Stainless Steel Grades for HHO: 304 vs 316L vs 316Ti

The Chloride Stress Issue

HHO electrolyte (KOH or NaOH in distilled water) is strongly alkaline but not inherently corrosive to stainless steel — unlike saltwater or acidic environments. However, any chloride contamination (from tap water or certain KOH sources) causes pitting corrosion preferentially at grain boundaries. Higher-quality stainless grades resist this better.

304 Stainless

304 (18/8 — 18% chromium, 8% nickel) is the most common stainless steel. Acceptable for HHO but shows visible corrosion at weld seams and edges over time in alkaline electrolyte. Produces minor chromium ion leaching into electrolyte over months of operation. Sufficient for budget builds and short-term use.

316L Stainless

316L adds 2–3% molybdenum to the 304 composition, dramatically improving pitting and crevice corrosion resistance. The "L" designation means low carbon (0.03% vs 0.08% for standard 316), reducing sensitization during welding. 316L is the minimum recommendation for HHO plates intended for multi-year operation. Produces 40–60% less chromium leaching than 304 in long-term operation.

316Ti Stainless

316Ti adds titanium stabilization to the 316 composition, preventing intergranular corrosion at weld heat-affected zones. The gold standard for HHO applications where welded plate assemblies are used. More expensive and harder to source but provides maximum longevity in alkaline electrolytic environments.