Large Openings in Cylindrical Pressure Vessels: An Assessment Based on Absolute Size
Clauses UG-36 through UG-43 of ASME Section VIII Division 1 [1], describe the method of calculating the adequacy of compensation of openings in shells, using an area-replacement method. The method is based on determining and suitably replacing the missing metal area along any section, with metal available or provided, within the limits of reinforcement on the shell and nozzle. Clause UG-36 (b) of ASME Section VIII Division 1 provides limits on the size of the opening for applicability of Clauses UG-36 through UG-43. If these limits are exceeded, supplemental rules of Clause 1-7 of Appendix 1 need to be complied with or alternatively the rules of Clause 1-10 of Appendix 1 may be applied. The rules for large openings as stated in the Code are not dependent upon the absolute size of the nozzle and shell. For example, same calculations would be required to be carried out whether a nozzle of NPS 1 is attached to a shell of NPS 1.5 or a nozzle of NPS 16 is attached to a shell of NPS 24. The work presented in this paper is an attempt to determine whether the additional calculations in Clause 1-7 need to be carried out for finished openings exceeding the limits of UG-36(b) irrespective of the absolute size of the nozzle and shell. This has been done by carrying out calculations for a wide range of nozzle-shell combinations and comparing the results so obtained with the results of a Finite Element Analysis.