ASTM A335 P91 Alloy Steel Seamless Pipes (Type 1 & Type 2)
Introduction
ASTM A335 P91 Type 1 (UNS K91560) and Type 2 (UNS K91561) are high-strength Chromium-Molybdenum-Vanadium (Cr-Mo-V) alloy steel grades developed for seamless ferritic alloy steel pipes used in ultra-high temperature and high-pressure environments. P91 pipes exhibit exceptional creep strength, superior stress-rupture resistance, and excellent oxidation behavior, making them the leading choice for advanced power generation, steam lines, and high-efficiency boiler systems.
Key Features
- Exceptional creep resistance for long-term elevated temperature service
- High tensile and yield strength compared to P22/P9 grades
- Superior resistance to thermal fatigue and oxidation
- Designed for ultra-supercritical and supercritical power plant applications
- Lower wall thickness requirements due to high strength
- Good structural stability with minimal deformation at high temperatures
- Available in Type 1 and Type 2 variants
Equivalent Grades
| Standard | P91 Type 1 | P91 Type 2 |
|---|---|---|
| ASTM | A335 P91 | A335 P91 |
| ASME | SA335 P91 | SA335 P91 |
| UNS | K91560 | K91561 |
| EN | X10CrMoVNb9-1 | X10CrMoVNb9-1 (modified) |
| DIN | 1.4903 | 1.4903 |
Sizes
- Outside Diameter (OD): 1/2” to 36”
- Nominal Bore (NB): DN15 to DN900
- Wall Thickness: SCH 20, SCH 30, SCH 40, SCH 80, SCH 160, XXS
ASTM A335 P91 Chemical Composition
| Element | Percentage (%) |
|---|---|
| Carbon (C) | 0.08 – 0.12 |
| Manganese (Mn) | 0.30 – 0.60 |
| Phosphorus (P) | ≤ 0.020 |
| Sulfur (S) | ≤ 0.010 |
| Silicon (Si) | 0.20 – 0.50 |
| Chromium (Cr) | 8.00 – 9.50 |
| Molybdenum (Mo) | 0.85 – 1.05 |
| Vanadium (V) | 0.18 – 0.25 |
| Niobium (Nb) | 0.06 – 0.10 |
| Nitrogen (N) | 0.03 – 0.07 |
| Nickel (Ni) | ≤ 0.40 |
| Aluminum (Al) | ≤ 0.04 |
Gr P91 Mechanical Properties
| Property | Value |
|---|---|
| Tensile Strength | ≥ 585 MPa |
| Yield Strength | ≥ 415 MPa |
| Elongation | ≥ 20% |
| Hardness | ≤ 250 HB |
| Impact Strength | High at elevated temperatures |
Gr P91 Physical Properties
| Property | Value |
|---|---|
| Density | 7.8 g/cm³ |
| Thermal Conductivity | 27–30 W/m·K |
| Modulus of Elasticity | 200–210 GPa |
| Melting Range | 1425 – 1475°C |
| Specific Heat Capacity | 460 J/kg·K |
Types of A335 P91 Pipes
- Seamless Alloy Steel Pipes
- Hot-Finished Pipes
- Cold-Drawn Pipes
- Boiler Pipes
- Superheater Tubes
- Reheater Tubes
- Header and Steam Line Pipes
- High-Pressure Service Pipes
Applications
- Ultra-Supercritical and Supercritical Power Plants
- High-Temperature Steam Lines
- Boilers, Economizers, and Reheaters
- Superheaters
- Thermal Power Stations
- Refineries and Petrochemical Units
- Heat Exchangers
- Chemical Processing Plants
- Industrial Pressure Vessels
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