ASME - Single Openings: Minimum Center - To - Center Distance Between Adjacent Opening on Dishend

A, B = the finished opening diameters of any two finished openings under consideration, in. (mm) (see d below)
D = the outside diameter of the shell, header, or dished head containing the opening, in. (mm) d = diameter of a finished opening, in. (mm)(see PG-33.3)
dmax. = the maximum permissible finished opening diameter for an uncompensated opening, in. (mm) (see PG-32.1.2)
K = PD/1.82St (where K shall not exceed 0.990)
Lh = the distance between centers of the two openings measured on the surface of the dished head
Ls = the distance between centers of the two openings measured on the surface of the shell or header
P = the maximum allowable working pressure
S = the maximum allowable stress value, taken from Tables 1A and 1B of Section II, Part D
t = the nominal thickness of the head, shell, or header, in. (mm)
X = the limits of compensation parallel to the vessel wall (see PG-36.2)