Titanium crevice corrosion

Resistance to crevice corrosion Titanium is more resistant to crevice corrosion than most conventional metals and alloys, particularly where differential aeration is involved, e.g. it is very resistant to crevice attack in sea water at normal temperatures. This form of corrosion becomes more severe when acidity develops in a crevice and this is more prone to occur under conditions of heat transfer . Under these circumstances, especially in the presence of halide, even titanium may suffer attack, and the metal should not be employed in strong aqueous halides at temperatures in excess of 130°C. This limiting temperature can be raised to 180°C by use of the Ti-0- 15Pd alloy " or by coating with noble metals. (See also Sections 1.4 and 1.6.)... 

Titanium is susceptible to pitting and crevice corrosion in aqueous chloride environments. The area of susceptibiUty for several alloys is shown in Figure 7 as a function of temperature and pH. The susceptibiUty depends on pH. The susceptibiUty temperature increases paraboHcaHy from 65°C as pH is increased from 2ero. After the incorporation of noble-metal additions such as in ASTM Grades 7 or 12, crevice corrosion attack is not observed above pH 2 until ca 270°C. Noble alloying elements shift the equiUbrium potential into the passive region where a protective film is formed and maintained. 

Fig. 7. Temperature—pH limits for crevice corrosion of titanium alloys in naturally aerated sodium chloride-rich brines. The shaded areas indicate regions...

In the construction of plants, titanium with 0.2% Pd is mainly used. It can be employed with advantage in nonoxidizing acid media and also has increased resistance to pitting and crevice corrosion because of its more favorable pitting potential [40]. 

Fig. 1.51 Crevice corrosion resulting from the crevice produced between the gasket and the flange of a titanium pipe used for conveying a hot hypochlorite solution. The attacked areas are coated with a hard deposit of titanium oxides, whilst the unattacked area of metal outside...

Griess has observed crevice corrosion of titanium in hot concentrated solutions of Cl , SOj I ions, and considers that the formation of acid within the crevice is the major factor in the mechanism. He points out that at room temperature Ti(OH)3 precipitates at pH 3, and Ti(OH)4 at pH 0-7, and that at elevated temperatures and at the high concentrations of Cl ions that prevail within a crevice the activity of hydrogen ions could be even greater than that indicated by the equilibrium pH values at ambient temperatures. Alloys that remain passive in acid solutions of the same pH as that developed within a crevice should be more immune to crevice attack than pure titanium, and this appears to be the case with alloys containing 0-2% Pd, 2% Mo or 2[Pg.169]

Metals and alloys vary in their ability to resist crevice corrosion, and this applies particularly to those that rely on passivity for their resistance to corrosion. Titanium and high-nickel alloys such as the Inconels and Hastel-loys are amongst the most resistant, but even these will be attacked under highly aggressive environmental conditions. 

Syrett and Davis conducted in-vivo studies wherein they implanted crevice corrosion specimens of Co-Cr-Mo in dogs and rhesus monkeys for up to two years. Their results indicated the alloy was not susceptible to crevice corrosion. Galante and Rostoker implanted crevice-type specimens of Co-Cr-Mo and Ti-6A1-4V in the back of rabbits for 12 months. Although no evidence of severe corrosion was found in any of the specimens, several of the titanium and cobalt specimens did show signs of single pits in the crevice regions. 

Greiss, J. C., Crevice Corrosion of Titanium in Aqueous Salt Solutions Corrosion, 24, 96 (1968)... 

Figure 35 Schematic showing the process of hydrogen absorption into titanium under passive corrosion conditions after a period of crevice corrosion.

What is clear from these analyses is that the avoidance of crevice corrosion will delay eventual container failure significantly, irrespective of whether it occurs by wall penetration or by HIC. With this is mind, the galvanic coupling technique (along with the associated analytical methods outlined above) can be used to compare qualitatively the crevice corrosion performance of a series of titanium alloys. Figs. 36A and B compare the parameter (/c, Ec, Ep) values ob-... 

Crevice Corrosion resistance of Alpha Titanium Alloys depends on Impurity Content/Alloying Additions... 

Titanium alloys suffer crevice corrosion in hot aqueous chloride media, but the alloy containing molybdenum, 3A1-8V-6 Cr-4Zr-4 Mo has good resistance to crevice corrosion and is successfully used in hot sour well and geothermal brine... 

Corrosion of Titanium in Neutral and Alkaline Solutions In water, steam, and seawater, titanium is resistant even at high temperatures [44]. In water with high chloride levels, crevice corrosion could appear if tight crevices are present. Titanium shows very low corrosion rates even in seawater [43],... 

Schmitt [52] reviewed the effect of elemental sulfur on corrosion of construction materials (carbon steels, ferric steels, austenitic steels, ferritic-austenitic steels (duplex steels), nickel and cobalt-based alloys and titanium. Wet elemental sulfur in contact with iron is aggressive and can result in the formation of iron sulfides or in stress corrosion cracking. Iron sulfides containing elemental sulfur initiate corrosion only when the elemental sulfur is in direct contact with the sulfide-covered metal. Iron sulfides are highly electron conductive and serve to transport electrons from the metal to the elemental sulfur. The coexistence of hydrogen sulfide and elemental sulfur in aqueous systems, that is, sour gases and oils, causes crevice corrosion rates of... 

Some materials are more susceptible to crevice corrosion than others. These materials depend on an oxide film to achieve corrosion resistance. Stainless steel and titanium are prime examples. In addition to improving the design to minimize crevices and to maintain a clean surface on certain materials, alloying of particular materials can be used to improve their resistance to corrosion. 

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