What is PD 5500 - Specification for unfired pressure vessels about?  
PD 5500 is a series on specifications for unfired pressure vessels. An unfired pressure vessel is a container designed to hold gases or liquids at a pressure substantially different from the ambient. PD 5500 specifies requirements for the design, construction, inspection, testing, and verification of compliance of new unfired pressure vessels. 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. PD 5500 does not exclude vessels subject to electrical heating or heated process streams.
NOTE: Whilst this specification is limited to the construction of new vessels, with the agreement of the relevant parties it can be used to guide the maintenance or any modification of existing vessels. Where these existing vessels were designed and constructed using an earlier edition of PD 5500, with the agreement of the relevant parties, that an earlier edition can be used to guide the maintenance or any modification. 
Who is PD 5500 - Specification for unfired pressure vessels for? 
 PD 5500 on unfired pressure vessels is useful for: 
- Purchaser of vessels
- Manufacturer of vessels
- Designers of vessels
- Inspecting authority
- Regulating authorities
- End consumers of vessels
Why should you use PD 5500 - Specification for unfired pressure vessels?  
The unfired pressure vessels can present hazards to employee safety and facility operability yet fired pressure vessels are at greater risk of overheating. Over time, pressure vessels can become cracked or damaged, which can lead to rupture failures and leakage. The tests specified in PD 5500 help to ensure that the vessels are safe to use.
PD 5500 specifies minimum requirements for design, inspection, testing, and durability while manufacturing the unfired pressure vessels to ensure superior performance. PD 5500 is to be applied for defining the way the provisions are applied and their appropriateness for the intended duty, which is defined in the other documents. Using PD 5500 you can specify requirements for the design, construction, inspection, testing, and verification of compliance of new unfired pressure vessels.
You can view the latest version of this standard here
