Torispherical Heads. The required thickness of a
torispherical head having pressure on the convex side,
either seamless or of built-up construction with butt joints,
shall not be less than that determined by the same design
procedure as is used for ellipsoidal heads given in (d)
above, using the appropriate value for Ro. An example
illustrating the use of this procedure is given in L-6.2.