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At the junction between the shell and the tube sheet, edge stresses, lateral shear forces generated by internal pressure, bending moments resulting from tube sheet deformation, as well as axial stresses caused by the pressure inside the shell, all lead to localized high stress levels in this area. The maximum stress at openings in the cylinder is generally along the axial direction of the shell. When openings are made near the tube sheet, these two types of stress combine, which may result in excessive localized stress at the junction between the tube sheet and the shell. So, how should the distance between openings be determined when they are located near the tube sheet? I think we should consider the following aspects: First, regarding the openings in the shell side, from a thermal engineering perspective, in order to ensure the flow pattern of the fluid in the shell side and make full use of the effective heat exchange area, we prefer that the nozzles with openings in the shell side be as close as possible to the tube sheet side ； Second: It is necessary to consider the range of reinforcement for the opening to be taken over, ensuring that this range is met at least ； Third: If the pipe opening is close to the tube sheet, stress accumulation occurs; in such cases, it is possible to consider adding an external guide cylinder on the shell side ； So how exactly is the distance between the takeover and the tube sheet determined? I think I should consider it mainly from the following two aspects. 1. Perform a local stress analysis calculation based on the actual opening distance; if the stress assessment is successful, then it’s fine – this distance is acceptable. 2. Reference can be made to ASME VIII-1 2021, clause UHX-4(i); the relevant provisions are as follows: (i) Except as limited in (1) and (2) below, nozzles in cylindrical shells or cylindrical channels adjacent to integral tube sheets (see Figure UHX-4-1) shall not be located at any distance from the tube sheet (refer to UG-37 and Figure UG-40 for terms not defined in this paragraph). These requirements do not apply to nozzles in shells or channels whose tube sheets are considered to be simply supported (see UHX-12.6, UHX-13.9, and UHX-14.7). (1) For a circular nozzle with a diameter d that is greater than 30% of D, no part of d shall be located within 1.8(Dt)1/2 of the adjacent tube sheet surface (see Figure UHX-4-1).