Equipment Material Selection for Chloride-Containing Feedstock (Part 2):

For evaporators and crystallizers treating chloride-containing feedstock, titanium is generally the preferred construction material because of its outstanding resistance to chloride-induced corrosion. However, the corrosion resistance of titanium depends not only on the chloride concentration but also on the operating temperature and the titanium grade selected.

This section presents the maximum recommended service temperatures for commercially pure titanium (Grade 2, TA2), Ti-0.2Pd alloy (Grade 7, TA9), and Ti-Ni-Mo alloy (Grade 12, TA10) in magnesium chloride (MgCl₂), sodium chloride (NaCl), and calcium chloride (CaCl₂) solutions at various concentrations.

When the operating temperature exceeds the recommended service limit, localized corrosion, including crevice corrosion and pitting corrosion, may occur.

Figure Legend

The symbols used in the following figures indicate the corrosion performance of titanium under different operating conditions:

•○ White circle: Suitable for continuous service.

• ● Black circle: High susceptibility to crevice or pitting corrosion; operation is not recommended.

• △ White triangle: Slight crevice corrosion may occur, but it generally does not affect normal equipment operation.

Magnesium Chloride (MgCl₂) Solution

Sodium Chloride (NaCl) Solution

Calcium Chloride (CaCl₂) Solution

 Performance Comparison

The comparison clearly demonstrates that titanium alloys provide better resistance to chloride-induced localized corrosion than commercially pure titanium.

Corrosion resistance ranking:

Grade 7 (TA9, Ti-0.2Pd) > Grade 12 (TA10, Ti-Ni-Mo) > Grade 2 (TA2, Commercially Pure Titanium)

For applications involving high chloride concentrations, elevated operating temperatures, or other severe service conditions, Grade 7 (TA9) is generally the preferred material due to its superior resistance to crevice corrosion and pitting corrosion. Grade 12 (TA10) also provides excellent corrosion resistance and is widely used where enhanced mechanical strength and high-temperature performance are required. Grade 2 (TA2) remains a cost-effective solution for moderate operating conditions within its recommended service temperature range.