Material comparison
Immunity to chloride cracking on one side, double the strength at half the price on the other. Temperature usually decides.
For seawater and chloride service these two are the usual shortlist. Titanium Grade 2 is effectively immune to the failure mode that kills stainless steel; super duplex is far cheaper per kilogram and much stronger. Which wins depends on temperature, on whether crevices exist, and on whether weight is being paid for.
| Titanium Grade 2 | Super duplex (2507 / Zeron 100) | |
|---|---|---|
| Density | 4.51 g/cm³ | 7.8 – 7.84 g/cm³ |
| Yield strength, typical min. | 275 MPa | 550 MPa |
| Modulus of elasticity | approx. 105 GPa | approx. 200 GPa |
| Chloride SCC | effectively immune | high resistance, not immunity |
| Crevice corrosion in seawater | risk above approx. 80 °C | risk from approx. 40 – 50 °C upward |
| Reducing acids (HCl, H₂SO₄) | poor | limited |
| Hydrofluoric acid | attacked; avoid | attacked; avoid |
| Thermal conductivity | approx. 21 W/m·K | approx. 15 W/m·K |
Titanium's density is about 43% lower than duplex. For a 3 × 1000 × 2000 mm plate that is 27 kg against 47 kg. On an offshore structure, on a vessel, or anywhere the supporting steelwork is sized by load, that difference changes the cost of everything around the plate as well. Comparing price per kilogram alone is misleading; compare price per installed part.
Our weight calculator gives the figure for any dimension and grade.
Temperature is the cleanest dividing line. In seawater above roughly 50 °C, super duplex becomes vulnerable to crevice corrosion under gaskets, at tube-to-tubesheet joints and beneath deposits. Titanium holds to around 80 °C before crevice corrosion needs considering. If the design temperature sits between those figures, titanium is usually the sounder engineering answer even at the higher price.
Titanium welding requires full inert gas shielding of the weld, the trailing zone and the root — above about 500 °C titanium picks up oxygen, nitrogen and hydrogen and becomes brittle. Iron contamination from ordinary workshop tooling initiates corrosion, so dedicated tools and a clean area are needed. None of this is difficult, but it has to be planned.
Super duplex welds with conventional equipment, but heat input must be controlled to keep the austenite–ferrite balance. Too hot and ferrite dominates in the heat-affected zone; too cold and the weld metal does. Sustained exposure between roughly 600 and 950 °C risks sigma-phase embrittlement.
Titanium Grade 2 is the standard commercially pure grade for corrosion service. Grade 7 adds palladium and extends crevice corrosion resistance to higher temperature and lower pH; Grade 12 is a lower-cost alternative with some of the same benefit. Grade 5 (Ti-6Al-4V) is the structural alloy — much stronger but less corrosion resistant than Grade 2, and the usual choice where titanium must also carry load.
In corrosion terms, largely yes. In engineering terms, not always. Titanium has roughly half the yield strength and half the stiffness of super duplex, so pressure-retaining and load-bearing parts need to be thicker or redesigned. It also performs poorly in reducing acids, where neither material is strong but duplex is less bad.
Crevice corrosion risk in seawater rises from roughly 40 to 50 °C, and this is a crevice issue rather than a general corrosion issue — it appears under gaskets, at tube joints and beneath deposits. Many operators treat the mid-forties as the practical ceiling for critical seawater service.
Per kilogram, Grade 2 typically runs at two and a half to four times 316L and roughly twice super duplex. Per part the gap narrows considerably because of the 43% lower density, and on weight-sensitive structures it can close entirely once the supporting steelwork is accounted for.
Not by conventional fusion welding — titanium and iron form brittle intermetallics. The practical routes are mechanical joints with flanges and gaskets, explosion-bonded transition pieces, or a bimetallic transition joint. Galvanic coupling must also be addressed, as titanium is the more noble of the two.
Send us the operating temperature, the medium and the pressure. We will come back with a material recommendation and the cost difference between the two options.
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