Comparison of the shell design methods for cylindrical liquid storage tanks

• A new stiffness–flexibility method based on thin shell theory is introduced.
• Shell design methods of API 650 steel liquid storage tanks are studied.
• One-foot method is most effective for smaller diameter tanks.
• Variable-design-point method is very efficient for larger diameter tanks.
• Linear analysis may be used instead of variable-design-point method to obtain more accurate designs.

The three methods for determining the shell thickness of steel cylindrical liquid storage tanks designed in conformance with API Standard 650, Welded Tanks for Oil Storage (API 650) are: (1) one-foot method (1FM), (2) variable-design-point method (VDM) and (3) linear analysis. We compared the shell designs based on these three methods for different tank properties: diameter, height and allowable stress. For linear analysis, we developed a stiffness–flexibility matrix method based on thin shell theory that gives the theoretical displacements and stresses at each shell course without any approximation or simplification. Results show that shell designs using VDM may produce overstressed shell courses for some of the large steel liquid storage tanks when VDM is permissible to use. Linear analysis would give more accurate shell designs for those cases.