Shell and tube heat exchanger

There are reliable measures to ensure that the operating temperature difference does not exceed the design pressure difference. It can be designed with a pressure difference.

For pressure-bearing components subjected to pressures from both the tube side and the shell side, if it is possible to ensure that the pressures on these two sides increase or decrease together, the design can be based on the pressure difference across the component. It is also necessary to take into account the maximum pressure difference that may occur. Generally, a pressure difference-based design is adopted when the thickness of the tube sheet is too great; reducing the thickness of the tube sheet does pose difficulties in terms of operation and maintenance.

The design specifications for shell-and-tube heat exchangers, GB151, can be referred to. . . . . . . . . . . . . 3.11.2 Design pressure: The design pressure refers to the maximum pressure specified at the top of the tube side and shell side of the heat exchanger. Together with the corresponding design temperature, it serves as the design load condition, and its value must not be lower than the operating pressure. For components that are subject to pressure from both the tube side and the shell side simultaneously, a pressure difference design can be adopted only if it is possible to ensure that the pressures on both sides increase or decrease at the same time; otherwise, the design pressure should be determined based on the operating pressures of each side, taking into account the most severe possible combination of pressures on those sides. When designing the pressure difference, its value should take into account the maximum pressure difference that may occur during the pressure test; meanwhile, the designer should specify the step-by-step procedure for the pressure test. The design pressure on the vacuum side of a vacuum heat exchanger is determined based on the external pressures it must withstand. When safety control devices such as vacuum relief valves are installed, the design pressure is set at 1.25 times the maximum difference between internal and external pressures, or the lower of these two values, i.e., 0.1 MPa. In the absence of such safety control devices, the design pressure is 0.1 MPa. The component on the non-vacuum side of a vacuum heat exchanger, which is subject to the pressures in both the tube side and the shell side, should have a design pressure equal to the sum of the design pressures on the internal pressure side and the vacuum side. . . . . . . . . . . . . . . . .

Look, there’s an explanation on GB151.

1. For heat exchangers with a differential pressure design, specific requirements for pressurization and depressurization during pressure testing should be specified. 2. For heat exchangers in which one of the design pressures for the tube side and the shell side is negative pressure, the test pressure on the positive-pressure side shall be taken as the sum of the test pressure determined based on the design pressure of the positive-pressure side and the absolute value of the design pressure of the negative-pressure side. 3. For heat exchangers where the design pressure of the tube side is greater than that of the shell side, detailed requirements shall be specified for the testing methods and test pressures of the joints connecting the heat exchange tubes to the tube sheet. 4. After determining the test pressure, in addition to performing stress verification on the cylinder at that pressure, verification must also be carried out on the head.

What is the best method to address internal leakage in this type of heat exchanger?

When leakage between the tubes and the fluid in the shell side of a shell-and-tube heat exchanger can cause serious hazards, a gas-tightness test should be conducted after the pressure test is successful.

For shell-and-tube heat exchangers in which the design pressure of the tube side is higher than that of the shell side, in order to check the tightness of the joints between the heat exchange tubes and the tube sheet, the following testing methods and requirements can be adopted according to the actual situation: 1. Increase the test pressure on the shell side to be equal to that on the tube side; under this condition, it is necessary to verify the stresses on the shell-side cylinder, nozzles, and flanges at this test pressure to ensure that they meet the strength requirements during the pressure test. 2. If the strength requirements during the pressure test cannot be met after the aforementioned checks, then after pressuring the shell side at the test pressure specified for this chamber, proceed as follows: ① Conduct an ammonia leakage test using compressed air with an ammonia volume concentration of approximately 1%, at a pressure equal to 1.0 times the design pressure of the shell side ； ②For heat exchangers with special requirements, such as high-pressure heat exchangers, leak testing can be carried out using low-pressure pure ammonia or methods such as halogen leak detection.

It connects one end tube sheet to the shell, while the other end tube sheet is not fixedly connected to the shell and can float freely along the axial direction, as shown in the diagram. This structure not only completely eliminates thermal stress but also allows the entire tube bundle to be removed from the housing during cleaning and maintenance. Therefore, despite its complex structure and high cost, it is widely used.

I have the electronic versions of 150 and 151, but I’m not allowed to share them. My QQ: 316685280 (Heat Exchanger Doctor); feel free to contact me.