ASTM A335 P11 Seamless Alloy-Steel Pipe for High-Temperature Service
ASTM A335 P11 is a specification for seamless ferritic alloy-steel pipe designed specifically for high-temperature and high-pressure service. It falls under the broader ASTM A335 standard and is commonly used in power plants and refineries.
Key Features of A335 P11:
Material: Low-chromium alloy steel (1¼% Chrome - ½% Molybdenum).
Manufacturing Process: Seamless (SMLS) only.
Primary Use: High-temperature piping systems including:
Power plant steam lines
Refinery process piping
High-temperature headers
Petrochemical plant piping
Key Property: Good elevated temperature strength and oxidation resistance up to approximately 540°C (1000°F).
Chemical Composition Requirements:
| Element | Composition (%) |
|---|---|
| Carbon (C) | 0.05 - 0.15 |
| Manganese (Mn) | 0.30 - 0.60 |
| Phosphorus (P), max | 0.025 |
| Sulfur (S), max | 0.025 |
| Silicon (Si) | 0.50 - 1.00 |
| Chromium (Cr) | 1.00 - 1.50 |
| Molybdenum (Mo) | 0.44 - 0.65 |
Mechanical Properties:
| Property | Requirement |
|---|---|
| Tensile Strength | ≥ 415 MPa (60,000 psi) |
| Yield Strength | ≥ 205 MPa (30,000 psi) |
| Elongation | ≥ 30% (in 50mm) |
Heat Treatment: P11 pipe is supplied in normalized and tempered condition to achieve optimal microstructure and mechanical properties.
Comparison with Related Grades:
| Grade | Key Difference from P11 |
|---|---|
| A335 P5 | Higher chromium (4-6% Cr), better oxidation resistance |
| A335 P9 | Higher chromium (8-10% Cr), better oxidation resistance |
| A335 P22 | Higher chromium (2-2.5% Cr), better high-temperature strength |
| A106 Gr. B | Carbon steel, not suitable for high-temperature service |
Important Notes:
P11 is the pipe equivalent of A213 T11 tube specification (same chemistry)
Suitable for service temperatures up to about 540°C (1000°F)
Requires post-weld heat treatment (PWHT) for most welding applications
Often specified for refinery fluid catalytic cracking (FCC) units and similar applications
P11 offers a good balance of cost and performance for medium-temperature applications where carbon steel lacks sufficient strength and oxidation resistance.
