Seamless Stainless Steel TP304H Pipe
What is a Seamless Stainless Steel TP304H Pipe?
Seamless Stainless Steel TP304H Pipe is a high-carbon variant of the widely used TP304 austenitic stainless steel, produced from a solid billet without any welded seam. The"H"suffix denotes a controlled higher carbon content (0.04–0.10 %), which gives the pipe superior strength retention at elevated service temperatures compared with standard 304L material.
Because the carbon is retained in solid solution through a minimum solution annealing temperature of 1040 °C, TP304H is qualified for pressure-retaining applications in boilers, superheaters and heat exchangers where long-term exposure above 500 °C is expected. The absence of a weld seam eliminates the heat-affected zone, delivering uniform corrosion resistance and mechanical properties around the entire circumference.
Supplied in accordance with ASTM A312, A213 and A269 (and ASME equivalents), TP304H seamless pipe combines the well-known general corrosion resistance of 18/8 stainless steel with improved high-temperature creep and rupture strength, making it a dependable choice for power generation, petrochemical and thermal processing plants.
Stainless Steel TP304H vs TP304 vs TP304L vs TP316H vs TP321H: Which Grade Do You Need?
The 300-series H grades are frequently confused at quotation stage. The comparison below summarizes the practical differences so the correct grade is ordered the first time.
| Grade | Key Chemistry / Condition | Where It Fits |
|---|---|---|
| TP304 | C ≤ 0.08 % | General-purpose 18/8; best economy for service below about 500 °C |
| TP304L | C ≤ 0.03 % | Low carbon for as-welded equipment exposed to intergranular corrosion risk |
| TP304H | C 0.04-0.10 %, grain size ASTM No. 7 | High-temperature strength; boilers, superheaters and pressure parts above 500 °C |
| TP316H | C 0.04-0.10 %, plus 2-3 % Mo | 304H strength with improved pitting resistance in chloride media |
| TP321H | C 0.04-0.10 %, Ti stabilized | High temperature with immunity to sensitization during slow cooling or repeated welding |
A single melt can frequently be dual-certified as both 304 (UNS S30400) and 304H (UNS S30409) when its carbon content falls in the overlapping 0.04-0.08 % band and the grain-size requirement of 304H is met — simplifying inventory for mixed-service projects.
Product Specifications
Specification data for Seamless Stainless Steel TP304H 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 A312 / ASME SA312 |
| Seamless & Welded Tube | ASTM A213 / A269 / ASME SA213 / SA269 |
| UNS Designation | S30409 |
| Werkstoff Number | 1.4948 |
| EN Designation | X5CrNi18-10 (H-modified) |
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 | 0.65 | 3.02 | 0.81 |
| 1/2" | 21.3 | 2.77 | 1.29 | 3.73 | 1.65 |
| 3/4" | 26.7 | 2.87 | 1.72 | 3.91 | 2.24 |
| 1" | 33.4 | 3.38 | 2.55 | 4.55 | 3.3 |
| 1-1/4" | 42.2 | 3.56 | 3.46 | 4.85 | 4.55 |
| 1-1/2" | 48.3 | 3.68 | 4.13 | 5.08 | 5.52 |
| 2" | 60.3 | 3.91 | 5.54 | 5.54 | 7.62 |
| 3" | 88.9 | 5.49 | 11.51 | 7.62 | 15.57 |
| 4" | 114.3 | 6.02 | 16.38 | 8.56 | 22.75 |
| 6" | 168.3 | 7.11 | 28.8 | 10.97 | 43.38 |
| 8" | 219.1 | 8.18 | 43.36 | 12.7 | 65.88 |
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) | 0.04 | 0.10 |
| Manganese (Mn) | — | 2.00 |
| Silicon (Si) | — | 0.75 |
| Phosphorus (P) | — | 0.045 |
| Sulfur (S) | — | 0.030 |
| Chromium (Cr) | 18.00 | 20.00 |
| Nickel (Ni) | 8.00 | 11.00 |
| Iron (Fe) | Balance | — |
Mechanical Properties
| Property | Value |
|---|---|
| Tensile Strength, min | 515 MPa (75 ksi) |
| Yield Strength (0.2 % offset), min | 205 MPa (30 ksi) |
| Elongation in 2 in. / 50 mm, min | 35 % |
| Hardness (typical, annealed) | ≤ 201 HBW |
| Heat Treatment | Solution annealed, min 1040 °C, rapid cooling |
Physical Properties
| Property | Value |
|---|---|
| Density | 8.00 g/cm³ |
| Melting Range | 1400 – 1455 °C |
| Elastic Modulus | 193 – 200 GPa |
| Coefficient of Thermal Expansion (0–100 °C) | 17.2 µm/m·°C |
| Thermal Conductivity (at 100 °C) | 16.2 W/m·K |
| Specific Heat Capacity | 500 J/kg·K |
| Electrical Resistivity | 72 µΩ·cm |
Equivalent Grades
| Standard System | Designation |
|---|---|
| UNS | S30409 |
| Werkstoff Nr. | 1.4948 |
| EN | X6CrNi18-10 (H) |
| JIS | SUS 304H |
| AFNOR | Z6CN18.10 |
Why TP304H Outperforms 304 and 304L Above 525 °C
The engineering case for TP304H rests on creep behaviour. Carbon in solid solution, guaranteed by the minimum 1040 °C solution anneal and the ASTM No. 7 (or coarser) grain-size requirement, gives the grade significantly higher creep and stress-rupture strength than 304 or 304L at temperatures above roughly 525 °C. In ASME code construction this translates directly into higher allowable stress values, so a TP304H line can carry the same pressure with a thinner wall than the low-carbon alternatives at boiler operating temperatures.
The seamless manufacturing route adds a second layer of performance. Because the pipe is pierced from a solid billet, there is no weld seam and no heat-affected zone — the two locations where high-temperature service typically takes its toll. For superheater, reheater and furnace-tube duty, this uniformity of structure and properties around the full circumference is the decisive advantage over welded alternatives.
Manufacturing Process
Our seamless production route for Seamless Stainless Steel TP304H 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 TP304H Pipe is specified in the following industries and services:
- Power Generation: Superheater and reheater tubes, boiler pressure parts and high-temperature steam lines in fossil-fired plants.
- Petrochemical & Refining: Furnace tubes, transfer lines and heat-exchanger tubing handling hydrocarbon streams above 500 °C.
- Chemical Processing: Vessels and piping for nitric acid, organic chemicals and mild corrosive media.
- Thermal Treatment Equipment: Radiant tubes, annealing-bell components and furnace fixtures exposed to cyclic high temperatures.
- Food & Pharmaceutical Plants: Sanitary process piping where cleanliness and corrosion resistance are essential.
- Pulp & Paper: Digesters and bleach-plant piping in mildly corrosive service.
Quality Assurance, Testing and Documentation
Every length of Seamless Stainless Steel TP304H 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 is the difference between TP304 and TP304H pipe?
A: Both share the same 18Cr/8Ni composition limits, but TP304H is restricted to a carbon range of 0.04–0.10 % and requires a minimum 1040 °C solution anneal. This gives TP304H higher allowable stress at temperatures above roughly 540 °C, which is why it is specified for boilers and superheaters.
Q2. Can TP304H pipe be used in sensitizing environments?
A: The H-grade is designed for high-temperature strength, not for resistance to intergranular attack after slow cooling through the sensitization range. For weldments exposed to corrosive media without post-weld annealing, a low-carbon (L) or stabilized (Ti/Nb) grade is the better choice.
Q3. What test certificates are supplied?
A: Each shipment is delivered with EN 10204 3.1 mill test certificates covering chemical analysis, tensile testing, hardness, flattening/flare tests where applicable, hydrostatic or non-destructive examination, and heat-number traceability.
Q4. Can you supply custom sizes and lengths?
A: Yes. In addition to standard ASME B36.19 dimensions, we produce non-standard outside diameters, heavy-wall schedules and fixed lengths up to 12 m, all from the same certified heat.
Ready to Request a Quotation?
Send us your size range, wall thickness/schedule, standard and quantity for Seamless Stainless Steel TP304H 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.
