The Pressure Vessels are defined as containers for the containment of pressure, either internal or external. This pressure may be obtained from an external source, or by the application of heat from a direct or indirect source, or any combination thereof. The vessels are leak-proof containers that store liquid or gas. The vessels used for separating components from the process input or raw materials, such as benzene splitter in an oil refinery. The vessels used in reactors for processes that need pressure to occur or to create pressure that result from the process. Immersion heaters can be mounted on a pressure vessel through flanged, welded or threaded connections. They are made available in various types. They are very useful.