904L Super Austenitic Stainless Steel Coil Cold Rolled 0.6mm-5mm 20Cr-25Ni-Mo-Cu Extreme Acid Resistant Grade SS Coil

Our 904L (UNS N08904) super austenitic stainless steel coil represents the pinnacle of standard stainless steel corrosion resistance, positioned at the transition between conventional austenitic grades and nickel-based alloys. With approximately 20% chromium, 25% nickel, 4.5% molybdenum, and 1.5% copper, 904L offers exceptional resistance to reducing acids including sulfuric, phosphoric, and acetic acids at concentrations and temperatures that rapidly attack 316L and even 2205 duplex. The high nickel content (25%) ensures a fully austenitic microstructure with outstanding chloride SCC resistance, while the combined molybdenum and copper addition provides synergistic protection in mixed acid environments. Originally developed for sulfuric acid service, 904L has expanded into demanding chemical processing, pollution control, and marine applications. Our 904L coils are manufactured through EAF/VIM melting with AOD/ESR refining for premium cleanliness, continuous casting, hot rolling, solution annealing at 1070-1130C followed by rapid water quenching, and cold rolling with bright annealing. Every heat undergoes complete OES/combustion chemical analysis, tensile testing, hardness measurement, and corrosion testing per ASTM G28 Method A to verify the characteristic low corrosion rate. Complete EN 10204 Type 3.1 certification is standard.

• Outstanding Sulfuric Acid Resistance: 904L provides exceptional resistance to sulfuric acid across a wide concentration and temperature range far exceeding 316L capabilities. In concentrations up to 65% at temperatures up to 50C, 904L exhibits corrosion rates below 0.1 mm/year, making it suitable for sulfuric acid storage tanks, process piping, heat exchangers, and reactor vessels. The copper addition specifically enhances resistance to reducing sulfuric acid environments where the passive chromium oxide film would otherwise be chemically unstable.
• Superior Phosphoric Acid and Mixed Acid Performance: The production of phosphoric acid by the wet process involves aggressive mixtures of phosphoric and sulfuric acids contaminated with chlorides and fluorides. 904L demonstrates excellent resistance to phosphoric acid at all concentrations up to 85% and temperatures to 80C, substantially outperforming 316L. This has established 904L as the standard material for phosphoric acid evaporators, heat exchangers, and piping systems in the fertilizer industry.
• Excellent Resistance to Chloride Pitting and Crevice Corrosion: With PREN of approximately 35 (comparable to 2205 duplex), 904L provides outstanding pitting and crevice corrosion resistance in chloride environments. Critical pitting temperature in 6% FeCl3 exceeds 45C, making 904L suitable for warm seawater service, brackish water heat exchangers, and desalination plant components where 316L would suffer rapid localized corrosion.
• Immunity to Chloride Stress Corrosion Cracking: The high nickel content of 25% provides virtual immunity to chloride SCC in neutral chloride solutions, a failure mechanism limiting 304/316 to service below approximately 60C in chloride environments. This SCC immunity expands the operational envelope for heat exchanger and process equipment handling chloride-containing process streams at elevated temperatures.
• Good Weldability with Over-Alloyed Filler: 904L is weldable using GTAW, GMAW, and SMAW with ERNiCrMo-3 (Inconel 625 type) or matching 904L filler metals. Over-alloyed nickel-based filler metals compensate for molybdenum microsegregation during weld solidification, ensuring weld metal corrosion resistance matches or exceeds parent material. Proper shielding gas and interpass temperature control maintain the corrosion resistance of the fully austenitic weld deposit.
• Seawater and Marine Atmosphere Performance: The combination of high molybdenum, copper addition, and excellent SCC resistance makes 904L suitable for critical seawater handling applications. Applications include seawater-cooled plate-and-frame and shell-and-tube heat exchangers, SWRO desalination high-pressure piping and energy recovery devices, offshore platform seawater lift pump columns and risers, and marine exhaust gas scrubber components handling acidic condensate from sulfur-containing fuels.
• Cost-Effective Alternative to Nickel Alloys: While 904L carries a significant cost premium over 316L (typically 3-5 times), it represents a cost-effective alternative to nickel-based alloys such as Alloy 625, C-276, and Alloy 22 for many corrosive applications. The substantially lower nickel content compared to true nickel-based alloys (25% versus 50-65%) provides favorable cost position, while corrosion resistance covers a substantial portion of the application space normally defaulting to nickel alloys for corrosion reasons alone.

904L super austenitic coils are specified for the most demanding corrosion applications where aggressive acid exposure, chloride contamination, and elevated temperature exceed 316L and duplex capabilities. Primary applications include chemical processing (sulfuric acid production, phosphoric acid plant evaporators and reactors, acetic acid purification, mixed acid pickling bath equipment), pollution control (wet FGD absorber vessel internals, inlet/outlet duct liners, mist eliminators, slurry piping; marine exhaust gas scrubber internals and washwater piping), seawater and desalination (MSF and MED evaporator stages handling warm concentrated brine; SWRO high-pressure feed and brine reject piping; seawater service plate heat exchangers), oil and gas (offshore seawater lift pump columns and risers, produced water treatment internals, downhole chemical injection lines), and pharmaceutical/food processing (highly corrosive pharmaceutical intermediate production reactors, citric acid processing equipment). The outstanding sulfuric acid resistance has made 904L the standard material for phosphate rock processing into phosphoric acid and fertilizer products, representing one of the most aggressive corrosion environments in the chemical process industry.

904L coils, as our highest-value product, receive premium protective packaging with acid-free interleaving paper, high-performance VCI inhibitors for high-alloy stainless steels, multi-layer UV-stabilized waterproof polyethylene with double heat-sealed seams, heavy-duty edge protection rings, and high-tensile steel strapping. Coils on steel cradles or reinforced ISPM 15 pallets. Container stowage with enhanced securing. Complete EN 10204 Type 3.1 certification with corrosion test certification (ASTM G28 Method A). Optional Type 3.2, G48 pitting, A262 IGC, and electrochemical CPT determination available for critical application qualification programs.