This calculation can be used to assess resistance to internal pressure for a cylindrical, conical or spherical vessel section not subject to significant external loads (as external loads are not considered there is no check performed on longitudinal stresses).
This calculation takes a single average thickness reading - it is assumed that point thickness readings or critical thickness profiles have been managed separately in order to get the average thickness.

Note on 'Y' factor
This entry is provided to allow the calc to be used for different design Codes (the symbol is taken from B31). It is the factor on P used in the denominator when calculating minimum thickness based on external radius.
For calculating based on internal radius a value of (1-Y) is used. Thus for ASME VIII Div. 1 and the default formulae in API 579-1, the appropriate value of Y is 0.4.

We have set it up in this manner so that it can be used for spherical vessels or hemispherical heads without change (as opposed to entering the factor used for formulae based on internal diameter).

For AS1210 use Y=0.5.
Calculation should be carried out by a qualified mechanical engineer.