The Crevice Corrosion Resistance of Some Titanium Materials A REVIEW OF THE BENEFICIAL EFFECTS OF PALLADIUM

The crevice corrosion that occurs on titanium in chloride solutions at elevated temperatures can constitute a serious problem. The resistance of three titanium materials to this form of corrosion has been evaluated by immersion and electrochemical tests. The results show that all three possess superior corrosion resistance to that of commercially pure titanium, and that the two which contain palladium are the best. On the basis of these tests, mechanical properties and in-service experience, guide lines for the advantageous use of these materials are proposed. It is well known that one of the important pro- perties of titanium is its immunity to both pit- ting corrosion and stress corrosion cracking in chloride solution, an environment which causes corrosion of stainless steels. Consequently titanium is used extensively for vessels in the chemical industries, and for heat transfer tubes in steam turbine condensers and multi-stage flashing type desalination plants. However titanium can suffer from crevice corrosion in hot chloride solution, and as titanium is com- monly used in such conditions this form of cor- rosion can constitute a practical problem. For these reasons the effects of environmen- tal factors such as chloride ion concentration, temperature, and the pH of the solution on crevice corrosion have already been in- vestigated ( I -4). Moreover, several methods of preventing crevice corrosion on titanium have been proposed, and some resistant materials have been developed. The most popular of these is titanium-0.15 per cent palladium (Ti-0. I 5Pd) (5). Currently titanium-0.3 per cent molybdenum-0.8 per cent nickel (Ti-o.3Mo-o.8Ni) is being investigated (6), because of its lower cost, while a mixture of palladium and titanium oxides (PdO/TiO , -Ti) is being applied to industrial equipment by a simple surface treatment. In this paper the crevice corrosion resistance of these three materials is compared with that of commercial- ly pure titanium (C.P. Ti).