Seamless Stainless Steel TP446 Pipe
What is a Seamless Stainless Steel TP446 Pipe?
Seamless Stainless Steel TP446 Pipe is a 25 % chromium ferritic heat-resisting stainless steel produced without a welded seam. With the highest chromium level of any standard ferritic grade, TP446 is engineered for exceptional resistance to oxidation and sulfidation at temperatures approaching 1100 °C.
The high chromium content forms an extremely stable, adherent oxide scale that protects the pipe in sulfur-bearing and low-oxygen furnace atmospheres where austenitic grades scale away rapidly. As a ferritic alloy it is also immune to chloride stress-corrosion cracking, a failure mode that affects austenitic steels in certain environments.
Produced to ASTM A268 (tubing) and A790 (pipe) equivalents, TP446 seamless pipe is used for furnace components, burner parts and pyrolysis equipment where extreme scaling resistance matters more than high strength.
Stainless Steel TP446 vs TP430 vs TP310S: High-Chromium Ferritic Duty
TP446 sits at the top of the conventional ferritic chromium range. This comparison locates it against the grades it commonly displaces or is displaced by.
| Grade | Key Chemistry / Condition | Where It Fits |
|---|---|---|
| TP446 | 25Cr ferritic, no Ni | Outstanding scaling resistance to about 1100 °C and strong sulfidation performance at a nickel-free price point |
| TP430 | 17Cr ferritic | Economical general ferritic grade with moderate oxidation resistance |
| TP310S | 25Cr-20Ni austenitic | Comparable oxidation resistance with better ductility and weldability, at higher nickel cost |
| TP304 | 18Cr-8Ni austenitic | Better all-round corrosion resistance but lower scaling temperature |
Product Specifications
Specification data for Seamless Stainless Steel TP446 Pipe is compiled from the governing ASTM/ASME/EN standards and our routine production records; typical values are shown where a standard leaves a limit open.
| Category | Standard / Designation |
|---|---|
| Seamless Pipe | ASTM A790 / ASME SA790 |
| Seamless & Welded Tube | ASTM A268 / ASME SA268 |
| UNS Designation | S44600 |
| Werkstoff Number | 1.4762 (equivalent high-Cr ferritic) |
| Typical EN Analogue | X10CrAlSi25 |
Size and Weight Chart
| NPS | OD (mm) | SCH 40 WT (mm) | SCH 40 kg/m | SCH 80 WT (mm) | SCH 80 kg/m |
|---|---|---|---|---|---|
| 1/4" | 13.7 | 2.24 | 0.61 | 3.02 | 0.77 |
| 1/2" | 21.3 | 2.77 | 1.23 | 3.73 | 1.56 |
| 3/4" | 26.7 | 2.87 | 1.63 | 3.91 | 2.13 |
| 1" | 33.4 | 3.38 | 2.42 | 4.55 | 3.13 |
| 1-1/4" | 42.2 | 3.56 | 3.28 | 4.85 | 4.33 |
| 1-1/2" | 48.3 | 3.68 | 3.92 | 5.08 | 5.24 |
| 2" | 60.3 | 3.91 | 5.26 | 5.54 | 7.24 |
| 3" | 88.9 | 5.49 | 10.93 | 7.62 | 14.79 |
| 4" | 114.3 | 6.02 | 15.56 | 8.56 | 21.61 |
| 6" | 168.3 | 7.11 | 27.36 | 10.97 | 41.21 |
| 8" | 219.1 | 8.18 | 41.19 | 12.7 | 62.59 |
Weights are theoretical for seamless pipe (kg per metre) calculated from the nominal dimensions; actual weights vary within the dimensional tolerances shown below. Intermediate sizes and schedules between SCH 10S and SCH 160 are produced to order.
Chemical Composition
| Element | Min (%) | Max (%) |
|---|---|---|
| Carbon (C) | — | 0.20 |
| Manganese (Mn) | — | 1.50 |
| Silicon (Si) | — | 1.00 |
| Phosphorus (P) | — | 0.040 |
| Sulfur (S) | — | 0.030 |
| Chromium (Cr) | 23.00 | 27.00 |
| Nitrogen (N) | — | 0.25 |
| Iron (Fe) | Balance | — |
Mechanical Properties
| Property | Value |
|---|---|
| Tensile Strength (typical, annealed) | 480 – 520 MPa |
| Yield Strength (typical, annealed) | 310 – 345 MPa |
| Elongation in 2 in. / 50 mm (typical) | 20 % |
| Hardness (typical, annealed) | ≤ 201 HBW |
| Heat Treatment | Annealed 780 – 880 °C, rapid cool to avoid 475 °C embrittlement |
Physical Properties
| Property | Value |
|---|---|
| Density | 7.60 g/cm³ |
| Melting Range | 1425 – 1510 °C |
| Elastic Modulus | 200 GPa |
| Coefficient of Thermal Expansion (0–100 °C) | 10.4 µm/m·°C |
| Thermal Conductivity (at 100 °C) | 20.0 W/m·K |
| Electrical Resistivity | 60 µΩ·cm |
Equivalent Grades
| Standard System | Designation |
|---|---|
| UNS | S44600 |
| Werkstoff Nr. | 1.4762 |
| EN | X10CrAlSi25 |
| JIS | SUS 446 |
Why TP446 Wins in High-Temperature Sulfur-Bearing Atmospheres
A 25 % chromium ferritic structure gives TP446 exceptional resistance to oxidation and — crucially — to sulfidation, where fully austenitic 18/8 grades fail early. In sulfur-bearing combustion atmospheres such as furnace flues, sulphite liquor handling and low-oxygen kiln environments, TP446 maintains a protective oxide layer where 304 and 316 would scale rapidly.
Being nickel-free, the grade is also immune to chloride stress-corrosion cracking and shields the buyer from nickel-price volatility. The trade-offs — lower ductility and a 475 °C embrittlement consideration on long exposure — are managed by correct design: we supply TP446 seamless pipe solution-treated and rapid-cooled, with straightening and testing performed to the applicable standard.
Manufacturing Process
Our seamless production route for Seamless Stainless Steel TP446 Pipe follows these documented stages:
- Billet Selection & Inspection: Certified EAF/AOD-melted rounds are ultrasonically inspected for internal soundness before entering the mill.
- Hot Piercing & Extrusion: The solid billet is cross-roll pierced or hot extruded at about 1150-1200 °C to form a hollow shell, consolidating the structure without any weld seam.
- Cold Drawing / Pilgering: Successive cold-drawing or cold-pilgering passes reduce diameter and wall to final size with tight dimensional control.
- Intermediate Annealing: Stress-relief or intermediate anneals between passes restore ductility for further reduction.
- Solution Treatment: A final solution anneal (typically 1040-1100 °C for austenitic grades) followed by rapid quench dissolves carbides and restores the fully austenitic, corrosion-resistant structure.
- Pickling & Passivation: Scale is removed in an acid bath, leaving the uniform passive surface required for corrosion service.
- Straightening, Cutting & Testing: Pipes are straightened, cut to length, then verified by eddy-current/ultrasonic examination, hydrostatic pressure testing and full dimensional inspection.
Surface Finish Options
- Pickled & Annealed: Standard supply condition; uniform matte passive surface, ideal for further fabrication.
- Bright Annealed: Annealed in hydrogen atmosphere for a reflective, scale-free surface used in instrumentation and sanitary lines.
- Mechanically Polished: Grit 180-600 finishes for decorative and hygienic applications.
- Mirror Polished: A fully reflective finish for architectural and high-purity service.
Dimensional Tolerances
Delivered dimensions are verified against the tolerances below; tighter tolerances can be negotiated for instrumentation and precision applications.
| Dimension | Tolerance |
|---|---|
| OD, tube ≤ 25.4 mm (cold worked) | ± 0.10 mm |
| OD, tube 25.4 – 38.1 mm | ± 0.15 mm |
| OD, tube 38.1 – 50.8 mm | ± 0.20 mm |
| OD, hot-finished pipe ≥ 50.8 mm | ± 1 % of OD |
| Wall thickness | - 12.5 % under-tolerance (min-wall basis) |
| Straightness | ≤ 1 mm per metre |
| Cut length | + 10 / - 0 mm (fixed lengths) |
Common Industrial Applications
Because of its characteristic property profile, Seamless Stainless Steel TP446 Pipe is specified in the following industries and services:
- Furnace & Burner Equipment: Burner nozzles, flame tubes and radiant panels in direct-flame service up to 1100 °C.
- Annealing & Sintering Plants: Retorts, radiant tubes and furnace internals in reducing or sulfur-bearing atmospheres.
- Petrochemical Pyrolysis: Fired-heater components and soot-blower parts exposed to hot flue gas.
- Waste Incineration: Combustion-chamber piping and flue-gas components resistant to sulfidation attack.
- Glass & Ceramic Industry: Kiln hardware, rolls and exhaust equipment in scaling conditions.
- Sulfur Recovery Units: Process piping handling hot sulfur-laden gas streams.
Quality Assurance, Testing and Documentation
Every length of Seamless Stainless Steel TP446 Pipe passes through a documented quality-control chain before dispatch:
- Material Certification: EN 10204 3.1 mill test certificates are issued for every heat; 3.2 certification with third-party witness (TUV, SGS, BV) is available on request.
- Chemical & Mechanical Testing: Heat-level chemical analysis plus tensile, hardness and, where applicable, flattening, flaring and reverse-flattening tests per the governing standard.
- Non-Destructive Examination: 100 % eddy-current or ultrasonic testing and hydrostatic or pneumatic pressure testing in line with the standard's supplementary requirements.
- Dimensional & Visual Inspection: Full OD, wall thickness, ovality and length verification with visual surface inspection after pickling or finishing.
- Traceability & Marking: Heat numbers stenciled or banded on every length, maintaining complete melt-to-pipe traceability.
Export and Packaging
Pipes are bundled with steel strapping and fitted with plastic or steel end caps, then packed in seaworthy wooden cases or crates and secured in containers for long-distance ocean freight. Standard export documentation — commercial invoice, packing list, certificate of origin, mill test certificates and, where required, third-party inspection reports — accompanies every shipment. Container-load and bulk project orders receive priority production slots and consolidated shipping documentation.
Frequently Asked Questions
Q1. What service temperature can TP446 pipe withstand?
A: In continuous, clean-air service the oxidation resistance extends to approximately 1100 °C. In sulfur-bearing or low-oxygen atmospheres the practical limit depends on atmosphere composition and should be confirmed case by case.
Q2. Why choose ferritic TP446 over austenitic 310 for furnace parts?
A: TP446 offers better sulfidation resistance, immunity to chloride stress-corrosion cracking, lower thermal expansion and higher thermal conductivity — usually at lower cost, since it contains no nickel.
Q3. Are there temperature-related embrittlement concerns?
A: Yes. Like all high-chromium ferritics, TP446 can embrittle with long exposure between roughly 370–540 °C (475 °C embrittlement) and above 600 °C (sigma phase). Proper grade selection for the actual operating band is essential, and our engineers can advise.
Q4. What certificates accompany TP446 pipe shipments?
A: EN 10204 3.1 mill certificates with chemistry, tensile data, flattening, hardness and NDT records, plus full heat traceability.
Ready to Request a Quotation?
Send us your size range, wall thickness/schedule, standard and quantity for Seamless Stainless Steel TP446 Pipe, and our engineering team will respond with a detailed technical and commercial offer within 24 hours. Custom sizes, third-party inspection and full export documentation are part of our standard service.
