A335 P1 Low Alloy Seamless Round Pipes
A335 P1 alloy pipe is a seamless ferritic alloy steel pipe for high temperature use. It has high thermal strength and resistance to hydrogen corrosion. It is widely used in high temperature and high pressure pipelines and equipment in petrochemical, electric power, nuclear power plants, aerospace and other industries.
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What Is A335 P1 Seamless Pipe?
A335 P1 is defined under ASTM A335 / ASME SA335 Standard Specification for Seamless Ferritic Alloy-Steel Pipe for High-Temperature Service.
It is a carbon-molybdenum (C-Mo) low alloy steel, and the lowest alloyed grade in the A335 P-series.
"P" stands for pressure-rated piping material
P1 contains no intentional chromium addition
Chromium content is limited to residual levels (≤0.30%)
Official UNS designation: K11522
Unlike higher grades such as P11 or P22, P1 does not belong to the chromium-molybdenum (Cr-Mo) family.
A335 P1 Chrome Moly Seamless Pipe Specification
Outer Diameter: 10.3 mm – 914.4 mm
Wall Thickness: SCH10 – SCH160 / XXS
Length: Random / Fixed (5.8m, 11.8m, R3)
Standards compliance:
ASTM A335 / ASME SA335
ASME B36.10M
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Chemical Composition (ASTM A335 Requirement)
P1 steel uses molybdenum as the primary strengthening element for high-temperature performance.
| Element | Range (wt%) | Function |
|---|---|---|
| Carbon (C) | 0.10 – 0.20% | Strength control |
| Manganese (Mn) | 0.30 – 0.80% | Improves strength and hardenability |
| Silicon (Si) | 0.10 – 0.50% | Deoxidation and oxidation resistance |
| Phosphorus (P) | ≤ 0.025% | Impurity control |
| Sulfur (S) | ≤ 0.025% | Impurity control |
| Chromium (Cr) | ≤ 0.30% | Residual element (not intentionally added) |
| Molybdenum (Mo) | 0.44 – 0.65% | Primary alloying element for creep strength |
Important clarification:
A335 P1 is a C-Mo steel, not a chrome-moly steel. True Cr-Mo grades begin at P5 (5% Cr) and P11 (1.25% Cr).
Mechanical Properties & Performance
Room Temperature Properties (Minimum Requirements)
Per ASTM A335:
| Property | Requirement |
|---|---|
| Tensile Strength | ≥ 55 ksi (380 MPa) |
| Yield Strength (0.2%) | ≥ 30 ksi (205 MPa) |
| Elongation | ≥ 30% (longitudinal, typical for standard thickness) |
Note: Tensile and yield values are minimum requirements, not fixed operating values.
ASTM A335 P1 vs Other Grades (P11 / P22)
| Grade | Alloy Level | Temperature Capability | Application |
|---|---|---|---|
| P1 | Low Cr-Mo | ~450°C | Medium-temp boiler & exchanger |
| P11 | Medium Cr-Mo | ~540°C | Power plant superheaters |
| P22 | Higher Cr-Mo | ~580°C | High pressure steam lines |
Selection insight:
Choose P1 for cost-sensitive medium-temperature systems
Choose P11/P22 for higher steam pressure and temperature stability
High-Temperature Behavior
A335 P1 is suitable for elevated-temperature service where creep resistance is required at moderate stress levels.
Key characteristics:
- Improved creep resistance compared to carbon steel
- Better strength retention at elevated temperature due to Mo addition
- Suitable for long-term service in moderate high-temperature environments
Important clarification:
ASTM A335 does not define a fixed maximum service temperature. Allowable temperature must be determined by ASME B31.1 / B31.3 design calculations and creep criteria.
Manufacturing Process
ASTM A335 P1 pipes are produced using:
Hot finished seamless process
Cold drawing (for tight tolerance requirements)
Heat treatment (normalizing or annealing)
Each pipe undergoes:
Hydrostatic testing
Ultrasonic testing (UT)
Eddy current testing
PMI (Positive Material Identification)
Heat Treatment Condition
Depending on application:
Fully annealed
Normalized
Normalized and tempered (for higher strength requirement)
Heat treatment ensures:
Uniform grain structure
Stable mechanical performance under long-term heat exposure
Applications of A335 P1 Seamless Pipe
ASTM A335 P1 is widely used in:
Boiler superheater tubes
Economizer tubing systems
High-temperature steam pipelines
Refinery catalytic cracking units
Heat recovery systems (HRSG)
Why engineers choose P1:
Stable performance under continuous heat exposure
Lower cost than higher alloy grades
Reliable long-term structural integrity
A335 P1 vs Carbon Steel (A106)
| Feature | A335 P1 | A106 Carbon Steel |
|---|---|---|
| Alloy content | Cr-Mo alloy | Carbon steel |
| High temp resistance | Excellent | Limited |
| Creep resistance | Strong | Weak |
| Cost | Higher | Lower |
👉 Conclusion:
A335 P1 is required when operating temperature exceeds carbon steel safety limits.
Standards & Equivalent Grades (Important Clarification)
P1 has chemically similar grades in other systems, but not all are direct equivalents due to differences in product form and design codes.
| Standard | Grade | Notes |
|---|---|---|
| ASTM / ASME | A335 P1 / SA335 P1 | Seamless pressure pipe |
| ASTM | A209 T1 | Similar C-Mo chemistry (boiler tube) |
| EN | 16Mo3 | Chemically similar C-Mo steel (not direct equivalent) |
| JIS | STPA11 | Similar high-temperature C-Mo steel |
| UNS | K11522 | Unified designation |
Important correction:
These grades are similar in composition but not strictly interchangeable due to differences in standard scope, heat treatment, and allowable stress design.
Quality Assurance & Testing
Each shipment includes full inspection documentation:
Mill Test Certificate (EN 10204 3.1 / 3.2)
Chemical composition report
Mechanical test report
Hydrostatic test report
NDT reports (UT/RT/PMI)
Optional third-party inspection:
SGS
BV
TUV
Packaging & Delivery
Plastic caps on both ends
Bundled with steel strips
Waterproof wrapping
Wooden box (for small OD pipes)
Shipping options:
Bulk vessel
Container loading
Break bulk shipment
A335 P1 Boiler Pipe in stock
FAQ
Q1: What is ASTM A335 P1 used for?
A335 P1 is used for high-temperature boiler, heat exchanger, and steam pipeline systems.
Q2: Is A335 P1 suitable for high pressure?
Yes, but it is best suited for medium to high pressure at moderate temperatures.
Q3: What is the difference between P1 and P11?
P11 contains higher chromium and molybdenum, making it suitable for higher temperature applications.
Q4: What temperature can A335 P1 withstand?
Typically up to around 450°C depending on design conditions.
Q5: Is PWHT required?
Not always. It depends on thickness, service conditions, and applicable design code.
Q6: Is it suitable for sour service?
Only for mild sour environments with proper qualification (NACE MR0175). Not suitable for severe sour service.
Q7: Difference between A335 P1 and A209 T1?
Similar chemistry, but different product forms:
P1: pipe
T1: boiler / heat exchanger tube
Q8: Is A335 P1 stainless steel?
No. It contains insufficient chromium to form a stainless protective layer.
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