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. These heads are also recommended in applications where lower head heights than ASME F&D heads are needed.