Horizontal shell-and-tube heat exchangers: the saddle problem
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For horizontal shell-and-tube heat exchangers equipped with saddles, is it necessary to perform calculations? This item is included in the calculations for horizontal containers in SW6, but not in those for heat exchangers. Has it been calculated before? Is it required to conduct further verification within the horizontal container?
Can’t we simply use a standard saddle?
Clause 6.16 of GB151 requires that the strength and stability of the supports and the shell be checked when necessary. As for what constitutes a necessary situation, is it appropriate to use the checks for horizontal vessel saddles outlined in SW6?
1. Is verification required? 2. How to verify? Answer: 1. Strictly speaking, verification is required, but in practice, when standard saddles are used, no verification is necessary. This applies to heat exchangers where the pressures in the tube side and the shell side are roughly equal. There is another reason: the shell-side cylinder is required to have a minimum thickness, so in principle this requirement is met. However, there is one situation that requires verification – for example, when the pressure on the tube side is very high while the pressure on the shell side is low; in such cases, thin walls are used for the shell side, which results in a higher total weight of the equipment. In these situations, it is necessary to verify the local stresses in the shell. 2. How to perform the verification? Generally, for heat exchangers without local loads, they are converted into uniformly distributed loads for calculation. To verify the partial stress of the saddle plate.
I generally agree with the opinion on the 4th floor, but there is one point: the pressure in the tube side is very high, while the pressure in the shell side is not high. These values are part of the design parameters. However, during hydrostatic testing, in order to check the condition of the tube ends, the water pressure in the shell side is artificially increased. As a result, the thickness of the shell side increases, making it relatively thicker. Therefore, as long as standard saddles are used, few people bother to conduct further verification.
I also consulted the evaluation experts, and their opinions were generally consistent with what others said. Additionally, the stress models for horizontal vessels and shell-and-tube heat exchangers are different; the checks performed on the supports of horizontal vessels can serve as a reference when applied to shell-and-tube heat exchangers. Clause 6.16 of GB151 requires that the supports and housings be checked for strength and stability as necessary. When necessary, such as in the case of stacked heat exchangers or large-diameter heat exchangers, it is up to the designer to determine factors such as the appropriate diameter.
The NB/T47042-2014 examples include calculations related to the design of heat exchanger saddles, and the calculation in question pertains to a U-tube heat exchanger.