Happy New Year! I will be trying to keep my New Year's resolution to blog more frequently. To start the year, let us look at what happens when API 2000 venting requirements are applied to a tank. My concern here comes about because of a tank I just designed for a client. The specifications said this tank was an atmospheric tank. Design and operating pressure are specified as atmospheric. All seems fine until we get futher into the specifications and come across the venting. In this section it was stated that the tank was to meet API 2000 venting requirements and provide the inflow and outflow rates. The rates are quite low as the tank is not very large. Even though the primary vent is to have a flame arrestor, the required pressure to provide the venting required for pressure and vacuum are both less than 1" of water. This had no affect on the tank. However, when we get to emergency venting the specifications said that the pressure required to provide full emergency venting could not exceed the design pressure by more than a certain percentage. Upon contacting the supplier of the emergency vent we discovered that we would have to design the tank for 4" of water pressure to meet this requirement based on the venting capability of the available vents. Needless to say this did have an affect on the tank design. We now have to anchor the tank for pressure where before the tank would not have required anchoring.
Venting requirements and the pressure and vacuum needed to meet these requirements can change the design of your tanks. A tank may be specifed to operate at atmospheric pressure. However, the venting and particular the emergency venting requirements may require the tank to be designed for pressure. Be aware of what pressure is required by the emergency and normal vents to meet the venting capacity. It may start relieving at a relatively low pressure but may require a higher pressure to meet the capacity required.