Book excerpt: Describes research that evaluated the ability of the present design criteria (API 650) to ensure the desired frangible joint behavior. Particular questions include: evaluation of the area inequality as a method to predict the buckling response of the compression ring; effect of roof slope, tank diameter, and weld size on the frangible joint; effect of the relative strength of the roof-to-shell joint compared to the shell-to-bottom joint. Charts, tables, graphs and photos. References.