Hello,

I am performing Tank re-rates and basic API-650/653 calculations for clients along the Gulf Coast. Almost all of the clients have a Hurricane preparedness procedure that involves filling their tanks to a recommended liquid level to provide overturning stability and additional stiffness to counteract the possibility of an elevated external pressure situation. I have developed a nice spreadsheet that takes care of most of this but I am now trying to incorporate this "Additional" liquid level calculation so I can recommend an liquid level to clients.

The second overturning condition of API-650 uses the M(f) term for fluid weight and determines the maximum liquid hold down moment based on a band of fluid a certain distance inward from the wall. I understand that this is supposed to account for the fact that the floor plate is relatively weak and acts as a membrane and after a certain point will begin to diaphragm thereby lifting the tank.

I have been instructed to just add the weight of the additional liquid level directly to the dead load and I believe this to be incorrect.

My question for you is: How can I correctly take into account additional liquid level to combat overturning ?

Thank You in advance for any input...