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In the extremely demanding modern industrial boundaries, super austenitic stainless steel tubing is a strategic special steel anti-corrosion ace designed for comprehensive defense. Relying on a breakthrough micro-alloying matrix of high nickel, high chromium, high molybdenum, and synergistic nitrogen fixation (such as 904L, 254SMO), this series of tubing maintains the traditional high toughness and excellent weldability of austenitic steel while directly pushing the anti-point corrosion equivalent (PREN) to a new height of over 40. It completely breaks the “defeat curse” of conventional materials in extreme environments such as high-temperature strong acid, extremely high chloride ions, etc., and plays an irreplaceable ultimate safety barrier role in core fluid control systems in aerospace, cutting-edge offshore engineering, and nuclear power.
In the extremely demanding modern industrial boundaries, super austenitic stainless steel tubing is a strategic special steel anti-corrosion ace designed for comprehensive defense. Relying on a breakthrough micro-alloying matrix of high nickel, high chromium, high molybdenum, and synergistic nitrogen fixation (such as 904L, 254SMO), this series of tubing maintains the traditional high toughness and excellent weldability of austenitic steel while directly pushing the anti-point corrosion equivalent (PREN) to a new height of over 40. It completely breaks the “defeat curse” of conventional materials in extreme environments such as high-temperature strong acid, extremely high chloride ions, etc., and plays an irreplaceable ultimate safety barrier role in core fluid control systems in aerospace, cutting-edge offshore engineering, and nuclear power.
From both a commercial and engineering perspective, the core advantage of the super austenitic pipe material lies in its ability to reshape the entire life cycle economics under extreme conditions. Traditional pipe materials often experience frequent cracking and downtime for maintenance when exposed to high-concentration sulfuric acid or extreme marine stress corrosion. However, this series of pipe materials, with its nearly defect-free metallurgical purity and self-healing passivation film, achieves zero-fault operation throughout the entire service life. It not only enables engineers to design complex high-pressure pipeline networks without blindly increasing wall thickness due to corrosion compromises, achieving structural lightweighting, but also with its absolute core strength of “one-time full-life service”, helps enterprises eliminate the hidden huge costs caused by frequent shutdowns and maintenance. It is a hard-core technological foundation for the advancement of high-end fluid engineering to the deep sea, deep earth, and green chemical fields.
| Grade | UNS | EN/DIN | Key Characteristics |
| 254SMO | S31254 | 1.4547 | High Cr, Ni, and Mo content; nitrogen-alloyed; PREN ≥ 43 |
| 904L | N08904 | 1.4539 | High copper content (approx. 1.5%); excellent performance in dilute sulfuric acid |
| AL-6XN | N08367 | — | High Mo (≥ 6%) and Ni (approx. 24%) content; strong resistance to chloride pitting |
| 654SMO | S32654 | 1.4652 | Higher degree of alloying; PREN > 50; suitable for extremely harsh corrosive environments |
|
Specification |
Range |
Notes |
|
OD |
6.0mm – 219mm |
Customizable; subject to specific customer technical requirements |
|
Wall Thickness |
0.5mm – 12mm |
Adjustable based on operating condition requirements |
|
Length |
5m – 12m |
Cut to length per customer specifications |
|
Coil Dimensions |
ID 508mm / 610mm |
Coil dimensions adjustable based on requirements |
Chemical Composition
| Chemical Element | 254SMO（S31254） | 904L（N08904） | AL-6XN（N08367） |
| C | ≤0.02 | ≤0.02 | ≤0.03 |
| Si | ≤0.80 | ≤1.00 | ≤1.00 |
| Mn | ≤1.00 | ≤2.00 | ≤2.00 |
| P | ≤0.030 | ≤0.040 | ≤0.040 |
| S | ≤0.010 | ≤0.030 | ≤0.030 |
| Cr | 19.5-20.5 | 19.0-23.0 | 20.0-22.0 |
| Ni | 17.5-18.5 | 23.0-28.0 | 23.5-25.5 |
| Mo | 6.0-6.5 | 4.0-5.0 | 6.0-7.0 |
| N | 0.18-0.22 | — | 0.18-0.25 |
| Cu | 0.50-1.00 | 1.0-2.0 | ≤0.75 |
| Fe | margin | margin | margin |
Mechanical Properties
| Grade | Tensile Strength Rm (MPa) | Yield Strength Rp0.2 (MPa) | Elongation A (%) | Hardness (HB) | Modulus of Elasticity (GPa) | Density (g/cm³) | Melting Range (°C) |
| 254SMO | ≥655 | ≥310 | ≥35 | ≤220 | ~195 | 8.0 | 1370-1400 |
| 904L | ≥490 | ≥215 | ≥35 | ≤220 | ~193 | 7.95 | 1300-1390 |
| AL-6XN | ≥650 | ≥310 | ≥30 | ≤230 | ~195 | 8.05 | 1370-1400 |
| 654SMO | ≥750 | ≥430 | ≥35 | 230-250 | ~200 | 8.24 | 1320 – 1390 |
| Industry | Operating Conditions | Recommended Grades | Product Form |
| Seawater Desalination | Seawater heat exchangers, condenser tubes, evaporators | 254SMO, AL-6XN | Thin-walled seamless pipes, heat exchanger tubes |
| Marine Engineering | Offshore platform hydraulic/instrumentation piping, subsea pipelines | 254SMO, 654SMO | Thick-walled seamless pipes, precision pipes |
| Petrochemicals | Refinery piping, chemical plant reactors, distillation tower internals | 904L, 254SMO | Seamless pipes, welded pipes |
| Flue Gas Desulfurization (FGD) | Absorber tower spray pipes, circulating slurry piping | 254SMO, 654SMO | Large-diameter piping |
| Pulp & Paper | Pulp bleaching equipment, filter presses, storage tanks | 254SMO | Piping, plate/sheet |
| Food & Pharmaceutical | Food processing piping, sanitary piping | 904L | Sanitary polished pipes (BA/EP) |
| Sulfuric/Phosphoric Acid Production | Evaporators, heat exchangers, mixers, sulfuric acid transfer systems | 904L | Acid-resistant piping |
| Power Generation | Power plant polluted cooling water piping systems | AL-6XN | Condenser tubes |
Vacuum Induction Melting (VIM) or Argon Oxygen Decarburization Refining (AOD) → Electroslag Remelting (ESR)
Strictly control the chemical composition to ensure ultra-low carbon content (C ≤ 0.02%) and low impurity content (P, S ≤ 0.010%)
Objective: To obtain steel ingots with high purity and uniform composition
The steel ingot is forged at high temperature to shape the initial round billet.
Hot-rolled punched tube billet preparation
Heat the tube billet to 1120 – 1180℃
Form the initial blank of the seamless pipe by using the hot extrusion process
The product is produced by the “hot extrusion + three passes of cold rolling” process.
Intermediate annealing treatment is carried out between the cold rolling passes.
Control the deformation amount during cold processing and optimize the microstructure – 51
Heat to 1120 – 1180℃ and maintain for 5 – 10 minutes.
Quick water quenching cooling, with a cooling rate not lower than 350℃/min
Obtain uniform austenite structure and eliminate the precipitation of σ phase –
Removing oxide scale through pickling and passivation
Bright annealing (BA) or precision polishing
Dimensional sizing, straightening, and finishing
To guarantee uncompromised field performance, every single batch undergoes a rigorous, multi-dimensional validation process prior to dispatch:
TIPTOP Company Advantages
Choose 904L: for environments with reducing acidic media (such as dilute sulfuric acid, phosphoric acid) and for medium to low corrosion conditions with high cost control requirements.
Choose 254SMO: for high chloride ion environments (seawater, salt water, flue gas desulfurization), high-temperature chloride-containing conditions, and for occasions requiring higher resistance to pitting corrosion.
Yes. Our company can arrange for a third-party inspection agency to conduct product testing according to customer requirements.
Common third-party inspection agencies include: SGS, BV, TÜV.
The decrease in the resistance to pitting corrosion in the heat affected zone can be controlled within 10%. After welding, no solution treatment is required to meet the usage requirements of most marine and chemical environments.
For joint connections of different types of steels in equipment such as pressure vessels and chemical pipelines, when appropriate welding materials and welding processes are selected, this welding joint can meet the safety usage requirements of conventional conditions.
