UNS N08904 904L Stainless Steel Heat Exchanger U Bend Tube ASTM A249 Cold Drawn Bright Annealed OD 19.05mm WT 2.11mm

Heat exchanger reliability in corrosive chemical processes hinges on tube integrity. Our UNS N08904 904L U-bend tubes combine the exceptional corrosion resistance of super austenitic stainless steel with precision cold-drawn manufacturing to deliver unmatched performance in shell and tube heat exchangers operating in sulfuric acid, phosphoric acid, and high-chloride process streams. ASTM A249 compliance ensures every tube meets the stringent dimensional, mechanical, and non-destructive testing requirements demanded by process engineers worldwide.

Each 904L tube is cold drawn through precision tungsten carbide dies to achieve tight outer diameter tolerances of ±0.05mm and wall thickness tolerances of ±10%. The cold working is followed by bright annealing in a controlled-atmosphere hydrogen furnace at 1070-1150°C, producing a mirror-smooth oxide-free surface with Ra ≤ 0.4 μm. This bright annealed finish is critical: it eliminates the need for post-fabrication pickling, reduces fouling rates in service, and provides the ideal surface condition for eddy current non-destructive testing sensitivity.

U-bends are formed on CNC mandrel bending machines with precise radius control down to R=1.0D minimum. After bending, each tube undergoes a low-temperature stress relief treatment at 450-500°C for 2 hours to reduce residual forming stresses without sensitizing the microstructure. Flattening and flaring tests per ASTM A450 are performed on each bend lot to verify formability after bending. The tubes are then subjected to 100% eddy current testing and helium leak testing (1*10⁻⁶ mbar·L/s sensitivity) to guarantee zero defects.

904L U-bend tubes are specified across demanding sectors: chemical processing (sulfuric acid coolers and reboilers), oil and gas refining (crude distillation overhead condensers), pharmaceutical manufacturing (high-purity solvent recovery), and pulp and paper (black liquor evaporators). The alloy's ability to resist both uniform corrosion and localized attack across diverse chemical environments makes it the preferred tube material for multi-purpose heat exchanger installations where process fluids vary seasonally.