CURRENT ASME MODEL [2]  

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... header boxes are rectangular pressure vessels and are commonly designed according to ASME Section VIII Division 1 Appendix 13 [2] and API 661 [3]. Figure 2 shows the current Appendix 13 [2] model used for the design of unpartitioned, plug-type header boxes. API 661 Section 7.1.10 ...

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... frame theory is an extension of standard beam theory where several beams are rigidly connected together, i.e. there is moment transfer from one beam to another. The model present in Division 1 Appendix 13 [2], Fig. 2, is identical to that in Division 2 Part 4.12 [7] and both work on a unit length basis. This implies that the vessel is assumed to be infinitely long and then a unit section is taken as the basis of the analysis. The effect of this is that the end plates are neglected and only the four side walls remain. This results in a classic rigid ...

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... in cross-section, as in Fig. 4. Only two of the forces in Fig. 3., F x and F y , and one of the moments, M z , exist in the cross-section and will be considered. The other nozzle loads will be neglected. Since the loading is asymmetric the stress distribution will no longer be symmetric. This means that instead of a single corner point, Q in Fig. 2, and two mid- side points, M and N in Fig. 2, as in the Appendix 13 [2] analysis, each corner and mid-side point will have a unique equation. The loads F x , F y and M z were then applied by distributing them over the entire nozzle width, N w , in Fig. 4. Bending moment and membrane force equations, Annex A, were then derived using ...

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... of the forces in Fig. 3., F x and F y , and one of the moments, M z , exist in the cross-section and will be considered. The other nozzle loads will be neglected. Since the loading is asymmetric the stress distribution will no longer be symmetric. This means that instead of a single corner point, Q in Fig. 2, and two mid- side points, M and N in Fig. 2, as in the Appendix 13 [2] analysis, each corner and mid-side point will have a unique equation. The loads F x , F y and M z were then applied by distributing them over the entire nozzle width, N w , in Fig. 4. Bending moment and membrane force equations, Annex A, were then derived using Kleinlogel [13], a classic text on rigid frames. ...

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... containing the maximum internal stress. Figure 6 shows an enlarged section of corner A for a case where the maximum tensile stress occurs at the sharp corner and the maximum compressive stress occurs a small distance away, at the red line. It is thought that this effect can be attributed to a difference between the way the 2D FEA model, as per Fig. 2 and Fig. 5, and the extended rigid frame model handle the corner joint. Since rigid frame theory is essentially beam theory, the walls are modelled as their mid-planes, which creates an overlap region and a region with no material, while the 2D FEA models the corner completely. This difference in modelling is shown in Fig. 7. The results of the ...