316L vs Duplex vs Titanium: Choosing Steel for Chloride-Bearing Liquors
Chloride is the single most common cause of unexpected corrosion in hydrometallurgical equipment. The three alloys buyers ask about most sit on a clear progression: 316L for benign, duplex for moderate chloride with strength needs, titanium for oxidizing chloride at temperature.
Practical limits
| Alloy | Chloride, ambient | Chloride at 60–80 °C | Fails when |
|---|---|---|---|
| 316L | Up to ~200–500 ppm | Up to ~100–200 ppm | Chloride rises, or crevices allow concentration |
| Duplex 2205 | Up to ~1,000–2,000 ppm | Up to ~500–1,000 ppm | Reducing acids, or H₂S; risk of SCC above limits |
| Titanium Gr2 | Excellent, any | Excellent in oxidizing chloride | Reducing acid, dry chlorine, HF, methanol — and it burns |
These are planning figures, not guarantees. Crevices, deposits, stagnant zones and weld quality move the real limit downward by a large margin, so any number must be confirmed against the actual chemistry and a corrosion test.
Why titanium is not the automatic answer
Titanium relies on a passive oxide film that needs oxygen or an oxidizing species to repair itself. In reducing acid with no oxidant, the film breaks down and corrosion can be rapid. Titanium also reacts with dry chlorine and with hydrofluoric acid, and it is a fire risk in oxygen-enriched atmospheres. Specify it because the chemistry is oxidizing chloride — not because it sounds premium.
Duplex is the middle path, with a caveat
Duplex 2205 gives roughly twice the yield strength of austenitic stainless, which lets you use thinner walls, and much better chloride resistance. The caveat is welding: wrong heat input or filler produces a unbalanced microstructure and the heat-affected zone becomes the failure point. Require qualified WPS/PQR and ferrite checking on duplex welds.
The cost step
Relative material cost per kilogram is roughly 1 : 1.5–2 : 4–6 for 316L : duplex : titanium, and fabrication cost rises with the alloy because of machining and welding difficulty. On a small pilot unit the absolute difference is modest; on a production vessel it drives the whole budget. That is why a 20-litre corrosion test is worth more than a week of debate.
Send the liquor analysis, temperature, and whether the system is oxidizing or reducing, and we will confirm the wetted material and flag the crevice risks.