Stainless Steel
Austenitic stainless grades cover corrosion resistance, food and chemical service, and high-temperature applications where carbon scaling fails. F316L is the workhorse. F304L follows. F321 and F347 cover specialty stabilized service. 904L and Alloy 20 handle severe corrosive duty.
F304 / F304L
18-8 chromium-nickel austenitic. F304 carries 0.08 percent max carbon. F304L caps carbon at 0.03 percent, which reduces sensitization risk in welded service. Dual-certified F304/F304L is the common product, meeting both grade specifications.
F316 / F316L
Molybdenum-bearing austenitic for chloride and acid resistance. The default stainless on chemical process, seawater-adjacent service, and food processing where chloride pitting is a concern. F316L low-carbon variant is the standard for welded fabrication. Dual-certified F316/F316L is common.
F321 / F347 (and the H-grade variants)
Titanium-stabilized (F321) and niobium-stabilized (F347) austenitic grades. The stabilizing additions tie up carbon and resist intergranular corrosion after exposure to sensitization temperatures (800 to 1500 degrees F). Used on power plant steam piping and on high-temperature process service. For sustained service above 800 degrees F where ASME Section II code-credit creep strength is required, specify the H-grade variants: F321H (UNS S32109) and F347H (UNS S34709). The H-grades carry the 0.04 to 0.10 percent carbon range and the solution-anneal heat-treat record needed for the higher-temperature allowable stress values.
904L (UNS N08904)
High-alloy austenitic with 25 percent nickel and 4.5 percent molybdenum. Resistance to sulfuric acid and other reducing acids better than F316L. Used in pickling, plating, and acid storage service.
Alloy 20 (UNS N08020)
Carpenter Alloy 20 nickel-iron-chromium-molybdenum with copper addition. Specifically engineered for sulfuric acid service. The copper addition resists pitting in sulfate environments where F316L and 904L would fail.
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