Application of titanium alloy materials such as titanium rod, titanium wire and titanium plate in construction industry

When there is a corrosive medium in the titanium tube heat exchanger, it is suitable to use composite plates and titanium-lined tube plates. Nowadays, large-scale exchangers are mostly made of integral tube sheets with a thickness of 100mm and integral heads of the same thickness. Since the use of titanium is often associated with strong corrosive media, in order to avoid corrosion, in the structural design of titanium equipment, attention should be paid to:

(1) Avoid gaps and stagnant areas. In order to achieve a complete seal and prevent a gap between the tube and the tube sheet, expansion and sealing welding should be adopted. Regardless of whether it is an all-titanium or composite board, many designers support the use of step welding based on the consideration of weld penetration, but some people think that this will cause greater difficulties in repair welding. The fasteners in the tower should be connected by wedges instead of bolts. The sealing surface of the flange should be covered with asbestos gasket with PTFE film. Under the conditions of high temperature, high pressure and strong corrosion, it is recommended to use titanium reinforced polytetrafluoroethylene winding and T0.2Pd metal pad.

(2) In the conductive medium, avoid contact between titanium and other metals as much as possible. In the structure, a third material with a potential between the two can be used as a transition layer (such as by surfacing) or isolated by insulating materials. When the medium is seawater, a heat exchanger made of titanium tubes filled with different metal tube sheets and rolled up can be used. The premise is that the tube sheet material is compatible with titanium.

(3) The expansion coefficient of titanium is smaller than that of steel. Therefore, thermal stress cracking may occur in the heating equipment of the titanium steel composite structure, and the thermal compensation link should be set in the design.

(4) In some corrosive media with high flow rates and sudden changes in flow rate, titanium equipment and components are prone to erosion, so when the flow rate exceeds 6m/s, an anti-scouring baffle should be installed. In the titanium tube heat exchanger, due to vibration, the contact between the titanium tube and the supporting hole is prone to fracture. Therefore, shock absorption measures should be taken and a PTFE ring can be caulked at the contact between the titanium tube and the supporting hole.

(5) The thermal conductivity of the titanium surface depends to a large extent on the design and process parameters. For the heat exchanger using cold water as the coolant, the available value is 425~550W/(m2·℃); for the heat exchanger using steam or hot water to heat the static liquid, the available value is 800~1450W/(m2·℃) . For the condenser cooled by seawater, when the tube wall thickness is 0.5~1.0mm and the flow velocity is lower than 3.9m/s, the measured data is 54006800W/(m2·℃).
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