316L vs 904L Austenitic Stainless Steels: Standard Marine-Grade vs Strong Acid Resistance

 

What are their core compositions and key performance differences?

316L contains 16–18% Cr, 10–14% Ni, 2–3% Mo, and ≤0.03% C. It has a Pitting Resistance Equivalent Number (PREN) of ~31, offering good resistance to seawater and mild chlorides.904L features 19–23% Cr, 23–28% Ni, 4–5% Mo, 1–2% Cu, and ≤0.02% C. Its high nickel and copper content stabilize the passive film in reducing acids like sulfuric acid, while its PREN of ~40 provides superior pitting resistance.Both grades are non-magnetic in the annealed state and offer excellent weldability.

How do their corrosion resistances perform in real-world environments?

316L performs well in marine atmospheres, freshwater, and neutral chloride solutions: ideal for boat fittings, heat exchangers, and food processing equipment. It will corrode in hot concentrated acids.904L dominates chemical processing environments: sulfuric acid plants, phosphoric acid production, and pulp bleaching. It resists stress corrosion cracking (SCC) better than 316L in chloride-containing acids.

In which applications is one grade irreplaceable over the other?

Choose 316L for standard marine, coastal, and low-acid industrial applications where cost is a factor.Opt for 904L for equipment handling sulfuric acid, acetic acid, or aggressive chemical mixtures where 316L would fail rapidly.

What are the cost and fabrication trade-offs between the two grades?

904L costs significantly more (often 2–3 times) than 316L due to its high nickel and molybdenum content.316L is readily available and easy to fabricate with standard tools.904L requires low-heat input welding (GTAW) and matching high-nickel filler metals (like ENiCrMo-4) to maintain its corrosion resistance; it is also prone to work hardening during machining.

What are the key limitations and selection guidelines?

316L is not suitable for strong acids or high-temperature chloride solutions.904L is over-specified for standard marine use; the extra cost does not provide significant benefits in seawater alone.