ASTM A369 FP21 (UNS K31545) Forged & Bored Cr-Mo Alloy Steel Pipe
ASTM A369 FP21 (UNS K31545) is a high-performance chromium-molybdenum (Cr-Mo) alloy steel grade designed for forged and bored heavy-wall pipes used in high-temperature and high-pressure environments. With superior creep resistance, strength, and thermal stability, FP21 is widely used in boiler components, pressure piping, superheater tubes, and power generation systems requiring long-term reliability. Its Cr-Mo composition also offers enhanced resistance to oxidation and thermal fatigue, making it ideal for severe industrial service.
Key Features
- Chromium-Molybdenum (Cr-Mo) alloy steel for high-temperature service
- Excellent creep and stress-rupture strength
- Superior resistance to oxidation, scaling & thermal fatigue
- Suitable for forged & bored heavy-wall pipe manufacturing
- Stable mechanical properties at elevated temperatures
- Ideal for boilers, pressure vessels & high-pressure piping systems
- Produced to strict ASTM A369 standards for critical applications
Equivalent Grades
| Standard | Equivalent Grade |
|---|---|
| ASTM | FP21 |
| UNS | K31545 |
| DIN / EN | — (No direct equivalent) |
| JIS | — |
| BS | — |
ASTM A369 FP21 Chemical Composition
| Element | % |
|---|---|
| Carbon (C) | 0.15 – 0.25 |
| Manganese (Mn) | 0.30 – 0.60 |
| Phosphorus (P) | ≤ 0.025 |
| Sulfur (S) | ≤ 0.025 |
| Silicon (Si) | 0.50 – 1.00 |
| Chromium (Cr) | 2.00 – 2.50 |
| Molybdenum (Mo) | 1.00 – 1.50 |
| Nickel (Ni) | ≤ 0.40 |
| Copper (Cu) | ≤ 0.40 |
Available Size Range
| Parameter | Available Range |
|---|---|
| Outside Diameter (OD) | 50 mm to 1200 mm |
| Wall Thickness (WT) | 5 mm to 150 mm (heavy-wall) |
| Inside Diameter (ID) | As per customer requirement |
| Length | Up to 12 meters (custom lengths on request) |
| Manufacturing Tolerances | As per ASTM A369 standard |
Mechanical Properties
| Property | Value |
|---|---|
| Tensile Strength | 485 MPa (Min) |
| Yield Strength | 275 MPa (Min) |
| Elongation | 20% (Min) |
| Hardness (HBW) | 179 – 217 |
Physical Properties
| Property | Value |
|---|---|
| Density | 7.80 g/cm³ |
| Melting Point | 1425–1475°C |
| Thermal Conductivity | ~ 30 W/m-K |
| Modulus of Elasticity | 200 GPa |
| Coefficient of Expansion | 11.3 µm/m°C |
Types Available
- ASTM A369 FP21 Forged Pipe
- ASTM A369 FP21 Bored Pipe
- ASTM A369 FP21 Heavy-Wall Pipe
- ASTM A369 FP21 Custom-Machined Pipe
- ASTM A369 FP21 Seamless Forged Cylinders
Applications
- Boilers & Superheater Systems
- Petrochemical Plants
- Pressure Piping Systems
- Steam Transmission Lines
- Power Generation Components
- Refinery High-Temperature Piping
- Heat Exchangers
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