Working Volume and Nominal Capacity

http://www.eng-tips.com/viewthread.cfm?qid=341296

First think to understand, the pressure vessels are different from Tanks (storage tanks) and they are subject to different codes.

One of the most important pressure vessel code is ASME B&PV Code.

Two of the most important storage tank codes are API 650 and API 620.

You cannot interchange the terms and codes, as many people tend to name the pressure vessels Tanks. In your first post mentioned pressure vessels and their capacities. Now you drifted in citing paragraphs from API 650, a totally different code.

Clarity is the name of the game in engineering.