Clause UG-27 of ASME Section VIII Division 1  provides rules for calculating the thickness of shells under internal pressure. Mandatory Appendix-2 of Code  provides rules for design of bolted flanged connections.
In certain high pressure and high thickness pressure vessels having a cylindrical shell with bolted cover flange, Manufacturers avoid a separate end flange welded to the shell, as the construction becomes bulky. Instead of the same, Manufacturers provide tapped holes in shell wall parallel to axis of the cylindrical shell. The cover is directly bolted to these tapped holes provided in the shell.
This type of construction may be economical as compared to welding a conventional flange to the end of the shell. However this type of construction is not covered in the Code .
When such tapped holes are provided in the cylindrical shell, generally the total metal thickness provided at the tapped hole location meets UG-27 requirement of the Code . However due to the tapped holes, the thickness from inside surface of vessel to inside surface of tapped hole is less than the required thickness of UG-27.
It is therefore required to analyze the stresses due to these tapped holes in the shell thickness to ensure that Code  allowable stresses are not exceeded.
The work reported in this paper was undertaken to determine the effect of internal pressure on the stresses in a cylindrical shell having tapped holes parallel to axis of the cylindrical shell.