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What are the expansion sequences of heat exchange tubes of heat exchange units

2021-11-25 15:26:13

When the heat exchange tube is expanded, a reaction force is generated to the tubesheet due to the extension of the tube. If the expansion sequence is unreasonable, various deformations may occur to the tubesheet. There are two different methods for general expansion sequence. One is that the tube plate at one end expands radially outward from the inside to the outside according to the diagonal line from the center.

The other is that when expanding the two end tubesheet, in order to reduce the residual longitudinal stress of the tubes of the heat exchange unit, the tubes in the outer layer of the tubesheet should be expanded first, gradually expand diagonally inward from the periphery, Zui and then to the center, otherwise the tensile stress of the tubes in the center will increase greatly. For the thin tubesheet, the strength expansion sealed flying heat exchanger unit shall be adopted. In particular, the expansion sequence shall be determined according to the wall thickness of the pipe and the structure and material of the tubesheet, otherwise the tubesheet will be damaged.

When reusing the heat exchange unit, there are more or less pricking and leakage, which is caused by lax sealing. For example, the cutting of high-pressure fluid will lead to leakage. Today, I will tell you about the causes of pricking and leakage of the heat exchange unit?

1. Effect of temperature difference

There is a temperature difference between the flange, cylinder, bolt, pipe box and gasket of the heat exchanger, resulting in uneven thermal expansion and cold contraction of each part, resulting in leakage of the flange gasket of the heat exchange unit.

2. Effect of temperature on gasket

The reason why this problem occurs is that the flange of the heat exchange unit uses the cushion made of oil-resistant asbestos rubber plate. The gasket will age and lose elasticity under the high temperature of 55 ~ 120 ℃ for a long time, resulting in the leakage of the cushion.

3. Effect of temperature on material properties

The floating head cover and floating head tubesheet of the heat exchange unit are sealed by two hook rings, which are clamped on the back of the tubesheet to form a hook flange, which is connected with bolts. The hook flange is cut into two pieces after overall processing. If the hook ring, bolt and other materials are used in the high temperature environment of 100 ~ 120 ℃ for a long time, their mechanical properties will be reduced, and creep and stress relaxation will occur (the thermal expansion of different parts of the same hook clamp is also different), so as to reduce the tensioning force of the bolt. It will directly lead to the reduction of the pressing amount of the flange on the cushion and the occurrence of puncture and leakage.

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