1. Standard Profile
ASTM A268/A268M is the standard specification for seamless and welded ferritic and martensitic stainless steel tubes intended for general corrosion-resisting and high-temperature heat transfer service. This specification covers multiple ferritic/martensitic stainless grades including TP409, TP410, TP430, TP444 and more, available in seamless cold-drawn, seamless hot-finished, or welded & cold-reduced manufacturing forms. Unlike austenitic stainless tubes (ASTM A688), ASTM A268 features chromium-only alloy composition without nickel, delivering cost advantages while maintaining good oxidation and corrosion resistance.
2. Manufacturing & Structural Characteristics
- Two mainstream production types
- Seamless tubes: Produced by billet piercing followed by hot rolling or precision cold drawing, with uniform wall thickness and zero weld seams for high-pressure service.
- Welded tubes: Rolled stainless steel strip formed and longitudinally welded, then cold reduced to achieve smooth uniform surface for low-to-medium pressure applications.
- Heat treatment process
All tubes undergo full annealing or tempering to stabilize ferritic/martensitic microstructure, balancing hardness, ductility and stress resistance after forming operations like bending and flaring. - Strict quality inspection
Mandatory tests include dimensional measurement, tensile and hardness tests, hydrostatic or air leak test, eddy current non-destructive testing, and intergranular corrosion inspection to eliminate surface and internal defects. - Surface finish
Cold-finished tubes feature smooth clean inner and outer surfaces to reduce scaling, fouling and heat transfer loss during long-term cyclic operation.
3. Core Performance Advantages
- High oxidation resistance at elevated temperatures, resisting high-temperature steam and air oxidation
- Good resistance to water-side corrosion, especially against stress corrosion cracking (SCC) caused by chloride ions, outperforming nickel-containing austenitic stainless steels
- Lower thermal expansion coefficient than austenitic stainless steel, less deformation under frequent temperature cycling
- Higher thermal conductivity for improved heat exchange efficiency
- Nickel-free alloy formula greatly cuts raw material cost compared to TP304/TP316 stainless tubing
- Acceptable ductility for secondary processing such as tube bending, expanding, rolling and U-bending for heat exchanger assembly
- Good resistance to mild sulfur-containing flue gas and cooling water media in power and industrial equipment
4. Main Industrial Applications
ASTM A268 ferritic and martensitic stainless tubes are widely used for heat transfer and cooling components under medium temperature and pressure conditions:
- Thermal power plants: Condenser cooling tubes, boiler economizer tubes, waste heat recovery heat exchanger tubes
- HVAC & cooling systems: Industrial air coolers, fluid cooling coils, radiator tubes
- Petrochemical industry: Process heat exchangers, furnace cooling pipes, residual fluid condenser tubing
- Boiler auxiliary equipment: Feedwater cooling tubes, flue gas heat recovery tubes
- Food & light industry: Medium-temperature heat exchange pipelines and cooling coils
- Marine equipment: Seawater cooling tubing with anti-chloride corrosion performance
This series is an economical alternative when austenitic stainless steel is not required, especially for services with chloride-laden cooling water that easily triggers stress corrosion cracking in nickel-bearing stainless tubes.
5. Service Limitations & Grade Differentiation
- Low-chromium grades (TP409): For moderate-temperature exhaust and low-corrosion cooling service
- Medium-chromium grades (TP430): For general industrial heat exchangers and medium-pressure condenser service
- High-chromium ferritic grades (TP444): For seawater, chloride-rich cooling water and long-term anti-corrosion thermal service
These tubes are not recommended for severe acid corrosion environments, where austenitic stainless steel standards like ASTM A688 shall be selected instead.
6. Full Summary Paragraph
ASTM A268 specification governs seamless and welded ferritic & martensitic stainless steel tubes designed for cost-effective heat exchange and cooling applications. Manufactured via seamless piercing or precision welded cold reduction and controlled annealing, these nickel-free chromium stainless tubes deliver outstanding chloride stress corrosion resistance, stable high-temperature oxidation resistance and superior heat conductivity. Subjected to comprehensive mechanical and non-destructive testing, they maintain dimensional stability and structural integrity under continuous thermal cycling. Widely adopted as condenser tubes, boiler heat recovery tubing and industrial cooling coils in power plants, refineries and cooling systems, ASTM A268 tubing serves as an economical substitute for austenitic stainless tubes, particularly suitable for medium-temperature service with chloride-containing cooling media where resistance to stress corrosion cracking is a priority
