Gasket issues on both sides of the tube sheet in liquid ammonia evaporators
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Currently, a liquid ammonia evaporator is being designed, with a U-tube heat exchanger (BKU) structure. The flange on the shell side cylinder is to use a metal-wound gasket. The question is as follows: Could there be any problems if PTFE is used for the flange on the tube box side? (The temperature and pressure of the fluid in the tube side can meet the requirements.) Is there any mandatory requirement in GB stating that the gasket materials on both sides of the type A tube sheet must be identical? I only know that a warning will appear in SW6. But TEMA and ASME can allow different materials. A concern is whether the excessive compressive force applied when pre-tightening the metal wound gasket might damage the elasticity of PTFE, and whether there are any methods to verify this Since it is a multi-tube bank system, the gaskets on the tube bank side require metal wound gaskets (with an inner ring) that must be custom-made. Also, the tube side pressure is very low, so the flange thickness does not need to be designed to be too thick. I hope everyone will discuss it
The original poster already knows what the problem is; why bother? Different gasket values result in different m and y values. The most direct impact is that the pre-tightening conditions for the flanges and studs, as well as the pre-tightening forces during operation, vary. So which gasket value should be used in the calculations? I still have to choose the same one. Your question can be understood in the same way as with flanges on clamped tube sheets: both flanges must be identical; it’s not acceptable to use a long-neck flange on one side and a type A flange on the other. What is taken into consideration is the impact of different pre-tension forces
This issue is worth exploring in depth; it is a problem that often arises in practice.
This post was last edited by xlxuiin on 2017-11-14 at 11:47. The gaskets on both sides of the pipe sheet should be identical. Other types of gaskets (PTFE, asbestos, graphite, etc.) can be used for the tube bank partitions, and this has indeed been done in practice. However, for pipe boxes with segmented structures, wave-tooth composite gaskets are generally used (which can be made as a single integrated unit).