Flat Heads are with flat surfaces, which makes them a perfect fit for installations that require flat inside surfaces. Flat heads are recommended to be ideal for no pressure applications. However, when used for pressure applications, these pressure vessel heads may turn out to be more costly than other heads. This is one of the reason why flat heads are predominantly used for storage tanks that stock state of matter at no pressure. Flat heads minimize the amount of space required for a tank when size constraints are critical.