General characteristics of the structural design of titanium equipment

The susceptibility of titanium to crevice corrosion is also related to the size of the gap. Narrow gaps are more prone to crevice corrosion than wide gaps. When titanium comes into contact with non-metallic materials, the tendency for crevice corrosion is much greater than that in titanium-titanium type gaps. In fact, the common crevice corrosion in equipment mostly occurs on the sealing surfaces of flanges that come into contact with non-metallic gaskets. Titanium tubes can also undergo crevice corrosion in solutions of hydrochloric acid, sulfuric acid, oxalic acid and formic acid. Due to the unique properties of various titanium tubes and titanium alloys in terms of physics, chemistry, mechanics, corrosion resistance and process performance, the structure design of titanium equipment cannot blindly apply the structures of commonly used black metals and other non-ferrous equipment. This regulation proposes general provisions for the structural design of titanium equipment based on the characteristics of titanium material performance.

1. Due to the different mechanical properties of titanium and titanium alloys from steel, titanium materials have a higher yield strength ratio, a narrower plastic deformation range, and greater resilience during cold stamping and cold bending processes. Therefore, the structure of titanium equipment should be as simple as possible. A good structure is also conducive to the cleaning of the surface near the weld seam, facilitating gas shielded welding and protecting the quality of the positive and negative electrode weld seams.

2. Titanium can be welded with metals such as cobalt, nickel, tungsten and lead, and there will be no brittle change after welding. This is because these metals have a high solubility in titanium. However, titanium has poor intermetallic fusion properties with other metals such as steel, so titanium cannot be directly fused with other metals. Connection can only be achieved through methods such as brazing, brazing, explosive welding and bolt connection.

3. Titanium has relatively poor impact toughness and fracture toughness. Therefore, during the design process, the continuity of the structure and the flatness of the welded joints should be maintained, and stress concentration should be avoided as much as possible.

4. Pure titanium is prone to crevice corrosion in chloride solutions, but the crevice corrosion of titanium is closely related to temperature, chloride concentration, pH value and crevice size.

5. The plastic deformation range of titanium is relatively narrow, and it has a distinct work hardening phenomenon. Therefore, for the bending and flanging of titanium components, a larger bending radius is usually adopted, while for expansion tubes, a smaller expansion rate is used.

Titanium will not corrode in seawater and sodium chloride brine when the temperature is below 149℃. When the temperature exceeds 121℃, titanium may corrode in extremely narrow gaps, especially at non-metallic gaskets. When the temperature exceeds 149℃, titanium may also corrode in wider gaps, such as the gaps between tubes and tube sheets. When there are hard chloride deposits on the metal surface, the effective chloride concentration beneath the deposits will be equivalent to the chloride solubility at the pipe wall temperature, and due to the insulating effect of the scale, the temperature will rise significantly. Therefore, the area beneath the scale is also a zone prone to crevice corrosion. The higher the temperature and chloride concentration, the greater the tendency of titanium to undergo crevice corrosion.