ASTM A335/A335M: Seamless Ferritic Alloy-Steel Pipe for High-Temperature Service
1. Overview
ASTM A335/A335M is the primary specification for seamless ferritic alloy-steel pipes intended for high-temperature service. These pipes are designed for bending, flanging, and similar forming operations, as well as for welding, in environments requiring elevated temperature strength and corrosion resistance.
2. Key Features
Type: Seamless (mandatory)
Material: Ferritic alloy steel (Cr-Mo, Cr-Mo-V alloys)
Application: High-temperature, high-pressure environments
Common Companion Standard: ASTM A450 (General Requirements)
3. Standard Grades & Chemical Composition
| Grade | UNS No. | Typical Composition | Key Alloying Elements | Notes |
|---|---|---|---|---|
| P1 | K11522 | C-Mo | 0.5Mo | Basic molybdenum steel |
| P2 | K11547 | 0.5Cr-0.5Mo | 0.5Cr, 0.5Mo | Low chromium-moly |
| P5 | K41545 | 5Cr-0.5Mo | 5Cr, 0.5Mo | Medium chromium |
| P5c | K41245 | 5Cr-0.5Mo | 5Cr, 0.5Mo | Modified P5 |
| P9 | S50400 | 9Cr-1Mo | 9Cr, 1Mo | High chromium |
| P11 | K11597 | 1.25Cr-0.5Mo | 1.25Cr, 0.5Mo | Standard Cr-Mo |
| P12 | K11562 | 1Cr-0.5Mo | 1Cr, 0.5Mo | Similar to P11 |
| P22 | K21590 | 2.25Cr-1Mo | 2.25Cr, 1Mo | Very common grade |
| P91 | K91560 | 9Cr-1Mo-V-Nb | 9Cr, 1Mo, V, Nb | High-strength, creep-resistant |
| P92 | K92460 | 9Cr-2W-0.5Mo-V-Nb | 9Cr, 2W, 0.5Mo, V, Nb | Advanced 9%Cr steel |
| P122 | K91603 | 12Cr-1W-1Cu-Mo-V-Nb | 12Cr, 1W, 1Cu, Mo, V, Nb | Highest chromium grade |
Note: Complete chemical requirements are specified in the standard with precise minimum/maximum percentages.
4. Mechanical Properties (Typical at Room Temperature)
| Grade | Tensile Strength Min (MPa) | Yield Strength Min (MPa) | Elongation Min (%) | Hardness Max (HB) |
|---|---|---|---|---|
| P1 | 380 | 205 | 30 | 163 |
| P2 | 380 | 205 | 30 | 163 |
| P5 | 415 | 205 | 30 | 163 |
| P9 | 415 | 205 | 30 | 163 |
| P11 | 415 | 205 | 30 | 163 |
| P12 | 415 | 205 | 30 | 163 |
| P22 | 415 | 205 | 30 | 163 |
| P91 | 585 | 415 | 20 | 250 |
| P92 | 620 | 440 | 20 | 250 |
| P122 | 620 | 400 | 20 | 250 |
*Note: Specific requirements vary by heat treatment condition; P91/P92/P122 require normalization and tempering.*
5. Manufacturing & Heat Treatment
| Process | Requirement | Purpose |
|---|---|---|
| Manufacturing | Seamless process only (hot finished or cold drawn) | Ensure homogeneity, no longitudinal weld |
| Heat Treatment | All pipes supplied in heat-treated condition | Develop required microstructure and properties |
| Normalizing | Required for P91, P92, P122 (~1040-1080°C) | Austenitize for tempered martensite structure |
| Tempering | Required after normalizing (~730-800°C) | Improve toughness, relieve stresses |
| Annealing/Stress Relief | For lower grades (P1-P22) as specified | Soften, relieve stresses, improve ductility |
6. Testing & Inspection Requirements
| Test Type | Frequency | Standard Reference | Purpose |
|---|---|---|---|
| Hydrostatic Test | Each pipe | A450/A335 | Verify pressure integrity |
| Tensile Test | Each heat, each heat treatment lot | A370 | Verify mechanical properties |
| Hardness Test | Each pipe or sample basis | E10/E18 | Verify uniform heat treatment |
| Flattening Test | Two pipes per heat lot | A450 | Check ductility/formability |
| Nondestructive Test (UT/ET) | Optional, as specified | E213/E309 | Detect internal/external defects |
| Visual Examination | 100% | - | Surface quality check |
7. Dimensions & Tolerances
| Dimension | Standard Tolerance (Per A450) | Common Sizes Available |
|---|---|---|
| Outside Diameter | ±0.75% or ±0.4mm (whichever greater) | 1/4" to 24" NPS (6-610mm) |
| Wall Thickness | +0/-12.5% for D≤101.6mm; +0/-10% for D>101.6mm | Schedules 10-160, XXS |
| Length | +3mm/-0 for random lengths; exact lengths as ordered | 6-12m standard random |
| Weight | ±10% per pipe; ±7.5% per lot | Varies by schedule |
8. Typical Applications by Grade
| Grade | Temperature Range | Common Applications |
|---|---|---|
| P1, P2 | Up to 480°C | General high-temperature service, steam lines |
| P11, P12, P22 | Up to 580°C | Power plant steam pipes, refinery process lines |
| P5, P9 | Up to 650°C | High-temperature refinery piping, reformer tubes |
| P91 | Up to 625°C | Modern power plant main steam & hot reheat lines |
| P92, P122 | Up to 650°C | Advanced ultra-supercritical power plants |
9. Material Advantages & Limitations
Advantages:
Excellent creep strength at elevated temperatures
Good oxidation/corrosion resistance (especially higher Cr grades)
Good weldability with proper procedures
High-temperature stability for long-term service
Better thermal fatigue resistance than carbon steels
Limitations:
Higher cost than carbon steel pipes
Requires post-weld heat treatment (PWHT) for most grades
Temper embrittlement susceptibility in some grades (P11, P22)
Special storage needed to prevent atmospheric corrosion
10. Ordering Information
When ordering ASTM A335 pipe, specify:
Specification: ASTM A335/A335M
Grade: P11, P22, P91, etc.
Size: NPS and schedule/thickness
Length: Random or exact
End finish: Plain, beveled (for welding)
Supplemental requirements: S1 (ultrasonic test), S2 (hydro test pressure)
General Requirements: Reference ASTM A450
Special requirements: Additional testing, marking, etc.
Example Order Designation:
ASTM A335 P22, NPS 12, Schedule 80, Random Length, Beveled Ends, +A450 +S1 (UT)
11. Comparison with Similar Specifications
| Specification | Material Type | Primary Use | Temperature Range |
|---|---|---|---|
| ASTM A335 | Ferritic alloy steels | High-temperature piping | Up to 650°C |
| ASTM A213 | Ferritic/austenitic alloys | Boiler/superheater tubes | Up to 700°C |
| ASTM A312 | Austenitic stainless | Corrosion/high-temp service | Up to 815°C |
| ASTM A106 | Carbon steel | General high-temp service | Up to 425°C |
12. Important Notes
ASTM A450 provides the general test methods and requirements unless otherwise specified in A335
P91 and higher grades require strict control of heat treatment parameters
Welding procedures must be qualified per ASME Section IX or equivalent
Material traceability is critical for high-temperature applications
Creep testing may be required for certain applications beyond standard requirements
This specification is extensively used in power generation, petrochemical, and refining industries where materials must withstand prolonged exposure to high temperatures and pressures. Proper selection, installation, and maintenance according to applicable codes (ASME B31.1, B31.3) are essential for safe and reliable operation.
