ASME Boiler Header Thickness Calculator

C = minimum allowance for threading and structural stability (see PG-27.4.3)
D = outside diameter of cylinder
E = efficiency (see PG-27.4.1)
e = thickness factor for expanded tube ends (see PG-27.4.4)
P = maximum allowable working pressure (see PG-21)
R = inside radius of cylinder; for pipe, the inside radius is determined by the nominal outside radius minus the nominal wall thickness
S = maximum allowable stress value at the design temperature of the metal, as listed in the tables specified in PG-23 (see PG-27.4.2)
Sb = maximum allowable stress value at the design temperature of the base metal, as listed in the tables specified in PG-23, for a bimetallic tube in which the clad strength is to be included (see PG-27.4.10) Sc = maximum allowable stress value at the design temperature of the clad metal, as listed in Section II, Part D, Tables 1A or 1B, for a bimetallic tube in which the clad strength is to be included (see PG-27.4.10)
t = minimum required thickness (see PG-27.4.7)
tb = minimum required thickness of the base metal for a bimetallic tube in which the clad strength is to be included (see PG-27.4.10)

tc = minimum required thickness of the clad for a bimetallic tube in which the clad strength is to be included (see PG-27.4.10)
tc′ = minimum effective clad thickness for strength purposes for a bimetallic tube in which the clad strength is to be included (see PG-27.4.10)
w = weld joint strength reduction factor per PG-26
y = temperature coefficient (see PG-27.4.6)