The PD 5500:2012 Specification covers the requirements for the design, manufacture, testing, inspection and verification of compliance for unfired fusion welded pressure vessels manufactured from carbon, ferritic alloy and austenitic steels, aluminium, copper and nickel used in a wide range of process and energy industry applications. 

The term 'pressure vessel' as used in this specification includes branches up to the point of connection to the connecting piping by bolting, screwing or welding, and supports, brackets or other attachments directly welded to the pressure containing shell. The term 'unfired' excludes vessels that are subject to direct generated heat or flame impingement from a fired process. It does not exclude vessels subject to electrical heating or heated process streams.