Heat Resistant 309S Stainless Steel Pipe Tube SS Pipe in 6m Length Pickling & Bright Surface Finishing

Heat Resistant 309S Stainless Steel Pipe Tube SS Pipe in 6m Length Pickling & Bright Surface Finishing

Products Specification

309S stainless steel pipe is a high-performance austenitic stainless steel product specifically designed for extreme temperature applications. This heat-resistant alloy exhibits exceptional performance in environments where temperatures range from 850°C to 1100°C (1562°F to 2012°F). The standard 6-meter length offers practicality for industrial installation and handling, while the pickling and bright surface finishing not only enhances its aesthetic appeal but also improves its corrosion resistance by removing impurities and creating a passive protective layer. This combination of properties makes 309S stainless steel pipes particularly valuable in industries requiring materials that can maintain structural integrity under thermal stress and corrosive conditions5.

The pickling process involves chemical treatment that removes scale and impurities from the surface after heat treatment, while the bright finishing provides a smooth surface that reduces the adhesion of contaminants and facilitates cleaning. These surface treatments are especially important for applications requiring strict hygiene standards or where minimizing friction and resistance to material flow is crucial. The pipes are manufactured through either seamless or welded processes, with seamless versions offering enhanced pressure containment capabilities for high-pressure applications26.

2 Key Parameters

2.1 Chemical Composition

The chemical composition of 309S stainless steel pipe is carefully balanced to provide optimal high-temperature performance and corrosion resistance. The controlled carbon content is particularly important as it minimizes carbide precipitation during welding and high-temperature exposure, thereby maintaining corrosion resistance in harsh environments1.

Table: Chemical Composition Requirements of 309S Stainless Steel Pipe

2.2 Mechanical Properties

The mechanical properties of 309S stainless steel pipes remain stable across a wide temperature range, making them suitable for high-temperature applications where many other materials would rapidly lose strength. The material offers an excellent combination of strength and ductility, allowing it to withstand both mechanical stresses and thermal cycling without failure17.

Table: Mechanical Properties of 309S Stainless Steel Pipe

3 Properties and Characteristics

3.1 High-Temperature Performance

309S stainless steel pipes exhibit exceptional heat resistance that qualifies them for long-term service at temperatures up to 980°C (1796°F) with intermittent exposure to 1000°C (1832°F). This remarkable performance stems from their high chromium content (22-24%), which forms a stable, self-healing chromium oxide layer on the surface when exposed to elevated temperatures. This protective layer effectively prevents further oxidation and degradation of the underlying material. The nickel content (12-15%) contributes to maintaining the austenitic structure and provides resistance against thermal creep—a gradual deformation under mechanical stress at high temperatures that affects many materials15.

The pipes demonstrate outstanding anti-scaling properties and resistance to cyclic oxidation, making them suitable for applications involving repeated heating and cooling cycles. Unlike ordinary stainless steels that might form brittle phases or suffer from significant scaling after prolonged high-temperature exposure, 309S maintains its structural integrity. This is particularly valuable in furnace applications where thermal cycling is common. The material's low carbon content (≤0.08%) specifically helps prevent sensitization—the formation of chromium carbides at grain boundaries—which can lead to intergranular corrosion in other stainless steels9.

3.2 Corrosion Resistance

The corrosion resistance of 309S stainless steel pipes extends beyond high-temperature oxidation to include various chemical environments. The elevated chromium and nickel content provides superior resistance to oxidizing acids and many organic chemicals compared to standard 304 and 316 stainless steels. This makes 309S pipes suitable for applications where both high temperature and corrosive media are present, such as in chemical processing heaters and refinery furnaces59.

Additionally, 309S exhibits good resistance to sulfidation attacks, which is particularly valuable in petroleum refining and coal processing applications where sulfur compounds are present at elevated temperatures. The material also resists carburization—the absorption of carbon into the metal surface in carbon-rich atmospheres at high temperatures—which can cause embrittlement and loss of mechanical properties in other steels. This combination of properties allows 309S pipes to maintain their wall integrity even when exposed to aggressive environments throughout their service life1.

3.3 Mechanical and Physical Properties

The room-temperature mechanical properties of 309S stainless steel pipes include a tensile strength of ≥515-520 MPa and a yield strength of ≥205-207 MPa, with elongation exceeding 35-40%. These properties provide excellent structural capability while maintaining good formability and weldability. The high elongation value indicates ductile behavior, which is important for withstanding mechanical shocks and thermal stresses without brittle fracture79.

As the temperature increases, 309S maintains its mechanical properties better than most standard stainless steels. The high-temperature strength remains adequate for structural support in furnace applications, while the thermal expansion coefficient (approximately 16.5 μm/m·°C between 20-100°C) is compatible with many other heat-resistant materials, reducing thermal stress issues in assemblies. The thermal conductivity of approximately 14.2 W/m·K at 100°C helps distribute heat evenly, minimizing localized hot spots that could lead to premature failure9.

4 Manufacturing Process

4.1 Production Workflow

The manufacturing of 309S stainless steel pipes follows a meticulous production workflow that ensures consistent quality and performance characteristics. For seamless pipes, the process begins with round steel billets that are heated to approximately 1200°C in a rotary furnace. These heated billets are then pierced through the center using a mandrel mill to create a hollow shell. The pierced billets undergo elongation through a plug mill or mandrel mill process to achieve the desired diameter and wall thickness. Subsequent sizing rolls ensure precise dimensional accuracy before the pipes are cut to the standard 6-meter length210.

For welded pipes, the process starts with cold-rolled coils that are slit to the required width. The strips then pass through forming rolls that gradually shape them into tubular form. High-frequency welding or TIG welding is employed to create a longitudinal weld seam without adding filler material. The weld flash is removed both internally and externally, and the weld zone is heat-treated to normalize the microstructure and ensure corrosion resistance equivalent to the parent metal6.

4.2 Heat Treatment and Surface Finishing

Heat treatment is a critical step in the manufacturing process of 309S stainless steel pipes. The pipes undergo solution annealing at temperatures between 1030°C to 1150°C (1886°F to 2102°F), followed by rapid cooling through water quenching. This process dissolves any secondary phases and carbides that may have formed during previous hot-working operations, ensuring that all chromium remains in solid solution to provide optimal corrosion resistance. The solution annealing also recrystallizes the microstructure, eliminating work hardening effects from cold forming operations and ensuring uniform mechanical properties throughout the pipe29.

The pickling process employs a mixture of nitric and hydrofluoric acids to remove scale and impurities that form on the surface during heat treatment. This is followed by passivation with nitric acid, which enhances the formation of the protective chromium oxide layer. For bright surface finishing, the pipes undergo electropolishing or mechanical polishing to achieve the desired surface smoothness. Electropolishing provides a superior surface finish with typical roughness values (Ra) of ≤0.15 μm, while mechanical polishing achieves Ra values of ≤0.3 μm. This bright surface finishing not only improves aesthetic appearance but also enhances corrosion resistance by reducing the surface area available for corrosive attack and facilitating easier cleaning34.

5 Standards and Quality Assurance

5.1 International Standards

309S stainless steel pipes are manufactured in compliance with various international standards that ensure consistency and reliability across different production batches and manufacturers. These standards specify requirements for chemical composition, mechanical properties, dimensional tolerances, testing methods, and inspection procedures. The material is recognized under multiple international designation systems, facilitating its global acceptance and use57.

The primary standards governing 309S stainless steel pipes include:

• ASTM A312/A312M: Standard Specification for Seamless, Welded, and Heavily Cold Worked Austenitic Stainless Steel Pipes

• ASTM A554: Standard Specification for Welded Stainless Steel Mechanical Tubing

• JIS G3459: Japanese Industrial Standard for Stainless Steel Pipes

• GB/T 12771: Chinese Standard for Stainless Steel Welded Pipes for Fluid Transportation

• DIN 17456: German Standard for Seamless Circular Stainless Steel Tubes

These standards ensure that 309S pipes meet minimum requirements for chemical composition, mechanical properties, dimensional accuracy, and pressure containment capabilities. Additionally, specific industry standards may apply for specialized applications such as pressure vessel components (ASME SA312) or high-temperature service (ASTM A312)7.

5.2 Quality Control Measures

Rigorous quality control measures are implemented throughout the manufacturing process of 309S stainless steel pipes. Chemical composition verification is performed using optical emission spectrometry to ensure compliance with standard requirements. Mechanical testing includes tensile tests, hardness surveys, and flattening tests for welded pipes to verify mechanical properties and weld quality. Non-destructive examination methods are extensively employed, including hydrostatic testing to verify pressure integrity, eddy current testing for detecting surface and near-surface defects, and ultrasonic testing for identifying internal imperfections6.

For pipes intended for high-temperature service, additional validation may include microstructural examination to verify grain size and absence of detrimental phases, as well as high-temperature tensile or creep tests for critical applications. Surface quality inspection ensures that the pickling and bright finishing processes have achieved the desired surface characteristics without over-etching or contamination. Dimensional checks confirm that outside diameter, wall thickness, and length conform to specified tolerances. These comprehensive quality assurance measures ensure that 309S stainless steel pipes deliver consistent performance even in demanding applications610.

6 Advantages of 309S Stainless Steel Pipes

The primary advantage of 309S stainless steel pipes lies in their superior heat resistance, which significantly exceeds that of common stainless steels like 304 (approximately 870°C maximum continuous service temperature) and 316 (approximately 800°C maximum continuous service temperature). This makes 309S the material of choice for applications involving extreme temperatures where other stainless steels would rapidly degrade. The high chromium and nickel content not only provides this exceptional heat resistance but also delivers excellent corrosion resistance in both high-temperature and ambient environments15.

Another significant advantage is the low carbon content of 309S, which minimizes carbide precipitation during welding and high-temperature exposure. This characteristic ensures that the pipes maintain their corrosion resistance after welding without requiring post-weld heat treatment in most applications. The standard 6-meter length offers practical advantages for installation, reducing the number of joints required in long pipe runs, which is particularly beneficial for high-temperature applications where joints represent potential failure points9.

The pickling and bright surface finishing provides both functional and aesthetic benefits. The smooth surface reduces friction losses in fluid transport applications, minimizes adhesion of deposits that could impede flow or create insulation effects, and facilitates cleaning in applications requiring hygiene. From an aesthetic perspective, the bright finish offers an attractive appearance that is desirable in architectural applications or where pipes are visible in installed equipment34.

7 Equivalent Grades

309S stainless steel is recognized globally under various national and international designation systems, facilitating material selection and specification across different regions and industries. These equivalent grades have essentially identical chemical composition requirements despite their different designation systems5.

Table: International Equivalent Grades of 309S Stainless Steel

While these equivalent grades have nearly identical chemical compositions, minor variations in permissible impurity elements or manufacturing practices might result in slight differences in performance characteristics. However, these materials are generally considered interchangeable for most applications. The S30908 designation under the Unified Numbering System is particularly useful for specifying the material in international procurement contexts57.

8 Applications

309S stainless steel pipes serve in numerous high-temperature applications across various industries. In the heat treatment industry, they are extensively used for radiant tubes, muffles, retorts, and annealing covers where temperatures routinely exceed 900°C. The chemical and petrochemical industries employ these pipes in furnace convection sections, heater tubes, and transfer lines handling hot process fluids. Their resistance to sulfidation makes them particularly valuable in refinery applications where sulfur-containing feedstocks are processed19.

The power generation industry utilizes 309S pipes in boiler components, heat recovery steam generators, and exhaust systems where both high temperature and corrosion resistance are required. In pollution control systems, these pipes serve in exhaust gas scrubbers, incinerator components, and after-treatment systems where acidic condensates may form. The ceramic and glass manufacturing industries employ 309S pipes for burner quills, sensor protection tubes, and material handling components in high-temperature kilns and furnaces59.

Beyond industrial applications, 309S stainless steel pipes find use in architectural and building services where fire resistance is critical, such as in fire protection systems and smoke extraction ducts. Their attractive bright surface finish also makes them suitable for visible architectural elements that must maintain appearance under elevated temperature conditions, such as in atrium roofing systems or exterior cladding that may be exposed to solar gain plus ambient heat