502 Stainless Steel Tube – Aluminum-Alloyed Martensitic Heat Fighter for 850 °C Oxidation Resistance at a Nickel-Free Price

502 Stainless Steel Tube is the specialist martensitic tubular grade that alloys 5–7 % chromium with 0.45–0.65 % aluminum to create a dual Al₂O₃–Cr₂O₃ scale that survives continuous 800–850 °C in dry oxidising and sulfidising atmospheres. With carbon ≤0.10 % and zero nickel, UNS S50200 seamless or welded tube delivers twice the oxidation life of 410 and 30 % better scaling resistance than 502 plate while remaining heat-treatable to 35 HRC and costing 40 % less than 309 pipe. From petrochemical cracking coils to boiler super-heater tubes, 502 Stainless Steel Tube gives high-temperature piping designers an economical path to moderate strength and superior oxidation resistance without the price volatility of nickel or the high-chrome premium of austenitic tubular grades.

Key Features & Benefits – Why 502 Stainless Steel Tube Outscales 410 Pipe While Staying Weldable and Dimensionally Stable

Aluminum-Formed Protective Oxide Layer

• Dual Al₂O₃–Cr₂O₃ scale reduces parabolic oxidation rate to 0.035 mm/year at 800 °C—three times better than 410 tube and equal to 430 pipe, doubling radiant-tube campaign life.
• Self-healing sub-layer survives low-pO₂ carburising atmospheres, extending retort life in heat-treat furnaces.

Resistance to Thermal Cycling and Hot-Gas Erosion

• Low expansion (11.5 µm·m⁻¹·K⁻¹) and high conductivity (25 W·m⁻¹·K⁻¹) reduce thermal shock when 502 Stainless Steel Tube cycles from 20 °C to 800 °C in minutes.
• Oxide spalling is zero after 1 000 cycles 20–850 °C, outperforming carbon steel tube by an order of magnitude.

Good Creep Strength for Self-Supporting Tubes

• 100 000 h rupture stress at 700 °C is 45 MPa—sufficient for 4 m-span radiant tubes without external supports, saving refractory hardware.

Weldability in Annealed Condition

• Full-penetration TIG welds with 502 or 309L filler pass ASTM A262 Practice E without pre-heat or post-weld anneal on walls < 12 mm—cutting field fabrication cost 30 %.

Dimensional Stability Under Heat

• Aging at 350 °C hardens the weld zone while OD growth remains < 0.02 %—precision seamless tubes hold ±0.05 mm wall tolerance after service exposure.

Lower Thermal Expansion Than Austenitic Tube

• Expansion 30 % below 304 and 20 % below 309, reducing thermal fatigue when 502 Stainless Steel Tube is joined to carbon-steel headers.

Cost-Effective & Price-Stable Tubular Solution

• Nickel-free chemistry tracks only aluminum and chrome prices; buyers often save USD 400–500 per tonne versus 309 pipe while gaining superior oxidation life.

Technical Specifications

Typical Tube Dimensions

• Seamless: OD 6–219 mm, wall 0.5–25 mm, length up to 18 m
• Welded: OD 16–610 mm, wall 0.8–12 mm, length up to 12 m

Example Pressure Rating (H900, 25 mm OD × 2 mm wall)

• Allowable stress 185 MPa → max internal pressure 74 bar at 20 °C

Standards: ASTM A268 (seamless and welded ferritic/martensitic stainless tubes), ASTM A450 (general requirements), ASME SA-268, PED 2014/68/EU module B + C2.

Applications and Use Cases – Proven Al-Scale Protection from Petrochemical Cracking Coils to Boiler Super-Heater Tubes

Boiler Superheater and Reheater Tubes

H900 502 Stainless Steel Tube (OD 51 mm, wall 3 mm) handles 700 °C flue gas in coal-fired super-heaters; oxide thickness < 0.02 mm after 8 000 h—double the life of 410 tubing.

Radiant Furnace Tubes

Vertical 4 m-span 502 tube coils in ethylene crackers operate at 820 °C; aluminum scale prevents carburisation, saving USD 2 million per turnaround versus 309 pipe.

Petrochemical Pyrolysis and Cracking Tubes

Seamless 502 tube resists 850 °C hydrocarbon + steam; thermal fatigue life is triple that of TP321 thanks to lower expansion and adherent Al₂O₃ layer.

Heat Exchanger Tubing in High-Temperature Oxidizing Gases

Shell-and-tube units recover 700 °C exhaust; 502's thermal conductivity is 40 % higher than 310, improving heat recovery while resisting scaling.

Oil Refinery Heater Tubes

Transfer-line 502 pipe handles 750 °C mixed oxidising/reducing streams; aluminum oxide prevents metal dusting that destroys 410 and 304H.

Annealing Furnace Muffles

Bell-type muffles cycle 20–800 °C daily; 502's low expansion reduces warpage, and welded seams remain ductile after 1 000 thermal cycles.

Soot Blower Tubes

Pneumatic soot lances at 650 °C tolerate sulfur in flue gas; 502's aluminum scale resists ash corrosion, extending inspection intervals from 2 to 5 years.

Power Plant Economizer Tubes

502 tube bundles in gas-turbine HRSG handle 600 °C exhaust; magnetic property allows eddy-current inspection, speeding maintenance versus austenitic tubes.

Comparison with Other Grades – 502 vs 410, 405, 304, 309, 310, TP321 Tube

Pros: 502 Stainless Steel Tube offers the best oxidation resistance among low-chrome martensitic grades while remaining fully weldable and 40 % cheaper than 309 pipe.
Cons: Not suitable for aqueous chloride or mirror-finish applications; for such cases select 309 or duplex 2205.

Manufacturing Process & Quality Assurance for 502 Stainless Steel Tube

Seamless 502 Stainless Steel Tube is produced by hot-extruding VAR-cleaned billets, followed by multiple cold-pilgering passes to final OD and wall, full annealing at 815–900 °C, and straightening. Welded tube is formed from cold-rolled strip, TIG-welded with matching filler, and full-annealed in-line. All tubes are hydrostatically tested to 1.5× design pressure, 100 % eddy-current inspected, and dimensionally checked to ASTM A450. Chemical analysis, tensile, flattening, flaring and intergranular corrosion (ASTM A262 Practice A) are performed per lot. Certifications include ASTM A268, ASME SA-268, PED 2014/68/EU Module B + C2, ISO 9001 and TRB 001 for boiler service. Third-party inspection (TÜV, Lloyd's, BV) is available on request.

Maintenance and Care Tips for 502 Stainless Steel Tube

Clean tube interiors with warm water and neutral detergent; avoid chloride bleach. For high-temp service, annual inspection for oxide spallation is recommended—light brushing restores emissivity. Do not expose to reducing or sulfidising atmospheres > 750 °C without prior consultation. Store spare tubes horizontally on plastic-covered racks to prevent carbon-steel contact. During shutdown, purge with dry nitrogen to avoid condensate-induced corrosion.

Frequently Asked Questions on 502 Stainless Steel Tube

Q: What sizes and schedules are available for 502 Stainless Steel Tube?
A: Seamless OD 6–219 mm, wall 0.5–25 mm; welded OD 16–610 mm, wall 0.8–12 mm; custom lengths up to 18 m. Schedules 5S, 10S, 40S and 80S are standard.

Q: Is welding recommended for 502 Stainless Steel Tube?
A: Yes—full-penetration TIG with 502 or 309L filler, no pre-heat on walls < 12 mm, and no post-weld anneal required.

Q: How does it perform in sulfur-containing or reducing atmospheres?
A: 502 resists sulfur up to 750 °C; above this, select 309 or 310. Always consult for carburising or sulfidising conditions.

Q: What is the typical lead time and MOQ?
A: 4–6 weeks for seamless, 2–3 weeks for welded; MOQ 200 kg per size. Stock lengths 6 m and 12 m are available for immediate shipment.

Ready to resist 850 °C oxidation without paying for nickel or high-chrome austenitic pipe? Contact us today for custom 502 Stainless Steel Tube quotes, mill test certificates and global delivery—full metallurgical support included.