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Common equipment such as heat exchangers, towers, vessels, and reactors need to be connected to each other through pipelines. These connecting pipelines exert horizontal loads, axial loads, as well as torque and bending moments on the equipment’s nozzles. Especially for nozzles with larger diameters, in order to ensure the safety of these nozzles under external loads, the equipment design team must evaluate the stress strength of those nozzles and conduct safety assessments in accordance with relevant standards and specifications. Software such as ANSYS, ADINA, ABAQUS, and NOZZLEPRO, along with procedures like WRC297, WRC107, and CSCBPV TD001, are typically used to verify the local stresses at the equipment nozzles. The following points should be taken into consideration in calculations, as a reminder to my peers. 1. Precautions regarding the load conditions at equipment connections 1.1 The load conditions specified by the piping discipline for the equipment discipline are generally based on various operating conditions. The equipment discipline must not only consider the design conditions but also evaluate various other operating conditions; the ASME standards provide quite detailed information on these conditions. The evaluation of design conditions and operating conditions is also different, and the loads considered for each condition vary as well; analysis can be carried out by referring to the load combination conditions specified in ASME VIII-2. 1.2 The loads specified by the piping team are usually at the connection point between the pipe end and the shell. When using ANSYS software for calculations and verification, it is necessary to consider the loads at the flange sealing surface of the pipe end; this requires translating the original loads to that location, and errors can easily occur during such translation. Therefore, it is advisable to ask the piping team to specify the loads at the flange sealing surface whenever possible. 1.3 The direction of the pipe ends in the pipeline load condition table should be consistent with that in the equipment drawings; only by doing so can the equipment team ensure that the applied loads correspond to the original load conditions when establishing the finite element model. 1.4 When the load is relatively large, designers should also consider the impact of the load on the equipment supports, and these supports need to be verified; the NOZZLEPRO software is suitable for performing such calculations. 1.5 It is necessary to confirm with the piping team whether the axial load at the pipe ends listed in the pipeline load conditions table already includes the equivalent load generated by the internal pressure of the equipment. 2. Precautions for finite element analysis of equipment nozzles 2.1 The equipment design team needs to verify the stress strength of the nozzles and their connections to the equipment housing, especially the stress strength in the intersection areas; therefore, the meshing in these areas should be regular, with hexahedral meshes being preferred to avoid stress singularities. The grid thickness directly affects the stress calculation results. 2.2 The fillet welds at the inner and outer wall corners of the junction area where the pipe outlet meets the equipment housing should have a concave shape for a smooth transition; the size of the chamfers must comply with standards – they should not be too large, as this can make welding difficult, nor too small, as this will not be sufficient for stress reduction. 2.3 The finite element model should take into account the influence of the flange on the calculations; particularly when the extension of the nozzle is short, the stress distribution within the flange itself, combined with that in the intersection zone, can have an impact on the flange seal. 2.4 The materials of the equipment nozzles and the shell are usually different; even if both are formed by rolling sheet metal, differences in thickness can lead to varying allowable stresses. When performing finite element analysis, a lower allowable stress value should be used for assessing the stresses at the welds, and the effects of welding dissimilar steels must be taken into account. Theoretical calculations should be as consistent as possible with actual conditions. 2.5 Due to the presence of external loads, the bending stress in the interference region has the characteristics of both primary and secondary stresses; therefore, special attention must be paid when conducting safety assessments. It is not possible to simply follow standards without consideration for these factors, and a one-size-fits-all approach is not acceptable. If the stress in most areas of the interference region already exceeds the yield limit, yet it is still evaluated using 3Sm as if it were secondary stress, this is very dangerous. The NOZZLEPro software provides useful warnings regarding this issue. The ASME standards specify different evaluation methods depending on whether the yield-to-tensile strength ratio of the material is greater than 0.7; specific criteria are also provided for secondary stresses in ratchets, and fatigue analysis imposes limits on such secondary stresses as well… 2.6 When the pipe outlet extends a significant distance outward and the design temperature is high, finite element calculations must take into account the thermal expansion of the fittings, as well as the effect of the static pressure of the liquid column. 2.7 When calculating stresses, it is necessary to take into account the sealing performance of the pipe end flanges in terms of whether there will be leakage in the piping system. 2.8 Many textbooks place the constraints at the ends of the pipe openings; this should not be copied verbatim, but rather the constraints should be applied based on actual conditions. 3. Precautions for manufacturing inspection and acceptance 3.1 Section 10.3.2 of GB/T150.4-2011 stipulates that for pipe fittings with a nominal diameter of 250 mm or more that are subject to external loads, as well as the butt welds between pipe fittings and high-neck flanges, and the joints between pipe fittings and such flanges, in containers other than those specified in Section 10.3.1, local radiographic or ultrasonic testing shall be carried out on their Class A and Class B weld joints. Designers can increase the requirements for inspection and evaluation based on the importance of the equipment. 3.2 High stresses exist in the fillet welds in the intersection area; a fully penetrated weld structure should be used, and volume testing as well as surface testing should be employed as much as possible to prevent defects such as cracks on the inner and outer surfaces of the welds. The welding joint factor should be 1.0. Whether welds are inspected or not in ASME directly affects the fatigue strength reduction factor. 3.3 As stipulated in Appendix E of GB/T 150.1-2011, design entities and designers conducting local structural analysis of pressure vessels in accordance with this appendix generally are not required to possess qualifications for analytical design. The design agency shall be responsible for the accuracy of the local structure analysis, and the analysis report shall serve as the strength calculation document for the local structure. The methods for stress classification and evaluation of stress analysis results shall comply with the provisions of JB4732. The design stress intensity of the material shall be in accordance with the allowable stress of the material as per GB/T150.2. The requirements for the manufacturing, inspection, and acceptance of local structures shall meet the corresponding provisions of JB4732.