Specify the design length of the section, which is typically the length of the vessel plus one-third the depth of the heads or, alternatively, the distance between stiffening rings.
For a vessel with two elliptical heads and no intermediate stiffeners, the design length is the tangent to tangent length plus the shell diameter divided by six.
For a vessel with two spherical heads and no intermediate stiffeners, the design length is the tangent length plus the diameter divided by three.
For a vessel with two flanged and dished heads and no intermediate stiffeners, the design length is the tangent length plus the diameter divided by nine.
When analyzing a conical head type the length along the axis of the cone, from the small end to the point where the nozzle center line penetrates the cone. If you are analyzing any other head types, type a 0 here and you must enter the required thickness of the component in the required field.