A boiler is a closed vessel in which fluid is heated. The fluid does not necessarily boil. The heated or vaporized fluid exits the boiler for use in various processes or heating applications, including water heating, central heating, boiler-based power generation, cooking, and sanitation.
A moveable (mobile) boiler (preserved, Historic Silver Mine in Tarnowskie Góry Poland).
A stationary boiler (United States).
1950s design steam locomotive boiler, from a Victorian Railways J class
A superheated boiler on a steam locomotive
A pressure vessel is a container designed to hold gases or liquids at a pressure substantially different from the ambient pressure.
A welded steel pressure vessel constructed as a horizontal cylinder with domed ends. An access cover can be seen at one end, and a drain valve at the bottom centre.
Spherical gas container.
Picture of the bottom of an aerosol spray can.
Composite overwrapped pressure vessel with titanium liner.