Where:
d = Inside diameter in inches;
E = 0.9 welded joint efficiency; except E = 1.0 for seamless heads;
P = Minimum required bursting pressure in psig;
S = Minimum tensile strength of plate material in p.s.i. as prescribed in AAR Specifications for Tank Cars, appendix M, Table M1;
t = Minimum thickness of plate in inches after forming.
Where:
E = 0.9 welded joint efficiency; except E = 1.0 for seamless heads;
L = Main inside radius to which head is dished, measured on concave side in inches;
P = Minimum required bursting pressure in psig;
S = Minimum tensile strength of plate material in psi as prescribed in AAR Specifications for Tank Cars, appendix M, Table M1 (IBR, see § 171.7 of this subchapter);
t = Minimum thickness of plate in inches after forming.
49 C.F.R. §§179.220-6