ethylene cracking furnaces and high-temperature synthesis gas transfer lines.
Customization & Supply
Surface Protection:
External black varnish, anti-rust oil, or shot-blasted bare surface; plastic end caps applied to both ends.
Beveled Ends:
Plain ends or standard ASME B16.25 pipe bevels (30° +5°/-0°) for welding.
Marking:
Stenciled heat number, specification (ASTM A335 P91), grade, size, and manufacturer ID applied continuously along the pipe length.
Logistics:
Bundled in heavy-duty steel strapping or packed in seaworthy wooden crates for container or break-bulk shipping.
FAQ
Q: What is the primary advantage of P91 over P22?
A: P91 contains 9% chromium and vanadium/niobium additions, allowing higher operating temperatures (up to 600°C) and thinner walls due to increased high-temperature creep strength, which reduces overall piping weight and thermal fatigue.
Q: What heat treatment condition are P91 tubes delivered in?
A: They are delivered in the normalized and tempered condition. Post-weld heat treatment (PWHT) is mandatory after any field welding or bending.
Q: Can you provide Third-Party Inspection (TPI)?
A: Yes. We regularly accommodate inspections by agencies such as SGS, BV, TUV, and LR prior to shipment.
Q: What is the standard manufacturing length?
A: Standard production lengths include Single Random Lengths (SRL 5–7m) and Double Random Lengths (DRL 10–12m). Cut-to-length options are available for specific isometric drawings.
Q: Are MTCs provided with the shipment?
A: Yes. EN 10204 3.1 Mill Test Certificates detailing chemical analysis, mechanical test results, hardness, heat treatment charts, and NDT results are dispatched with every order and available digitally beforehand.
Q: What is the typical lead time for stock vs. production orders?
A: Common sizes (NPS 2" to 12") are maintained in stock for immediate dispatch. Custom rolling or specific wall thickness requirements typically require 4 to 8 weeks depending on mill scheduling.
Request a Quote
To receive a formal quotation for your project, please provide the following parameters:
• Outer Diameter & Wall Thickness (or Schedule)
• Quantity (Total Meters, Tonnes, or Piece Count)
• Required Standard & Supplementary Testing (e.g., ASME SA335, specific impact testing temperatures, TPI requirement)
• Destination Port / Project Site
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