ASME A335 / ASTM A335 P11 Seamless Alloy Steel Pipe
UNS K11597 - ASME SA-335 / ASTM A335 P11 is a seamless 1.25% Chromium - 0.5% Molybdenum (1.25Cr-0.5Mo) ferritic alloy steel pipe, engineered for continuous service in boilers, superheaters, pressure vessels, and high-temperature steam piping. Known in the industry as chrome-moly or Cr-Mo pipe, P11 delivers reliable creep and oxidation resistance above 400°C, making it the standard material choice across power generation, petrochemical plants, oil refineries, and industrial heating systems worldwide.
Chemical Composition (ASTM A335 Table 1)
| Element | C | Mn | Si | Cr | Mo | P (max) | S (max) |
|---|---|---|---|---|---|---|---|
| P11 | 0.05–0.15 | 0.30–0.60 | 0.50–1.00 | 1.00–1.50 | 0.44–0.65 | 0.025 | 0.025 |
Chromium in the 1–1.5% range builds a stable chromium oxide layer that shields the pipe against high-temperature oxidation and scaling. Molybdenum at 0.44–0.65% strengthens the ferrite matrix and slows dislocation creep under sustained load at elevated temperatures. Together, these two alloying elements give P11 its characteristic combination of heat resistance and long-term mechanical stability.
Mechanical Properties (Minimum Values per ASTM A335)
| Property | Value |
|---|---|
| Tensile Strength (min) | 415 MPa (60 ksi) |
| Yield Strength (min, 0.2% offset) | 205 MPa (30 ksi) |
| Elongation (longitudinal, min, strip test ≥8mm wall) | 30% (in 2" or 50 mm) |
| Elongation (transverse, min, strip test ≥8mm wall) | 20% |
| Hardness (max) | 250 HBW (25 HRC max) |
International Grade Equivalents
The table below lists the closest material equivalents to ASTM A335 P11 across major international standards. These grades are functionally similar and are often accepted as substitutes in global projects where one standard system is specified and another is sourced.
| Standard | Grade / Material Number |
|---|---|
| ASTM A335 / ASME SA-335 | P11 |
| UNS | K11597 |
| EN 10216-2 | 13CrMo4-5 (1.7335) |
| JIS G3458 (pipe) | STPA23 |
| JIS G3462 (tube) | STBA23 |
| GB/T 5310 | 15CrMoG |
| DIN 17175 | 13CrMo44 |
| ASTM A213 (small-diameter tube form) | T11 |
Heat Treatment
ASTM A335 mandates that P11 pipe be delivered in the normalized and tempered condition (full or isothermal annealing is also permitted).
- Normalizing: The pipe is heated to 900–960°C, held at temperature to achieve full austenitization, then cooled in still air. This refines the grain structure and homogenizes the carbide distribution.
- Tempering: The pipe is reheated to a minimum of 650°C (1200°F), held for the prescribed soak time, then cooled. Per ASTM A335, the tempering temperature must be at least 50°C (100°F) above the intended service temperature to ensure microstructural stability during operation.
The resulting ferrite-carbide microstructure delivers the creep strength, ductility, and toughness required for long-term high-temperature pressure service.
Size Range
| Parameter | Range |
|---|---|
| Outer Diameter | 1/8" – 24" (10.3 mm – 609.6 mm); larger sizes available upon request |
| Wall Thickness | SCH 40 – SCH 160 (and custom thicknesses) |
| Length | Random mill lengths (5.8–7.3 m) or fixed lengths (6 m, 12 m, custom) |
| Max Length | 16,000 mm; U-bending also available |
Applications
- Power Plants: Main steam piping, hot reheat lines, boiler headers, superheater and reheater tubes where continuous operating temperatures exceed 500°C and ASME B31.1 compliance is required.
- Petrochemical & Refining: Hydrocracking effluent pipes, catalytic reformer heater tubes, hydrogen reformer outlet piping, and furnace coils handling corrosive hydrocarbons at elevated pressure.
- Oil & Gas: High-temperature process piping in refineries and gas processing plants, including sulfur recovery units and delayed coker heaters.
- Heat Exchangers: Feedwater heater tubing, process heat exchanger bundles, and condenser piping that must withstand thermal cycling under design pressure.
- Industrial Boilers & Furnaces: Radiant and convection sections of industrial furnaces, waste heat recovery boilers, and fluidized bed combustor piping.
Key Performance Attributes
- Elevated-Temperature Strength: P11 retains useful mechanical strength up to approximately 593°C (1100°F) in oxidizing environments, far beyond the 425°C ceiling of carbon steel grades such as A106 Gr.B.
- Creep Rupture Life: The Cr-Mo alloy system resists time-dependent deformation under sustained stress, giving P11 a well-characterized creep rupture curve that enables life-cycle design per ASME Section II Part D allowable stress tables.
- Oxidation & Hydrogen Attack Resistance: The chromium-derived oxide scale protects against high-temperature scaling. The molybdenum addition also helps resist hydrogen attack in high-pressure hydrogen service common in refinery hydroprocessing.
- Field Weldability: With controlled preheat (150–250°C depending on wall thickness) and mandatory post-weld heat treatment at 700–750°C, P11 joints achieve full code compliance (ASME B31.1 / B31.3) with standard SMAW, GTAW, GMAW, or SAW processes.
- Cost Efficiency vs. Alternatives: Compared to stainless steel (304H/347H) or nickel alloys (Incoloy 800), P11 offers comparable high-temperature performance at a substantially lower material cost, making it the default choice for moderate-temperature Cr-Mo service.
Inspection and Testing
- Hydrostatic Testing: Conducted per ASTM A999 - each pipe is pressurized to verify leak-tightness and burst margin.
- Non-Destructive Examination: Ultrasonic testing per ASTM A388 (or equivalent) is performed on 100% of the production. Radiographic and magnetic particle testing are available on request.
- Chemical Verification: Spectrographic analysis (OES or XRF) of each heat confirms conformance to Table 1 limits.
- Mechanical Qualification: Tensile, yield, elongation, hardness, flattening, and flare testing per ASTM A370.
- PMI (Positive Material Identification): Alloy grade verification via portable XRF analyzer on every pipe, with documented traceability.
- Mill Test Certificate: A full MTC with heat number, chemistry, and mechanical results is included with each shipment. Third-party inspection (SGS, BV, TÜV, or customer-nominated) is supported as standard practice.
P11 Stock Inventory
The table below reflects a portion of our current stock. Contact us for updated availability, additional sizes, or non-standard specifications.
| Spec | Grade | O.D. (mm) | W.T. (mm) | Length (mm) | QTY (pcs) | QTY (T) |
|---|---|---|---|---|---|---|
| ASTM A335 | P11 | 60.30 | 8.74 | >100 | ||
| ASTM A335 | P11 | 73.00 | 7.00 | >100 | ||
| ASTM A335 | P11 | 73.00 | 9.00 | >100 | ||
| ASTM A335 | P11 | 88.90 | 5.49 | 12000 | >100 | 0.938 |
| ASTM A335 | P11 | 88.90 | 5.49 | 6000–12000 | >100 | 1.472 |
| ASTM A335 | P11 | 88.90 | 7.62 | 12000 | >100 | 1.450 |
| ASME SA335 | P11 | 88.90 | 7.62 | 6000–12000 | >100 | 0.312 |
| ASTM A335 | P11 | 88.90 | 7.62 | >100 | ||
| ASTM A335 | P11 | 88.90 | 11.13 | >100 | ||
| ASTM A335 | P11 | 114.30 | 6.02 | >100 | ||
| ASTM A335 | P11 | 114.30 | 8.56 | 6000–12000 | >100 | 0.930 |
| ASTM A335 | P11 | 141.30 | 6.55 | >100 | 0.356 | |
| ASTM A335 | P11 | 168.30 | 7.11 | 8000–12000 | >100 | 15.152 |
| ASTM A335 | P11 | 168.30 | 10.97 | 6000–12000 | >100 | 1.204 |
| ASTM A335 | P11 | 168.30 | 10.97 | >100 | ||
| ASTM A335 | P11 | 219.10 | 12.70 | >100 | ||
| ASTM A335 | P11 | 273.00 | 16.00 | >100 | ||
| ASTM A335 | P11 | 273.00 | 18.50 | >100 | ||
| ASTM A335 | P11 | 325.00 | 14.00 | >100 | ||
| ASTM A335 | P11 | 325.00 | 16.00 | >100 | ||
| ASTM A335 | P11 | 325.00 | 20.00 | >100 | ||
| ASTM A335 | P11 | 325.00 | 22.00 | >100 | ||
| ASTM A335 | P11 | 325.00 | 26.00 | >100 | ||
| ASTM A335 | P11 | 325.00 | 30.00 | >100 | ||
| ASTM A335 | P11 | 609.60 | 30.75 | >100 |
Length: 5800mm / 6000mm / 6096mm / 7315mm / 11800mm / 12000mm (custom available)
Max length: 16000mm; U-bending also available.
Note: The above table shows a portion of our current stock. For additional sizes, quantities, or non-stock grades, please contact us.
Why Choose Shuangzhong for P11 Pipe?
- ISO 9001:2015 & API Certified - Quality management system certified; API monogram available for critical service applications.
- Full Size Range - Stocking OD from 21.3 mm to 609.6 mm in popular schedules, with access to mill-direct production for non-standard sizes.
- MTC with Every Order - Full chemical and mechanical traceability per EN 10204 Type 3.1 or 3.2.
- Third-Party Inspection Friendly - SGS, BV, TÜV, or customer-nominated inspectors welcome at every stage of production.
- Global Export Experience - Supplying to North America, Europe, the Middle East, and Southeast Asia with packaging and documentation compliant with international shipping standards.
- Custom Solutions - U-bending, special lengths, end preparation (bevel / threading), custom packaging, and marking available.
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