The head thickness tables may be applied to ellipsoidal 2:1 heads or torispherical heads. They may be applied to seamless heads (joint efficiency = 1.0), double-welded butt heads that have been fully ...

Due to their shape, ellipsoidal heads are more economical than some other types of end caps. The height of the head is just 25% of the diameter, and the radius varies between the major and minor axes.