Storage Tanks are containers that hold liquids, compressed gases (gas tank) or medium used for the short- or long-term storage of heat or cold, they are available in many shapes: vertical and horizontal cylindrical, open top and closed top, flat bottom, cone bottom, slope bottom and dish bottom. (Wikipedia) Depending on the used pressure, designing code can be divided into two categories:

API 650: 0<P(kpa)<18

API 620: 18<P(Kpa)<25