External / Internal loads: External loads on a tank may result from adjoining piping or structures. These loads may be due to for example their static weight or as a result of thermal growth. Due to the use of relatively thin and therefore flexible steel plates, tanks have a poor ability to resist external loads and therefore measures should be taken to minimize all external loads. Methods to analyze external pipe loads can be found in API 650.
Wind / Earthquake Loads: Wind and earthquake loads depend greatly on the environmental conditions of the proposed site. Guidance on how to analyze wind and earthquake loads can be found in the appropriate design codes however particular attention should also be given to the risk of wind and earthquakes during tank erection where the full stability of the tank is not yet available and temporary facilities have to be deployed.
Loads in Storage Tank due to Pressure / Vacuum Condition: Although the maximum external design pressure of tanks is very low (6 mbar), it should be noted that tanks are inherently very poor at resisting partial vacuums. Care must be taken to ensure that vacuum breaker valves are correctly sized to prevent a partial vacuum from forming during for example liquid draw off/draining. See the below slide for an example photo of a tank collapse due to a vacuum.
Storage Tank Foundations: Although a fabricated tank is relatively light for its physical size, due to the static head from the liquid contents the overall load onto the foundations can be considerable. The design of the foundations is especially important where the ground conditions are soft or inconsistent which could result in the risk of sinking or uneven settlement which could cause the failure of the tank. To prevent this problem from occurring it is important that a soil survey of the proposed site is performed early in the project and the foundations designed to suit. This analysis may be performed by a civil engineering contractor.
