All hydrocarbon processing facilities have storage tanks. However, water (H2O) can enter during processing and handling operations such as loading or transportation, through a leaking roof or by condensation and then settle to the tank's bottom. Thus, it is necessary to prevent bottom plate corrosion and product degradation by draining bottom H2O periodically.
By observing a tank's product and H2O withdrawal flows, it can be seen that flows may become stratified if slowed down or if the velocity is limited. This makes it possible to selectively withdraw products and H2O with limited-flow velocity through different outlet pipes. Generally, the product outlet pipe and the H2O drain pipe are at the lowest shell course and the tank's bottom, respectively. It may be constructed as in Fig. 1 or other designs.1