ASME SA335 High-Pressure Alloy Pipe
Dec 03, 2025
What Is ASME SA335 Pipe
The SA335 standard primarily applies to seamless alloy steel pipes that maintain excellent mechanical properties at high temperatures. Based on varying alloy compositions, the standard classifies seamless pipes into multiple grades (P1, P5, P9, P11, P12, P22, P91), with differences primarily in chemical composition and mechanical properties to suit specific operating environments. The chromium-molybdenum chemistry provides elevated-temperature strength, oxidation resistance, and creep resistance that plain carbon pipe cannot achieve.
Specification Overview
Diameter: 16-1016 mm. Thickness: 2-120 mm. Steel grades: P1, P2, P5, P9, P11, P12, P22, and P91. Surface: oiled or black painted to prevent rust. Application fields: industrial boilers, power plants, and nuclear plants.
Chemical Composition (Selected Grades)
| Grade | C (%) | Si (%) | Mn (%) | P max | S max | Mo (%) | Cr (%) |
|---|---|---|---|---|---|---|---|
| P1 | 0.10-0.20 | 0.10-0.50 | 0.30-0.80 | 0.025 | 0.025 | 0.44-0.65 | - |
| P5 | 0.15 max | 0.50 max | 0.30-0.60 | 0.025 | 0.025 | 0.45-0.65 | 4.00-6.00 |
| P11 | 0.05-0.15 | 0.50-1.00 | 0.30-0.60 | 0.025 | 0.025 | 0.45-0.65 | 1.00-1.50 |
| P12 | 0.05-0.15 | 0.50 max | 0.30-0.61 | 0.025 | 0.025 | 0.44-0.65 | 0.80-1.25 |
| P22 | 0.05-0.15 | 0.50 max | 0.30-0.60 | 0.025 | 0.025 | 0.87-1.13 | 1.90-2.60 |
Mechanical Properties (Annealed)
| Grade | Tensile strength min (MPa) | Yield strength min (MPa) | Elongation min (%) |
|---|---|---|---|
| P1 | 380 | 205 | 30 |
| P5 | 415 | 205 | 30 |
| P11 | 415 | 205 | 30 |
| P12 | 415 | 205 | 30 |
| P22 | 415 | 205 | 30 |
Wall Thickness Tolerances
| NPS [DN] designator | Over (%) | Under (%) |
|---|---|---|
| 1/8 to 2-1/2 [6 to 65], all t/D ratios | 20.0 | 12.5 |
| Above 2-1/2 [65], t/D up to 5% | 22.5 | 12.5 |
| Above 2-1/2 [65], t/D above 5% | 15.0 | 12.5 |
t = specified wall thickness; D = specified outside diameter.
Testing and Inspection
Chemical composition analysis by spectral methods, mechanical property testing (tensile, impact, hardness), non-destructive testing (ultrasonic, X-ray, magnetic particle), visual inspection for surface defects, hydrostatic testing to verify pressure resistance, and heat treatment inspection when necessary to confirm the microstructure and mechanical properties.
Frequently Asked Questions
Q: What is ASME SA335? A> The specification for seamless ferritic alloy steel pipe for high-temperature service.
Q: What grades are available? A> P1, P2, P5, P9, P11, P12, P22, and P91.
Q: What is the tensile strength of P22? A> 415 MPa minimum, with 205 MPa minimum yield strength.
Q: What is the size range? A> 16-1016 mm diameter with 2-120 mm wall thickness.
Q: Where is SA335 pipe used? A> Industrial boilers, power plants, and nuclear plants in high-temperature service.
Q: What tests are performed? A> Chemical analysis, tensile, impact, hardness, NDT, visual, and hydrostatic testing.
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