Clause 4.5 of ASME Section VIII Div. 2 [1] provides rules for compensation of openings in cylindrical shells having fitted nozzles.

There appears to be no definition of “nozzle” in either ASME Section VIII Div. 2 or ASME Section VIII Div. 1 [2].

The rules provided in Clause 4.5.5 of ASME Section VIII Div. 2 are based on pressure area method which ensures that the reactive force provided by the vessel material is greater than or equal to the load from the pressure.

The key element in applying this method is to determine the dimensions of the reinforcing zone, i.e, the length of the shell, height of the nozzle and reinforcing pad dimensions (if reinforcing pad is provided), that resist the applied pressure.

There appears to be no restriction on the physical dimensions of the nozzle or shell, so long as the required area AT is obtained and the stresses are within allowable limits.

It is therefore possible that all of the required area AT is obtained from the nozzle or from the shell. While both these alternatives would be acceptable, the actual stresses at the shell/nozzle junction may vary considerably.

The work reported in this paper was undertaken with a view to determining if there needs to be any restriction on the proportion of area contributed by shell or nozzle to ensure that actual stresses were within allowable limits.

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