A pressure vessel is a closed leak-tight container (normally cylindrical or spherical) designed to hold fluids (i.e, gases or liquids) at a pressure substantially different (higher or lower) from the ambient pressure. They are usually made from Carbon Steel or Stainless Steel and assembled from plates by welding method. However, other materials like Aluminium, Copper, Non-Metals, etc also find usage as pressure vessel material in some specific situations. Even though most pressure vessels are basically long cylinders with two heads at both ends, they can take the shape of a sphere or cone.